,where GR is the growth rate, K1 and K2 the lump rate coefficients, p the precursor partial pressure. The variation of GRtop with pSi depicted in Fig. (a) is fitted with Eq. ( ) and denoted with the dashed curve. For pSi > 10 Pa the GRtop can be fitted well with Eq. ( ); however, the point at pSi= 7 Pa lies below the expected curve. We interpret this as an indication that at this psi the amount of precursor molecules is not sufficient to occupy all the available sites. The pressure dependence observed at pSi = 10 Pa -40 Pa does not completely follow the ideal first-order Langmuir adsorption where the order of pressure dependence should decrease from 1 to 0 when entering from low to higher pressures. This non-linear pressure dependence at lower pressures and weak dependence at higher pressures can be better described by a Freundlich isotherm where the order of pressure dependence is not restricted to 1 and 0. However, the gradually declining pressure dependence of the GRtop still implies that the growth of 3C-SiC films undergoes a transition from mass-transport limited to surface-reaction limited regime. Yang et. al. attributed this growth rate saturation to surface site blocking. At lower partial pressures, the precursor molecules can readily adsorb on the available surface sites, reacting to form films and the growth rate is limited by the precursor flow rate, i.e. precursor partial pressure. At higher pressures, more precursor molecules are present in the reaction zone, the surface sites are blocked by the adsorbed but unreacted molecules. Consequently, the number of available surface sites is largely reduced, leading to a surface-reaction limited growth and the growth rate becomes independent on the precursor partial pressure . The precursor molecules approaching the saturated surfaces will either return to the gas phase, which is the case for planar substrates, or continue diffusing downward into the trenches and form film at available sites. This flow of unreacted precursor molecules can reduce the pressure drop in the trench, resulting in a steady film growth along the wall and the bottom of the trench. In