Abstract:
There is described a semiconductor device which has an isolation region, the isolation region being polished by means of chemical-and-mechanical polishing, and which prevents occurrence of variations in a finished state of active regions even in a case where a large isolation area is present. An isolation region for separating active regions is formed on a semiconductor wafer. An annular dummy pattern is formed in an inactive region of greater than a predetermined size, so as to surround the isolation region. An isolation region is ensured between the active regions surrounding the inactive region and the dummy pattern.

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 whose isolation regions are flattened by means of chemical-and-mechanical polishing (hereinafter called simply “CMP”) as well as to a method of manufacturing the semiconductor device.  
           [0003]    2. Description of the Background Art  
           [0004]    [0004]FIG. 6 is a plan view showing a semiconductor wafer processed according to a conventional manufacturing method. As shown in FIG. 6, reference numeral  10  designates an isolation region formed by means of the trench isolation technique. Reference numeral  12  designates active regions separated by the isolation region  10 . FIG. 7 is a cross-sectional view for describing the conventional trench isolation technique for forming on a semiconductor wafer the isolation region  10  shown in FIG. 6.  
           [0005]    According to the trench isolation technique, a nitride film  16  is formed on a silicon layer  14  of the semiconductor wafer. Next, a trench  18  which is to become the isolation region  10  is formed in the silicon layer  14  and the nitride film  16 . Next, an oxide is deposited over the entire surface of a semiconductor wafer so as to be embedded in the trench  18 . Finally, undesired oxides are removed by means of CMP while the nitride film  16  is used as a stopper film. As a consequence, oxides remain only within the trench  18 , thus forming the isolation region  10  which separates the isolation regions  12 .  
           [0006]    A CMP operation employed in the course of forming the isolation region  10  is performed on condition that an oxide film is abraded at a higher rate than is a nitride film. For this reason, a so-called dishing phenomenon arises in the isolation region  10  when the isolation region  10  occupies a comparatively large area of the semiconductor wafer, as shown in FIG. 7.  
           [0007]    If a dishing phenomenon arises in a specific isolation region  10 , intensive force arises in the active regions  12  adjoining the isolation region  10 . Consequently, the nitride film  16  covering the active regions  12  that undergo intensive stress is abraded much more than is the nitride film  16  covering other regions. As mentioned above, in a case where a large isolation region  10  is present, the structure of a conventional semiconductor device and the conventional trench isolation technique pose a problem of an active region being apt to vary in its finished state.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention has been conceived to solve the foregoing problem and is aimed at providing a semiconductor device which prevents occurrence of variations in a finished state of active regions even in a case where a large isolation area is present.  
           [0009]    The present invention is also aimed at providing a method of manufacturing a semiconductor device, which device prevents occurrence of variations in a finished state of active regions even in a case where a large isolation area is present.  
           [0010]    The above objects of the present invention are achieved by . . . The . . . includes.  
           [0011]    The above objects of the present invention are achieved by . . . The . . . includes.  
           [0012]    Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a plan view showing a semiconductor wafer processed by a manufacturing method according to a first embodiment of the present invention;  
         [0014]    [0014]FIG. 2 is a cross-sectional view showing the semiconductor wafer shown in FIG. 1;  
         [0015]    [0015]FIG. 3 is a plan view for describing a proffered variation of the first embodiment;  
         [0016]    [0016]FIGS. 4A and 4B are plan views for describing a method for determining width of a dummy pattern in the first embodiment;  
         [0017]    [0017]FIG. 5 is a plan view for describing a method for selecting inactive regions in which dummy patterns are to be formed in the first embodiment;  
         [0018]    [0018]FIG. 6 is a plan view showing a semiconductor wafer processed according to a conventional manufacturing method; and  
         [0019]    [0019]FIG. 7 is a cross-sectional view of the semiconductor wafer shown in FIG. 6. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]    A preferred embodiment of the present invention will be described hereinbelow by reference to the accompanying drawings. Throughout the drawings, like reference numerals designate like elements, and repetition of their explanations is omitted.  
         [0021]    [0021]FIG. 1 is a plan view showing a semiconductor wafer processed by a manufacturing method according to a first embodiment of the present invention. As shown in FIG. 1, a plurality of active regions  12  are formed on the surface of a semiconductor wafer. In the area where no active region  12  is formed; that is, in an inactive region on the semiconductor wafer are formed an isolation region  10  and a dummy pattern  20 . The dummy pattern  20  is an annular pattern having no electrical function, and being formed in an inactive region having greater size than a predetermined size such that an isolation region  10  of predetermined width is formed between the dummy pattern  20  and active regions  12 .  
         [0022]    [0022]FIG. 2 is a cross-sectional view showing the semiconductor wafer shown in FIG. 1. Next will be described the method of manufacturing a semiconductor device according to the present embodiment, by reference to FIG. 2. As shown in FIG. 2, according to the manufacturing method of the present embodiment, the nitride film  16  is formed on the silicon layer  14  of the semiconductor wafer. Further, the trench  18  which is to become the isolation region  10  is formed in the silicon layer  14  and the nitride film  16 . At this time, in the inactive region  22  having greater size than a predetermined size, there are formed trenches  18  in an area surrounded by the dummy pattern  20  and an area between the dummy pattern  20  and the active regions  12 .  
         [0023]    An oxide is deposited over the entire surface of the semiconductor wafer so as to be embedded in the trenches  18 . At this time, the oxide is deposited not only in the trenches  18  but also on the surface of the nitride film  16 .  
         [0024]    In order to remove undesired oxides deposited on the surface of the nitride film  16 , the semiconductor wafer is subjected to CMP. As a consequence, oxides remain in only the trench  18 , whereby the isolation region  10  is formed in the areas between the individual active regions  12 , the areas between the active regions  12  and the dummy pattern  20 , and the area surrounded by the dummy pattern  20 .  
         [0025]    In the present embodiment, the CMP operation is performed while the nitride film  16  is taken as a stopper film. For this reason, the CMP operation is performed on condition that the oxide film is abraded at a higher rate than is the nitride film  16 . During the CMP operation, a recess attributable to a so-called dishing phenomenon is apt to be formed in the isolation region  10  formed within the dummy pattern  20 ; that is, the isolation region  10  of a comparatively large area. In the present embodiment, since the width of the isolation region  10  located between the dummy pattern  20  and the active regions  12  is set so as not to cause a dishing phenomenon, no recess attributable to a dishing phenomenon is formed in the isolation region  10 .  
         [0026]    [0026]FIG. 2 shows a recess which is formed by means of a dishing phenomenon in the isolation region  10  surrounded by the dummy pattern  20 . If such a recess is formed in the isolation region  10 , during a CMP operation intensive force arises in the nitride film  16  of the dummy pattern  20  adjoining the isolation region  10 . At a point in time when smoothing of the surface of the semiconductor substrate using CMP is completed, the nitride film  16  of the dummy pattern  20  has become thinner than the nitride film  16  of the active regions  12 , especially along the inner periphery thereof.  
         [0027]    In contrast, during the course of the CMP operation, substantially uniform force acts on the nitride film  16  formed outside the dummy pattern  20 ; that is, the nitride film  16  formed over the active regions  12 . For this reason, according to the manufacturing method of the present embodiment, the nitride film  16  covering the active regions  12  can be made substantially uniform over the entire semiconductor wafer.  
         [0028]    In the present embodiment, no electrical function is imparted to the dummy pattern  20 . Therefore, variations in the thickness of the nitride film  16  covering the dummy pattern  20  do not affect the characteristic of the semiconductor device at all. Accordingly, the manufacturing method and the structure of the semiconductor device according to the present embodiment enables materialization of a semiconductor device having a stable characteristic and the active regions  12  uniformly formed over the entire surface of a semiconductor chip.  
         [0029]    In the first embodiment, the dummy pattern  20  is limited to a continuous annular pattern. However, the present invention is not limited to such an embodiment. More specifically, as shown in FIG. 3, the dummy pattern  20  may be embodied by means of arranging a plurality of isolated patterns  24  into an annular layout.  
         [0030]    In the present embodiment, the width of the dummy pattern  20  is set to an arbitrary value. However, the width of the dummy pattern  20  may be determined by the size of the isolation region  10  formed inside the dummy pattern  20  or by the size of the inactive region  22  in which the dummy pattern  20  is located. As shown in FIGS. 4A and 4B, in a case where the isolation region  10  and the inactive region  22  have small areas (designated by, for example, A 1 ), the width of the dummy pattern  20  may be made small (W 1 ). In contrast, in a case where the isolation region  10  and the inactive region  22  have large areas (designated by, for example, A 2 ), the width of the dummy pattern  20  may be made large (W 2 ).  
         [0031]    In the previous embodiment, the dummy pattern  20  is formed within the inactive region  22  having greater size than a predetermined size. The predetermined size may be limited to a size in which a circle having a diameter of 10 μm or more can be formed, as shown in FIG. 5. By means of such a limitation, the dummy pattern  20  can be arranged in only the area where an actual effect is expected.  
         [0032]    Since the present invention is configured in the manner as mentioned above, the following advantages are yielded.  
         [0033]    According to a first aspect of the present invention, a dummy pattern is formed within an inactive region having greater size than a predetermined size. A recess may arise in an isolation region surrounded by the dummy pattern, for reasons of a dishing phenomenon during the course of formation of the dummy pattern. Even in such a case, an adverse effect which would be caused by the recess is absorbed by the dummy pattern. Therefore, all active regions are formed uniformly.  
         [0034]    According to a second aspect of the present invention, no electrical function is imparted to the dummy pattern. Therefore, the characteristic of a semiconductor device can be made stable regardless of the state of a dummy pattern.  
         [0035]    According to a third aspect of the present invention, the width of a dummy pattern is changed in accordance with the size of an isolation region which is to be surrounded by the dummy pattern. As a consequence, a wasteful dummy pattern region is minimized, and active regions can be efficiently protected.  
         [0036]    According to a fourth aspect of the present invention, a dummy pattern can be formed in only the inactive region where a dishing phenomenon would arise. For this reason, according to the present invention, active regions can be efficiently protected without involvement of formation of a wasteful dummy pattern.  
         [0037]    Further, the present invention is not limited to these embodiments, but variations and modifications maybe made without departing from the scope of the present invention.  
         [0038]    The entire disclosure of Japanese Patent Application No. 2000-197552 filed on Jun. 30, 2000 including specification, claims, drawings and summary are incorporated herein by reference in its entirety.