Metal Contacts on Metal Gates and Methods Thereof

Abstract

A semiconductor structure includes a metal gate structure including a gate dielectric layer and a gate electrode, the gate electrode including at least a first metal; a conductive layer formed above the gate electrode, the conductive layer including an alloy layer, the alloy layer including at least the first metal and a second metal different from the first metal, the alloy layer extending from a position below a top surface of the metal gate structure to a position above the top surface of the metal gate structure; and a contact feature disposed above the metal gate structure, wherein the contact feature is in direct contact with a top surface of the conductive layer.

What is claimed is: 
     
         1 . A semiconductor structure, comprising:
 a metal gate structure including a gate dielectric layer and a gate electrode, the gate electrode including at least a first metal;   a conductive layer formed above the gate electrode, the conductive layer including an alloy layer, the alloy layer including at least the first metal and a second metal different from the first metal, the alloy layer extending from a position below a top surface of the metal gate structure to a position above the top surface of the metal gate structure; and   a contact feature disposed above the metal gate structure, wherein the contact feature is in direct contact with a top surface of the conductive layer.   
     
     
         2 . The semiconductor structure of  claim 1 , wherein the conductive layer further includes a metallic film of the second metal disposed above the alloy layer. 
     
     
         3 . The semiconductor structure of  claim 1 , wherein the first metal is selected from a group of tantalum, titanium, and aluminum, and the second metal is selected from a group of tungsten, cobalt, gold, and copper. 
     
     
         4 . The semiconductor structure of  claim 1 , wherein the conductive layer further includes a metal oxide, and a concentration of the metal oxide in the conductive layer increases in a direction towards the gate electrode. 
     
     
         5 . The semiconductor structure of  claim 1 , further comprising:
 a composite of a metal oxide, a metal nitride, or a metal oxynitride, wherein the composite is accumulated at an interface between the conductive layer and the gate electrode, wherein the conductive layer is substantially free of the composite.   
     
     
         6 . The semiconductor structure of  claim 1 , wherein a contact resistance at an interface between the contact feature and the conductive layer is lower than a contact resistance at an interface between the contact feature and the metal gate structure. 
     
     
         7 . The semiconductor structure of  claim 1 , wherein the gate electrode further includes a third metal different from either the first metal or the second metal, and the alloy layer includes a center portion rich of the first metal and a side portion rich of the third metal. 
     
     
         8 . The semiconductor structure of  claim 1 , wherein the conductive layer is self-aligned with the gate electrode. 
     
     
         9 . The semiconductor structure of  claim 1 , wherein the conducive layer includes a top portion above the top surface of the metal gate structure and a bottom portion below the top surface of the metal gate structure, wherein a ratio of a thickness of the top portion over the bottom portion ranges from about 1:8 to about 1.5:1. 
     
     
         10 . A semiconductor structure, comprising:
 a metal gate structure;   an alloy layer deposited on the metal gate structure, the alloy layer extending from a position below a top surface of the metal gate structure to a position above the top surface of the metal gate structure, the alloy layer including at least a first metallic element and a second metallic element;   a metal film of the second metallic element deposited on the alloy layer; and   a gate contact landing on the metal film.   
     
     
         11 . The semiconductor structure of  claim 10 , wherein the metal gate structure includes the first metallic element and is substantially free of the second metallic element. 
     
     
         12 . The semiconductor structure of  claim 10 , wherein the metal film has a concave top surface. 
     
     
         13 . The semiconductor structure of  claim 10 , wherein the metal film has a convex top surface. 
     
     
         14 . The semiconductor structure of  claim 10 , wherein the first metallic element is selected from a group of tantalum, titanium, and aluminum, and the second metallic element is selected from a group of tungsten, cobalt, gold, and copper. 
     
     
         15 . The semiconductor structure of  claim 10 , wherein the metal gate structure includes a gate dielectric layer, a capping layer over the gate dielectric layer, and a gate electrode over the capping layer, and wherein a boundary of the alloy layer is aligned with a boundary of the gate electrode. 
     
     
         16 . The semiconductor structure of  claim 10 , wherein the metal gate structure includes a gate dielectric layer, a capping layer over the gate dielectric layer, and a gate electrode over the capping layer, and wherein a boundary of the alloy layer is aligned with a boundary of the capping layer. 
     
     
         17 . A semiconductor structure, comprising:
 a metal gate structure including a gate dielectric layer and a gate electrode layer;   a conductive layer deposited on and in contact with the gate electrode layer, wherein the conductive layer is laterally bounded by the gate dielectric layer; and   a gate contact landing on the conductive layer.   
     
     
         18 . The semiconductor structure of  claim 17 , wherein the gate electrode layer includes a first metal and a second metal different from the first metal, and the conductive layer includes the first metal, the second metal, and a third metal different from either the first metal or the second metal. 
     
     
         19 . The semiconductor structure of  claim 17 , wherein the conductive layer extends vertically from a position below a top surface of the metal gate structure to a position above the top surface of the metal gate structure. 
     
     
         20 . The semiconductor structure of  claim 19 , wherein a portion of the conductive layer below the top surface of the metal gate structure has a thickness less than 8 nm.