We have studied chemical vapor deposition (CVD) of Si from an SiH4 + Ar mixture, using excimer laser beam excitation parallel to a Si substrate. The growth mechanisms were studied by analyzing the effects of the temperature, pressure, laser repetition rate and intensity on the deposition rate and on the film microstructure. In addition, absorption measurements and gas analysis were performed during the deposition. This paper discusses the results of thickness measurements and calculations of the activation energy. A Gaussian-shaped transverse thickness distribution was obtained with a maximum corresponding to the center of the laser beam. This distribution depended on the deposition parameters and was attributed to the diffusion process of the silane decomposition products in the gas phase to the substrate. An Arrhenius plot of the deposition rate vs. the substrate temperature could be divided into two regimes associated with different activation energies. Between 340 and 460 degrees C, the activation energy is 0.25-0.3 eV, while it is 1.1 eV between 500 and 560 degrees C. The activation energy in the higher temperature regime is similar to that found for thermal CVD without the use of a laser. However, in the lower temperature regime, the deposition process is mainly laser induced, and the value of the activation energy was attributed to the process of adsorption of the gas species onto the substrate.