Large scale arrays of more than 67k micromirrors of monocrystalline silicon with underlying planar actuation electrodes have been fabricated. The mirrors were fabricated by transferring a 300nm thick silicon layer from a silicon-on-insulator (SOI) wafer to a wafer containing metal electrodes by adhesive wafer bonding in a thermo-compression bonding tool. The bonding was followed by grinding and spin-etching of the handle silicon and the buried oxide, which leaves only the thin device silicon on the electrode wafer. Mirrors and metal plugs were formed using standard micromachining techniques such as sputtering and dry etching. The arrays consist of 16μm×16μm mirrors with 0.7μm wide and 2μm long torsional hinges. Deflection is achieved by applying a voltage between the mirrors and one of two underlying electrodes. It was found that 15V is enough to deflect the mirrors 48nm, which is sufficient to create a black pixel in a diffractive deep UV application that involves modulation of 193nm light. Furthermore, no measurable instability due to plastic hinge deformation or charging could be determined by static deflection for more than one hour. The developed fabrication process is fully CMOS ompatible and can be directly applied to fabricate spatial light modulators (SLM) with mirror arrays in excess of one megapixels with individually addressable analog mirrors that are truly drift free. Application areas are photolithographic mask writers or systems for maskless lithography.
