The hardness of SiO2 films grown or deposited on silicon was measured by use of nanoindentation techniques to determine the effect of the substrate on the film hardness. These experiments were compared with polishing experiments of SiO2 films. Our results indicate that the substrate had no influence on the polish rate, although it strongly influenced the hardness. The observations suggest that the depth of deformation of films by abrasives during polishing is much shallower than that by the diamond indenter. A greater influence on polishing rate is expected for SiO2 films on softer substrates, such as aluminum, where greater deformation of the film by abrasives would take place.