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

In this work, LPCVD Germanium-Silicon films were deposited on thermally oxi dised silicon wafers using a horizontal LPCVD system, at a deposition tempe rature in the range between 430 and 480 degreesC 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 d eposition parameters. It has been shown that at the deposition temperature of 430 degreesC and total pressure of 20 Pa the grain size varied between 4 0 and 80 nm for a < 100-nm thick poly-Ge0.6Si0.4 fft and the root-mean-squa re surface roughness did not exceed 2.5 rim. A decrease of the Germanium co ntent from 60 to 40 atomic percent caused an increase of both the grain siz e and surface roughness due to nucleation matters. The polycrystalline laye rs mainly contained (110)- and (111)-oriented grains with its ratio dependi ng on both deposition pressure and film thickness. The appearance of the bi g grains and roughening of the surface was also observed with increasing fi lm thickness. Rising the total pressure above a certain level (100-200 Pa) caused an enhanced formation of the amorphous phase and appearance of rando mly situated surface convexities. Reducing the total pressure below 10 Pa l ed to roughening of the surface, probably due to a dominance of (111)orient ed grains in the film bulk at such a low pressure.