We have used Remote Plasma CVD with plasma excited He to grow films of hydrogenated amorphous silicon, a-Si:H, with substrate temperatures, Ts, between 38 and 400°C. These films differ from glow discharge (GD) and sputtered films, most notably in the Ts dependence of the hydrogen bonding environments (SiH, SiH2, etc.) and the photoconductivity. For RPECVD of a-Si:H, we have investigated: 1) the effect of replacing He in the plasma with Ar; 2) the silane mass spectrum and film growth rate as a function of rf power supplied to the plasma; and 3) the helium emission lines and hydrogen concentration in the films as a function of dilution of the He plasma with oxygen and nitrogen. Based on these observations we present a model for the deposition chemistry that includes SiH3 radicals as precursors to film growth.