Effects of i n s i t u plasma supply in undoped and boron-doped polycrystalline silicon by low-pressure chemical vapor deposition at 500–840 °C

Abstract

Undoped and boron-doped polycrystalline silicon films were prepared on a fused quartz at 500–840 °C by low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD) from a SiH4+B2H6+H2 mixture, using the same fabrication system. The effects of plasma (rf power) supply on the structural and electrical properties were investigated. Below 700 °C, all films show a 〈110〉 preferential orientation (P.O.), increasing with an increase in rf power. Particularly between 650 and 700 °C, an extremely stronger 〈110〉 P.O. is found at a rf power >15 W. Above 730 °C, undoped LPCVD and PECVD films and boron-doped LPCVD films represent a nearly random orientation. On the other hand, for boron-doped PECVD films, a strong 〈111〉 texture is observed in the intermediate doping range. The 〈110〉 texture increasing with rf power in undoped PECVD films is interpreted as indicating enhanced nucleation at the surface in contact with the gas phase. The plasma supply also has essential effects for smoothing the surface and improving the boron-doping efficiency. The effects of plasma supply are discussed in terms of increased surface diffusion of adsorbates, sputtering effect, and a contribution of hydrogen covering the surface. PECVD films are more stable for foreign contamination after fabrication than LPCVD films.