Low-Temperature LPCVD of Polycrystalline Ge_xSi_1-x Films with High Germanium Content

A study of low-pressure chemical vapor deposition LPCVD of GexSi1−x x 0.65 films was carried out. The films were deposited on thermally oxidized silicon wafers at deposition temperatures of 430–480°C. Pure GeH4 and SiH4 or Si2H6 gas sources were used. It has been found that the reactive sticking probability ratio between GeH4 and SiH4 varies between 11 and 3.5, depending on both the deposition temperature and film composition. An increase of germanium content from 40 to 60 atom % caused a sharp increase of deposition rate. The polycrystalline layers mainly contained 110- and 111-oriented grains. The 111-oriented grains were overgrown by the 110-oriented grains at 430°C after a film thickness of about 100 nm. Reducing the total pressure below 10 Pa led to a dominance of 111-oriented grains. A relative GeH4 depletion in the downstream direction influenced both the composition and crystallinity of the layers, and the deposition rate. To minimize the depletion effect, Si2H6 has been used instead of SiH4. No improvement has been obtained but the depletion from Si2H6 occurred instead of the depletion from GeH4. A proper mixture of SiH4, Si2H6, and GeH4 can be suggested to compensate the depletion effects. © 2006 The Electrochemical Society. DOI: 10.1149/1.2177006 All rights reserved.