One Resistivity Sensor for All Stages of Water Treatment METTLER TOLEDO Thornton’s cutting-edge UniCond ® technology provides increased performance and higher accuracy for conductivity / resistivity measurements over a very wide range. Robust, titanium bodied, digital sensors operate in all stages of water treatment, without compromising sensitivity, reliability, or accuracy. Limitations of conventional sensors Conventional conductivity / resistivity measurements, especially with analog sensors and transmitters, are limited by the effects of sensor polarization in higher conductivity waters, transmitter errors and by interference from cable impedance and capacitance. This results in the need to utilize two or more sensors with differ- ent cell constants to cover the range from seawater, raw water, reclaimed or recycled waters through the purification stages to ultrapure water. Consequently, the use of multiple sensors, additional spare parts and fittings is re- quired, which introduces the possibility of installation of an incorrect sensor for the application. Also, with conventional sen- sors the user must remember to manually enter the precise cell constant and tem- perature calibration data for each indi- vidual sensor into the transmitter’s memory to achieve rated accuracy. In addition, conductivity / resistivity sensors are typically located at a considerable distance from the transmitter and control panel, resulting in accuracy errors caused by analog sensors and cable capacitance. Over the years, METTLER TOLEDO Thornton has optimized the wiring and signal handling to minimize cable ca- pacitance and resistance effects so that accurate measurements are provided. Nevertheless, these multiple effects result in reduced accuracy and limitations in measurement range. 11 News Microelectronics Perspectives in Pure Water Analytics THORNTON Leading Pure Water Analytics
Transcript
One Resistivity Sensorfor All Stages of Water TreatmentMETTLER TOLEDO Thornton’s cutting-edge UniCond® technology provides
increased performance and higher accuracy for conductivity / resistivity
measurements over a very wide range. Robust, titanium bodied, digital
sensors operate in all stages of water treatment, without compromising
sensitivity, reliability, or accuracy.
Limitations of conventional sensors Conventional conductivity / resistivity measurements, especially with analog sensors and transmitters, are limited by the effects of sensor polarization in higher conductivity waters, transmitter errors and by interference from cable impedance and capacitance. This results in the need to utilize two or more sensors with differ-ent cell constants to cover the range from seawater, raw water, reclaimed or recycled waters through the purification stages to ultrapure water.
Consequently, the use of multiple sensors, additional spare parts and fittings is re-quired, which introduces the possibility of installation of an incorrect sensor for the application. Also, with conventional sen-
sors the user must remember to manually enter the precise cell constant and tem-perature calibration data for each indi-vidual sensor into the transmitter’s memory to achieve rated accuracy. In addition, conductivity / resistivity sensors are typically located at a considerable distance from the transmitter and control panel, resulting in accuracy errors caused by analog sensors and cable capacitance.
Over the years, METTLER TOLEDO Thornton has optimized the wiring and signal handling to minimize cable ca-pacitance and resistance effects so that accurate measurements are provided. Nevertheless, these multiple effects result in reduced accuracy and limitations in measurement range.
11News
MicroelectronicsPerspectives in Pure Water Analytics
THORNTONLeading Pure Water Analytics
2 METTLER TOLEDO Microelectronics News 11
Unified and universal solution METTLER TOLEDO Thornton, the tech-nology-leading experts in conductivity / resistivity measurements, recognized these limitations and has made signifi-cant improvements in conductivity / resis-tivity sensor and measurement technol-ogy. Our engineers developed a miniaturized measuring circuit that is embedded in the head of the sensor and sends a robust digital signal to the transmitter.
This unified design reduces the effective wiring distance between the sensor and the measuring circuit to just a couple of centimeters. Without the effects of long cable capacitance and resistance, more sophisticated measuring techniques are possible. Leadwire effects are thus negli-gible, and electrochemical factors and sensor polarization affecting the measure-ment can be dealt with more directly to improve the sensor measurement range. Measurement from ultrapure water to seawater up to 50,000 μS / cm can now be made with a single UniCond sensor with excellent accuracy.
Superior accuracy and reliability The UniCond digital sensor is more ac-curate because it is calibrated as a system which includes the cell constant, the temperature sensor, and the measuring circuits. With all these components inte-grated for calibration, individual errors are no longer cumulative, i.e., there is no added error caused by combining separate sensors, transmitters, and cables. The re-sult is a sensor with an accuracy improve-ment of 33 % over conventional analog sensors.
Covering the entire range of most water treatment systems, the UniCond sensor is universal and simplifies specification, documentation, installation, wiring, op-eration, and ordering of spare parts.
Intelligent Sensor Management provides Plug and Measure convenience UniCond sensors utilize METTLER TOLEDO’s Intelligent Sensor Management (ISM®) technology. One of the many ad-vantages of ISM is that sensors maintain precise factory calibration data, as well as
sensor identification, serial number, etc. in the sensor’s internal memory. This enables fast and simple Plug and Measure installation, eliminating manual data entry and any chance of operator error at start-up.
ISM’s intelligent diagnostics tools allow real-time monitoring of sensor condition and provides valuable information for predictive maintenance and scheduled calibrations, thereby reducing downtime and service costs.
The METTLER TOLEDO Thornton ISM conductivity / resistivity digital sensors and transmitters are the only digital measurement loop that allows for calibra-tion of the sensor and the transmitter in the field. Another breakthrough devel-oped by Thornton engineers.
• Setup and Configuration for Sodium and Silica Analyzers
• Preventive Maintenance for TOC Sen-sors, Sodium Analyzers, and Silica Ana-lyzers
Service tools created by the expertsOur Service Technicians are equipped with tools designed by the industry experts at METTLER TOLEDO. When it comes to calibrations and proactive maintenance tasks on your process measurement equip-ment, nothing but the very best will do. This is why our team of experts designs, manufactures, and equips our Service Technicians with the world’s best in cali-bration and testing equipment.
Be readyEnsure your process measurement equip-ment delivers peak performance and ac-curate results. Contact your local METTLER TOLEDO Representative or visit us online to learn more.
c www.mt.com/pro-service
Industry prefers service by the original manufacturerIn a recent survey of companies that purchase process measurement equip-ment, 75 % said they prefer to have services performed by the original manufacturer. This is not surprising since services pro-vided by the manufacturer are aligned with the performance and accuracy stan-dards of the equipment. At METTLER TOLEDO we are proud of our offerings through both products and services. Com-bined, we offer a complete solution no one can beat!
Good preparation includes a service planHow do you know if your analytics are optimized for the most efficient measure-ments? A proactive service plan is the best way to maintain readiness, accuracy, and compliance to industry standards or guidelines. Service Plans by METTLER TOLEDO help ensure your success from setup to calibration, from preventive maintenance to up-to-date standard op-erating documentation, and everywhere in-between.
Service offerings to fit your businessMETTLER TOLEDO provides many perfor-mance enhancing, cost saving services such as:• Calibration for Conductivity / Resistivity
Sensors and TOC Sensors
Ensure Optimum Measurement Performancewith Service from METTLER TOLEDOMaintain accurate measurement of your processes and critical quality standards with
our Service offerings. Our teams of highly-trained Service Technicians are ready to help
you get the most value from your water analytics instrumentation.
Is Essential for Semiconductor Quality A large Asian semiconductor foundry requires very low dissolved oxygen in their ultrapure
water system. The METTLER TOLEDO Thornton Optical DO system provides speed of
response, low detection levels and reduced maintenance that exceed their requirements.
Concentrations of DO in the point-of-use (POU) water during wafer processing are maintained at less than 5 ppb to prevent loss of control of gate oxide thickness. A higher level of DO at the POU can result in unexpected etching by the oxygenated water, resulting in failures and low yields – at great financial cost.
Instrumentation choices Dissolved oxygen instrumentation has been a high priority at this semiconductor foundry facility. For this reason, the foundry’s original instrument choice was a very expensive system with a reputation for accurate measurement. However, the equipment also requires extensive, fre-
quent, and time-consuming maintenance, often involving costly replacement parts. In addition, after installing a maintained or new sensor, foundry technicians have to wait three to four days before the DO read-ings are sufficiently stable to be used.
In frustration with the situation, techni-cians at the foundry evaluated METTLER TOLEDO Thornton’s Optical DO Sensor and M800 Transmitter solution. Unlike their existing system the Thornton sensor utilizes fluorescence quenching to accu-rately and rapidly determine DO levels. This highly dependable technique is be-coming established as the preferred DO measurement technology in semiconduc-tor fabs across the globe.
It is favored not simply for its speed and accuracy: Optical technology requires no polarization time, so measurement system availability is very high. It is also low in maintenance, further contributing towards measurement point availability.
Accuracy and response advantagesTechnicians at the foundry were pleased to discover that when compared with the more expensive existing instrumentation, the Thornton Optical DO sensor produced the same accuracy and sensitivity at low DO levels.
Why measure dissolved oxygen in a semiconductor foundry?To ensure reliable performance of their technology-leading foundry operations, one of Asia’s largest semiconductor pro-ducers must control and minimize dis-solved oxygen (DO) in all of the ultrapure water (UPW) system polishing loops in their foundries.
Dissolved oxygen is measured after de-gasification of UPW to confirm oxygen removal from the water. Reducing DO maintains the low conductivity of the water, which is critical for subsequent treatment steps, particularly continuous electrodeionization.
They were also impressed by the Thornton sensor’s speed of response and stability: After an air calibration the sensor stabi-lized and dropped to ppb levels within minutes of operation, rather than the days required for the existing system.
The Thornton sensor’s very low mainte-nance requirement was also very much appreciated as it amounts to no more than approximately annual replacement of the one-piece oxygen-sensing element, the OptoCap.
In addition, the M800 Transmitter offers multi-channel, multi-parameter capabili-ties, which enable the DO measurement to be paired with conductivity / resistivity plus temperature measurements, TOC and pH, all on the same transmitter. Having a common platform for multiple parameters saves substantially on documentation, training, maintenance and spare parts.
The other great benefits of the system noted by the technicians are due to its Intelligent Sensor Management (ISM®) technology. ISM simplifies sensor handling and instal-lation, and provides advanced diagnostic tools that predict when maintenance will be required. The Dynamic Lifetime Indica-tor monitors the quality of the OptoCap after each calibration and, together with information on the current process condi-tions, calculates and displays on the M800 Transmitter the remaining lifetime of the OptoCap. Unscheduled downtime due to sudden failure of the sensing element is therefore avoided.
Long-term savings The combination of measurement accu-racy, fast response, extended maintenance intervals plus the sensor’s competitive price has convinced the foundry techni-cians of the value of the Thornton DO solu-tion and plans are being made to install
the sensor across the various measure-ments and control points on the foundry’s UPW systems.
ficiency. The quality of the UPW after production and in the distribution system is monitored in-line using high-precision conductivity and TOC measurements. In addition, a decision is made, based on these measurements, as to whether low-contamination rinse water is to be recycled to the UPW treatment system or reclaimed, which can substantially reduce the sig-nificant water treatment costs.
High-accuracy conductivity measurementThe greatest demands on water purity are imposed in the semiconductor and photo-voltaic industry. Water is used having a conductivity equivalent to the theoretical value of 0.005501 μS / cm at 25 °C. In these industries the reciprocal value of the electrolytic conductivity, the specific resis-tance, is indicated for monitoring for ionic contaminants. Here the aim is a value of 18.18 MΩ × cm at 25 °C. With a coefficient of 4 to 7 % / K the temperature behavior of UPW is clearly different to other common electrolytes (e.g. approx. 2 % / K for KCl). Therefore, special algorithms for UPW must be established for precise tempera-ture compensation. Along with this com-putation the exact determination of the cell constants of the conductivity sensors is of great significance for the accuracy of the measurement.
Since 1964, METTLER TOLEDO Thornton has led the field of UPW analytics and is recognized as having the most precise
measurement systems for determining specific resistance / electrolytic conductiv-ity in pure and ultrapure water. Our latest UniCond technology has improved the accuracy and stability of resistivity mea-surement using digital technology to en-sure our customers benefit from more precise measurement and control of their UPW while improving their production yields.
At the Thornton manufacturing plant the cell constants of UniCond sensors are de-termined with a maximum unreliability of only 1 %. In this process UPW is used as the calibration medium which corresponds also to the later operating range of the measurement cells in UPW applications. The cell constants are, moreover, traceable to generally accepted standards such as those established by ASTM and NIST.
Fastest TOC determinationSince no statement on organic contamina-tion can be made using specific resistance, it must be monitored using a TOC ana-lyzer. According to information from solar cell manufacturers, the limit value for UPW is 1 or 0.5 ppb of carbon.
The Thornton 5000TOCi sensor is cur-rently the fastest analyzer on the market. Instead of batch oxidation that requires analysis times of typically 7 to 15 minutes, the 5000TOCi uses the dynamic UV oxida-tion process. A sample stream of the UPW permanently flows through the analyzer.
The importance of UPW in solar cell manufactureLarge quantities of high quality UPW are required in solar cell production. After the raw wafers are cut from silicon ingots using wire saws, slurry is removed from the wafers in a cleaning process and the wafers are then thoroughly rinsed with UPW.
After texturing the surface using potas-sium hydroxide (KOH) or mixtures of hy-drofluoric acid and nitric acid (HF / HNO3), residues from the etching are removed with another UPW rinse. Next the p / n transi-tion is created by phosphor diffusion. The resulting phosphor glass layer on the surface must be removed by oxide etching, which requires a further UPW rinse, before a blue anti-reflection coating is deposited for the purpose of reducing optical losses and for electrical surface passivation.
A clean wafer surface is indispensable prior to the phosphor diffusion and coating process steps for achieving maximum ef-ficiency of the subsequent solar cell. The clean surface of the special glass panes plays a critical role also at the time of processing the solar cells into modules in the matrix unit, before the cells are imbed-ded in the glass foil sandwich in the laminator.
A final rinse with high-quality UPW en-sures that the silicon and glass surfaces are not contaminated by deposits of salts or organic compounds that would affect ef-
Sola
r Cel
l Pro
duct
ion Ensure Your UPW Quality
for Maximum Efficiency of Solar CellsIn the manufacture of solar wafers and solar cells the highest purity requirements are
imposed on the water used for cleaning and rinsing. High-precision, modern conductivity
and TOC instruments provide real-time confidence in the quality of ultrapure water.
The entry conductivity is measured, then the sample flows through a silicon glass coil and is irradiated with high-energy UV light. The exposure to strong UV-light re-sults in any organic molecules present in the solution breaking down into carbon dioxide and water. The carbon dioxide generated during UV exposure partly dis-solves in water, which in turn leads to the formation of carbonic acid. The UPW now has a slightly higher conductivity, and using the difference in conductivity before and after UV oxidation the TOC content is calculated.
This method is not only especially fast but also particularly maintenance-friendly
since no moving parts such as pumps, chemicals or membranes are involved. It is only the UV lamp that must be periodi-cally replaced. With a detection limit of 0.025 ppb C and a response time of < 1 minute the stringent requirements of the photovoltaic and semiconductor industry on the measurement system are completely satisfied.
Highly flexible transmitter The M800 Transmitter is a multi-channel measurement instrument with Intelligent Management System (ISM®) technology that features two analog pulse inputs and four ISM channels. ISM provides pre-cali-bration for sensors for Plug and Measure
start-up speed and simplicity, while im-proving measurement accuracy, perfor-mance and predictive maintenance capa-bilities. The analog pulse inputs are utilized for additional flow measurement, a common requirement in UPW monitor-ing and control.
Confidence in UPWThe purity of UPW is decisive for product quality of solar wafers, cells and modules. Modern UPW analysis systems ensure the required water quality with regard to conductivity and TOC, and in virtue of their modular design are very versatile for utilization in system control and quality assurance.c www.mt.com/conductivityc www.mt.com/TOC
Ultrapure Water in Semiconductor ManufacturingUltrapure water is a highly effective, com-monly used solvent to remove impurities in the production and cleaning of wafers. Semiconductor fabricators rely on water for all wet processes, including etching, cleaning, stripping, spuddering, photoli-thography and chemical-mechanical planarization. With changes to ITRS standards, manufac-turing equipment and water systems must be upgraded.
Measuring Total Organic CarbonAs semiconductor manufacturing be-comes more advanced and wafers become larger, reduction in use of expensive ul-trapure water becomes more important. Recycled water can be used, but it must meet UPW feedwater requirements to avoid contamination. One aspect of monitoring recycled water efficiently is through continuous measurement of Total Organic Carbon (TOC) so that or-
ganic impurities are detected immedi-
ately and issues
Standard Enforcer for the IndustryThe competitive nature of the semicon-ductor industry makes it ever changing, with innovations steadily emerging. This attribute results in manufacturers being understandably reluctant to reveal their projects and ideas, making it seemingly impossible to predict the needs of future technologies. However, looking beyond the interests of individual companies, it be-comes clear that collaboration is key to maintaining the health of the industry.
The ITRS is a global partnership that helps make the health and growth of the indus-try possible. The bodyʼs International Roadmap Committee, made up of industry experts, works with chip manufacturers, equipment suppliers and R & D experts from around the world to create policies and guidelines to facilitate progress among all interested parties by harmoniz-ing the standards in North America, Eu-rope, Japan, China and Taiwan.
Semiconductor applications cover a wide range of topics, so the standards published and enforced by ITRS often originate from more specialized groups such as the Liquid Chemicals and Facilities committees within SEMI, the global association that serves manufacturers in the micro and nanoelectronics industries. These two committees set the standards relevant to ultrapure water in the semiconductor in-dustry.
ITRS
and
UPW
The Road Aheadfor Ultrapure Water MeasurementThe International Technology Roadmap for Semiconductors (ITRS) exists
to further the progress of the global semiconductor industry. With
linewidths continuing to narrow, the requirements for ever-purer water
within a water system can be pinpointed and quickly resolved.
Challenges with Critical OrganicsComponents in the semiconductor manu-facturing process are extremely small and sensitive. Linewidths can be as narrow as 7 nanometers (a standard sheet of paper has a thickness of around 100,000 nano-meters) and the slightest presence of im-purities or particles can result in reduced yield, with a loss of productivity and rev-enue for semiconductor manufacturers.
Removal of impurities is therefore essen-tial. This has led to greater tightening of specifications in the ITRS Roadmap for critical organics, metal ions and particles in ultrapure water.
Organics can be either critical or non-critical, where critical organics are of greater concern because they may react with wafer surfaces and create pattern defects and resist-adhesion defects in photolithography. TOC measurement fo-cuses on polar organics and harmful or-ganics with boiling points above 200 °C, which can result in metal corrosion or metal deposition defects (and under cer-tain conditions organics with high boiling
points can form silicon carbide on wafer surfaces).
Measuring both critical and non-critical organics is important, but to varying de-grees. ITRS and SEMI are reviewing a “double standard” for organic levels, where the limit for critical organic com-pounds is less than 1 ppb and the limit for non-critical organics is less than 3 ppb. The challenge with these different limits is that current water purification technol-ogy cannot differentiate between critical and non-critical organics to produce two separate measurements. Even if ITRS publishes a tighter standard, semiconduc-tor manufacturers are limited by the current technology to measure particle levels. ITRS carries on constant conversa-tions about the challenge of setting stan-dards that can actually be met techno-logically.
Moving ForwardThe purpose of ITRS is to publish stan-dards that facilitate current and future semiconductor processes and progress. ITRS attempts to predict the needs and define the path of the entire industry as it becomes more advanced. Because they are such an important industry authority,
their focus on the challenges of measuring critical and non-critical organics will encourage the semiconductor community to develop innovative solutions as they continue to strive for increased yield and profitability.
The 2800 Si Analyzer provides reliable, repeatable, and accurate
measurements of silica in ultrapure water. Advanced features, including
unattended calibration and automatic zeroing, allow users to prevent
UPW-related issues such as spot formation on wafers.
By integrating technological ad-vances and satisfying user needs, the 2800 Si Analyzer provides reli-able measurements of silica while having one of the lowest costs of ownership among all silica analyzers.
Find out more at:c www.mt.com/Thornton-silica
Water spots on wafers lead to a number of quality issues, including reduced film adhesion and contact resistance.
To minimize these, the silica level in ultrapure water has to be continu-ously monitored and controlled at sub-ppb levels.
Your benefits
Long service intervals Large reagent containers allow longer service intervals and reduce analyzer downtime.
Save Time ProgrammingYour M800 TransmittersMETTLER TOLEDO Thornton’s configuration tool is now included with each M800 ISM® Transmitter to enhance the value of simple and consistent programming. This tool provides a means to upload or download transmitter configuration and can store configuration files for later use. The transmitter configuration tool, with its bi-directional capability, greatly reduces the time required to program transmitters and assures consistency in programming for multiple transmitters or to duplicate existing configurations.
The M800 Transmitter measures conductivity, resistivity, pH, ORP, dissolved oxygen, dissolved ozone, TOC and flow. With four dis-play lines and eight analog outputs, the M800 can provide full capability on all analytical measurement parameters.
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