The Effects of Small Concentrations of Oxygen in RTP Annealing of Low Energy Boron, BF2 and Arsenic Ion Implants

Abstract

ABSTRACTIon implants of 1.0 keV 11B+, 5 keV BF 2+, and 2.0 keV As+ at a dose of IeI5/cm2 were rapid thermal annealed (RTA) in a STEAG AST-2800µ with varying percents of oxygen in N2, ranging from 0-lppm to 50,000 ppm to investigate the effects of low concentrations of oxygen during anneal. Sheet resistance (Rs), ellipsometry, SIMS, Tapered Groove Profilometry (TGP), and Scanning Force Microscopy (SFM) were employed to characterize these layers. For each of these implant cases, an optimal RTA condition is established which maximizes retained dose while still producing shallow junctions. As a function of O2 content, anneal temperature and implant condition, three regimes are observed that affect after anneal retained dose. These regimes are: dopant loss to the ambient resulting from etching of Si, dopant loss by out-diffusion from evaporation/chemical reactions, a capping regime that minimizes out-diffusion. In this later regime the dopant loss results from consumption into the RTA grown oxide. In addition, this paper also discusses oxidation enhanced diffusion (OED) and identifies its extent as a function of temperature and O2 content of the anneal for the three implant conditions investigated. For example, a 1.0 keV 11B+wafer annealed at 1050°C lOs in a controlled 33 ppm of O2 in N2 yields a SIMS junction depth 320 Å shallower than previously reported by others.