Fabrication of high-density electrical feed-throughs by deep-reactive-ion etching of Pyrex glass

This paper describes the fabrication technology for high-density electrical feed-throughs in Pyrex glass wafers. Small through holes (40-80 μm in diameter) in Pyrex glass wafers have been fabricated using deep-reactive-ion etching (DRIE) in a sulfur hexafluoride (SF₆) plasma. The maximum aspect ratios obtained were between 5 and 7 for a hole pattern and 10 for a trench pattern. Through the wafer etching of a hole pattern of 50 μm diameter was carried out using 150-μm-thick Pyrex glass wafers. The electrical feed-throughs in the wafers were fabricated by filling the through-holes with electroplated nickel. We were able to successfully bond the glass wafer to silicon by anodic bonding after removing the electroplated nickel on the surface of the wafer by chemical-mechanical polishing (CMP). The electric resistance of the feed-through was estimated by a 4 point wire sensing method to be about 40 mΩ per hole. The heat cycles test shows that the resistance changes were within 3% after 100 cycles. The fabrication of high density electrical feed-throughs is one of the key processes in the field of MEMS. Probable applications of this technology are in electrical feed-throughs between logic elements and microprobe arrays for high-density data storage and for packaged devices.