Surface Characteristics of (100) Silicon Anisotropically Etched in Aqueous KOH

Anisotropic etching with KOH has become a standard and important processing step in the fabrication of bulk micro-machined devices. The surface quality of etched regions can play an Important role in device performance. In this paper we examine the effect of surface preparation, wafer rotation, and wet/dry loading on the roughness of KOH etched surfaces. In our work, over 1500 wafers have been etched. The process was continually improved until a stable operating point was achieved. Surface preparation techniques were varied to determine the etch character. However, despite the wide range of surface preparations tested, we found that surface preparation had no statistically significant effect on roughness. Instead, our results lead us to conclude that roughness is mainly due to conditions within the KOH etching solution, and in particular to the hydrogen gas bubbles evolved during etching.