High-quality conformal silicon oxide films prepared by multi-step sputtering PECVD and chemical mechanical polishing

High-quality conformal oxide films were obtained by using multi-step sputtering (MSSP) plasma enhanced chemical vapor deposition (PECVD) process with argon ion sputtering and chemical mechanical polishing (CMP). The repeated deposition by plasma enhanced chemical vapor deposition (PECVD) and anisotropic etching of oxide films by multi-step sputtering PECVD improve the step coverage and gap filling capability significantly. The argon plasma treatment enhances the binding energy of Si-O in the SiO₂ network, and the temperature dependence of stress for MSSP oxide film showed no hysteresis after the heating cycle up to 440 °C. The stress-temperature slope of MSSP oxide film was found to be much less than that of conventional PECVD oxide film. The slope for 1.1 μm thick film is about 5.8×10⁵ dynes/cm²/°C which is smaller than that of thermally grown oxide film. It seems that MSSP oxide film reduces stress-temperature hysteresis and becomes more dense and void-free in the narrow gaps with inter-metal spacing of 0.5 μm. After filling of the narrow gap, we adopted the CMP process for global planarization and obtained good planarization performance. The uniformity of the film thickness was about 4% and the degree of the planarization was over 95% after CMP process.