LabVIEW and FieldPoint Automate a Chemical Solution Concentration System

Author(s):
Mike Fortenberry - G Systems Inc.
Carlos Yapura - G Systems Inc.
Chris Koehler - G Systems Inc.
Naresh Kumar Shenkeshi - G Systems Inc.

Industry:
Semiconductor

Products:
Compact FieldPoint, LabVIEW, FieldPoint,

The Challenge:
Transforming the manual process of determining the active species concentration in a chemical into a fully automated monitoring system using self-contained test instrumentation hardware.

The Solution:
Developing a LabVIEW application for automatic determination of unknown solution concentrations and isolating the instrumentation and test computer using FieldPoint modules.

Automating a Manual Process
Air Liquide Electronics in Dallas approached us at G Systems to automate the process of determining the chemical concentration of a blend used in semiconductor manufacturing. Previously, engineers manually determined the solution concentration in a lab environment on a per sample basis at irregular intervals as requested by the customer. Air Liquide devised a method, patent pending, so that users could automatically determine the solution concentration from the blender, which ensures the use of the correct concentration in the process. Air Liquide designed a test unit to separately take measurements and process data from the test computer so that any computer running the necessary software could be used without installing additional hardware on it. We provided a solution using FieldPoint modules with an RS-232 serial interface and a custom-built rack to hold the spectrophotometer instrument and bottles containing the calibration standards.

The system consists of a portable rack with three compartments. The top section holds the test instrumentation – a spectrophotometer and FieldPoint modules, the middle section holds the pumping mechanism, and the bottom section holds the solution bottles. The system provides an input for a water source and an input from the chemical source. An RS-232 serial interface achieves communication to the FieldPoint modules and the spectrophotometer.

With the spectrophotometer, the operator measures the absorbance of light at a user-selected wavelength through the solution. The spectrophotometer has an input and output for fiber optic cables, which are positioned perpendicular to the sample solution passing through the flow cell. Light is transmitted through the liquid from the emitter end of the fiber optic cable and is detected by the detector end of the cable. Liquid absorbance then calculates based on attenuation of the incident light.

Designers created this unit to perform self-calibration automatically, to verify the check standards, and to determine the concentration of unknown solutions. The software controls the spectrophotometer, valve relays, and a pump through an RS-232 serial interface. The software graphically displays the status of the relays and pump and allows the operator to review the results history over a user-specified time interval.

The system connects to the source of the chemical whose concentration is to be monitored, through the Web. The system also checks concentration at regular intervals ensuring that the correct concentration is supplied to the process tool where the chemical is being used. The results history screen displays how the concentration changes over time.

Software Operation
The main LabVIEW application screen allows the operator to enter the test location and select whether the sample is online or offline. Through the test parameters screen, the user inputs the timing for opening the solenoid valves, the standards concentration, and the test limits.
Measurement System
The test begins by measuring the absorbance of water through the spectrophotometer to determine the baseline for subsequent intensity measurements. Next, the software determines the calibration curve between absorbance and concentration by measuring the absorbance of five solutions with known concentrations. Then, a calibration check is performed by measuring the absorbance of a check standard solution and determining its concentration from a calculated equation. When the calculated concentration lies within the range of the check standard concentration tolerance limits, the calibration check passes, and the sample measurement is performed on the online solution. The solution concentration’s measurement is then displayed on the screen.

To ensure that the system is calibrated correctly, the check standard measurement operates prior to the sample measurement. The software checks the concentration at regular intervals set by the user. The operator can use the “Snap Shot” button to take a measurement while the software waits to make the next scheduled measurement. The main screen graphically shows the progress of the test and also displays a status description at the top of the screen.

Report Generation
LabVIEW 6i report functions automatically generate HTML reports. Through the report generation screen, the user can print or save the report. Other options include plotting the raw absorbance history for each standard, plotting the concentration of each solution over time, and viewing the calibration curves by specifying start and end dates. The user can check to see how often the calibration sequence is performed during a sample measurement and can also analyze the trend of the samples’ concentration variation over time.

Using NI products, we created a customized, integrated, and automated system for determining the concentration of a chemical blend used in semiconductor manufacturing. With the real-time feedback from the instrument, the end user can quickly detect out-of-spec products and intervene before it impacts the process. Ease of operation and reliability of measurements allow this robust, on-line analyzer to be efficiently used for process monitoring.

For more information, contact:
Mike Fortenberry
G Systems, Inc.
Tel: 972-516-2278
Fax:972-424-2286
E-Mail: info@gsystems.com

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