A study of morphology and texture of LPCVD germanium-silicon films

In this work, LPCVD Germanium-Silicon films were deposited on thermally oxidised silicon wafers using a horizontal LPCVD system, at a deposition temperature in the range between 430 and 480 °C and total pressure between 5 and 200 Pa. Pure GeH4 and SiH4 gases were used as precursors. Morphology and texture of the GexSi1-x (X=0.3-0.6) films were investigated versus deposition parameters. It has been shown that at the deposition temperature of 430 °C and total pressure of 20 Pa the grain size varied between 40 and 80 nm for a <100-nm thick poly-Ge0.6Si0.4 film, and the root-mean-square surface roughness did not exceed 2.5 nm. A decrease of the Germanium content from 60 to 40 atomic percent caused an increase of both the grain size and surface roughness due to nucleation matters. The polycrystalline layers mainly contained (110)- and (111)-oriented grains with its ratio depending on both deposition pressure and film thickness. The appearance of the big grains and roughening of the surface was also observed with increasing film thickness. Rising the total pressure above a certain level (100-200 Pa) caused an enhanced formation of the amorphous phase and appearance of randomly situated surface convexities. Reducing the total pressure below 10 Pa led to roughening of the surface, probably due to a dominance of (111)-oriented grains in the film bulk at such a low pressure.