The spin coating of polymer solutions onto silicon substrates was investigated using both commercially formulated polyimide precursors and model polymer solutions. The latter included solutions of polystyrene, polymethyl methacrylate and poly(ethylene oxide) in appropriate solvents. Experiments were conducted to determine the influence of the various process, material, and geometrical variables on the thickness and thickness uniformity of films deposited on planar as well as patterned substrates; dry film thickness was measured with the help of profilometry. For flat substrates, the film thickness decreased with increasing spin speed, and, in the case of volatile solvents, increasing solvent volatility led to thicker films. Although solution viscosity could be changed by changing either the polymer concentration or the molecular weight, film thickness was more sensitive to changes in concentration. Process conditions that gave thicker films also tended to yield more uniform films. From experiments on substrates with topography, it is concluded chat low spin speeds in conjunction with concentrated solutions of low molecular weight polymer in nonvolatile solvents favor planarization.