Mechanisms of chemical anisotropic etching of single crystals consistently applicable throughout Micro/Meso-scopic domains

该项目的目的是澄清从原子到微米范围内的所有尺度上的单晶（如硅和石英）的各向异性蚀刻机制。我们阐明了硅的两种主要蚀刻剂的蚀刻特性的差异;即，KOH和四甲基氢氧化铵（TMAH）溶液，与这些蚀刻机制有关。我们还实验研究了少量的杂质的蚀刻剂，影响蚀刻速率，其各向异性，和蚀刻表面形貌的影响。我们通过使用蒙特-卡罗模拟计算晶体表面的扭结和台阶处的原子去除率来分析验证蚀刻机制，该模拟基于考虑由暴露表面上的OH基附着引起的原子键弱化的模型。对硅（111）及其附近的腐蚀机理进行了很好的解释。宏观腐蚀行为明显地由硅（111）上存在的台阶的活性所支配。该模型可以很好地解释各向异性随刻蚀种类的不同而发生逆转的现象。我们最近发现，各向异性的逆转也发生在溶液浓度的变化。因此，各向异性的逆转被证明不是蚀刻剂的单一问题，而是通过台阶和扭结的活性变化而更普遍地可接受的现象。我们正在进一步研究（111）以外的其他取向的蚀刻模型。与硅平行，我们还使用与硅相同的方法表征了石英的各向异性蚀刻特性。我们评估了石英晶体的蚀刻速率作为取向的函数。这使我们能够通过使用模拟进行3-D蚀刻轮廓预测。该技术为MEMS器件中石英的刻蚀工艺设计提供了有效的方法。

The aim of the project is to clarify anisotropic etching mechanisms of single crystals such as silicon and quartz throughout all scales from atomistic to micrometer range. We clarified the difference in etching characteristics of two major etchants for silicon ; i.e., KOH and Tetra Methyl Ammonium Hydroxide(TMAH) solutions, in relation to those etching mechanisms. We also experimentally studied the effects of a small amount of impurities in the etchant that affect the etching rate, its anisotropy, and etched surface morphologies. We analytically verified the etching mechanism by calculating atomic removal rates at kinks and steps of a crystal surface using Monte-Carlo simulation that is based on a model considering weakening of atomic bonds caused by attachment of OH-base on the exposed surface. Etching mechanisms are well explained for silicon (111) and its vicinity. Macroscopic etching behavior is apparently dominated by the activeness of steps existing on silicon (111). This model can well explain the reverse in the anisotropy according to the difference in etching species. We recently found that the reverse in anisotropy also happens by a change in concentration of the solution. Thus the reverse in anisotropy proved not being a singular problem of the etchant, but more commonly acceptable phenomena by the change in activeness of the steps and kinks. We are further investigating the etching models for other orientations than (111).In parallel to the silicon we also characterized the anisotropic etching properties of quartz, using the same methodologies applied to silicon. We evaluated the etching rate of quartz crystal as a function of orientations. This allowed us a 3-D etching profile prediction by using a simulation. This technology is effective to design etching process of quartz for fabricating MEMS devices.