Development of Process Technology for Semiconductor Surface Cleaning by Using VUV Photochemical Reactions

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Thermally grown silicon dioxide (Si <O_2> ), crystalline Gallium Arsenide (GaAs) and silicon (Si) surfaces was exposed to an etching gas under an ArF excimer laser irradiation. The reaction products on the surface and their chemical bonding features were studied by in-situ x-ray photoelectron spectroscopy at each step of the photochemical etching. Reaction kinetics of photochemical etching and resulting products on the solid surfaces have been revealed from the chemical shifts of adsorbates and substrate atoms. Etching products in Si <O_2> /(N <F_3> + <H_2> ) system are confirmed to be Si <F_4> , <N_2> O, and N <O_2> . For the etching of GaAs in HCl, Ga <Cl_3> and As <Cl_3> are found to be the most probable products in the gas phase. The photoluminescence measurements and the current-voltage characteristics of the Schottky barrier diodes indicate that the surface-defect density of the photochemically-etched sample is as low as that of the conventional wet etching. In the case of the etching of Si in N <F_3> , it was found that Si <F_X> (1 <-!<> X <-!<> 4) units and molecular fluorine exist in the reacting surface region. The surface Si-Si bonds attacked with fluorine are progressively fluorinated and the final surface products are mainly Si <F_4> and Si <F_3> . A possible mechanism of fluorine etching is discussed on the basis of a valence electron transfer (VET) model.