Four different process routes were designed and compared to investigate the SiO₂ film thickness uniformity of temperature-compensated surface-acoustic-wave filters after leveling. The results show that chemical– mechanical polishing （CMP） can reduce the film thickness uniformity， whereas scanning ion beam etching can optimize the uniformity. Scanning etching only after or before CMP improves the SiO₂ film thickness uniformity from 5. 4% to 3. 3% and 3. 1%， respectively， whereas scanning etching both before and after CMP improves the SiO₂ film thickness uniformity to 2%.