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SEMATECHTechnology Transfer 92051107A-STD

SEMATECH Guide for ContaminationControl in Design, Assembly, and

Delivery of SemiconductorManufacturing Equipment

© 1996 SEMATECH, Inc.

SEMATECH and the SEMATECH logo are registered service marks of SEMATECH, Inc.

SEMATECH Guide for Contamination Control in Design, Assembly,and Delivery of Semiconductor Manufacturing Equipment

Technology Transfer # 92051107A-STDSEMATECH

July 10, 1992

Abstract: The purpose of this document is to establish a guide for contamination control in the design,assembly and delivery of equipment for manufacturing devices with 0.35 µm minimum designrules. This guide is intended to assist the device manufacturer by providing a basis for thedevelopment of unique build specifications for individual tools. It will assist the tool manufacturerin the development of new tools, materials, assembly techniques, and facilities to meet the designrules. The guide also may establish a framework for discussion between customer and supplier anda possible basis for joint development. SEMATECH has granted copyright permission toSemiconductor Equipment and Materials International (SEMI) to develop this document forindustry standards. Portions of this document have been incorporated into the SEMI ToolAccommodations Standards.

Keywords: Contamination Control, Equipment Design, Equipment Assembly, Construction Materials

Authors: Nora Sylvestre

Approvals: Nora Sylvestre, Program ManagerJackie Marsh, Director of Standards ProgramJohn Pankratz, Director, Technology TransferJeanne Cranford, Technical Information Transfer Team Leader

Technology Transfer # 92051107A-STD SEMATECH

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SEMASPEC #92051107A–STD

SEMATECH Guide for Contamination Control in the Design, Assembly, and Delivery ofSemiconductor Manufacturing Equipment

1. Introduction

1.1 Purpose

The purpose of this document is to establish a guide for contamination control in thedesign, assembly, and delivery of equipment for manufacturing devices with 0.35 µmminimum design rules. Its goal is to provide tooling that will not significantlycontaminate either the product or the surrounding cleanroom. To achieve this, thedocument provides guidelines to minimize the generation of particles and vapors by thetooling itself, to limit the redistribution of these contaminants within the tooling, and toprotect the tooling and product from external contamination sources.

This guide is intended to assist the device manufacturer by providing a basis for thedevelopment of unique build specifications for individual tools. It will assist the toolmanufacturer in the development of new tools, materials, assembly techniques, andfacilities to meet the design rules. This guide also may extablish a framework fordiscussion between customer and supplier and possibly for joint development.

1.2 Organization

Following this introduction, a list of referenced documents (Section 2) and definitions(Section 3) is provided. The bulk of this guide presents the detailed tooling designcriteria (Section 4). The approach is to start at a distance from the tool and first considerthe operating environment (Section 4.1). Then the overall tool (Section 4.2) and itseffect on the cleanroom is addressed. Moving next into the critical process region, thedesign requirements for incoming process fluids (Sections 4.3–4.5), process surfaces(Section 4.6), chambers (Section 4.7), vacuum systems (4.8) and wafer handling(Section 4.9) are discussed. The guideline concludes with descriptions of techniques tointegrate the components into a finished system (Section 5), which includes assembly,certification (except PWP), packaging and delivery.

SEMATECH Technology Transfer # 92051107A-STD

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1.3 Scope

1.3.1 This guide is generic in nature in order to cover as many equipment types as possible. Therecommendations in this guide apply not only to the supplier, but also to subcontractors. Thisdocument deals with contamination-related issues only; its intent is not to develop processspecifications or contamination targets.

1.3.2 This guide can be used outside 0.35 µm semiconductor manufacturing equipment, but may notbe all inclusive for smaller geometries and may be overly aggressive for larger geometries.

1.3.3 In many cases, the guidelines do not provide specific solutions. Rather, they alert the toolingdesigner to areas of concern and suggest courses of action.

1.3.4 Particles per wafer pass (PWP) certification of the tooling is outside the scope of this guideline.SEMI E14 (see Referenced Documents, Section 2.1.6) provides details of the procedure to befollowed.

1.4 Impact

1.4.1 Compliance with this document is expected to assist in developing a cleaner tool that will morereadily meet contamination control performance specifications. It is anticipated that morestringent specifications will follow and become the norm in the equipment manufacturingindustry.

1.4.2 Compliance with this document may affect the cost of semiconductor manufacturingequipment.

1.5 Limitations

1.5.1 Some of the technologies related to contamination issues may not exist or are in development.These technology gaps are identified in the Contamination-Free Manufacturing Task ForceTechnology Gap List. (See Section 2.5.1.)

1.5.2 This document does not specifically address the issues associated with micro-environments(such as SMIF boxes); however, significant portions of the document are applicable.

1.5.3 It is the responsibility of the supplier to ensure compliance by subcontractors.

1.5.4 This guide is based on present knowledge and may require revision as more detailedinformation becomes available.


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2. Referenced Documents

2.1 Standards and SEMASPECs

2.1.1 American Society for Testing and Materials (ASTM).1

ASTM D257 Standard Test Methods for D–C Resistance or Conductance of InsulatingMaterial

ASTM E595 Standard Test Method for Total Mass Loss and Collected VolatileCondensable Materials from Outgassing in a Vacuum Environment

ASTM D3302 Standard Test Method for Total Moisture in Coal

ASTM D2116 Standard Specification for FEP–Fluorocarbon Molding and ExtrusionMaterials

ASTM D1925 Standard Test Method for Yellowness Index of Plastics

ASTM F1-68 Standard Specification for Nickel-Clad and Nickel-Plated Steel Strip forElectron Tubes

2.1.2 General Services Administration2

FED–STD–209 Federal Standard Clean Room and Work Station Requirements, ControlledEnvironment

2.1.3 Institute of Environmental Sciences (IES)3

IES–RP–CC–001 Recommended Practice for HEPA Filters

IES–RP–CC–003 Recommended Practice for Garments Required in Clean Rooms andControlled Environmental Areas

IES-RP-CC-002 Recommended Practice for Laminar Flow Clean Air Devices

IES-RP-CC-006 Recommended Practice for Testing Cleanrooms

IES-RP-CC-015 Recommended Practice for Cleanroom Product and Support Equipment

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Available from the American Society for Testing and Materials (ASTM), 1916 Race St., Philadelphia, PA. 19103

2Available from Naval Publications and Forms Center, 5801 Tabor Ave., Philadelphia, PA 19120.

3Available from the Institute of Environmental Sciences, 940 East Northwest Highway, Mount Prospect, IL 60056.


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2.1.4 National Association of Corrosion Engineers (NACE).4

(General) NACE Material Requirements and Recommended Practices.

NACE Coatings and Linings Handbook. Houston, TX 1985.

NACE Corrosion Engineers Reference Handbook. 1980.

NACE Handbook, Forms of Corrosion: Recognition and Prevention. Dillon, C.P.Houston, TX. 1982.

2.1.5 SEMATECH

[Note: The following are provisional SEMASPEC test methods for evaluating gasdistribution system components. These methods are currently being validated.5

#90120390A–STD SEMATECH Test Method for the Determination of ParticleContribution by Gas Distribution System Components (Provisional)

#90120391A–STD SEMATECH Test Method for the Determination of Helium LeakRate for Gas Distribution System Components (Provisional)

#90120392A–STD SEMATECH Test Method for the Determination of RegulatorPerformance Characteristics for Gas Distribution SystemComponents (Provisional)

#90120393A–STD SEMATECH Test Method for the Determination of Filter FlowPressure Drop Curves for Gas Distribution System Components(Provisional)

#90120394A–STD SEMATECH Test Method for the Determination of Valve FlowCoefficients for Gas Distribution System Components (Provisional)

#90120395A–STD SEMATECH Test Method for the Determination of Cycle Life ofAutomatic Valves for Gas Distribution System Components(Provisional)

#90120396A–STD SEMATECH Test Method for the Determination of TotalHydrocarbon Contribution by Gas Distribution System Components(Provisional)

#90120397A–STD SEMATECH Test Method for the Determination of MoistureContribution by Gas Distribution System Components (Provisional)

#90120398A–STD SEMATECH Test Method for the Determination of OxygenContribution by Gas Distribution System Components (Provisional)

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See the Information Handling Services, Industry Standards and Engineering Data Index, published by VSMF DataControl Services for specific documents.

5Available from SEMATECH, 2706 Montopolis Dr., Austin, TX (512)356-SEMA.


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#90120399A–STD SEMATECH Test Method for the Determination of Ionic/OrganicExtractables of Internal Surfaces–IC/GC/FTIR for Gas DistributionSystem Components (Provisional)

#90120400A–STD SEMATECH Test Method for the Determination of SurfaceRoughness by Contact Profilometry for Gas Distribution SystemComponents (Provisional)

#90120401A–STD SEMATECH Test Method for SEM Analysis of Metallic SurfaceCondition for Gas Distribution System Components (Provisional)

#90120402A–STD SEMATECH Test Method for EDX Analysis of Metallic SurfaceCondition for Gas Distribution System Components (Provisional)

#90120403A–STD SEMATECH Test Method for ESCA Analysis of SurfaceComposition and Chemistry of Electropolished Stainless SteelTubing for Gas Distribution System Components (Provisional)

#90120404A-STD SEMATECH Test Method for Determination of SurfaceRoughness by Scanning Tunneling Microscopy for Gas DistributionSystem Components (Provisional)

#91060573A–STD SEMATECH Test Method for AES Analysis of Surface and OxideComposition of Electropolished Stainless Steel Tubing for GasDistribution System Components (Provisional)

#91060574A–STD SEMATECH Test Method for Metallurgical Analysis for GasDistribution System Components (Provisional)

2.1.6 Semiconductor Equipment and Materials International (SEMI).6

SEMI E1 Specification for 3", 100 mm. 125 mm, and 150 mm Plastic andMetal Wafer Carriers

SEMI E2 Standard 125 mm and 150 mm Quartz and High Temperature WaferCarriers; Standard 200 mm Quartz and High Temperature WaferCarriers

SEMI E14 Measurement of Particle Contamination Contributed to the Productfrom the Process or Support Tool

SEMI S2 Product Safety Guidelines

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Available from SEMI, 805 East Middlefield Rd., Mountanview, CA 94043.


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2.2 Other Referenced Documents

2.2.1 Liu, B.Y.H., et al. "Particle Generation During Vacuum Pump Down," Institute ofEnvironmental Sciences 1991 Conference Proceedings. 1991.

2.2.2 Wu, J.J., et al. "Process Control for Prevention of Particle Generation During PressureReduction." Microcontamination 1990 Conference Proceedings. 1990.

3. Terminology

3.1 Acronyms and Abbreviations

HEPA—high efficiency particulate air

IPA—isopropyl alcohol

MFC—mass flow controller

MSLD—mass spectrometer leak detector

NRe—Reynolds Number, dimensionless, (DVρ/µ)

PVDF—polyvinylidene fluoride

PFA—perflouroalkoxy

PTFE—polytetrafluorethylene

PWP—particles per wafer pass

RGA—residual gas analyzer

SMIF—standard mechanical interface

TOC—total oxidizable carbon; total organic carbon

UHP—ultrahigh purity

ULPA—ultralow particulate air

VLF—vertical laminar flow

3.2 Definitions

particles per wafer pass (PWP)—the number of particles added to a wafer as it passesthrough a tool, expressed in particles/cm2/pass.

4. Design Criteria

4.1 Operating Environment

To achieve the 0.35 µm device design rule objectives, the facility containing the toolingshould meet a set of minimum criteria. The basic requirements are listed below. Pleaserefer to the IES Recommended Practices listed in Section 2.1.3 for recommendedprocedures for evaluating the criteria. In some cases (e.g., lithography), more stringentstandards may be required and additional variables may need to be included.


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4.1.1 Cleanroom Air - Product Vicinity

Critical areas of the tooling may be located in an open ballroom, a process bay, a hood,or a mini-environment. Air quality supplying these regions is subject to supplier anduser interaction, but should generally meet the following minimum criteria:

Particles Class 1 (per FED-STD-209)Velocity 22.87 m/m ± 12% (75 f/m ± 12%)Directional uniformity < 14°Temperature 20 ± .6 °C (68 ± 1 °F)Relative humidity 40 ± 2.5%

35 ± 2.5% (in litho areas)

4.1.2 Independent Clean Air Systems

In cases where stringent control of temperature, humidity, static pressure, and vaporcontaminants or any combination thereof is required, a local recirculating system maybe used. The recirculation system should draw at least 15% of the air from the ceilingULPA filters to avoid local stagnation and heat buildup, and it should exhaust excessair. The design should be carefully analyzed to control the impact on adjacentcleanroom airflow. These systems should meet Class 1 criteria so that the productreceives air directly from the ULPA filters with minimum impact on the VLF directionand velocity.

4.1.3 Cleanroom Air - Support Areas

In SEMATECH, service chases, at a minimum, should meet Class 100 criteria. Regionsexternal to mini-environments should meet, at a minimum, Class 1000 criteria.Velocity, directionality, temperature and relative humidity are not specified.

4.1.4 Process Utilities

The gases and liquids that come in contact with the wafers during processing should bepure. The facility should provide fluids of the following quality at point of connection:

4.1.4.1 Deionized water

Resistivity > 18 megohm-cmLive bacteria < 5 per literTotal oxidizable carbon < 5 ppbvSi/SiO2 < 5 ppbvDissolved O2 < 3 ppbvParticles > 0.5 µm < 1000 per literO3 < 100 ppbv


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4.1.4.2 Chemicals

Individual metals ≤ .1 ppbvTotal metals ≤ 5 ppbvIndividual anions ≤ 10 ppbvTotal organics ≤ 100 ppbvParticles ≥ 0.03 µm ≤ 4000 per liter

4.1.4.3 Process gases (N2, H2, O2, and Ar)

H2O < 1 ppbvH2 < 1 ppbvN2 < 1 ppbvO2 < 1 ppbvCO < 1 ppbvCO2 < 1 ppbvTotal hydrocarbons < 1 ppbvParticles > 0.003 µm < 10 per cubic foot

4.2 Overall Tooling Considerations

This section describes the techniques to be used for portions of the tooling which do notroutinely impact the wafer environment, but which are located in relatively clean areas,such as service chases or areas external to mini-environments. Examples are supportequipment such as pumps, compressors, power supplies, and heat exchangers. Otherexamples are portions of the tooling that are downstream of the wafer region. Here therequirements are less stringent than those for the process vicinity (see Section 4.7,below), but they exist nonetheless. Equipment interiors are exposed to this environmentduring maintenance. Also, contaminated air from these regions can compromise thequality of the air returning to the product vicinity.

4.2.1 Process Bay - Service Chase Separation

Depending on circumstances, tooling may be largely in the process bay, largely in theservice chase, or partly in both. Process bay pressure will exceed service chase pressureby up to 0.038 mm Hg (0.02 inches H2O). The tooling should be partitioned and sealed,as far as practical, to maintain this separation even during maintenance. It is time-consuming and potentially contaminating for personnel to pass from the process bay tothe service chase, and consideration for these concerns should be given to equipmentcommunications protocol. In general, mini-environments are not subject to this concern.

4.2.2 Equipment Surfaces

In addition to the preferred materials and finishes described in Section 4.6.1, paintedsteel, and anodized aluminum are permitted. Decorative and galvanized finishes areexcluded. Surfaces need not be static dissipative. All surfaces should be corrosionresistant and cleanable. Free-standing components are to be packaged in cabinets andinterconnected via readily accessible ducts and raceways. Provide drip pans under allcomponents where leakage is possible. All support furniture and tools should becompatible with Class 100 cleanroom operation.


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4.2.3 Airflow

Mechanical and electronic cabinet cooling air should be filtered prior to re-entering thesurroundings, using HEPA filters having a 95% efficiency at 0.3 µm (11.8 µin). Ingeneral, any concentrated exhaust airflow in excess of 0.14 m3/s (300 f3/m) should beanalyzed to control the impact on surrounding airflow.

Tools should be designed so that the operator is not required to interfere with the cleanair flow upstream of the product during normal operation.

4.2.4 Heat

Components generating more than 500 watts of heat or operating with surfacetemperatures in excess of 49 °C (120 °F) are capable of disrupting local airflow and canimpact temperature uniformity in recirculated air. These instances should be analyzed,and in some cases may require separate ducts to remove the heat. Use of water-cooledcomponents is encouraged.

4.2.5 Noise

No single piece of equipment should generate a sound level in excess of 55 Db, 60 secL(Aeq), free field, when measured at a distance of 4.5 m (15 ft) with background noiselogarithmically deleted. Local damping or enclosure or both may be used to meet thiscriteria.

4.2.6 Vibration

Tooling vibration, if transmitted to the cleanroom walls, raised floor, or structure, canadversely affect adjacent and even distant tooling. When installed, equipment shouldnot significantly degrade the baseline vibration signature of the facility. Specific levelsmust be negotiated with the customer based on the vibration and transfer characteristicsof the facility.

Subsystems and assemblies with moving parts, especially rotating equipment such asfans, pumps, or motors, should be mounted on appropriately sized vibration isolators orabsorber blocks. They should also be isolated from the equipment they serve so that theprocess region requirements of Sections 4.6.3.6 and 4.7.5 are met.

Certain levels of seismic and structural vibration will always be present in the facility.If specific vibration levels are necessary for tool performance, these should bequantified, and acceptable facility vibration limits should be negotiated with thecustomer dependent on the baseline vibration characteristics of the facility (see Sections4.6.3.7 and 4.7.5).

4.2.7 Maintainability

All equipment components that require frequent preventive maintenance or cleaningshould be accessible from the service chase side. These components should also beaccessible by removal of a minimum number of fasteners. All fasteners must be of thesame type and large enough for easy removal. Exterior cleanroom panels that cannot beaccessed for cleaning should be eliminated.


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Tools should be designed so that access for service in one area does not requireexposing other areas or the entire tool to the cleanroom. Components that requireabrasive cleaning must be detachable whenever possible for cleaning outside thecleanroom. Situations where routine maintenance is likely to degrade the localcleanliness should be identified so that installation of retractable protective curtains canbe arranged.

Virtually all service is done in a cleanroom environment where a service technician’sdexterity is limited due to cleanroom suits and two pairs of gloves. Because of this,easy access is essential to minimize wear from operator’s gloves and cleanroom suits.Consideration must also be given to what areas of the tool must be exposed (e.g.,leaning over a wafer handling area) to the technician when servicing other areas.

CRTs used for servicing equipment should be remote from wafer handling areas.

4.3 Process Gas and Organic Liquid Delivery Systems

The following discussion addresses the sections of the tooling which can have a directadverse impact on the product. At this point, considerable effort has been expended bythe end users to deliver process fluids of the purities described in Section 4.1.4, above.An extremely small amount of leakage, outgassing, or cross contamination can easilydegrade this purity by several orders of magnitude. Therefore, it is imperative that theinternal tooling plumbing be designed and assembled in a manner that will not degradethe incoming gas quality.

Distinctions between the requirements for process gasses and liquids are minor. Wherethey occur, they are noted in the text below. The term fluid refers to both gases andliquids. In particular, the leak rate requirements for the liquids are less stringent(Section 4.3.5.2).

4.3.1 General Design Considerations

4.3.1.1 Unitized construction—Minimize fittings by using welded sub-assemblies wherever possible.All welded joints should be automatically orbital, butt welded. Socket welds are not allowed,and saddle welds are not recommended. Also, tubing manifolds utilizing saddle welds are notrecommended.

4.3.1.2 Dead legs—Dead volumes along the main flow paths should be minimized. The use of amonoblock valving arrangement or multiple valves welded together is required to isolateadditional purging circuits from the main flow path. The contained volume within the toolshould be minimized, and blind runs, including Bourdon gauges, are not recommended.

4.3.1.3 Filter locations—On incoming fluid lines, filters are recommended downstream of anyregulator and as close to the process chamber as possible. Additional filters may be located inother locations as desired (e.g., inlet of mass flow controller). The system should notincorporate any type of screen filter (e.g., inlet screen to MFC).

Point-of-use filtration is required as close as possible to reaction chambers. In gassystems, this filter should be followed by an isolation valve on systems where thereaction chamber cycles to atmosphere every wafer or batch of wafers. This also appliesto loadlock chambers.


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4.3.1.4 Purge capability—All corrosive, toxic, and flammable gasses should have both upstream anddownstream MFC purging and vacuum capability. In a vacuum system, all gas loops shouldhave the capability of being directed to a vacuum pump to allow cycle purging.

Both gas and liquid designs should include a means of thoroughly purging upstream anddownstream of components to be removed. This is done to displace residual fluid priorto component removal but also to prevent atmospheric contamination while the systemis open.

4.3.1.5 Maintainability—Components that require regular maintenance (e.g., MFCs and filters) shouldbe accessible from the service chase. Sample ports should be included for leak checking,particle or vapor contaminant testing, and sample extraction of fluids for off-line analysis.

4.3.1.6 Other concerns

Contamination monitoring—Provisions should be made for in-line or in situ particlecounters, or both, and other impurity analyzers. The end user and supplier shouldnegotiate the exact location and type of sensor.

Cleanroom compatibility—Low temperature lines should be insulated to preventcondensation.

Vibration—Systems should be isolated from vibration to prevent particle generation dueto vibration of components. Special attention should be paid to isolation of vacuumpumps.

Hazards—Care should be taken not to mix fluids with reaction potential on the samemanifold (e.g., SiH4 and O2).

Electrostatic control—If potential for static buildup by fluid movement exists,grounding or neutralization techniques are recommended.

4.3.2 Process Tubing

4.3.2.1 Material—Low-sulfur-content (0.007-0-010), vacuum-arc-remelt (VAR), seamless, high-puritytubing material is recommended for enhanced welding and lower surface defect density. Allwetted stainless steel surfaces must be 316L SS electropolished with ≤ 0.254 µm (10.0 µin) Raaverage surface finish, Cr/Fe ≥ 1.1 and Cr2O3 thickness ≥ 25 Å. Other materials, such as highnickel content alloys, may be requested in highly corrosive environments.

4.3.2.2 Weld fittings—Weld fittings should be electropolished and equivalent to tubing specifications.All manifolding should be accomplished by means of welded fittings and tubing or bymonoblock or welded valving arrangements. Machined manifolds are not recommended, withthe exception of where the gas may enter a machined reaction chamber component. Thismachined portion should be electropolished to a < 0.254 µm (10.0 µin) Ra average surfacefinish.


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4.3.3 Components

4.3.3.1 Valves—Valves should be selected for low leakage, low outgassing, low particle generation,and high cycle life. They are to be slow acting (~3 seconds travel) and of packless metaldiaphragm or metal bellows design. Use of spring-loaded check valves is strongly discouraged.Electronic check valves, consisting of a valve, upstream and downstream pressure transducers,and appropriate logic, are preferred.

4.3.3.2 Filters—Filters are to be rated at 0.01 µm (0.39 µin) for gases and 0.10 µm (3.9 µin) for organicliquids and are to be selected for low outgassing and high retention. They should be capable ofbeing effectively purged of initial contaminants, with moisture and other impurity levelsdropping to less than 50 ppb within one hour of startup at rated flow.

4.3.3.3 Demountable fittings and manifolds—All fitting connections for process and purge fluids are tobe metal-gasket sealed, boreline seal, and antitorque. Fitting assemblies should provide a non-contaminating means of preventing thread galling. Metal-seal gaskets should be unplatednickel or stainless steel. This also applies to gaskets that may be used as orifices.

4.3.3.4 Regulators and flow controls—Regulators should be performance tested per the SEMATECHTest Method for Determining Regulator Performance Characteristics for Gas DistributionSystem Components, #90120392A–STD (see Section 2.1.5) for particle generation andoutgassed contaminants. Mass flow controllers should be all metal sealed and selected for lowparticle generation and low outgassing. When liquid flowmeters are used on flow loops, theyshould be installed on the outlet side to help detect leaks within the tool.

4.3.3.5 Nozzles—Nozzles or discharge parts used in process chambers should be compatible withdelivery pressures, velocities, temperatures, and chemicals. Erosion at the nozzle due to processvariables can generate significant numbers of particles; nozzles should not corrode, flake, oroutgas under process conditions.

4.3.3.6 Gauges—Only flow-through pressure transducers are recommended.

4.3.4 Assembly

4.3.4.1 Preparation—Stainless steel tubing should be cut, faced, and deburred in a Class 10environment. Facing and deburring should not contribute visible (no magnification)particulates to the inside of the cut end. If bending of tubing is required, centerline bend radiishould be a minimum of 8 times the tube outer diameter, and bending should be performedprior to finishing and assembly. A hot DI water rinse should be immediately followed by apurge of 0.01 µm filtered hot nitrogen or argon from a cryogenic source until the tube is dry (<10 ppb H2O). Subsequent to purging, the inside surface of the tube should only be contacted by0.01 µm filtered nitrogen or argon from a cryogenic source or DI (17.5 megohm or better)water.

4.3.4.2 Technique—All welding should be accomplished by means of automatic, orbital-butt welders ina Class 100 or better environment operated by suitably gowned personnel per IES RP-003 (seeSection 2.1.3). Argon or argon/helium mix purge gas should have < 10 ppb oxygen, H2O, andhydrocarbons. Internal welds and heat affected zones should exhibit no visible discoloration,bluing or otherwise. A representative weld coupon should be made available to the customer.No wet processing of the internal surfaces after welding is recommended due to the potentialfor entrapping contaminants.


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4.3.5 Performance Testing

4.3.5.1 Components—All gas handling components should be tested per SEMATECH methods. (SeeSection 2.1.5 for test methods.)

4.3.5.2 Leak testing—Gas delivery systems should be tested using a helium mass spectrometer leakdetector having a minimum sensitivity of 1 x 10-10 atm-cc/s He at a pressure differential of 1atm. No leaks are allowed, using 100% electronic grade He and a probe speed of 2.54 cm/s(0.083 f/s) or less. Organic liquid systems should be tested at a minimum sensitivity of 1 x 10-6

atm-cc/s.

4.3.5.3 Contamination testing—The output of the system is to be tested for particles and outgassedcontaminants (e.g., THC, O2, H2O). This is to be done by sampling a flow of nitrogen in staticmode (i.e., no valve cycling). During test, internal surfaces should be exposed to only 0.01 µm(0.39 µin) filtered nitrogen with < 10 ppb oxygen and H2O. The delivery system should add nomore than 10 ppb H2O and 0.35 particles per liter (10 particles/f3) ≥ 0.01 µm (0.39 µin) in size.

4.3.5.4 Storage and shipment—Following assembly and test, the system should be pressurized withfiltered semiconductor grade argon or nitrogen, and sealed with a closed valve and metal fittingcap or plug. If the gas system is to be stored or shipped separately it should also be triplebagged before it leaves the cleanroom.

4.4 Inorganic Liquid Delivery Systems

Corrosive liquids and deionized water are representative of these systems. Althoughthey require purity levels comparable to those for process gas and organic liquid systemsdescribed above (Section 4.3), the materials of construction are quite different.


4.4.1.1 Dead legs—Liquid plumbing systems should not have dead legs larger than 3 pipe diameters.To ensure this, locate bypass bleeder loops as close as possible to the fluid dispense valvesclosest to the process chamber.

4.4.1.2 Maintainability—DI systems should be designed to be compatible with ozonated water orhydrogen peroxide and should be provided with injection ports for sanitation purposes.

Filters and pumps should be installed to allow easy access during replacement.

Provisions to flush systems completely with DI water should be an integral part of alldesigns, with special precautions taken to prevent contamination of the DI water loop.


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4.4.1.3 Recirculation systems—Despite many improvements made in the purity of these fluids, the useof recirculation will continue to increase because of stringent point-of-use requirements. Suchsystems should comply with these guidelines. Care has to be taken to determine the fluidquality after it has passed through the tooling. It is desirable to direct these fluids through intothe return side of the recirculating system whenever possible, rather than down the drains.

4.4.1.4 Contamination monitoring—Particle detection for incoming fluids at point of use is stronglyrecommended as an integral part of the tool. Point-of-use DI monitoring (TOC in final rinsebaths and resistivity in all rinse baths) is recommended as an integral part of the equipment.

4.4.1.5 Other concerns:

Particle Generators—Design of the systems should take into account thatfluoroelastomers are permeable, and metals should not be located close to the deliverysystems.

Electrostatic control—Static buildup is a potential problem, but at this time there is noknown approach to preventing it due to no known universally accepted static dissipativepolymeric materials.

Vibration—Pumps should be isolated to prevent transmission of vibration to othercomponents.

4.4.2 Materials

4.4.2.1 Applications—Preferred materials are as follows:

For DI water: PVDF or PFAFor corrosive liquid: PFA

Materials used in exhaust construction should be compatible with the materials beingexhausted.

4.4.2.2 General considerations—Materials for piping, fittings, and valves should be semiconductorgrade 150 psi (10 bars) rated at 20 °C (68 °F). Materials should be cleaned by themanufacturer, capped, sealed in a bag, and enclosed in a container to prevent contaminationduring shipment.

4.4.2.3 PFA specifications

Pure perfluoroalkoxy of a type that will not introduce contamination into the high puritychemicals should be used. Specifically, raw materials used in manufacturing should befree of chemical additives, fillers, and property enhancers and reinforcements such asantioxidants, antistatic agents, colorants, flame retardants, heat stabilizers, lubricants,mold release agents, pigments, plasticizers, processing aids, ultraviolet stabilizers, andviscosity depressants. The following criteria are recommended for PFA:

Melt flow rate : 11.7-18.1 grams/10 minimumColor Index : YID -5.0 max, %G 51 minimum

Extractable fluorides : 1.0 ppmw maximum

Trace ionic contamination: recommended level 100 ppbw maximum

TOC extraction: recommended level 50 ppbw maximum


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4.4.3 Components

4.4.3.1 Fittings—Butt fusion joints are preferred, but sanitary coupling and flared gripper fittings maybe used as alternatives. Threaded seals should not be used.

4.4.3.2 Valves—Drain valves should be normally open and fill valves normally closed. On/off valvesshould be pneumatically actuated diaphragm or bellows valves with fluoropolymer diaphragms,bellows and seals. Diaphragm valves may tend to have a shorter life cycle than bellows valves;however, they are perceived as being cleaner in operation. Valve bodies should have integrallymolded end connectors.

4.4.3.3 O-rings—O-rings should be free of chemical additives (see Section 4.4.2.3). Fluoroelastomer isacceptable for DI applications. PFA encapsulated O-rings are also acceptable.

4.4.3.4 Pumps—It is perceived at this time that diaphragm pumps are operationally cleaner, but have ashorter life cycle than bellows pumps. Pump bodies should have integrally molded endconnectors. All wetted services must be nonmetallic. Pumps should incorporate a flowdampening device.

4.4.3.5 Filter housings—Fluoropolymer should be used for housings and all internal components.Sample and drain ports should be provided.

4.4.3.6 Flowmeters—When flowmeters are used on flow loops, they should be installed on the outletside of the tool to help detect leaks within the tool.

4.4.3.7 Gauges—Only flow-through pressure transducers are recommended.

4.4.3.8 Spray guns—Spray guns are not recommended due to potential for bacterial growth. If they areused, material of construction should be fluoropolymer with recirculating DI loop and O-ringsas indicated in Section 4.4.3.3.

4.4.4 Assembly

4.4.4.1 Preparation—Cutting tool edges should be titanium nitride coated or ceramic. All welding andassembly should be performed in a Class 100 or better environment operated by suitablygowned personnel per IES RP-003 (see Section 2.1.3).

4.4.4.2 Technique—Joints should be accomplished without glues or solvents. Welding of pipingshould provide a beadless, crevice-free joint by using an appropriate automatic welder andclean techniques.

4.4.5 Performance Testing

4.4.5.1 Leak testing

The system should be leak checked and should exhibit a pressure decay less than 0.25psi (0.017 bar) over a 24-hour period after initial nitrogen pressurization to 30 psi (2bars).


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4.4.5.2 Contamination testing—The end user may require further testing to determine the number ofparticles or metallic ions added to a DI stream.

4.4.5.3 Storage and shipment—If the system has been checked with DI water, active steps should betaken to avoid bacterial growth (i.e., unstabilized hydrogen peroxide rinse or ozonation). Itshould be dried so there is no trapped water. If the system is to be stored or shipped separatelyit should also be triple-bagged before it leaves the cleanroom.

4.5 Resist Delivery Systems

The resist delivery system typically consists of a pump or a pressurized vessel thatcontrols the flowrate and timing of the resist dispense. The pump or pressure vessel canbe supplied by a bulk fill system, bottles, or a bag. The resist is then carried to adispense nozzle in the apply tool via tubing. The overall requirements for these systemsare comparable to those for inorganic liquid delivery systems described above inSection 4.4. The high viscosity and chemical activity of resists require some specialconsiderations as follows:

4.5.1 Sealed System

The resist dispense system should be sealed so that the solvent vapors do not escape intothe cleanroom space. If venting is required to displace used resist (as in the case withbottled systems), ultrapure nitrogen and a filtered check valve should be used.

4.5.2 Flow Paths

Eliminate cavities such as dead legs, which can trap air which later can cause airbubbles in the dispense stream. The use of threads should be minimized.

Eliminate sharp corners at junctures, within the valves, pumps or pressure vessels. Allcomponents should be deburred; a burr or sharp corner can be a nucleation site forcrystallization, and the crystals can break loose to form particles.

4.5.3 Materials

Pumps and pressure vessels should be made of PTFE, PFA, or 316L stainless steel.

Tubing from supply to pumps and pressure vessels should be made of PFA or 316Lstainless steel.

4.5.4 Finishes

Wetted stainless steel surfaces should first be cut to length and bent if required. Ifbending of tubing is required, centerline bend radii should be a minimum of 8 times thetube outer diameter. The surface should then be electropolished to ≤ 0.254 µm(10.0 µin) Ra. PTFE and PFA surfaces should have equivalent finishes.

4.5.5 Assembly, Test and Storage

Refer to Sections 4.4.4.1, 4.4.5.1 and 4.4.5.3 (preceding).


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4.6 Process Surfaces and Subsystems

This portion of the guideline describes the treatment of parts of the tooling that directlyinteract with the wafers. In general, first try to reduce the generation of contaminantsand then reduce their transport to the wafers. Submicrometer particles and undesirablevapors can be generated in a wide variety of ways, so every aspect of the tooling shouldbe examined for possible problem areas, and the potential impact on the productdetermined.


4.6.1.1 Materials

Surfaces should demonstrate resistance to shedding, chipping, cracking, peeling,particulate generation, and outgassing. Electropolished 304L stainless steel is thepreferred material for exposure to the product area. Other materials can be used, as longas they do not have the potential to degrade and generate particulates with normal wearand tear. Nonreactive plastics are appropriate in the presence of corrosive chemicals.

Because material quality may vary between manufacturers, the materials used should beidentical (manufacturer and formulation) to the materials tested. The NACEHandbooks and Reference Materials (see Section 2.1.4) may be used for checkinggeneral compatibility of materials.

Surfaces must be nonvolatile. Plastics, adhesives, elastomers, seals, and finishes shouldbe properly formulated and cured and should pass modified the ASTM E595–90 (seeSection 2.1.1) outgassing test (less than 1% mass loss and less than 0.1% condensablevolatiles when held at 25 °C (77 °F) above the maximum normal operating temperatureand 5 x 10-5 mm Hg (2 x 10-6 in Hg) for 24 hrs.). Hot melt adhesives should not bepermitted.

4.6.1.2 Finishes

All surfaces should be inherently clean; that is, surfaces must not be particle or vaporgenerators, and should not be adversely affected by repeated wiping.

Surfaces should be protected against corrosion as applicable. Cr-Ni plated steel, treatedaluminum, and finishes may be approved where appropriate.

Elastomeric urethane is preferred for painted surfaces. Urethane enamels and epoxyenamels are also acceptable. After application, the painted surface should be examinedto ensure that there is no surface shedding or chalking, and that the bond between thepaint and surface is firm. All surfaces are to demonstrate 106–109 ohms/sq resistivityper ASTM-D257 (see Section 2.1.1). Decorative finishes, e.g., crackle, wrinkle, andtexture, should not be used.


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4.6.1.3 Wet stations

Liquid chemical process equipment cabinetry, trim, labels, and peripheral equipmentshould be made entirely of plastic or chemical-resistant metal. No aluminum, copper, orcarbon steel parts should be used on any wet process tooling. The type of material usedshould be determined on a chemical compatibility basis and on the potential forleaching or absorption when contact or proximity to product is possible.

Chemical process tanks, counter tops, and direct wafer contact equipment should befabricated of materials determined to be compatible and nonleaching throughout theirdesign lifetime. Analysis of the test chemicals must show no cation concentrationincrease > 10 ppb, and < 50 added particles per liter (> 0.5 µm) when analyzed in theactual process chemicals that contact the materials.

Chemical process surfaces should be certified to pass a thermogravimetric (weightloss/gain) test performed at 100 °C (212 °F) (or 25 °C above the maximum normaloperating temperature, whichever is greater) for 1000 hours and not exceed 0.5% totalweight loss or 1.0% total weight gain.

Appropriate techniques include ICP–MS (inductively-coupled plasma massspectroscopy) for cations, GC–MS (gas chromatography–mass spectroscopy), fororganics, as well as laser particle counters.

4.6.2 Airflow

4.6.2.1 Open construction—If the flow of Class 1 cleanroom air does not move smoothly around andthrough the tooling, turbulence and eddies can cause deposition of particles on nearby product.Heating, cooling, and motion of tool mechanisms can add to the number of particles generatedby the equipment. Physical configurations should be aerodynamically designed to reducestagnation and turbulence. If blocking surfaces cannot be avoided, perforations having at least50% open area should be used to permit the smooth flow of air.

4.6.2.2 Heat—All heat sources should be analyzed to characterize levels of outgassing and particlesthat may contaminate product surfaces. Surfaces running hotter than 49 °C (120 °F) can bepredicted to cause upward convective air velocities above 3.05 m/m (10 f/m). Such heatsources should be relocated or exhausted so that airflow is not compromised. An exception tothis is the use of thermophoresis (product heating) to reduce airborne particle deposition.Radiant heat sources should be shielded to prevent any significant heat absorption by adjacentsurfaces.

4.6.2.3 Modeling, visualization and testing—Computer modeling can be a useful tool to identify areasof concern. The best understanding comes from testing actual equipment mockups in VLFhoods, using a deionized water fog or other flow visualization to verify the design. The finaldesign should be tested as a component in a cleanroom to measure particle generation.


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4.6.3 Particle and Vapor Generators

4.6.3.1 Abrasion

In general, objects that rub against each other in any way generate particles. Surfacesshould operate well within their thermal and mechanical design limits. Taber abrasiontests and microscopic examination can be used to verify a design in a coarse fashion.Avoid rapid motions, heavily loaded motions, and impacts. Try to determine the PV(pressure times velocity) limit of materials, and stay within the limit.

Some wear control coatings can actually increase particle generation, and hard materialsin moving contact can generate many submicrometer particles with little evidence ofwear. Lubricants must be nonvolatile and their use strictly controlled. Dry powderlubricants and silicone lubricants are not recommended.

Titanium nitride and titanium carbide coatings on steel can greatly reduce friction andparticle generation. Synergistic coatings, in which the base metal is treated and theninfused with a low friction polymer, can give excellent results.

4.6.3.2 Corrosion and deterioration

Rusting of steel, oxidation of paint, and drying of gaskets are typical of this class ofparticle generators. Where used, gaskets should be closed-cell with a continuous skinsurface. Gaskets should be compatible with cleaning solutions.

Elastomer O-ring usage should be limited and evaluated for initial particle generationpotential and extended use particle generation potential. When extended use dries outthe O-rings, procedures and frequencies for changeout should be recommended, eventhough seal integrity is being maintained.

4.6.3.3 Flexing—Flexing of materials with brittle coatings, such as anodized aluminum, should beavoided. Thermal expansion and contraction can cause flexing sufficient to generate particles,as with heating elements in particular. Where possible, recirculating fluids are recommendedfor heating (and cooling). Heating elements in particular are subject to spalling and should notbe located upstream of product. Indirect heaters (muffles) are acceptable. On/off contactorcontrol is not recommended; proportioning SCR control, using zero crossover, is preferred.

4.6.3.4 Hydraulics and pneumatics—The use of hydraulic systems is discouraged because of the highprobability of leaks and the volatility of the fluids used. Their use requires stringentprecautions, including monitored exhausted enclosures.

Pneumatic systems may be used if proper precautions are taken. Air discharged fromthe system must be exhausted. Seal regions should be exhausted if they are determinedto be a source of particles. Design details should include cushioned cylinders and slowacting valves. The systems should be designed to run dry rather than use air containingoil. Vacuum cylinders may be used as an alternate method.


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4.6.3.5 Fans and motors—Integral cooling fans, or other necessary air moving devices, should bedesigned so that air exits smoothly in the direction of bulk airflow. Fans in the product vicinityshould not generate particles in excess of the class of air in which they are installed.

Intermittent and continuous motion, materials, and integrated fans in most motors causeparticle generation. Brushless, direct drive units are preferred. Electric motorplacement as remote as possible from the wafer environment is recommended.

4.6.3.6 Vibration—Tooling vibration, if excessive, can generate particles simply by shaking them outof tooling components. Examples include the shaking of particles from process chamber wallscausing particulate contamination, the motion of wafers relative to process carriers or processsurfaces causing the formation of silicon dust, and the disintegration of composite materialsresulting from vibrational induced stress. Cables that connect directly to the tool frame shouldbe long enough to allow enough looping of the cables during installation to preventtransmission of vibration.

In the product vicinity, vibration levels should be barely noticeable. Guidelines forvibration levels are:

• For frequencies < 100 Hz, velocity should not exceed 0.076 cm/s (0.030 in/s).• For frequencies > 100 Hz, acceleration should not exceed 0.050 g.

4.6.3.7 Electrostatics—The system should be designed to prevent electrostatic buildup. All surfacesshould demonstrate 106–109 ohm/sq resistivity per ASTM-D257 (see Section 2.1.1). Wherethis is not possible, electrostatic buildup should be controlled by the use of static eliminatingdevices. No surface should be allowed to accumulate charge in excess of 100 volts.Radioactive ionizers are not recommended due to emission of alpha particles.

All metal surfaces should be grounded to prevent electrostatic charge accumulation.Ground lines of isolated surfaces should have approximately one megohm of resistanceto limit current and protect personnel in case of contact with electrical power sources.

4.6.4 Treatment of Particle and Vapor Generators

When questionable design, materials, or components are encountered, they should beaddressed by one or more of the following methods:

4.6.4.1 Subassembly test—Check the equipment in question for generation of contaminants, andcompare this with the acceptable level for the particular process step.

4.6.4.2 Redesign—Change the design to eliminate the problem. In all cases of suspect contamination(particulate and gaseous), elimination should take priority.

4.6.4.3 Enclosure and exhaust—Build an enclosure around the source of particles or vapors that fits aswell as is practical, but is not airtight. Attach an exhaust manifold to the enclosure. Ensure thatsufficient air is drawn through the enclosure to draw a visible inert test vapor into any openingin the enclosure while the tool is operating, idle, or undergoing maintenance. Exhaust shouldbe minimized. Tests should be performed and data made available to the customer to showcontamination levels associated with closed and exhausted subassemblies.


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4.6.5 Contamination Monitoring

4.6.5.1 Instrumentation—Appropriate instrumentation is recommended as part of the tooling toguarantee the quality of the services supplied (e.g., gases or chemicals).

Contamination monitoring and control at actual point of use (the wafer) is critical.Therefore, installation of real-time in situ monitors for both particulate and gaseouscontaminants in the wafer processing and handling areas is also recommended.

4.6.5.2 Outputs—Output from all sensors described in this section should be directed to the systemcontroller and have the capability of interlocking to process startup or being flagged as out-of-specification per user-definable limits.


4.6.6.1 Cleanability—All surfaces should be cleanable, resistant to water-based and organic solvent-based cleaners, and polished where possible. External buttons and knobs should be avoided.Flush mounted fasteners, knobs, or membrane key pads are preferred.

Blind holes or any holes, slots, or crevices that cannot be cleaned should be minimized.All surfaces should be oriented so it is possible to wipe the entire surface. Generousfillets and radii are recommended on all interior corners.

4.6.6.2 Documentation—Documentation should be provided in software wherever possible. If hardcopy documentation is required, it should be provided on laminated sheets and enclosed incleanroom compatible binders. Even large size drawings should be handled in this manner.

4.7 Process Chambers

This section discusses process chambers in general. Vacuum chambers have a uniqueset of requirements and are described in Section 4.8.


Chamber volumes should be minimized to reduce usage of processing materials andresulting effluents. Generous fillets and radii are recommended on all interior corners.Protect against electrostatic discharge through grounding or dissipative measures.

4.7.2 Materials and Finishes

Materials used in the process chambers should not flake, corrode, or outgas duringprocessing. They should be compatible with process chemicals, operating pressures,and temperatures, and should be able to withstand the necessary cleaning processes.Surfaces should be finished to minimize generation of particles from the material,eliminate absorption or trapping of particles that may enter from external sources, andprovide efficient cleaning for preventive maintenance.

316L stainless steel, electropolished to a 0.254 µm (10 µin) Ra finish or better is thepreferred material choice. In some cases, where corrosion and abrasion are not a majorconcern, 6000 series aluminum, carefully brought to a mirror finish, may be used.Anodized aluminum is not recommended for the process area. Some processes, due to


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their aggressive nature, will require polymers or metals with protective, i.e., synergistic,coatings.

4.7.3 Particle and Vapor Generation

4.7.3.1 Cross contamination—Within a particular process tool, the possibility of cross-contamination,which may affect the process, exists between various parts of the tool. For example, moisturecan be carried from the entry or load lock chamber into the process chamber and residualprocess fluids can be carried in the opposite direction. Care should be taken to minimize thispossibility by appropriate sequencing and/or purging.

4.7.3.2 Moving parts—Moving parts can be particle generating sources and should be minimized orenclosed where feasible.

4.7.3.3 Backstreaming—Backstreaming of contaminants can occur due to improper seals, softwareerrors, poorly designed exhausts or drains, or uncontrolled pressure gradients which result inparticle or vapor generation. Process equipment plumbing should be designed to minimize theseproblems and include pressure monitors where applicable.

4.7.3.4 Thermal Stability—Excessive thermal fluctuations can cause material degradation and particlegeneration. Minimize these effects by choosing appropriate materials and controlling thermalcycling. An example is the particles generated by fused quartz as it traverses the 600 °C (1112°F) range.

4.7.3.5 Seals—All elastomeric seal materials should be evaluated to the chemical and processenvironment to characterize and minimize generation of contamination.


Chambers should be designed to include in situ process and contaminationinstrumentation. Monitoring instrumentation should be selected and placed to detectcontamination associated with the process step. In multiple chamber tools, thecontamination levels should be measured on a chamber basis and on an integrated toolbasis.

4.7.5 Vibration

4.7.5.1 General—Process chambers should be isolated to prevent vibration from shaking residues loosefrom chamber walls to form particle contamination. In the product vicinity, vibration levelsshould be barely noticeable.

For frequencies < 100 Hz, velocity should not exceed 0.076 cm/s (0.030 in/s).For frequencies > 100 Hz, acceleration should not exceed 0.050 g.

4.7.5.2 Optical Stability—Scanning electron microscopes, lithography tools, and optical inspectiontools may require additional isolation devices to prevent vibration from affecting the processchamber. Tuned damping and corrective feedback systems are examples.


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4.7.6.1 In situ cleaning—Wherever possible, the process in the tool should be adapted to include toolcleaning. Cleaning should be performed without leaving residual contaminants. The chambershould be designed to be cleaned while minimizing chamber downtime. Minimize closed areasthat may trap particles.

4.7.6.2 Access—Periodic chamber cleaning should be minimized and easily accomplished. Thechamber design should minimize the number of chamber parts and tools handled duringmaintenance or component replacement. The design should also minimize the amount ofparticles generated by disassembly during maintenance (e.g., screw threads).

4.8 Vacuum Systems

Many vacuum design techniques, particularly those for ultrahigh vacuum, have much incommon with good contamination control design. Treatment of moving parts, choice ofmaterials, elimination of blind holes, and baffling of vapors are some examples.

Vacuum systems do offer some advantages over atmospheric systems. At pressuresbelow about 50 millitorr, the gas density is so low that micron sized particles fall severalthousand times more rapidly than at atmospheric pressure. Thus there is nothingcomparable to an airborne particle distribution. Outside of process particle generation,which is significant but beyond the scope of this guide, particles are transferredballistically. In short, if the source of particles is known, the product can be protectedby appropriately placed shielding.


4.8.1.1 Contamination monitoring—An in situ vacuum particle monitoring system should beincorporated in the roughing line of each vacuum chamber that cycles to atmospheric pressureevery wafer or batch of wafers. This sensor should be positioned as close to the chamber aspossible and should also be positioned so that slow and fast pumping are conducted through thesensor.

A residual gas analyzer (RGA) should be installed in each separate process region. Thiswill identify gaseous contaminants, including leaks. Minimum specifications for theunit should include a 1 – 100 amu (atomic mass unit) range and a 1 × 10-10 mm Hg (3.9x 10-12 in Hg) sensitivity.

4.8.1.2 Thermal considerations—Deposited films are frequently brittle, and can suddenly createairborne particles when thermally stressed. For this reason, wherever practical, inner surfacesshould be thermally stable; cooling jackets are preferred over cooling coils; and bare heatingelements are discouraged, particularly simple on/off units.


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Surface outgassing rates approximately double with every 5 °C (9 °F) increase intemperature. Advantage may be taken of this fact by heating chambers toapproximately 80 °C (144 °F) prior to venting and by keeping the chambers hot duringmost of the subsequent pumpdown. This minimizes condensation of volatiles, primarilywater vapor, while the chamber is open to air, and speeds up subsequent outgassing.

All systems should be equipped to allow initial and periodic bakeout to at least 125 °C(257 °F).

4.8.1.3 Vacuum integrity—The assembled systems should be tested using a helium mass spectrometerleak detector having a minimum sensitivity of 1 × 10-10 atm-cc/s He at a pressure differential of1 atm. No leaks are allowed, using 100% electronic grade He and a probe speed of 2.54 cm/s(1 in/s) or less.

4.8.1.4 Vibration—Vacuum chambers should be isolated to prevent vibration from shaking particlesloose from fixtures or chamber walls. Vibration levels should be barely noticeable.

For frequencies < 100 Hz, velocity should not exceed 0.076 cm/s (0.030 in/s).For frequencies > 100 Hz, acceleration should not exceed 0.050 g.

4.8.1.5 Electrostatic control—Use grounding or dissipative means to prevent electrostatic discharge.

4.8.1.6 Cleanroom compatibility—Whenever possible, pumps should be installed remote to serviceareas. Pumps that cannot be installed remote to service areas should be placed in soundattenuating enclosures that have vibration isolation (see Sections 4.2.6 and 4.8.1.3). Theseenclosures should be exhausted separately from the rest of the system and sealed to protect theprocessing and cleanroom environment.

4.8.1.7 Maintainability—Ideally, components used in the vacuum system should be designed tofacilitate easy (minimal) tool removal for cleaning the outside of the process area. Therequirement for cleaning in and around process areas should be minimized (see Section 4.2.7).

4.8.2 Materials and Finishes

4.8.2.1 General—Even if the process operating pressure is relatively high, materials should be selectedas if the system were required to operate in the 10-8 mm Hg range or lower. This will excludevolatiles and minimize vapor contamination. Vacuum chamber materials should be selected tominimize initial outgassing.

4.8.2.2 Treatment of vacuum materials—The preferred construction material is 316L stainless steel.After welding, machining and initial leak testing, interior surfaces should be mechanicallypolished to a 0.813 µm (32 µin) Ra finish or better. The interior surfaces should then be chem-polished or electropolished to a 0.254 µm (10 µin) Ra or better finish.

In critical applications, a stress relieving step and/or a glow discharge passivation stepmay be required.

As in the case of nonvacuum chambers, where corrosion or abrasion are not majorconcerns, 6000 series aluminum, carefully brought to a mirror finish, may be used.Anodized aluminum is not recommended, due to its high surface area and particleformation. Some processes, due to their aggressive nature, will require polymers ormetals with protective, e.g., synergistic, coatings.


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4.8.2.3 Seals—O-ring seals should be selected for chemical compatibility with the process and also tominimize outgassing. Gold, copper, and silver sealing systems may be undesirable for certainprocess applications.

4.8.2.4 Lubricants—Few lubricants are considered satisfactory for use in vacuum systems.Hydrocarbon-based lubricants are generally too volatile. Graphite or metal bearing lubricantsliberate many particles. Silicone based lubricants are not very effective and form insulatingelectrostatic charge enhancing deposits when exposed to gas discharges.

Pentaphenyl ether has a vapor pressure in the 10-8 mm Hg (10-10 in Hg) range and is agood choice for an oil. Some grades of perfluoropolyether oils also have acceptably lowvapor pressures. Gold and silver plating have been used successfully and are stable tohigh temperatures.

As with seals, lubricants must be carefully selected with regard to the process.

4.8.3 Components

4.8.3.1 Roughing pumps—Multi-stage oil free pumps, which incorporate a molecular drag modulebacked by diaphragm and piston modules, are recommended.

Roots blowers may be used for high capacity requirements if they are provided with adynamic gas purge in their inlet line (Section 4.8.4.4).

The use of oil-sealed roughing pumps (as distinct from forepumps) is stronglydiscouraged from both a processing and cleanroom compatibility standpoint. Suchpumps typically require additional servicing, which adds to oil vapor generation andunnecessary contamination from maintenance procedures. In addition, these pumps addto oil backstreaming, which can outgas during normal processing and chamber cleaning.

4.8.3.2 High-vacuum pumps—Cryogenic and oil-free or gas-purged turbomolecular pumps arepreferred. Ion pumps are recommended for low load UHV regions that are rarely brought toatmosphere. Oil diffusion pumps are not recommended, for the reasons given above regardingoil-sealed roughing pumps.

4.8.3.3 Valves—These should be selected for system compatibility and should exhibit smooth, slowtravel. The control air exhaust from pneumatic valves should be directed into the buildingexhaust, rather than back into the cleanroom.

4.8.3.4 Gauges—Install all gauges vertically, on top of components, so they do not accumulate debris.Equip each separate section of the system with an independent rough vacuum gauge that has ausable range of 1 × 10-3 to 1 × 103 mm Hg (1x 10-5 to 10 in H2O) to aid in trouble shooting andgross leak testing. This can be accomplished with a Pirani or conduction/convection gauge, butnot with a conventional thermocouple gauge. Ion gauges with dual filaments are recommendedto avoid losing measurement capability when a single filament burns out.


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4.8.4 Special Procedures

4.8.4.1 Slow pumpdown—When a roughing or vent valve is initially opened, flow near it is veryturbulent, and the gas in the chamber cools significantly. Considerable product contaminationcan result from particle redistribution and from vapor condensation during pumping. Systemsshould be individually analyzed, but these general guidelines can minimize the problems:

Use small parallel motor driven valves for initial roughing.Open and close all valves slowly.Keep Reynolds numbers < 500 at the chamber inlet to avoid turbulence.Design systems with respect to Z–factor analysis to avoid condensation (see Sections2.3.2 and 2.7).

4.8.4.2 Slow venting—Systems should be vented to atmosphere using UHP argon or nitrogen (< 10 ppbH2O), which minimizes contamination and speeds subsequent pumpdown.

Venting should not be implemented through any portion of the roughing line. Ventinginto the direct vicinity of the wafers should be avoided. Vent nitrogen or argon gaspressure should not exceed 3 psig static. A slow opening valve should be used wheneverany vacuum chamber is vented (this includes purging during process) to maintain aninstantaneous Reynolds number < 500 at the chamber inlet.

4.8.4.3 Crossover techniques—The pressure differential between vacuum chambers should be < 500 ×10-3 mm Hg (19.7 x 10-3 in Hg) prior to opening gate valves that separate the chambers. Prior toany wafer movement within vacuum, pressure should be < 100 × 10-3 mm Hg (3.9 x 10-3 in Hg).To prevent cross-contamination in a multiple-chamber system, no three chambers should beexposed simultaneously.

4.8.4.4 Dynamic gas purge—Idle chambers (no wafer movement, storage, or processing), inactive for >4 hours, should be maintained at a pressure of ~100 × 10-3 mm Hg (3.9 x 10-3 in Hg) by meansof a process grade nitrogen purge.

Oil-sealed roughing and Roots pumps can backstream oil if they reach too low apressure. To prevent this, introduce a flow of nitrogen several line diameters upstreamof the pump, and aimed toward the pump. Provide a flowmeter and adjust the flow tomaintain the following relationship between the pump minimum inlet pressure and theline diameter:

P x D ≥ 4 × (10-3 mm Hg × mm) [P x D ≥ 100 × (10 Torr × inches)]

Subsequent to cleaning any vacuum chamber, a minimum of three fast pump and ventcycles should be completed prior to introduction of any wafers. Turbulent flow (NRe >5000) at the outlet and inlet of the vacuum chamber during pump down and venting isrecommended in this case. This procedure should be a standard function in themaintenance mode.


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4.8.4.5 Leak detection—Vacuum systems should not have to be shut down or partially disassembledbefore they are connected to a leak detector. To avoid this, permanently install a manualshutoff valve at the mechanical pump inlet downstream of a test tee having a leak detectorconnection valve. By doing this, four benefits are derived:

1) The mechanical pump can be tested independently from the rest of the system.2) The mechanical pump can aid the leak detector while it is pumping on the rest of the

system.3) The system chamber and pump can be tested independently.4) The mechanical pump can be isolated and the entire system backed by the leak

detector to achieve greatest sensitivity after all major leaks have been found andrepaired.

4.9 Wafer Handling


In general, tooling should operate in a carrier-to-carrier mode. For wafer carrierspecifications, refer to SEMI wafer carrier standards (see Section 2.1.6).

Another concern in the design of handling systems occurs when a wafer handlingsystem services more than one process chamber, residual contamination contributed tothe wafer handler from the process chamber is a potential source of cross contamination.Outgassing or residual contamination from the wafer itself may cause contamination tothe wafer handler.

4.9.2 Materials and Components

Wafer contact between wafer and handler surfaces, including the wafer handler endeffector, should be non-metallic. Points of contact between the wafer and the handlershould be minimized in both number and size. Wafer handling materials should beresistant to wear, such as scuffing, scraping, and chipping.

Wafer handling materials should operate well within their thermal and mechanicaldesign limits. The material used for constructing the handler should be compatible withthe process temperature, pressure, and chemical reactions.

4.9.3 Particle and Vapor Generators

The wafer-retaining mechanisms can generate particles through abrasion and chippingwhen closed abruptly or firmly. However, insufficient wafer retention may result inrelative motion between the handler and wafer, potentially creating particles. Bothextremes should be avoided.

4.9.4 Cleanroom Compatibility

The route and motion of the wafer handling mechanism should not degrade the clean airquality by causing turbulence or generating particles. The wafer carrier should bepositioned to take maximum advantage of laminar flow for wafer contaminationcontrol. Non-vacuum wafer handling should occur within a full ULPA filtered laminarair flow stream.


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A particle sensor is recommended on wafer and cassette handling robots to detectparticles generated by the robot. This would be inclusive of all types of robots, but ismore important on those of increased complexity, which present increased potential forparticle generation due to mechanical motion of moving parts.

4.9.6 Performance Criteria

Particles per wafer pass (PWP) may be measured using the SEMI E14 (seeSection 2.1.6). Wafer handles should be tested and certified as sub-assemblies. Theircontamination contribution should be identified as part of the total tool allowance.

4.9.7 Electrostatic Control

Nonmetallic materials are preferred for wafer handlers. Methods should be employed toprevent static buildup on wafer handling systems. It should be recognized that movingparts can generate static charges which should be controlled. All surfaces are todemonstrate 106–109 ohms/sq resistivity per ASTM-D257 (see Section 2.1.1).

4.9.8 Vibration

Handler velocity, acceleration, deceleration, and vibration can contribute to particlegeneration. Vibration contribution by a wafer handler should be damp so it does notaffect the process chamber, any portion of the load/unload system, the wafer transportsystem, any other equipment in the vicinity, or the facility itself. Once positioned,wafers should be motionless relative to the process surface or process carrier to preventgeneration of silicon particles by vibratory motion.

In order to function, a handler will have to greatly exceed the velocity criteria and mayexceed the acceleration criteria of Section 4.6.3.6. Care should be taken that therequired motions are performed as smoothly as possible.

4.9.9 Maintainability, Serviceability, and Cleanability

All wafer handling surfaces should be cleanable, resistant to water-based cleaners (nochlorofluorocarbons), and polished where possible. Blind holes, or any holes, slots, orcrevices that cannot be cleaned should be minimized or eliminated wherever possible.All surfaces should be oriented so it is possible to wipe the entire surface. Generousfillets and radii are recommended on all interior and exterior corners.

The wafer handling mechanism should be capable of being cleaned and recoveringquickly to acceptable particle levels.

5. System Integration

At no time during final assembly, certification, packaging, or shipment should thecleaned parts, equipment or completed system be exposed to an environment that doesnot meet Class 100 or better conditions.


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5.1 Assembly

Because particles, ionics, and organics are extremely difficult to remove from surfaces,it is important to minimize their accumulation.

5.1.1 Preparation

5.1.1.1 Tools—Maintain a set of clean tools in the clean assembly area. If this is not possible, toolsshould be cleaned according to the following section (cleaning) each time they reenter the cleanassembly area.

5.1.1.2 Cleaning—Assembly tools and all system components should be vacuumed, blown off withfiltered air and cleaned with a solution of 10% IPA in DI water immediately prior to beingbrought into the clean assembly area. Use swabs and wipes rated for Class 100 service.

Cutting oils, lubricants, and solder flux should be removed before parts are brought in tothe clean assembly area.

5.1.1.3 Exclusions—Machining, sawing, welding, brazing, grinding and sanding operations must becompleted before components are brought into the clean assembly area.

5.1.2 Operating Conditions

5.1.2.1 Cleanroom—Assembly, test, and preparation for shipment should take place in a Class 100 (perFED–STD–209) or better clean assembly area. Exhaust trunks should be provided to removeany fumes generated by the equipment, e.g., pump, process or cylinder exhaust. A cleanroomvacuum should be readily available.

5.1.2.2 Personnel—Personnel in the clean area should be entirely gowned and gloved in approvedcleanroom garments so that the feet are entirely enclosed, the face is covered across the mouth,and a hair net is worn, in accordance with IES RP-003 (see Section 2.1.3).

5.1.2.3 Procedures—When assembling components, procedures that minimize generation ofcontamination should be followed. Debris should immediately be vacuumed. Drilling,soldering, and other small tool operations should be a two person effort, with one vacuuming.

5.2 Certification

Specific testing on each individual tool may be required and should be negotiatedbetween the supplier and end user. Test methodology should accompany test data.Examples of such testing are PWP, and gas and vacuum system leak rates.

Suppliers should be prepared to generate and present proof of adherence to thisguideline on those portions that are negotiated with the end user and become part of thecontractual agreement.


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5.2.1 Air Return Particle Generation

Class 1 air will flow through and past the tooling and support equipment, and then intothe return air stream. Particles generated by the tooling and support equipment shouldnot add to the return flow either:

more than 1.06 particles (0.5 µm [19.7 µin] or larger) per liter ormore than 0.071 particles (2.0 µm [78.74 µin] or larger) per liter

Laser particle counter(s), placed downstream of the tooling and support equipment, inthe return air flow, should be used to measure particle concentration before and aftertool installation. The number of positions tested should be at least equal to the squareroot of the tool cross section (in square feet), and the locations should be determined bymutual agreement during the final design review.

The supplier's clean assembly area will generally not meet Class 1 requirements, so thistest cannot be performed with precision until the final user installation. However, areduced sensitivity version of the test can be run prior to shipment, based on actualconditions.

5.2.2 Particles per Wafer Pass

The equipment should not add particles to the wafer ambient environment to the extentthat the environment is degraded to a class greater than Class 1 per FED–STD–209 orper the facility specification.

As the wafers proceed through the more than one hundred steps required to completetheir manufacture, they collect and shed particles in a variety of ways. The effect thatparticles have on yield varies greatly from one process step to another. The PWPrequirement for a particular process step is a matter to be negotiated between the toolingsupplier and end user. Tests should be conducted per SEMI E14 (see Section 2.1.6).

As in the case of air return particle count, it may not be possible to perform a PWP testwith precision prior to shipment, and a reduced sensitivity version will have to benegotiated.

5.2.3 Other Measurements

The end user may specify certifications of certain operating parameters, assemblyconditions, or components. In these cases, test methodology and actual test data shouldaccompany certifications. Examples of such certifications are compliance to FED-STD-209 for cleanrooms, surface morphology and chemistry data on gas handlingcomponents, and data on a supplier's DI water quality, purge gas purity, and welding gaspurity. Materials certification, including outgassing, weight loss, absorption andleaching may also be requested. Sound and vibration certification of equipment may berequested as well.


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5.3 Packaging and Delivery

5.3.1 Triple Wrap Strategy

The individual wraps are intended to be removed in stages and should adhere to thefollowing guidelines:

5.3.1.1 Inner wrap—This wrap should stay with the tooling all the way into the final cleanroom or astaging area of the same order wipe down. The wrap should be cleaned prior to movement intothe cleanroom.

5.3.1.2 Middle wrap—This wrap should stay with tooling until it reaches a Class 10,000 intermediatestaging area. The wrap should be cleaned before leaving the receiving area and again before itis removed in the staging area.

5.3.1.3 Outer wrap—This wrap is used to protect the tooling while in transit to the loading dock.While the equipment is on the loading dock, outer shipping material should be removed and thewrap cleaned and removed.

5.3.2 Clean Assembly Area

Following final assembly and test, all exposed parts should be thoroughly wiped downwith deionized water, using cleanroom wipes. Approved materials for cleaning aredescribed in Section 5.3.4. Tooling should then be totally enclosed in a clean, oil-freeinner wrap using transfer tape as required.7 If two sets of pallets are used, the innerpallet should meet the requirements of Section 4.2.2 and should be enclosed with thetool. Jacking points should be identified to facilitate rigging.

5.3.3 Dedicated Packaging Area

After the first wrap has been applied, the equipment should be moved to a dedicatedclean (Class 10,000 or better) packaging area. Here the outer two wraps of clearpolyethylene are installed and taped.

After the equipment is triple wrapped, it should be placed on a pallet so that the triplewrapping is not damaged or violated. The pallet should be movable (with equipmentattached to it) with a conventional pallet jack or fork lift. The equipment as well shouldbe capable of placement on and removal from the pallet with a conventional pallet jackor fork lift without compromising or tearing any of the triple wrapping.

After the equipment is on the pallet, the manufacturer may use any conventionalpackaging materials (e.g., bubble wrap, styrofoam, or wood) to ensure that theequipment is not damaged in transit. However, these conventional materials cannotcompromise or tear the triple wrapping.

7

Tycleen, a nonshedding wrap from W. S. Tyler, Inc. or Marvelseal 470, from Ludlow Corp. are recommended.


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5.3.4 Recommended Materials

5.3.4.1 For cleaning and triple wrap packaging:

DI Water, resistivity 18.0 Megohm-cm, minimumUHP isopropyl alcohol (IPA)Cleaning solution, 10% IPA + DI waterLintfree cleaning swabsPolyester cleanroom wipes with thermally sealed edgesOil-free 6 mil polyethylene sheeting (for middle and outer wrap)A nonshedding polyethylene wrap (such as Tycleen) is recommended for inner wrap7

Nonparticulate adhesive tape

5.3.4.2 For packaging outside the triple wrap:

Paper or cardboard of any typeWoodBubblewrap, styrofoam, and foam rubberMasking tape, duct tape, and paper tapeNoncleanroom wipers

5.3.5 Other Delivery Considerations

Three axis shock sensors and tilt sensors should be attached to the crate that houses theequipment. These indicators should be checked upon delivery to see if the package hassuffered trauma during shipment.

Ground transport of the equipment should be via air ride vans.


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Task Force Participants

David Jensen (Group Leader)

Digital

Don Deal

FSI

Chuck Holland

Lam Research

Ed Rode

Genus

Jim Ogg

Millipore

Tom Smart

National Semiconductor

Jeff Davis

Motorola

Jackie Marsh

SEMATECH

Terry Francis

Applied Materials

Sarat Misro

LSI

Kevin Hassett

Intel

Mike Slama

NSC/SEMATECH

Richard Novak

Submicron Systems

Wayne Harnad

Motorola

SEMATECH Technology Transfer2706 Montopolis Drive

Austin, TX 78741

http://www.sematech.org

Date post:	20-Feb-2018
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