Abstract:
A method of forming a semiconductor device having aluminum lines therein, wherein the occurrence of lateral extrusions and voids are reduced. The method comprises the formation of a metal stack on a surface of the substrate, wherein the aluminum layer of the metal stack is deposited under controlled conditions; etching the metal lines in the metal stack; and exposing the substrate to a subsequent anneal.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates generally to the field of semiconductor processing. More particularly, the present invention provides a method of producing aluminum lines on a substrate which prevents lateral extrusions between the lines, and the device so formed. 
     2. Related Art 
     When forming metal lines, a general three step process is often used. First, metal layers are formed on a substrate by sputtering a specific sequence of metals, including aluminum. Second, the desired metal lines are formed by photolithographically etching the metal layers. Third, the substrate is annealed to set the lines. Conventional sputtering techniques, however, tend to produce lateral extrusions during the photolithographic and annealing steps of the aluminum line formation process. These lateral extrusions may produce metal shorts between the aluminum lines. This becomes increasingly problematic as the devices become smaller, which forces the metal lines closer together. In addition, lateral extrusions pose reliability concerns-due to the metal “opens” or voids which may be produced within the metal lines due to volume changes. 
     Therefore, there exists a need in the industry for a method of forming aluminum metal lines on a substrate which prevents lateral extrusions between the aluminum metal lines. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method of forming a semiconductor device that solves the above stated problems, and the device so formed. 
     The present invention provides a method for controlled deposition of aluminum onto a substrate, comprising the steps of: providing a substrate; heating the substrate to a temperature less than about 200° C.; providing a target from which aluminum is released; and sputtering aluminum onto the substrate, wherein the sputtering step includes controlling a power density to the target to be less than about 11 W/cm 2 . This aspect allows for the reduced production of lateral extrusions during the formation of the aluminum lines of a semiconductor device. This aspect further provides for reduced occurrences of shorts within the device. This aspect also provides a clampless deposition procedure without the need for temperature control, and wherein the power density to the target is controlled to be less than 11 W/cm 2 . 
     The second general aspect provides a method of forming aluminum lines, comprising the steps of: providing a substrate; heating the substrate to a temperature less than about 200° C.; and sputtering aluminum from a target onto the substrate, wherein the sputtering comprises control of a power density to the target to be less than about 11 W/cm 2 . This aspect allows for advantages similar to those associated with the first aspect. 
     The third general aspect provides a method of reducing lateral extrusion in aluminum lines on a substrate, comprising the steps of: providing a substrate; heating the substrate to a temperature less than about 200° C.; and sputtering aluminum from a target onto the substrate, wherein the sputtering comprises control of a power density to the target to be less than about 11 W/cm 2 . This aspect allows for advantages similar to those associated with the first aspect. 
     The fourth general aspect provides a semiconductor device having reduced lateral extrusions produced therein during the formation of aluminum lines. This aspect provides a semiconductor device produced using the method of, and possessing advantages similar to, the first aspect. 
     The foregoing and other features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The preferred embodiments of this invention will be described in detail, with reference to the following figures, wherein like designations denote like elements, and wherein: 
     FIG. 1 depicts a flow chart which illustrates a method of forming a semiconductor device in accordance with a preferred embodiment of the present invention; 
     FIG. 2 depicts a cross-sectional view of a substrate having a dielectric layer thereon in accordance with a preferred embodiment of the present invention; 
     FIG. 3 depicts a cross-sectional view of the substrate having a first metal layer thereon in accordance with a preferred embodiment of the present invention; 
     FIG. 4 depicts a cross-sectional view of the substrate having a second metal layer thereon in accordance with a preferred embodiment of the present invention; 
     FIG. 5 depicts a cross-sectional view of the substrate having a third metal layer thereon in accordance with a preferred embodiment of the present invention; 
     FIG. 6 depicts a cross-sectional view of the substrate having a refractory layer thereon in accordance with a preferred embodiment of the present invention; 
     FIG. 7 depicts a top view of the device having metal lines thereon in accordance with a preferred embodiment of the present invention; 
     FIG. 8 depicts a sputtering tool having metal deposition chambers therein in accordance with a preferred embodiment of the present invention; and 
     FIG. 9 depicts a metal deposition chamber in accordance with a preferred embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Although certain preferred embodiments of the present invention will be shown and described in detail, it should be understood that various changes and modifications may be made without departing from the scope of the appended claims. The scope of the present invention will in no way be limited to the number of constituting components, the materials thereof, the shapes thereof, the relative arrangement thereof, etc., and are disclosed simply as an example of the preferred embodiment. Although the drawings are intended to illustrate the present invention, the drawings are not necessarily drawn to scale. 
     Referring to the drawings, FIG. 1 illustrates a flow chart generally describing the process used to manufacture a semiconductor device having metal lines, such that the formation of lateral extrusions and voids are reduced. In particular, FIG. 2 illustrates a substrate  10 , preferably a silicon wafer, having an inter-layer-dielectric (ILD)  12  formed on a first surface  11  of the substrate  10  using conventional methods. The substrate  10  is then placed in a degas chamber  30 , shown in FIG.  8 . Within the degas chamber  30 , the substrate  10  is exposed to temperatures less than approximately 200° C. for about 30 seconds, to prepare the substrate  10  for processing (step  1  of FIG.  1 ). 
     The substrate  10  then passes along path  29  to a first metal deposition chamber  32  within a sputtering tool  28  (refer to FIG.  8 ). The first metal deposition chamber  32  contains a high vacuum, approximately 10 −9  torr, produced by a vacuum pump  34 . The first metal deposition chamber  32  has an operating or deposition pressure of approximately 2-6 millitorr therein. A power density of approximately 1.21 W/cm 2  is applied via a power source  36  to the first metal deposition chamber  32  to sputter a first metal layer  14  on the substrate  10 , as shown in FIG. 3 (step  2  of FIG.  1 ). The first metal layer  14  is preferably titanium (Ti), having a thickness of approximately 20-50 nm, however, other refractory metals may also be used, i.e., tungsten (W), etc. 
     The substrate  10  is then transferred along path  29  to a second metal deposition chamber  38  of the sputtering tool  28  (FIG.  8 ). A gas mixture of approximately 2:1 N 2 :Ar is input into the second metal deposition chamber  38 . The second metal deposition chamber  38  also contains a high vacuum, approximately 10 −9  torr, provided by a vacuum pump  40 . The second metal deposition chamber  38  has an operating pressure of approximately 2-6 millitorr therein. A power density of approximately 4.83 to 7.26 W/cm 2  is applied, via a power source  41 , to the second metal deposition chamber  38  to sputter a second metal layer  16  onto the substrate  10 , as shown in FIG. 4 (step  3  of FIG.  1 ). The second metal layer  16 , preferably titanium nitride (TiN), has a thickness of approximately 20-50 nm. 
     The substrate  10  is then transferred along the path  29  to a third metal deposition chamber  42  of the sputtering tool  28  (FIG.  8 ). The third metal deposition chamber  42  contains argon (Ar) gas under approximately 2-6 millitorr of pressure. The third metal deposition chamber  42  contains a vacuum of approximately 10 −9  torr, similar to that of the first and second metal deposition chambers  32 ,  38 , which is provided by a vacuum pump  44 . The third metal deposition chamber  42  has an operating or deposition pressure of approximately 2-6 millitorr therein. The power density applied to the substrate  10  within the third metal deposition chamber  42  is controlled to be less than about 11 W/cm 2 . As a result, a third metal layer of aluminum  18  is formed, via sputtering, on the substrate  10 , as shown in FIG. 5 (step  4  of FIG.  1 ). The third metal layer  18  has a thickness of approximately 200-700 nm. 
     The substrate  10  is then transferred along path  29  to a fourth metal deposition chamber  48  of the sputtering tool  28  (FIG.  8 ). A gas mixture of approximately 2:1 N 2 :Ar is input into the fourth metal deposition chamber  48 . The fourth metal deposition chamber  48  also contains a high vacuum, approximately 10 −9  torr, provided by a vacuum pump  50 . The fourth metal deposition chamber  48  has an operating pressure of approximately 2-6 millitorr therein. A power density of approximately 4.83 to 7.26 W/cm 2  is applied, via a power source  52 , to the fourth metal deposition chamber  48  to sputter a refractory layer  20  onto the substrate  10 , as shown in FIG. 6 (step  5  of FIG.  1 ). The refractory layer  20  is preferably TiN, having a thickness of approximately 20-50 nm. 
     After the metal stack  22  is formed, as illustrated in FIG. 6, the substrate  10  is removed from the sputtering tool  28 , and  15  transferred along the path  29  to a cooling chamber  54  (FIG.  8 ), having a temperature between about 25-50° C. The substrate  10  is held in the cooling chamber  54  for approximately 30-60 seconds (step  6  of FIG.  1 ). 
     The metal stack  22  of the substrate  10  is patterned, then etched to form metal lines  24  (step  7  of FIG.  1 ). FIG. 7 shows a top view of a device  26  produced after the metal lines  24  are formed within the substrate  10 . The device  26  is then annealed at a temperature less than approximately 400° C. for about 30 minutes to set the metal lines  24  (step  8  of FIG.  1 ). The device  26  formed using the above described method does not contain lateral extrusions or voids that often lead to shorts and other problems. 
     FIG. 9 shows the first metal deposition chamber  32  of the  5  sputtering tool  28  in greater detail. Each of the four metal deposition chambers  32 ,  38 ,  42 ,  48  function in a similar manner. As an example, the first metal deposition chamber  32  contains a connection to a vacuum pump  34 , a gas valve  56 , and a power source  36 . In addition, each chamber  32 ,  38 ,  42 ,  48  contains a clampless pedestal or wafer holder  58 , upon which the substrate  10  rests, and a target  60  from which the metal  62  is released toward the substrate  10  for the formation of the respective metal layers  14 ,  16 ,  18 ,  20 . 
     It should be noted that the second metal layer  16  and refractory layer  20 , are preferably TiN because this compound is extremely compatible with the aluminum used in the third metal layer  18  which forms the metal lines  24 . For instance, the TiN used in the refractory layer  20  provides a redundant layer for electro migration of the aluminum in the third metal layer  18 . 
     It should also be noted that the pedestal  58 , within the metal deposition chambers  32 ,  38 ,  42  and  48 , does not need to have active temperature control of the substrate  10 . Rather, the process described in the present invention reduces the occurrence of lateral extrusions by controlling the power density to the target. 
     While this invention has been described in conjunction with the specific embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the preferred embodiments of the invention as set forth above are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention as defined in the following claims.