Moderately in situ phosphorus-doped polycrystalline silicon by single wafer reduced pressure chemical vapor deposition

Abstract

Rapid thermal chemical vapor deposition of in situ boron-doped polycrystalline silicon-germanium films on silicon dioxide for complimentary-metal-oxide-semiconductor applications A study of moderately in situ doped polycrystalline silicon deposition from SiH 4 , PH 3 , and H 2 by single-wafer reduced pressure chemical vapor deposition has been carried out. The process window which yielded P concentrations on the order of 10 19 cm Ϫ3 was a pressure of 80 Torr in a hydrogen carrier with a PH 3 /SiH 4 mole fraction range of 0.1ϫ10 Ϫ4 -1ϫ10 Ϫ4 , and temperatures of 600-700°C. It was found that the PH 3 /SiH 4 mole fraction in this process window has little effect on the deposition rate unlike the rate reduction caused by PH 3 in a saturation-doped polysilicon process with doping levels in excess of 10 20 cm Ϫ3 . The activation energy of the process, 48 kCal mol Ϫ1 , over this temperature range approaches one of a hydrogen desorption limited process, 49 kCal mol Ϫ1 , suggesting that the deposition rate is dominated by the high H 2 pressure. The transition of the as-deposited film structure from predominately amorphous to completely polycrystalline occurs at about 675°C, about 100°C higher than in typical low-pressure chemical vapor deposition and is likely due to a combination of high H 2 pressure and high deposition rates. To a first order, the post-anneal film resistivity appears to be dominated by the grain structure and not by the P incorporation rate in the moderately doped concentration regime.