Wafer-level Fabrication of Ball Lens by Cross-cut and Reflow of Wafer-bonded Glass on Silicon

Novel wafer-level fabrication of a glass ball-lens is realized for optoelectronic applications. A Pyrex wafer is bonded to a silicon wafer and cross-cut into a square-tile pattern, followed by wet-etching of the underlying silicon. Cubes of Pyrex on the undercut silicon are then turned into ball shapes by thermal reflow, and separated from the wafer by further etching of the silicon support. Radial variation and surface roughness are measured to be less than <TEX>±3\;μm</TEX> and <TEX>±1\;nm</TEX>, respectively, for ball diameter of about <TEX>500\;μm</TEX>. A surface defect on the ball that is due to the silicon support is shown to be healed by using a silicon-optical-bench. Optical power-relay of the ball lens showed the maximum efficiency of 65% between two single-mode fibers on the silicon-optical-bench.