LOW-TEMPERATURE DIFFERENTIAL OXIDATION FOR DOUBLE POLYSILICON VLSI DEVICES

Dry O2 oxidation characteristics of heavily doped polycrystalline silicon in the temperature range of 750°-900°C were studied for use in a double polysilicon VLSI device process with a large differential oxidation ratio. These differential effects are optimized at temperatures around 800°C, where the oxidation process is primarily controlled by surface reactions as opposed to diffusion reactions which are rate controlling at higher temperatures. For a 28 hr oxidation in dry O2 at 800° C a 505Å oxide was formed on single crystal (100) p-type silicon while 2020Å was produced on the n-type polysilicon doped using a 34 min POCl3 predeposition at 950°C. A decrease in differential oxidation ratio is shown to occur for longer oxidation times. Using ion implantation of As at 50 keV, a dose of 3.2 × 1016 cm-2 is needed to produce a differential oxidation effect as large as that for POCI3 doping of the polysilicon. The linear rate constant is shown to increase by a factor of 55 for the doping range studied; whereas the parabolic rate constant increases by less than a factor of four. © 1979, The Electrochemical Society, Inc. All rights reserved.