An end-point visualization test structure for all plasma dry release of Deep-RIE MEMS

We propose a test structure for an easy visual check of the progress of a MEMS dry release process. The release process of MEMS on a silicon-on-insulator (SOI) wafer is done by plasma etching of the silicon substrate (SOI handle). The Si MEMS movable structure is protected from etching by the underneath buried oxide (BOX) layer and by a Teflon layer on the walls. Improper etching conditions, however, damage the Teflon layer and harm MEMS structure. Therefore, a check method of the progress of process is essential to release MEMS structure successfully. The test structure has two purposes. First, it enables the detection of the completion of the release process. Second, it helps determining the undercut speed according to the opening sizes and plasma conditions.