Micropyramidal hillocks on KOH etched {100} silicon surfaces: formation, prevention and removal

The formation, prevention and removal of micropyramids at the {100} bottom of anisotropically etched cavities are investigated and discussed. In the c ase of pure KOH solutions the base of micropyramids has been found to be al ways rectangular or octagonal shaped. The formation is independent of the K OH supplier and the etchmask opening process. The arrangement of the rectan gular based micropyramids on the {100} etch bottom depends on the etching t ime, etching position of the chip (vertical or horizontal) and on the oxyge n content in connection with the thermal history of the wafer material. For both types of micropyramid the surface density and size increase with decr easing KOH concentration and etching temperature. Moreover the proportion o f octagonal micropyramids rises in those conditions. The origin is discusse d in terms of micromasking by H-2-bubbles in connection with plateau genera tion and layer by layer peeling of {111} planes. Other mechanisms which are suggested in the literature are discussed. Furthermore it was exhibited th at already arisen micropyramids can be removed by a short re-etching in the same etch bath in the same conditions.