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As feature size shrinks to the deep sub-micron regime, the RC delay of metal interconnection will increase and limit the performance of high-speed devices. To address this problem, fluorine-doped silicon dioxide (SiOF) has been introduced in advanced IMD applications. Many deposition methods have been studied, including PECVD and HDP CVD. HDP CVD was finally applied to most deep sub-micron processes because it can meet the gap-filling requirement. However, the fluorine-doped silicon dioxide film is an unstable film. It suffers from high water absorption and a fluorine instability problem. This problem will cause a device reliability issue and even defects to appear at the final alloy step. In this paper, the fluorine-doped silicon dioxide deposition temperature and post-thermal processes, including N2 alloy and vacuum-bake have been studied, find a way to overcome these problems. The fluorine-doped silicon dioxide film properties including the fluorine concentration, RI, and film thickness will be compared to the as-deposition after film is alloyed. The film SIMS and TDS data have also been studied in this paper. The result of the experiments show that a lower deposition temperature has a poorer film property and the post-thermal process can degas the unstable fluorine. The optimized combination of conditions, of fluorine-doped silicon dioxide deposition temperature and post-thermal treatment can create a good quality fluorine-doped silicon dioxide without a reliability issue.