| Summary: | 碩士 === 國立成功大學 === 航空太空工程學系碩博士班 === 90 === Abstract
High density plasma chemical vapor deposition (HDP-CVD) is an newly thin film process for the fabrication of microelectromechanical systems (MEMS). The HDP film has many excellent film properties than the PECVD film. However, thin film materials are normally under residual stresses as a result of fabrication processes. Unlike microelectronic devices, a microstructure is no longer constrained by its underlying sacrificial layer after anisotropic etch undercutting; therefore, residual stresses and residual gradient stress may result in bending and buckling of a microstructure.
The objective of this present work is to use HDP-CVD technology to fabricate a low stress silicon nitride films and study the effects of deposition parameters on microstructure and stress distribution of there films in as-deposited state. The experimental results showed that the residual stress in the silicon nitride films can be reduced to the range of -200~200MPa by adjusting proper deposition parameters. The chemical contents and stress distribution were studied as a function of the annealing temperatures in the range from 400℃ to 600℃. The residual gases decreases with the increase in annealing temperatures from 75℃ to 300℃, causing the out-diffusion of NH3. Meanwhile, the stress in silicon nitride film could be transformed from the compressive region to the tensile region.
In addition, self-deformed micromachined cantilevers are fabricated to exhibit the residual gradient stress from curvature of the bending beams. The silicon nitride cantilever beams bent upward by a positive residual gradient stress. The present work shows that adjusting the HDP-CVD deposition parameters, the residual stress of the deposited films can be significantly reduced and a flat microstructures can be fabricated.
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