EPITAXIALLY STACKED STRUCTURES OF SI/AL2O3/SI FOR SENSOR MATERIALS

Epitaxially stacked structures of Si(100)/ Al2O3(100)/Si(100) were investigated for sensor applications. The Si-on-insulator (SOI) structures were grown on 2-in Si wafers by double heteroepitaxial growth of Al2O3(100) single insulator films and then SI(100) films were grown at about 1000°C with the chemical vapor deposition method. These films had mirror-like surfaces. It was found from ellipsometric measurements that the Al2O3 films cannot be etched by KOH (7 mol/l) at 70°C or dilute HF at 20°C for 60 min. Therefore, the Al2O3 films can be used as an etch-stop layer for micromachining for, e.g., a microdiaphragm. This was demonstrated with membranes which consisted of Al2O3 film (0.1 μm) and Si film (5 μm). The membrane surfaces of Al2O3 films were very flat in comparison with etched Si surfaces. © 1990.