Characterisation and implications of the boron rich layer resulting from open-tube liquid source BBR3 boron diffusion processes

Abstract

Boron diffusion is commonly associated with the formation of an undesirable boron rich layer (BRL), which is often made responsible for degradation of the carrier lifetime in the bulk. We therefore investigate the phenomenology of the BRL formation and its impact on sheet resistance and bulk lifetime. We use scanning electron microscopy (SEM) to investigate the thickness of the boron silicate glass (BSG) and the BRL. Additionally, we present sheet resistance measurements of diffused wafers and corresponding MWPCD lifetime mappings. We investigate these properties as a function of gas composition during deposition, BSG-deposition thickness and position on the diffused wafer. We find that a BRL layer of more than 10 nm thickness causes a degradation of the carrier lifetime in the bulk of the silicon wafer.