While several studies have suggested that secondary electrons dominate electron beam induced deposition (EBID), we demonstrate that primary electrons (PE's) contribute significantly to the deposition for nanoscale EBID over the electron beam energy range (500-20 keV). High-aspect ratio pillar growth is a signature of EBID; W nanopillar growth on SiO2 substrate yielded a growth rate of 6 mn s(-1) and a nanopillar aspect ratio of similar to 50. A simple integration of the primary, secondary, and backscattered electron distributions versus a dissociation cross section for WF6 suggests that all three electron species should contribute to the total volume of the deposited nanopillar, contrary to reports that suggest that secondary electrons dominate the process. A three-dimensional, Monte Carlo simulation including time correlated gas dynamics and species specific deposition was developed to help elucidate which of the relevant electron species, primary (PE's), secondary (SE's), and/or backscattered electrons (BSE's), induce the dissociation of precursor gas and lead to nanopillar growth. PE's and secondary electrons produced from the incident beam (SEI's) were found to induce the vertical nanopillar growth component relative to secondary electrons induced from backscattered electrons (SEII's) and BSE's. (c) 2005 American Vacuum Society.