Phosphorus profile control in low-temperature silicon epitaxy by reduced pressure chemical vapor deposition

Abstract

Phosphorus incorporation around 10 18 cm −3 has been studied during low-temperature (660–750 °C) silicon epitaxy by chemical vapor deposition under reduced pressure (20 torr) using silane (SiH 4) or dichlorosilane (SiH 2Cl 2) as silicon precursor. Strong surface segregation of phosphorus was observed. The phosphorous segregation could be reduced either by decreasing the growth temperature or adding HCl during growth of the undoped layer. Neither reduced growth temperature nor HCl addition was able to produce steep turn-off of the phosphorus concentration with an acceptable growth rate. Therefore, ex situ removal of the phosphorus surface layer was tested using either a chemical oxidation or a low-temperature thermal oxidation. In both cases, a dramatic reduction in surface segregation was observed with a slope less than 15 nm/decade in the resulting dopant profile. A subsequent epitaxial Si/SiGe (17%) growth on the ex situ cleaned sample was found to result in layers exhibiting high crystalline quality according to high resolution X-ray diffraction mapping.