In Fig. , the thickness of the B-C film at the top and the bottom of the 8:1 aspect ratio feature deposited for 120 min is plotted as function of deposition temperature. Films deposited at ≤450 °C were perfectly conformal, with identical thickness at the top and the bottom of the 8:1 aspect-ratio, 8.5 μm wide trenches. The resulting step coverage (thickness at the bottom/thickness at the top) is plotted together with the deposition rate at the top surface of the features in Fig. , showing that the upper temperature limit for conformal film deposition is 450 o C at a deposition rate of ~0.57 Å/s. In addition, Fig. shows that above 450 °C, the deposition rate at the bottom and the top surfaces varies as two different functions of temperature. We suggest that our results can be explained by slow kinetics of the gas phase reactions needed for the deposition, in line with the theory developed by Yanguas-Gil et al. , stating that the fundamental approach for conformal films is to reduce the surface reaction probability, β. As a result, many of the incoming molecules can continue diffusing along the trench without being consumed immediately at the trench opening, which in turn leads to a more conformal deposition. This means to our depositions that above 450 °C, the TEB molecules arriving at the top surfaces of the 8:1 aspect ratio feature has higher probability to decompose than to diffuse to the bottom surfaces of the trench. This leads to a higher consumption rate for the TEB molecules at the top of the trench resulting in an off-set in the distribution of incident flux to the surface along the trench and nonuniformity in film thickness.