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29 September 1999 Silicon surface micromachining over active devices
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Abstract
Reported modification of CMOS processes to incorporate MEM structure require the structure to be located outside the active area. This paper describes the fabrication of microstructures directly over active devices rather than alongside them. Several issues need to be addressed with this fabrication process. The first issue is the choice of the metal to be used for metalization. Aluminium is no longer a viable option as some of the post-metalization processing steps exceed its melting point. Tungsten and titanium are the alternative candidates with sufficiently high melting point and low resistivity. The second issue is the non-planar surface profile across the wafer after the fabrication of the active devices. The sacrificial layer must be greater than the surface profile across the wafer and furthermore planarization of the sacrificial layer is necessary before the structural layer is deposited or electroplated. The final issue is post-metalization process temperature considerations for stress relaxation where either rapid thermal annealing or a relatively low temperature annealing of the microstructure is carried out. In this paper, these issues will be addressed, using the processes developed for the fabrication of an opto- mechanical microaccelerator as an illustration.
© (1999) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Ekalak Chaowicharat, Chee Yee Kwok, and Graham A. Rigby "Silicon surface micromachining over active devices", Proc. SPIE 3891, Electronics and Structures for MEMS, (29 September 1999); https://doi.org/10.1117/12.364441
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