Abstract:
The controllable semiconductor switching element blocks in both directions. The semiconductor switching element is formed with a first conduction region and a second conduction region of a first type of conductivity, a blocking region of a second type of conductivity which is disposed between the first and second conducting regions, and a control electrode which is arranged opposite the blocking region and insulated from it. A recombination region is configured in the blocking region and is comprised of a material that promotes a recombination of charge carriers of the first and second type of conductivity.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application is a continuation of copending International Application No. PCT/EP00/07603, filed Aug. 4, 2000, which designated the United States and which was not published in English. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    Field of the Invention  
           [0003]    The present invention relates to a controllable semiconductor switching element, in particular a field-effect-controllable semiconductor switching element, having the following features:  
           [0004]    a first conduction zone and a second conduction zone of a first conductivity type;  
           [0005]    a channel zone of a second conductivity type between the first and second conduction zones; and  
           [0006]    a control electrode insulated from the channel zone.  
           [0007]    Such semiconductor switching elements are, for example, MOSFETs (Metal Oxide Field Effect Transistor) known according to the prior art. One embodiment of a vertical power MOSFET according to the prior art is described in Stengl/Tihanyi: “Leistungs-MOSFET-Praxis” [Power MOSFETs in practice], Pflaum Verlag, Munich, 1992, page 29 et seq., and is partially illustrated in cross section in FIG. 1A. The MOSFET has a source zone as first conduction zone  12  of a first conductivity type (n), which is introduced into a well-like channel zone (also called body zone or depletion zone) of a second conductivity type (p). The source zone  12  can be externally contacted via a source electrode  40 , the source electrode  40  reaching through the source zone  12  right into the channel zone and thus short-circuiting the source zone  12  and the channel zone  18 .  
           [0008]    The channel zone  18  is introduced into a second conduction zone  14 ,  16  of the first conductivity type (n)—the drain zone of the MOSFET—the second conduction zone having an n-doped zone  14  surrounding the channel zone  18  and a more heavily n-doped zone  16  for connection of a drain electrode. A gate electrode is insulated from the channel zone  18  and the source and drain zones  12 ,  14 . The gate electrode forms a control electrode  20  of the MOSFET above a semiconductor body wherein are formed the source zone  12 , which is also designated as forward direction, and the drain zone, which is also designated as reverse direction.  
           [0009]    An equivalent circuit diagram of the vertical MOSFET according to FIG. 1A is illustrated in FIG. 1B, which is illustrated as a combination of an ideal MOSFET T 1  and a diode D 1 . The diode is connected in the forward direction between the source terminal S and the drain terminal D of the MOSFET. The diode, which conducts when a positive voltage is applied in the source-drain direction, results from the pn junction between the drain zone  14 ,  16  and the body zone  18  and the short circuit between the body zone  18  and the source zone  12 .  
           [0010]    The presence of the integrated diode is disadvantageous for some applications of the MOSFET since it has the effect that the MOSFET only conducts when a forward voltage is applied in the drain-source direction, while it conducts like a diode when a voltage is applied in the source-drain direction.  
           [0011]    Without the short circuit between the source zone and the body zone, a parasitic bipolar transistor formed by the sequence of the differently doped zones, namely the source zone of the first conductivity type, the channel zone of the second conductivity type complementary to the first conductivity type and the drain zone of the first conductivity type, would be active in the MOSFET, the base of the bipolar transistor being formed by the channel zone and the emitter/collector of the bipolar transistor being formed by the source zone/drain zone.  
           [0012]    [0012]FIG. 1C shows the electrical equivalent circuit diagram of a MOSFET without a short circuit between the source zone and the drain zone, which is illustrated as a combination of an ideal MOSFET T 1  with a bipolar transistor. The collector/emitter path C-E of the bipolar transistor B 1  is connected in parallel with the drain-source path D-S of the MOSFET T 1 . The base zone of the parasitic bipolar transistor B 1  is formed by the channel zone of the MOSFET, the emitter zone is formed by the source zone of the MOSFET and the collector zone is formed by the drain zone of the MOSFET.  
           [0013]    The parasitic bipolar transistor B 1  influences the dielectric strength of the semiconductor switching element in accordance with FIG. 1C, as shown by the family of characteristic curves of this semiconductor switching element in FIG. 1D. In the case of a drain-source voltage U DS  having the value U CE0 , the collector-emitter breakdown voltage of the parasitic bipolar transistor B 1  and thus the maximum reverse voltage of the semiconductor switching element in the drain-source direction D-S are reached. As the gate-source voltage increases, the dielectric strength rises slightly, as can be gathered from the family of characteristic curves. Until the breakdown voltage is reached, the behavior of the semiconductor switching element corresponds to that of an ideal MOSFET.  
           [0014]    The reduction of the dielectric strength in a MOSFET with non-short-circuited source zone and depletion zone results from the fact that charge carriers accumulate in the substrate during operation, that is to say when a drive potential is applied to the gate terminal and when a forward voltage is applied between drain and source. These charge carriers drive the base of the parasitic bipolar transistor, as a result of which the latter is turned on. The dielectric strength of such a MOSFET in the drain-source direction is approximately only ⅓ of the dielectric strength of a comparable component with short-circuited source zone and body zone.  
         SUMMARY OF THE INVENTION  
         [0015]    It is accordingly an object of the invention to provide a controllable, dual blocking semiconductor switching element, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which provides for a controllable semiconductor switching element that blocks in both directions without reduction of the reverse voltage in a main voltage direction (forward direction).  
           [0016]    With the foregoing and other objects in view there is provided, in accordance with the invention, a controllable semiconductor switching element, comprising:  
           [0017]    a first conduction zone and a second conduction zone of a first conductivity type;  
           [0018]    a channel zone of a second conductivity type between the first and second conduction zones;  
           [0019]    a control electrode insulated from the channel zone;  
           [0020]    the second conduction zone having a more heavily doped second terminal zone for connection to a terminal electrode and a more weakly doped second transition zone adjacent the channel zone;  
           [0021]    the first conduction zone having a more heavily doped first terminal zone for connection to a terminal electrode and a more weakly doped first transition zone adjacent the channel zone; and  
           [0022]    at least one recombination region formed in the channel zone and made of a material promoting a recombination of charge carriers of the first and second conductivity types.  
           [0023]    With the above and other objects in view there is also provided, in accordance with the invention, a method for fabricating a semiconductor switching element, which comprises the following steps:  
           [0024]    providing a semiconductor body with a second terminal zone of a first conductivity type, a second transition zone of the first conductivity type adjacent the second terminal zone and more weakly doped than the second terminal zone, a channel zone of a second conductivity type adjacent the second transition zone, a first transition zone of the first conductivity type adjacent the channel zone, a first terminal zone of the first conductivity type adjacent the first transition zone and doped more heavily than the second transition zone;  
           [0025]    fabricating at least one control electrode surrounded by an insulation layer and extending at least from the first transition zone through the channel zone as far as the second transition zone; and  
           [0026]    fabricating at least one recombination zone in the channel zone made of a material that promotes a recombination of charge carriers of the first and second conductivity types.  
           [0027]    In other words, the objects of the invention are achieved with the novel semiconductor switching element that has at least one recombination region formed in the depletion zone and made of a material which promotes a recombination of charge carriers of the first and second conductivity types. In the semiconductor switching element according to the invention, no short circuit is provided between the channel zone and one of the two conduction zones.  
           [0028]    By virtue of the sequence of, arranged next to one another, the first conduction zone of the first conductivity type, the channel zone of the second conductivity type and the second conduction zone of the second conductivity type, a parasitic bipolar transistor is formed in the semiconductor switching element according to the invention. However, the provision of the recombination region in the channel zone of the semiconductor switching element, or in the base zone of the parasitic bipolar transistor, alters the electrical behavior of the parasitic bipolar transistor. When a forward voltage is applied between the first and second conduction zones, charge carriers of the first and second conductivity types, namely holes and electrons, are generated in the space charge zone between one of the two conduction zones and the channel zone. Charge carriers of the first conductivity type can easily recombine with charge carriers of the second conductivity type at the boundary with respect to the recombination region, or at the surface thereof. What is thus achieved by virtue of the recombination zone is that the parasitic bipolar transistor is only driven to a very small extent, or what is achieved is that the parasitic bipolar transistor no longer becomes active when a sufficiently large recombination zone is present.  
           [0029]    The dielectric strength of the semiconductor switching element according to the invention thus corresponds in one direction (forward direction) to the dielectric strength of a conventional semiconductor switching element of this type with a short circuit between one of the conduction zones and the channel zone. At the same time, the semiconductor switching element according to the invention also blocks when a forward voltage is applied in the other direction (reverse direction) since there is no short circuit present between one of the conduction zones and the channel zone.  
           [0030]    In accordance with an added feature of the invention, the material of the recombination region is preferably a metal. Further embodiments provide for the recombination region to be formed from polysilicon, or a different semiconductor material, or from silicide, or a different corresponding semiconductor compound.  
           [0031]    In accordance with an additional feature of the invention, the recombination region is formed in a plate-type manner in order to provide, in conjunction with a small volume, a surface that is as large as possible for the recombination of the charge carriers. The semiconductor switching element according to the invention is preferably constructed in a cell-like manner, that is to say a multiplicity of identically constructed and driven cells are present which each have a first conduction zone, a channel zone and a second conduction zone. In this case, each cell has a recombination region.  
           [0032]    It is possible to form a plurality of recombination regions, which are formed in particular in a plate-type or strip-type manner, spaced apart from one another in the channel zone, preferably in the channel zone of each cell. In this case, the individual recombination regions are preferably connected to one another by heavily doped regions of the second conductivity type in order to enable an easy exchange of charge carriers between the recombination regions, or the various sections of the recombination region that are arranged separately from one another.  
           [0033]    In addition to embodiments wherein the recombination regions are completely surrounded by the channel zone, that is to say a zone made of material of the second conductivity type, further embodiments of the invention provide for the recombination regions to be connected to the first conduction zone by zones made of material of the first conductivity type. When a metal or a silicide is used as material for the recombination region, a Schottky contact is produced between the depletion zone, which is also designated as body zone in MOSFETS, and the first conduction zone, the Schottky contact determining the dielectric strength of the component in the reverse direction.  
           [0034]    In accordance with a further embodiment of the invention, the first conduction zone has a heavily doped terminal zone for connection of a first terminal electrode and a more weakly doped transition zone between the terminal zone and the channel zone, and the second conduction zone has a heavily doped second terminal zone for connection of a second electrode and a more weakly doped second transition zone arranged between the second terminal zone and the channel zone. The dielectric strength of the semiconductor switching element according to the invention is essentially determined by the doping of the transition zones and the distance between the terminal zones and the channel zone, the distance being determined by the transition zones. In this embodiment, wherein each conduction zone has a more weakly doped transition zone, a dielectric strength of the semiconductor switching element that is approximately identical in the forward direction and in the reverse direction can be set by means of the thickness and the doping of the transition zones.  
           [0035]    Other features which are considered as characteristic for the invention are set forth in the appended claims.  
           [0036]    Although the invention is illustrated and described herein as embodied in a controllable semiconductor switching element that blocks in both directions, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.  
           [0037]    The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0038]    [0038]FIG. 1 shows a MOSFET according to the prior art in cross section (FIG. 1A) and its equivalent circuit diagram (FIG. 1B), equivalent circuit diagram (FIG. 1C) and family of characteristic curves (FIG. 1D) of a MOSFET without a short circuit between the source region and body region;  
         [0039]    [0039]FIG. 2 shows a detail from a semiconductor switching element according to the invention in accordance with a first embodiment in cross section;  
         [0040]    [0040]FIG. 3 shows a cross section through the semiconductor switching element in accordance with FIG. 2 along a line III-III;  
         [0041]    [0041]FIG. 4 shows a cross section through the semiconductor switching element in accordance with FIGS. 2 and 3 along a line IV-IV in FIG. 3;  
         [0042]    [0042]FIG. 5 shows a detail from a semiconductor switching element according to the invention in accordance with a second embodiment in cross section;  
         [0043]    [0043]FIG. 6 shows an equivalent circuit diagram of the semiconductor switching element in accordance with FIG. 5;  
         [0044]    [0044]FIG. 7 shows a detail from a semiconductor switching element according to the invention in accordance with a third embodiment in cross section;  
         [0045]    [0045]FIG. 8 shows a cross section through the semiconductor switching element in accordance with FIG. 7 along a line VIII-VIII;  
         [0046]    [0046]FIG. 9 shows a detail from a semiconductor switching element according to the invention in accordance with a fourth embodiment in cross section;  
         [0047]    [0047]FIG. 10 shows a semiconductor switching element according to the invention in a lateral design;  
         [0048]    [0048]FIG. 11 shows a cross section through a semiconductor switching element according to the invention in accordance with a further embodiment in side view;  
         [0049]    [0049]FIG. 12 shows a cross section through the semiconductor switching element according to FIG. 11 in cross section along the sectional plane XII-XII;  
         [0050]    [0050]FIG. 13 shows a cross section through an edge region of the semiconductor switching element according to FIGS. 11 and 12 in side view;  
         [0051]    [0051]FIG. 14 shows a cross section through a semiconductor switching element according to FIGS. 11 and 12 during various method steps of the fabrication method. 
     
    
       [0052]    Unless specified otherwise, identical reference symbols designate structurally identical and functionally equivalent parts and regions throughout the figures.  
       DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0053]    Referring now once more to the figures of the drawing in detail, and particularly to FIG. 2 thereof, there is shown a cross section through a detail from a semiconductor switching element according to the invention in accordance with a first embodiment. The semiconductor switching element illustrated has the construction of a vertical n-conducting MOS transistor, in particular of an n-conducting MOSFET. In this case, in an n-conducting semiconductor body  10 , a p-conducting zone is formed as channel zone  18 , which is also designated as body zone or depletion zone, into which, in turn, a highly doped n-conducting zone  12  is introduced, which serves as first conduction zone, or source zone, of the MOSFET. The semiconductor body  10  has an n-conducting region  14  and, in the region of a side remote from the source zone, a highly doped n-conducting region  16 , which together form the second conduction zone, or drain zone. The heavily doped region  16  serves for connection to a drain electrode D.  
         [0054]    The source zone  12  is connected to a source electrode  40 , S, for example made of aluminum, the source electrode  40  making contact with the source zone at a surface of the semiconductor body  10 . At least one gate electrode  20 , which serve as control electrode of the MOSFET, are arranged above the depletion zone  12  and in a manner isolated from the latter by an insulation layer  30 . The gate electrode  20  is composed of polysilicon, for example, and the insulation layer  30  is composed of a silicon oxide, for example. The structure illustrated is preferably repeated a number of times toward the left and right and perpendicularly to the plane of the drawing, thereby producing a cell-like structure of the semiconductor switching element. The current-carrying strength of the semiconductor switching element rises with the number of cells.  
         [0055]    The MOSFET illustrated has a parasitic bipolar transistor, the emitter zone thereof being formed by the source zone  12 , the base zone thereof being formed by the channel zone  18  and the collector zone thereof being formed by the drain zone  14 ,  16  of the vertical MOSFET.  
         [0056]    A recombination zone  19  made of a material that promotes the recombination of n-type charge carriers and p-type charge carriers in this zone is arranged in the channel zone  18  of the MOSFET, or the base zone of the parasitic bipolar transistor. The recombination zone is preferably composed of a metal, a polysilicon or a silicide and is formed in a plate-type manner, for example.  
         [0057]    If, in the semiconductor switching element according to the invention, a positive voltage is applied between the drain zone  14 ,  16 , or a drain electrode which is applied to the zone  16  and is not illustrated in any greater detail, and the source zone  12 , or the source electrode  40 , charge carriers, namely electrons and holes, are generated in the space charge zone between the drain zone  14  and the channel zone  18 . In this case, on account of the field in the space charge zone, the holes flow into the drain zone  14 ,  16 , and the holes flow into the depletion zone. A recombination of the injected holes with electrons takes place to an intensified extent at the surface of the recombination region  19 , thereby preventing the parasitic bipolar transistor from becoming active and reducing the reverse voltage in the drain-source direction.  
         [0058]    In other words: the good possibility of recombination of n-type and p-type charge carriers in the base zone of the parasitic bipolar transistor reduces the current gain β thereof and thereby increases the collector-emitter breakdown voltage thereof, which concomitantly determines the dielectric strength of the MOSFET over the drain-source path.  
         [0059]    For the rest the illustrated semiconductor switching element functions like a MOSFET, that is to say that when a positive drive potential is applied to the gate electrode  20 , a conductive channel forms in the channel zone between the source zone  12  and the drain zone  14 , which channel, when a forward voltage is applied between the drain zone  16  and the source electrode  14 , enables a current flow between the drain terminal D and the source terminal S.  
         [0060]    Through a suitable choice of the material and the geometrical structure of the recombination region  19 , the breakdown voltage of the MOSFET can be increased to the extent that would result in the event of a short circuit between the first conduction zone (source zone)  12  and the channel zone  18 , i.e. in the event of a short-circuited base-emitter junction of the parasitic bipolar transistor, but without having to accept the disadvantageous effect of such a short circuit, namely the lack of dielectric strength in the reverse direction (source-drain direction). The MOSFET illustrated blocks even when a positive voltage is applied between the source electrode  40 , or the source zone  12 , and the drain zone  14 ,  16  in a manner governed by the pn junction between the depletion zone  18  and the source zone  12 .  
         [0061]    As is indicated in FIG. 2, the region  16  can be heavily p-doped instead of heavily n-doped. The semiconductor switching element then functions as an IGBT (Insulated Gate Bipolar Transistor).  
         [0062]    The recombination region  19  is preferably formed in such a way that it has a large area in conjunction with a small volume requirement.  
         [0063]    The recombination region is therefore preferably formed in a plate-type manner, or, as is illustrated in FIG. 3 using a cross section along the line III-III from FIG. 2, from a plurality of strip-type sections which essentially run parallel. The dash-dotted lines in FIG. 3 illustrate the position of the overlying gate electrode  20 . The dashed lines illustrate the position of the overlying source electrode  40 , S.  
         [0064]    [0064]FIG. 4 shows a cross section through the semiconductor switching element along a sectional line IV-IV depicted in FIG. 3, from which the parallel position of the strips forming the recombination region  19  becomes clear. The individual subregions of the recombination region  19  are preferably connected to one another by heavily p-doped regions  181  in order to promote the charge exchange between the subregions of the recombination region  19 .  
         [0065]    [0065]FIG. 5 shows a further embodiment of the semiconductor switching element according to the invention, the recombination region  19  and the heavily n-doped source zone  12  being connected to one another by an n-conducting zone  13 . The material of the recombination region  19  is preferably a metal or a silicide in this embodiment.  
         [0066]    [0066]FIG. 6 shows the equivalent circuit diagram of the semiconductor switching element according to FIG. 5. A Schottky junction is formed between the n-conducting region  13 , which is part of the source zone, and the recombination region  19 , said Schottky junction being depicted as Schottky diode D S  between the source terminal S and the substrate terminal of the MOSFET. The diode D 2  between the drain terminal D and the substrate terminal is formed by the pn junction between the drain zone  14 ,  16  and the depletion zone  18  (also referred to as p-type body region). The Schottky diode D S  determines the reverse voltage of the semiconductor switching element in the reverse direction (source-drain direction), and the diode D 2 , or the pn junction between the drain zone  14 ,  16  and the depletion zone  18 , determines the dielectric strength of the MOSFET in the forward direction (drain-source direction).  
         [0067]    [0067]FIG. 7 partially shows a cross section through a semiconductor switching element in accordance with a further embodiment of the invention. FIG. 8 shows a cross section through this semiconductor switching element along the sectional line VIII-VIII depicted in FIG. 7. In this embodiment, a gate electrode  60  is arranged in a “buried” manner in a semiconductor body  105  and is surrounded by an insulation layer  70 . A source electrode  80  terminates the semiconductor body  101  toward the top. First heavily n-doped conduction zones (source zones)  52  are arranged below the source electrode  80  and between the trench structure of the gate electrode  60 . The source zones  52  are adjoined by p-doped depletion zones  58  wherein are arranged recombination regions  59  made of a material which promotes the recombination of n-type and p-type charge carriers. The structure comprising gate electrode  60  and surrounding insulation layer  70  extends downward as far as an n-doped zone  54  which, together with an adjoining heavily n-doped zone  56 , forms a second conduction zone (drain zone) of the MOSFET illustrated.  
         [0068]    In addition to an exemplary embodiment of a recombination region  19  which is completely surrounded by the p-conducting channel zone  58 , FIG. 7 shows an exemplary embodiment of a recombination region  59 ′ which is insulated by an insulation layer  90  from the source electrode  80 , S and the source zone  52 . This results from a possible fabrication method of the recombination zone  59 ′ in the depletion zone. In this case, before the deposition of the source electrode  80 , holes are introduced into the depletion zone  58 , for example by etching, and subsequently filled to a height below the source zone  52  with a material which promotes the recombination. Afterward, the insulation layer  90  is applied in the hole above the material which promotes the recombination.  
         [0069]    As becomes clear in particular from the plan view in FIG. 8, the semiconductor switching element according to the invention in accordance with FIG. 7 has a grid-type gate electrode  60 , the channel zone  58  with the recombination zone  59 , which is insulated from the gate electrode  60  by an insulation layer  70 , being arranged in interspaces of the grid. The semiconductor switching element thus has a multiplicity of identically constructed cells which are driven simultaneously, the current-carrying strength of the semiconductor switching element according to the invention rising with the number of cells. When a positive drive potential is applied to the gate electrode  60 , a conductive channel forms in the channel zone in the vertical direction of the semiconductor body  105  along the gate electrode  60 , a current flow between the drain electrode D and the source electrode S being enabled when a forward voltage is applied between the drain electrode D and the source electrode S.  
         [0070]    [0070]FIG. 9 partially shows in cross section a further embodiment of a semiconductor switching element according to the invention with a trench-type structure comprising gate electrode  60  and insulation layer  70 . In this embodiment, the source zone comprises a heavily n-doped zone  52  arranged adjacent to the gate electrode  60  and the source electrode  80 , and a normally n-doped zone  53  which surrounds the heavily doped zone  52  in the remaining regions. In this embodiment, the recombination region  59  extends from the p-doped depletion zone  58  arranged below the zone  53  right into the n-doped zone  53  and is insulated toward the top from the source electrode  80  by an insulation layer  90 . In this embodiment, the recombination region  59  is preferably composed of a metal or a silicide and forms a Schottky contact with the n-doped zone  53 . The equivalent circuit diagram of the semiconductor switching element according to FIG. 9 corresponds to that illustrated in FIG. 6.  
         [0071]    While a conductive channel forms in the lateral direction in the depletion zone  18  when a positive voltage is applied between the gate and source electrodes G, S and a positive voltage is applied between the drain and source electrodes D, S in the case of the semiconductor switching elements illustrated in FIGS.  2  to  6 , a conductive channel forms in the vertical direction in the case of the exemplary embodiments according to FIGS. 7 and 8. This embodiment saves more space relative to the embodiments illustrated in FIGS.  2  to  6 .  
         [0072]    If the heavily n-doped zone  56  is replaced by a heavily p-doped zone, the components illustrated in FIGS.  7  to  9  function as IGBTs.  
         [0073]    [0073]FIG. 10 shows a further embodiment of a semiconductor switching element according to the invention, which is formed as a MOSFET in a lateral design. In this case, heavily n-doped drain and source zones  216 ,  212  are arranged in a p-doped depletion zone  218  of the semiconductor body  200  and can be contact-connected by means of source and drain electrodes S, G from the same side of the semiconductor body  200 . A gate electrode G is arranged in a manner insulated by an insulation layer  230  on the semiconductor body  200 . A recombination region made of a material which promotes the recombination of n-type and p-type charge carriers is arranged in the depletion zone  218 .  
         [0074]    [0074]FIG. 11 shows a further exemplary embodiment of a semiconductor switching element according to the invention which blocks in both directions, in side view in cross section. FIG. 12 illustrates a cross section through the arrangement according to FIG. 11 along the sectional plane XII-XII.  
         [0075]    The semiconductor switching element according to the invention has a semiconductor body  100  having a heavily n-doped second terminal zone  112  and an n-doped second transition zone  114 , which is arranged adjacent to the second terminal zone  112  and is doped more weakly than the second terminal zone  112 , the second terminal zone  112  and the second transition zone  114  forming a second conduction zone (drain zone) of the semiconductor switching element. A p-doped channel zone  116  is formed adjacent to the second transition zone  114 , which channel zone is not necessarily doped homogeneously and is adjoined by an n-doped first transition zone  118 . A heavily n-doped first terminal zone  110  is formed adjacent to the first transition zone  118  and is doped more heavily than the first transition zone  118 , the first terminal zone  110  and the first transition zone  118  forming a first conduction zone (source zone) of the semiconductor switching element. In the exemplary embodiment, the second terminal zone  112 , the second transition zone  114 , the channel zone  116 , the first transition zone  118  and the first terminal zone  110  are arranged in a layer-like manner one above the other, a second terminal electrode  140 , preferably made of metal or polysilicon, being applied to a rear side of the semiconductor body  100  for contact-connection of the second terminal zone  112 , and a first terminal electrode  141  being applied to a front side of the semiconductor body for contact-connection of the first terminal zone  110 .  
         [0076]    When a positive drive potential is applied to the gate electrode, in this semiconductor switching element, a conductive channel forms along the surface of the semiconductor body between the source zone  212  and the drain zone  216 . In this embodiment, too, n-type charge carriers and p-type charge carriers can recombine with one another at the recombination zone  219 , thereby preventing a parasitic bipolar transistor formed by the sequence of the n-conducting source zone  212 , the p-conducting channel zone  218  and the n-conducting drain zone  216  from being driven.  
         [0077]    The second terminal zone  112  and the adjoining second transition zone  114  form the drain zone of the MOSFET; the first terminal zone  110  and the adjoining first transition zone  118  form the source zone of the MOSFET, the drain and source terminals being interchangeable on account of the symmetrical construction of the FET illustrated in FIG. 11.  
         [0078]    In order to enable the formation of a conductive channel in the channel zone between the drain zone  112 ,  114  and the source zone  110 ,  118 , a control electrode  120 ,  122 ,  124 ,  126  is provided, which is surrounded by an insulation layer  121 ,  123 ,  125 ,  127  and extends in the vertical direction of the semiconductor body  100  from the n-doped first transition zone  114  through the p-doped channel zone  116  right into the n-doped second transition zone  118 . As can be seen from FIG. 12, in the exemplary embodiment, a number of approximately parallel control electrodes  120 ,  122 ,  124  are provided, which are connected by a common plate  126 , as a result of which the control electrodes  120 ,  122 ,  124  can be connected to a common drive potential. The common plate is insulated from the semiconductor body  100  by an insulation layer  127  and extends in the vertical direction preferably as far as the front side or rear side of the semiconductor body  100  in order to be connected to a drive potential. The first and/or second terminal zone  110 ,  112  preferably does not extend as far as the common plate  126 , in order to prevent the formation of a current-carrying channel along the common plate  126 . It goes without saying that, in addition to the common plate  126 , any other embodiments desired are conceivable in order to connect the control electrodes  120 ,  122 ,  124  to a common drive potential.  
         [0079]    The more control electrodes  120 ,  122 ,  124  are provided in the semiconductor body  100 , the larger the electrode area along which a current-carrying channel can form, and the larger the current-carrying strength of the MOSFET.  
         [0080]    The regions made of insulation material above the control electrodes  120 ,  122 ,  124  and below the terminal electrode  141  are produced by filling the trenches wherein the control electrodes  120 ,  122 ,  124  are formed with insulation material after the fabrication of the control electrodes  120 ,  122 ,  124 .  
         [0081]    According to the invention, recombination zones  130 ,  132 ,  134  are provided in the channel zone  116  adjacent to the control electrodes  120 ,  122 ,  124 , which recombination zones promote the recombination of n-type and p-type charge carriers in the channel zone  116 . The recombination zones  130 ,  132 ,  134  are preferably composed of a metal, such as platinum for example, or of a silicide. The distance between the recombination zones  130 ,  132 ,  134  and the control electrodes is preferably small and is preferably less than 5 μm.  
         [0082]    [0082]FIG. 13 shows an edge region of the semiconductor body  100  wherein the semiconductor switching element according to the invention is formed. As can be seen from FIG. 3, the channel zone  116  does not reach as far as the edge of the semiconductor body  100  in the lateral direction. Furthermore, in the lateral direction of the semiconductor body  100 , the second terminal electrode  141  only reaches as far as a point above a control electrode  126  nearest to the edge. The second terminal zone  110  reaches only as far as that side of the insulation region  127  which is remote from the edge above the outermost control electrode  126 . At that side area of the outermost control electrode  126  which faces the edge, it is thus not possible for a conductive channel to form between the first terminal zone  112  and the second terminal zone  110 . The first transition zone  114  and the second transition zone  118  are connected to one another in the edge region.  
         [0083]    If, in the semiconductor switching element according to the invention, a positive voltage is applied between the first terminal electrode (drain electrode)  140 , D and the second terminal electrode (source electrode)  141 , S, charge carriers, namely electrons and holes, are generated in a space charge zone between the drain zone  112 ,  114  and the channel zone. In this case, on account of the field in the space charge zone, the electrons flow into the drain zone  112 ,  114 , or to the drain electrode  140 , and the holes flow into the channel zone  116 . In the channel zone, the recombination zones  130 ,  132 ,  134 ,  136 , preferably composed of a metal, promote the recombination of the holes injected into the channel zone with electrons. This prevents a parasitic bipolar transistor formed by the sequence of the n-conducting drain zone  112 ,  114 , the p-conducting channel zone  116  and the n-conducting source zone  118 ,  110  from becoming active and reducing the reverse voltage of the MOSFET in the drain-source direction.  
         [0084]    If, in addition to the drain-source voltage, a positive drive potential is applied to the control electrodes  120 ,  122 ,  124 ,  126 , conductive channels form along the control electrodes  120 ,  122 ,  124 ,  126  and enable a charge carrier exchange between the drain zone  112 ,  114  and the source zone  110 ,  118 .  
         [0085]    The dielectric strength of the MOSFET in the drain-source direction is crucially determined by the doping of the second transition zone  114  and the “thickness” of the second transition zone  114 , that is to say the distance between the heavily doped second terminal zone  112  and the channel zone  116 .  
         [0086]    When a positive voltage is applied in the source-drain direction, charge carriers are generated in a space charge zone between the second transition zone  118  and the channel zone  116 , holes being injected into the channel zone  116 , where they recombine with electrons at the recombination zones  130 ,  132 ,  134 ,  136 , whereby the parasitic bipolar transistor is prevented from becoming active. The dielectric strength of the component in the source-drain direction is crucially determined by the doping of the first transition zone  118  and the distance between the heavily doped first terminal zone  110  and the channel zone  116 .  
         [0087]    The component according to the invention blocks in both directions, that is to say both in the drain-source direction and in the source-drain direction. Preferably, the first and second transition zones  114 ,  118  are doped identically and have the same layer thickness in order to obtain the same reverse voltage in the drain-source direction and in the source-drain direction. In contrast to the semiconductor switching elements in accordance with FIGS.  1  to  8 , wherein only a heavily n-doped zone is present as source zone, and wherein the reverse voltage is larger in the drain-source direction than in the source-drain direction, in the circuit arrangement in accordance with FIGS.  11  to  13 , identical reverse voltages can thus be achieved in the drain-source direction and in the source-drain direction.  
         [0088]    Given fabrication of the component using silicon technology and given a thickness a of the channel zone of between 0.5 μm and 1 μm and a thickness b of the first and second transition zones  114 ,  118  of about 5 μm, it is possible, given a weak doping of these zones  14 ,  18 , to obtain reverse voltages of about 50 V.  
         [0089]    The distance x between the recombination zones and the control electrodes is preferably less than 1 μm.  
         [0090]    [0090]FIG. 14 illustrates a method for fabricating a semiconductor switching element according to the invention. In this case, in first method steps (FIG. 14A), a semiconductor body  100  is fabricated, which has a heavily n-doped second terminal zone  112  and a more weakly n-doped second transition zone  114  arranged adjacent to the second terminal zone. In the semiconductor body  100 , a p-doped channel zone  116  is formed adjacent to the second transition zone  114 , said channel zone being adjoined by an n-doped first transition zone  118 . The first transition zone  118  is doped more weakly than a heavily n-doped first terminal zone  110  arranged adjacent to the first transition zone  118 .  
         [0091]    In a next method step (FIG. 14B), first trenches  160 ,  162 ,  164  are produced which, proceeding from a front side  170  of the semiconductor body  100 , extend right into the second transition zone  114 . As an alternative, the trenches can be produced in such a way that, proceeding from the rear side  172  of the semiconductor body  100 , they extend right into the first transition zone  118 . Moreover, second trenches  161 ,  163 ,  165  which, proceeding from the front side  170 , extend right into the channel zone  116  are produced adjacent to the first trenches  160 ,  162 ,  164 . As an alternative, the second trenches, proceeding from the rear side  172 , may extend right into the channel zone  116 .  
         [0092]    In a next method step (FIG. 14C), a layer  121   a ,  123   a ,  125   a  made of an insulation material is fabricated on side areas of the first trenches  160 ,  162 ,  164 , in order to insulate the later electrodes  120 ,  122 ,  124  from the semiconductor body  100 .  
         [0093]    In next method steps, in order to fabricate the control electrodes  120 ,  124 ,  126 , a layer made of electrode material is deposited in the first trenches  160 ,  162 ,  164 , the layer reaching right into the first transition zone  118  in the vertical height of the semiconductor body  100 . Moreover, a layer made of a recombination material is deposited in the second trenches  161 ,  163 ,  165 , which layer extends to a point below the boundary with respect to the second transition zone  118  in the vertical height of the semiconductor body, so that the resultant recombination zones  130 ,  132 ,  114  are only surrounded by the channel zone  116 .  
         [0094]    In next method steps, the first and second trenches are filled with an insulation material before the terminal electrodes  140 ,  141  are applied to the front and rear sides  170 ,  172  of the semiconductor body, in order to arrive at the configuration illustrated in FIG. 11.