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Method of Creating a Wirebonding Surface for a Thinned Cap Wafer

IP.com Disclosure Number: IPCOM000146351D
Publication Date: 2007-Feb-12
Document File: 3 page(s) / 18K

Publishing Venue

The IP.com Prior Art Database

Abstract

In a capped wafer package, a wirebond connects the substrate wafer to the capped wafer which has Al metallization to keep the two wafers at the same potential. In order to create a thinner package the cap wafer is thinned from the top. This removes Al on the surface required for wirebonding. The method being published is to create a recessed area in a wafer prior to Al deposition by etching a shelf or hole lower than the top of the cap that will be metallized with Al, and will be left behind after thinning. This can be accomplished in several different ways including 2X anisotropic wet etch, DRIE etch + wet etch, and etching only a small area for wirebonding.

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Method of Creating a Wirebonding Surface for a Thinned Cap Wafer

Abstract

            In a capped wafer package, a wirebond connects the substrate wafer to the capped wafer which has Al metallization to keep the two wafers at the same potential. In order to create a thinner package the cap wafer is thinned from the top. This removes Al on the surface required for wirebonding. The method being published is to create a recessed area in a wafer prior to Al deposition by etching a shelf or hole lower than the top of the cap that will be metallized with Al, and will be left behind after thinning.

This can be accomplished in several different ways including 2X anisotropic wet etch, DRIE etch + wet etch, and etching only a small area for wirebonding.

Introduction

            One method of building MEMS accelerometers is to create a structure on a substrate wafer and constrain the substrate wafer with a silicon cap using glass frit.  This is typically done at the wafer level and is sawn into individual die.  The substrate wafer and the cap should be electrically connected so as to be at the same potential in order to minimize voltage differentials between the cap and the substrate.  These differentials, which can be caused by charge building up on the cap, induce fields within the MEMS cavity which in turn may produce adverse electrostatic forces on the MEMS structures.  Electrically connecting the cap wafer and the substrate also helps to reduce noise from EMI.  Typically this connection is made by wirebonding the substrate wafer to the cap.  The cap is metallized, typically with Al, in order to create a reliab...