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

该项目的目的是在从原子到微米范围的所有尺度上阐明单晶(如硅和石英)的各向异性腐蚀机理。我们阐明了两种主要的硅腐蚀剂，即KOH和TMAH溶液的腐蚀特性的差异，以及它们与这些腐蚀机制的关系。我们还实验研究了腐蚀剂中的少量杂质对腐蚀速率、各向异性和腐蚀表面形貌的影响。我们通过蒙特卡罗模拟计算了晶体表面扭结和台阶处的原子去除率，对刻蚀机理进行了分析验证。该模拟基于一个模型，该模型考虑了羟基在裸露表面上的吸附导致原子键的减弱。对硅(111)及其附近的刻蚀机理进行了很好的解释。宏观刻蚀行为显然是由硅(111)上存在的台阶的活性决定的。该模型可以很好地解释不同刻蚀种类对各向异性反转的影响。我们最近发现，各向异性的反转也发生在溶液浓度的变化上。因此，各向异性的反转被证明不是蚀刻剂的单一问题，而是更常见的可接受的现象，通过步骤和扭结的活动性的变化。我们正在进一步研究除(111)晶向以外的其他取向的刻蚀模型。除了硅，我们还使用了应用于硅的相同方法来表征石英的各向异性刻蚀特性。我们评估了石英晶体的刻蚀速率作为取向的函数。这使得我们可以通过使用模拟来预测3D刻蚀轮廓。该技术对设计制作MEMS器件用石英的刻蚀工艺是有效的。

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.