Patent Publication Number: US-8114743-B2

Title: Integrated circuit device with a semiconductor body and method for the production of an integrated circuit device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This Utility patent application is a divisional application of U.S. application Ser. No. 12/020,077, filed Jan. 25, 2008, which claims the benefit of the filing date of German Application No. DE 10 2007 061 191.0, filed Dec. 17, 2007, which is herein incorporated by reference. 
    
    
     BACKGROUND 
     The application relates to an integrated circuit device with a semiconductor body and to a method for the production of an integrated circuit device. The semiconductor body includes a cell field with a drift zone of a first conduction type. In addition, the semiconductor device includes an edge region surrounding the cell field. Field plates with a trench gate structure are arranged in the cell field. 
     In semiconductor devices with field plate compensation structures, the cell field is surrounded by an edge region for which an edge termination has to be provided. For this purpose, the active region, which is initially completely free of a field oxide, is defined as a cell field. In the cell field, the field plates in the trench structure are surrounded by a field plate insulation. The outer trenches or field plates of the cell field are provided with a field plate insulation which is brought out to a field oxide on the front side of the semiconductor body in the edge region. 
     In addition, a continuous trench, a edge trench, surrounds the entire cell field, its clearance generally corresponding to the spacing of the trench structures in the cell region. 
     Such a structure of a semiconductor device is subject to two types of problems. First, the edge trench is subjected to the highest loading, as compensation is no longer complete on the side of the edge trench remote from the cell field. As a result, a breakdown may occur at the continuous edge trench, the location of the breakdown being the curvature at the trench base adjacent to the cell field. There is therefore a risk that this edge breakdown may occur earlier than the cell field breakdown, so that the blocking capability of the edge trench has to be increased. A further problem is found in the region of the source fingers with conductive contact material, as these contacts are only provided outside the active cell field, leaving a certain minimum distance between the end of the body zones and the continuous edge trench. 
     In the region of the edge trench, the potential can directly reach the field oxide from below in the semiconductor body, which could cause problems. In principle, doping must not exceed a critical value, otherwise a potential breakdown at the trench base could jump upwards to a trench contact, whereby breakdown voltage is significantly reduced. A reduction of the concentration of doping material towards the surface, which is possible in an epitaxial process, slightly reduces the ability of the potential to reach the field oxide while reducing the load on the continuous edge trench. The reduction of the concentration of doping material, however, adversely affects on resistance. 
     For these and other reasons, there is a need for the present invention. 
     SUMMARY 
     An integrated circuit device with a semiconductor body and a method for the production of an integrated circuit device is provided. The semiconductor body includes a cell field with a drift zone of a first conduction type. In addition, the semiconductor device includes an edge region surrounding the cell field. Field plates with a trench gate structure are arranged in the cell field, while an edge trench surrounding the cell field is provided in the edge region. In the edge region, the front side of the semiconductor body includes an edge zone of a conduction type complementing the first conduction type and identical to the conduction type of the body zones of the cell field. The edge zone of the complementary conduction type extends both within and outside the edge trench. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the present invention and are incorporated in and constitute a part of this specification. The drawings illustrate the embodiments of the present invention and together with the description serve to explain the principles of the invention. Other embodiments of the present invention and many of the intended advantages of the present invention will be readily appreciated as they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts. 
         FIG. 1  illustrates a diagrammatic top view of a section of an integrated circuit semiconductor device according to an embodiment. 
         FIG. 2  illustrates a schematic representation of a cross-section through the section of the semiconductor device  1  along line A-A through a field plate or trench structure. 
         FIG. 3  illustrates a perspective schematic representation of the section of the semiconductor device according to  FIG. 1  along line A-A through a body zone or mesa structure. 
         FIG. 4  illustrates a diagrammatic cross-section through the section of the semiconductor device according to  FIG. 1  along line B-B. 
         FIGS. 4   a  to  4   c  illustrate diagrammatic cross-sections through field plates in the cell field with different gate structures in the same trench of the field plates. 
         FIGS. 5 to 12  illustrate diagrammatic cross-sections through field plates in the cell field with different gate structures in the same trench of the field plates. 
         FIG. 5  illustrates a diagrammatic cross-section through a section of a semiconductor body after the introduction of trench structures. 
         FIG. 6  illustrates a diagrammatic cross-section through the section from  FIG. 5  after the application of an insulating layer. 
         FIG. 7  illustrates a diagrammatic cross-section through the section from  FIG. 6  after the trench structure has been filled with a conductive material. 
         FIG. 8  illustrates a diagrammatic cross-section through the section from  FIG. 7  after the removal of the conductive material from a field oxide on front sides of mesa structures. 
         FIG. 9  illustrates a diagrammatic cross-section through the section from  FIG. 8  after the application of a covering to the field oxide in the edge region. 
         FIG. 10  illustrates a diagrammatic cross-section through the section from  FIG. 9  after the removal of the field oxide above the cell field and the etching in the trench. 
         FIG. 11  illustrates a diagrammatic cross-section through the section from  FIG. 10  after the upper region of the trench structure has been filled with a conductive material. and 
         FIG. 12  illustrates a diagrammatic cross-section through the section from  FIG. 11  after the ion implantation of body zones. 
     
    
    
     DETAILED DESCRIPTION 
     In the following Detailed Description, reference is made to the accompanying drawings, which form a part hereof, and in which is illustrated by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc., is used with reference to the orientation of the Figure(s) being described. Because components of embodiments of the present invention can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. 
       FIG. 1  illustrates a diagrammatic top view of the layout of a section of an integrated circuit semiconductor device  1  according to an embodiment. A strip-shaped trench structure  25  is formed in a cell field  4 . This cell field  4  is surrounded by an edge trench  10  with a field plate  14 . In this embodiment, an edge zone  12  extends both in the interior as an inner edge zone  35  and on the outside as an outer edge zone  34  and is characterised by a doping material of a complementary conduction type near the surface of the semiconductor body  3 , which is identical to that of the body zones of the semiconductor device  1 . This edge zone  12  is indicated in  FIG. 1  by a hatching of broken lines and is, outside the edge trench  10 , surrounded by a channel stopper region  17  indicated by a hatching of continuous lines bounded by the edge of the semiconductor chip. 
     This results not only in an outer edge zone  34  extending from the edge trench  10  to the annular channel stopper  17 , but also in an inner edge zone  35  extending from the edge trench  10  to the outer body zones  49  of the cell field  4 . 
     The effect of such an inner edge zone  35 , which extends from the edge trench  10  along line A-A from  FIG. 1  parallel to the cell field trenches  25  to the outer body zones  49 , is illustrated by a modified or improved potential profile which can be verified by simulation. The transition from the active region of the cell field  4 , this being the part of the cell field  4  where there are p-type body zones  13 , is addressed. At the same time, up to the edge termination of the MOS transistor with compensation by field plates in trenches as illustrated by way of example in  FIG. 1 , there is no field oxide in this cell field  4 . 
     The channel stopper  17  is at drain potential and is represented by a polysilicon field plate in this embodiment. This field plate also marks the body implantation in this region and therefore provides the necessary break in the outer edge zone  34 . A metal may be used in place of polysilicon. Adjacent to the strip-shaped trench structure  25  in the cell field  4  and the flatness of the inner and outer edge zones  35  and  34  respectively,  FIG. 1  illustrates metallization surfaces for a metallization layer  32  for a source connection electrode  36 , which in this top view covers two fields of the surface of the semiconductor device  1 , and a simultaneously applied metallization layer  33  for a gate connection electrode  37 , which in the active cell field  4  connects the electrodes  9  made of an electrically conductive material, which are illustrated in  FIG. 4 , to one another. 
       FIG. 2  illustrates a schematic representation of a cross-section through the section of the semiconductor device  1  along line A-A through a field plate  8  or trench structure  7 . The line A-A initially runs from the outer edge zone  34  in the edge region  6  through the edge trench  10  and then parallel to the elongated field plates  8  of the cell field  4  to the body zones  13  in the body zone region  50 . The section illustrated in cross-section in  FIG. 2  is the transitional region from a cell field  4  to an edge region  6 . The edge region  6  includes an edge zone  12 , the edge zone  12  being divided into an outer edge zone  34  and an inner edge zone  35  by the edge trench  10  surrounding the cell field  4 . 
     In the edge region  6 , a breakdown voltage which is at least equal to that in the cell field  4  has to be achieved. 
     To avoid a premature breakdown, an inner edge zone  35  of this embodiment, which extends within the cell field  4  from the edge trench  10  to outer body zones  49 , is doped with a material of the same conduction type as the body zones  13  of the cell field  4  and therefore has a complementary conduction type and a p-n junction  47  to the n-type material of the drift zone  5  located below. For this purpose, the doping materials have, during the production of the body zones  13 , been implanted through a thinned field oxide  16  up to mesa structures of the cell field  4  of the semiconductor device  1  with its strip-shaped trench structures  7 . As a result, the impurity concentration is lower in the inner edge zone  35  and the outer edge zone  34  than in the body zones  13 . In addition, penetration depth is correspondingly reduced, as the body zones  13  are implanted while the front side  11  of the semiconductor body  3  is completely free of oxide in the cell region  4 . Nevertheless, as a result the potential in the inner edge zone  35  is restricted to the semiconductor body  3  and does not reach the field oxide  16 . This is illustrated in  FIG. 3  by using the plotted profile of the space charge zone in the off state. 
     It further has to be ensured that the outer edge zone  34  does not extend to the outer-most edge of the semiconductor chip. In this embodiment, this can be achieved by using the structure of a channel stopper as described above, which at the same time serves as a masking structure for the ion implantation of the doping materials of the complementary conduction type, which are used both for the base zones  13  in the cell field  4  and for the edge zone  12  in the edge region  6  as well as partially in the cell field  4 . 
     In the embodiment according to  FIGS. 1 ,  2  and  3 , the body zone implantation is designed such that it just extends through the oxide  16  in the edge zone  12 . The thickness of the oxide on the front side  11  of the edge zone  12  is expediently reduced by various process processes in the course of the production of the semiconductor body  3 , so that the oxide has a significantly reduced thickness at the time of the body zone implantation, which is now used to reach the edge zone  12  with complementary doping using doping materials of the ion implantation for the body zone  13 . 
     While a proposed thickness of the oxide layer is provided in the trench structure for the required blocking capability, the thickness of the oxide on the front side is less at the time of the body zone implantation. At a preset implantation energy, the body zone  13  can now be produced within the active cell field  4 , while at the same time, as illustrated in  FIGS. 2 and 3 , a region of a complementary conduction type of the inner and outer edge zones  35  and  34 , respectively, is formed in the edge zone  12  on the front side  11 . By suitably adjusting the thickness of the field oxide on the front side, a through-implantation of part of the p-doping is made possible, so that a p-doping is obtained in the critical region and a premature breakdown is prevented at this point. 
       FIG. 3  illustrates a perspective schematic representation of the section of the semiconductor device  1  according to  FIG. 1  along line A-A through a body zone  3  or a mesa structure, wherein the section illustrated in  FIG. 2  is viewed from the other side. 
     Comparative simulations with semiconductor structures without complementary doping in the inner edge zone  35  show with regard to potential distribution that the potential reaches upwards in the region between the continuous edge trench  10  and the field plate  8  of the cell field  4  in a conventional structure, while the inner edge zone  35  with its complementary doping efficiently pushes the potential, which follows the form of the space charge zone indicated by a dot-dash line  51 , downwards. 
     The potential is therefore not deflected towards the front side between the last trench structure  7  of the cell field  4  and the edge trench  10 , but is pushed downwards into the semiconductor body  3 , and it does not reach the field oxide  16  even in the edge region  6  after the edge trench  10 , but is likewise displaced into the semiconductor body  3  by the p-n junction between the edge zone  12  with its complementary doping and the drift zone-doped semiconductor material located below, as described above. This potential profile insures that avalanche generation is reduced in a breakdown situation and remains restricted to the lower trench region  45  up to the active cell region without jumping to the front side  11  of the semiconductor body  3 . As a result, an improvement is achieved in a breakdown situation owing to reduced avalanche generation, in particular owing to the fact that the curvature of the p-n junction at the body end  49  is unloaded and the major part of the avalanche generation is found at the trench base  46  in an embodiment with an existing p-type region. 
     The semiconductor devices structured according to  FIGS. 1 to 3  are characterized by a noticeably improved potential profile, and avalanche generation can be reduced even in a breakdown situation, because the curvature of the p-n junction at the body zone end  49  is unloaded and the major part of avalanche generation is found at the trench base  46  of the edge trench  10  in an embodiment with an existing inner edge zone  35  of a complementary conduction type. 
     Simulations show a significant improvement of the potential profile and an increased electric strength in the region of the edge trench  10 . This further improves the performance of the semiconductor device, which finds expression in a significant reduction of stationary losses in the on state. 
     In place of an implantation of impurities for the inner edge zone  35  synchronous with the implantation of the body zones  13 , a separate ion implantation can be provided for the inner edge zone  35 , in particular if the orientation and characteristics of the body zones  13  are not to be changed in a predetermined cell structure in the cell field  4 . In a second ion implantation of this type, the energy used is chosen such that the thick oxide in the region of the inner edge zone  35 , which has been applied, is penetrated. The dose may however be significantly less than the dose for the body zones  13  and only has to cause a re-doping of the n-type region in the inner edge zone  35  near the front side  11  of the semiconductor body  3 . This separate, additional implantation for the production of an inner edge zone  35  of a complementary conduction type may be carried out immediately following the body zone implantation, or else following the driving-in using a diffusion process of the body zones  13 . 
     In such an additional implantation process, an interruption of the generated p-type region of the outer edge zone  34  up to the edge of the semiconductor chip has likewise to be insured as described above, and the complementary doping of the edge zone  12  has to be sufficient in order not to be depleted by the drain potential. The inventive principle of an edge zone  12  of a complementary conduction type below the field oxide  16  can be applied both to n-channel MOSFETs and to p-channel MOSFETs. 
     In the embodiment according to  FIG. 3 , the body zone implantation is designed such that is just extends through the oxide  16  in the edge region  6 . At the time of the body zone implantation, the thinning of the oxide  16  on the front side  11  during the preceding process steps is sufficient for a penetration of the oxide  16  using the doping materials of the body zones  13 . However, as the thickness of the oxide  16  in each field plate trench determines the blocking capability of the transistor, the body zone implantation is individually adapted to suit the different blocking classes, in order to ensure the formation of an edge zone  12 , in particular the inner edge zone  35 , of a complementary conduction type. 
       FIG. 4  illustrates a diagrammatic cross-section through the section of the semiconductor device  1  according to  FIG. 1  along line B-B. The section illustrated in cross-section in  FIG. 4  is a transitional region from the cell field  4  to the edge region  6 . Of the cell field  4 , a last field plate  8  and two trench gate structures  9  surrounding the field plate  8  are illustrated. The trench structure  7  of the cell field  4  is therefore provided with a field plate  8 , which may for example be surrounded by two gate electrodes  23  and  24  adjacent to the field plate  8 . 
     As  FIG. 4  illustrates, the trench structure  7  is, in the cell field  4  on the trench walls  27 , provided with an oxide layer  26  for insulation in the lower region  45  of the trench structure  7  and thus of the field plate  8 . In the cell field  4  and in the edge trench  10 , the field plate  8  is made of a conductive material  38 . In the upper region  28  of the trench structure  7  in the cell field  4 , a gate oxide  18  insulates the trench gate electrodes  34  and  24  from a base zone  13  located in the upper region of the semiconductor body  3 . The conduction type of this base zone  13  complements that of the drift zone  5  located below. 
     Finally, there are source zones  19  located near the front side  11  of the semiconductor body  3  in the cell field  4 ; these have the same conduction type as the drift zones  5 , but are doped more highly. When a suitable potential is applied to the trench gate electrodes  23  and  24 , a channel  44  forms in the body zone  5  to create a connection between the source zone  19  and the drift zone  5 , enabling a current to flow from the source metallisation layer  32  through a via  21  from a contact hole  31  to a drain zone  50 , the cell region  4  gating in this process. 
     The edge trench  10  illustrated in  FIG. 4  includes a field plate  14  at source potential, which is insulated from the surrounding semiconductor material of the semiconductor body  3  by a field plate insulation  15 . The field oxide  16  on the edge zone  12  of a complementary conduction type is less thick in the process of body zone implantation than the field plate insulation  15  of the edge trench  10 . As  FIG. 2  illustrates, the edge trench  10  may divide the edge zone  12  of a complementary conduction type into two zones, these being the inner edge zone  35  between the cell region  4  and the edge trench  10  and an outer edge zone  34  from the edge trench  10  to a continuous annular channel stopper illustrated in  FIG. 1 , which in the present case is at drain potential, or to an annular layer not illustrated in the drawing, which masks the ion implantation. In this embodiment, the edge zone  12  of the complementary conduction type extends laterally from a channel stopper of a conductive material, which surrounds the semiconductor chip, via the edge trench  10  to the marginal body zones  49  of the cell field  4 , virtually extending into the marginal body zones  49  of the cell field  4 . 
       FIGS. 4   a  to  4   c  illustrate diagrammatic cross-sections through field plates  8  in the cell field  4  with different gate structures  61 ,  62  and  63  in the same trench. 
       FIG. 4   a  illustrates a diagrammatic cross-section through a field plate  8  in the cell field  4  with two gate electrodes  23  and  24  of a first gate structure  61 , which can already be seen in  FIG. 4 . Components of the same function as those in  FIG. 4  are identified by the same reference numbers and not explained again. If a suitable gate voltage is applied, the gate electrodes  23  and  24  cause the formation of two channels  44  in the body zones  13  between a highly doped n + -type source zone  19  and less highly doped n − -type drift zones. 
       FIG. 4   b  illustrates a diagrammatic cross-section through a field plate  8  in the cell field  4  with a joint gate electrode  23  of a second trench gate structure  62 . If a suitable gate voltage is applied, the gate electrode  23  causes the formation of two channels  44  extending on either side of the second trench gate structure  61 . 
       FIG. 4   c  illustrates a diagrammatic cross-section through a field plate  8  in the cell field  4  with two separate gate electrodes  23  and  24  of a third trench gate structure  63 . In the region of the gate electrodes  23  and  24 , however, there is no electrically conductive field plate material, but rather an insulating material. If a suitable voltage is applied to the gate electrodes  23  and  24 , two conductive channels  44  are formed in the body zones  13  between a highly doped n + -type source zone  19  and less highly doped n − -type drift zones. 
       FIGS. 5 to 12  illustrate cross-sections along a line B-B of  FIG. 1  through a section of a semiconductor body  3  in the process of the production of the device  1  according to  FIG. 1 . 
       FIG. 5  illustrates a diagrammatic cross-section through a section of a semiconductor body  3  after the introduction of trench structures  7 . These trench structures  7  are introduced into an n-type drift zone material in this embodiment; in this process trench walls  27  are formed and mesa structures  39  remain standing in the cell field  4  made of a semiconductor body material. The trench structures  7  and the mesa structures  39  are then coated with a silicon oxide layer by oxidation of the silicon, with the result that, as illustrated in  FIG. 6 , a silicon oxide acting as an insulating layer covers the front side  11  of the semiconductor body  3 . As an alternative, an insulating material can be deposited from the gas phase. The insulating material may also be applied in several layers. 
       FIG. 6  illustrates a diagrammatic cross-section through the section from  FIG. 5  after the application of an insulating layer  26 . This insulating layer  26  forms a field oxide  16  on the top of the mesa structures and, on the trench walls  27 , an insulating layer for field plates to be installed. 
       FIG. 7  illustrates a diagrammatic cross-section through the section from  FIG. 6  after the trench structure  7  has been filled with a conductive polysilicon material  38 . In place of the conductive polysilicon material  38 , a conductive metallic material could be applied to the insulating layer  26  in the trench structure  7 . In this process, the front side  11  of the semiconductor body  3  is simultaneously coated with a conductive polysilicon material or a conductive metallic material. As  FIG. 8  illustrates, this is later removed from the front side  11  of the semiconductor body  3 . 
       FIG. 8  illustrates a diagrammatic cross-section through the section from  FIG. 7  after the removal of the polysilicon material or the conductive metallic material from a field oxide  16  on front sides  11  of mesa structures  39 . Now both the cell field  4  and the edge trench  10  have field plates  8  insulated from the semiconductor body  3 . While the field plates  8  in the cell field  4  are strip-shaped as illustrated in  FIG. 1 , the edge trench  10  with its field plate  14  surrounds the entire cell field  4 . 
       FIG. 9  illustrates a diagrammatic cross-section through the section from  FIG. 8  after the application of a photoresist covering  41  to the field oxide  16  in the edge regions  34  and  35 . The mesa structures  39  on the front side  11  of the semiconductor body  3  are, however, not yet exposed, because these regions are still covered by the field oxide  16 . 
       FIG. 10  illustrates a diagrammatic cross-section through the section from  FIG. 9  after the removal of the field oxide  16  above the cell field  4  and the etching in the trench. This exposes an upper region  28  of the trench structure in the cell field  4 , allowing the trench gate structures to be introduced here while the trench ends  45  remain surrounded by the field oxide. 
       FIG. 11  illustrates a diagrammatic cross-section through the section from  FIG. 10  after the removal of the photoresist covering on the edge zones  34  and  35 , after the application of an insulating region  42  around the upper region of the field plate  8  and after the introduction of trench gate structures into the upper region  28  of the trench structures in the cell field  4 . These upper regions  28  of the trench structures are now provided with a gate oxide  18  and gate electrodes  24  of a conductive material on the trench walls  27 , an oxide layer  42  insulating the field plates  8  from the gate electrodes  9 . 
     For this purpose, the upper region  28  of the trench structure  7  in the cell field  4  is filled with a conductive material, wherein for example the whole front side  11  of the semiconductor body  3  is covered with a polysilicon material or a conductive metallic material, which is subsequently removed from the front side, whereby mutually insulated trench gate structures  9  are created in the upper region  28  of the trench structure  7  in the cell field  4 . 
       FIG. 12  illustrates a diagrammatic cross-section through the section from  FIG. 11  after the removal of the gate oxide layer  18  on the front side  11  of the semiconductor body  3 , followed by ion implantation. By ion implantation in the direction of the arrows A and a subsequent diffusion process, the body zones  13  illustrated in  FIG. 12  are created, while the edge zones  34  and  35  of a conduction type complementing that of the drift zones  5  are created in the edge zone  12 . As explained above, the edge zone  12  of the complementary conduction type can be introduced at a later point in time, but the oxide thickness values in the edge region  6  have already been almost doubled, with the result that a separate ion implantation for the edge zones  12  would involve a higher implantation energy but a lower dose than the implantation of the body zone region. In either case, the channel stopper region illustrated only in  FIG. 1  is capable of interrupting the outer edge zone  34  in the edge region  6  up to the edge of the semiconductor chip. 
     Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.