Morphological studies of porous silicon surface formed by chemically etching

In terms of scanning electron microscope(SEM), transmission electron microscope(TEM) and atom force microscope(AFM), etc., the surface morphology of porous silicon, formed by chemically etching, was studied. It was shown that the porous silicon layer will be broken off after reaching a certain depth because of the horizontal corrosion. A large stress was formed in the Si substrate because of appearance of lots of H_2 gas. The stress make the microcracks at the brittle crystal boundaries. The porous silicon was formed between microcracks.