SIMS analysis of silicon on insulator structures formed by high-dose O + implantation into silicon

Abstract

Silicon on insulator (SOI) structures are promising candidates for the fabrication of VLSI circuits with very high packing densities. The preparation of such structures can now be achieved by high dose implantation of reactive ion species such as oxygen to produce buried layers of SiO 2 in silicon. In this paper we report experiments to depth profile these layered structures by SIMS. SOI samples have been prepared by implantating (100) silicon wafers with 400 keV molecular oxygen ions at a dose of 1.8×10 18 O + cm −2. During the implantation the wafers were maintained at temperatures between 325 and 600°C, using beam heating, which achieved in situ-annealing and ensured that the top silicon layer remained single crystal. Analysis was carried out on an Atomika DIDA-II spectrometer using 10 keV Ar + ions with a low current density of less than 1 mA cm −2. During analysis negative secondary ions were monitored which provided a high detection sensitivity for oxygen and revealed fine detail in the measured yields with reflected both the composition and structure of the samples. Depth distributions of the oxygen compare well with results obtained by other techniques, including Rutherford backscattering and sectional TEM. It has been shown that prolonged high temperature annealing leads to diffusion of oxygen with the formation of a denuded layer of thickness 1000–1500 Å which is of a suitable quality for successful fabrication of high performance MOS devices.