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

氮化铝（AlN）是一种很有前途的微机电系统（MEMS）材料，特别是在MHz-GHz频率范围内工作的器件。MEMS微细加工的一个关键步骤是等离子体刻蚀压电层直至底层电极材料。Teledyne DALSA半导体公司在Ar-BCl3-Cl2等离子体化学中对具有柱状微结构的AlN薄膜的蚀刻特性进行了初步研究，发现在沟槽底部有粗糙的锥体特征，根据等离子体条件的不同，粗糙度可达0.5 μ m。此外，在图案的侧壁上观察到重要的蚀刻副产物的再沉积，这对于大多数应用来说是不可接受的。柱状氮化铝等离子体刻蚀的其他复杂性不仅是由于这种材料的多组分性质，导致更复杂的表面化学，而且由于其柱状微观结构产生的等离子体刻蚀反应不仅在最表面，而且在穿过晶界的体中更深。通过UdeM和Teledyne-DALSA之间的新合作，我们希望深入了解与MEMS柱状AlN等离子蚀刻中表面粗化动力学和特征轮廓演变相关的具体方面。提出的研究建立在我们小组在低温等离子体物理学及其在复杂材料加工中的应用方面的专业知识之上。它还利用了UdeM在等离子体蚀刻反应器，等离子体诊断和特征轮廓模拟器以及Teledyne-DALSA的微加工和材料表征工具方面的独特基础设施。由于这项研究将与Teledyne-DALSA密切合作，预计从这项研究中产生的知识将在他们优化和开发等离子体蚀刻工艺和配方方面发挥至关重要的作用，这些工艺和配方是应对当前和未来aln基器件制造挑战的战略需要。这对加拿大其他从事复杂纳米结构材料蚀刻的公司也是有益的。

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.