GROWTH MECHANISMS OF SILICON FILMS PRODUCED BY LASER-INDUCED CHEMICAL-VAPOR-DEPOSITION

We have studied chemical vapor deposition (CVD) of Si from an SiH4 + A r mixture, using excimer laser beam excitation parallel to a Si substr ate. The growth mechanisms were studied by analyzing the effects of th e temperature, pressure, laser repetition rate and intensity on the de position rate and on the film microstructure. In addition, absorption measurements and gas analysis were performed during the deposition. Th is paper discusses the results of thickness measurements and calculati ons of the activation energy. A Gaussian-shaped transverse thickness d istribution was obtained with a maximum corresponding to the center of the laser beam. This distribution depended on the deposition paramete rs and was attributed to the diffusion process of the silane decomposi tion products in the gas phase to the substrate. An Arrhenius plot of the deposition rate vs. the substrate temperature could be divided int o two regimes associated with different activation energies. Between 3 40 and 460 degrees C, the activation energy is 0.25-0.3 eV, while it i s 1.1 eV between 500 and 560 degrees C. The activation energy in the h igher temperature regime is similar to that found for thermal CVD with out the use of a laser. However, in the lower temperature regime, the deposition process is mainly laser induced, and the value of the activ ation energy was attributed to the process of adsorption of the gas sp ecies onto the substrate.