Study of the surface roughening dynamics and feature profile evolution in plasma etching of AIN thin films for advanced MEMS microfabrication

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Aluminium nitride (AlN) is a promising material for MicroElectroMechanical Systems (MEMS), particularly for devices operating in the MHz-GHz frequency range. One critical step in MEMS microfabrication is the plasma etching of the piezoelectric layer down to the underlying electrode material. Preliminary investigations of the etching characteristics of AlN thin films with a columnar microstructure performed at Teledyne DALSA Semiconductor in Ar-BCl3-Cl2 plasma chemistries have shown rough, pyramidal features at the bottom of the trenches with roughness as large as 0.5 µm depending on the plasma conditions. In addition, important redeposition of etching by-products was observed on the sidewalls of the patterns, which is unacceptable for most applications. Additional complications in plasma etching of columnar AlN are due not only to the multi-component nature of this material, resulting in a more sophisticated surface chemistry, but also to its columnar microstructure yielding plasma etching reactions not only on the topmost surface but also deeper in the bulk through grain boundaries. Through this new collaboration between UdeM and Teledyne-DALSA, we would like to gain insights into specific aspects related to the surface roughening dynamics and feature profile evolution in plasma etching of columnar AlN for MEMS. The proposed research builds on the expertise of our group in the physics of low-temperature plasmas and their applications to complex materials processing. It also capitalizes on the unique infrastracture of UdeM in terms of plasma etching reactors, plasma diagnostics, and feature profile simulators as well as the microfabrication and materials characterization tools of Teledyne-DALSA. Since this research will be performed in close collaboration with Teledyne-DALSA, it is expected that the knowledge generated from this study will play a crucial role in their optimization and development of plasma etching processes and recipes that are strategically needed to meet current and future challenges in AlN-based device manufacturing. It should also be benificial to other companies in Canada dealing with the etching of materials with a complex nanostructure.