LPCVD of polysilicon

One of the most widely used materials for the fabrication of modern VLSI circuits is polycrystalline silicon, commonly referred to as polysilicon. It is used for the gate electrode in metal oxide semiconductor (MOS) devices, for the fabrication of high value resistors, for diffusion sources to form shallow junctions, for conduction lines, and for ensuring ohmic contact between crystalline silicon substrates and overlying metallization structures. 

Typical conditions for depositing polysilicon are temperatures in the range 580-650°C and pressures in the range 25-130 Pa (0.2-1.0Torr). The overall chemical reaction is 

The process can be used to deposit polysilicon on 100-200 wafers in one run with within-wafer and wafer-to-wafer thickness uniformities of better than a few per cent. Deposition rates are typically 10-20 nm min-1. 

Others have reached similar conclusions, with Duchemin etal. [23] showing that at the low pressures used for polysilicon deposition the hydrogen is 

For a rate-controlling step involving the gas-phase decomposition of SiH4 one would, on the basis of Rice, Ramsperger, Kassel and Marcus (RRKM) theory, expect a difference in activation energies obtained for 

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There is clearly now some understanding of the underlying chemistry of the LPCVD of polysilicon, but, as already indicated, it is important to relate that basic understanding to practical issues of layer characteristics. 

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