单晶硅表层机械力学特性的各向异性分析

Analysis of anisotropic mechanical properties of monocrystalline silicon callow

摘要:

为探究挠性筋结构单晶硅材料的各向异性特性以及KOH腐蚀工艺对其力学性能的影响规律,进行纳米压痕实验,并结合原子力显微镜观察单晶硅表层3个主晶面上压痕裂纹形貌随晶向的变化规律,分析单晶硅材料表层弹性模量、硬度、断裂韧性等机械力学特性参数在(001)、(110)及(111)3个主要晶面上沿各个晶向的变化规律；分析挠性筋结构单晶硅材料(001)晶面的KOH腐蚀工艺对其材料表面机械特性的影响规律. 结果表明:挠性筋单晶硅在(001)晶面上弹性模量的各向异性变化幅度明显,硬度及断裂韧性各向异性的变化幅度不大；挠性筋单晶硅在(110)晶面弹性模量和断裂韧性的各向异性变化幅度明显,硬度各向异性变化幅度不大；挠性筋单晶硅在(111)晶面硬度值、弹性模量及断裂韧性参数的变化幅度幅值均较小；确定了单晶硅表层3个晶面裂纹最易扩展的晶向方向,KOH腐蚀工艺使得单晶硅表面质量降低,腐蚀后暴露的表面微裂纹、缺陷等会使得单晶硅(001)晶面表层硬度、断裂韧性降低,从而降低了挠性筋结构的实际断裂强度.

Abstract:

To explore the effect of anisotropy and KOH corrosion process on the mechanical properties of monocrystalline silicon flexible rib structure, the morphological changes of indentation-induced cracks with respect to the crystal orientation on the three primary crystal planes were observed by nano-indentation experiments combined with atomic force microscope (AFM). The change rule of elastic modulus, hardness, fracture toughness of monocrystalline silicon on the three primary crystal planes (001), (110) and (111) with respect to crystal orientation was analyzed. Meanwhile, the influence of KOH corrosion process on the surface mechanical properties of (001) crystal plane was investigated as well. The result shows that with the variation of crystal orientation, the elastic modulus on the (001) crystal plane appears the greatest change, while the hardness and fracture toughness have no significant changes. On the (110) crystal plane, both the elastic modulus and fracture toughness show obvious changes, but the hardness possesses no significant change. However, on the (111) crystal plane, the mechanical parameters (including elastic modulus, fracture toughness and hardness) of flexible rib monocrystalline silicon have no obvious anisotropic behaviors. The directions which are sensitive to the crack propagation are determined on the three primary crystal planes of flexible rib monocrystalline silicon. The surface quality of silicon processed by KOH erosion would deteriorate and the exposed surface micro-cracks and defects would result in the decrease of hardness and fracture toughness, which should greatly weaken the actual fracture strength of flexible rib structure.