The conformal deposition is corroborated by cross section micrographs of the trenches (Fig. ), showing the films deposited at 450 °C as perfectly conformal with equal thickness around the features forming the trenches. The elemental distribution of Si from the Si(100) substrate and the film constituents B and C from EDX mapping is uniform in the film, see Fig. . The elements are equally distributed over the trench depth. From the elemental mapping and the cross-sectional micrographs, it can be observed that the deposition process does not cause any intermixing between the substrate and the film. The EDX result confirms that compositional homogeneity is maintained over the 3D surface. It has previously been reported that BxC films can be deposited conformally from TMB at 700 C in a hydrogen ambient with atomic hydrogen or dihydrogen suggested to act as an inhibitor, blocking surface sites. This was confirmed by experiments in argon ambient that did not result in conformal deposition. Consequently, we performed experiments in argon ambient at 450 °C with TEB to study the influence of hydrogen on conformal deposition. Cross-sectional SEM micrographs (Fig. ) show that films deposited in argon ambient have the same film thickness at both the top and the bottom of the trenches, i.e., a step coverage of 1. This suggests that the conformal deposition from TEB at 450 °C does not follow the same mechanism as conformal deposition from TMB at 700 °C. Site blocking by hydrogen is therefore not the expected mechanism for the conformal deposition from TEB, strengthening the assumption that the conformal deposition is due to the lower β, as discussed above. We note a higher deposition rate in hydrogen compared to argon ambient i.e., 0.57 Å/s and 0.13 Å/s, respectively. We suggest that this difference is due to the H2 assisted ligand removal which has been suggested to enhance the thermal decomposition of TEB at temperatures below 500 °C. This result, and the suggested gas phase chemistry model in Ref. 19, suggest that the film deposition is dependent on gas phase decomposition of the TEB molecule and that the surface chemistry is dominated by BHx(C2H5)3-x species.