After etch focus control

摘要

Currently semiconductor manufacturing control loops are based on measured parameters like overlay (OVL), CD (dose). Focus (using scatterometric measurements and SEM), typically after development inspection (ADI)- For CD typically after etch CD values are obtained in order to determine dose corrections applied during exposure in order to achieve a better after etch CDU. Apart from after etch CDU minimization using dose control also other parameters (Focus/OVL) may benefit from an after-etch optimization strategy. It has been observed that the Best Focus (BF) of an ADI Bossung curve does not coincide with a BF of an After Etch Inspection (AEI) Bossing curve. Besides a BF (mean) shift also a fingerprint deltamap is observed between 'focus' ADI and AEI. The exact mechanism behind this is not known, likely candidates are: Etch induced changes in feature profile (SWA). Etch induced charging effects Impact of other processing steps (deposition, ..). The AEI-ADI BF shift is observed on multiple metrology tools, hence indicating that difference is real and not related to metrology specific characteristics.