Direct wafer temperature measurements for etch chamber diagnostics and process control

It is well known that wafer temperature has significant impact on plasma etching performance. Instability of (peak) wafer temperatures during process can be linked to such issues as post-metal etch residues, undercut or sloping sidewall profiles and inconsistent photoresist selectivity. Direct wafer temperature measurements can yield valuable diagnostic information. This information can be used to characterize the process as well as to improve process control. This paper presents two direct wafer measurement techniques which when used in combination can be powerful tools for chamber diagnostics, tool to tool matching, as well as process control in a production environment. Real time, in situ wafer temperature measurement using a thermal optical system is used to understand the effect of process parameters such as backside He cooling, RF power and gas flows on wafer temperature and temperature uniformity. This data is then correlated to measurements from a novel technique employing arrays of peak temperature indicators mounted on a single-use-instrumented wafer. The latter technique is ideal for quick chamber qualifications and day to day process control while the former can be used for more detailed chamber diagnostics and analysis of the thermal cycle during the etch process.