A study of base contact formation in epitaxial [formula omitted] HBT structures

Abstract

An HBT structure was grown by LP-VPE and comprises a 45 nm thick Si 0.88Ge 0.12 base layer, of which the central 25 nm is doped with boron (2 × 10 19 cm −3). The base was capped by a 150 nm thick low doped emitter (LDE) layer (10 18 As cm −3). Three different implantation conditions were employed in order to make contact to the base through the LDE, two of which involved preamorphisation with Ge +. The redistribution of epitaxial and implanted boron after low temperature (600°C) furnace annealing and rapid thermal processing (RTP) at 1000°C was studied by SIMS. The information from SIMS is correlated with observations of the defect structures (TEM and RBS/C) and amorphous layer thicknesses before and after annealing. This study shows that preamorphisation leads to a significant reduction in the defect density of the LDE after RTP, reduces the amount of implant channelling and increases control over the boron profile. Care must be taken to ensure that the residual damage from the implants, does not intersect the base layer.