Fabirication Technology of Three-Dimentional Microstructures Made of Single-crystal Silicon

我们评估了两种不同的刻蚀液：氢氧化钾(KOH)和四甲基氢氧化铵(TMAH)水溶液对单晶硅刻蚀速率的取向依赖性。在不同的刻蚀条件下，测量了多种晶向的刻蚀速率，发现随着刻蚀液浓度和温度的变化，刻蚀速率随刻蚀浓度和刻蚀温度的变化而显著变化。我们还发现TMAH和KOH溶液在(111)附近的刻蚀速率与取向有不同的关系。这意味着单晶硅晶格的键能不是单一的影响晶格取向的因素，并且存在不同的刻蚀机制。我们进一步研究了单晶硅在KOH水溶液化学各向异性刻蚀过程中的粗化。粗糙度的变化很大程度上取决于晶体取向。我们制作了一张地图，显示了粗糙度随方位的分布。光滑表面出现在包括(100)、(200)和(311)的区域中。非常粗糙的表面出现在包括(320)和(210)的区域。我们明确了粗糙表面是由某些晶面组成的小平面织构，所获得的数据为我们提供了蚀刻轮廓的数值模拟，这是工业上设计MEMS器件制造工艺所必需的。另一方面，这对于物理化学家研究各向异性腐蚀过程的原子尺度模型也很重要。我们将从1998财政年度开始与荷兰特温特大学合作开展一项国际联合研究，作为助学金计划，研究原子尺度上的蚀刻机制。

We evaluated orientation dependence in the etching rate of single-crystal silicon for two different etchants ; potassium-hydroxide (KOH) and tetramethyl-ammonium-hydroxide (TMAH) water solutions. Etching rates for a number of crystallographic orientations were measured for a wide range of etching conditions in terms of etchants' concentration and temperature.We found that the orientation dependence significantly varied according to changes both in concentration and temperature. We also found different types of orientation dependence in etching rate around (111) between TMAH and KOH solutions. This means the bonding energy of the silicon crystal lattice is not a single factor that dominates orientation dependence, and there exist different etching mechanisms, for the two etchants.We further investigated roughening of single-crystal silicon during chemical anisotropic etching using KOH water solutions. The change in roughness strongly depends on the crystallographic orientation. We made a map showing roughness distribution as a function of orientation. Smooth surface appears in a region including (100), (200), and (311). Very rough surface appears in a region including (320) and (210). We clarified that roughened surface shows the facet textures composed of certain crystallographic planes.The obtained data allowed us numerical simulation of etching profiles which is necessary for designing fabrication process of MEMS devices in industry. On the other hand, it is also of importance for physical chemists investigating atomic-scale models of the anisotropic etching process. We are going to start an international joint research as a Grant-in-Aid Program from 1998 fiscal year investigating the etching mechanisms on the atomic scale in collaboration with the University of Twente, the Netherlands.