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Development and Characterisation of Vapour Phase Sacrificial Etching and Organic Deposition for MEMS Fabrication

Daniel Drysdale, Changhai Wang, Marc Desmulliez
Vapour phase sacrificial etching and organic film deposition are key process steps in the manufacture of many MEMS devices. [read more]

Vapour phase sacrificial etching and organic film deposition are key process steps in the manufacture of many MEMS devices. The vapour phase sacrificial etching is used to release certain structures that define the functionality of the device. The organic film deposition has been extensively used as an anti-stiction coating which improves the yield of these MEMS devices and is now being used to add further functionality to devices such as hydrophilic, anti-fouling and bio-active properties.

The sacrificial etching is defined by the materials of the completed structure. Using silicon as the sacrificial material XeF2 etching is employed which selectively removes the silicon and does not etch the surrounding materials. When silicon dioxide is used as the sacrificial material, vapour HF etching is employed. Both these processes are at a very early stage of development and the techniques used in the MEMSSTAR process modules are unique. Also, the sacrificial etching of MEMS devices is applied to many different types and sizes of structures adding a complexity to the etching not normally seen in standard semiconductor etching. In this project, these etching processes will be characterised with different structures and materials. The characterisation will be performed using statistical design of experiments where the process control parameters will be determined for the different etch regimes.

The MEMSSTAR organic deposition system is capable of depositing organic films using a wide range of precursor materials. These films are invariably self-assembled monolayers (SAM’s) which by their very nature are very thin. This makes film measurement very difficult and applications currently under investigation include: ellipsometry, AFM and contact angle measurement. In this project, these techniques will be used to determine the optimal process conditions to deposit these various precursor materials. These coatings are applied to various structures and the coating conformality will be investigated using specifically designed test structures.

This project is a collaboration between Heriot-Watt University and MEMSSTAR a part of Point 35 Microstructures.