Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a semiconductor component, in particular a field-effect-controllable transistor. 
     DE 198 28 191 C1 discloses a lateral high-voltage transistor having, on an n-conducting substrate, an epitaxial layer in which source and drain zones and also a channel zone surrounding the source zone are formed. Trenches are provided in the epitaxial layer. The sidewalls of these trenches are heavily doped with a complementary dopant with respect to the rest of the epitaxial layer. A conductive channel in the channel zone can be controlled by means of a gate electrode insulated from the channel zone. 
     When a source-drain voltage is applied, a space charge zone propagates in this transistor—if no gate-source voltage is applied—proceeding from the source zone, and as the voltage rises, the space charge zone gradually reaches the complementarily doped sidewalls of the trenches in the direction of the drain zone. Where the space charge zone propagates, free charge carriers of the doped sidewalls of the trenches and free charge carriers of the surrounding epitaxial layer mutually compensate one another. In these regions in which the free charge carriers mutually compensate one another, a high breakdown voltage results for lack of free charge carriers. The reverse voltage of the transistor can be set by means of the doping of the trenches, the epitaxial layer preferably being highly doped, as a result of which the transistor has a low on resistance when the gate is driven. 
     Such transistors having a low on resistance but a high reverse voltage are currently available only as discrete components, that is to say only the transistor is realized in a semiconductor body. However, for many applications, for example for switching loads, it is desirable to integrate a transistor as a switching element and its associated drive circuit, for example using CMOS technology, in a single semiconductor body. 
     SUMMARY OF THE INVENTION 
     The semiconductor component according to the invention has a semiconductor body with a substrate of a first conduction type and, situated above the latter, a first layer of a second conduction type. In the layer of the second conduction type there is formed a channel zone of the first conduction type with a first terminal zone of the second conduction type arranged adjacent to it. Furthermore, a second terminal zone of the second conduction type is formed in the second layer. In a transistor, the first terminal zone forms the source zone and the second terminal zone forms the drain zone. The source zone is surrounded in the second layer by the channel zone, in which a conductive channel can form as a result of the application of a drive potential to a control electrode or gate electrode which is arranged in a manner insulated from the channel zone. 
     In order that the first layer can be highly doped for the purpose of achieving a low on resistance, and, on the other hand, in order that a high reverse voltage is achieved, compensation zones of the first conduction type are provided in the first layer, a second layer of the second conduction type being formed between these compensation zones and the substrate of the first conduction type, said second layer preferably being doped more lightly than the first layer. 
     In integrated circuits, the substrate is usually at a reference-ground potential. The second layer then prevents charge carriers from passing into the substrate when a high potential is applied to one of the terminal zones; in the substrate said charge carriers could pass to other circuit components in the semiconductor body, for example to a drive circuit, and interfere with their functioning. In the event of a large potential difference between one of the terminal zones and the substrate, the second layer is depleted on account of the space charge zone which then forms, that is to say the free charge carriers in the second layer and free charge carriers of the substrate and/of the compensation zones mutually compensate one another. The second layer then forms a potential barrier for free charge carriers of the first conduction type between the first layer and the substrate. 
     One embodiment of the invention provides a boundary zone which extends in the vertical direction of the semiconductor body. This boundary zone preferably reaches in the lower region of the semiconductor body as far as the substrate and extends in the upper region of the semiconductor body as far as the channel zone or is arranged offset with respect to the channel zone in the lateral direction of the semiconductor body and reaches as far as a first surface of the semiconductor body. The boundary zone of the first conduction type, which is thus doped complementarily with respect to the first layer, bounds the semiconductor component according to the invention in the lateral direction of the semiconductor body. A charge carrier exchange in the lateral direction is prevented by the boundary zone, as a result of which further semiconductor circuits, for example drive circuits using CMOS technology, can be realized beyond said boundary zone, the drive circuit and the semiconductor component according to the invention not mutually interfering with one another. 
     One embodiment of the invention provides for the compensation zones in the first layer to extend in a pillar-shaped manner in the vertical direction of the semiconductor body, in which case, according to a further embodiment, at least some of the compensation zones adjoin the channel zone. In transistors, the source zone as first terminal zone and the channel zone are usually short-circuited, so that the compensation zones adjoining the channel zone are at the same potential as the first terminal zone. 
     According to a further embodiment of the invention, the compensation zones are of spherical design and arranged such that they are distributed in the first layer of the second conduction type. 
     A further embodiment provides for the first layer of the second conduction type to be weakly doped and for more heavily doped second compensation zones of the second conduction type to be formed adjacent to the compensation zones, which, in particular, are of pillar-shaped design. When a high voltage is applied between the first and second terminal zones, the compensation zones of the first conduction type and the respectively adjacent second compensation zones of the second conduction type mutually deplete one another, that is to say the free charge carriers of the compensation zone of the first conduction type and the free charge carriers of the second compensation zone of the second conduction type mutually compensate one another. 
     One embodiment of the semiconductor component according to the invention provides for the second terminal zone to be formed in a well-like manner in the region of the first surface of the semiconductor body or the first layer. In this exemplary embodiment, the charge carriers move between the first and second terminal zones essentially in the lateral direction of the semiconductor body. A further embodiment provides for the second terminal zone to extend in the vertical direction of the semiconductor body as far as the second layer and to run in the region of the second layer in the lateral direction of the semiconductor body below the first terminal zone. In this embodiment, in which the lateral section of the highly doped second terminal zone runs in a manner buried in the semiconductor body and can be contact-connected by means of the vertical section at the first surface of the semiconductor body, the charge carriers move essentially in the vertical direction of the semiconductor body. 
     A further embodiment provides for vertical sections of the second terminal zone and the laterally running section of the second terminal zone to enclose the first terminal zones and at least some of the compensation zones in a well-like manner. 
     In accordance with an added feature of the invention, the first layer has a number of dopant atoms of the first conduction type and a number of dopant atoms of the second conduction type that are approximately identical. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross sectional view of a first exemplary embodiment of a semiconductor component; 
     FIG. 2 is a plan view of an embodiment of a semiconductor component with elongate first terminal zones; 
     FIG. 3 is a plan view of an embodiment of a semiconductor component with an annularly closed first terminal zone; 
     FIG. 4 is a cross sectional view of another exemplary embodiment of a semiconductor component; 
     FIG. 5 is a cross sectional view of another exemplary embodiment of a semiconductor component with a plurality of first terminal zones and compensation zones running in a pillar-shaped manner; 
     FIG. 6 is a cross sectional view of another exemplary embodiment of a semiconductor component with a plurality of first terminal zones and compensation zones of spherical design; 
     FIG. 7 is a cross sectional view of another exemplary embodiment of a semiconductor component with a plurality of first terminal zones and with first compensation zones adjacent second compensation zones; and 
     FIG. 8 is a cross sectional view of another exemplary embodiment of a semiconductor component with a plurality of first terminal zones and with a second terminal zone surrounding the first terminal zones in a well-like manner. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the figures, unless specified otherwise, identical reference symbols designate identical sections and zones with the same meaning. 
     FIG. 1 shows a semiconductor component according to the invention, designed as a MOS transistor, in a lateral sectional illustration, FIG. 2 showing a section through the semiconductor component according to FIG. 1 along the sectional plane A—A′ in the case of a first embodiment, and FIG. 3 showing the semiconductor component according to FIG. 1 in a plan view of the sectional plane A—A′ in the case of a second embodiment. The exemplary embodiments illustrated in FIGS. 2 and 3 do not differ in their side view, which is shown for both exemplary embodiments in FIG.  1 . 
     The MOS transistor according to the invention has a semiconductor body  20  with a weakly p-doped substrate  22  and, situated above the latter, an n-doped first layer  24 . A p-doped channel zone  50  is introduced in a well-like manner in the first layer  24 , proceeding from a first surface  201 , a heavily n-doped first terminal zone  40  being formed in a well-like manner in said channel zone. In this case, the first terminal zone  40  forms the source zone of the MOS transistor. In the n-doped first layer  24 , a heavily n-doped second terminal zone  60  is introduced spaced apart from the channel zone  50  in the lateral direction of the semiconductor body  20 , which terminal zone is likewise formed in a well-like manner proceeding from the first surface  201  in the exemplary embodiment according to FIG.  1 . The second terminal zone  60  forms the drain zone of the MOS transistor. The drain zone  60  is contact-connected by means of a drain electrode  62  which is arranged on the first surface  201  and forms a drain terminal of the MOS transistor. In a corresponding manner, the source zone  40  is contact-connected by means of a source electrode  52  which short-circuits the source zone  40  and the channel zone  50  and which forms the source terminal S of the MOS transistor. 
     For driving the MOS transistor, provision is made of a gate electrode  70  above the channel zone  50 , which is insulated from the semiconductor body  20  by means of an insulation layer  72  and which forms a gate terminal of the MOS transistor. 
     FIG. 1 shows, in cross section, two source zones  40  and channel zones  50 , in each case in the lateral direction of the semiconductor body  20  on the left and right beside the drain zone  60 . These source zones  40  are connected to one another and, as is illustrated in FIG. 2, may be designed as elongate strips in the semiconductor body  20  between which a likewise elongate drain zone  60  is formed. The elongate source zones and the elongate drain zone can extend as far as edges or edge regions of the semiconductor body. The channel zone  50  and the source zone  40  can also enclose the drain zone  60  annularly as is illustrated in FIG.  3 . FIG. 1 illustrates a cross section both through the semiconductor component according to the invention according to FIG.  2  and through the semiconductor component according to the invention according to FIG.  3 . 
     P-doped compensation zones  30  are formed in the n-doped layer  24  and, in the exemplary embodiment according to FIG. 1, extend in a pillar-shaped manner in the vertical direction of the semiconductor body  20 . The cross section of these pillar shaped compensation zones  30  is circular in the exemplary embodiments according to FIGS. 2 and 3, but this cross section can assume virtually any other geometric shapes and be, for example, rectangular, square or octagonal. 
     In the exemplary embodiment according to FIG. 1, the pillar-shaped compensation zones  30  start at the level of the first surface  201  and extend in the vertical direction as far as a second n-conducting layer  26  formed between the compensation zones  30  and the substrate  22 . In this case, this second n-conducting layer  26  is preferably doped more weakly than the first n-conducting layer  24 . 
     Furthermore, a p-doped layer  32  is formed below the first surface  201  of the semiconductor body  20 , which layer preferably reaches as far as the channel zone  50  and connects the compensation zones  30  to one another. The p-doped layer  32  preferably does not reach as far as the second terminal zone  60 . Equally, a compensation zone  30 A formed below the drain zone  60  does not reach as far as the drain zone  60 . 
     The region of the first layer  24  in which the compensation zones  30  are formed forms the drift path of the MOS transistor. The MOS transistor or its drift path is bounded in the lateral direction of the semiconductor body by a p-doped boundary zone  80  which, in the exemplary embodiment according to FIG. 1, extends in the vertical direction of the semiconductor body proceeding from the channel zone  50  as far as the substrate  22 . In this case, like the source zone  40  in FIG. 2, the boundary zone  80  can run below the source zone in an elongate manner as far as the edges of the semiconductor body  20  or, in accordance with the source zone  40  in FIG. 3, it can annularly surround the drift path. 
     The boundary zone  80 , which is preferably doped more highly than the p-doped substrate  22 , forms a pn junction with the first layer  24  and prevents n-type charge carriers from passing through the boundary zone  80  into n-doped zones  124  of adjacent components, or adjacent semiconductor circuits, which are represented by way of example in FIG. 1 by two CMOS transistors T 1 , T 2  and a terminal for supply potential +U. Such a drive circuit might be, for example, a drive circuit for the MOS transistor according to the invention illustrated on the right in FIG. 1, which drive circuit is realized with the MOS transistor in the same semiconductor body. 
     Typical doping concentrations of the individual zones of the semiconductor component according to FIG. 1 are specified below by way of example: 
     
       
         
               
               
               
               
             
           
               
                   
               
             
             
               
                 Substrate 22: 
                 Volume doping 
                 10 14 -10 15   
                 cm −3   
               
               
                 n-doped zone 124: 
                 Volume doping 
                 10 15 -10 16   
                 cm −3   
               
               
                 Drain zone 60: 
                 Volume doping 
                 10 18 -10 20   
                 cm −3   
               
               
                 Compensation zones 30: 
                 Area doping 
                 10 12   
                 cm −2   
               
               
                 Drift path 24: 
                 Area doping 
                 10 12   
                 cm −2   
               
               
                 Second layer 26: 
                 Area doping 
                 10 12   
                 cm −2   
               
               
                 Zone 32: 
                 Area doping 
                 &lt;10 12   
                 cm −2   
               
               
                   
               
             
          
         
       
     
     This MOS transistor has a low on resistance and a high breakdown voltage, the second n-conducting layer  26  preventing charge carriers from passing from the drift zone of the MOS transistor into the substrate  22 , as is explained below. 
     If, in the MOS transistor according to the invention, a positive voltage is applied between the gate terminal G and the source terminal S, then a conductive channel forms in the channel zone  50  below the gate electrode  72 . If a positive voltage is applied between the drain electrode D and the source electrode S, a charge carrier current flows in the lateral direction of the semiconductor body  20  through the drift path between the source zone  40  and the drain zone  60 . The drain-source voltage is represented as voltage +U D  in FIG. 1, it being assumed that the source electrode is at a reference-ground potential of the circuit, in particular ground. The on resistance R on  of the MOS transistor is lower, the higher the doping of the first layer  24  with n-type charge carriers. 
     If the MOS transistor is in the off state, that is to say there is no drive potential at its gate electrode, then when a drain-source voltage is applied, a space charge zone propagates proceeding from the source zone  40  or the channel zone  50  in the drift path in the direction of the drain zone  60 . This space charge zone advances in the direction of the drain zone  60  as the drain-source voltage increases. If the space charge zone reaches a compensation zone  30 , then the compensation zone  30  assumes the potential of the space charge zone upon reaching the compensation zone  30 . Free p-type charge carriers (holes) of this compensation zone  30  and free n-type charge carriers (electrons) from the regions of the drift path which surround the respective compensation zone mutually compensate one another. The number of free charge carriers thereby decreases in the drift path as the reverse voltage increases, or as the space charge zone extends further. The compensation of the free charge carriers means that the MOS transistor has a high reverse voltage. 
     In semiconductor bodies in which a plurality of semiconductor components are realized, the substrate  22  is usually at reference-ground potential. In the exemplary embodiment according to FIG. 1 the substrate  22  can be contact-connected by means of an electrically conductive layer  90 , for example a metalization layer applied on the substrate. The voltage between the drain terminal  60  and the substrate  22  then corresponds to the drain-source voltage of the MOS transistor. As the drain potential +U D  increases, a space charge zone propagates upward proceeding from the substrate  22 , as a result of which the second n-conducting layer is depleted, that is to say the free n-type charge carriers of the second layer  26  and holes in the surrounding substrate  22  or the upwardly adjoining compensation zones  30  mutually compensate one another. The second layer  26 , which is preferably doped in such a way that it can be completely depleted, thus forms a potential barrier for free charge carriers of the drift path and prevents said free charge carriers from passing into the substrate  22 , where they could propagate unimpeded and interfere with the functioning of other semiconductor components integrated in the semiconductor body  20 . 
     The dopings of the compensation zones  30 , of the drift path  24  and of the second layer  26  are preferably co-ordinated with one another in such a way that the number of p-type charge carriers approximately corresponds to the number of n-type charge carriers, so that at the maximum possible reverse voltage, when the space charge zone reaches the drain zone  60  proceeding from the source zone  40 , the compensation zones  30 , the drift path  24  and the second layer  26  are completely depleted, that is to say no free charge carriers are present. The breakdown voltage then corresponds to the breakdown voltage of an undoped drift path  24 . 
     The MOS transistor according to the invention, with the source zone  40 , the channel zone  50  surrounding the source zone, the drain zone  60 , the drift path  24  with the compensation zones  30 , the boundary zone  80 , an n-conducting layer  26  between the compensation zones  30  and with the substrate  22 , can be integrated together with further semiconductor components in a semiconductor body. Consequently, a MOS transistor as power switch with a low on resistance and a high reverse voltage can be integrated together with its drive circuit in a semiconductor body or a chip in a space-saving manner. 
     FIG. 4 shows a further exemplary embodiment of a semiconductor component according to the invention in cross section. Whereas in the exemplary embodiment according to FIG. 1 the p-conducting boundary zone  80  extends as far as the substrate  22  proceeding from the channel zone  50  in the vertical direction of the semiconductor body  20 , in the exemplary embodiment according to FIG. 4 the boundary zone  80  is arranged such that it is spaced apart from the channel zone  50  in the lateral direction and extends from the first surface  201  in the vertical direction of the semiconductor body  20  as far as the substrate  22 . Pillar-like compensation zones  30 B,  30 C,  30 D are formed in the n-conducting layer  24  between the channel zone  50  and the boundary zone  80 , said compensation zones extending in the vertical direction of the semiconductor body  20  from the first surface  201  as far as the second n-conducting layer  26 . Unlike the compensation zones  30  between the channel zone  50  and the drain zone  60 , the compensation zones  30 B,  30 C,  30 D between the channel zone  50  and the boundary zone  80  are not connected to one another by a p-conducting layer  32 . Consequently, the compensation zones  30 B,  30 C,  30 D between the channel zone  50  and the boundary zone  80  are designed in a “floating” manner in the second layer  24 , that is to say they are not at a defined potential and assume the potential of a space charge zone which extends as far as the compensation zones  30  when the semiconductor component is in the off state. Discharging of the compensation zones  30 B,  30 C,  30 D when the MOS transistor is switched on again can be effected by thermal charge carriers. 
     The compensation zones  30 B,  30 C,  30 D between the channel zone  50  and the boundary zone  80  increase the breakdown voltage between the MOS transistor, which is formed within a well, formed by the boundary zone  80  and the n-conducting second layer  26 , and adjacent semiconductor components, which are not illustrated in FIG. 4 for reasons of clarity. 
     The sectional illustration according to FIG. 4 furthermore shows field plates  90 ,  91 ,  92 ,  93 ,  94 , which are arranged on the first surface  201  in a manner insulated from the semiconductor body  20  by an insulation layer  74 . These field plates influence, in a known manner, the field line profile within and outside the semiconductor body and prevent a voltage breakdown in the edge regions of the MOS transistor or edges thereof. In this case, a first field plate  90  running obliquely upward is connected to the boundary zone  80 , a second and third field plate  91 ,  92  are connected to the source terminal S and a fourth and fifth field plate  93 ,  94  are connected to the drain terminal D. 
     FIG. 5 shows a further exemplary embodiment of a semiconductor component according to the invention, designed as a MOS transistor, in a lateral sectional illustration. The semiconductor component according to this exemplary embodiment has a plurality of source zones  40 A,  40 B,  40 C and respective channel zones  50 A,  50 B,  50 C surrounding the latter, the source zones  40 A,  40 B,  40 C and the channel zones  50 A,  50 B,  50 C being connected to a common source electrode  52 ,S. The source zones  40 A,  40 B,  40 C are, in particular, of annular design, FIG. 5 showing a section through the center of these annular source zones. 
     In the component according to FIG. 5 gate electrodes  70 A,  70 B,  70 C,  70 D are arranged on the semiconductor body in a manner insulated by insulation layers  72 A,  72 B,  72 C,  72 D and are connected to a common gate electrode G. The gate electrodes  70 A,  70 B,  70 C,  70 D illustrated in FIG. 5 may be, in particular, constituent parts of a single gate electrode of grid-like design, in which case the source zones  40 A,  40 B,  40 C,  40 D with the channel zones  50 A,  50 B,  50 C are arranged below cutouts of the grid and, in the cutouts of the grids, the source zones are contact-connected by means of the source electrode  52 . 
     Compensation zones  30  are formed in the first n-conducting layer  24  arranged above the substrate  22 , some of these compensation zones adjoining the channel zones  50 A,  50 B,  50 C and extending in a pillar-like manner in the vertical direction of the semiconductor body  20 . Other compensation zones  30 E are formed between the channel zones  50 A,  50 C and the boundary zones  80 , the boundary zones extending from the first surface  201  of the semiconductor body  20  as far as the substrate  22 . In the exemplary embodiment according to FIG. 5, the drain zone  60  extends proceeding from the first surface  201  in the vertical direction as far as the n-doped second layer  26  formed between the substrate  22  and the first n-conducting layer  24 . The drain zone  60  additionally extends in the lateral direction of the semiconductor body in the region of the second layer  26  below the first terminal zones  40 A,  40 B,  40 C. Whereas in the exemplary embodiments according to FIGS. 1 to  4  the charge carrier transport runs between the source zones and the drain zones essentially in the lateral direction of the semiconductor body  20 , the charge carriers in the exemplary embodiment according to FIG. 5 propagate, with the gate electrode G being driven, in the vertical direction of the semiconductor body between the source zones  40 A,  40 B,  40 C and the laterally running section of the drain zone  60 . In the exemplary embodiment according to FIG. 5, the volume of the drift path can be better utilized as a result of the larger area of the drain zone  60 , at which charge carriers can be taken up from the drift path, and the larger channel area resulting from the provision of a plurality of source zones  40 A,  40 B,  40 C and channel zones  50 A,  50 B,  50 C. In other words, the MOS transistor according to FIG. 5 has a higher current-carrying capacity than the MOS transistors according to FIGS. 1 to  4 . In the exemplary embodiment according to FIG. 5, the second layer  26  and the laterally running section of the drain zone  60  form a potential barrier for charge carriers from the drift path into the substrate  22 . 
     The drain zone  60  has a first section  100  extending vertically to the second layer  26  and a second section  102  extending laterally at the level of the second layer  26 . 
     FIG. 6 shows a further exemplary embodiment of a semiconductor component according to the invention, which differs from that illustrated in FIG. 5 by virtue of the fact that the compensation zones  30  in the first n-conducting layer  24  are of spherical design and are arranged spaced apart from the channel zones  50 A,  50 B,  50 C,  50 D. 
     In the exemplary embodiment according to FIG. 7, the n-conducting layer  24  is weakly n-doped, second n-conducting compensation zones  25  being formed beside the p-conducting compensation zones  30 , the respectively adjacent compensation zones  30 ,  25  mutually depleting one another when a space charge zone propagates in the first layer  24 , in order thus to bring about a high breakdown voltage of the semiconductor component. In the exemplary embodiment according to FIG. 7, some of the p-conducting compensation zones  30  are connected to the channel zones  50 A,  50 B,  50 C and are thus at source potential. 
     FIG. 8 shows a further exemplary embodiment of a semiconductor component according to the invention, in which the drain zone  60  is of U-shaped design in cross section and encloses the first terminal zones  40 A,  40 B,  40 C and the channel zones  50 A,  50 B,  50 C and some of the compensation zones  30 . The drain zone  60  is preferably in the form of a well and encloses the first terminal zones  40 A,  40 B,  40 C and the channel zones  50 A,  50 B,  50 C and some of the compensation zones  30  on all sides in the lateral direction of the semiconductor body  20 . 
     LIST OF REFERENCE SYMBOLS 
       20  Semiconductor body 
       22  Substrate 
       24  First n-conducting layer 
       26  Second n-conducting layer 
       30 ,  30 A Compensation zone 
       32  p-conducting layer 
       40  Source zone 
       50 ,  50 A,  50 B,  50 C Channel zone 
       52  Source electrode 
       60  Drain zone 
       62  Drain electrode 
       70  Gate electrode 
       70 A,  70 B,  70 C,  70 D Gate electrodes 
       72  Insulation layer 
       72 A,  72 B,  72 C,  72 D Insulation layers 
       80  Boundary zone 
       90  Metalization layer 
       90 ,  91 ,  92 ,  93 ,  94  Field plates 
       95  Field plate 
       124  n-conducting layer 
       126  n-conducting layer 
       201  First surface of the semiconductor body 
     T 1 , T 2  CMOS transistors 
     S Source terminal 
     G Gate terminal 
     D Drain terminal 
     +U D  Drain potential 
     n n-doped zone 
     p p-doped zone

Technology Category: h