Boron Ultrashallow Junction Formation in Silicon by Low‐Energy Implantation and Rapid Thermal Annealing in Inert and Oxidizing Ambient

Abstract

For the formation of ultrashallow junctions, a controlled gaseous ambient during rapid thermal annealing is indispensible. To understand the diffusion/activation mechanism, the influencing and depending variables have to be clarified precisely. Ion implantations of 1 keV boron at a fluence of are annealed isothermally for 10 s at 1000, 1050, and 1100°C in an AST2800ε rapid thermal processing system under controlled concentrations of oxygen in nitrogen ambient (0–1 ppm up to 1%). The concentration‐depth profiles, measured by secondary ion mass spectroscopy, are analyzed within the framework of the kick‐out model involving diffusion enhancement via supersaturation of silicon self‐interstitials and the Fermi‐level effect. The validity of this interpretation is supported by the simulated results which are in good agreement with experimental data. Two input parameters for the SSUPREM IV simulator yield finite values of silicon self‐interstitial supersaturation as a function of temperature and oxygen concentrations, values for the boron diffusion coefficient via neutral and positively charged silicon self‐interstitials, and data for transient enhanced diffusion. After rapid thermal annealing for 10 s at 1050°C, the junctions vary within 800–1400 Å depending on the annealing ambient. © 1999 The Electrochemical Society. All rights reserved.