Mechanical strengthening of silicon torsion bar of scanning micro mirror by hydrogen anneal

The report on hydrogen anneal to enhance the torsional fracture strength of dry-etched single crystal silicon (SCS) microstructures. Moving-magnet-type scanning minors with torsion bars were employed as fracture test specimens. Two types of device were fabricated using SCS and silicon-on-insulator (SOI) wafers by deep reactive ion etching (DRIE). For the SCS-wafer-based device, scalloping on DRIE sidewalls were smoothed out, and the fracture strength of the torsion bar was improved by a factor of 3 by 120 min hydrogen anneal. For the SOI-wafer-based device, hydrogen anneal introduced surface inegularity on Si sidewalls by hydrogen-induced etching under the existence of S/O2. As a result, the fracture strength of the torsion bar was degraded contrarily. Therefore, hydrogen anneal is effective to improve the mechanical reliability of SCS microstructures without S/O2.