Nanocrystals Formation and Microstructure Evolution of Amorphous Si and Si_(0.7)Ge_(0.3) by Using Low Pressure Chemical Vapor Deposition

摘要

The initial stage of amorphous film deposition of Si and Si_(0.7)Ge_(0.3) deposited on SiO_2 by low-pressure chemical vapor deposition (LPCVD) was evaluated. The experimental results show that the surface roughness of amorphous Si or Si_(0.7)Ge_(0.3) layer deposited at higher temperature is smaller than that at lower temperature in the temperature range from 375 to 450℃. Also, amorphous Si or Si_(0.7)Ge_(0.3) film with the thickness of about 5 nm can be deposited as islands rather than continuous film, which is dependent on deposition temperature. In this paper, the islands formation at the initial stage of amorphous Si or Si_(0.7)Ge_(0.3)deposition was explained with the nuclealion and growth behavior in LPCVD process in the viewpoint of thermodynamics and kinetics. The thermodynamic driving force for Si nucleation in LPCVD was calculated with the degree of supersaturation defined by the ratio of Si vapor pressure in the gas phase equilibrium stale to Si vapor pressure in the overall equilibrium state. In our experimental condition, the driving force is higher at higher deposition temperature in the temperature range below 800 K. which is the temperature range for amorphous film deposition. Besides of the calculation of thermodynamic driving force, mechanism of adatom attachment was considered. The mechanism of adatoms attachment was explained with the preferential deposition on deposited Si or Si_(0.7)Ge_(0.3) cluster rather than on SiO_2 substrate. Also, the dependency of surface roughness on deposition was explained with preferential deposition and surface coverage effect.