Etch-stop in germanium induced by ion implantation for bulk micromachining applications in the IR domain

At high boron concentration, silicon shows a severe reduction of the etching rate in alkaline solutions, property which is largely used for achieving etch-stop zones for bulk micromachining. The desired boron concentration can be reached in silicon by thermal diffusion or by ion implantation. In an attempt to extend the bulk micromachining techniques over germanium, we verified that boron also reduces the etch rate of this material - this time, in acidic solutions. Doping germanium by diffusion being far from a standard technology, we found ion implantation a better-suited doping process. Experiments and simulations were made to draw the process parameters for controlling the boron concentration and its distribution in germanium. The germanium wafers were implanted through a lithographic structured resist layer. The annealing of the implanted Ge took place in N2 atmosphere, at 700 degrees C. We succeeded putting into evidence a reduction of the etch rate of Ge in a H3PO4:H2O2:C2H5OH solution in the implanted area, relative to the non- implanted one. The effect is similar to that in silicon. As a parasitic phenomenon, during the anisotropic etching, the roughness increased more on the implanted areas, where the defect-related typical square pits were of higher depth and size.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.