Optical housings for packaging components at wafer level

May 28, 2020

© Fraunhofer ISIT
Optical housings with slanted covers on a 200 mm glass wafer.

The Fraunhofer ISIT operates state-of-the-art production lines for processing silicon with an accuracy in the nanometer range. These precise methods of structure generation in silicon have been successfully transferred to other materials, for example the shaping of different glasses – a process that allows the production of precise optical components at wafer level. These cost-effective components can be used for various applications.

Glass consists mainly of silicon dioxide. Thus, some chemical and mechanical properties of glass and silicon are similar. For this reason, silicon wafers and glass wafers with approximately the same coefficient of thermal expansion can be firmly joined together by anodic bonding. This material compound remains stable even under large temperature changes. If the silicon wafer is previously provided with structured recesses, the glass can be moulded into these embossed structures if the silicon-glass compound is increased to temperatures above the transformation temperature of the glass. The glass then becomes a highly viscous fluid that can be pressed into molds, for example, when the external pressure exceeds the gas pressure in the recessed molds. The resulting glass structures are exposed by dissolving the original silicon wafer in a caustic solution at room temperature.

The structured glass wafer can be used in so-called wafer-level bonding processes which lead to low production costs, since many components can be manufactured in parallel. With suitable automatic wafer bonders, a vacuum or other defined gas volumes can also be included in this process. Applications include camera chips, light sensors and optical scanners with micromirrors.