Damascene interconnect structure having air gaps between metal lines and method for fabricating the same

Abstract

An exemplary damascene interconnect structure includes a substrate ( 20 ), a first dielectric layer ( 21 ) on the substrate, a plurality of trenches ( 27 ) formed in the first dielectric layer, and a plurality of metal lines ( 24 ) filled in the trenches. The first dielectric layer includes multi sub-dielectric layers ( 211, 212, 213 ). Wherein a plurality of air gaps ( 28 ) are maintained between the metal lines and at least one of the sub-dielectric layers. A method for fabricating the damascene interconnect structure is also provided.

1 . A damascene interconnect structure, comprising:
 a substrate;   a first dielectric layer on the substrate, the first dielectric layer comprising a plurality of sub-dielectric layers;   a plurality of trenches formed in the first dielectric layer; and   a plurality of metal lines filled in the trenches;   wherein a plurality of air gaps are maintained between the metal lines and at least one of the sub-dielectric layers.   
   
   
       2 . The damascene interconnect structure as claimed in  claim 1 , wherein the plurality of sub-dielectric layers comprises a first, a second, and a third sub-dielectric layers arranged in that order from bottom to top, and the air gaps are maintained between the metal lines and the second sub-dielectric layer. 
   
   
       3 . The damascene interconnect structure as claimed in  claim 2 , wherein the first and the third sub-dielectric layers are silicon nitride layers, and the second sub-dielectric layer is a silicon oxide layer. 
   
   
       4 . The damascene interconnect structure as claimed in  claim 2 , wherein the first, the second, and the third sub-dielectric layers are silicon nitride layers, and a density of each of the first and the third sub-dielectric layers is greater than that of the second sub-dielectric layer. 
   
   
       5 . The damascene interconnect structure as claimed in  claim 2 , wherein the first, the second, and the third sub-dielectric layers are silicon oxide layers, and a density of each of the first and the third sub-dielectric layers is greater than that of the second sub-dielectric layer. 
   
   
       6 . The damascene interconnect structure as claimed in  claim 1 , further comprising a capping layer and a second dielectric layer, the capping layer covering the first dielectric layer and the metal lines, and the second dielectric layer covering the capping layer. 
   
   
       7 . The damascene interconnect structure as claimed in  claim 2 , wherein material of the metal lines is at least one of copper, silver, aluminum, and an alloy comprising any one or more of copper, aluminum and silver. 
   
   
       8 . A method for fabricating a damascene interconnect structure, the method comprising:
 providing a substrate;   depositing a multilayer dielectric film on the substrate;   forming a patterned photoresist on the multilayer dielectric film;   etching the multilayer dielectric film to form a plurality of trenches, a portion of each of the trenches having an enlarged width at each of sidewalls thereof;   filling the trenches with conductive metal to form conductive lines such that air is trapped in extremities of the enlarged width portions of the trenches.   
   
   
       9 . The method for fabricating a damascene interconnect structure as claimed in  claim 8 , wherein the conductive metal filled in the trenches is formed by means of physical vapor deposition. 
   
   
       10 . The method for fabricating a damascene interconnect structure as claimed in  claim 8 , wherein the multilayer dielectric film comprises a first, a second, and a third sub-dielectric layer, and the air is trapped between the second sub-dielectric layer and the conductive lines. 
   
   
       11 . The method for fabricating a damascene interconnect structure as claimed in  claim 10 , wherein the first and the third sub-dielectric layer are silicon nitride layers, and the second sub-dielectric layer is a silicon oxide layer. 
   
   
       12 . The method for fabricating a damascene interconnect structure as claimed in  claim 10 , wherein all three sub-dielectric layers are silicon nitride layers or silicon oxide layers, and a deposition rate of each of the first and the third sub-dielectric layers is greater than that of the second sub-dielectric layer. 
   
   
       13 . The method for fabricating a damascene interconnect structure as claimed in  claim 8 , wherein the multilayer dielectric layer is etched by a wet etching method. 
   
   
       14 . The method for fabricating a damascene interconnect structure as claimed in  claim 13 , wherein an etchant of the wet etching method is a mixture of hydrogen fluoride and ammonium fluoride. 
   
   
       15 . The method for fabricating a damascene interconnect structure as claimed in  claim 8 , wherein the multilayer dielectric layer is etched by a dry etching method. 
   
   
       16 . The method for fabricating a damascene interconnect structure as claimed in  claim 15 , wherein an etchant of the dry etching method is a mixture of sulfur hexafluoride and carbon tetrafluoride. 
   
   
       17 . The method for fabricating a damascene interconnect structure as claimed in  claim 8 , further comprising forming a capping layer covering the multilayer dielectric layer and the conductive lines, and forming a dielectric layer on the capping layer. 
   
   
       18 . The method for fabricating a damascene interconnect structure as claimed in  claim 8 , wherein material of the conductive lines is at least one of copper, aluminum, silver, and an alloy comprising any one or more of copper, aluminum and silver.