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High density plasma chemical vapor deposition (HDP-CVD) technology is currently not able to provide the semiconductor industry with a void-free fill process for shallow trench isolation (STI) with 100 nm gap width and aspect ratios (AR) higher than 4:1. For the first time a method is shown, which can extend the well-known HDP-CVD technology to provide void-free gap fill to gap widths below 90 nm and AR higher than 6:1. Key to this is the addition of nitrogen trifluoride (NF3) to the conventional silane/oxygen HDP-CVD chemistry. As a result of this component, an in-situ fluorine based isotropical oxide etch, gap fill capability will be improved. Compared to other fill alternatives a very good oxide quality is obtained for this process. The incorporated F and N show only a minor impact on film quality. The integration scheme does not need to be changed. Results from fully integrated DRAM wafers showed comparable yield to conventional HDP split groups with no additional reliability risk.