Wet etching of silicon structures bounded by (311) sidewalls

Abstract

Wet chemical etching of narrow recessed ridges and bossed structures on (100) silicon is presented with emphasis on convex and concave corner dynamic behaviour during maskless etching. Ridge and boss sidewalls that arise from the new masking technique are (311) crystal planes and offer a new dimension in wet micromachining. It was found that convex corner undercutting is significantly reduced if (311) planes are utilised instead of (111) bounding planes. Rounding of concave corners that arise through prolonged etching is reported which is particularly emphasised in KOH and less in TMAH etchant. Addition of IPA is experimentally investigated showing minor influence on etching conditions and on reducing the maskless undercut of convex corners. Etch rates and dimensional control of some microstructures are discussed and presented comparatively for both etching systems in a temperature range from 70 to 100°C.