30 December 2008 Development of thick film PECVD amorphous silicon with low stress for MEMS applications
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Abstract
This paper presents a solution for the deposition of thick amorphous silicon (α-Si:H) in plasma-enhanced chemical vapor deposition (PECVD) reactors for MEMS applications. Thick α-Si film up to 2 μm is widely used as a sacrificial layer in the MEMS release process, however, the film quality and smoothness are limited by the cracking or peeling of thick film due to their intrinsic stress. This achievement of as thick as 12 μm film was possible by tuning the deposition parameters to a 'zero' value of the residual stress in the α-Si:H layer. The influence of the PECVD process parameters, such as power, frequency mode, temperature, pressure and SiH4/Ar flow rates on tuning the residual stress and a good deposition rate was analyzed. As a result, an almost "zero-stress" α-Si:H film and a deposition rate of 85nm/min was achieved for a temperature of 200ºC, a pressure of 800 mTorr, a high-frequency power of 120W, with SiH4 flow rate of 120 sccm and Ar flow rate of 500 sccm. The deposition of low-stress and thick (more than 12 μm in our case) α-Si:H layers was possible without generation of peeling or hillock defects. Finally, the paper presents some MEMS applications of such a deposited α-Si:H layer: a very good masking layer for dry and deep wet etching of glass; and a sacrificial layer for dry or wet release of bridge/cavity structure.
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Bangtao Chen, Francis E. H. Tay, Ciprian Iliescu, "Development of thick film PECVD amorphous silicon with low stress for MEMS applications", Proc. SPIE 7269, Micro- and Nanotechnology: Materials, Processes, Packaging, and Systems IV, 72690M (30 December 2008); doi: 10.1117/12.810441; https://doi.org/10.1117/12.810441
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