Reflectometry-based approaches for in situ monitoring of etch depths in plasma etching processes

Tighter control requirements for plasma etch processes drive the search for more accurate and robust methods for monitoring processes in situ. Conventional optical methods such as optical emission spectroscopy and interferometry, while easy to use, have their limitations especially in their ability to compensate for incoming material variations. As an alternative, we have successfully developed a broadband (UV-VIS-NIR) reflectometry-based approach for in situ monitoring of etch processes such as shallow trench isolation (STI) and recess etch processes. This approach enables us to estimate in real time the vertical dimensions of features of interest on patterned wafers. The approach has proven to be robust in that it works for a given application without modification for a variety of pattern densities and incoming material variations. It has proven to be easy to use in that there is minimal user/operator input required. We present results for a couple of applications that we have studied.