Design and fabrication of an electronic system for pressure and temperature measurement in thin film deposition systems
Tuwei, Abraham Kirwa
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Temperature and pressure are quantities of great importance in various applications such as integrated circuit (IC) manufacture and vacuum coating just to mention a few. Therefore, their accurate measurement is inevitable. However, it is tiresome to measure and record these quantities manually by pen and paper when operating a thin film deposition system. This approach is not only time consuming but also causes human errors on the measured physical parameters. To solve this problem, an automated instnimentation and measurement system was designed to offer a more reliable and fast method of measuring pressure and temperature in thin film deposition systems. It is based on thermocouple type K temperature sensor and pressure sensor MP20C-OI-F2 from Mindman Company based in USA. The voltage outputs from these sensors, proportional to measured temperature and pressure, were fed to a thermocouple amplifier (AD595CQ) and an operational amplifier 741, respectively. The amplified voltages were transmitted through the electronic filters to isolate the noise signals that might affect the true voltages obtained from the two sensors. The two signals were multiplexed by AD8180 multiplexer and then digitized one at a time by the ADC0804LCN analog to digital converter before feeding to the computer through the parallel port interface for processing. A software design using Lab VIEW graphical programming language was used to access the digital signals from the parallel port, process and display the temperature and pressure data to the user. The functionality of the designed electronic temperature and pressure measuring system was tested in Edward auto 306 magnetron sputtering system. The designated process parameters: pressure and temperature, were measured in-situ by the designed system during evaporation of SnSe and sputtering of AIOxNy thin films samples in the chamber and stored their values in a text file. The designed system had temperature and pressure ranges ofOto 1'251 °c and 0 to 1.01 xl03 mbar, respectively and temperature error of± 1°C. However, the designed system recorded varied pressure errors. In higher vacuum, pressures range 1 to 1 x 10-2 mbar, the error was ± 1 x 10-2 mbar and in the lower range lxlO-4 to Ix10-5 mbar, the error of IxlO-5 mbar was observed. These errors were within acceptable range and therefore, the system is viable to be used in thin film deposition systems to automate the measurement of process parameters: temperature and pressure.