Abstract:
A controllable field-effect semiconductor component has a semiconductor body including a first surface, a first layer of a first conduction type, and a second layer of the first conduction type lying above the first layer. The semiconductor component also has a first terminal zone that can be contact-connected at the first surface of the semiconductor body. The first terminal zone is formed in the second layer. A channel zone of a second conduction type surrounds the first terminal zone. Compensation zones of the second conduction type that are formed in the second layer are provided. Additionally, the semiconductor component has a second terminal zone of the first conduction type that can be contact-connected at the first surface of the semiconductor body. The second terminal zone is formed in the second layer.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention:  
           [0002]    The present invention relates to a field-effect controllable semiconductor component having a low on resistance, high current-carrying strength and a high breakdown voltage, in which a first and a second load terminal can be contact-connected at one side of the semiconductor body.  
           [0003]    Published German Patent Application DE 196 04 043 A1 discloses a vertical MOSFET which has a heavily n-doped substrate with a more weakly n-doped epitaxial layer lying above it. P-doped channel zones are introduced into the epitaxial layer, and heavily n-doped source zones are embedded, in turn, in the channel zones. These source zones can be contact-connected at the surface of the semiconductor body. Gate electrodes make it possible to form a conductive channel in the channel zone between the source zone and a drift zone which is formed in the epitaxial layer between the channel zone and the substrate. Furthermore, p-doped first compensation zones and n-doped second compensation zones are formed in the epitaxial layer, resulting first in low on resistance of the MOSFET when the gate electrode is driven, and in a high reverse voltage, or breakdown voltage, when the gate electrode is not driven. When the gate electrode is driven, the n-doped regions in the epitaxial layer enable charge to be transferred between the source zone and the heavily n-doped substrate which forms the drain zone. When the gate electrode is not driven and a drain-source voltage is applied, a space charge zone forms proceeding from the source zone, or the channel zone, and has the effect that free charge carriers of the first and second compensation zones recombine with one another, whereby the number of free charge carriers in the epitaxial layer is considerably reduced, and this results in a high breakdown voltage.  
           [0004]    In the known vertical MOSFET, the substrate forms the drain zone which can be contact-connected from the rear side of the semiconductor body, that is to say the side opposite to the side of the source terminal.  
           [0005]    Such an arrangement of the source terminal and drain terminal at opposite sides of the semiconductor body is disadvantageous for those applications in which a further chip is applied to the front side of the semiconductor body, or of a chip, in which the MOSFET is accommodated, especially when the terminals of which further chip have to be connected to the source terminal and the drain terminal of the MOSFET. By way of example, a diode may be realized in the second chip, which diode, in specific applications, is connected between the source terminal and the drain terminal of a MOSFET.  
         SUMMARY OF THE INVENTION  
         [0006]    It is accordingly an object of the invention to provide a field-effect controllable semiconductor component which overcomes the above-mentioned disadvantages of the prior art apparatus of this general type. In particular, it is an object of the invention to provide a field-effect controllable semiconductor component having a low on resistance, high current-carrying strength and a high breakdown voltage, in which a first and a second load terminal can be contact-connected at one side of the semiconductor body.  
           [0007]    With the foregoing and other objects in view there is provided, in accordance with the invention, a field-effect controllable semiconductor component that has a semiconductor body having a first layer of a first conduction type, and lying above the layer, a second layer of the first conduction type. The first layer preferably is doped more heavily than the second layer. At least one first terminal zone is formed in the second layer, which terminal zone can be contact-connected at a first surface of the semiconductor body. The at least one first terminal zone is surrounded within the second layer by a channel zone of a second conduction type.  
           [0008]    Furthermore, compensation zones of the second conduction type are formed in the second layer. According to the invention, a second terminal zone of the first conduction type is formed in the second layer, which terminal zone can be contact-connected at the first surface of the semiconductor body. The second terminal zone is formed such that it is spaced apart from the at least one first terminal zone in the lateral direction of the semiconductor body.  
           [0009]    In the case of a MOS transistor, the first terminal zone forms the source zone of the transistor, the second terminal zone forms the drain zone of the transistor and a control electrode which is arranged adjacent to the channel zone and is insulated from the semiconductor body forms the gate electrode of the transistor.  
           [0010]    The second terminal zone is preferably connected to the first layer by means of a connecting zone which is a good electrical conductor and extends in the vertical direction in or along the second layer. This first layer is preferably doped more heavily than the second layer, and thus conducts better. When a drive potential is applied to the control electrode and a voltage is applied between the first and second terminal zones, a charge current occurs in the semiconductor component, which charge current, in a drift zone formed between the channel zone and the first layer, having emerged from the channel zone, runs in the vertical direction of the semiconductor body to the heavily doped first layer, from where the charge carriers pass via the connecting zone to the second terminal zone.  
           [0011]    When the control electrode is not driven and a voltage is applied between the first and second terminal zones, a space charge zone propagates in the semiconductor body proceeding from the channel zone. If this space charge zone encompasses one of the compensation zones, then free charge carriers of this compensation zone recombine with free charge carriers from the regions of the second layer which surround the respective compensation zone. As the reverse voltage increases, or the space charge zone propagates to an increasing extent, charge carriers are thus depleted in the second layer, resulting in a high breakdown voltage. The number of charge carriers of the first conduction type in the second layer preferably corresponds to the number of charge carriers of the second type in the compensation zones, so that the second layer and the compensation zones can mutually completely deplete one another, i.e. there are no longer any free charge carriers in the second layer at the maximum possible reverse voltage.  
           [0012]    In accordance with an added feature of the invention, the connecting zone is formed as a heavily doped zone of the first conduction type which extends, in the vertical direction of the semiconductor body, from the second terminal zone that is arranged in the region of the first surface as far as the first layer. In this case, the second terminal zone is preferably formed in the edge region of the semiconductor body.  
           [0013]    In accordance with a concomitant feature of the invention, the first layer and the second terminal zone are connected by means of a layer which is a good electrical conductor and is formed on a, preferably inclined, side area of the semiconductor body.  
           [0014]    Other features which are considered as characteristic for the invention are set forth in the appended claims.  
           [0015]    Although the invention is illustrated and described herein as embodied in a vertical field-effect transistor with compensation zones and terminals at one side of a semiconductor body, 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.  
           [0016]    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  
       [0017]    [0017]FIG. 1 shows a cross section of a first embodiment of a semiconductor component;  
         [0018]    [0018]FIG. 2 shows a partial illustration of a cross section taken through the sectional plane A-A′ depicted in FIG. 1; and  
         [0019]    [0019]FIG. 3 shows a cross section of a second embodiment of a semiconductor component. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]    In the figures, unless specified otherwise, identical reference symbols designate identical parts and regions with the same meaning. The present invention is explained below, without restricting the generality, with reference to an n-conducting MOSFET in which a source zone represents a first terminal zone, a drain zone represents a second terminal zone and a gate electrode represents a control electrode.  
         [0021]    Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown a first exemplary embodiment of a MOSFET in a side view in cross section. FIG. 2 illustrates a section taken through the semiconductor component along the sectional plane A-A′ depicted in FIG. 1.  
         [0022]    The MOSFET shown in FIG. 1 has a semiconductor body  10  having a heavily n-doped substrate  12  and a more weakly n-doped epitaxial layer  14  arranged on the substrate. In the exemplary embodiment, a plurality of p-doped channel zones  40 A,  40 B,  40 C are formed in the epitaxial layer  14 , which channel zones are formed like wells and, in the exemplary embodiment, two source zones  30 A,  30 B,  30 C are embedded in each of the channel zones. The source zones  30 A,  30 B,  30 C are jointly contact-connected by means of a source electrode  32  at a surface  102  of the semiconductor body. The source electrode  32  short-circuits the source zones  30 A,  30 B,  30 C and the channel zones  40 A,  40 B,  40 C which respectively surround the source zones  30 A,  30 B,  30 C. The source zones  30 A,  30 B,  30 C are of annular design in the exemplary embodiment, as can be seen in particular from the plan view in FIG. 2.  
         [0023]    A gate electrode  50  is applied, in a manner insulated from the semiconductor body  10 , on the first surface  102  of the semiconductor body  10 , which extends in the lateral direction of the semiconductor body  10  from each of the source zones  30 A,  30 B,  30 C along the channel zone  40 A,  40 B,  40 C as far as the n-doped region of the second or epitaxial layer  14 . The n-doped region of the second or epitaxial layer  14  between the channel zone and the substrate  12  forms the so-called drift zone or drift path of the MOSFET.  
         [0024]    [0024]FIG. 1 shows respective sections  50 A,  50 B,  50 C,  50 D of the gate electrode  50 , which is illustrated by broken lines with dash-dotted contours in FIG. 2, in order to illustrate the position of the gate electrode  50  above the channel zones  40 A,  40 B and the source zones  30 A,  30 B. The gate electrode  50  is designed in plate form and has respective annular cutouts  51 A,  51 B above the source zones  30 A,  30 B,  30 C and above the channel zones  40 A,  40 B,  40 C, through which cutouts the source electrode  32  extends. The gate electrode  50  is insulated from the source electrode by means of insulation layers  54 B,  54 C,  54 D. The insulation layer  52 A,  52 B,  52 C,  52 D between the gate electrode  50  and the semiconductor body  10  and the insulation layers  54 B,  54 C,  54 D between the gate electrode and the source electrode  32  are preferably composed of a semiconductor oxide such as e.g. silicon oxide.  
         [0025]    The provision of a large number of source zones  30 A,  30 B,  30 D which are each part of a so-called cell of the MOSFET enables the MOSFET to have a large current-carrying strength, where the current-carrying strength can be set through the number of cells.  
         [0026]    The MOSET shown in FIG. 1 has a drain zone  20  spaced apart from the source zones  30 A,  30 B,  30 C in the lateral direction of the semiconductor body  10 . This drain zone is formed like a well in the epitaxial layer  14  and is contact-connected by means of a drain electrode  22  on the first surface  102  of the conductor body  10 .  
         [0027]    In the drift zone, that is to say in the region of the epitaxial layer  14  between the channel zones  40 A,  40 B,  40 C and the substrate  12 , p-doped compensation zones  60 ,  62 ,  64 ,  65 ,  66  are formed which, in the exemplary embodiment, are designed in pillar form and, in their longitudinal direction, extend in the vertical direction of the semiconductor body  10 . The compensation zones  60 ,  62 ,  64 ,  65  that are arranged between respective ones of the channel zones  40 A,  40 B,  40 C and the substrate  12  can be like the compensation zone  60  which adjoins the channel zone  40 A or can be separated from the channel zone  40 B,  40 C by part of the epitaxial layer  14 , like e.g. the compensation zones  62 ,  64 ,  65 . Moreover, a plurality of compensation zones  64 ,  65  may be arranged one below the other in the vertical direction of the semiconductor body  10 .  
         [0028]    The drain zone  20  and source zones  30 A,  30 B,  30 C are arranged spaced apart from one another in the lateral direction of the semiconductor body  10 . Compensation zones  66  likewise are formed in the epitaxial layer  14  between the channel zone  40 A and the drain zone  20 , which compensation zones run like pillars in the vertical direction of the semiconductor body  10 .  
         [0029]    In order to connect the drain zone  20  to the substrate  12 , a connecting zone  16  is provided which extends in the vertical direction of the semiconductor body  10  from the drain zone  20  as far as the substrate  12 . This connecting zone  16  is preferably doped more heavily than the remaining regions of the epitaxial layer  14 , and the doping of the connecting zone  16  may correspond to the doping of the substrate  12 .  
         [0030]    If, in the MOSFET illustrated in FIG. 1, a positive voltage is applied between the gate electrode  50  and the source zones  30 A,  30 B,  30 C, then conductive channels form in the channel zones  40 A,  40 B,  40 C, which channels run below the gate electrode  50 . When a voltage is applied between the drain electrode  22  and the source electrode  32 , n-type charge carriers pass from the source zones  30 A,  30 B,  30 C into the drift zone. These charge carriers move in the epitaxial layer  14  essentially in the vertical direction of the semiconductor body  10  into the heavily doped substrate  12 , from where they pass via the connecting zone  16  to the drain zone  20 . The drain zone, which is provided with the reference symbol  20  in FIG. 1, the connecting zone  16  and the substrate  12  together form the drain zone of the MOSFET according to the invention. In order to connect the zone  20  to the substrate  12  in a manner exhibiting the least possible resistance, no p-doped compensation zones  66  are provided between the zone  20  and the substrate  12 .  
         [0031]    If the gate electrode is not driven in the MOSFET shown in FIG. 1, and if a voltage is applied between the drain electrode  22  and the source electrode  32 , then free charge carriers of the compensation zones  60 ,  62 ,  64 ,  65 ,  66  start to recombine with free charge carriers of the epitaxial layer  14 , as a result of which, as the reverse voltage increases, free charge carriers are depleted in the epitaxial layer  14 , as explained with reference to the various compensation zone  60 ,  62 ,  64 ,  65 .  
         [0032]    The compensation zone  60  is connected via the channel zone  40   a  to the source potential, which is usually a fixed reference potential, in particular ground. If the potential rises in the substrate  12 , or in the region of the epitaxial layer  14  which surrounds the compensation zone  60 , when the drain potential increases, then a space charge zone containing many free charge carriers propagates in a manner proceeding from the compensation zone  60  in the lateral direction of the semiconductor body  10 .  
         [0033]    The compensation zone  62  is arranged in a floating manner, i.e. not connected to a fixed potential, in the epitaxial layer  14 . If a space charge zone propagates in a manner proceeding from the channel zone  40   b  when a reverse voltage is applied, then the compensation zone  62  assumes the value of the potential of the space charge zone in the region of the compensation zone  62 . If the space charge zone of the channel zone  40   b  reaches the compensation zone  62 , then a space charge zone no longer containing free charge carriers propagates in a manner proceeding from the compensation zone  62  in the lateral direction. The same applies correspondingly to the compensation zones  64  and  65 , a space charge zone forming in a manner proceeding from the lower compensation zone  64  only when the latter is encompassed by the space charge zone of the upper compensation zone  65 .  
         [0034]    The maximum reverse voltage of the MOSFET is reached when the space charge zones proceeding from the individual compensation zones  60 ,  62 ,  64 ,  65  have encompassed the entire epitaxial layer  14 . The doping of the epitaxial layer  14  and of the compensation zones  60 ,  62 ,  64 ,  65 ,  66  is preferably coordinated with one another in such a way that the number of n-type charge carriers in the epitaxial layer  14  corresponds to the number of p-type charge carriers in the compensation zones  60 ,  62 ,  64 ,  65 ,  66 , with the result that there are no free charge carriers when the space charge zone has encompassed the entire epitaxial layer  14 .  
         [0035]    The compensation zones  66 , which are arranged in a floating manner in the epitaxial layer  14  between the source zone  30   a  and the drain zone  20 , prevent a breakdown of the MOSFET in the lateral direction of the semiconductor body  10  in the epitaxial layer  14 . In the MOSFET, the compensation zones  66  are successively encompassed by a space charge zone which proceeds from the channel zone  40   a.    
         [0036]    [0036]FIG. 1 furthermore shows field plates  90 ,  91 , which are formed above the semiconductor body  10  in a manner isolated from the latter by an insulation layer  92 . One of the field plates  90  is connected to the drain zone  20  and one of the field plates  91  is connected to the source electrode  32 . The field plates  90 ,  91  influence the field strength profile in the semiconductor body  10 , and as is known, prevent a premature voltage breakdown.  
         [0037]    In the MOSFET shown in FIG. 1, the drain zone  20  is formed at the edge of the semiconductor body  10 . The side area  101  terminates the semiconductor body  10  in the lateral direction. The area  101  is usually the area produced when the semiconductor body  10  is sawn from a wafer having a multiplicity of semiconductor bodies.  
         [0038]    [0038]FIG. 3 shows a further exemplary embodiment of a MOSFET, which differs from that illustrated in FIG. 1 by virtue of the fact that the drain zone  22  and the substrate  12  are connected to one another by a layer  23 , in particular a metallization layer, which is a good electrical conductor and is applied on a side area  104  of the semiconductor body  10 . The side area in FIG. 3 is slightly inclined, proceeding from the substrate  12  in the direction of the drain zone  20 . The substrate  12  extends below the area  104  in the lateral direction as far as a side area  103 , which forms the lateral boundary of the semiconductor body  10  and which results for example from the semiconductor body  10  being sawn from a wafer. The area  104  is thus set back relative to the terminating area  103 . The metallization layer  23  simultaneously forms the drain electrode of the MOSFET.  
         [0039]    The application of a metallization layer  70  to the substrate, as is provided in the MOSFET in accordance with FIG. 1, is dispensed with in the MOSFET in accordance with FIG. 3.