We carried out a multiparameter fabrication study designed to reduce the line edge roughness (LER) of electron beam (e-beam) patterned hydrogen silsesquioxane resist for the purpose of producing low-loss silicon strip waveguides. Reduced mask roughness was achieved for 50°C pre-exposure baking, dose with a beam spot size more than twice as large as the electron beam step size, development in 25% tetramethylammonium hydroxide and postdevelopment baking with rapid thermal annealing in an ambient at 1000°C. The LER caused by pattern fracturing and stage stitches was reduced with multipass writing and per-pass linear and rotational offsets. Si strip waveguides patterned with the optimized mask have root-mean-square sidewall roughness of 2.1 nm with a correlation length of 94 nm, as measured by three-dimensional atomic force microscopy. Measured optical propagation losses of these waveguides across the telecommunications C-band were 2.5 and for the transverse magnetic and transverse electric modes, respectively. These reduced loss waveguides enable the fabrication of advanced planar lightwave circuit topologies.