Effects of chamber wall conditions on plasma etching processes

The effects of chamber wall conditions on plasma etching processes are investigated through the use of multiple plasma and surface diagnostics including gas phase FTIR absorption spectroscopy, in situ MTIR-FTIR (Multiple Total Internal Reflection - Fourier Transform Infrared) spectroscopy, optical emission actinometry, and Langmuir probes. These diagnostics are used to measure the key plasma properties, such as gas phase composition, ion flux, and electron temperature. The distinguishing feature of this study is the MTIR-FTIR surface probe, an in situ diagnostic technique developed for monitoring the films and adsorbates on the plasma chamber walls. Prior to the development of this probe, fundamental understanding of the effect of wall conditions on plasma properties was severely limited due to the lack of any diagnostic for characterizing plasma chamber wall conditions.;Cl2/O2 plasma etching of silicon in an inductively coupled plasma reactor was taken as a model system to investigate the effect of chamber wall conditions on plasma etching. The Cl2/O plasma etching process is widely used for isolating transistors from each other by etching shallow trenches in Si. During this etching process, etch products such as SiClx fragments react with the O in the plasma to deposit a SiClxOy layer on the reactor walls which can alter the reactivity of the walls and the properties of the plasma from wafer to wafer. The Cl gas phase composition and ion flux, the fundamental parameters that govern the etching process, were found to depend sensitively on the species deposited on the chamber walls. Optimum strategies for cleaning the chamber wall deposits to maintain Cl composition and ion flux and consequently for maintaining etching reproducibility, while maximizing throughput, were developed for a variety of etching conditions. Similar plasma cleaning strategies were also developed for the etching of multi-film stacks using different gases. The results of this study were directly applicable to realistic etching processes and hence enabled technological advances in semiconductor manufacturing through improvements in process reproducibility and increased production throughput, achieved through a fundamental understanding of plasma-wall interactions.