Estimates of the effective deposition probability for plasma‐deposited amorphous silicon (a‐Si:H) films were obtained from computer simulations using a Monte Carlo technique. Randomized scattering events are tracked to simulate the deposition ofa‐Si:H along etched trenches under a metallic shadow mask. The resulting film thickness profiles are consistent with scanning electron micrographs obtained from step coverage experiments. Device quality materials tend to have effective deposition probabilities lower than 0.01 and are associated with CVD‐like deposition involving SiH3radicals. Defective materials are found to have deposition probabilities near unity and are associated with a PVD‐like process involving SiH and SiH2radicals.