Characterization of Porous Silicon Layers by Means of X-ray Double-crystal Diffractometry

Abstract

(111) and (100) p-type silicon wafers of 0.55 to 33 Ωcm resistivities were anodized in 50 wt% HF solution and formed porous silicon layers were investigated by using X-ray double-crystal diffraction techniques. The porous layer is shown to be a monolithic single crystal, and its lattice spacing is slightly larger than that of the unanodized substrate, resulting in elastic bending of the wafer. The difference in lattice spacing between the porous layer and the substrate was nearly identical independent of wafer orientation and wafer resistivity. The crystal lattice of porous silicon layer is found to be elastically distorted predominantly in the direction normal to the wafer surface. The lattice spacing of porous layer increased slightly with time and the crystalline quality degraded. The results suggest that stresses, generated by the growth of native oxide layers on pore surfaces, are responsible for the elastic lattice distortion of porous layer. It is also shown tht the crystalline quality of the porous layer produced on the (111) wafers appears superior to that of the (100) wafers for all the wafer resistivity studied.