Fabrication of high aspect ratio through-wafer vias in CMOS wafers for 3-D packaging applications

Abstract

A process for fabrication of through-wafer vias in CMOS wafers is presented. The process presented offers simple and well controlled fabrication of through-wafer vias using DRIE formation of wafer through-holes, low temperature deposition of through-hole insulation, doubled sided sputtering of Cr/Au, and electroless deposition of Cu. A novel characteristic of the process is the use of a metal etch stop layer providing perfect control of the etch profile of the wafer through-holes in combination with a remarkably improved etch uniformity across the wafer. Excellent through-hole insulation is provided through the use of a CVD deposited polymer, Parylene C, whereas electroless deposition of Cu ensures even distribution of the via metallization.