Integration of AlN with molybdenum electrodes and sacrificial amorphous silicon release using XeF₂

Abstract

This paper presents a new post-CMOS-compatible integration scheme for AlN-based MEMS devices. The proposed scheme integrates molybdenum (Mo) bottom electrodes with an amorphous silicon (a-Si) sacrificial layer, which is etched using XeF2 to release the MEMS structures. This integration approach faces two potential issues, which are solved in this work: (i) poor adhesion of AlN with a-Si, and (ii) XeF2 attacking the Mo electrode during the removal of the a-Si sacrificial layer. The adhesion problem was solved by introducing a thin oxide layer between a-Si and AlN. The sidewalls of the Mo electrodes were protected by a 0.2 µm thick SiN spacer layer from the XeF2 attack. The robustness of the integration scheme was verified by fabricating an FBAR band pass filter. RF measurements on the FBAR band pass filter show that the proposed integration works well and can be utilized for other AlN-based MEMS devices in post-CMOS applications.

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“…Many requirements have to be fulfilled for successful device integration with CMOS. These include low thermal budget for the post-CMOS processes, good adhesion between layers, removal of sacrificial layers without damage to CMOS and MEMS materials, and selection of suitable electrodes and isolation materials that have to be compatible with all the processes and materials used in the fabrication of CMOS 22 . Existing FBAR architectures make this extremely challenging.…”