Modeling of orientation-dependent etching of silicon and effects of ions in the solution

研究了单晶硅的各向异性湿法碱性腐蚀。我们通过蚀刻液含量的微小变化阐明了易于改变蚀刻速率各向异性的机制。理论和实验都表明，铜离子作为杂质存在于蚀刻液中，会显著抑制蚀刻速率，降低蚀刻表面粗糙度。此外，我们还阐明了在蚀刻液中加入少量表面活性剂后，各向异性发生显著变化的机理。这是我们通过原位FTIR观察蚀刻液与硅之间的液固界面首次发现的。利用蚀刻速率的可变各向异性，我们以最小的工艺成本发明了用于MEMS应用的3D微结构的新制造工艺。

We investigated wet anisotropic etching of single crystal silicon using alkaline solutions. We clarified the mechanisms of easily changeable anisotropy in the etch rate by a small change in the etching solution contents. It was clarified both theoretically and experimentally that a cupper ion as an impurity in etching solution significantly suppresses etch rate and deteriorates etched surface roughness. Also, we clarified a mechanism of dramatic anisotropy change occurring by a small amount of surfactant added to etching solution. This was first found by our in-situ FTIR observation of liquid-solid interface between etching solution and silicon. By utilizing the variable anisotropy in etch rate, we invented new fabrication processes for 3D microstructures for MEMS applications with a minimal process cost.