The influence of the chlorine-hydrogen ratio in the gas phase on the stability of the {113} faces of silicon in Si-H-Cl CVD

The orientation dependence of silicon crystal growth in the Si-H-Cl CVD system has been studied as a function of the chlorine-hydrogen ratio of the gas phase. This was done by the use of hemispherical single crystal substrates. As was reported before, the stability of faces with the indices {hhk}_{h < k} is dependent on temperature: above a certain critical temperature flat {113} and {337} faces are found on the hemispheres, while below this temperature only macroscopic steps appear in positions corresponding to these faces. In this study it is found that the above-mentioned critical temperature is strongly dependent on the chlorine-hydrogen ratio in the gas phase. It will be demonstrated that this "chemical roughening" effect is caused by the competitive adsorption of chlorine and hydrogen. From the experimental dependencies values for the heat of chemisorption of chlorine and hydrogen can be derived of - 370+-70 kJ mol^-1 and - 316+-5 kJ mol^-1, respectively. These values are in good agreement with literature values of Si-Cl and Si-H bond strengths.