Accurate Depth Profiling of Ultra-Thin Oxide Films by Secondary Ion Mass Spectrometry
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ACCURATE DEPTH PROFILING OF ULTRA-THIN OXIDE FILMS BY SECONDARY ION MASS SPECTROMETRY STEPHEN P. SMITH, MING HONG YANG and VICTOR K.F. C-HIA Charles Evans and Associates, 301 Chesapeake Drive, Redwood City, CA 94063 ABSTRACT SurfaceSIMS depth profile measurements of dopants in silicon wafers with thin thermal oxide layers are presented. Complete and accurate calibration of these profiles requires layered data reduction to adjust for residual matrix effects of a factor of two in the sputter rate and SIMS relative sensitivity factor in SiO 2 compared with bulk silicon. Properly calibrated profiles show good agreement with expected ion implant profile shapes, and can reveal dopant pile-up at SiO 2/Si interfaces (phosphorus, for example). Measured SurfaceSIMS profiles of B doping within the first 10 nm of the substrate Si of experimental large area MOS capacitors show good agreement with dopant profiles independently obtained from experimental C-V data. INTRODUCTION The importance of thin thermal oxide films in IC processing is illustrated by their many applications, including gate oxide in MOSFET, capacitor oxide in DRAM, tunnel oxide in EAROM, and sacrificial screen oxide to randomize ion implants and reduce junction depths and surface contamination. The growth rate of high quality stable oxide films formed at high temperatures has been successfully predicted by the Deal-Grove model for silicon having surface doping levels below 10'9 atoms/cm3 . However, for thin films (
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