Date post: | 11-Jan-2016 |
Category: |
Documents |
Upload: | ursula-ray |
View: | 212 times |
Download: | 0 times |
TOPICS IN (NANO) BIOTECHNOLOGY
Microfabrication techniquesJanuary 9th, 2007
PhD Course
Introduction
Microsystem components
Definition
Terminology
Benefits of Microsystems
Benefits of microsystems
Benefits of Microsystems
Benefits of Microsystems
History
Applications
Example...
Microsensors
Microactuators
Microfluidics
Microsystem Applications
Concentrated System in a Single Box
Bipolar, BCD, CMOSBiCMOS, VIP,µ-Machining
Power Management
InformationProcessing(Super Integration)
MultifunctionPeripheral (System
Oriented Tech.)
Data Acquisitionand Conversion
Bipolar, CMOS,RF-BiCMOS,µ-Machining
Central Processing(µP, DSP)
Digital CMOS
PowerActuators
Bipolar, BCD,CMOS, HVCMOS,VIP, µ-Machining
Memories
CMOS, Flash,DRAM, µ-Machining
Line, Batteries,Alternators, Solar Cells, Fuel Cells
Sensors
Antennas
Keyboards
LineInterfaces
Switches
Clock Clock
Clock
Lamps
Motors
Displays
Solenoids
Speakers
CRTs
Inkjets
Antennas
Microfabrication - applications
Microfabrication - applications
History of Lab-on-a-Chip-Systems and µTAS
1975: Gas chromatograph by S. Terry (Stanford-University)
1990: Micro channel liquid chromatograph
1990: „Micro Total Analysis System (µTAS)“ introduced by A. Manz
1992: Development of first capillary electrophoresis chips
1994: massive increase of publication about Lab-on-a-Chip and µTAS
1998: First PCR-micro chips
End 90th: Start of several Lab-on-a-Chip- and Bio-MEMS-companies
Applications of Lab on a Chip
• Medical diagnostics (PoC, …)
• Pharmaceutical development (HTS, HCS, …)
• Environmental analysis (monitoring, portable analysis, …)
• Food analysis
• Process control
• Process development (screening)
• Small scale production (e.g. fine chemicals, rare molecules, …)
µTAS
Design Scheme for a Lab on a Chip / µTAS
Sample inlet
Target identification• DNA primer• Antibody• Aptamers
Amplification• Enzymatic reaction• PCR / NASBA• “Secondary reaction”
Sample preparation• Cell sorting• Filtration• Washing• Cell lysis• Purification
Sensor
• Electrochemical / Amperometric / Voltametric / Impedance /…
• Optical / Fluorescence / Absorption /…
• Mechanical / Oscillator / Deflection / …
• Temperature
Instrument output
User
Lab-on-a-Chip Systems
Generic Characteristics
• Integrated
• Miniaturized (Small channels)
• Automatic operation
Lab-on-a-Chip Systems: Derived Characteristics
• Low chemistry consumption
• Laminar fluidics
• High control (no chaotic processes)
• Fast diffusion (fast operation for diffusion limited processes)
• Easy parallelization
• “New” effects due to smaller dimensions
• Higher production costs (with respect to system volume)
What is special in µ-fluidics?… At least one characteristic dimension in the
micron range (1-100 µm)
• Inertia has low effects
• Surface tension is dominant
• Gravity has minor importance
• Mixing is due to diffusion mainly (not due to convection)
• Fast heat transfer due to small distances
• High Surface-To-Volume: Inhomogeneous reactions (surface reaction) are essential (e.g. catalysis, sensors, unspecific binding)
• …
Challenges during developmentPerformance
• Sensitivity
• Selectivity
• Reproducibility
Hardware
• Speed of development
• Availability of sufficient systems /chips
Know how
• Intellectual property situation
• Theoretical understanding
Challenges for commercialization
• Robustness
• Reproducibility (QM, GMP, …)
• Approval of the product (CE, FDA, …)
• Self life
• Pricing
• Availability of sufficient systems (producibility of the product)
Reaction
Protocol
• Metering of sample
• Mixing of sample and reagents
• Optical detection
Detection principle
• Absorption at 545 nm
Lab-on-a-Chip an Example
Commercial Systems: Glucose detection
Roche; AccuCheck
Glucose in blood
Lifescan; SureStep Flexx
Glucose monitor
Commercial Systems: Blood Analyzer
Abbott; i-STAT
Siemens; Quicklab
CARESIDE
Analyzer
Commercial SystemsAdvalytix
1 µl PCR slides for forensic
Commercial Systems
Nanostream; Velove microparallel LC
(micro parallel liquid chromatography)
Tecan; LabCD(development stop 7.05)
Gyros; Gyrolab
Commercial Systems
Agilent/Caliper
Product: Bioanalyser
Electrophoresis
Commercial Systems
Aclara Biosciences
Product: Labcard
(Electrophoresis)
Microfabrication Techniques
Overview
Overview • Micromachining technologies
• Bulk micromachining• Surface Micromachining
• Basic Processes• Lithography• Wet etching• Dry etching• Deposition
UV-lithography • Lithography refers to a process whereby the
top layer on a wafer is selectively removed or patterned.
• Photolithography; light-stone-writing in greek
UV-lithography
Laser Sources
Wmin = k1 .
NA
Types of UV-lithography
UV-lithography
UV-lithography • Mask making
• Resist spinning
• Alignment of wafer and mask
• Resist tone, Tg, critical dimensions
• Lithography resolution
• Depth of Focus
• Resist wall profile manipulation
• Clean-rooms, wafer cleaning
• Process sequence
UV-lithography
• Resist applied to the surface using a spin-coating machine, which holds the wafer of a semiconductor, using a vacuum, and spins it at high-speed (3000-6000 rpm) for a period of 15-30 seconds.
• Preparation concluded by a pre-bake, where wafer is generally heated in a convection oven and then a hotplate to evaporate resist solvent
Photoresist
Developer
Process
UV-lithography
• Fiducals are patterns used for alignment on wafer steppers. These fiducials are located outside of the array or fields.
• Alignment of the mask is critical and must be achieved in the x-y plane
• Double alignment is especially important in the fabrication of micromachines
Advanced Lithography
• Electron-beam lithography
• Ion beam lithography
• X-ray lithography
• Extreme UV-lithography
Wmin = k1 .
NA Reduce k1
Reduce
Increase NA
Advanced Lithography
Advanced Lithography
Wavelengths started with the g-line (436 nm) of Hg - good down to 0.4m
Next came the 365nm i-line in the near-UV - this took us down to 0.3m
BUT no light bulb that emits enough intensity at wavelengths considerably smaller than 365nm
The solution was excimer lasers - 248nm, 194nm and 157nm (deep UV lithography)
this spelt …… the END of UV-lithography!
Advanced Lithography
Extreme UV Lithography
Technology breakthrough - 13.4nm wavelength of this light is more than 10 times shorter - allows patterning of lines below 50nm dimensions
Intel leading a consortium of six semiconductor companies called the EUV LLC to develop this technology
Extreme UV Lithography: Sources
Electron beam Lithography
Pattern directly written into resist by scanning e-beam
Eliminates the diffraction limits of optical lithography
Performance records:
- in PMMA (organic resist): 7nm
- in AlF3(inorganic resist): 2nm
Optical Electron Beam
Advantage
Low ~High precision Fast exposure speed Relatively low cost
No diffraction Easy to control Available for small features
Disadvantage
Light diffraction Alignment problem Debris between mask and wafer
Needs vacuum High system cost Slow
UV vs E-beam Lithography
Ion-beam Lithography• Variation of the electron-beam lithography technique - uses a focused ion beam instead of an electron beam
• The ions are field extracted from a liquid metal ion source (LMIS) that consists of a tungsten needle with a radius of curvature of 1mm that is wetted by a liquid metal.
• The application of an electric field (>108cm/V) to the wetted tip results in the formation of a cone with a radius of curvature of 10nm from which the ions are field extracted
• The extracted ions are accelerated, collimated and focused by a series of apertures and electrostatic lenses
• Spot-sizes of 10nm to 500nm are possible.
Ion-beam Lithography
X-ray Lithography
As shown in this figure, the penumbral blur, , on the adge of the resist image is given by:
= ag/L
a is the diameter of the x-ray source
g is the gap between mask and wafer
L is the distance from the source to the x-ray mask
LIGA
© M.J, Madou
LIGA
Allows the creation of 3-D structures with excellent tolerances and extremely high aspect ratios
Main drawback – very expensive to implement
Soft LithographyTransfer of a self-assembled monolayer precursor with an elastomeric stamp onto a substrate
1) A master is generated by photolithography and a stamp is obtained by casting of an elastomer (PDMS etc.)
2) A pattern is generated by stamping a SAM on a substrate
Ink-jet micromachining
Bulk, surface, DRIE
Bulk micromachining • As the name implies, bulk micromachining
focuses on the creation of patterns or features within the bulk of some sort of starting material. In doing so, we rely on the physical structure of the material in question (amnogst other variables) to control the shape of these features
• Although materials such as quartz, pyrex, GaAs, Ge, etc. Are used as teh starting material for this technology, the material that is most commonly used is silicon
• Silicon has well understood lattice structure composed of two interpenetrating face-centered-cubic (FCC) lattices
Silicon
Miller Index
Miller Index are symbolic vector representations of the orientation of the atomic planes that make up the crystal lattice
Miller Index
Greater density of atoms slower etch rates
Silicon wafer
• Silicon boules are grown using a seed material of known orientation. The boule is subsequently sliced into wafers that will have this same orientation.
• Silicon etchants and silicon wafer orientations are selected to create the necessary features within the bulk of the wafer.
Silicon wafer
Bulk micromaching
Bulk micromachining
• Anisotropic etchants such as KOH:H2O (alkaline) tend to
etch different crystal planes at different rates, thus giving rise to structures having well defined sidewalls with precise and predictable angles of inclination (very little undercutting).
Anisotropic etchants
Examples
• Isotropic etchants such as mixtures of HF:HNO3:CH3COOH (acidic) tend to etch different crystal planes at the same rate, thus giving rise to rounded structures with much undercutting.
Isotropic etchants
Isotropic etchants
Wet isotropic etching
Examples of etchants
Examples of etchants
Etch Stop
Dry isotropic etching
Dry anisotropic etching
Deep reactive ion etching
Deep reactive ion etching
Surface micromachining • In the case of surface micromachining,a different
approach is taken in that rather than etching into the bulk of the starting material, structures are built up on the substrate surface
• These structures are created via the repetitive addition of layers selected for their various material properties, followed by the selective removal of these layers in a specific sequence.
• The vast array of materials that can be “deposited” includes polysilicon, silicon nitride, oxide, polyimide, metals, etc.
Deposition
a) Chemical Vapor Deposition (CVD) systemsWhich rely on the chemical reaction of the constituents of a vapor phase at the substrate surface to deposit a solid film on this surface.
b) Physical Vapor Deposition (PVD) systemsWhich directly deposit the source material onto a given substrate in a “line-of-site impingement type deposition”.
Deposition systems may be divided into two groups:
a) CVD: Common film types & sample chemistries
Polysilicon:
Silicon Nitride:
Silicon Dioxide:
Deposition
DepositionTable 1. APCVD, LPCVD, and PECVD Comparisons CVD
ProcessAdvantages Disadvantages Applications
APCVD Simple, Fast Deposition,Low Temperature
Poor Step Coverage,Contamination
Low-temperature Oxides
LPCVD Excellent Purity,Excellent Uniformity,Good Step Coverage,Large Wafer Capacity
High Temperature,Slow Deposition
High-temperature Oxides, Silicon Nitride, Poly-Si, W, WSi2
PECVD Low Temperature,Good Step Coverage
Chemical and Particle Contamination
Low-temperature Insulators over Metals, Nitride Passivation
Deposition
b) Physical Vapor Deposition (PVD) systems
– In these types of thin film deposition systems, the source materials to be deposited take on a variety of forms:
• Solid• Liquid• Vapor
– In the case of PVD systems, the materials to be deposited are physically deposited using a variety of methods including:
• Thermal Evaporation • Sputtering• Etc. (Laser Ablation, Molecular Beam Epitaxy)
Deposition
a) Physical Vapor Deposition (PVD) systems -
continued
– The range of materials that may be deposited using these methods include:
• Metals such as:
– Al – Cu– Au– Ag– etc.
• Compound & hard materials such as:
– Cr– TiN– CrN– AlCuSi– etc.
Deposition
– The material to be deposited is placed in a crucible within a high-vacuum chamber.
– After the chamber is pumped down, the source is heated via (typically) resistive or e-beam heating. The material is heated to its boiling point such that it sublimates onto all exposed surfaces in the vacuum chamber.
– The amount of material deposited is controlled via a thickness monitor which is placed within the deposition chamber.
– The source material must be of high purity.
– Vacuum levels are on the order of 10-5 to 10-7 Torr.
Thermal Evaporation –
Resistive Heating
Thermal Evaporation –
e-Beam
Thermal Evaporation - General
Deposition
Thermal Evaporation - drawbacks
– Resistive heating is the simplest method of evaporating metals such as Al
or Au, but it is also the “dirtiest” in that contaminants which find their way
onto the filament tend to be evaporated along with the metal.
– The purity issue can be addressed via e-beam evaporation since the
cooled, non-molten high-purity material to be deposited acts as a crucible
during the process (see schematic on previous slide).
– In the case of resistive heating, temperature uniformity across the filament
is difficult to control and therefore, evaporation uniformity onto the
substrates may be a problem. This is not an issue with e-beam
evaporation
– E-beam evaporation may cause surface damage due to ionizing radiation
and/or X-rays (@ voltages above 10kV, the incident electron beam will
give rise to X-ray emission).
Deposition
Sputtering
Sputtering – principle of operation• A solid slab (ie., target) of the material to be deposited is placed in a
vacuum chamber along with the substrate on which the deposition is to
take place.
• The target is grounded.
• Argon gas is introduced into the chamber and ionized to a positive
charge.
• The Ar ions bombard the target and cause the target atoms to scatter,
with some of them landing on the substrate.
• The plasma is composed of the Ar atoms, Ar ions, the sputtered
material, gas atoms and electrons generated by the sputtering process.
• Allows the deposition of a large assortment of materials on any type of
substrate
Deposition
Deposition: sputtering
Sputtering – advantages/disadvantages
M.J. Madou
Deposition
Surface micromachining
Surface micromachining
Surface micromachining
Sealed cavity
Examples
Examples
Bulk vs Surface
• Both bulk and surface micromachining concepts are most often combined to create both intricate and simple devices and systems.
• Other observations (M.J. Madou):
Process Flow
Process Flow
Process Flow
Process Flow
Process Flow
http://www.thoughtequity.com/video/clip/1659037_021.do