In-situ Measurement of Plasma Etch Rate Using EtchRate Wafer

This paper presents the EtchRate Wafer, a wireless monitoring silicon wafer that was invented by KLA-Tencor Corporation and patented in September 2014. This monitoring wafer measures the film thickness change in the etching plasma chambers while the etching process is running. The monitoring wafer has three sensors to measure the uniformity of thickness change across the wafer. The sensor is an optical stack that mainly consists of a collimator, an optical window, coated mirror, optical filter, and an optical detector. To measure the etch rate, the specific target material is coated on the optical window to be able to simulate the same test as in the plasma chamber. By placing the monitoring wafer instead of the regular target wafer in the chamber, the etch rate is measured by the use of the interference phenomenon. The transmitted light from the material layer produces an interference pattern on the optical detector, which can be analyzed to compute the layer thickness. Monitoring the changes in the interference pattern in the etching or deposition processes can help to measure the film layer thickness as a function of time. This thesis reviews the semiconductor fabrication processes include plasma etching processes and the interference phenomenon that is the basic concept of EtchRate sensor function. The EtchRate wafer and its sensors are described in detail and two methods for mathematical analysis are discussed. The Zemax modeling for the EtchRate sensor is also presented. In conclusion, it is possible to measure the plasma etch rate in situ by EtchRate wafer which is a convenient and time-saving method