The effects of using tertiarybutylphosphine (TBP) as a source of phosphorus dopants during polycrystalline silicon (polysilicon) deposition in a rapid thermal processor (RTP) was investigated using TEM, SIMS, spectrophotometry, and 4-point probe analysis. It was found that the introduction ot TBP significantly inhibited the deposition of polysilicon on silicon dioxide, but only slightly reduced the growth rate of polysilicon on polysilicon. The introduction of TBP during the last 20% of the deposition time formed a thin phosphorus-rich layer on the top surface. Adsorption of the phosphorus was found to be gas-transport-limited. Incorporation of the dopant into the rest of the polysilicon layer was accomplished with an in-situ anneal (RTA) in nitrogen, resulting in a resistivity as low as 720 μΩ-cm.
The grain size of the polysilicon was found to increase with deposition temperature, however was not affected by the introduction of the dopant, or any subsequent anneal. It ispostulated that unincorporated phosphorus, and oxygen and carbon in the grain boundariesprevent the combination and growth of silicon crystals.