Investigation on the etching characteristics of Si{100} in low concentrations of TMAH solutions for MEMS-based sensors

This study examines the wet anisotropic etching behavior of silicon (Si){100} using various low-concentrated tetramethylammonium hydroxide (TMAH) solutions (such as 1 wt%, 2 wt%, 3 wt%, and 4 wt%), without and with the addition of 1000 ppm of Triton X-100 as a surfactant. In this work, a thin film of silicon dioxide (SiO2) acted as a masking layer as well as a structural layer. Key etching characteristics, namely, etch rate, undercutting rate, and average surface roughness of etched Si, are investigated in the corresponding etchant solution. Relatively high etch rate, undercutting rate, and average surface roughness are attained when pure TMAH solutions are utilized. However, the addition of Triton X-100 significantly reduced the etch rate and undercutting rate and smoothened the etched surface. The favorable etchant solution to achieve optimum etch and undercutting rates with a smooth etched surface is identified to be 4 wt% TMAH with Triton X-100.