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Selective deposition of polycrystalline silicon for tuning micro-electro-mechanical resonators: Experiment and simulation.

机译：用于调谐微机电谐振器的多晶硅的选择性沉积：实验和仿真。

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Micro-electro-mechanical systems (MEMS) with identical properties cannot be readily produced. There are sub-micron differences in size and other variations, which especially in resonators, cause frequency scatter, and reduce yield. A post-fabrication process was developed to correct variations in micromachining processes. It consisted of electrically-heating suspended polysilicon structures in a silane environment to locally decompose the gas and deposit polysilicon. The volume of polysilicon deposited followed the temperature distribution of the structures. The temperature during selective deposition was found using an ABAQUS finite element electro-thermal analysis. The electrical current necessary to obtain deposition was found experimentally for some samples and predicted for others. The development of the electro-thermal simulations involved estimating material properties for polysilicon. A study of the sensitivity of temperature to the values of the thermal conductivity and the temperature coefficient of resistance was done. Significant dependence on these parameters was found.; In order to design microbeam resonators, a versatile numerical method of solving the pull-in problem was developed. Solutions for various boundary conditions (compliant supports, fixed and cantilever beams) are presented.; A new, special comb-drive resonator which had the standard four-beam suspension on one side replaced with a single-beam was designed. The latter feature enables one to predict the thermal hotspots. A finite-element thermal-stress simulation was developed to design against buckling at deposition temperatures, while keeping frequency at levels measurable by optical observation. Depending on the initial resistance of the sample, the power dissipation during heating and process time used, some variability in the deposited polysilicon (volume and texture) was found. Continuously and uniformly deposited layers, judged to be the best, were found for longer process times. Increases in frequency from 0.7% to 2.6% were obtained from the selective deposition of polysilicon on the special comb-drive resonators. For certain continuous and uniform depositions, the percent change in frequency due to the location and amount of deposition was determined and validated by using simulation. Large changes in frequency were predicted for situations in which deposition occurred at the root of a beam and its anchor.
机译：具有相同特性的微机电系统（MEMS）不易生产。存在尺寸和其他变化的亚微米差异，尤其是在谐振器中，会引起频率分散并降低良率。开发了后加工工艺来纠正微加工工艺中的变化。它由在硅烷环境中对悬浮的多晶硅结构进行电加热以局部分解气体并沉积多晶硅组成。沉积的多晶硅的体积遵循结构的温度分布。使用 ABAQUS 有限元电热分析法发现了选择性沉积过程中的温度。实验上发现了一些样品获得沉积所需的电流，而另一些则进行了预测。电热模拟的发展涉及估算多晶硅的材料性能。研究了温度对热导率和电阻温度系数的敏感性。发现对这些参数的显着依赖性。为了设计微束谐振器，开发了一种通用的数值方法来解决引入问题。提出了各种边界条件（顺应性支撑，固定梁和悬臂梁）的解决方案。设计了一种新的特殊梳状驱动谐振器，该谐振器的一侧将标准的四束悬架替换为单束。后一种功能使人们可以预测热点。开发了有限元热应力模拟程序，以设计成可防止沉积温度下的屈曲，同时将频率保持在可通过光学观察测量的水平。根据样品的初始电阻，加热过程中的功率耗散以及所用的处理时间，发现沉积的多晶硅有一些变化（体积和质地）。发现连续和均匀沉积的层（被认为是最好的）的过程时间更长。通过在特殊的梳状驱动谐振器上选择性沉积多晶硅，可以将频率从0.7％提高到2.6％。对于某些连续且均匀的沉积，通过模拟确定并验证了由于沉积位置和数量导致的频率变化百分比。对于在梁的根部及其锚定处发生沉积的情况，可以预测频率会发生较大变化。

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