Abstract:
The present invention discloses a Schottky barrier diode (SBD) and a manufacturing method thereof. The SBD includes: a semiconductor layer, which has multiple openings forming an opening array; and an anode, which has multiple conductive protrusions protruding into the multiple openings and forming a conductive array; wherein a Schottky contact is formed between the semiconductor layer and the anode.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of Invention 
         [0002]    The present invention relates to a Schottky barrier diode (SBD) and a manufacturing method of an SBD; particularly, it relates to such SBD having a semiconductor layer which includes an opening array, and a manufacturing method thereof. 
         [0003]    2. Description of Related Art 
         [0004]    A Schottky barrier diode (SBD) is a semiconductor device. Compared to a P-N junction diode, the SBD has a higher forward current and a shorter recovery time in operation because of a Schottky barrier formed by Schottky contact between a metal layer and a semiconductor layer. However, the SBD has a higher leakage current and therefore more power loss in a reverse biased operation because of an anode made of conductive materials. 
         [0005]    To overcome the drawback in the prior art, the present invention proposes an SBD and a manufacturing method thereof, wherein a work function of the conductive material is adjusted by forming an opening array in the semiconductor layer, to decrease the leakage current in the reverse biased operation such that the power loss is decreased. 
       SUMMARY OF THE INVENTION 
       [0006]    A first objective of the present invention is to provide a Schottky barrier diode (SBD). 
         [0007]    A second objective of the present invention is to provide a manufacturing method of an SBD. 
         [0008]    To achieve the objectives mentioned above, from one perspective, the present invention provides an SBD, including: a semiconductor layer, which has a plurality of openings forming an opening array; and an anode, which has a plurality of conductive protrusions protruding into the plural openings and forming a conductive array; wherein a Schottky contact is formed between the semiconductor layer and the anode. 
         [0009]    From another perspective, the present invention provides a manufacturing method of an SBD, including: providing a semiconductor layer; forming a plurality of openings downward from an upper surface of the semiconductor layer to form an opening array; and forming a plurality of conductive protrusions in the openings to form a conductive array, and thereby forming an anode; wherein a Schottky contact is formed between the semiconductor layer and the anode. 
         [0010]    In one embodiment, the semiconductor layer preferably includes a gallium nitride (GaN) layer or a silicon (Si) layer. 
         [0011]    In another preferable embodiment, each of the openings is a nanohole structure formed from an upper surface of the semiconductor layer downward, by a lithography process and an etch process. 
         [0012]    In another embodiment, the SBD preferably further includes a conductive layer formed on the semiconductor layer, wherein an ohmic contact is formed between the semiconductor layer and the conductive layer. 
         [0013]    In another preferable embodiment, the openings have an average diameter not larger than 300 nm, a pitch between the openings not larger than 1 um, and a depth between 50 nm to 200 nm from an upper surface of the semiconductor layer downward. 
         [0014]    The objectives, technical details, features, and effects of the present invention will be better understood with regard to the detailed description of the embodiments below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIGS. 1A-1E  show a first embodiment of the present invention. 
           [0016]      FIG. 2  shows a second embodiment of the present invention. 
           [0017]      FIG. 3  shows a third embodiment of the present invention. 
           [0018]      FIGS. 4A-4B  show dimensions of the openings and the conductive protrusions schematically. 
           [0019]      FIGS. 5 and 6  show two examples illustrating that the shape of the openings is not limited to a circle. 
           [0020]      FIG. 7  shows a fourth embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    The drawings as referred to throughout the description of the present invention are for illustration only, to show the interrelations between the regions and the process steps, but not drawn according to actual scale. 
         [0022]      FIGS. 1A-1E  show a first embodiment of the present invention.  FIGS. 1A-1D  are schematic cross-section diagrams showing a manufacturing flow of a Schottky barrier diode (SBD)  100  according to this embodiment. As shown in  FIG. 1A , first, a substrate  11  is provided, which has an upper surface  111 . The substrate  11  is for example but not limited to a silicon carbide (SiC) substrate or a sapphire substrate. 
         [0023]    Next, referring to  FIG. 1B , a semiconductor layer  13  is formed on the upper surface  111 . The semiconductor layer  13  has an upper surface  131  which does not face the upper surface  111 , as shown in the figure. The semiconductor layer  13  is for example but not limited to a gallium nitride (GaN) layer or a silicon (Si) layer. 
         [0024]    Next, as shown in  FIG. 1C , multiple openings  12   a  are formed in the semiconductor layer  13  from the upper surface  113  downward, by for example but not limited to a lithograph process and an etching process. The multiple openings  12   a  form an opening array  12  from top view (not shown). The aforementioned etching process for example can be, but not limited to, an inductively coupled plasma reactive ion etching (ICP-RIE) process. The opening  12   a  is for example but not limited to a nanohole structure. 
         [0025]    Next, referring to  FIG. 1D , in the semiconductor layer  13 , multiple conductive protrusions  16   a  are formed in the multiple openings  12   a , and thus a conductive array  16  is formed. As shown in the figure, an anode  14  is formed by the conductive array  16 . A cathode  15  is formed on an upper surface  131  away from the anode  14 . A Schottky contact is formed between the anode  14  including the conductive array  16 , and the semiconductor layer  13 . An ohmic contact is formed between the cathode  15  and the semiconductor layer  13 . Therefore, the anode  14  (including the conductive array  16 ), the semiconductor layer  13 , and the cathode  15  form the SBD  100 . 
         [0026]      FIG. 1E  shows a schematic 3D view of this embodiment. It should be noted that, in order to better illustrate the major feature of the present invention, the anode  14  including the conductive protrusions  16   a  and the cathode  15  are shown separated from the semiconductor layer  13  in  FIG. 1E , but they should be in contact with the semiconductor layer  13  in a practical device. According to the present invention, the topography variation of the contact surface between the anode  14  (conductive array  16 ) and the semiconductor layer  13  helps to adjust the work function of the conductive material of the anode  14 , such that the characteristic of the SBD can be adjusted, such as to achieve a higher forward current, a higher breakdown voltage in reverse operation, or lower power loss, etc. 
         [0027]      FIG. 2  shows a second embodiment of the present invention.  FIG. 2  is a schematic cross-section diagram showing an SBD  200  according to this embodiment. As shown in  FIG. 2 , similar to the first embodiment, first, a substrate  21  is provided. The substrate  21  is for example but not limited to the SiC substrate or a sapphire substrate. Next, a semiconductor layer  23  is formed on an upper surface  211 . The semiconductor layer  23  is for example but not limited to the GaN layer or the Si layer. This embodiment is different from the first embodiment in that, the anode  24  includes a first region  24   a  and a second region  24   b . As shown in the figure, conductive protrusions of the first region  24   a  have a shorter diameter compared to the diameter of the conductive protrusions of the second region  24   b , and a pitch of the conductive protrusions of the first region  24   a  is also shorter. The advantage of this arrangement is that, for example, the conductive protrusions formed in two regions  24   a  and  24   b  of the anode  24  may have two different work functions, such that the SBD  200  may have a higher forward current in a forward biased operation, and a lower leakage current in a reverse biased operation with a higher breakdown voltage. 
         [0028]      FIG. 3  shows a third embodiment of the present invention.  FIG. 3  is a schematic cross-section diagram showing an SBD  300  according to this embodiment. As shown in  FIG. 3 , similar to the second embodiment, first, a substrate  31  is provided. The substrate  31  is for example but not limited to the SiC substrate or a sapphire substrate. Next, a semiconductor layer  33  is formed on an upper surface  311 . The semiconductor layer  33  is for example but not limited to the GaN layer or the Si layer. This embodiment is different from the second embodiment in that, the anode  34  includes a first region  34   a  and a second region  34   b . As shown in the figure, the first region  34   a  has conductive protrusions, but the second region  34   b  has not. This embodiment illustrates that, according to the present invention, the anode of the SBD may have different work functions at different regions by having or not having the conductive protrusions. 
         [0029]      FIGS. 4A-4B  show preferable dimensions of the openings and the conductive protrusions. As shown in  FIG. 4A , the openings have an average diameter d preferably not larger than 300 nm, and a pitch p between the openings not larger than 1 um. As shown in  FIG. 4B , wherein the first embodiment is taken as an example, a depth h downward from the upper surface  131  of the semiconductor layer  13  is preferably between 50 nm to 200 nm. 
         [0030]      FIGS. 5 and 6  show two examples of the shape of the openings, to illustrate that the shape is not limited to a circle as shown in all the aforementioned embodiments, but it may be a rectangular or any other regular or irregular shape. The dimensions of these rectangular or irregular openings can be designed with reference to the aforementioned preferable dimensions. 
         [0031]      FIG. 7  shows a fourth embodiment of the present invention.  FIG. 7  is a schematic cross-section diagram showing an SBD  400  according to this embodiment. This embodiment is different from the first embodiment in that, the semiconductor layer  43  of this embodiment is not formed on any substrate. That is, the substrates  11 ,  21  and  31  are not necessarily required in the present invention. For example, if the semiconductor layer is a Si semiconductor layer, it does not need to be formed on a substrate. 
         [0032]    The present invention has been described in considerable detail with reference to certain preferred embodiments thereof. It should be understood that the description is for illustrative purpose, not for limiting the scope of the present invention. Those skilled in this art can readily conceive variations and modifications within the spirit of the present invention. For example, other process steps or structures which do not affect the primary characteristics of the device, such as an aluminum gallium nitride (AlGaN) layer between the semiconductor layer and the anode in the SBD, can be added. For another example, the semiconductor layer may be P-type or N-type in the SBD. In view of the foregoing, the spirit of the present invention should cover all such and other modifications and variations, which should be interpreted to fall within the scope of the following claims and their equivalents.