Abstract:
Sides of via hole do not bow horizontally, thereby preventing an increase of a resistance of a wiring layer connected to a conductor in the via hole. A semiconductor device comprises a first wiring layer, an insulating layer over the first wiring, a second wiring on the insulating layer, a first hole formed in the first wiring, a second hole formed in the insulating layer connecting with at least a part of the first hole, and a conductive material in first and second holes that electrically connects the first wiring layer to the second wiring layer.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a semiconductor device and a method of manufacturing the same, and more particularly to a semiconductor device and a method of manufacturing the same in which resistance of a wiring layer having a large area is not increased.  
           [0003]    2. Description of the Related Art  
           [0004]    As the size of wiring formations decrease, there is a tendency for the wiring intervals to become narrower, the wiring capacitance to increase, and the operating speed of the circuit to decrease. In order to prevent such a tendency, various kinds of interlayer films of low dielectric constant have been proposed. In FIG. 10, a related art which uses HSQ (Hydrogen Silsesquioxane) as an interlayer insulating film is shown. As shown in FIG. 10, a first oxide film  102  is formed on a substrate (not shown) and a first wiring layer  101  is formed on the oxide film  102 . A liner oxide film  106 , a HSQ film  107  and a plasma oxide film  108  are formed over the first wiring layer  101  together form an interlayer insulator. A second wiring layer  113  on the oxide film  108  is connected to the first wiring layer  101  by a tungsten plug  112 , which is formed in a via hole  109 . According to this related art, the HSQ film in the interlayer insulator, prevents the wiring resistance from increasing.  
           [0005]    However, in this related art, a cavity  100  forms in the sides of via hole  109  when etching through the interlayer insulator. The HSQ  107  is horizontally etched so that the sides of via hole  109  bow outwardly. In this event, via hole  109  is not completely filled with tungsten, leaving cavity  100  around the tungsten plug  112 . As a result, the absence of HSQ around the via hole causes the resistance to increase.  
           [0006]    Specifically, when the wiring layers cover a large area, the sides of the via hole are more easily swelled into the bow shape. The reason is that an application film, such as HSQ, is easily formed in a thick layer on the wiring layer having a large area. In order to perfectly bore the via hole in the interlayer insulator that includes the thick HSQ film, the etching is carried out so that the bottom of the via hole  109  exposes the underlying wiring layer  101 , once the wiring layer  101  is exposed, the etching does not progress downwardly, but progresses horizontally in the HSQ film  107 . When the etching rate of the HSQ is higher than that of any of the layers, the bowing of the sides of the via hole  109  occurs.  
           [0007]    Thus, it is desirable to prevent the horizontal spreading of the via hole in order to prevent the resistance from increasing.  
         SUMMARY OF THE INVENTION  
         [0008]    Therefore, the object of the present invention is to solve the above problem.  
           [0009]    In order to accomplish this object, according to a first aspect of the present invention, there is provided a semiconductor device comprising a first wiring layer, an insulating layer over the first wiring layer, a second wiring layer on the insulating layer, a first hole formed in the first wiring layer, a second hole formed in the insulating layer connecting with at least a part of the first hole, and a conductive material in the first and second holes that electrically connects the first wiring layer to the second wiring layer.  
           [0010]    According to a second aspect of the present invention, there is provided a method of manufacturing a semiconductor device comprising, forming a first wiring layer, forming a first hole in the first wiring layer, forming an insulating layer on the wiring layer and in the first hole, forming a second hole in the insulating layer, the second hole exposing at least a part of an inner side surface of the first hole, and filling the second hole with a conductive material.  
           [0011]    According to a third aspect of the present invention, there is provided a method of avoiding of over-etching of an insulator layer, comprising, forming a first horizontal wiring layer, forming a first hole in the first wiring layer, forming an insulating layer on the wiring layer and in the first hole, etching a second hole in the insulating layer, the second hole exposing at least a part of an inner side surface of the first hole, the first hole having a depth that avoids horizontal over-etching of the insulating layer above the first hole when forming the second hole, and filling the second hole with a conductive material.  
           [0012]    According to the present invention, the second hole is preventing from horizontally swelling. Therefore, a resistance of the wiring layer does not increase. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The above and other objects as well as advantages of the present invention will become clear by the following description of the preferred embodiments of the present invention with reference to the accompanying drawings, wherein:  
         [0014]    [0014]FIG. 1 is a plan view showing the structure of an embodiment of a semiconductor device according to the present invention;  
         [0015]    [0015]FIG. 2 is a cross sectional view taken along the line II-II in FIG. 1;  
         [0016]    [0016]FIG. 3 is a cross sectional view showing an embodiment of a method of manufacturing a semiconductor device according to the present invention;  
         [0017]    [0017]FIG. 4 is a cross sectional view showing a step next to the step shown in FIG. 3;  
         [0018]    [0018]FIG. 5 is a cross sectional view showing a step further next to the step shown in FIG. 4;  
         [0019]    [0019]FIG. 6 is a cross sectional view showing a step further next to the step shown in FIG. 5;  
         [0020]    [0020]FIG. 7 is a graphical representation showing the confirmation of the effect;  
         [0021]    [0021]FIG. 8 is a plan view showing the structure of another embodiment of a semiconductor device according to the present invention;  
         [0022]    [0022]FIG. 9 is a cross sectional view taken along the line IX-IX in FIG. 8; and  
         [0023]    [0023]FIG. 10 is a cross sectional view showing the structure of a semiconductor device according to a related art. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    The width of a underlying wiring layer  1  shown in FIG. 1, is equal to or larger than 250 μm. This is considered to provide a large area for the wiring layer, when the wiring layer extends at least a similar distance in a perpendicular direction. As shown in FIG. 2, a first oxide film  2  is formed on the upper surface of a substrate (not shown). The thickness of the first oxide film  2  is about 800 nm. The first wiring layer  1  is formed on the upper surface of the first oxide film  2 .  
         [0025]    The first wiring layer  1  has three layers, i.e., in the order from the lowest layer, a barrier metal layer  3  about 80 nm thick, an aluminum layer  4  about 400 nm thick, and an antireflection film  5  about 70 nm thick. The barrier metal layer  3 , in the order from the lowest layer, has a titanium layer with about 30 nm thickness and a titanium nitride layer with about 50 nm thickness. Also, the antireflection film  5 , in the order from the lowest layer, has a titanium layer with about 50 nm thickness and a titanium nitride layer with about 20 nm thickness.  
         [0026]    A liner oxide film  6  is formed on the surface of the underlying wiring layer  1 . In this connection, the liner oxide film  6  is formed of a plasma oxide film about 50 nm thick. An HSQ (Hydrogen Silsesquioxane) layer  7  is formed on the liner oxide film. A plasma oxide film  8  is formed on the HSQ layer  7 . The liner oxide film  6 , the HSQ layer  7  and the plasma oxide film  8  constitute an interlayer insulator.  
         [0027]    A first hole  9  is formed through the interlayer insulator. A second hole  11  is formed in the underlying wiring layer  1  and is an extension of the first hole  9 . Though the depth of the second hole  11  in the underlying wiring layer  1  is arbitrary, the second hole  11  has a sufficient depth to expose a portion of the aluminum layer  4 . It is preferable in terms of the etching rate that the effective diameter (or the cross-sectional area) of the second hole  11  is slightly smaller (or narrower) than the effective diameter (or the cross-sectional area) of the first hole.  
         [0028]    As an example, if the diameter of the first hole  9  is 0.28 μm, then the diameter of the second hole  11  is 0.24 μm. The second hole  11  may extend into the oxide film as shown in FIG. 2, although this is not required.  
         [0029]    Tungsten  12  may be used to fill the first hole  9  and the second hole  11 . A second wiring layer  13  is formed on the upper surfaces of the tungsten  12  and the plasma oxide film  8 . The second wiring layer  13  has three layers, i.e., in the order from the lowest layer, a barrier metal layer  14 , an aluminum layer  15  and an antireflection film  16 . The barrier metal layer  14 , in the order from the lowest layer, has a titanium layer about 30 nm thick and a titanium nitride layer about 50 nm thick. The antireflection film  16 , in the order from the lowest layer, has a titanium layer about 20 nm thick and a titanium nitride layer about 50 nm thick.  
         [0030]    FIGS.  3  to  6  are cross sectional views respectively showing the steps of a manufacturing method of manufacturing the semiconductor device shown in FIG. 2. As shown in FIG. 3, the first oxide film  2  is formed on the upper surface of a semiconductor device substrate (not shown) so as to have a thickness of 800 nm by utilizing a plasma CVD (Chemical Vapor Deposition) method. Next, the barrier metal layer  3 , the aluminum layer  4 , and the antireflection film  5  are respectively formed on the upper face of the first oxide film  2  in this order by sputtering.  
         [0031]    Next, the three layers which have been formed in the previous process are patterned by photolithography and reactive ion etching to form the underlying wiring layer  1 . By carrying out this patterning, the second hole  11  is formed through the underlying wiring layer  1  at the same time.  
         [0032]    Next, as shown in FIG. 4, the liner oxide film  6  formed of the plasma oxide film is formed over the underlying wiring layer  1 . Next, the HSQ layer  7  is formed over the upper surface of the liner oxide film  6  by utilizing an application and baking technique. Next, the plasma oxide film  8  1,400 nm thick is formed on the upper surface of the HSQ layer  7 . Then, the surface of the plasma oxide film  8  is polished by utilizing a CMP (Chemical Mechanical Polishing) method to flatten the surface thereof, thereby adjusting the thickness of the plasma oxide film  8 .  
         [0033]    Next, as shown in FIG. 5, the first hole  9  is selectively formed by utilizing a photolithography process and reactive ion etching. After completion of the formation of the first hole  9 , over-etching is carried out to remove the HSQ layer  7  and the liner oxide film  6  in the second hole  11 . The depth of the second hole  11  may be adjusted so that the bowing of the sides of the HSQ  7  does not occur excessively in the first hole  9 . According to this method, of the present invention when this over-etching is carried out the etching is allowed to progress downwardly, that is into the second hole  11 . Since the etching is allowed to progress downwardly the horizontal etching of the HSQ is avoided, thereby preventing the formation of the cavity around the tungsten plug.  
         [0034]    When reactive ion etching the first hole  9  and the second hole  11 , C 4 F 8 , Ar, O 2  and CO may be collectively employed as the etching gas, the atmospheric pressure may be about 50 mTorr, the temperature may be about 0° C., and the electric power may be about 2,000 W.  
         [0035]    Next, as shown in FIG. 6, the inner surfaces of the first hole  9  and the second hole  11  are coated with a titanium nitride layer  21  about 50 nm thick by sputtering. Then, the first hole  9  and the second hole  11  are filled with tungsten  12  by a CVD method. Next, parts of the titanium nitride layer  21  and the tungsten  12  which are formed on the plasma oxide film  8  are removed by a CMP method. Then, the layers  14 ,  15  and  16  as described above are sequentially formed by sputtering, and finally, those layers are patterned by photolithography and reactive ion etching to form the second wiring layer  13 .  
         [0036]    By way of further explanation, when the reactive ion etching of the first hole  9  reaches the underlying wiring layer  1 , the material that remains to be etched is the wiring layer  1  and the HSQ layer  7  since the etching rate of HSQ is high under the conditions described above, the HSQ layer  7  is more easily etched than the wiring layer and thus the HSQ is etched horizontally.  
         [0037]    On the contrary, according to the present invention, during the reactive in etching of the first hole  9 , the HSQ that fills the second hole is etched and sides of the via hole  9  are effectively prevented from being etched horizontally.  
         [0038]    [0038]FIG. 7 is a graphical representation showing the effect of the present invention. FIG. 7 shows the relation between the width of the underlying wiring layer  1  and the yield of the via holes. One via hole is present at the center of the underlying aluminum wiring layer  1  and the size thereof is 0.28 μm. With respect to the yield of the via holes, there is established the standard in which when the via hole resistance (including the wiring resistance) is equal to or lower than 100 ohms, the via hole of interest is judged to be acceptable.  
         [0039]    In FIG. 7, the ordinate represents the percentage which is obtained by dividing the number of acceptable chips on a wafer by the total number of chips. As is apparent from FIG. 7, in the case of the prior art example in which the second hole is not provided in the underlying aluminum wiring layer, when a width of the aluminum wiring layer becomes equal to or larger than 250 μm, the yield of the via holes is abruptly reduced. In the case of the first and second embodiments according to the present invention, it is possible to maintain the yield of 100% over the range shown in FIG. 7.  
         [0040]    [0040]FIGS. 8 and 9 show a second embodiment of the semiconductor device according to the present invention. In this embodiment, the cross-sectional area or the effective diameter of the first hole  9  is roughly equal to that of the second hole  11 . Both of the first hole  9  and the second hole  11  are slightly shifted horizontally (in the direction intersecting perpendicularly the layer lamination direction). In addition, the second hole  11  is slightly horizontally shifted with respect to the first hole  9  in the range of ¼ to ½ of the effective diameter of the first hole  9 . Thereby, the HSQ film  7  remains in a part of the second hole. In this embodiment, the side surface of the via hole  9  is effectively prevented from being etched horizontally. Therefore, as shown in FIG. 7, it is possible to maintain the yield of 100% over the range. Further, in the present embodiment, since the contact area between the upper face of the underlying wiring layer  1  and tungsten filled in the via hole  9  s larger than that of the first embodiment as already described, it is possible to reduce the via hole resistance.  
         [0041]    While the present invention has been particularly shown and described with reference to the preferred embodiments, it will be understood that the various changes and modifications will occur to those skilled in the art without departing from the scope and true spirit of the invention. The scope of the invention is therefore to be determined solely by the appended claims.