Middle-Of-Line Interconnect Structure Having Air Gap And Method Of Fabrication Thereof

Abstract

Middle-of-line (MOL) interconnects that facilitate reduced capacitance and/or resistance and corresponding techniques for forming the MOL interconnects are disclosed herein. An exemplary MOL interconnect structure includes a device-level contact disposed in a first insulator layer and a ruthenium structure disposed in a second insulator layer disposed over the first insulator layer. The device-level contact physically contacts an integrated circuit feature, and the ruthenium structure physically contacts the device-level contact. An air gap separates sidewalls of the ruthenium structure from the second insulator layer. A top surface of the ruthenium structure is lower than a top surface of the second insulator layer. A via disposed in a third insulator layer extends below the top surface of the second insulator layer to physically contact the ruthenium structure. A remainder of a dummy contact spacer layer may separate the first insulator layer and the second insulator layer.

What is claimed is: 
     
         1 . An interconnect structure comprising:
 a source/drain contact disposed in an insulator layer; and   a local contact disposed in the insulator layer, wherein the local contact is disposed on the source/drain contact and the local contact includes:
 a metal-comprising layer disposed directly on the source/drain contact, wherein the metal-comprising layer has a first width, 
 a ruthenium-comprising layer disposed directly on the metal-comprising layer, wherein the ruthenium-comprising layer has a second width, wherein the second width is about equal to the first width and a metal of the metal-comprising layer is different than ruthenium, and 
 an air gap between the metal-comprising layer and the insulator layer and between the ruthenium-comprising layer and the insulator layer. 
   
     
     
         2 . The interconnect structure of  claim 1 , wherein the metal is titanium. 
     
     
         3 . The interconnect structure of  claim 1 , wherein:
 the insulator layer includes a first oxide layer, a second oxide layer, and an amorphous silicon layer between the first oxide layer and the second oxide layer;   the source/drain contact is disposed in the first oxide layer and the local contact is disposed in the second oxide layer and the amorphous silicon layer;   the air gap is between the metal-comprising layer and the amorphous silicon layer; and   the air gap is between the ruthenium-comprising layer and the second oxide layer.   
     
     
         4 . The interconnect structure of  claim 3 , wherein the air gap has a third width, the amorphous silicon layer has a thickness, and the third width is about equal to the thickness. 
     
     
         5 . The interconnect structure of  claim 1 , wherein:
 the insulator layer includes a first oxide layer, a second oxide layer, and an amorphous carbon layer between the first oxide layer and the second oxide layer;   the source/drain contact is disposed in the first oxide layer and the local contact is disposed in the second oxide layer and the amorphous carbon layer;   the air gap is between the metal-comprising layer and the amorphous carbon layer; and   the air gap is between the ruthenium-comprising layer and the second oxide layer.   
     
     
         6 . The interconnect structure of  claim 5 , wherein the air gap has a third width, the amorphous carbon layer has a thickness, and the third width is about equal to the thickness. 
     
     
         7 . The interconnect structure of  claim 1 , wherein:
 the insulator layer includes a first oxide layer, a second oxide layer, a third oxide layer, and a metal oxide layer between the second oxide layer and the third oxide layer;   the source/drain contact is disposed in the first oxide layer and the local contact is disposed in the second oxide layer; and   a thickness of the metal oxide layer is less than a distance between a top surface of the second oxide layer and a top surface of the ruthenium layer.   
     
     
         8 . The interconnect structure of  claim 1 , wherein the metal-comprising layer has a first thickness, the ruthenium-comprising layer has a second thickness, and a ratio of the first thickness to the second thickness is about 1:2 to about 1:50. 
     
     
         9 . The interconnect structure of  claim 8 , wherein the first thickness is about 1 nm to about 5 nm, and the second thickness is about 10 nm to about 50 nm. 
     
     
         10 . An interconnect structure comprising:
 a device-level contact layer;   a local contact layer disposed directly on the device-level contact layer, wherein the local contact layer includes a ruthenium-comprising contact disposed in a first dielectric layer, wherein air gaps are disposed between sidewalls of the ruthenium-comprising contact and the first dielectric layer, the ruthenium-comprising contact has a first thickness, the first dielectric layer has a second thickness, and the first thickness is less than the first thickness; and   a global contact layer disposed directly on the local contact layer, wherein the global contact layer includes a global contact disposed in a second dielectric layer and a metal oxide layer, wherein the metal oxide layer is between the first dielectric layer and the second dielectric layer and the metal oxide layer is disposed on a top and sidewalls of the first dielectric layer.   
     
     
         11 . The interconnect structure of  claim 10 , wherein the device-level contact layer includes a source/drain contact disposed in a third dielectric layer, wherein the ruthenium-comprising contact is disposed directly on the source/drain contact and the first dielectric layer is disposed directly on the third dielectric layer. 
     
     
         12 . The interconnect structure of  claim 10 , wherein the device-level contact layer includes a source/drain contact disposed in a third dielectric layer and the local contact layer further includes an amorphous material layer, wherein the ruthenium-comprising contact is disposed directly on the source/drain contact, the amorphous material layer is between the first dielectric layer and the third dielectric layer, and the air gaps are disposed between the sidewalls of the ruthenium-comprising contact and the amorphous material layer. 
     
     
         13 . The interconnect structure of  claim 10 , wherein the metal oxide layer is a first metal oxide layer, the device-level contact layer includes a source/drain contact disposed in a third dielectric layer, and the local contact layer further includes a second metal oxide layer, wherein the ruthenium-comprising contact is disposed directly on the source/drain contact, the second metal oxide layer is between the first dielectric layer and the third dielectric layer, the air gaps are disposed between the sidewalls of the ruthenium-comprising contact and the second metal oxide layer, and the first metal oxide layer includes a first metal that is different than a second metal of the second metal oxide layer. 
     
     
         14 . The interconnect structure of  claim 10 , wherein the device-level contact layer includes a source/drain contact disposed in a third dielectric layer and the local contact layer further includes a silicon-and-nitrogen-comprising layer, wherein the ruthenium-comprising contact is disposed directly on the source/drain contact, the silicon-and-nitrogen-comprising layer is between the first dielectric layer and the third dielectric layer, and the air gaps are disposed between the sidewalls of the ruthenium-comprising contact and the silicon-and-nitrogen-comprising layer. 
     
     
         15 . The interconnect structure of  claim 10 , wherein the ruthenium-comprising contact includes a ruthenium plug disposed over a titanium-comprising layer, wherein the titanium-comprising layer is between the ruthenium plug and the device-level contact layer. 
     
     
         16 . A method comprising:
 forming a device-level contact layer, wherein the device-level contact layer includes a device-level contact disposed in a first dielectric layer;   forming a local contact layer directly on the device-level contact layer, wherein the forming the local contact layer includes:
 forming a ruthenium-comprising contact, wherein the ruthenium-comprising contact is disposed directly on the device-level contact, 
 after forming a material layer along sidewalls of the ruthenium-comprising contact, forming a second dielectric layer over the first dielectric layer, wherein a recess in the local contact layer is formed by a top surface of the ruthenium-comprising contact and sidewalls of the second dielectric layer, and 
 forming air gaps between sidewalls of the ruthenium-comprising contact and the second dielectric layer by removing the material layer; and 
   forming a global contact layer directly on the local contact layer, wherein the forming the global contact layer includes:
 forming a metal oxide layer over the second dielectric layer, wherein the metal oxide layer lines the recess in the local contact layer, 
 forming a third dielectric layer over the metal oxide layer, and 
 forming a global contact directly on the ruthenium-comprising contact, wherein the global contact is formed in the third dielectric layer and the global contact extend through the metal oxide layer. 
   
     
     
         17 . The method of  claim 16 , wherein a depth of the recess is a distance between a top surface of the ruthenium-comprising contact and a top surface of the second dielectric layer and the distance is about 1 nm to about 20 nm. 
     
     
         18 . The method of  claim 16 , wherein the forming the material layer along sidewalls of the ruthenium-comprising contact includes:
 depositing the material layer over a top surface of the first dielectric layer and the ruthenium-comprising contact; and   performing an etching process that removes the material layer from the top surface of the first dielectric layer, wherein the second dielectric layer directly contacts the first dielectric layer.   
     
     
         19 . The method of  claim 16 , wherein the forming the material layer along sidewalls of the ruthenium-comprising contact includes:
 depositing the material layer over a top surface of the first dielectric layer and the ruthenium-comprising contact; and   forming the second dielectric layer over the material layer, wherein the material layer is between the second dielectric layer and the first dielectric layer.   
     
     
         20 . The method of  claim 16 , further comprising forming the recess by removing a mask layer from over the ruthenium-comprising contact.