OXIDATION OF PHOSPHORUS-DOPED LOW-PRESSURE AND ATMOSPHERIC-PRESSURE CVD POLYCRYSTALLINE-SILICON FILMS

The oxidation of low pressure and atmospheric pressure poly-silicon films has been investigated and compared to that of single crystal silicon. Samples were either undoped or doped with phosphorus, generally by a gaseous predeposition using a POCl3 source. For one doping cycle a wide range of oxidation conditions was employed, while a surface-reaction-rate-controlled oxidation was used for films containing widely varying dopant concentrations. The low pressure and atmospheric pressure poly-silicon oxidize at approximately the same rate, which may be markedly different from that of single crystal silicon doped during the same predeposition cycle. The oxidation rate of moderately doped poly-silicon appears to be controlled by the electrically active carrier concentration at the surface of the poly-silicon film. The carrier concentration at the beginning of the oxidation is especially important, and dopant pile-up at the surface during the oxidation does not dominate the results. The marked differences seen between single crystal and poly-silicon samples are related to the different diffusivities of dopant atoms in the two materials and the presence of an oxide layer under the poly-silicon films. An upper limit of the oxidation rate was found in heavily doped samples, probably corresponding to carrier concentrations expected for solid-solubility dopant concentrations in the films. Lightly doped poly-silicon films oxidize at a rate between those of (100)- and (111)-oriented single crystal silicon, with the low pressure material oxidizing slightly more rapidly, suggesting that the crystallite orientation in the poly-silicon films dominates in this region. The ratio of poly-silicon consumed during the oxidation to oxide grown was found to be 0.43, close to the value used for single crystal silicon. © 1979, The Electrochemical Society, Inc. All rights reserved.