Method and apparatus for improving accuracy of plasma etching process

摘要

The invention provides a process and apparatus for improving the accuracy of plasma etching processes such as trench and recess etch processes. In such processes, a trench or recess is etched into a layer of material which does not have a stop layer at the desired depth of the etched openings. Instead, the etching process is carried out for a set time period calculated to achieve a desired etch depth on the basis of measured or estimated etching rates. For example, the duration of etching to achieve a target depth may be based on statistical analysis or real-time measurements of etch depths by interferometry. However, use of estimated etching rates or interferometry to control when etching should be terminated to achieve a desired etch depth can result in defective structures due to etched openings which are too deep or too shallow. According to the invention, a technique is provided for controlling the etching process in a manner which achieves more accurate etch depths in a more reproducible way by conducting a masking layer thickness measurement as part of the etching process.