Abstract:
A system and method for reducing contamination in a semiconductor device formed on a substrate is disclosed. The method and system include providing a barrier metal layer on the substrate. A first portion of the barrier metal layer is thinner than a second portion of the barrier metal layer. The method and system further include removing the first portion of the barrier metal layer.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to semiconductor processing and more particularly to a method and system for reducing the contamination due to copper interconnect formation.  
         BACKGROUND OF THE INVENTION  
         [0002]    Copper interconnects can be used formed during semiconductor processing. In forming copper interconnects, for a trench is first provided in the silicon substrate. Next, a barrier metal is typically deposited to prevent the copper to be used in an interconnect or via from migrating. Then, copper plating is performed, filling the trench and providing the interconnect.  
           [0003]    Typically, the barrier metals that are used also work as a seed layer for copper. Such barrier metals are used to allow the growth of the copper on the barrier metal in the trench or the via. If barrier metals which cannot act as a seed layer are used, the copper will not properly grow in the trench or via unless a separate seed layer is provided.  
           [0004]    Although the above process forms copper interconnects, the barrier metal is deposited at the edge and rear of the silicon substrate as well as in the trenches or vias. Because the barrier metal acts as a seed layer for copper, a copper film also develops at the edge and rear of the substrate during copper plating. Because this copper film is thin, it does not adhere well to the silicon substrate and peels during processing. Pieces of the peeled copper film may then contaminate the circuitry formed towards the center of the silicon substrate.  
           [0005]    Accordingly, what is needed is a system and method for providing copper interconnects and vias without introducing copper contamination due to films formed at the edge of the substrate. The present invention addresses such a need.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention provides a method and system for reducing contamination in a semiconductor device formed on a substrate. A first portion of the barrier metal layer is thinner than a second portion of the barrier metal layer. The method and system further comprise removing the first portion of the barrier metal layer.  
           [0007]    According to the system and method disclosed herein, the present invention reduce copper contamination, thereby increasing overall system performance. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a block diagram of a conventional system for providing copper interconnects.  
         [0009]    [0009]FIG. 2A is a block diagram of a system for providing copper interconnects in accordance with the method and system just after deposition of a barrier metal layer.  
         [0010]    [0010]FIG. 2B is a block diagram of a system for providing copper interconnects in accordance with the method and system during etching.  
         [0011]    [0011]FIG. 2C is a block diagram of a system for providing copper interconnects in accordance with the method and system after etching. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]    The present invention relates to an improvement in semiconductor processing. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the preferred embodiment will be readily apparent to those skilled in the art and the generic principles herein may be applied to other embodiments. Thus, the present invention is not intended to be limited to the embodiment shown but is to be accorded the widest scope consistent with the principles and features described herein.  
         [0013]    [0013]FIG. 1 is a block diagram of a conventional substrate during formation of copper interconnects and vias. The substrate  12  is typically silicon. The substrate is placed on an apparatus including a base  18 . After formation of trenches or via holes, not shown, a layer of barrier metal  14  is deposited onto the substrate  14 . The barrier metal layer  14  is used to block the migration of copper outside of the interconnects and vias. Typically, the barrier metal layer  14  is formed through chemical vapor deposition (“CVD”). In some instances a seed layer  16  is also grown on the barrier metal layer  14 . After the seed layer  16  is provided, a copper layer, not shown, is deposited. Typically, the copper layer is formed by electroplating copper.  
         [0014]    Although the system shown in FIG. 1 allows formation of copper interconnects and vias, those with ordinary skill in the art will realize that copper deposited during formation of the interconnects and vias will contaminate the structures formed on the substrate  12 . The barrier metal layer  14  covers not only the open portion, but also covers the edge and a portion of the back of the substrate  12 . Thus, a thin layer of the barrier metal chosen for the barrier metal layer  14  is present at the edge and rear of the substrate  12 . Typically, the barrier metal layer  14  is approximately 300 Angstroms near the center of the substrate  12  and approximately 30 Angstroms at the edge and rear of the substrate  12 .  
         [0015]    The barrier metal layer  14  can typically act as a seed layer for copper. For example, tungsten-nitride (WN x  where x is an integer) or titanium-nitride (TiN) is typically used to form the barrier metal layer  14 . This feature of the barrier metal layer  14  is important in aiding the growth of the copper to form the interconnects and vias. Because the barrier metal layer  14  is a seed layer, the copper plating causes a thin layer of copper, not shown, to grow on the thin portion of the barrier metal layer  14 , at the edge and back of the substrate  12 . The thin copper layer does not adhere well to the substrate  12 . As a result, the thin copper layer peels off of the edge and back of the substrate  12 , contaminating the circuits formed on the substrate  12 .  
         [0016]    The present invention provides for a method and system for removing a portion of the barrier metal layer. The present invention will be described in terms of a particular process for etching a portion of the barrier metal layer. However, one of ordinary skill in the art will readily recognize that this method and system will operate effectively for other types of methods for removing the portion of the barrier metal layer.  
         [0017]    To more particularly illustrate the method and system in accordance with the present invention, refer now to FIG. 2A depicting a block diagram of one embodiment of such a system  100  just after deposition of a barrier metal. The system  100  of the present invention includes a base  118 . The substrate  112  is placed on the base  118 . Trenches or vias are then formed in the substrate  112 . Next, a barrier metal layer  114  is deposited to prevent diffusion of any copper deposited later. In a preferred embodiment, the barrier metal layer  114  is deposited using CVD. Typically, the barrier metal layer  114  is much thicker near the center of the substrate  112  than near the edge. In a preferred embodiment, the barrier metal layer  114  is approximately three hundred Angstroms near the center at approximately thirty Angstroms near the edge of the substrate  114 . Generally, the barrier metal layer  114  is on the order of ten times thicker at the center of the substrate  112  than at the edge and back of the substrate  112 . After deposition of the barrier metal layer  114 , a seed layer  116  is deposited. The seed layer  116  improves adhesion of the copper layer, not shown, which is to be deposited later. FIG. 2B depicts the system  100  after deposition of the seed layer  116 .  
         [0018]    In accordance with the method and system, the barrier metal layer  114  is etched after deposition of the seed layer  116 . This etch removes the thin portions of the barrier metal layer  114  at the edge and back of the substrate. In a preferred embodiment, if the barrier metal layer  114  is composed of tungsten nitride, the etching gas is preferably NF 3 . In another embodiment, if the barrier metal layer  114  is composed of titanium nitride, the etching gas used may be chlorine.  
         [0019]    Etching the barrier metal layer  114  removes the portion of the barrier metal layer  114  at the edge and back of the substrate  112 . Because of the presence of the seed layer  116 , the metal in the central portion of the substrate  112  is not significantly etched. This removes the thinner portion of the barrier metal layer  114 . Typically, the thinner portion of the barrier metal layer  114  is at the edge and back of the substrate  112 . Thus, the etch removes the portion of the barrier metal layer  114  to which copper would otherwise adhere. Because of the seed layer  116 , the thinner portions of the barrier metal layer  114  have been removed while the thicker portion of the barrier metal layer  114  lying beneath the seed layer  116  remains substantially unchanged. Thus, in accordance with the method and system, the thin portion of the barrier metal layer  114  will be removed.  
         [0020]    Refer now to FIG. 2C, depicting one embodiment of the system  100  after etching of the barrier metal layer  114 . The thin portions of the barrier metal layer  114  have been removed, leaving only the thicker central portion lying beneath the seed layer  116 . Because the portion of the barrier metal layer at the edge and back of the substrate  114  was etched while the portion of the barrier metal layer at the center of the substrate  114  was protected by the seed layer  116 , the portion of the barrier metal layer  114  remaining can still prevent diffusion of the copper, not shown, that will be plated later. In addition, because the portion of the barrier metal layer  114  at the edge and back of the substrate  112  has been removed, there is no seed layer for copper to adhere to at these portions of the substrate. As a result, deposition of copper at the edges and back of the substrate is greatly reduced. The contamination due to copper peeling off of the substrate  112  is thereby reduced.  
         [0021]    A method and system has been disclosed for providing copper interconnects with reduced contamination due to copper deposited at the edge or rear of the substrate.  
         [0022]    Although the present invention has been described in accordance with the embodiments shown, one of ordinary skill in the art will readily recognize that there could be variations to the embodiments and those variations would be within the spirit and scope of the present invention. Accordingly, many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims.