Development of RF power measurement sensor for plasma equipment monitoring*

Recently, in the semiconductor industry, various sensors are used to monitor semiconductor processes, find out the cause of abnormalities in processes and equipment, and conduct research to finally improve the yield. Precise control of plasma in semiconductor processes is an important issue because the proportion of semiconductor manufacturing processes using plasma is currently over 80%. It is important to measure the exact state of the RF generator and impedance matching device, which are the core components of generating such plasma, and VI probe is used for this purpose. The current VI probe measures the amplitude and phase of RF voltage and current and calculates the RF power transmitted to the plasma chamber. In general, in the case of a capacitance pick-up circuit measuring voltage in the VI probe and a inductance pick-up circuit measuring current, the accuracy of the amplitude measurement of voltage and current was secured. However, in the phase measurement used to measure RF power, a small phase error becomes a big problem in accurate RF power measurement when the phase angles of voltage and current are large.

In this study, a VI probe equipped with a sensor circuit of a directional coupling method was developed to solve this problem. Using this, performance evaluation in a plasma module with a 50ohm dummy load and a non-50ohm condition was conducted. The developed VI probe confirmed that the RF power measurement error was less than 1%. The developed VI probe is expected to be able to precisely control plasma by applying it to plasma process equipment.