The carbonization of the Si (100) surface in an APCVD reactor using propane as the carbon source gas and hydrogen as the carrier gas was studied. The layer thickness as a function of carbonization time exhibits a parabolic behavior indicative of a self-limiting process. Voids are produced in the carbonization layer when hydrogen is used during the cool-down step, but not when hydrogen is replaced by argon. Other than the presence of voids, the surface morphology of the carbonization layer is relatively smooth, suggesting that the carbonization layer forms via quasi-two dimensional growth.