This paper presents the development of a dry etch recipe for molybdenum (Mo), based on SF6, BCl3 and Ar gases for high-topography MEMS device fabrication. The recipe was optimized for a high Mo etch rate, a low Mo by-product generation and a low Mo undercut using photoresist (PR) masks. The presented optimized recipe is very effective in Mo etching using a PR mask. The Mo by-product generated during the Mo etch can be easily removed using the ACT NE-14 etch residue remover. This optimized recipe was also used for etching Mo electrodes using oxide, PR or composite oxide-PR masks to select the better mask and selectivity. It was observed in this study that Mo has a better selectivity when using an oxide hard mask. However, it has the serious drawback of generating by-products which are difficult to clean later on. On the other hand, Mo has a poor selectivity with PR masks compared with oxide masks but there was no issue of by-product cleaning. At the same time, no extra mask layer deposition is required for Mo etching. The optimized recipe was also used for Mo electrode etching using PR and PR-oxide composite masks for the demonstration of working film bulk acoustic wave resonators and actuator microelectromechanical system devices.

Various types of polyimide have been used widely in the manufacturing of integrated circuits and MEMS’ (Micro Electrical Mechanical Systems) such as sensors. These organic spin-on polymers exhibit a wide range of mechanical and electrical properties and have been commonly used for electrical insulation as well as device passivation and protection. In addition, these organic spin-on polymers serve as excellent sacrificial materials for forming cavities on MEMS structures. This work studies the gapfill properties of several polyimides after spin-coating and curing. In addition, this work examines and compares the gapfilling and planarization properties of a number of different polyimides, including multiple layers of polyimides for gapfilling and planarization.

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.