Abstract:
A trench power semiconductor component is described which has an edge cell in which an edge trench is provided. The edge trench, at least on an outer side wall, has a thicker insulating layer than an insulating layer of trenches of the cell array. This simple configuration provides a high dielectric strength and is economical to produce.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a trench power semiconductor component having a cell array and an edge termination which surrounds the latter and is composed of at least one edge trench which is lined with an insulating layer and is also filled with a conductive material which forms a field plate. 
     In the development of trench power semiconductor components, such as for example DMOS power transistors, the edge termination is of particular significance. This is because there are higher electrical field strengths in the edge of a power semiconductor component owing to the curvatures in the equipotential lines that inevitably occur there, so that the dielectric strength of the edge termination must be greater than the dielectric strength of the actual cells of the power semiconductor component. In addition, for reasons of cost, care must be taken to ensure that the edge termination takes up the smallest possible area in comparison with the cell array of the power semiconductor component because the edge termination as such is not, like the cell array, an active part of the component. 
     Therefore, for power semiconductor components an edge termination is aimed at which takes up as little area as possible and at the same time has a dielectric strength that is significantly greater than the dielectric strength of the actual cell array. 
     For many years intensive efforts have been made to fulfil this requirement and from the large number of publications that have arisen from this the following publications have been selected specifically with respect to trench power transistors. German Patent DE 199 35 442 C1 describes a method for manufacturing a trench MOS power transistor in which trenches are provided in the cell array with polycrystalline silicon as the field plate while trenches in the edge termination are lined with a field oxide layer made of silicon dioxide. Here, the field oxide layer is also drawn out onto the surface of the semiconductor element forming the power transistor in the cell array, which masks the implantation for the production of the source zone and body region. 
     International Patent Application PCT/EP00/8459 (10483) discloses a power semiconductor component with trenches in the active cell array, the trenches being provided on their side walls with insulating layers with different layer thickness in order to reduce the reactive capacitance. Further details on the problem of edge termination are not given here. 
     In addition, U.S. Pat. No. 5,763,915 discloses a DMOS power transistor configuration in which trenches which are wider than the trenches of the active cell array, and additionally are provided at a distance from one another, or from the outermost trench of the cell array, which differs from the distance between the trenches of the cell array, are used for the edge termination. The trenches of the cell array and of the edge termination are filled with polycrystalline silicon. 
     Finally, U.S. Pat. No. 4,941,026 describes a power semiconductor component in which trenches are lined with insulating layers that have a smaller layer thickness in an upper region of each trench than in a lower region thereof. 
     Layer-shaped electrodes are applied to the insulating layers that are provided with two different layer thicknesses in this way. 
     Specific publications relating to the solution of the problems connected with the edge termination relating to trench power transistors with field plates in the trenches of the cell array and of the edge termination have not been disclosed hitherto. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide a trench power semiconductor component which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which is distinguished by a configuration which is economical in terms of area and at the same time permits an edge termination which has a simple configuration and a high dielectric strength. 
     With the foregoing and other objects in view there is provided, in accordance with the invention, a trench power semiconductor component. The trench power semiconductor component contains a cell array having a trench formed therein and a first insulating layer lining the trench, and the first insulating layer has a first thickness. An edge cell surrounds the cell array and has at least one edge trench formed therein with an outer side wall in relationship to the cell array. The edge cell has a second insulating layer lining the edge trench and a conductive material at least partially fills the edge trench, and the conductive material forms a field plate. The second insulating layer of the edge trench has a second thickness that is greater than the first thickness at least on the outer side wall of the edge trench opposite the cell array. 
     The object is achieved according to the invention with a trench power semiconductor component of the type mentioned at the beginning by virtue of the fact that the insulating layer of the edge trench is made thicker at least on the outer side wall of the edge trench opposite the cell array than an insulating layer in trenches of the cell array. 
     In the trench power semiconductor component, the edge cell composed of the edge trench is preferably also supplemented by a “normal” trench of the cell array, namely the outermost trench of the cell array, and the semiconductor region that is positioned between the edge trench and the outermost trench and is composed, for example, of silicon. 
     The insulating layer which is of a thicker configuration on the outer side wall of the edge trench is located only in the edge trench and does not extend as far as the surface of the semiconductor element on the inner side in the direction of the cell array. In this way, masking resulting from the more thickly configured insulating layer during the implantations of source zone and body region is avoided so that lateral profile deformations for the source zone and the body region, and punches in the trench power semiconductor component caused by these deformations are avoided. 
     The inner side wall of the edge trench can be configured in various ways: it is thus possible to provide the same insulating layer with the same thickness for the inner side wall of the edge trench and the insulating layer in the trenches of the cell array. Furthermore, the inner side wall of the edge trench can be configured in the same way as the outer side wall. In this case, the more thickly executed insulating layer therefore extends both over the outer side wall and over the inner side wall, but it is to be noted that this more thickly configured insulating layer (thick oxide) is not located on the semiconductor surface between the edge cell and the cell array. 
     Furthermore, it is possible to allow the thick insulating layer to end at various levels on the inner side wall and then provide a thinner insulating layer (gate oxide) starting from the respective level. 
     In all of the variants, the edge trench is also filled with the conductive material, in particular polycrystalline silicon, so that in each case a field plate edge trench is provided, the extent of the field plate depending on the junction between the thick oxide and the gate oxide. The trench of the cell array is also filled with the conductive material being polycrystalline silicon. 
     The overall edge also generally includes a drain-end terminal that preferably contains a field plate of drain potential, with the purpose of a channel stopper in order to interrupt the formation of a channel between the drain and source in the case of a drain/source polarity reversal (see German Patent DE 199 35 442 C1). 
     In accordance with an added feature of the invention, a substrate is provided and the cell array and the edge cell are formed on and in the substrate. The substrate has a further edge trench formed therein and an additional conductive material fills the further edge trench. The additional conductive material and the conductive material are formed so as to be coherent. 
     In accordance with a further feature of the invention, the second insulating layer is formed of a field oxide or a thick oxide. 
     In accordance with another feature of the invention, the first insulating layer is a gate oxide. 
     In accordance with an additional feature of the invention, the second insulating layer is at least 20% thicker than the first insulating layer. 
     In accordance with a concomitant feature of the invention, the trench power semiconductor component is a trench power transistor. 
     Other features which are considered as characteristic for the invention are set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in a trench power semiconductor component, 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. 
     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 
     FIG. 1 is a diagrammatic, sectional view through a first exemplary embodiment of a trench power semiconductor component according to the invention; 
     FIG. 2 is a sectional view through an edge cell according to a second exemplary embodiment; 
     FIG. 3 is a sectional view through an edge trench according to a third exemplary embodiment; 
     FIG. 4 is a sectional view through the edge trench according to a fourth exemplary embodiment; and 
     FIG. 5 is a sectional view through the edge trench according to a fifth exemplary embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown, in a sectional view, a trench power transistor with a cell array Z, an edge cell RZ made of a last trench  4  of the cell array Z and a first edge trench  5  and with further edge trenches RT, one edge trench  6  of which is illustrated. It is possible, if appropriate, to dispense with the further edge trenches RT. However, it is also possible to provide just one further edge trench RT, namely the edge trench  6 . 
     In the cell array Z and in the edge cell RZ there is a trench power transistor made of a semiconductor element (i.e. substrate)  1  which is, for example, n-type conductive, and is composed of silicon or another suitable semiconductor material, for example SiC, A III B v , and so on, a p-type doped body region  2  and an n-type doped source zone  3 . 
     The trench  4  is lined in its upper region with a relatively thin insulating layer  7  made of silicon dioxide (gate oxide or GOX) and in its lower region with a relatively thick insulating layer  13  made of silicon dioxide (field oxide or FOX). The insulating layer  7  is also partially disposed on a surface of the semiconductor element  1  which is adjacent to the trench  4  in the cell array Z. In an interior of the trench  4  and of the trench  5  and also of the trench  6  there is a conductive material, in particular polycrystalline silicon  8  or  9 . If appropriate, silicides may also be used instead of polycrystalline silicon. 
     The polycrystalline silicon  8  forms gate electrodes in the trenches  4  and  5 , while the polycrystalline silicon  9  forms, specifically in the trench  6 , a field plate which is connected to a gate metallization  15  for a gate terminal G on an insulating layer  14  made of borophosphorous silicate glass (BPSG). Furthermore, a source metallization  10  is also provided for a source terminal S, and a drain terminal D is provided on the surface of the semiconductor element  1  lying opposite the source terminal S. The metallizations  10  and  15  may be composed, for example, of aluminum. 
     It is also to be noted that the polycrystalline silicon  8  of the trenches  4  and  5  is connected to the gate terminal G or the gate metallization  15  by conductive connections before or after the plane of the drawing. 
     According to the invention, the trench  5  that is located at the outer edge of the edge cell RZ is provided with the thicker insulating layer  13  (FOX) at least on its outer side wall  11 . The thicker insulating layer can extend as far as an edge R (see FIG. 2) of the trench power semiconductor component. However, it does not extend beyond an inner side wall  12  of the trench  5 . Instead, the thinner insulating layer  7  is provided there on the surface of the source zone  3 . 
     The edge cell RZ is therefore composed of the last trench  4  of the cell array Z, which has the same structure as the other trenches of the cell array Z, and is lined with the gate oxide (above) or the field oxide FOX (below) and filled with polycrystalline silicon  8 , and of the trench  5  which is provided on the outer side wall  11  with the thicker field oxide FOX and is also filled with polycrystalline silicon  8 . The polycrystalline silicon  8  of the trench  5  can be coherent with the polycrystalline silicon of the further trench  6  or else be separated from it. In addition, it is possible also to provide a plurality of edge trenches corresponding to the trench  6  and/or a plurality of normal trenches corresponding to the trench  5  for the edge cell RZ. The cell array Z can be composed of a plurality of trench power transistors of the type represented. The power transistors are then connected parallel to one another. 
     In the exemplary embodiment in FIG. 2, only one edge cell RZ is illustrated, while the exemplary embodiments in FIGS. 3 to  5  show only the edge trench corresponding to the trench  5 . Furthermore, the exemplary embodiments in FIGS. 2 to  5  are structured in a similar way to the exemplary embodiment in FIG.  1 . 
     Although FIG. 1 shows a vertical structure of the trench power transistor, it is of course also possible to have a lateral configuration in which the drain terminal D is provided on the same surface as the gate terminal G and the source terminal S. 
     FIG. 2 shows the edge cell RZ with the normal trench  4 , which is provided so as to be continuous with the thin insulating layer  7  (gate oxide) like the other trenches of the cell array, while the edge trench  5  is provided here on the outer side wall  11  with the thicker insulating layer  13  (field oxide) and on an inner side wall  12  with the thinner insulating layer  7  (field oxide) and is also filled with polycrystalline silicon  8 . In the exemplary embodiment in FIG. 2, the field oxide extends approximately as far as the bottom of the trench  5 . 
     FIGS. 3 to  5  show different configuration possibilities for the edge trench  5 . The field oxide which forms the thicker insulating layer  13  can extend approximately as far as halfway along the inner side wall  12  (see FIG. 3) or may end higher or lower (see FIG.  4 ). It is also possible for the field oxide that forms the thicker insulating layer  13  to extend as far as the end of the inner side wall  12  (see FIG.  5 ). In other words, the field plate formed by the polycrystalline silicon  8  can lie at a higher or lower position in the trench  5  in comparison with the trench  4  of the cell array Z, and thus extend directly as far as the topmost edge of the trench, as illustrated in FIG.  5 . 
     The field oxide has a layer thickness that is approximately 20% greater than the layer thickness of the gate oxide and extends from 0.1 to 2.0 μm, while the gate oxide has layer thicknesses of 0.05 to 0.1 μm.