Microstructure of boron-doped silicon layers prepared by low pressure chemical vapour deposition

Abstract

The microstructures of silicon layers 0.55–0.60 μm thick with boron contents of about 10 17 or 10 20 atoms cm -3, prepared by low pressure chemical vapour deposition at 570 or 620°C on thermally oxidized silicon wafers, were characterized in the as-grown condition and after chemical thinning. The microstructural characteristics obtained from transmission electron microscopy examination on cross-sections, reflection high energy electron diffraction patterns, Raman spectrometry at 488 nm and UV absolute reflectance measurements as well as the optical and mechanical roughness of the sample surfaces were compared. The results showed the following. 1. (i) The layers are polycrystalline throughout their depth, with an external region of columnar character, intense twinning and 〈110〉 texture, and with a near-interface zone 50–100 nm thick of randomly oriented grains of size not greater than 10nm. 2. (ii) The thickness of the interfacial zone decreased as the deposition temperature increased. In the external region the texture became more developed as the level of boron doping and the deposition temperature increased, whereas the twinning, dislocation density, vacancy and/or impurity concentrations (from Raman results) and excess volume fraction (from absolute reflectance results) appear to be enhanced by increases in doping and decreased by increases in temperature. 3. (iii) The surface roughness was also clearly higher for layers with lower boron contents.