Glass Wafer Level Packaging Enabled by Laser Induced Deep Etching of Closed Cavities

Glass capping wafers are regularly used in wafer level packaging-(WLP) applications. There are several reasons to use glass in these applications such as high surface quality, chemical inertia, hermeticity and among others silicon matched CTE, high thermal stability, transparency and low cost. The objective of this paper is to demonstrate the capability to manufacture closed pockets for glass capping wafers based on Laser Induced Deep Etching (LIDE). Today’s glass capping wafers are usually manufactured by masked isotropic wet etching. Isotropic wet etching is associated with under etching which results in pockets showing pronounced fillet at the bottom of the pocket. Obviously, to be packaged, a device requires a pocket with a depth bigger than the height of the device. As the radius of the fillet at the bottom of the pocket equals the depth of the pocket, the device pitch in wafer level packaging using today’s glass capping wafers is ultimately limited by the manufacturing process of the capping wafers. Authors will present closed cavities with rectangular shaped profile in glass made by LIDE technology. The demonstrated cavities have a depth of $>300\mu \mathrm{m}$ and a surface roughness of Ra $\approx 0.5\mu \mathrm{m}$.