Etching of under bump metallization layer and resulting device

Abstract

Methods for wet etching a UBM layer and the resulting devices are disclosed. Embodiments may include patterning metal bumps on a wafer that has at least two metal layers thereon; exposing the wafer to a first acid solution to remove a portion of a first of the two metal layers exposed by the patterning of the metal bumps; and exposing the wafer to a second acid solution to remove a portion a second of the two metal layers exposed by the patterning of the metal bumps and the exposure of the wafer to the first acid solution, wherein an undercut below the metal bumps, formed by removal of the portions of the first and second metal layers, is less than 1.5 microns.

What is claimed is: 
     
         1 . A device comprising:
 a substrate;   a metal seat layer above the substrate; and   a metal bump above the metal seat layer,   wherein the metal seat layer is formed by a wet etch of an under bump metallization layer and an undercut of the metal seat layer below the metal bump is less than 1.5 microns (μm).   
     
     
         2 . The device according to  claim 1 , wherein the metal seat layer comprises a copper (Cu) layer above a titanium (Ti) layer. 
     
     
         3 . The device according to  claim 2 , wherein the copper layer has a thickness of 200 to 400 nanometers (nm). 
     
     
         4 . The device according to  claim 2 , wherein the titanium layer has a thickness of 100 to 200 nm. 
     
     
         5 . The device according to  claim 1 , wherein the undercut of the metal seat layer below the metal bump is 1 μm. 
     
     
         6 . A device comprising:
 a wafer;   a metal seat layer above the wafer, the metal seat layer including a first and second metal layer; and   a metal bump above the metal seat layer,   wherein the metal seat layer is formed by a wet etch of an under bump metallization layer and an undercut of the metal seat layer etched back past an edge of a bottom portion of the metal bump is between 1 and 1.5 microns (μm).   
     
     
         7 . The device according to  claim 6 , wherein the first metal layer comprises copper (Cu) and is formed over the second metal layer comprising titanium (Ti). 
     
     
         8 . The device according to  claim 7 , wherein the first metal layer has a thickness of 200 to 400 nanometers (nm). 
     
     
         9 . The device according to  claim 7 , wherein the second metal layer has a thickness of 100 to 200 nm. 
     
     
         10 . The device according to  claim 6 , wherein the undercut of the metal seat layer below the metal bump is 1 μm. 
     
     
         11 . The device according to  claim 6 , wherein the bottom portion of the metal bump comprises nickel (Ni). 
     
     
         12 . The device according to  claim 11 , wherein the bottom portion of the metal bump is formed to a thickness of 2.7 to 3.3 microns. 
     
     
         13 . The device according to  claim 6 , wherein the metal bump comprises a top portion formed over the bottom portion. 
     
     
         14 . The device according to  claim 13 , wherein the top portion comprises tin (Sn) and silver (Ag). 
     
     
         15 . The device according to  claim 14 , wherein the Sn to Ag ratio is 98:2. 
     
     
         16 . The device according to  claim 6 , wherein the metal bump is formed to a height of 63 to 77 μm. 
     
     
         17 . The device according to  claim 16 , wherein the metal bump is formed to a width of 50 to 70 μm. 
     
     
         18 . A device comprising:
 a wafer;   a metal seat layer above the wafer, the metal seat layer including a first metal layer comprising copper (Cu) formed over a second metal layer comprising titanium (Ti); and   a metal bump formed above the metal seat layer, the metal bump comprising a top portion and bottom portion,   wherein the metal seat layer is formed by a wet etch of an under bump metallization layer and an undercut of the metal seat layer etched back past an edge of the bottom portion of the metal bump is between 1 and 1.5 microns (μm).   
     
     
         19 . The device according to  claim 18 , wherein the first metal layer has a thickness of 200 to 400 nanometers (nm). 
     
     
         20 . The device according to  claim 18 , wherein the second metal layer has a thickness of 100 to 200 nm.