A New Method for Microlens Fabrication by a Heating Encapsulated Air Process

This letter reports a new method to fabricate thin microlens array on a silicon substrate by a heating encapsulated air process. We use silicon bulk micromachining, wafer-to-wafer bonding, and photoresist (PR) spin coating to achieve the air sealing process. Under a heating process, the PR filled in the micro-through-hole of cap wafer is compressed by the thermal expansion of the sealed air to form a thin microlens with out-of-plane sphere shape. By adjusting the heating temperature and the sealed air volume, the curvature and size of the lens are controllable. A typical microlens with a diameter of 1475 \mu m and sag height of 486 \mu m was fabricated. The calculated radius of curvature and focal length are about 800 and 1200 \mu m, respectively. The fabrication provides an alternative way to manufacture thin microlens or microlens mold serve as master elements for replication.