Metal interconnect layer of semiconductor device and method for forming a metal interconnect layer

Abstract

A metal interconnect layer of a semiconductor device, and a method for forming a metal interconnect layer of a semiconductor device are provided. The lower portion of a metal interconnect layer is wider than the upper portion of the metal interconnect layer. In another interconnect structure in accordance with the invention, the middle portion of the metal interconnect layer is wider than the upper and lower portions of the metal interconnect layer.

1 . A method for forming a metal interconnect layer of a semiconductor device, the method comprising the steps of: 
 (a) forming an interlevel dielectric (ILD) film over a semiconductor wafer;    (b) forming a photoresist pattern on the ILD film, the photoresist pattern defining a metal interconnect region;    (c) etching an upper portion of the ILD film using the photoresist pattern as an etch mask to form an initial trench having a first width, resulting in a polymer layer serving as an etch barrier on the sidewalls of the initial trench;    (d) etching an middle portion of the ILD film using the photoresist pattern and the polymer layer on the initial trench sidewalls as an etch mask, to deepen the trench to form a second portion of the trench, the second portion of the trench having a second width wider than first width of the initial trench;    (e) forming a polymer layer serving as an etch barrier on the lower end of the etched middle portion of the ILD film;    (f) etching the remaining lower portion of the ILD film using the photoresist pattern and the polymer layers on the initial trench sidewalls and the sidewalls of the second portion of the trench as an etch mask, to further deepen the trench to form a third portion of the trench having a third width, the third width being smaller than the second width of the second portion of the trench;    (g) removing the photoresist pattern;    (h) forming a barrier layer along the semiconductor wafer and in the deepened trench;    (i) depositing a conductive layer over the barrier layer; and    (j) polishing the semiconductor wafer with the conductive layer by chemical and mechanical polishing such that the conductive layer remains within only the deepened trench surrounded by the ILD film.    
   
   
       2 . The method of  claim 1 , wherein, in steps (c) and (e), a hydrogen containing CF-based gas and an inert gas are used to cause the polymer layer on the initial trench sidewalls and the lower end of the second portion of the trench.  
   
   
       3 . The method of  claim 1 , wherein, in steps (d) and (f), a non-hydrogen containing CF-based gas and an inert gas are used together with at least one of oxygen and nitrogen.  
   
   
       4 . The method of  claim 1 , wherein the thickness of the middle portion of the ILD film is in the range of 20-50% of the thickness of the entire ILD film.  
   
   
       5 . The method of  claim 1 , wherein the ILD film is formed of at least one of a undoped silicate glass (USG) layer, silicon oxide fluoride (SiOF) layer, tetraethylorthosilicate (TEOS) layer, spin-on glass (SOG) layer and a borophosphosilicate glass (BPSG).  
   
   
       6 . The method of  claim 1 , wherein the barrier layer is formed of at least one of a Ta layer, TaN layer, Ti layer, TiN layer and a bilayer of these layers, acting as both a metal-diffusion barrier and an adhesive layer between the ILD film and the conductive layer.  
   
   
       7 . The method of  claim 1 , wherein the conductive layer is formed of at least one of a Cu and a W layer.  
   
   
       8 . A method for forming a metal interconnect layer of a semiconductor device, the method comprising: 
 forming a first interlevel dielectric (ILD) film over a semiconductor wafer;    forming a second ILD film over the first ILD film, the second ILD film having a higher etch rate than the first ILD film;    forming a third ILD film over the second ILD film, the third ILD film having a lower etch rate than the second ILD film;    forming a photoresist pattern over the third ILD film, the photoresist pattern defining a metal interconnect region;    etching the third ILD film, the second ILD film, and the first ILD film in sequence using the photoresist pattern as an etch mask, to form a trench having a lower width, a middle width and an upper width, the middle width in the second ILD film being wider than the upper width in the third ILD film and the lower width in the first ILD film;    removing the photoresist pattern;    forming a barrier layer along the semiconductor wafer and in the trench;    depositing a conductive layer over the barrier layer; and    polishing the semiconductor wafer with the conductive layer by chemical mechanical polishing such that the conductive layer remains within only the trench surrounded by the first, second and third ILD films.    
   
   
       9 . The method of  claim 8 , wherein the thickness of the second ILD film is in the range of 20-50% of the sum of the thicknesses of the first, second and third ILD films.  
   
   
       10 . The method of  claim 8 , wherein each of the first and third ILD films is formed of at least one of an undoped silicate glass (USG) layer, silicon oxide fluoride (SiOF) layer, tetraethylorthosilicate (TEOS) layer, spin-on glass (SOG) layer and a borophosphosilicate glass (BPSG); and the second ILD film is formed of at least one of a flowable oxide (FOX) layer and a hydride organic siloxane polymer (HOSP) layer such that the second ILD film has a higher etch rate than the first and third ILD films.  
   
   
       11 . The method of  claim 8 , wherein the barrier layer is formed of at least one of a Ta layer, TaN layer, Ti layer, TiN layer and a bilayer of these layers, acting as both a metal-diffusion barrier and an adhesive layer between the first, second and third ILD films, and the conductive layer.  
   
   
       12 . The method of  claim 8 , wherein the conductive layer is formed of at least one of a Cu and a W layer.  
   
   
       13 . A method for forming a metal interconnect layer of a semiconductor device, the method comprising: 
 forming an interlevel dielectric (ILD) film over a semiconductor wafer;    forming a photoresist pattern on the ILD film, the photoresist pattern defining a metal interconnect region;    etching a portion of the ILD film using the photoresist pattern as an etch mask to form an initial trench, a polymer layer serving as an etch barrier on the sidewalls of the initial trench;    etching the remainder of the ILD film using the photoresist pattern and the polymer layer on the initial trench sidewalls as an etch mask, to deepen the trench, the resulting deeper trench having a lower width and an upper width, the lower width being wider than the upper width;    removing the photoresist pattern;    forming a barrier layer on the semiconductor wafer and in the deeper trench;    depositing a conductive layer over the barrier layer; and    polishing the conductive layer by chemical mechanical polishing (CMP), such that the conductive layer remains within only the deeper trench.    
   
   
       14 . A method for forming a metal interconnect layer of a semiconductor device, the method comprising: 
 forming a first interlevel dielectric (ILD) film over a semiconductor wafer;    forming a second ILD film over the first ILD film, the second ILD film having a lower etch rate than the first ILD film;    forming a photoresist pattern over the second ILD film, the photoresist pattern defining a metal interconnect region;    etching the second ILD film and the first ILD film in sequence using the photoresist pattern as an etch mask, to form a trench having a lower width in the first ILD film and an upper width in the second ILD film, the lower width being wider than the upper width;    removing the photoresist pattern;    forming a barrier layer along the semiconductor wafer and in the trench;    depositing a conductive layer over the barrier layer; and    polishing the semiconductor wafer with the conductive layer by chemical mechanical polishing such that the conductive layer remains within only the trench surrounded by the first and second ILD films.