Abstract:
A junction barrier Schottky diode has an N-type well having surface and a first impurity concentration; a p-type anode region in the surface of the well, and having a second impurity concentration; and an N-type cathode region in the surface of the well and horizontally abutting the anode region, and having a third impurity concentration. A first N-type region vertically abuts the anode and cathode regions, and has a fourth impurity concentration. An ohmic contact is made to the anode and a Schottky contact is made to the cathode. The fourth impurity concentration is less than the first, second and third impurity concentrations.

Description:
BACKGROUND AND SUMMARY OF THE DISCLOSURE 
       [0001]    The present disclosure relates generally to a junction barrier Schottky diode (JBS) and, more specifically, to a junction barrier Schottky diode with higher reverse blocking voltage. 
         [0002]    Integrated circuits have generally included Schottky diodes for power applications. Schottky diodes tend to be very leaky at high reverse bias and high temperatures. Circuit designers have used junction barrier Schottky diodes to provide a solution to the leaky Schottky diodes. This combination provides a Schottky-like forward conduction and PN diode like reverse blocking of voltage. It basically includes a PN junction and a Schottky junction diode in parallel Although this has solved the leakage problems, the JBS diodes built to date have historically had reverse blocking voltages in the range of 30 volts. There is a need to provide an improved JBS diode with substantially greater reverse blocking voltage. 
         [0003]    The present junction barrier Schottky diode has an N-type well having a surface and a first impurity concentration; a p-type anode region in the surface of the well, and having a second impurity concentration; and an N-type cathode region in the surface of the well and horizontally abutting the anode region, and having a third impurity concentration. A first N-type region vertically abuts the anode and cathode regions, and has a fourth impurity concentration. An ohmic contact is made to the anode and a Schottky contact is made to the cathode. The fourth impurity concentration is less than the first, second and third impurity concentrations. 
         [0004]    The cathode and anode regions have substantially the same depth. The cathode and anode regions may be concentric. The cathode region may be between two spaced anode regions or the anode region may be between two spaced cathode regions. 
         [0005]    The maximum impurity concentration of the anode region is below the surface. The fourth impurity concentration&#39;s maximum may be one order of magnitude less than the second impurity concentration&#39;s maximum, and the fourth impurity concentration&#39;s minimum is one order of magnitude less than the third impurity concentration&#39;s maximum. The second, third and fourth impurity concentrations are of a value to produce a diode having a reverse blocking voltage of at least 60 volts. 
         [0006]    The N-type well may include a buried p-type region below and vertically abutting the first N-type region and having a fifth impurity concentration. The second, third, fourth and fifth impurity concentrations may be of a value to produce a diode having a reverse blocking voltage of at least 70 volts or at least 90 volts. 
         [0007]    Although the junction barrier Schottky diode is generally used in integrated circuits, the present junction barrier Schottky diode may be a discrete device. 
         [0008]    These and other aspects of the present disclosure will become apparent from the following detailed description of the disclosure, when considered in conjunction with accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]      FIG. 1  is cross-sectional view of an integrated circuit including a junction barrier Schottky diode incorporating the principles of the present disclosure. 
           [0010]      FIG. 2  is plain view of a first arrangement of the anode and cathode regions of a junction barrier Schottky diode incorporating the principles of the present disclosure. 
           [0011]      FIG. 3  is plain view of a second arrangement of the anode and cathode regions of a junction barrier Schottky diode incorporating the principles of the present disclosure. 
           [0012]      FIG. 4  is plain view of a third arrangement of the anode and cathode regions of a junction barrier Schottky diode incorporating the principles of the present disclosure. 
           [0013]      FIG. 5  is plain view of a fourth arrangement of the anode and cathode regions of a junction barrier Schottky diode incorporating the principles of the present disclosure. 
           [0014]      FIG. 6  is cross-sectional view of a first junction barrier Schottky diode incorporating the principles of the present disclosure. 
           [0015]      FIG. 7  is a graph of impurity concentration along cutline  3  of  FIG. 6 . 
           [0016]      FIG. 8  is a graph of impurity concentration along cutline  1  of  FIG. 6 . 
           [0017]      FIG. 9  is a graph of impurity concentration along cutline  2  of  FIG. 6 . 
           [0018]      FIG. 10  is cross-sectional view of a second junction barrier Schottky diode incorporating the principles of the present disclosure. 
           [0019]      FIG. 11  is a graph of impurity concentration along cutline  3  of  FIG. 10 . 
           [0020]      FIG. 12  is a graph of impurity concentration along cutline  1  of  FIG. 10 . 
           [0021]      FIG. 13  is a graph of impurity concentration along cutline  2  of  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]      FIG. 1  illustrates an integrated circuit  10  including a field effect transistor FET  12  and a junction barrier Schottky diode  14 . A p-type substrate  16  includes lateral oxide isolation regions  18  offering lateral isolation at the surface between various devices including the FET  12  and the JBS  14 . The FET  12  is illustrated as including an N-type source  20  and drain  22  in the P-type substrate  16 . A gate  24  is separated from the channel region between the source  20  and the drain  22  by a gate oxide  26 . Source contact  28  and drain contact  29  are also shown. 
         [0023]    The junction barrier Schottky diode  14  includes an N-type well  30  having a buried N+ layer  32 . The upper portion or surface region of the JBS  14  includes an N+ region  34 . A pair of P-type anode regions  38 A and  38 B are formed in the surface of region  34 . A cathode region  40  laterally abuts the pair of anode regions  38 . The N+ region  34  has a lower impurity concentration than the P anode regions  38  and N cathode region  40 . It also has a lower impurity concentration than the N well  30 . It should be noted that the cathode region  40  has generally the same depth as the anode  38  such that in the lateral direction there is a higher impurity concentration between the anodes  38  A and B while the lower or vertical abutment of the anodes  38 A and B is with the lower impurity N+ region  34 . The plus and minus is to illustrate their relative impurity concentration. A more detailed explanation of the impurity concentration are illustrated to be discussed below. 
         [0024]    Anode contacts  42 A and  42 B are made to the anode region  38 A and  38 B and a Schottky barrier contact  44  is made with cathode region  40 . An N+ cathode contact region  46  extends from the surface to the N+ buried layer  32 . A contact  48  is made to the cathode contact region  46 . Materials that form these contact to produce the appropriate functions are well-known. The cathode region  40  is an active cell partition. The N+ region  34  is a lower doping region and the N+ buried layer  32 , which carries the current laterally to the cathode. The anode PN contacts  42 A and  42 B and Schottky contact  44  are shown as connected to a common point. This may be by the interconnect structure or by extending the Schottky contact  44  laterally onto the P-region  38 . 
         [0025]    An example of a cross-section of the implementation of the junction barrier Schottky diode  10  is illustrated in  FIG. 6 . The P-region  38  is ion implanted and is selected to have a peak impurity concentration below the surface of the well  30 . In, the implementation shown, it is generally along the cutline  3  at about 0.5 microns from the surface. The N+ region  40  is also formed by ion implantation. The example shown is for a JBS 50  which indicates that for the one micron dimension, that the anode and cathode regions of the two parallel diodes are implanted to represent half of the one-micron dimension. 
         [0026]    The lateral abutment of the anode region  38  and the cathode region  40  may take various configurations. As previously mentioned, they are generally of the same depth from the surface of the well  30 . In one embodiment illustrated in  FIG. 2 , the cathode region  40  separates to anode region  38 A and  38 B. As an alternative illustrated in  FIG. 3 , a single anode region  38  may separate a pair of cathode regions  40 A and  40 B. The space between the two anode regions  38 A and  38 B or the two cathode regions  40 A and  40 B is less than 1 micron and is selected for a specific forward voltage drop and leakage current. 
         [0027]    A concentric embodiment is illustrated in  FIGS. 4 and 5 . In  FIG. 4  the cathode region  40  is surrounded by the anode region  38 . In  FIG. 5  the anode region  38  is surrounded by cathode region  40 . 
         [0028]    Even though the original implantation of the anode  38  and the cathode  40  are each for half a micron due to other heat steps in the process, the P-type impurities of the anode migrate laterally into the cathode region.  FIG. 7  illustrates cutline  3  which is the lateral profile of the impurity concentration. As will be noted, there is a small region of approximately 0.05 microns where the n and p impurity concentrations cancel each other out. 
         [0029]      FIG. 8  illustrates at cutline  1 , which is from the surface through the anode region  38  into regions  34 ,  30  and  32 . It should be noted at about approximately a half micron is the peak impurity concentration for the anode region  38 . This peak is greater than 1×10 17  carriers per cubic centimeter. You will note that the surface cathode region  40  has an impurity concentration of just greater than 1×10 16  carriers per cubic centimeter. That is true for  FIGS. 7 and 9 . Cutline  2  illustrates the specific doping profile for the cathode region  40 , region  34 ,  30  and  32 . The structure shown produces a reverse blocking voltage of least 60 volts. 
         [0030]    A modification to the junction barrier Schottky diode of  FIGS. 1 and 6  is illustrated in  FIG. 10 . In addition to the lightly doped region  34  which reduces the doping level of the well  30 , a P-type region  36  is provided between the region  34  and the well portion  30 . As illustrated in  FIGS. 12 and 13 , this provides a disruption or discontinuity in the N impurity concentration of the well at between 4 and 4.3 microns from the surface. In comparing  FIGS. 8 and 12 , the impurity concentration for the P-region  38  and the N+ region  40  is not affected by the addition of the buried P region  36 . What is changed is the N impurity concentrations as illustrated by the difference between  FIGS. 8-9  and  12 - 13 . With the addition of the P region, the N region  34  is below 1×10 16  in  FIG. 12  where it is above 1×10 16  in  FIG. 8  for the N region  34 . Also in comparing  FIGS. 9 and 13 , the drop-off of the N-type impurity regions diminishes quicker in the cathode region  40  for that of  FIG. 9  versus that of  FIG. 13 . Also the region  40  in cutline  3 , which is approximately 0.9 microns, is above 1×10 16  in  FIG. 7  but below than in  FIG. 11 . By addition of the P-type region  36 , the reverse blocking voltage has been increased to 90 volts. 
         [0031]    A comparison of a Schottky diode and a PN diode to four different structures of the junction barrier Schottky diode of that illustrated in  FIG. 10  is shown in Table 1. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Vf @ 
                 Vr @ 
                 log (lhole) 
                 lhole @ 
               
               
                   
                 100 A/cm2 (V) 
                 1 mA/cm2 (V) 
                 @ vf 
                 100 A/cm2 (%) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Schottky2 
                 0.46 
                 32 
                 0 
                 0 
               
               
                 JBS30 
                 0.5 
                 70 
                 −10.45 
                 0.004 
               
               
                 JBS40 
                 0.52 
                 82 
                 −10.2 
                 0.006 
               
               
                 JBS50 
                 0.575 
                 91 
                 −9.13 
                 0.07 
               
               
                 JBS60 
                 0.68 
                 95.5 
                 −7.15 
                 7.08 
               
               
                 PN2 
                 .0733 
                 102 
                 −6 
                 100 
               
               
                   
               
             
          
         
       
     
         [0032]    The diodes JBS 30 ,  40 ,  50  and  60  have different structures. As discussed previously, the number represents the size of the implementation of the anode region  38  with the portion of a one micron length. Thus, the remainder of the area being the Schottky cathode region  40 . One can see that the reverse blocking voltage increases 70 volts for JBS 30  up to 95.5 volts for JBS 60 . Thus as the Schottky cathode region  40  diminishes relative to the size of the anode region  38 , the reverse breakdown voltage increases. 
         [0033]    Although the present disclosure has been described and illustrated in detail, it is to be clearly understood that this is done by way of illustration and example only and is not to be taken by way of limitation. The present junction barrier Schottky diode may also be a discrete device. The scope of the present disclosure is to be limited only by the terms of the appended claims.