Abstract:
A damascene wire and method of forming the wire. The method including: forming a mask layer on a top surface of a dielectric layer; forming an opening in the mask layer; forming a trench in the dielectric layer where the dielectric layer is not protected by the mask layer; recessing the sidewalls of the trench under the mask layer; forming a conformal conductive liner on all exposed surface of the trench and the mask layer; filling the trench with a core electrical conductor; removing portions of the conductive liner extending above the top surface of the dielectric layer and removing the mask layer; and forming a conductive cap on a top surface of the core conductor. The structure includes a core conductor clad in a conductive liner and a conductive capping layer in contact with the top surface of the core conductor that is not covered by the conductive liner.

Description:
FIELD OF THE INVENTION 
   The present invention relates to the field of integrated circuit manufacture; more specifically, it relates to an interconnect structure and method of fabricating the interconnect structure for wiring levels of an integrated circuit. 
   BACKGROUND OF THE INVENTION 
   Advanced integrated circuits utilize copper and other metallurgy in the interconnect or wiring levels in order to increase performance of the integrated circuit. Because of the possibility of copper and other metal diffusion through interlevel dielectric layers, copper and other metal interconnects are fabricated with conductive diffusion barrier liners on the sides and bottoms of the wires and dielectric copper and other metal diffusion barrier caps on the top surface of the wires. However, it has been found that wires using dielectric diffusion barrier caps are susceptible to reliability failures. 
   Therefore, there is a need for improved diffusion barrier capped interconnect structures. 
   SUMMARY OF THE INVENTION 
   The present invention utilizes electrically conductive diffusion barrier caps to seal surfaces of damascene and dual damascene interconnect structures not covered by electrically conductive liners or dielectric layers that may also act as diffusion barriers. The caps (and electrically conductive liners and dielectric layers, when acting as diffusion barrier) are diffusion barriers to a material contained in the core electrical conductor of a damascene or dual damascene line. 
   A first aspect of the present invention is a method, comprising: providing a substrate having a dielectric layer; forming a hard mask layer on a top surface of the dielectric layer; forming an opening in the hard mask layer; forming a trench in the dielectric layer where the dielectric layer is not protected by the hard mask layer, the trench having sidewalls and a bottom; recessing the sidewalls of the trench under the hard mask layer; forming a conformal electrically conductive liner on all exposed surfaces of the trench and the hard mask layer; filling the trench with a core electrical conductor; removing portions of the electrically conductive liner extending above the top surface of the dielectric layer and removing the mask layer; and forming an electrically conductive cap on a top surface of the core electrical conductor. 
   A second aspect of the present invention is a method comprising: providing a substrate having a dielectric layer; forming a hard mask layer on a top surface of the dielectric layer; forming an opening in the hard mask layer; forming a trench in the dielectric layer where the dielectric layer is not protected by the hard mask layer, the trench having sidewalls and a bottom, the sidewalls of the trench aligned with the opening in the hard mask; performing an isotropic etch of the sidewalls and bottom of the trench, the isotropic etch undercutting the hard mask layer and forming a hard mask overhang projecting over the trench; forming a conformal electrically conductive liner on all exposed surfaces of the trench and on all exposed surfaces of the hard mask layer, an upper portion of the electrically conductive liner in physical contact with the hard mask overhang and forming an electrically conductive overhang projecting over the trench; forming a core electrical conductor over the electrically conductive liner, the core electrical conductor filling the trench; performing a chemical-mechanical polish to remove the hard mask layer and all core electrical conductor extending above the top surface of the dielectric layer, the chemical-mechanical-polishing making coplanar a top surface of the dielectric layer, a top surface of the electrically conductive liner and a top surface of the core electrical conductor in the trench, the electrically conductive layer extending over and in direct physical contact with the core electrical conductor; and forming an electrically conductive cap on the top surface of the core electrical conductor. 
   A third aspect of the present invention is a structure, comprising: a core electrical conductor having a top surface, an opposite bottom surface and sides between the top and bottom surfaces; an electrically conductive liner in direct physical contact with and covering the bottom surface and the sides of the core electrical conductor, embedded portions of the electrically conductive liner in direct physical contact with and extending over the core electrical conductor in regions of the core electrical conductor adjacent to both the top surface and the sides of the core electrical conductor; and an electrically conductive cap in direct physical contact with the top surface of the core electrical conductor that is exposed between the embedded portions of the electrically conductive liner. 
   A fourth aspect of the present invention is a structure, comprising: a core electrical conductor having a top surface, an opposite bottom surface and sides between the top and bottom surfaces; a dielectric liner formed on the sides of the core electrical conductor; an electrically conductive liner in direct physical contact with and covering the bottom surface of the core electrical conductor and the dielectric liner, embedded portions of the electrically conductive liner extending over the dielectric liner and the core electrical conductor in regions of the core electrical conductor adjacent to both the top surface and the sides of the core electrical conductor; and an electrically conductive cap in direct physical contact with the top surface of the core electrical conductor that is exposed between the embedded portions of the electrically conductive liner. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     The features of the invention are set forth in the appended claims. The invention itself, however, will be best understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
       FIGS. 1A through 1H  are cross-sectional views illustrating common process steps for fabricating an interconnect structure according to both first and second embodiments of the present invention; 
       FIGS. 2A through 2C  are cross-sectional views illustrating process steps for fabricating an interconnect structure according to the first embodiment of the present invention; 
       FIGS. 3A through 3E  are cross-sectional views illustrating process steps for fabricating an interconnect structure according to the second embodiment of the present invention; 
       FIG. 4  is a cross-sectional view illustrating multiple wiring levels fabricated according to the first embodiment of the present invention; and 
       FIG. 5  is a cross-sectional view illustrating multiple wiring levels fabricated with additional diffusion barriers applicable to the first and the second embodiments of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   For the purposes of describing the present invention, the terms conductor and conductive should be reads as electrical conductor and electrically conductive. 
   A (single) damascene process is one in which wire trench or via openings are formed in a dielectric layer, an electrical conductor deposited on a top surface of the dielectric of sufficient thickness to fill the trenches and a chemical-mechanical-polish (CMP) process performed to remove excess conductor and make the surface of the conductor co-planer with the surface of the dielectric layer to form damascene wires (or damascene vias). 
   A dual damascene process is one in which via openings are formed through the entire thickness of a dielectric layer followed by formation of trenches part of the way through the dielectric layer in any given cross-sectional view. All via openings are intersected by integral wire trenches above and by a wire trench below, but not all trenches need intersect a via opening. An electrical conductor is deposited on a top surface of the dielectric of sufficient thickness to fill the trenches and via opening and a CMP process performed to make the surface of the conductor in the trench co-planer with the surface the dielectric layer to form dual damascene wire and dual damascene wires having integral dual damascene vias. 
   The structure of present invention will be described as being fabricated to connect to a contact level of an integrated circuit chip using a dual damascene process copper metallurgy process, though the present invention is applicable to metallurgies other than copper. A contact level is a transitional level, connecting devices such as metal-oxide-silicon field effect transistors (MOSFETs) to the first of wiring level of an integrated circuit, where the individual devices are “wired” into circuits. It should be understood that the structure of the present invention may be formed in any or all of these wiring levels as illustrated in  FIGS. 4 and 5  and as well as using a single damascene process. 
     FIGS. 1A through 1H  are cross-sectional views illustrating common process steps for fabricating an interconnect structure according to both first and second embodiments of the present invention. In  FIG. 1A , formed on a substrate  100  is a dielectric layer  105 . A dielectric diffusion barrier  110  is formed on a top surface  115  of dielectric layer  105 . Formed through diffusion barrier  110  and dielectric layer  105  is a stud contact  120 . A top surface  125  of stud contact  120  is coplanar with a top surface  130  of barrier layer  110 . In one example, barrier  110  is a diffusion barrier to materials contained in subsequently formed wires. In one example, barrier  110  is a diffusion barrier to copper. 
   In  FIG. 1B , a dielectric layer  135  is formed on top surface  130  of barrier layer  110  and a hard mask layer  140  is formed on a top surface  145  of dielectric layer  135 . In one example, dielectric layer  135  is a low K (dielectric constant) material, examples of which include but are not limited to hydrogen silsesquioxane polymer (HSQ), methyl silsesquioxane polymer (MSQ) and polyphenylene oligomer (SiO x (CH 3 ) y ). A low K dielectric material has a relative permittivity of about 4 or less. In a second example, dielectric layer  135  comprises SiO 2 . Dielectric layer  135  may be, for example, between about 50 nm and about 1,000 nm thick. In one example, hard mask layer  140  may comprise, for example, silicon dioxide (SiO 2 ), silicon nitride (Si 3 N 4 ), silicon carbide (SiC), silicon oxy nitride (SiON), silicon oxy carbide (SiOC), hydrogen doped silica glass (SiCOH), plasma-enhanced silicon nitride (PSiN x ) or NBLoK (SiC(N,H)). Hard mask layer  140  may be, for example, between about 5 nm and about 100 nm thick. It is possible for hard mask layer  140  to comprise a metal. 
   In  FIG. 1C , a patterned photoresist layer  150  is formed on a top surface  155  of hard mask layer  140 , the photoresist is layer patterned by any number of well known lithographic processes and a trench  155  etched through hard mask layer  140 , exposing top surface  145  of dielectric layer  140 . 
   In  FIG. 1D , patterned photoresist layer  150  (see  FIG. 1C ) is removed and a trench  160  is formed, for example using a reactive ion etch (RIE) process, into dielectric layer  135  to expose top surface  125  of stud contact  120  using patterned hard mask layer  140  as an etch mask. 
   In  FIG. 1E , another patterned photoresist layer  165  is formed on a top surface  155  of hard mask layer  140 , the photoresist is layer patterned by any number of well known lithographic processes and trenches  155 A (trench  155  of  FIG. 1C  widened) and  170  are etched through hard mask layer  140 , exposing top surface  145  of dielectric layer  140 . 
   In  FIG. 1F , patterned photoresist layer  165  (see  FIG. 1E ) is removed and a trenches  175  and  180  are etched, for example using an RIE process, part way into dielectric layer  135 . Trench  180  intersects trench  160 . 
   In  FIG. 1G , overhangs  185  of hard mask layer  140  are created by isotropic removal of a layer of dielectric layer  135  exposed in trenches  160 ,  175  and  180 . In a first example, the isotropic removal of a layer of dielectric layer  135  may be accomplished by wet etching in solution comprising HNO 3 , HCl, H 2 SO 4 , HF, NH 4 OH, NH 4 F or combinations thereof. In a second example, the isotropic removal of a layer of dielectric layer  135  may be accomplished by a high-pressure plasma etch having low directionality. 
   Using trench  175  as an example, if the widest portion of the opening in hard mask layer  140  is W 1 , and the overhang has a width W 2 , then the ratio W 2 /W 1  may be between about 0.03 and about 0.48 
   In  FIG. 1H , a conformal conductive liner  190  is formed over top surface  155  of hard mask layer  140 , all exposed surfaces of overhangs  185 , including bottom surfaces  195  of the overhangs, exposed surfaces  200  of trenches  160 ,  175  and  180 , and a top surface  125 A of stud contact  120 . In one example, liner  190  is a diffusion barrier to the material(s) of a core conductor  210  (see  FIG. 2A  or  3 C) that will be later formed over the liner. In one example, liner  190  is a diffusion barrier to copper. In one example liner  190  comprises Ta, TaN, Ti, TiN, TiSiN, W, Ru or combinations thereof. In one example, liner  190  is between about 2 nm and about 100 nm thick. Liner  190  may be formed, for example by chemical vapor deposition (CVD) or atomic layer deposition (ALD). 
   Alternatively, liner  190  may be formed in a process of conformal deposition of liner material followed by a simultaneous sputter etch (using a charged sputtering species) and liner deposition as metal neutrals process as taught in U.S. Pat. No. 6,784,105 to Yang et al., issued on Aug. 31, 2004 which is hereby incorporated by reference in its entirety. In one example, metal neutrals comprises include Ta, TaN, Ti, TiN, TiSiN, W, Ru or combinations thereof and the gas used to generate the sputtering species comprises Ar, He, Ne, Xe, N 2 , H 2 NH 3 , N 2 H 2  or combinations thereof. The liner material previously deposited is removed from the bottom of the trench along with any metal oxide that may be present on top surface  125 A of stud contact  120  (or any core conductor as illustrated in  FIGS. 5 and 6 ). When sputtering is stopped but metal neutral deposition continued, a new layer of liner  190  is formed to replace that which was removed. 
     FIGS. 2A through 2C  are cross-sectional views illustrating process steps for fabricating an interconnect structure according to the first embodiment of the present invention.  FIG. 2A  continues from  FIG. 1H . In  FIG. 2A , a core conductor  210  is formed on top of liner  190 . In one example core conductor  210  comprises Al, AlCu, Cu, W, Ag, Au or combinations thereof. In the example of core conductor  210  being copper, a thin copper layer is evaporated or deposited and then a thicker layer of copper is electroplated. The thickness of core conductor  210  is sufficient to completely fill trenches  160 ,  175  and  180 . 
   In  FIG. 2B , a chemical-mechanical-polish (CMP) process is performed to co-planarize a top surface  145 A of dielectric layer  135 , a top surface  215  of liner  190  and a top surface  220  of core conductor  210 . After the CMP process, a damascene wire  225  and a dual damascene wire  230  having with an integral damascene via  235  are formed. 
   In  FIG. 2C , conductive diffusion barrier caps  240  are selectively formed on top surface  220  of core conductor  210 . In one example, barrier caps  240  comprises CoWP, CoSnP, CoP and Pd or combinations thereof. In one example caps  240  are about 5 nm to about 80 nm thick. In one example, caps  240  are diffusion barriers to the material(s) of core conductor  210 . In one example, caps  240  is a diffusion barrier to copper In one example, caps  240  are formed by a process that includes electroless plating. Methods of forming CoWP, CoSnP, CoP and Pd layers are disclosed in U.S. Pat. No. 5,695,810 to Bubin et al, issued on Dec. 9, 1997 and U.S. Pat. No. 6,342,733 to Hu et al., issued on Jan. 29, 2002 which are hereby incorporated by reference in their entireties. Barrier caps  240  are in direct physical contact with top surface  220  of core conductor  210 . 
     FIGS. 3A through 3E  are cross-sectional views illustrating process steps for fabricating an interconnect structure according to the second embodiment of the present invention.  FIG. 3A  continues from  FIG. 1H . In  FIG. 3A  a dielectric liner  245  is formed on all exposed surfaces of liner  190 . In one example, dielectric liner  245  may comprise, for example, silicon dioxide (SiO 2 ), silicon nitride (Si 3 N 4 ), silicon carbide (SiC), silicon oxy nitride (SiON), silicon oxy carbide (SiOC), hydrogen doped silica glass (SiCOH), plasma-enhanced silicon nitride (PSiN x ) or NBLoK (SiC(N,H)) or combinations thereof. In one example dielectric liner  245  is about 5 nm to about 100 nm thick. Dielectric liner  245  may be formed, for example by CVD or ALD. 
   In  FIG. 3B , a directional etch process (such as an RIE) is performed to remove dielectric liner  245  from horizontal surfaces of liner  190  disposed on bottom surfaces of trenches  160 .  175  and  180 . The directional etch process may be followed by a simultaneous sputter etch and liner deposition as metal neutrals process as described supra, in reference to  FIG. 1H . 
   In  FIG. 3C , core conductor  210  is formed as described supra ion reference to  FIG. 2A . The thickness of core conductor  210  is sufficient to completely fill trenches  160 ,  175  and  180 . 
   In  FIG. 3D , a CMP process is performed to co-planarize top surface  145 A of dielectric layer  135 , top surface  215  of liner  190 , top surface  220  of core conductor  210  and a top surface  250  of dielectric liner  245 . After the CMP process, a damascene wire  255  and a dual damascene wire  260  having with an integral damascene via  265  are formed. 
   In  FIG. 3E , caps  240  are selectively formed on top surface  220  of core conductor  210 . Caps  240  are in direct physical contact with and completely covers top surface  220  of core conductor  210 . 
     FIG. 4  is a cross-sectional view illustrating multiple wiring levels fabricated according to the first embodiment of the present invention. In  FIG. 4 , an interlevel dielectric layer  270  containing a damascene wire  275  and dual damascene wire  280  having with an integral damascene via  285  is formed over dielectric layer  135  (which can also be considered an interlevel dielectric layer). An interlevel dielectric layer  290  containing a dual damascene wire  295  with an integral damascene via  300  and dual damascene wire  305  having with an integral damascene via  310  is formed over interlevel dielectric layer dielectric layer  270 . Interlevel dielectric layers  270  and  275  are similar to dielectric layer  135 . Damascene wire  275  is similar to damascene wire  225  and dual damascene wires  280 ,  295  and  305  with respective integral vias  285 ,  300  and  310  are similar to dual damascene wire  230  and integral via  235 . Caps  240 A and  240 B are similar to caps  240 . While three wiring levels are illustrated in  FIG. 4 , any number of similar wiring levels may be so stacked. Damascene wires and vias and dual damascene wires and vias having structures of the second embodiment of the present invention may be similarly formed in stacked interlevel dielectric layers. 
     FIG. 5  is a cross-sectional view illustrating multiple wiring levels fabricated with additional diffusion barriers applicable to the first and the second embodiments of the present invention.  FIG. 5  is similar to  FIG. 4  with the difference that a dielectric layer  135 A includes dielectric layer  135  and a dielectric diffusion barrier  315 , an interlevel dielectric layer  270 A includes dielectric layer  270  and a dielectric diffusion barrier layer  320  and an interlevel dielectric layer  290 A includes dielectric layer  290  and a dielectric diffusion barrier layer  325 . Diffusion barrier  315  is formed between dielectric layer  135  and interlevel dielectric layer  275 , diffusion barrier  320  is formed on top of interlevel dielectric layer  275 . Diffusion barriers  315 ,  320  and  325  are similar to diffusion barrier  110 . In one example, diffusion barriers  315 ,  320  and  325  are diffusion barriers to materials contained in wires  225 ,  230 ,  275 ,  280 ,  295  and  305 . In one example, diffusion barriers  315 ,  320  and  325  are diffusion barriers to copper. While three wiring levels are illustrated in  FIG. 5 , any number of similar wiring levels may be so stacked. Damascene wires and vias and dual damascene wires and vias having structures of the second embodiment of the present invention may be similarly formed in stacked interlevel dielectric layers. 
   Thus, the present invention provides improved diffusion barrier capped interconnect structures. 
   The description of the embodiments of the present invention is given above for the understanding of the present invention. It will be understood that the invention is not limited to the particular embodiments described herein, but is capable of various modifications, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, it is intended that the following claims cover all such modifications and changes as fall within the true spirit and scope of the invention.