Morphological and structural changes in laser CVD of silicon: comparison of theoretical temperature calculations with experimental results

The paper considers to what extent theoretical calculation of the laser induced temperature profile in a substrate can be used to predict the morphology and structure of silicon tracks deposited by pyrolytic LCVD. The micron scale tracks are deposited from silane using a focussed argon ion laser onto a substrate consisting of 1000 Å SiO₂ upon a 300 μm thick, 100 mm diameter, [100] silicon wafer. The influence of various experimental parameters such as scan speed, laser power, gas pressure and gas composition on the temperature profile and on the deposited silicon track is investigated. Temperature profiles and their time evolution are simulated by numerically solving the heat diffusion equation using a finite difference approach. The track deposition is simulated using experimental temperature and pressure dependent growth rates. Gaussian shaped low laser power track profiles are well reproduced but the volcano like structures of high power deposition are not explained by the present model alone. The calculations are found to explain, at least qualitatively, the observed relationships between various experimental parameters.