Abstract:
A method for manufacturing a semiconductor device includes preparing a substrate having a low-dislocation region and a high-dislocation region having a higher dislocation density than dislocation density of the low-dislocation region; forming an insulating film on the low-dislocation region surrounding the high-dislocation region but not covering the high-dislocation region; and forming a nitride-based semiconductor layer on the substrate, after forming the insulating film.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a method for manufacturing a semiconductor device provided with a nitride semiconductor layer formed on a substrate having a low-dislocation region and a high-dislocation region; and specifically, relates to a method for manufacturing a semiconductor device that can improve the surface flatness of the nitride semiconductor layer. 
         [0003]    2. Background Art 
         [0004]    When a nitride semiconductor layer is formed on a substrate having a low-dislocation region and a high-dislocation region, abnormal growth generated on the high-dislocation region may be transmitted to the low-dislocation region causing the degradation of the flatness of the nitride semiconductor layer. To solve such a problem, ,a method for preventing abnormal growth on the high-dislocation region by forming an insulating film so as to cover the high-dislocation region has been proposed (for example, refer to Japanese Patent Application Laid-Open No. 2004-221480). 
       SUMMARY OF THE INVENTION 
       [0005]    Conventionally, since an insulating film has been formed so as to cover a high-dislocation region, the insulating film has inevitably widened. Therefore, during the growth of the nitride semiconductor layer, materials are diffused from the insulating film, and the nitride semiconductor layer is thickened in the vicinity of the insulating film. As a result, there have been problems wherein the surface flatness of the nitride semiconductor layer is degraded, and the yield of elements is lowered. 
         [0006]    In view of the above-described problems, an object of the present invention is to provide a method for manufacturing a semiconductor device that can improve the surface flatness of the nitride semiconductor layer. 
         [0007]    According to the present invention, a method for manufacturing a semiconductor device comprises: preparing a substrate having a low-dislocation region and a high-dislocation region having a higher dislocation density than a dislocation density of the low-dislocation region; forming an insulating film on the low-dislocation region so as to surround the high-dislocation region but not to cover the high-dislocation region; and forming a nitride-based semiconductor layer on the substrate after forming the insulating film. 
         [0008]    The present invention makes it possible to improve the surface flatness of the nitride semiconductor layer. 
         [0009]    Other and further objects, features and advantages of the invention will appear more fully from the following description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIGS. 1 to 3  are sectional views for illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. 
           [0011]      FIG. 4  is a top view showing a semiconductor device manufactured using the manufacturing method according to the comparative example. 
           [0012]      FIG. 5  is a top view showing a semiconductor device manufactured using the manufacturing method according to the present embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0013]    A method for manufacturing a semiconductor device according to an embodiment of the present invention will be described referring to the drawings.  FIGS. 1 to 3  are sectional views for illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention. 
         [0014]    First, as shown in  FIG. 1 , a GaN substrate  14  having a low-dislocation region  10  and a high-dislocation region  12  having a higher dislocation density than the low-dislocation region  10  is prepared. The low-dislocation region  10  has Ga polarity, and the high-dislocation region  12  has N polarity. 
         [0015]    Next, as shown in  FIG. 2 , an insulating film  16  composed of SiO 2  or SiN is formed on the low-dislocation region  10  so as to surround the high-dislocation region  12  but not to cover the high-dislocation region  12 . The width w of the insulating film  16  is 10 μm, and the thickness thereof is 1000 Å. The insulating film  16  is formed using vapor deposition, sputtering, CVD or the like. Here, the insulating film  16  is formed 10 μm apart from the outer edge of the high-dislocation region  12 . 
         [0016]    Next, as shown in  FIG. 3 , a nitride semiconductor layer  18  composed of Al x In y Ga (1−x−y) N (0≦x≦1, 0≦1) is formed on the GaN substrate  14 . At this time, the nitride semiconductor layer  18  is little grown on the high-dislocation region  12  and the insulating film  16  having reverse polarity from the polarity of the low-dislocation region  10 . However, the nitride semiconductor layer  18  is formed on the GaN substrate  14  between the high-dislocation region  12  and the insulating film  16 . 
         [0017]    In addition, light-emitting elements (not shown) are periodically formed on the nitride semiconductor layer  18  formed on the low-dislocation region  10 . Specifically, the nitride semiconductor layer  18  is constituted of an n-type GaN layer of a thickness of 1 μm, an n-type A 0.07 Ga 0.93 N of a thickness of 1 μm, an n-type GaN layer of a thickness of 100 nm, an active layer, an p-type Al 0.2 Ga 0.8 N layer of a thickness of 20 nm, a p-type GaN layer of a thickness of 10 nm, a p-type Al 0.07 Ga 0.93 N of a thickness of 400 nm, and a p-type GaN layer of a thickness of 100 nm sequentially laminated from the GaN substrate  14 . The active layer is a multiple quantum well wherein 3 cycles of In 0.02 Ga 0.9 N layers each having a thickness of 3.5 nm and In 0.02 Ga 0.98 N layers each having a thickness of 7 nm are laminated. 
         [0018]    The effects of the present embodiment will be described comparing with a comparative example.  FIG. 4  is a top view showing a semiconductor device manufactured using the manufacturing method according to the comparative example. In  FIG. 4 , the nitride semiconductor layer  18  is seen through. In the comparative example, since no insulating film  16  is formed, abnormal growth  20  generated on the high-dislocation region  12  is transmitted into the low-dislocation region  10 . 
         [0019]      FIG. 5  is a top view showing a semiconductor device manufactured using the manufacturing method according to the present embodiment. In the present embodiment, since the insulating film  16  is formed on the low-dislocation region  10  so as to surround the high-dislocation region  12 , the transmitting of abnormal growth  20  generated on the high-dislocation region  12  into the low-dislocation region  10  can be prevented. 
         [0020]    Also, since the high-dislocation region  12  is not covered by the insulating film  16 , the width w of the insulating film  16  can be reduced. Therefore, the thickening of the nitride semiconductor layer  18  in the vicinity of the insulating film  16  due to the diffusion of materials can be prevented. As a result, the surface flatness of the nitride semiconductor layer  18  can be improved, and the yield of the semiconductor devices can be elevated. Specifically, in order to improve the surface flatness, the width w of the insulating film  16  is made to be not more than 30 μm. However, in order to prevent the transmitting of abnormal growth, the width w of the insulating film  16  must be not less than 1 μm. 
         [0021]    Also, the thickness of the insulating film  16  is preferably 500 to 5000 Å. This is because if the insulating film  16  is thinner than 500 Å, the nitride semiconductor layer  18  is laterally grown on the insulating film  16  to cover the insulating film  16 ; and if the insulating film  16  is thicker than 5000 Å, stress due to the formation of the insulating film  16  is significantly enlarged to warp the substrate. It is further preferable to make the thickness of the insulating film  16  be 1000 to 2000 Å. 
         [0022]    Also, the insulating film  16  is preferably composed of SiO 2  or SiN. Thereby, the nitride semiconductor layer  18  is little grown on the insulating film  16 . SiO 2  or SiN is stable even at a high temperature of around 1000° C. 
         [0023]    In the present embodiment, although the high-dislocation region  12  and the insulating film  16  are stripe-shaped, if the insulating film  16  has the shape to surround the high-dislocation region  12 , the high-dislocation region  12  and the insulating film  16  may have the shape other than stripe-shape. 
         [0024]    Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described. 
         [0025]    The entire disclosure of a Japanese Patent Application No. 2010-010056, filed on Jan. 20, 2010 including specification, claims, drawings and summary, on which the Convention priority of the present application is based, are incorporated herein by reference in its entirety.