Semiconductor Perspectives in Pure Water Analytics 11 News THORNTON Leading Pure Water Analytics Thornton Vortex Flow Sensor Reduces Risk of Contamination Monitoring of ultrapure water quality with the THORNTON Vortex flow sensor eliminates any risk of contributed metal ion contamination and therefore improves reliability and prevents loss of yield. Background As the on-line information age continues to grow and evolve, the reliability of datastorage systems becomes an increasingly important consideration for users and manufacturers alike. For this reason, providers of sub-systems for hard disk manufacturers must be highly selective when choosing components and vendors. When faced with such a choice, a major subsystem manufacturer in Malaysia selected THORNTON PVDF vortex flow sensors to meet the critical needs of their precision hard disk cleaning systems. Critical processes Flow-sensing is necessary to monitor the quantity of Ultrapure Water being used to clean the hard disk substrate during the manufacturing and cleaning process. The all-plastic wetted construction of the Thornton vortex flow sensor eliminates any risk of metal ion contamination during use of the precision cleaning system. The elimination of moving components in the vortex design also removes concern over particulate generation during operation which can lead to costly yield issues. Long-term reliability Thornton s new vortex flow sensor design virtually eliminates any concern over long-term component reliability through component wear. This maintenance-free design maximizes system productivity through extended up-time. When combined with high accuracy specifications of ± 1 % of full scale and ± 0.25 % repeatability, the Thornton vortex flow sensor provides simple, reliable and precise flow
measurement required for integration into a precision cleaning system. Global Support Mettler-Toledo Thornton s extensive international product support capabilities provide additional confidence that any needed support can be easily obtained, regardless of where it is needed. The extensive water-system capability supplied by THORNTON technical experts provides the added assurance that this support will not only cover specific components, but can extend into the entire water system. Vortex Flow Meters The ultimate solution for measuring the flow rates of ultrapure water and chemicals: Our range of Vortex Flow sensors consist of a molded unibody, available in PFA, PVC or PVDF. These sensors have no moving parts, and any potential for fluid contamination is eliminated by the corrosive-resistant all-plastic construction. PVC and PVDF Version Straight Pipe 10 pipe diameters upstream, 5 pipe diameters downstream Requirements Pressure / PVC: 10 bar at 21 C (150 psi at 70 F) Temperature 6.5 bar at 38 C (93 psi at 100 F) PVDF: 10 bar at 21 C (150 psi at 70 F) 9 bar at 65 C (130 psi at 150 F) Viscosity For liquids more viscous than water, consult THORNTON Accuracy ± 1 % of full scale Enclosure Rating: NEMA 4X (IP 65) Electrical 1 2" NPTF port with screw terminal wiring. Wiring may be Connections run up to 305 m (1,000 ft) with 3-conductor, 20 gauge, shielded cable, such as Belden 9364. Power supply One external 12 V DC isolated power supply 1000-65 is required for one or two pulse input sensors. one kit 1000-67 is required for each pulse input sensor. Certificates CSA and CE, Certificate of Calibration included Publisher / Production Mettler-Toledo AG Process Analytics Im Hackacker 15 CH-8902 Urdorf Switzerland Vortex flow meter, PVDF version. Illustrations Mettler-Toledo AG Subject to technical changes. Mettler-Toledo AG 07/08 Printed in Switzerland. www.mt.com/thornton 2 METTLER TOLEDO Semiconductor News 11
Conductivity Sensor Calibrations Unique Calibration Solution to Meet Industry Requirements A new calibration method for conductivity sensors allows a closer control of water purification process with real-time testing using 5000TOC conductivity sensors. Using a newly developed unique calibration method the system inaccuracy at the calibration point can be reduced to 0.5 %. Calibration process It is well documented that up to 75 % of the error associated with a conductivity measurement system is attributed to the conductivity sensor. It is therefore crucial that, to produce accurate conductivity measurements, the conductivity sensor undergoes a well-defined calibration process that enhances and improves accuracy. Improvements Mettler-Toledo Thornton has improved system accuracy by first calibrating the analyzer s resistance and temperature circuits with known traceable standards. The sensor is then placed in known and traceable conductivity standards at a known and fixed temperature. Using the previously calibrated analyzer, the sensor s cell and temperature constant are computed. By computing the sensor s constants with its own analyzer, the only unknown inaccuracy is the conductivity solution. Thus, only the sensor s inaccuracies and the conductivity standard solution contribute to the overall system accuracy. In most cases, even the cable which connects the sensor to the analyzer is used during the calibration process to further reduce inaccuracies. Using this method, system inaccuracy can be reduced to about 1 % over the dynamic range of sensor and analyzer, and to less than 0.5 % at the calibration point, usually ultrapure water. METTLER TOLEDO solution Continuous flow TOC sensors such as the 5000TOC provide rapid response to an excursion with an opportunity in realtime to respond to and divert contaminated water. This allows closer control of the entire water purification process through the understanding of the UPW system characteristics. It also ensures that end users are receiving reliable highquality water for the various uses in production. Detection of organic contamination is criti cal in our industry to achieve the purest water possible. The Mettler-Toledo Thornton 5000TOC and 770MAX platform ensures analytical accuracy, fast response and reliability, and can help determine in real-time if organics are being reduced in your system. Transmitter 770MAX. THORNTON 5000TOC sensor. Link for further information This article is based on the Mettler-Toledo Thornton white paper: Conductivity Sensor Calibrations to Meet Industry Requirements. To read the full text of this paper, and other readings on the importance of conductivity measurements in Pure Water applications, please visit: www.mt.com/pro-calibration www.mt.com/thornton METTLER TOLEDO Semiconductor News 11 3
Accurate Resistivity Measurement Accurate Temperature Compensation for Resistivity Measurements in UPW THORNTON expertise solved a quality problem in measuring resistivity due to superior applications know-how. A professional customer support team is key to understanding customers processes. The accurate temperature compensation was found to be a critical factor in measurement accuracy. Your temperature compensation does not work correctly in hot deionized water. This exact statement, made by a European customer in semiconductor water purification, challenged specialists of Mettler-Toledo Thornton. Experts from the local organization as well as the headquarter in Bedford, Massachusetts, USA initiated an investigation on the resistivity measurement that was in question. Well-adapted UPW temperature compensation is key Resistivity measurements are commonly used in many applications and industries. In semiconductor applications though, the nature of the water itself and its characteristic change over temperature is quite unique and requires well adapted temperature compensation algorithms for accurate interpretation of its resistivity at any temperature. THORNTON s expertise over more than four decades For more than 40 years, Mettler-Toledo Thornton designs and manufactures ultra accurate precision measurement equipment for quality monitoring of ultrapure water. The resistivity of this essential liquid in a semiconductor manufacturing process is of central interest for the entire process understanding and control. Technologies including Reverse Osmosis, Deionization and Electro-Deionization as well as Filtration and Ultrafiltration processes are used to purify the water starting from well or surface water to the final product of ultrapure water. Reliable measurement of UPW resistivity is of utmost importance Now, ultrapure water is widely used for the critical cleaning processes of wafers and other semiconductor products throughout their travel during a sequence of production steps. In a variety of applications, this water is heated to elevated temperatures in order to be able to benefit from the improved cleaning capabilities provided by hot water. Still, at these high temperatures an accurate and reliable measurement of the resistivity is of utmost importance to the fabrication plant. Evidence provided by customer Having this in mind, our Mettler-Toledo Thornton specialists reviewed the data on the resistivity measurement provided by the fabricator and arranged for a meeting on site. The data charts taken from an in-line Mettler-Toledo Thornton M300 instrument provided by the customer contained a series of peaks between 16.8 18.3 MΩ cm and showed a rather unstable measurement full of fluctuations. An initial review of the data suggested this measurement was not capable of reproducing the resistivity of UPW at the elevated temperature of 65 ºC see pictures below. Sensitivity of pure water conductivity to changes in temperature. Measurement peaks as reported by the fabrication plant. Water Conductivity % Change per C 8 7 6 5 4 3 2 1 0 0 10 20 30 40 50 60 70 80 90 100 Temperature ( C) Resistivity (MΩ) 18.5 18 17.5 17 16.5 Time (Minutes) 4 METTLER TOLEDO Semiconductor News 11
Resistivity (MΩ) Data expansion on a different scale revealed short fluctuation trends that repeatedly occurred. Competitive instrument indicated stable process Increasing the customer concern over instrument accuracy, measurement data of the same water provided by a competitive instrument did not match the behavior of THORNTON resistivity results and reported a stable resistivity reading. During the investigation, a close up of the measurement results, however, indicated a real trend of process upsets at certain time intervals see pictures below. This conclusion at this time only based upon recorded data charts was presented to a team composed of the customers Facilities Manager, Facilities Engineer and Head of Laboratory. The close up charts of all peaks started an interesting discussion, but were not completely convincing. No information was provided to identify what event occurred within the process system to cause these measurement fluctuations. Time (Minutes) Real measurement behavior during sampling of batch analyzers and thus change in flow and temperature. On-site inspection In cases like the one described here, a site visit and visual inspection of the installation can help to understand recorded data better and improve interpretation results and time. Hence, after the presentation of the conclusion a visual inspection of the installation of the resistivity loop completed the site visit. Batch techniques alter flow characteristics In series with other analytical instruments for on-line Ion Chromatography (IC), Dissolved Oxygen (DO), Total Organic Carbon (TOC) and Particle Measurement, the Mettler-Toledo Thornton resistivity sensor was assembled as the last parameter in an open bypass line. Several of the instruments installed on the sensing line such as IC, TOC and Particle analyzer use batch techniques that do not require continuous water flow. Temperature gradient due to missing insulation and fluctuating water flow These system quality monitors were situated in rather remote locations, and thus the non-insulated bypass line was not positioned as close as possible to the main water loop. Due to the stop-and-go operation of three batch-type analyzers which required water only at certain time intervals, a temperature gradient from main loop to the analyzers was determined to be responsible for the variations in the measured resistivity. to install the resistivity sensor in a different position, where it is not exposed to temperature gradients caused by significant flow changes in a non-insulated bypass line. Following this recommendation by Mettler-Toledo Thornton, a written confirmation was received that the problem was finally resolved to full satisfaction. The Facilities Manager requested additional information on latest developments. While a competitive instrument that was used as a comparison to the results from the Mettler-Toledo Thornton in-line measurement could not sense these cha nges due to inappropriate temperature compensation, the Mettler-Toledo Thornton measurement loop reproduced the change in temperature and resistivity in every second of the data recording. Conclusion: Competent application support is key Once more the expertise about our customer s applications and processes was key to support our customer, this time one of the world s largest chip manufactures. The customer s quote after closing the files: Thank you very much for your support in localizing the cause of the measurement fluctuations. Resistivity (MΩ) 18.2 18 17.8 17.6 17.4 17.2 17 16.8 16.6 1:59:00 2:00:00 2:01:00 2:02:00 2:03:00 2:04:00 Time Solution provided by THORNTON: Improved installation of resistivity sensor The pattern of measurement cycles of the IC, TOC and Particle analyzers could be matched by the Mettler-Toledo Thornton experts to the chart demonstrating fluctuations in the UPW resistivity. As a result of the visit, recommendations were made www.mt.com/thornton METTLER TOLEDO Semiconductor News 11 5
Conductivity What to Consider When Measuring Conductivity / Resistivity and Flow Rate? Mettler-Toledo Thornton s experience in the semiconductor industry as the paramount supplier for ultrapure water treatment systems has resulted in a unique know-how about what to consider for accurate measurement. The following is a Q & A guide to help you to avoid mistakes. My conductivity sensor has been removed from my water system and allowed to dry. Will this affect the readings upon re-installation? THORNTON conductivity cells can be left dry between uses without affecting performance. If used in dirty water, they should be cleaned first. ph and ORP sensors, on the other hand, must be kept wet at all times and may be stored with their original shipping cap on, filled with water. I have a conductivity sensor that is in the original box and has never been installed in my system. Is the original certificate of calibration still valid, or do I need to get the sensor re-calibrated? You could send the sensor back to us for re-calibration and re-certification, however, since the cell constant of the concentric cell design is reliable and stable, we have added a statement at the bottom of our Certificate of Accuracy which should help eliminate the need for this. The statement is as follows: Conductivity cell constant and temperature constant calibrations are generally valid for one year from date of installation. However, rough handling or use in samples containing suspended solids which accumulate on cell surfaces can degrade sensor constant accuracy and require more frequent calibration. Therefore, if you can verify that the sensor has not been installed, then the original calibration is still valid. Does flow velocity affect conductivity readings? Conductivity or resistivity depends on the composition or purity of the water and is basically independent of the flowrate past the sensor. However, several secondary effects can influence the composition and measurement, especially in high purity water. To what extent do trace impurities affect resistivity? Trace impurities dissolving from the surfaces of a new or altered piping system are more likely to accumulate and reduce resistivity at low flows and especially in dead legs. We observed an air leak in our piping system producing air bubbles. Do these air bubbles somehow disturb the conductivity sensor? Any large air leaks producing bubbles in the sensor will cause unstable, high resistivity readings. Low flowrate will allow these bubbles to cling to sensor surfaces which changes the effective cell constant. Orientation of the sensor should allow bubbles to rise and escape through the outlet. How much does a change of temperature influence the conductivity reading? Dissolved air in cold water will become less soluble when it reaches a warmer, lower pressure part of a treatment system and may produce bubbles within a sensor and cause the same problems noted above. The same effect can occur when carbon dioxide is released following a cation exchanger. 6 METTLER TOLEDO Semiconductor News 11
What do we have to consider if the flow to be measured is very low? Where conductivity/resistivity is measured in a side stream or sample line, low flows will cause delays in sensing the actual process. They are also subject to the same problems of air leaks. Is it an advantage to keep the flow high in respect to constant and precise measuring results? High flowrates are usually better conditions for measurement. However, extremely high flow can cause a very large pressure drop when hitting the conductivity cell and cause cavitation in the sensor the product of water vapor bubbles due to a partial vacuum. This will produce wildly varying readings and could damage the sensor. What is the best flow velocity? As a rule of thumb, flow velocities between 0.3 to 3 m/s (1 and 10 feet / second) usually produce good results, however, the above considerations should be taken into account as they apply to a particular installation. What does cell constant mean? A conductivity sensor cell constant describes the precise geometry of the two electrodes of the sensor. It is the ratio of the distance between electrodes divided by the cross-sectional area of sample between them. It directly affects the sensitivity and accuracy of measurement. Lower cell constants are needed to provide good signals to the measuring instrument for low conductivity (high resistivity) samples. Higher cell constants are needed to measure high conductivity samples. The measuring instrument must know the precise cell constant of the sensor connected and normalize the readout accordingly. With THORNTON Smart Sensors for 770-Series instruments, this is communicated automatically when the sensor is connected. For M300 instruments and sensors, the value is provided on the sensor label and certificate of calibration and should be entered into the instrument manually at startup. www.mt.com/thornton METTLER TOLEDO Semiconductor News 11 7
Process Analytics Product Catalog New Edition 08 / 09 Available Get an overview of the latest INGOLD and THORNTON products available for your process application with the new product catalog 08 / 09. The catalog offers comprehensive overview on product features and specifications, benefits and recommended application areas, order details and much more for process analytics measurement solutions. The product catalog covers complete measuring solutions for the parameters: ph Dissolved oxygen and O 2 in gases Ozone Dissolved CO 2 Conductivity Turbidity TOC Flow The featured product range includes: Electrodes / sensors Housings Process connections Transmitters / analyzers Cleaning and Calibration systems Cables Accessories Order your copy of this useful desk tool today! Mettler-Toledo AG Process Analytics Im Hackacker 15 CH-8902 Urdorf Switzerland www.mt.com/pro Visit for more information