Improvements of Roughness Control in Micromachining of Silicon Microchannels

Investigation of wet anisotropic etching of silicon microchannels on (100) silicon is presented with the emphasis to simultaneously fabricate bifurcated silicon channels in <100> and <110> directions. Silicon crystal planes that are playing major role of microchannels sidewalls are characterized for their roughness and etch rates. Beside the standardly smooth {111} crystal planes, microroughness of {110} sidewalls is of particular interest. It is shown that by implementing TMAH-Triton etchant, the roughness of {110} sidewalls was significantly improved over the standard KOH-IPA or TMAH-IPA etching system without affecting the neighboring crystal plane sidewalls. Agitation of the etching solution is found to have significant influence on both, the etch rate and surface roughness. Optimal etching conditions were determined to obtain smooth microchannel sidewalls in two major directions. Furthermore, reduced convex corner underetching was obtained compared to other etching system. Two viable solutions for the connecting through holes or vias are presented by using single or double mask layer photolithography prior to performing the etching step.