基于一体式电磁载荷设计的硅微机械结构力学性能研究

Deep Reactive Ion Etching (DRIE) are widely used for manufacturing silicon microstructures with high aspect ratios. Employing a novel micro-beam-electomagnetic-load integration structure, this project will study the mechanical characteristics and its microscopic mechanisms of DRIE-fabricated silicon micro-beams during the loading process from elastic deformation to failure by in-situ micro Raman spectroscopy, providing knowledge about the mechanical reliability of silicon microstructures produced by DRIE. The thickness of micro beams ranges from several to one hundred microns; the load is imposed onto the beams by an integrated electro-magnetic module, and is continuously adjustable with the maximum load capability of up to tens of millinewtons, surpassing the 7 GPa strength yield of bulk silicon at weak sites of the beams. The perturbation to this system of the ambient noise is suppressed to less than one over ten thousand of the load. This integration structure provides well-defined loading of various modes, is resistant to system drift and environmental disturbance, is spatially open to probing the whole beam and is beneficial to collection of detailed data for comparison. In-situ micro-Raman spectroscopy is used to map the crystal lattice structure near the surface of the beam which is crucial to mechanical behaviors, with the strain resolution of one over ten thousand and spatial resolution of sub-micron. By analyzing data of Raman spectroscopy and other supporting measurements, the mechanical behavior and inherent physical mechanisms will be studied with better certainty and depth.

针对高深宽比硅微机械结构制作中广泛使用的反应离子深刻蚀工艺，利用特有的硅微梁-电磁载荷一体结构，通过微区拉曼散射光谱原位监测，研究承载硅微梁从弹性形变到失效的力学行为及微观机制，借此较为系统地建立反应离子深刻蚀工艺、刻蚀结构侧壁形貌和微结构可靠性之间的关系，为该工艺的应用提供力学可靠性方面的指导。其中，微梁厚度约为几微米到百微米之间；载荷通过电磁力施加于微梁上，连续可调，最高可达上百毫牛顿，微梁局部应力可超过体硅7GPa的屈服强度，借助磁场的均匀性将常规环境噪声对系统的扰动抑制在载荷万分之一以下。该设计中施载方式定义明确，具有拉伸和扭转等多种模式，探测空间开放，系统稳定，便于细致收集对比数据。原位微区拉曼光谱技术空间分辨率可达亚微米，应变分辨率约为万分之一，可获得微梁表面附近晶格结构空间分布图像等对失效行为有关键影响的数据，结合其他检测手段，可对力学行为内在的物理机制进行深入准确的研究。

在项目资助期内，实现了一体式电磁载荷设计的硅微机械结构的设计和加工。完成了实验方案的设计与优化,实现了硅微梁结构和微型平面线圈的圆片级加工，以及磁路的组装，总体上足以对微梁的应力集中区域施加超过其屈服强度的应力。微区原位拉曼散射谱测试发现，拉曼峰的峰位和深反应离子刻蚀工艺的刻蚀效果之间存在依赖关系，拉曼光谱检测可以实现预期的从无应力到失效断裂间10-4量级的应变分辨率。综上,本项目已经在设计和制作目做了细致艰苦且系统化的工作，并在硅微梁的力学测试方面获得了一定的认识。本项目面向实际使用场景，具有不稳定小、原位亚微米分辨率探测、结合常用的深刻蚀工艺等特点，通过开展进一步深入的力学行为测试，有望形成系统性的综合见解，补充已存理论。