Digital Control of SiO2−TiO2 Mixed-Metal Oxides by Pulsed PECVD

Abstract

Pulsed plasma enhanced chemical vapor deposition (PECVD) was used to deliver digital control of SiO(2), TiO(2), and SiO(2)-TiO(2) composites at room temperature. Alloy formation was investigated by maintaining constant delivery of TiCl(4) while varying the SiCl(4) flow. Film composition was assessed by spectroscopic ellipsometry, XPS, and FTIR. It is shown that the alloy composition and refractive index can be tuned continuously over a broad range using pulsed PECVD. The two precursors were found to be highly compatible, with the alloy growth rate simply reflecting the sum of the contributions from the two individual precursors. Digital control over both thickness and composition was demonstrated through the production of antireflection (AR) coatings for crystalline silicon. AR coatings were synthesized on the basis of optimized designs, and in each case the measured optical performance was found to be in excellent agreement with model predictions. The average reflectance across the visible spectrum was reduced from 39% for uncoated wafers to 2.5% for the three-layer AR coating.