Quantitative secondary ion mass spectrometry analysis of SiO 2 desorption during in situ heat cleaning

Abstract

Analysis of silicon oxide (SiO 2) desorption was performed by a combination of thermal annealing in an ultra high vacuum (UHV), consecutive growth of a thin silicon (Si) layer by molecular beam epitaxy (MBE) and ex situ secondary ion mass spectrometry (SIMS). Together with the Si substrate the Si-MBE layer creates a uniform Si matrix which allows quantitative analysis by SIMS. The protective oxide on as-received wafers stored for a few months turned out to be 0.8–1.6 nm thick. Desorption in a vacuum takes place in a narrow temperature window below 875°C. The main residual contaminations were carbon (C) with a surface concentration of about 10 12 cm −2 and boron (B) with a concentration of 6×10 10–6×10 11 cm −2. Metallic impurities were below the SIMS detection limit.