STUDY OF SI SURFACE MODIFICATION WITH IRRADIATION, PLASMA AND ULTRASOUND FOR GAS SENSING APPLICATION

In order to search the new physical principles for high sensitive and selective gas sensors on the base of porous silicon creating we examined gas sensitivity of the silicon surface modified with charge particle irradiation, chemical plasma and ultrasound. Single crystal Si and SiO2/Si structures were irradiated with ions (6.8 MeV H, 27.2 MeV He, 290 MeV Ar, 372 MeV Xe, 710 MeV Bi), treated with chemical plasma with 80-100eV F-content and with ultrasound (Р=0.5 W, 8 MHz). The sample’s absorption properties were obtained from the analysis of the optical parameters changes (refraction index and absorption coefficient, and a thickness of near-surface region, too). The latest were studied by the method of multiangular monochromatic ellipsometry in test camera in ethyl alcohol, ammonia and acetone environment. Scanning electron microscope (SEM) and atomic force microscope (AFM) were used to analyze the surface morphology. Protons and alpha particles were found to lead to the Si near-surface layer destruction of and an enhancement of the surface roughness. The proton irradiated samples revealed a higher sensitivity to the absorption of ammonia and acetone molecules. Plasma treated Si displays surface modification (loosening of near-surface layer), though, gas absorption is not clearly revealed. Optical properties of Si/SiO2 structures depend on the dimensions and the depths of nanopores, created by the etching of latent tracks in dioxide after irradiation. The greatest optical constant changes occurred in irradiated with 209Ві structures, where tracks penetrated the whole dioxide. Accordingly bismuth-irradiated structures have the best gas sensitivity. Ultrasound influences on the optical parameters of porous Si/SiO2 structure (loosening of the near-surface layer). However, these changes are unstable; and optical characteristics relax to the initial value in time. The best result was obtained for SnO2 /SiO2 /Si structure, where nanopores etched in the Xe latent tracks areas, were filled with SnO2