Porous silicon formation by stain etching

An empirical study was carried out on the porous silicon layer (PSL) format ion process by stain etching on p- and n-type silicon wafers having differe nt doping concentrations. PSL formation differs from the electrochemical et ching process, since the top surface of the porous layers is continuously e tched during formation. A porosity gradient is developed in the porous laye rs formed on p-, p(+)-, n- and n(+)-type silicon because stain etching, as a wet chemical etching method attacks the pore walls. This complex process can result in limited thickness for PSLs depending on the doping type and c oncentration of the substrate. The total mass of the silicon dissolved from the top surface and from the pores, was measured by gravimetry. The porosi ty and thickness values extracted from spectroscopic ellipsometrical (SE) m easurements and with the measured mass of dissolved silicon are used for st udying the etching process. The structure of the layers was characterized b y backscattering spectrometry (BS) and cross-sectional transmission electro n microscopy (XTEM). The PSLs exhibit amorphous structure on p-type silicon , while p(+) layers have crystalline structure according to ion beam channe ling experiments, and XTEM images. (C) 2001 Elsevier Science B.V. All right s reserved.