Abstract:
The present invention relates to the field of semiconductor technology, particularly to a super-junction schottky diode. According to the present invention, the effective area of schottky junction is increased by forming the schottky junction in the trench located in the body of the device. Therefore, the current capacity of this novel schottky diode can be greatly improved. In addition, a super-junction structure is used to improve the device&#39;s reverse breakdown voltage and reduce the reverse leakage current. The super-junction schottky diode provided in the present invention can achieve a larger forward current, a lower on-resistance and a better reverse breakdown characteristic.

Description:
CROSS REFERENCE 
       [0001]    The present application is based on, and claims priority from, Chinese application number 201610596069.4, filed on Jul. 25, 2016, the disclosure of which is hereby incorporated by reference herein in its entirety. 
       TECHNICAL FIELD OF THE INVENTION 
       [0002]    The present invention relates to the technical field of semiconductor devices, particularly to a super-junction schottky diode. 
       BACKGROUND OF THE INVENTION 
       [0003]    Diodes are one of the most commonly used electronic devices. The types of traditional diodes are schottky diodes and PN junction diodes. PN junction diodes can withstand high reverse blocking voltage and has better stability. However, PN junction diodes have a larger forward voltage and a longer reverse recovery time. Schottky diodes are based on the principle of metal-semiconductor junction. Schottky diodes have a lower forward voltage and a faster reverse recovery since it has no minority carrier accumulation during the forward conduction. However, schottky diodes have a larger reverse leakage current and a poor temperature characteristic. There is a tradeoff between schottky diode&#39;s breakdown voltage and the forward voltage, which is called the “silicon limit”. In order to improve the breakdown voltage of a schottky diode, the thickness of drift region must be enhanced and the doping concentration of drift region must be reduced, which leads to an increase of forward conduction loss. Therefore, the main application field of schottky diode is for low or middle voltage applications. 
         [0004]    In order to improve the schottky diode&#39;s breakdown voltage without increasing its forward voltage, the super-junction structure is introduced into the schottky diode&#39;s drift region. For example, Chinese patent application “A super-junction schottky semiconductor device and its preparation method” (application number: 201210141949.4) provided a schottky diode based on the charge balance principle. However, the schottky junctions existing in schottky diodes are located on the surface of the devices, so that the current capacity of the schottky diode is limited since the surface area is limited. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention provides a novel super-junction schottky diode. The effective area of the schottky junction is increased by forming the schottky junction at the trench located in the body of the device. Therefore, the current capacity of the novel schottky diode can be greatly improved. In addition, a super-junction structure is used to improve the device&#39;s reverse breakdown voltage and reduce the device&#39;s reverse leakage current. 
         [0006]    According to an aspect of the invention, there is provided a super-junction schottky diode including: a metallized cathode electrode  1 , a N+ substrate  2  (i.e., a heavily doped substrate of a conductivity type N), an N-type drift region  3  (i.e., a drift region of a conductivity type N), and a metalized anode electrode  9 . Said N-type drift region  3  includes a P-type buried layer  4  (i.e., a buried layer of a conductivity type P), a P-type column  5  (i.e., a column of a conductivity type P), a P+ heavily doped region  6  (i.e., a heavily doped region of a conductivity type P), a N-type lightly doped region  8  (i.e., a lightly doped region of conductivity type N), and a trench  7 . The P-type buried layer  4  is under the trench  7 , and the top surface of the P-type buried layer  4  contacts with the bottom surface of the trench  7 . The P-type column  5  is located between two adjacent trenches  7 . The P+ heavily doped region  6  is disposed above the P-type column  5 , and the bottom surface of the P+ heavily doped region  6  contacts the top surface of the P-type column  5 . The N-type lightly doped region  8  is located on the side of the trench  7  and on the top surface of the N-type drift region  3 . Said trench  7  is filled with metal, and the metal together with the N-type lightly doped region  8  form a schottky junction. The top surface of the N-type lightly doped region  8  is covered with metal that is the same as the metal in the trench  7 , and the metal together with the N-type lightly doped region  8  also form a schottky junction. The top surfaces of said metal and the P+ heavily doped region  6  contact the bottom surface of the metalized anode electrode  9 . The junction depth of said P-type buried layer  4  is the same as the that of the P-type column  5 . 
         [0007]    Additionally, the bottom surface of said P-type buried layer  4  and P-type column  5  can contact the top surface of the N+ substrate  2 . 
         [0008]    Furthermore, the P-type buried layer  4  can be replaced with the thick oxide layer  10 . 
         [0009]    Some beneficial effects of the present invention are as follow. Compared to the existing super-junction schottky diode, the structure of this invention has a larger forward current, a smaller forward voltage, and a better reverse breakdown characteristic. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  shows a diagrammatic sectional view of a power device according to the Embodiment 1 of the present invention. 
           [0011]      FIG. 2  shows a diagrammatic sectional view of a power device according to the Embodiment 2 of the present invention. 
           [0012]      FIG. 3  shows a diagrammatic sectional view of a power device according, to the Embodiment 3 of the present invention. 
           [0013]      FIG. 4  to  FIG. 12  show diagrammatic sectional views of steps for fabricating the device in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    In the following detailed description, the features of the various exemplary embodiments may be understood in combination with the drawings. 
       Embodiment 1 
       [0015]    As shown in  FIG. 1 , the first embodiment of the present invention provides a super-junction schottky diode. 
         [0016]    FIG. 1  illustrates a super-junction schottky diode in accordance with thee present invention. The super-junction schottky diode includes: a metallized cathode electrode  1 , a N+ substrate  2 , an N-type drift region  3  and a metalized anode electrode  9 . Said N-type drift region  3  includes a P-type buried layer  4 , a P-type column  5 , a P+ heavily doped region  6 , an N-type lightly doped region  8  and a trench  7 . The P-type buried layer  4  is under the trench  7 , and the top surface of the P-type buried layer  4  contacts with the bottom surface of the trench  7 . The P-type column  5  is located between two adjacent trenches  7 . The P+ heavily doped region  6  is disposed above the P-type column  5  and the bottom surface of the heavily doped region  6  contacts the top surface of the P-type column  5 . The N-type lightly doped region  8  is located on the side of the trench  7  and on the top surface of the N-type drift region  3 . Said trench  7  is filled with metal, and the metal together with the N-type lightly doped region  8  form a schottky junction. The top surface of the N-type lightly doped region  8  is covered with metal that is the same as the metal in the trench  7  and the metal together with the N-type lightly doped region  8  also form a schottky junction. The top surfaces of said metal and the P+ heavily doped region  6  contact the bottom surface of the metalized anode electrode  9 . The junction depth of said P-type buried layer  4  is the same as the that of the P-type column  5 . 
         [0017]    The mechanism of the present super-junction schottky diode provided by embodiment 1 will be explained as follows. 
         [0018]    During the forward conduction period, the metalized anode electrode  9  is applied with high potential and the metallized cathode electrode  1  is connected to a low potential (e.g., ground). The trench  7  is filled with metal, and the metal trench together with the N-type lightly doped region  8  form a schottky junction. Because the trench  7  is embedded in the body of the device, the trench&#39;s sidewall area is large and thus the effective area of the schottky junction is enlarged. Therefore, the current capability of this power diode can be improved. In addition, the forward conduct voltage drop can be decreased to reduce the forward conduction loss by increasing the doping concentration of the N-type drift region  3  since there is a super-junction structure in the N-type drift region  3 . The doping concentrations of the N-type lightly doped region  8  and the N-type drift region  3  can be designed independently. As a result, a lower turn-on voltage can be obtained by decreasing the doping concentration of the N-type lightly doped region  8 , and a lower forward conduction voltage can be achieved by increasing the doping concentration of the N-type drift region  3 . 
         [0019]    During the reverse blocking period, the metalized anode electrode  9  is connected to a low potential and the metallized cathode electrode  1  is at a high potential. The P-type column  5  together with the N-type drift region  3  with a relatively high doping concentration can realize a charge compensation and generate a horizontal electric field. This horizontal electric field depletes the N-type drift region  3  and then the electrical characteristic of the N-type drift region  3  is the same as the one of the intrinsic semiconductors in the vertical direction. Therefore, this schottky diode can withstand higher reverse breakdown voltage, and the reverse leakage current is decreased. Additionally, the horizontal electric field will appear between the P-type buried layer  4  and the N-type drift region  3 . Therefore, the reverse breakdown voltage is increased and the reverse leakage current can be further reduced. What&#39;s more, since the P-type buried layer  4  is located at the bottom of the metal trench  7 , the reverse leakage current can be reduced. 
         [0020]    In embodiment 1, the structure of the present invention can be produced by the following steps. 
         [0021]    Step 1—monocrystalline silicon preparation and epitaxy: The N-type drift region  3  with a certain thickness and doping concentration is deposited on the N-type heavily doped monocrystalline silicon substrate  2  by vapor phase epitaxy (VPE) or other methods, as shown in  FIG. 4 . 
         [0022]    Step 2—etching trench: A hard mask  11  (such as silicon nitride) is deposited on the surface of the silicon wafer as a barrier layer for subsequent etching. Then the hard mask  11  is etched after the lithography and then the deep trench is etched by the shelter of hard mask  11 , as shown in  FIG. 5 . The etching process can be reactive ion etching or plasma etching. 
         [0023]    Step 3—P-type column epitaxy: The deep trench is filled with P-type silicon material by an epitaxy process. Subsequently, superfluous P-type silicon on the surface of the wafer is removed by chemico-mechanical polishing (CMP). Thus, the P-type column  5  is formed, as shown in  FIG. 6 . 
         [0024]    Step 4—etching trench again: Another hard mask  12  (such as silicon nitride) is deposited on the surface of the silicon wafer as a barrier layer for subsequent etching. Then the hard mask  12  is etched after the lithography and then the deep trench is etched by the shelter of hard mask  12 , as shown in  FIG. 7 . The etching process can be reactive ion etching or plasma etching. 
         [0025]    Step 5—implanting ion: As shown in  FIG. 8 , P-type buried layer  4  is formed on the bottom of the trench by ion implantation with the shelter of hard mask  12 . 
         [0026]    Step 6—implanting ion again: As shown in  FIG. 9 , the hard mask  12  is removed before the ion implantation. A bevel ion implantation is adapted to implant P-type impurity ions. The N-type lightly doped region  8  is formed by impurity compensation of the implanted P-type impurities with the N-type drift region  3 . 
         [0027]    Step 7—filling metal: As shown in  FIG. 10 , the deep trench is filled with proper schottky metal (such as Platinum). The metal together with the N-type lightly doped region  8  form schottky junction. 
         [0028]    Step 8—etching contact hole: As shown in  FIG. 11 , the metal above the P-type column  5  is etched to produce a contact hole. The P-type heavily doped region  6  is formed by P-type ion implantation. 
         [0029]    Step 9—depositing metalized electrode: As shown in  FIG. 12 , metal is deposited. on the top surface of the device to form the anode, electrode  9 . The anode electrode  9  is contacted with the metal trench  7  and the P-type heavily doped region  6 . Then the back of wafer is thinned and the cathode electrode  1  is produced by metallization. 
       Embodiment 2 
       [0030]    As shown in  FIG. 2 , based on the embodiment 1, the P-type column  5  and the trench  7  are extended. The bottom surfaces of both P-type column  5  and trench  7  touch the substrate  2 . The beneficial effect of this embodiment is that the reverse breakdown voltage and leakage current of the device can be improved further. 
       Embodiment 3 
       [0031]    As shown in  FIG. 3 , based on the embodiment 1, the P-type buried layer  4  is replaced with the thick oxide layer  10 . The breakdown can he prevented to occur at the bottom of the trench  7  and thus the reverse breakdown voltage of the device can be unproved. 
         [0032]    In addition, other semiconductor materials such as silicon carbide, gallium arsenide, indium phosphide and germanium silicon can be used to replace silicon in manufacturing.