Acoustic window with liquid-filled pores for chemical mechanical polishing and methods of forming pads

Abstract

A chemical mechanical polishing apparatus includes a platen, a polishing pad supported on the platen, a carrier head to hold a surface of a substrate against a polishing surface of the polishing pad, and a motor to generate relative motion between the platen and the carrier head so as to polish an overlying layer of the substrate. The polishing pad includes a polishing layer of a solid matrix material with liquid-filled pores, and a backing layer. An in-situ acoustic monitoring system includes an acoustic sensor coupled to the backing layer to receive acoustic signals from the substrate, and a controller is configured to detect a polishing transition point based on received acoustic signals from the in-situ acoustic monitoring system.

What is claimed is: 
     
         1 . A chemical mechanical polishing apparatus, comprising:
 a platen;   a polishing pad supported on the platen, the polishing pad including
 a polishing layer comprising a solid matrix material with liquid-filled pores, and 
 a backing layer; 
   a carrier head to hold a surface of a substrate against the polishing layer of the polishing pad;   a motor to generate relative motion between the platen and the carrier head so as to polish an overlying layer of the substrate;   an in-situ acoustic monitoring system comprising an acoustic sensor coupled to the backing layer to receive acoustic signals from the substrate; and   a controller configured to detect a polishing transition point based on received acoustic signals from the in-situ acoustic monitoring system.   
     
     
         2 . The apparatus of  claim 1 , wherein the backing layer comprises a first matrix material including a first polymer and a second polymer and the polishing layer comprises a second matrix material having pores, the second matrix material including the first polymer and the second polymer in a different percentage contribution than the first matrix material that the backing layer is more compressible than the polishing layer. 
     
     
         3 . The apparatus of  claim 1 , wherein the backing layer is non-porous. 
     
     
         4 . The apparatus of  claim 1 , wherein the polishing layer has a polishing surface with a first region without grooves and a second region that surrounds the first region that has a plurality of grooves, and wherein the acoustic sensor is aligned with the first region. 
     
     
         5 . The apparatus of  claim 1 , wherein the polishing layer comprises a porous portion and a non-porous solid portion that extends through the thickness of the polishing layer, and the acoustic window is arranged within the backing layer in contact with the solid portion. 
     
     
         6 . The apparatus of  claim 1 , wherein the controller is configured to indicate an exposure of an underlying layer in response to detection of the polishing transition point. 
     
     
         7 . The apparatus of  claim 1 , wherein the controller is configured to change a polishing parameter in response to detection of the polishing transition point. 
     
     
         8 . The apparatus of  claim 7 , wherein the polishing parameter comprises a carrier head pressure or a polishing liquid composition. 
     
     
         9 . The apparatus of  claim 8 , wherein the controller is configured to cause a dispenser to switch from dispensing a first polishing liquid to a second polishing liquid having a lower polishing rate or lower selectivity in response to detection of the polishing transition point. 
     
     
         10 . The apparatus of  claim 1 , wherein the controller is configured to halt polishing in response to detection of the polishing transition point. 
     
     
         11 . A method of fabricating a polishing pad, comprising:
 successively depositing a first plurality of layers with a 3D printer to form a backing layer of the polishing pad, each layer of the first plurality of layers including a backing material portion and an acoustic window portion having a lower acoustic impedance than the backing material portion, the backing material portion and the acoustic window portion deposited by ejecting a plurality of precursor materials from one or more nozzles and solidifying the plurality of precursor materials to form a solidified backing material and a solidified acoustic window, wherein ejecting the plurality of precursor materials from the one or more nozzles forms an interface with intermingled polymer that directly bonds the solidified acoustic window and the solidified backing material; and   successively depositing a second plurality of layers with the 3D printer to form a polishing layer of the polishing pad on the backing layer.   
     
     
         12 . The method of  claim 11 , wherein the ejecting the plurality of precursor materials comprises ejecting a first precursor material for the backing material portion and a ejecting a second precursor material for the window portion. 
     
     
         13 . The method of  claim 11 , wherein ejecting the plurality of precursor materials includes ejecting a first precursor and a second precursor for the backing material portion and ejecting the first precursor and the second precursor in a different percentage contribution than the backing material portion to form the window portion. 
     
     
         14 . The method of  claim 11 , wherein ejecting the plurality of precursor materials includes ejecting a first precursor and a second precursor for the backing material portion, and wherein successively depositing a second plurality of layers includes ejecting the first precursor and the second precursor in a different percentage contribution than the backing material portion to form the polishing layer. 
     
     
         15 . The method of  claim 11 , wherein successively depositing the second plurality of layers with the 3D printer to form the polishing layer includes ejecting a liquid material that forms liquid filled pores at selected voxels in the polishing layer after curing of the second plurality of layers. 
     
     
         16 . The method of  claim 15 , comprising ejecting the liquid material at a region in the polishing layer over the window in the backing layer. 
     
     
         17 . The method of  claim 15 , comprising refraining from ejecting the liquid material at a region in the polishing layer the window in the backing layer such that the portion is non-porous. 
     
     
         18 . The method of  claim 11 , wherein each layer of the second plurality of layers includes a polishing material portion and a second acoustic window portion having a lower acoustic impedance than the polishing material portion, the polishing material portion and the second acoustic window portion deposited by ejecting a second plurality of precursor materials from the one or more nozzles and solidifying the second plurality of precursor materials to form a solidified polishing material and a solidified acoustic window material, wherein ejecting the second plurality of precursor materials from the one or more nozzles forms an second interface with intermingled polymer that directly bonds the solidified acoustic window and the solidified polishing material. 
     
     
         19 . A method for manufacturing a polishing pad, comprising:
 depositing a backing layer comprising a first material;   curing the backing layer;   depositing a polishing layer atop the backing layer, the polishing layer comprising a second material;   curing the polishing layer;   removing a portion of the backing layer creating an aperture; and   inserting an acoustic window comprising a third material into the aperture.   
     
     
         20 . The method of  claim 19 , further comprising, between removing the portion of the backing layer and inserting the acoustic window, removing a portion of the polishing layer corresponding with the portion of the backing layer. 
     
     
         21 . The method of  claim 19 , wherein the second material comprises a polymer matrix with liquid-filled pores. 
     
     
         22 . The method of  claim 19 , wherein the third material has a same compressibility as the first material.