Abstract:
A method of manufacturing semiconductor wafers using electroless plating processing. A partially completed semiconductor wafer having trenches and vias formed in a layer of interlayer dielectric has a barrier layer globally formed on the surface of the partially completed semiconductor wafer. A seed layer is globally formed on the surface of the barrier layer. The barrier and seed layers are removed from portions of the surface of the partially completed semiconductor wafer on which plating is not to occur. The partially completed semiconductor wafer is then subjected to an electroless plating process and conductive material is plated on those portions of the seed layer that remains on the partially completed semiconductor wafer.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a method of manufacturing high performance semiconductor devices utilizing selective electroless plating processing and more specifically, this invention relates to a method of manufacturing high performance semiconductor devices utilizing a method of defining copper seed layers for selective electroless plating processing. 
     2. Discussion of the Related Art 
     As the performance of semiconductor devices have progressed to higher speeds, the use of aluminum as an interconnect material is causing a speed bottleneck Alternate materials such as gold (Au), silver (Ag), nickel (Ni), palladium (Pd), copper (Cu), and platinum (Pt) have all been explored. Of these, copper has become the preferred alternate replacement due to its low resistance and low cost. However, unlike aluminum, copper is not easily etched into wires or via plugs. An alternative method for manufacturing integrated circuits using multilevel copper interconnects has been developed that utilizes single damascene mask methodology. 
     As the price of semiconductor devices continues to decrease, there is pressure on the semiconductor manufacturing industry to minimize total cost. One of the major requirements to minimize total cost is to minimize the number of process steps. One method to minimize the number of processing steps is to combine the filling of conductive layers of metallization, for example, into both a trench and a via in a single step. Because current and future devices may have five or more layers of metallization (wire and via equal to one layer), combining the two will have a significant impact upon the total cost of the semiconductor device. Furthermore, the use of copper reduces contact resistance since this will eliminate every other barrier, glue, and seal layers between the current layer&#39;s via and wire, as shown in FIG.  1 . 
     FIG. 1 shows a semiconductor device  100  in which vias and wire interconnects have been formed by standard damascene methods. The semiconductor device  100  includes a layer  102  that could be a semiconductor substrate on and in which active devices (not shown) have been formed. The next layer  104  is a layer of interlayer dielectric in which metal structures, such as a wire  106  is formed. As is known in the semiconductor manufacturing art, a wire is used to connect one portion of a semiconductor device to another portion of the semiconductor device on the same layer. The wire  106  is typically formed in a trench formed in the layer of interlayer dielectric  104 . The walls of the trench are covered with a barrier layer  108 . The barrier layer  108  is typically formed from a metallic nitride material such as TiN or TaN. The trench is then filled with a conductive material. Conductive materials that can be used to fill the trench include tungsten, aluminum and copper. If copper is to be the conductive material to fill the trench, a seed layer  109  is formed on the barrier layer  108 . The seed layer is typically a thin layer of copper that may be sputtered onto the barrier layer  108 . A seal layer or hard mask layer  110  is formed on the surface of the layer  104  of interlayer dielectric. The layer  110  is a seal layer if the conductive material is to be copper. A seal layer prevents copper ions from diffusing into the surrounding material. A typical seal layer is made up of a material such as Si z N y  or SiO z N y . A layer  112  of interlayer dielectric is formed on the layer  110  and metal structures such as via  114  are formed in the layer  112  of interlayer dielectric. The walls of via  114  are covered with a barrier layer  116  similar to barrier layer  108 . If via  114  is to be filled with copper, a seed layer  117  is formed on the barrier layer  116 . Via  114  is then filled with a conductive material. A seal layer or hard mask layer  118  is formed on the surface of the layer  112  of interlayer dielectric. The layer  118  is a seal layer if the via  114  is to be filled with copper. A layer  120  of interlayer dielectric is formed on the layer  118 . Trenches shown at  122  and  124  are formed in the layer  120  of interlayer dielectric. Barrier layers  126  and  128  are formed on the walls of the trenches  122  and  124  respectively and the trenches  122  and  124  are filled with conductive material. If the trenches  122  and  124  are to be filled with copper, seed layers  123  and  125  are formed on the barrier layers  126  and  128 . As is known in the semiconductor manufacturing art, trenches and vias are etched into a layer of interlayer dielectric material and a blanket layer of conductive material is then typically formed on the surface of the wafer and a polishing process, such as a chemical mechanical polishing process, is conducted to remove unwanted conductive material. As can be appreciated, the above process of forming individual-metal structures requires numerous steps. 
     FIGS. 2A-2C show a method of eliminating several steps from the process of forming a semiconductor device as described above in conjunction with FIG.  1 . Like numerical designations denote like structures in the figures. FIG. 2A shows a partially completed semiconductor device  200 . The partially completed semiconductor device  200  shows layer  102  with metal structure  106  formed in layer  104  of interlayer dielectric. The metal structure  106  is formed by forming a via or trench in the layer  104 , forming a barrier layer  108  on the walls of the via or trench in the layer  104 , and forming a seed layer  109  on the barrier layer  108  if the via or trench in the layer  104  is to be filled with copper. The seal layer or hard mask layer  110 , the layer  112  of interlayer dielectric, the seal layer or hardmask layer  118  and the layer  120  of interlayer dielectric are formed on the layer  104 . The layer  110  is a seal layer if the subsequently formed vias and trenches are to be filled with copper. A series of masking and etching processes are then conducted to form vias, such as the via  114  and trenches, such as the trenches  122  and  124 , in the layers  104 ,  110 ,  112 ,  118 , and  120 . A barrier layer  202  is formed on the walls of the vias and trenches. A seed layer  204  of copper is formed on the barrier layer  202  if via  114  and trenches  122  and  124  are to be filled with copper. There are several methods to deposit copper, however, only two of the methods can successfully form copper into the small geometries required for modern semiconductor technology. These two methods are chemical vapor deposition (CVD) and electroplating. Of the two, CVD is too expensive because of the gases used to supply the copper ions. Electroplating is the preferred method because electroplating can be done in batches, unlike a CVD process, which can only be done on one wafer at a time. When an electroplating process is utilized, the seed layer  204  of copper is formed on the barrier layer  202 . In this instance, a global deposition or sputtering of the conductive seed layer  204  is formed on the entire surface of the wafer. If the conductive material to be used is copper, the seed layer formation process consists of depositing or sputtering a thin layer of copper onto the entire wafer, which includes the sidewalls and bottom of the trenches and vias that have been formed in the semiconductor device  200 . The entire wafer is then submerged into a bath of ionic solution containing copper ions and an electroplating process causes a layer  206  of copper to be formed on the surface of the wafer. It is noted that the thickness of the layer  206  must be thick enough so that via  114  and trench  122  can be completely filled. Because some materials such as copper are difficult to polish, the process of planarizing the copper layer  206  is very difficult. 
     FIG. 2B shows the partially completed semiconductor device  200  as shown in FIG. 2A after a polishing process to remove undesired portions of the layer  206  of copper and of the seed layer  204 . However, as known in the semiconductor manufacturing art, the polishing of copper is a difficult process and it is therefore desirable to keep the thickness of the layer  206  of copper to a minimum. 
     FIG. 2C shows the partially completed semiconductor device  200  as shown in FIG. 2B after a polishing process to remove undesired portions of the barrier layer  202  from the top surfaces of the partially completed semiconductor device  200 . As can be appreciated, the via  114  and trench  122  are filled with a conductive material during the same process thus saving one or more process steps when compared to the process necessary to form the structure as shown in FIG.  1 . As will be noted, the semiconductor device  100  in FIG. 1 is the same as the semiconductor device  200  shown in the FIGS. 2A-2C. 
     The semiconductor device shown in FIG. 1 requires multiple steps to form the individual metal structures using the damascene method of forming metal filled vias and trenches. The semiconductor device shown in FIGS. 2A-2C requires extensive chemical mechanical polishing to remove excess copper that has been electroplated on the entire surface of the partially completed semiconductor device. 
     Therefore, what is needed is a method of manufacturing semiconductor devices that form multiple layers of metal filled vias and trenches in the minimum number of processes and that does not require extensive polishing processes. 
     SUMMARY OF THE INVENTION 
     According to the present invention, the foregoing and other objects and advantages are attained by a method of manufacturing a semiconductor device that utilizes an electroless plating process that has low cost, is conducted at a low temperature and that yields high purity copper film. 
     In accordance with an aspect of the invention, a partially completed semiconductor wafer having trenches and vias formed in a layer of interlayer dielectric has a barrier layer globally formed on the surface of the partially completed semiconductor wafer. A seed layer is globally formed on the surface of the barrier layer. The barrier and seed layers are removed from portions of the surface of the partially completed semiconductor wafer on which plating is not to occur. The partially completed semiconductor wafer is then subjected to an electroless plating process and conductive material is plated on those portions of the seed layer that remains on the partially completed semiconductor wafer. 
     In accordance with another aspect of the invention, the seed layer and barrier layer are removed from portions of the surface of the interlayer dielectric by a polishing process. 
     In accordance with still another aspect of the invention, the seed layer and barrier layer are removed from portions of the surface of the interlayer dielectric by self aligning masking portions of the surface of the interlayer dielectric and etching the seed layer and barrier layers from the surface of the interlayer dielectric. 
     The described method thus provides a method of manufacturing semiconductor wafers that utilizes the advantages of electroless plating of copper that has low cost, can be conducted at low temperature and that yields high purity copper film. 
    
    
     The present invention is better understood upon consideration of the detailed description below, in conjunction with the accompanying drawings. As will become readily apparent to those skilled in the art from the following description, there is shown and described embodiments of this invention simply by way of illustration of the best mode to carry out the invention. As will be realized, the invention is capable of other embodiments and its several details are capable of modifications in various obvious aspects, all without departing from the scope of the invention. Accordingly, the drawings and detailed description will be regarded as illustrative in nature and not as restrictive. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, and further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiments when read in conjunction with the accompanying drawings, wherein: 
     FIG. 1 shows a semiconductor device in which vias and wire interconnects have been formed by standard damascene methods; 
     FIGS. 2A-2C show a prior art method of manufacturing semiconductor devices by global deposition or sputtering a conductive seed layer on the entire surface of the wafer and submerging the wafer into a bath of ionic solution containing copper ions that results in a thick layer of copper on the entire surface of the semiconductor wafer; 
     FIG. 2A shows a portion of a partially completed semiconductor wafer showing a thick layer of copper formed on the surface of the wafer, 
     FIG. 2B shows the portion of the partially completed semiconductor wafer as shown in FIG. 2A after a polishing process to polish the thick layer of copper, including the seed layer, formed on the surface of the wafer down to the barrier layer; 
     FIG. 2C shows the portion of the partially completed semiconductor wafer as shown in FIG. 2B after a polishing process to polish the barrier layer down to the surface of the semiconductor wafer; 
     FIGS. 3A-3D show a method of manufacturing semiconductor devices in accordance with the present invention, wherein; 
     FIG. 3A shows a portion of a partially completed semiconductor wafer by forming a seed layer on the surface of the partially completed semiconductor wafer; 
     FIG. 3B shows the portion of the partially completed semiconductor wafer after a polishing process to remove portions of the seed layer and barrier layer from surfaces on which the metal layer is not to be formed; 
     FIG. 3C shows the portion of the partially completed semiconductor wafer after trenches and vias in the partially completed semiconductor wafer have been filled with conductive material; 
     FIG. 3D shows the portion of the partially completed semiconductor wafer after excessive conductive material in the trenches have been polished; 
     FIGS. 4A-4F show an alternative method of manufacturing semiconductor devices in accordance with the present invention, wherein portions of a seed layer formed on the surface of the semiconductor wafer on which copper is to be formed are masked and portions of the seed layer on which copper is not to be formed are removed, wherein; 
     FIG. 4A shows a portion of a partially completed semiconductor wafer showing a seed layer formed on the surface of a the partially completed semiconductor wafer; 
     FIG. 4B shows the portion of the partially completed semiconductor wafer with a layer of photoresist formed on the surface of the partially completed semiconductor wafer; 
     FIG. 4C shows the portion of the partially completed semiconductor wafer after the layer of photoresist has been removed from portions of the seed layer on which copper is not to be formed; 
     FIG. 4D shows the portion of the partially completed semiconductor wafer after the seed layer and the underlying barrier layer have been removed from those portions of the semiconductor wafer that are not protected by photoresist; 
     FIG. 4E shows the portion of the partially completed semiconductor wafer after the remaining photoresist has been removed; and 
     FIG. 4F shows the portion of the partially completed semiconductor wafer after the trenches and vias in the wafer have been filled with conductive material. 
    
    
     DETAILED DESCRIPTION 
     Reference is now made in detail to specific embodiments of the present invention that illustrate the best mode presently contemplated by the inventors for practicing the invention. 
     FIGS. 3A-3D show a method of manufacturing semiconductor devices in accordance with the present invention in which portions of the seed layer and barrier layer are removed from portions of the semiconductor wafer on which copper is not to be formed, wherein; 
     FIG. 3A shows a portion of a partially completed semiconductor wafer  300 . The partially completed semiconductor device  300  shows a layer  302  with a metal structure  306  formed in a layer  304  of interlayer dielectric. The metal structure  306  is formed by forming a via or trench in the layer  304 , forming a barrier layer  308  on the walls of the via or trench in the layer  304 , and forming a seed layer  309  on the barrier layer  308  if the via or trench in the layer  304  is to be filled with copper. The via or trench is then filled with the appropriate conductive material to form the metal structure  306 . The seal layer or hard mask layer  310 , the layer  312  of interlayer dielectric, the seal layer or hard mask layer  318  and the layer  312  are formed on the layer  304 . The layer  310  is a seal layer if the subsequent vias and trenches are to be filled with copper. A series of masking and etching processes are then conducted to form vias, such as the via  314  and trenches, such as the trenches  322  and  324 , in the layers  304 , 310 , 312 , 318 , and  320 . A barrier layer  326  is formed on the surface of the partially completed semiconductor wafer  300 , including the walls of the vias and trenches. A seed layer  328  is formed on the barrier layer  326  of the partially completed semiconductor device  300 . Typically, the seed layer  328  is typically a material such as copper. As discussed above, there are several methods to deposit copper, however, only two can successfully form copper into the small geometries required for modern semiconductor technology. These are chemical vapor deposition (CVD) and electroplating. Of the two, CVD is too expensive because of the gases used to supply the copper ions. Electroplating is preferred because an electroplating can be done in batches, unlike a CVD process, which can only be done on one wafer at a time. When an electroplating process is utilized, a seed layer  328  is formed on the barrier layer  326  as described above. The present invention selectively deposits conductive material by means of electroless plating. Since electroless plating does not require a continuous sheet of seed layer as does electrolytic plating, the seed layer can be selectively placed where wires and vias are to be formed. The present invention will be discussed in relation to the use of copper electroless plating and a single damascene mask process. However, it is to be understood that the present invention is not limited to only copper and a single damascene process. 
     FIG. 3B shows the partially completed semiconductor wafer  300  as shown in FIG. 3A after a polishing or buffing process to remove portions of the seed layer  328  and barrier layer  326  from surfaces of the semiconductor wafer  300  on which copper is not to be formed. As can be seen, the via or trench is recessed and will not be affected by the polishing and buffing process. 
     FIG. 3C shows the partially completed semiconductor wafer  300  as shown in FIG. 3B after an electroless plating process has been conducted to plate copper onto surfaces that have a seed layer, such as the via  314  and trenches  322  and  324 . 
     FIG. 3D shows the partially completed semiconductor wafer  300  as shown in FIG. 3C after a polishing process to planarize the surface of the semiconductor wafer  300 . 
     FIGS. 4A-4F show an alternate method of manufacturing semiconductor devices in accordance with the present invention, wherein portions of a seed layer formed on the surface of the semiconductor wafer on which copper is be formed are self aligned, masked and portions of the seed layer on which copper is not to be formed are removed. 
     FIG. 4A shows a portion of a partially completed semiconductor wafer  400 . The partially completed semiconductor device  400  shows the layer  402  with the metal structure  406  formed in the layer  404  of interlayer dielectric. The metal structure  406  is formed by forming a via or trench in the layer  404 , forming a barrier layer  408  on the walls of the via or trench in the layer  404 , and forming a seed layer  409  on the barrier layer  408  if the via or trench in the layer  404  is to be filled with copper. The via or trench is then filled with the appropriate conductive material to form the metal structure  406 . The seal layer or hard mask layer  410 , the layer  412  of interlayer dielectric, the seal layer or hard mask layer  418  and the layer  412  are formed on the layer  404 . The layer  410  is a seal layer if subsequent vias and trenches to be formed will be filled with copper. A series of masking and etching processes are then conducted to form vias, such as the via  414  and trenches, such as the trenches  422  and  424 , in the layers  404 ,  410 ,  412 ,  418 , and  420 . A barrier layer  426  is formed on the surface of the partially completed semiconductor wafer  400 , including the walls of the vias and trenches. A seed layer  428  is formed on the barrier layer  426  of the partially completed semiconductor device  400 . Typically, the seed layer  428  is typically a material such as copper. As discussed above, there are several methods to deposit copper, however, only two can successfully form copper into the small geometries required for modern semiconductor technology. These are chemical vapor deposition (CVD) and electroplating. Of the two, CVD is too expensive because of the gases used to supply the copper ions. Electroplating is preferred because an electroplating can be done in batches, unlike a CVD process, which can only be done on one wafer at a time. When an electroplating process is utilized, a seed layer  428  is formed on the barrier layer  426  as described above. 
     FIG. 4B shows the partially completed semiconductor wafer  400  as shown in FIG. 4A after a layer  430  of a photo-sensitive or non-photo sensitive resist is formed on the surface of the partially completed semiconductor wafer  400 . 
     FIG. 4C shows the partially completed semiconductor wafer  400  as shown in FIG. 4B after the resist has been stripped from surfaces of the wafer  400  on which copper plating is not to be formed. Because of the thickness differences between the via/trench cavities and the surface, photoresist in the non-cavity regions are removed by anisotropic stripping method. The exposed seed and barrier layers are etched away. 
     FIG. 4D shows the partially completed semiconductor wafer  400  as shown in FIG. 4C after an etch process to remove the seed layer  428  and the barrier layer  426  from the portions of the wafer  400  not protected by the layer  430  of resist. 
     FIG. 4E shows the partially completed semiconductor wafer  400  as shown in FIG. 4D with the remaining portions of the layer  430  of resist removed. 
     FIG. 4F shows the partially completed semiconductor wafer  400  as shown in FIG. 4F after the via  414  and the trenches  422  and  424  have been filled with a conductive material, such as copper. 
     The advantages of conductive material deposition, such as copper, by electroless plating are as follows: 
     1. conformal deposition, 
     2. low temperature, 
     3. high copper purity, 
     4. planar surfaces, and 
     5. low cost. 
     The basic mechanism for copper deposition by electroless plating is a two step reaction and is as follows: 
     1) Anodic oxidation of reducing agents on catalytic metal surface: 
     
       
         HCHO+2OH − =HCOO − +2H 2 +½H 2 +e −   
       
     
     2) Cathodic reduction of copper ions on catalytic metal surface: 
     
       
         Cu 2+ +2e − =Cu 
       
     
     The chemical components utilized are as follows: 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Chemicals 
                 Function 
               
               
                   
                   
               
             
             
               
                   
                 copper sulfate 
                 supplies Cu ions 
               
               
                   
                 TMAH 
                 supplies OH −  ions 
               
               
                   
                 EDTH (ethylene 
                 complexing agent 
               
               
                   
                 diamine tetra acetic 
               
               
                   
                 acid) 
               
               
                   
                 Formaldehyde 
                 reducing agent 
               
               
                   
                 Ammonium cyanide 
                 complexing agent 
               
               
                   
                 Surfactant 
                 reduce surface tension and allow solution 
               
               
                   
                   
                 to reach small features 
               
               
                   
                   
               
             
          
         
       
     
     The requirements for the seed material are as follows: 
     1. must be catalytically active for nucleation 
     2. must be conductive, and 
     3. must be non-oxidized, non-contaminated, and have a clean surface. 
     Suitable seed layer materials are as follows: 
     Palladium, Platinum, Nickel, Gold, Silver, Cobalt, Tungsten (ok/poor adhesion). The commonly used materials; Ti, TiN, Ta, and Al are not suitable as the seed layer. Tungsten is not catalytic, but galvanic displacement results in monolayer copper formation, thus initiating deposition. Therefore, if tungsten is used as a seed layer, it is essential that the surface is ultraclean. 
     The deposition conditions for the electroless plating of copper are as follows: 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 Temperature 40-80° C. 
                 (70° C. typical) 
               
               
                 Deposition Rate: 150-300 Å/min 
                 (200 Å/min typical) 
               
               
                 pH value: must &gt;12 
                 (12.5 typical) 
               
               
                 Resistivity: 
                 2.0 micro ohms cm 
               
               
                 Microstructure: 
                 epitaxial growth on Cu, grain size - 
               
               
                   
                 0.1 μm. 
               
               
                   
               
             
          
         
       
     
     In summary, the results and advantages of the method of the present invention can now be more fully realized. The described method provides a method of manufacturing a semiconductor device that utilizes the advantages of electroless plating of copper that has low cost, can be conducted at low temperature and that yields high purity copper film. 
     The foregoing description of the embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.