Yanguas-Gil et. al. have proposed several mechanisms that can explain how the addition of an inhibitor can reduce the surface reaction probability and, thus, improve the coating conformality. Among them, the inhibitory effect of HCl investigated in this work can be understood from the following mechanisms. Assuming that the deposition chemistry occurs close to thermal equilibrium, the HCl molecules initially adsorbing on the available surface sites will block them from the adsorption of other active film-forming species . At 950 ℃ the steady state surface coverage of HCl on SiC was estimated to be 0.8 monolayer according to Schulberg et. al. , which suggests that a blocking effect from HCl is very probable. Moreover, if the assumption of thermal equilibrium still holds, an increased partial pressure of HCl, the primary by-product of the SiCl4 + C2H4 deposition chemistry, will shift the CVD reactions towards the reagents according to the Le Chaterlier's principle and, subsequently, the growth rate of SiC coating is reduced. In this regard, using SiCl4 as the Si-precursor alone could possibly already afford a SiC coating with improved conformality. These three mechanisms all lead to a decrease in surface reaction probability of film forming species on the top surface, reducing their partial pressure drop along the depth of trench and makes the coating more even in the recessed features. C2H4, may also be a factor that makes the transferal of conformal CVD approach to our high-temperature process possible. First, for SiCl4 and C2H4, it is relatively easy to achieve high precursor partial pressure because liquid SiCl4 has a vapor pressure of 31.6 kPa at room temperature and C2H4 is itself gaseous. Furthermore, the inhibitor HCl is intrinsically abundant in our process because it is the byproduct of chlorinated SiC CVD growth.