Abstract:
A method for producing a semiconductor component has the following step: the front side ( 101 ) of the semiconductor body ( 100 ) is irradiated with high-energy particles using the terminal electrode ( 40 ) as a mask, in order to produce recombination centres ( 80 A,  80 B) in the semiconductor body ( 100 ) for the recombination of the first and second conduction type of charge carriers.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional application of U.S. patent application Ser. No. 11/246,345 filed Oct. 7, 2005, which is a continuation of co-pending International Application No. PCT/EP2004/003321 filed Mar. 29, 2004, which designates the United States of America, and claims priority to German application number DE 103 16 222.4 filed Apr. 9, 2003, the contents of which are hereby incorporated by reference in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a method for producing a vertical semiconductor component which has a semiconductor body having an inner region, at least one pn junction in the inner region and an edge region that is arranged between the inner region and an edge. A current flows through components of this type when a suitable voltage is applied in the vertical direction, that is to say perpendicular to a front and a back of the semiconductor body. U.S. Pat. No. 6,351,024 B1, for example, describes a vertical semiconductor component of this type having an inner region, which has a pn junction, and an edge region that adjoins the inner region. 
       BACKGROUND 
       [0003]    When switching off semiconductor components of this type, that is to say when applying a voltage at which the pn junction is reverse-biased, the edge region is particularly important, as explained briefly below. In the case of a forward-biased pn junction, the edge regions are likewise flooded with charge carriers, that is to say electrodes and holes, as a result of diffusion. When switching off the component, these charge carriers need to be removed from the edge regions, which results in the need to dissipate a considerably higher charge in those regions of the inner region which adjoin the edge region than in the other regions of the inner region. The charge carriers, particularly holes, which flow out of the edge regions during the switching-off operation may, in this case, contribute to the production of additional charge carriers (avalanche effect), which leads to increased switching losses as a result of the avalanche effects which begin dynamically and, in the worst case, to destruction of the component. This current density which is higher in the edge region than in the inner region during the switching-off operation limits the currents which can be switched overall using the component. 
         [0004]    In order to alleviate this problem, it is known, in principle, from the abovementioned U.S. Pat. No. 6,351,024 B1, to shorten the charge carrier lifetime in the edge region. This is effected, for example, by producing additional recombination centers by irradiating the edge region with high-energy particles. The disadvantage of the known method is that a complicated technique using metallic masks which are difficult to adjust is required. In addition, it is also advantageously intended to shorten the charge carrier lifetime in the inner region of the component, which requires a second complicated mask and irradiation technique. 
       SUMMARY 
       [0005]    Therefore, it is an object of the present invention to provide a simple and cost-effective method for producing a vertical semiconductor component having improved switch-off properties and to provide a vertical semiconductor component having improved switch-off properties. 
         [0006]    This object can be achieved by a method for producing a semiconductor component, said method comprising the following method steps of providing a semiconductor body which has a front side, a back side, an inner region, an edge, an edge region which is arranged between the inner region and the edge, a first semiconductor zone of a first conduction type in the inner region and edge region and at least one second semiconductor zone of a second conduction type that is complementary to the first conduction type, said second semiconductor zone being arranged in the inner region in the region of the front, producing a connection electrode in the second semiconductor zone on the front of the semiconductor body, and irradiating the front with high-energy particles using the connection electrode as a mask in order to produce recombination centers in the semiconductor body for the purpose of recombining charge carriers of the first and second conduction types. 
         [0007]    The operation of introducing the high-energy particles can be followed by a temperature process for stabilizing the recombination centers in the semiconductor body. The temperature process can be carried out at a temperature of between 220° C. and 360° C. for a period of between 30 minutes and 4 hours. The high-energy particles can be protons or helium atoms. The energy of the high-energy particles and the thickness of the connection electrode that can be used as a mask are matched to one another in such a manner that recombination centers are produced, at least approximately, exclusively in the second semiconductor zone beneath the connection electrode. The edge region of the semiconductor body may have at least one third semiconductor zone of the second conduction type in the region of the front, the energy of the high-energy particles being selected in such a manner that the recombination centers in the edge region are produced, at least approximately, exclusively in the first semiconductor zone. The semiconductor body may have a third semiconductor zone whose doping concentration, starting from the inner zone, decreases in the direction of the edge. The third semiconductor zone may adjoin the second semiconductor zone. The semiconductor body may have at least two third semiconductor zones which are arranged at a distance from one another in the direction of the edge and at a distance from the second semiconductor zone. A fourth zone of the first conduction type can be produced in the region of the back of the semiconductor body, said fourth zone being more highly doped than the first zone. 
         [0008]    The object can also be achieved by a semiconductor component comprising a semiconductor body which has a front, a back, an inner region, an edge region which is arranged between the inner region and an edge, a first semiconductor zone of a first conduction type in the inner region and edge region and at least one second semiconductor zone of a second conduction type that is complementary to the first conduction type, said second semiconductor zone being arranged in the inner region in the region of the front, a connection electrode which is applied to the front of the semiconductor body in the second semiconductor zone, and a recombination zone which has recombination centers and is arranged beneath the connection electrode in the second semiconductor zone and in the edge region in the first semiconductor zone. 
         [0009]    At least one third semiconductor zone of the second conduction type can be provided in the edge region in the region of the front. There can be a third semiconductor zone whose doping concentration, starting from the inner zone, decreases in the direction of the edge. The third semiconductor zone may adjoin the second semiconductor zone. There can be at least two fourth semiconductor zones which are arranged at a distance from one another in the direction of the edge and at a distance from the second semiconductor zone. There can be a fourth zone of the first conduction type in the region of the back of the semiconductor body, said fourth zone being more highly doped than the first zone. 
         [0010]    The inventive method for producing a semiconductor component involves providing a semiconductor body which has a front, a back, an inner region, an edge, an edge region which is arranged between the inner region and the edge, a first semiconductor zone of a first conduction type in the inner region and edge region and at least one second semiconductor zone of a second conduction type that is complementary to the first conduction type, said second semiconductor zone being arranged in the inner region in the region of the front. The production of such a semiconductor body having a pn junction in the inner region and having an edge region is sufficiently well known, with the result that it will not be discussed in any more detail. 
         [0011]    A connection electrode which can be used to make electrical contact with the second semiconductor zone of the subsequent component is then produced in the second semiconductor zone on the front of the semiconductor body. The front of the semiconductor body is then irradiated with high-energy particles, for example protons or helium atoms, with the connection electrode being used as a mask for the irradiation process and ensuring that, in that region of the inner zone which is covered by the connection electrode, the particles do not penetrate as deeply into the semiconductor body as in that region of the edge zone which is not covered by the connection electrode. 
         [0012]    The particles which are introduced into the semiconductor body produce recombination centers, with irradiation preferably being followed by a temperature step which is used to stabilize the recombination centers. The recombination centers used are double blanks or A centers (blanks/oxygen complexes) which are produced by irradiation and the temperature step which optionally follows. The heat treatment is carried out, for example, at temperatures of between 220° C. and 360° C. for a period of between 30 minutes and 4 hours, depending on the temperature. 
         [0013]    The defects which are caused by irradiation and are used as recombination centers have higher recombination effectiveness in an n-doped region than in a p-doped region and thus shorten the charge carrier lifetime to a greater extent in an n-doped region. The irradiation energy of the high-energy particles and the thickness of the connection electrode that is used as a mask are matched to one another in such a manner that recombination centers are produced, at least approximately, exclusively in the second semiconductor zone beneath the connection electrode. 
         [0014]    This makes it possible, when the first semiconductor zone is n-doped and the second semiconductor zone is p-doped, to shorten the charge carrier lifetime to a lesser degree in the second semiconductor zone in the inner region (which is desirable in order to set the static and dynamic properties), while the charge carrier lifetime is considerably shortened, as desired, in the first semiconductor zone in the edge region in order to diminish the avalanche effects (explained) during the switching-off operation. 
         [0015]    In order to increase the dielectric strength in the edge region, the edge region of the semiconductor body has at least one third semiconductor zone of the second conduction type in the region of the front. In this case, one exemplary embodiment has at least two third semiconductor zones which are at a distance from one another in the direction of the edge and are at a distance from the second semiconductor zone. The mode of action of such third semiconductor zones which preferably surround the inner region in an annular manner and are therefore referred to as field rings is described, for example, in Baliga: “Power Semiconductor Devices”, PWS Publishing, 1995, pages 98-100. 
         [0016]    In another exemplary embodiment, a third semiconductor zone adjoins the second semiconductor zone, the doping of this third semiconductor zone decreasing in the direction of the edge. A semiconductor zone of this type is also referred to as a VLD (Variation of Lateral Doping) zone. 
         [0017]    The irradiation energy of the high-energy particles is selected in such a manner that the particles in the edge region penetrate so deeply into the semiconductor body that the recombination zones are essentially produced beneath the third semiconductor zone which is used to increase the dielectric strength in the edge region, that is to say in the first semiconductor zone. The semiconductor body is advantageously beveled at the edge, this constituting a further known measure for increasing the dielectric strength in the edge region but not being required for the effectiveness of the method. 
         [0018]    Using the connection electrode as a mask, the inventive method makes it possible, in a simple manner, to produce a recombination zone having lower recombination effectiveness in the second semiconductor zone in the inner region and a recombination zone having higher recombination effectiveness in the first semiconductor zone in the edge region. 
         [0019]    The inventive semiconductor component comprises a semiconductor body which a front, a back, an inner region, an edge, an edge region which is arranged between the inner region and the edge, a first semiconductor zone of a first conduction type in the inner region and edge region and at least one second semiconductor zone of a second conduction type that is complementary to the first conduction type, said second semiconductor zone being arranged in the inner region in the region of the front. A connection electrode is applied to the front of the semiconductor body in the second semiconductor zone. In addition, there is a recombination zone which has recombination centers and is arranged beneath the connection electrode in the second semiconductor zone and in the edge region in the first semiconductor zone. 
         [0020]    In order to increase the dielectric strength in the edge region, field rings of the second conduction type or a VLD zone is/are preferably provided in the edge region beneath the front. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The present invention will be explained in more detail below in exemplary embodiments and with reference to figures, in which: 
           [0022]      FIG. 1  shows a partial cross section through a semiconductor body on which the inventive method is based, 
           [0023]      FIG. 2  shows the semiconductor body as shown in  FIG. 1  during the next method steps for producing a semiconductor component, 
           [0024]      FIG. 3  shows a partial cross section through a semiconductor component which has been produced using the inventive method, 
           [0025]      FIG. 4  shows a schematic plan view of the semiconductor component shown in  FIG. 3 , 
           [0026]      FIG. 5  shows a partial cross section through another semiconductor body which forms the starting point for an exemplary embodiment of the inventive method, 
           [0027]      FIG. 6  shows the semiconductor body as shown in  FIG. 5  during further method steps for producing the semiconductor component, and 
           [0028]      FIG. 7  shows a partial cross section through an inventive semiconductor component. 
       
    
    
       [0029]    Unless stated otherwise, identical reference symbols denote identical parts with the same meaning in the figures. 
       DETAILED DESCRIPTION 
       [0030]    The inventive method for producing a semiconductor component is explained below with reference to  FIGS. 1 to 3  for producing a vertical power diode. The method involves providing a semiconductor body  100  which is partially shown in cross section in  FIG. 1 . The semiconductor body  100  has a front  101 , a back  102  and an edge  105  which runs in a beveled manner in the exemplary embodiment. The semiconductor body comprises an inner region  103  at a distance from the edge  105  and an edge region  104  arranged between the inner region  103  and the. edge. The semiconductor body  100  shown has n-type basic doping, the semiconductor regions having this basic doping being referred to below as the first semiconductor zone  20 . A p-doped second semiconductor zone  30  is introduced into said first semiconductor zone  20  in the inner region  103  beneath the front  101 , with the result that a pn junction is formed between said second semiconductor zone  30  and the first semiconductor zone  20  in the inner region  103 . Provided in the edge region  104  beneath the front  101  are p-doped field rings  62 ,  64  which, starting from the second semiconductor zone  30 , are arranged at a distance from one another in the direction of the edge  105  and at a distance from the second semiconductor zone  30 . In the region of the front  101 , an n-doped semiconductor zone  70 , which is used as a channel stopper, directly adjoins the edge  105 . 
         [0031]    The semiconductor body  100  also comprises a highly n-doped fifth semiconductor zone  50  which adjoins the first semiconductor zone  20  in the region of the back  102 . This highly n-doped semiconductor zone  50  which is used as an n-type emitter forms the cathode zone of the subsequent semiconductor component in the form of a diode. In the inner region  103 , the first semiconductor zone  20  forms the n-type base and the p-doped second semiconductor zone  30 , which is used as a p-type emitter, forms the anode zone. The field rings  62 ,  64  in the edge region  104  are used, in a known manner, to increase the dielectric strength of the component in the edge region. The bevel (which is likewise known) of the edge  105  serves the same purpose. 
         [0032]    The provision of a semiconductor body (shown in  FIG. 1 ) having the semiconductor zones which have been explained is sufficiently well known, with the result that it is possible to omit a further explanation of this. 
         [0033]    As shown in  FIG. 2 , a connection electrode  40  is applied to the front  101  of the semiconductor body  100  in the region of the second semiconductor zone  30  (p-type emitter), said connection electrode being used to make subsequent electrical contact with the p-type emitter  30 . The front  101  of the semiconductor body is then irradiated with high-energy particles, for example protons or helium atoms, which penetrate into the semiconductor body  100 . In this case, the penetration depth beneath the connection electrode  40  is shallower than in the other regions, since the connection electrode  40  brakes the high-energy particles even before they penetrate into the semiconductor body  100 . Irradiating the semiconductor body  100  with high-energy particles serves to produce recombination centers in the semiconductor body with the aim of shortening the charge carrier lifetime. These recombination centers, for example double blanks or A centers, are formed by defects in the crystal lattice, which defects are caused by the high-energy particles. During irradiation, for example with protons or helium atoms, use is made, in this case, of the effect that the highest concentration of defects is produced in a relatively narrow zone, the “end of range” region, in which the irradiation particles emit most of their energy and are thus braked. This irradiation with high-energy particles is preferably followed by a heat treatment method in which the semiconductor body is heated to temperatures of between 220° C. and 360° C. for a period of between 30 minutes and 4 hours in order to stabilize the recombination centers. 
         [0034]    The penetration depth of the high-energy particles depends on the irradiation energy and, in the region of the connection electrode  40 , on the thickness of this connection electrode  40 . In this case, the irradiation energy and the thickness of this connection electrode  40  are matched to one another in such a manner that the recombination centers are produced beneath the connection electrode  40  in the p-doped second semiconductor zone  30 . The recombination centers have lower recombination effectiveness in the p-doped zone  30  than in the n-doped first semiconductor zone  20  in the edge region, with the result that the recombination centers in this p-doped region  30  shorten the charge carrier lifetime to a lesser degree than in the n-doped regions  10 . In addition to in the first semiconductor zone  20  in the edge region  104 , it is also desirable to shorten the charge carrier lifetime to a certain degree in the p-doped anode zone  30  in order to be able to use it to set the static and dynamic properties of the component. 
         [0035]    The irradiation energy of the high-energy particles is also selected in such a manner that the recombination centers in the edge region  104  are essentially produced in the first semiconductor zone  20  (n-type base) beneath the field rings  62 ,  64  and the channel stopper  70 . 
         [0036]    As the result,  FIG. 3  schematically shows the physical position of the recombination centers beneath the connection electrode  40  in the inner region  103  and in the edge region  104 , the reference symbol  80 A denoting the recombination zone in the anode zone  30  and the reference symbol  80 B denoting the recombination zone in the edge region  104 . In this case, the recombination zone  80 A beneath the connection electrode is closer to the front  101 , since the high-energy particles are braked in this region by the connection electrode  40  even before they penetrate into the semiconductor body  100 . In the edge region  104 , which does not contain a connection electrode, the high-energy particles correspondingly penetrate more deeply into the semiconductor body  101 , with the result that the recombination zone  80 B is further away from the front  101  here. Since the irradiation energy of the individual particles is subject to fluctuations and on account of random scatter effects in the semiconductor lattice, recombination zones  80 A,  80 B having a particular width in the vertical direction of the semiconductor body are produced, this width being dependent, inter alia, on the irradiation energy. In this case, most of the recombination centers are in the “end of range” region of irradiation. 
         [0037]    The inventive method makes it possible, in a simple manner, to produce a vertical semiconductor component having a pn junction, in the edge region  104  of which the charge carrier lifetime is effectively shortened by means of recombination centers, with the charge carrier lifetime likewise additionally being shortened in the inner region  103  in the second semiconductor zone  30  (which, in the case of diodes, is used as a p-type emitter) but to a lesser degree than in the edge region. 
         [0038]    The inventive method is not restricted to producing semiconductor diodes but rather can be used for any desired vertical semiconductor components, for example MOS transistors, IGBTs or thyristors, which have a pn junction in the inner region and in which it is desirable to shorten the charge carrier lifetime in the edge region. 
         [0039]    In addition to the abovementioned possible way of using the thickness of the connection electrode  40  to set the penetration depth of the high-energy particles in the inner region  103 , it is also possible to influence this penetration depth using the choice of electrode material. In this case, the high-energy particles penetrate less deeply into the semiconductor body  100 , the “denser” the electrode material. Examples of suitable electrode materials are: gold (Au), copper (Cu), molybdenum (Mb), titanium (Ti) or tungsten (W). 
         [0040]      FIG. 4  schematically shows a plan view of the front  101  of the semiconductor component which is shown in  FIG. 3  and, in the example, is formed in a circular manner with a circumferential edge  105  and edge region  104 . It will be pointed out that the illustration in  FIG. 4 , in which the area of the edge region  104  is considerably larger than that of the inner region  103 , is not to scale. 
         [0041]      FIGS. 5 to 7  illustrate a method for producing a further semiconductor component in the form of a diode, the method differing from that shown in  FIGS. 1 to 3  by virtue of the fact that, instead of field rings (reference symbols  62 ,  64  in  FIGS. 1 to 3 ), the semiconductor body used has a VLD zone  60  as a third semiconductor zone, which adjoins the second semiconductor zone  30  in the direction of the edge  105  and the doping of which, starting from the second semiconductor zone  30 , decreases in the direction of the edge  105 . A VLD zone of this type is achieved, for example, by the zone  60  being constructed from a plurality of semiconductor zones  60 A,  60 B,  60 C which are arranged next to one another in the lateral direction. The doping within these semiconductor zones  60 A- 60 C may be respectively homogeneous in this case, the doping decreasing from semiconductor zone  60 A,  60 B to semiconductor zone  60 B,  60 C in the direction of the edge  105 . 
         [0042]    The other method steps for producing the semiconductor component, namely applying a connection electrode  40 , irradiating the front  101  of the semiconductor body with high-energy particles and, optionally, a heat treatment step that follows irradiation, correspond to the method explained with reference to  FIGS. 1 to 3 . In this case, the energy of the high-energy particles is also selected here in such a manner that the recombination zone  80 B in the edge region  104  is essentially produced in the n-type base  20 , that is to say beneath the VLD zone  60 . 
         [0043]    In order to complete the components, a further connection electrode  90  may be applied to the back  102 , said further connection electrode making it possible to make electrical contact with the highly n-doped semiconductor zone and being used as a cathode electrode in the case of diodes. 
       LIST OF REFERENCE SYMBOLS 
       [0000]    
       
           20  First semiconductor zone, n-type base 
           30  Second semiconductor zone, p-type emitter 
           50  Fourth semiconductor zone, n-type emitter 
           60 ,  60 A,  60 B,  60 C VLD zone 
           62 ,  64  Third semiconductor zone, field rings 
           70  Channel stopper 
           80 A,  80 B Recombination zone 
           100  Semiconductor body 
           101  Front 
           102  Back 
           103  Inner region 
           104  Edge region 
           105  Edge