IN SITU DOPED SILICON VIA LPCVD: INTERACTIONS OF THE DOPANT/SILANE/SILICON SURFACE SYSTEM.

Abstract

The difficulties associated with the phosphine (phosphorus) doped LPCVD polysilicon process are demonstrated, and the origins of severe growth rate suppression that is observed are investigated. This is attributed to the formation of a stable layer of adsorbed phosphine (or bare phosphorus dependent upon temperature), which acts to inhibit the adsorption of silane (and thus film deposition) on the silicon surface. The effect has been modeled under UHV conditions, and values of the sticking coefficient s(phosphine) equals 1. 0 versus s(silane) equals . 025 have been obtained, which are consistent with the magnitude of growth rate suppression observed. Diborane adsorbed very weakly on the silicon surface, and thus has little or no impact on silane adsorption, consistent with the observed behavior of diborane doped films.