Investigation of STI-etch process with hercules sensor

A Hercules sensor provided by Plasmetrex GmbH was used to gain and evaluate plasma parameters of a 90 nm technology STI etch process performed at a LAM2300 Versys StarT chamber. It was found that there is a strong correlation between the trend of the electron collision rate at the resist strip step and the reaction with the organic resist, i.e., the complete consumption of the resist. The findings could be verified by the inspection of wafer surfaces with a SEM, where no resist residues could be detected even for reduced strip etch times and could also be supported with theoretical considerations. In addition to that there was found a dependance of the collision rate on the RF-hours, indicating a changed etch chamber state, despite it is run in clean mode and should therefore always maintain a similar state. For this work the evaluation of Hercules data resulted in a better process understanding and revealed a high potential for process shortening. Moreover, the use of the electron collision rate as an automated endpoint (EP) parameter for the resist strip step is possible.