Effects of dry plasma releasing process parameters and induced in- plane stress on MEMS devices yield

摘要

An investigation into the effects of dry plasma etching release process parameters, local wafer position and induced in-plane stress on the yield of MEMS devices is presented. Several identical wafer quarters, each subjected to different releasing process conditions, are studied. Yield is evaluated by observational measurements of the stiction of MEMS nanocantilevers fabricated alongside with bent beam strain sensors. Results show that lower yield is found for larger processing times as well as higher releasing temperatures. On the other hand, yield improves when thicker nanocantilevers are released using the same processing parameters. The distribution of process-induced in-plane stress of PECVD silicon nitride films is shown to change widely from compressive to tensile based on the local wafer position, whereas no clear correlation between stiction and stress distribution is found. Viability of determining MEMS yield at the wafer-level based on process-induced residual stress is discussed. Other possible root causes of yield in MEMS due to dry plasma release etching are also briefly touched.