Novel techniques of RF high power measurement

Abstract

RF diagnostic systems provide essential parameters for both statistical process control (SPC) and automated process control (APC) in plasma based semiconductor and flat panel processing driven at RF frequencies. To achieve repeatability and control of RF plasma processes such as plasma-enhanced chemical vapor deposition (PECVD) and plasma etching (PE) it has become necessary to accurately (<1 %) monitor and control the actual plasma impedance and RF power delivered to the plasma. This thesis is based on the design and test of novel RF power instrumentation that is accurate even with RF powers in the range of tens of kilowatts. The trend in RF process is to go to two extremes: very high frequency (>200 MHz) and high power (>50 KW) (large area flat panels). Industry requirements are already 50kW at 13.56 MHz and up to 200 MHz in frequency. There are emerging applications reported at even higher frequency (915 MHz ISM band). Today's state of the art instruments can measure RF power with 1% accuracy at its best; typical accuracy is around 3% and it is rapidly degrading with the increase in Voltage Standing Wave Ratio (VSWR) due to unmatched loads. My thesis research proved that by using a proper digital correction algorithm better then 1% RF measurement accuracy could be obtained. An improved power measurement technique for real impedance lines and loads is presented along with test results at powers up to 3kW. For the case of RF power measurements into complex impedances I tested an entirely novel direct digital sampling method that is frequency agile. Finally I contributed to the art of RF calorimeters as well as more accurate RF measurements. Absolute accuracy of the RF metrology is compounded by errors introduced primarily from the measurement system, the chosen calibration method and power references. RF high power standards are not traceable directly to primary metrology references provided by NIST. In order to improve the calibration accuracy of the instruments, I researched novel calibration techniques and determined the errors involved in the RF high power calibration methods.