Surface Pretreatment for Thin Film Surface Reactivity

Abstract

The formation of a self-limiting interface layer for the integration of high-k dielectric materials into silicon based transistor devices was investigated. Chlorine atoms were used to activate a liquid cleaned Si(100) surface for the reaction with H₂O(g). A saturation coverage of 0.8 monolayers of chlorine atoms was deposited on a hydrogen terminated Si(100) surface by exposure to Cl₂ gas at 10 Torr under ultraviolet illumination at 300 K. The self-limiting interface layer was formed by exposing the chlorine terminated surface to water vapor at P(HOH)=100 Torr and temperatures ranging from 325 to 373 K. The coverage of oxygen resulting from H₂O exposures was directly correlated with a decrease in the Cl coverage and ranged from 0.2-1.2 monolayers. Complete removal of surface chlorine was achieved by 100°C water exposures in 45 minutes. The final chapter summarizes three papers published which describe the moisture absorption into borophosphosilicate glass (BPSG) films and an investigation of a gas phase etching process applied to borosilicate glass (BSG), phosphosilicate glass (PSG), and BPSG films. The absorption and reaction of water with doped and undoped oxides as well as the effect of annealing was investigated using a variety of annealed BPSG films. Asdeposited (AD) and annealed (500, 750, and 900°C) borophosphosilicate glass (BPSG) films were characterized during aging, baking, and etching using transmission Fourier transform infrared spectroscopy and ellipsometry. The water content in the BPSG films increased steadily during storage at ambient conditions. The B-O bond was shown to be the primary site for water adsorption on the surface of the film. Water absorption into the film was consistent with a reaction-limited model. It is likely that the water present reacted readily with P=O groups forming P-O and PO-H. This slower reaction with P=O species is proposed as the rate-limiting step for water absorption. The etching of BPSG with gas phase HF produced a low volatility residue consisting of a mixture of boric acid B(OH)₃, phosphoric acid H₃PO₄, and water. Partial removal of the residue was accomplished using both direct and indirect UV–Cl₂ processes.