A plasma processing combined with trench isolation technology for large opening of parylene based high-aspect-ratio microstructures

• A parylene based trench isolation method for high-aspect-ratio MEMS structures.
• A simple low temperature and dry etching fabrication process.
• One macro commands of ICP process for HARS structures.
• A test device with 50 μm of thickness, 10 of maximum trench aspect ratio is demonstrated.
• Can be used for large in-plane-displacement to increase the sensitivity for the sensors and actuators.

This paper presents a parylene-based trench isolation method with which to create high-aspect-ratio microelectromechanical system structures. The silicon-based structures were electrically isolated by supported parylene beams, and the movements of suspended silicon structures used to sense or actuate were not confined by trench openings. The proposed process is a simple, low-temperature, and dry-etching fabrication process for structure releasing and electrical isolation, and does not involve the LPCVD, PECVD, ion implantation, sputtering processes, or sandwiched oxide/polysilicon/metal isolation traditional methods require. The parylene-based electrical isolated beams can be created through multiple steps of parylene deposition/remove inside a silicon mold. By enhancing the microtrenching effect, the suspended structure does not thoroughly remove the floor polymer inside the trenches when the trench aspect ratio is relatively small. The steps of trench etching, sidewall protection, structure release, and photoresist stripping can be finished by modifying the etching or passivation steps in the BOSCH process, and it can be integrated as the macro commands of ICP etcher. The single-run of the ICP-RIE process can automatically finish the suspended silicon structure creation. By using the proposed process, a test device 50 μm thick and with a maximal trench aspect ratio of 10 and a maximal suspended structure width of 40 μm was created. The proposed process can be used to fabricate devices for large in-plane displacement, increasing the sensitivity of the sensors and actuators.

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