A Glass-in-Silicon Reflow Process for Three-Dimensional Microsystems

This paper reports a new batch-mode fabrication process that combines glass and silicon into a single wafer. The technique requires only a single mask to lithographically define recesses in silicon using deep reactive ion etching. The patterned silicon wafer is anodically bonded to a glass wafer, and a high-temperature step reflows the glass into this silicon mold. The reflowed wafer stack is then planarized and thinned. Through-glass vias can be realized in this manner while additional process-flow modifications enable features such as molded cavities in the glass. A capacitive pressure sensor and a hermetically sealed resonator are described to illustrate applications of the process. Finally, a three dimensional packaging technique for implantable biomedical microsystems is shown by vertically stacking glass-in-silicon wafers.