Abstract:
High aspect ratio trenches may be filled with metal that grows more from the bottom than the top of the trench. As a result, the tendency to form seams or to close of the trench at the top during filling may be reduced in sonic embodiments. Material that encourages the growth of metal may be formed in the trench at the bottom, while leaving the region of the trench near the top free of such material to encourage growth upwardly from the bottom.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a divisional to U.S. patent application Ser. No. 12/948,897, filed on Nov. 18, 2010. This application is incorporated herein by reference in its entirety and for any purpose. 
     
    
     BACKGROUND 
       [0002]    This relates to semiconductor processing and, particularly, to techniques for filling cavities. 
         [0003]    A high aspect ratio cavity is a cavity, hole, depression, or trench whose depth is twice its width or more. Because of the high aspect ratio, cavity tilling tends to be problematic. For example, in the course of Idling such cavities, seam formation may result. A seam is basically an opening or crack within the tilled material. The seam is then prone to subsequent etching in ensuing processing. Another possibility is the formation of overhangs near the top of the trench which close off the trench and prevent complete filling of the trench. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1  is an enlarged, cross-sectional view of one embodiment at an early stage of manufacture; 
           [0005]      FIG. 2  is an enlarged, cross-sectional view subsequent thereto in accordance with one embodiment; 
           [0006]      FIG. 3  is an enlarged, cross-sectional view subsequent thereto in accordance with one embodiment; 
           [0007]      FIG. 4  is an enlarged, cross-sectional view in accordance with another embodiment; 
           [0008]      FIG. 5  is an enlarged, cross-sectional view subsequent thereto in accordance with the embodiment of  FIG. 4 ; and 
           [0009]      FIG. 6  is an enlarged, cross-sectional view subsequent thereto in accordance with one embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    Referring to  FIG. 1 , a high aspect ratio cavity  16  may he defined in a semiconductor structure  10  including a dielectric material  14 , such as a silicon dioxide dielectric material. The cavity may be formed in a dielectric material made up of a number of different layers in some embodiments. In one embodiment, the dielectric material  14  is over a semiconductor substrate  12 , such as a silicon substrate. 
         [0011]    In one conventional application, the substrate  12  may have a silicide  22  formed therein. The silicide may be covered by a metal layer  20 . For example, the metal layer  20  may be titanium and the suicide  22  may be titanium silicide. 
         [0012]    The metal layer  20  may be covered by a liner or layer  18  which partially lines the vertical extent of the cavity  16 , covers the metal layer  20 , and extends all the way down past the metal layer  20  to the substrate  12  in one embodiment. 
         [0013]    Generally, the layer  18  is a thin, conformal layer or layers which lines the bottom and sidewall of the cavity  16 . It may be grown, deposited, or formed using any technique. In one embodiment, the layer  18  may be titanium nitride. 
         [0014]    In sonic embodiments, the layer  18  is an adhesion promoting layer. As used herein, an “adhesion promoting layer” is a layer between two other layers that increases the adhesion between the two other layers. 
         [0015]    The cavity  16  may then be cleaned by a pattern dependent etch, a polish or by any technique that removes the upper horizontal portion of the layer  18  and an upper vertical portion of the layer  18  to expose only the upper sidewall portion  28 , as shown in  FIG. 2 . A “pattern dependent etch” is an etch whose etch rate depends on the pattern spacing. Thus, a pattern dependent etch tends to clear the upper sidewall portion  28  because it is more closely spaced than other features exposed directly to the etch. The pattern dependent etch or polish may be tuned to clean more or less of the depth of the cavity by adjusting etch or polish parameters, including processing time, chemistry, and energy. 
         [0016]    The etch or polish exposes surfaces of different composition, inside the cavity  16 , including the exposed sidewall portion  28 , which may be dielectric, for example, and bottom or lower surface of the cavity formed of the layer  18 , which may be a metal nitride, for example. These various exposed surfaces may be selected to have different deposition rates for a given deposited material. In such case, the deposited material may be “selectively” deposited on one exposed material because it builds up preferentially on that material. Thus, a material, blanket deposited over the structure, may build up preferentially or even exclusively on one exposed surface, because of the chemical composition of that surface, relative to others of the exposed surfaces. 
         [0017]    Thereafter, the exposed surfaces of the cavity may be subjected to chemical vapor deposition, resulting in different growth kinetics on different surfaces, and allowing control over the deposition location, fill direction, and growth rate inside the cavity, as shown in  FIG. 3 . Generally, in some embodiments, it is desirable to cause deposition to occur from growth that extends upwardly from the bottom of the cavity. The bottom up deposition may reduce the tendency to form overhangs and/or seams in the deposits that are undesirable. 
         [0018]    In some embodiments, the layer  18  may be an adhesion promoting layer to adhere the layer  24 . Thus, while layer  18  may be titanium nitride, the layer  24  may be tungsten in one embodiment. In one embodiment, the layer  18  increases the adhesion between a silicon dioxide dielectric  14  and the layer  24 . 
         [0019]    For example, in one embodiment, an adhesion promoting layer  18  may be deposited in the cavity  16  at the stage shown in FIG,  2 , using physical vapor deposition or chemical vapor deposition, to mention two examples. This may be followed by a pattern dependent etch or polish that removes the adhesion promoting layer from the sidewall portion  28 , while leaving the adhesion promoting layer at the bottom of the cavity. 
         [0020]    Then, when a metal or other layer  24  is selectively deposited, for example by chemical vapor deposition, and directional growth occurs from the bottom of the cavity upwardly, as shown in  FIG. 3 . This upward growth is due at least in part to the fact that there is no adhesion promoting layer  18  on the sidewall portion  28  and, therefore, the deposited layer  24  does not adhere to the sidewall portion  28 , in one embodiment, to the extent that it adheres to the layer  18 . This selective deposition may result in bottom up deposition in some embodiments. 
         [0021]    As another example, the adhesion promoting layer  18  may be deposited as described above, followed by the deposition of a thin metal nucleation layer. For example, the metal nucleation layer may be a pulsed nucleation layer in one embodiment. Thus, as an example, the pulsed nucleation layer  26 , shown in  FIG. 4 , may be a tungsten nucleation layer. 
         [0022]    Following the deposition of the thin nucleation layer  26 , a pattern dependent etch or polish may be used to remove the nucleation and adhesion promoting, layers  26  and  18  from the upper sidewall portion  28 , while leaving nucleation and adhesion promoting layers on the bottom of the cavity, as shown in  FIG. 5 . Thereafter, the same metal as used for the nucleation layer may be deposited or grown using selective deposition and directional growth from the bottom of the cavity. Again, this upward growth results where the nucleation layer and the adhesion promoting layer are present, which encourages growth of the deposited material, such as tungsten. 
         [0023]    Thus, as shown in  FIG. 6 , a layer  24 , such as metal, is deposited starting from the bottom of the cavity  16  and moving upwardly because of the presence of the layer  26  at the bottom of the cavity, but not at its upper extent. As a result, the metal does not begin to grow near the top of the cavity, but, preferentially, grows from the bottom. Because the upper sidewall portion  28  of the cavity is cleared or exposed, metal growth does not occur preferentially in this area, but, rather, fills up via selective deposition from the bottom, as opposed to filling from the top or from the sides of the top of the cavity. Filling from the top may have the tendency to close off the cavity, resulting in undesirable void formation. 
         [0024]    In some embodiments, cavity filling may he improved without the need to widen the open upper end of the cavity. This may be important in many densely populated technologies, such as semiconductor memory and logic circuitry. 
         [0025]    References throughout this specification to “one embodiment” or “an embodiment” mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one implementation encompassed within the present invention. Thus, appearances of the phrase “one embodiment” or “in an embodiment” are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may he instituted in other suitable forms other than the particular embodiment illustrated and all such forms may be encompassed within the claims of the present application. 
         [0026]    While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.