Anisotropic etching of single crystalline SiC using molten KOH for SiC bulk micromachining

摘要

Microelectromechanical systems (MEMS) devices made of single crystalline silicon carbide (SiC) are attractive for applications in harsh environment, because SiC is chemically inert and semiconductor devices made of SiC can be operated at very high temperature. On the other hand, due to its chemical inertness, controllable etching of SiC has been difficult. Molten KOH etching has been widely used to detect crystalline defects in SiC as etch pit in crystal growth researchers. Some etch pits have hexagonal shape, indicating anisotropic etching nature. Therefore, molten KOH etching may have potential as a SiC MEMS fabrication process. In this study we have developed the anisotropic wet chemical etching of single crystalline hexagonal SiC using molten KOH for SiC bulk micromachining. 6H-SiC (0001)Si face and (000-1)C face substrates are used. Etching rates of (0001)Si and (000-1)C faces at 490 °C are evaluated to be 37 nm/min and 3.1 μm/min, respectively, indicating that the (0001)Si face is etched almost 100 times slower than the (000-1)C face is. Cross sectional analysis of etched structure of (000-1)C face revealed that inclined crystal plane was formed as a sidewall with some undercut. To assess in-plane etching anisotropy, ring shape mesa structures are formed on SiC (0001)Si face by REE and then etched by molten KOH. Ring shape changed into hexagonal shape, clearly indicating etching rate along < 11-20 > direction is larger than < 1-100 > direction in (0001)Si face.