A new feature scale model has been developed for the hydrogen plasma assisted chemical vapor deposition (PACVD) of copper from Copper(II) bis-hexafluoroacetylacetonate, Cu(Hfa)(2). PACVD of Cu(Hfa)(2) enables low temperature deposition and conformal coverage to be achieved. Copper is formed via a surface reaction between dissociatively adsorbed precursor and the atomic hydrogen that is produced in the plasma by the dissociation of molecular hydrogen. Our feature model shows that the transport of Cu(Hfa)(2) and atomic hydrogen into trenches/vias is restricted by the feature walls, which reduces gap fill. Also, it predicts conservatively that the concentration of Cu(Hfa)(2) is essentially constant and that the formation of voids is due largely to the variation in the concentration of atomic hydrogen. Using a variable diffusion, free boundary model that we have applied to copper PACVD, we show that gap fill can be very good and that voidless via fill can be achieved under proper conditions. These conditions are sensitive to the pressure and the angle of the walls, and they insure high diffusion rates of atomic hydrogen from the reactor space through the mouth of the feature and low recombination rates to molecular hydrogen along the feature walls. Furthermore, increasing the slope of the feature walls increases the effective diffusion rate of atomic hydrogen, which improves the gap fill markedly. A favorable agreement between the variable diffusion model calculations and experiments also is demonstrated.