HF Vapor Release Assessment to Address NEMS Applications

Due to the devices downscaling, the HF vapor release process, one of the most effective techniques for MEMS release, becomes more challenging regarding stiction. An initial compatibility study shows that many metals are compatible excepted Ni and Cu. Then a design of experiment (DOE) was performed on thermal oxide wafers to obtain the parameters for a free stiction process. Nevertheless, current MEMS release processes can not be used on NEMS structures due to more aggressive shape factor. The solution to adapt current HF vapor MEMS release process to NEMS consists in the reduction of the etchrate, reducing the water layer on the surface during the etch step and thereby stiction occurrence. For very challenging structures, reducing the etch rate is not sufficient to avoid stiction, heated processes have then to be used.