Development of the Silicon Through Anisotropic Plasma Etching Process

A method of increasing the silicon plasma etching temperature regime stability to depths exceeding 100 μm is proposed. The influence of the substrate temperature gradient on the etching rate unevenness, the inclination angle of the side walls, undercut under the mask, the mask structural defects and the etching profile bottom roughness (the "black" silicon effect) has been investigated. It was revealed that the programmed segmentation of the process into the etching and cooling stages ("interval" etching method) allows keeping the substrate temperature at a level below 100°C. This eliminates the structural defects occurrence in the photoresist layers. With "continuous" etching, the substrate temperature can rise above 145°C, resulting to cracks in the photoresist layer and multiple tears. The "interval" method proposed in this work made it possible to develop the silicon through etching process with an etching rate unevenness across the wafer of less than ± 3%, a wall inclination angle of from 88° to 90°, and almost complete absence of lateral undercut under the mask.