We systematically explore the relationship between gas-phase kinetics and film microstructure in the hot-wire CVD technique using diluted silane (1% in He) and additional hydrogen. Using a wire temperature of 2000°C, films were grown on Si (100) at 300°C using 1 mTorr SiH4 and 99 mTorr He at hydrogen pressures from 0-100 mTorr. Transmission electron microscopy and atomic force microscopy measurements indicated that continuous microcrystalline films had a columnar grain structure and that grain size increased from 40 nm using SiH4/He to 85 nm using SiH4/He/H2 with 20:1 H2:SiH4 ratio due to the etching of silicon by hydrogen. Etching rate measurements using a quartz deposition monitor show that, under the current deposition conditions, a transition from net film growth (0.17 nm/s using only SiH4) to net etching occurs at a H2:SiH4 ration of 80:1. The effect of atomic H on the nucleation density during the initial stages of growth has also been investigated, revealing a sublinear dependence of nucleation density with time and a decrease in nucleation density with increasing H2 dilution. High deposition rate growth with no H2 dilution has been achieved on a low-density array of seed nuclei produced using high H2 dilution.