Abstract:
Integrated transistor and method for the production is disclosed. An explanation is given of, inter alia, a transistor having an electrically insulating isolating trench extending from a main area in the direction of a connection region remote from the main area. Moreover, the transistor contains an auxiliary trench extending from the main area as far as the connection region remote from the main area. The transistor requires a small chip area and has outstanding electrical properties.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of international application PCT/EP2004/053137 filed Nov. 26, 2004, which claims priority to German Patent Application No. DE 102004002181.3 filed Jan. 15, 2004, both of which are incorporated in their entirety by reference herein. 

   FIELD OF THE INVENTION 
   The present invention relates to an integrated transistor and method for the production thereof. 
   BACKGROUND 
   Generally, bipolar transistors include connection regions referred to as the emitter region and base region. In a bipolar transistor, the reverse doping region is referred to as the base region. In field effect transistors, by contrast, the connection regions are referred to as the source region and drain region. In a field effect transistor, the reverse doping region serves for forming an inversion channel. 
   In so-called high-voltage transistors, a drift path is present in order to switch voltages of more than 40 volts, more than 50 volts or even more than 100 volts between the connection zones during normal operation. 
   A multiplicity of high-voltage transistors have been proposed heretofore whose electrical properties are improved by constructive measures, for example by field plates or by field rings. In particular, the breakdown voltage is increased or the chip area requirement is reduced by means of these measures. However, these transistors may have increased complexity with regard to design and manufacture. 
   SUMMARY 
   The invention relates to an integrated transistor having a semiconductor substrate, which is preferably monocrystalline or contains monocrystalline layers, a connection region remote from the main area and contained in the semiconductor substrate, said connection region being doped in accordance with a basic doping type and being arranged at a distance from a main area of the semiconductor substrate, a drift region contained in the semiconductor substrate, said drift region being doped in accordance with the basic doping type with a lower dopant concentration than the connection region remote from the main area, and said drift region being arranged between the connection region remote from the main area and the main area, a connection region near the main area, said connection region being doped in accordance with the basic doping type and being arranged, for example, at the main area of the substrate, a reverse doping region, which is doped in accordance with a different doping type than the basic doping type and separates the drift region from the connection region near the main area. 
   It is nevertheless one aspect of the invention that specifies an improved transistor which, in particular, is simple to produce, which, in particular, has outstanding electrical properties and which, in particular requires only a small chip area. Moreover, a production method is specified by means of which a transistor can be produced in a simple manner. 
   The invention is based on the consideration that the number of trenches does not influence, or influences only slightly, the production outlay for an integrated circuit arrangement. Even different trench depths and different trench fillings can be produced with little outlay. Furthermore, the invention is based on the consideration that diffusion zones for the connection of the connection region remote from the main area easily exceed a lateral dimensioning of greater than 20 micrometers on account of the all-around diffusion in the case of high-voltage transistors. Trenches are particularly suitable for avoiding long diffusion paths or for laterally delimiting a deep diffusion. A further function which can be provided by trenches in a simple manner is the isolating function, which can likewise be used for reducing the chip area for a transistor. However, specific functions cannot be performed simultaneously by trenches, for example the connection function and the isolating function. Consequently, only double trenches or triple trenches per component are suitable for improving the electrical properties in conjunction with a small chip area. 
   In addition to the features mentioned in the introduction, therefore, a transistor in one embodiment of the invention has an electrically insulating isolating trench extending from the main area in the direction of the connection region remote from the main area and consequently having an isolating function, and an auxiliary trench extending from the main area as far as the connection region remote from the main area and serving for connection of the connection region remote from the main area, for example the auxiliary trench offers access for a doping material that diffuses into the surroundings of the trench, or the auxiliary trench forms the lateral boundary of a diffusion process. 
   In one development, the isolating trench and/or the auxiliary trench has at least one of the following features: a trench width greater than one micrometer or greater than two micrometers, so that a sufficient dielectric strength is provided in the case of an isolating trench, a trench width less than ten micrometers or less than five micrometers, so that an excessively large amount of chip area is not required for the trench, a trench depth greater than ten micrometers or greater than fifteen micrometers, a sufficient voltage drop across the drift path being achieved only through these depths. 
   In another development, the isolating trench contains an electrical isolation that completely fills the trench. As an alterative, the isolating trench contains an electrically insulating isolation on the trench walls and on the trench bottom and also an electrically conductive region in the trench. By way of example, deep trenches can be filled with doped polycrystalline silicon, with undoped silicon, with an oxide, or be filled with some other material. 
   In another development, the isolating trench has the same depth as the auxiliary trench, so that it is not necessary to take measures for producing different depths. As an alternative, the auxiliary trench is deeper than the isolating trench. By way of example, the isolating trenches are covered at the beginning or at the end of the etching of the auxiliary trenches, only one additional photolithographic step being required, for example. 
   In a development with different trench depths, the distance between the bottom of the isolating trench and the connection region remote from the main area is in the range of ⅕ to ⅘ or in the range of ⅓ to ⅔ relative to the distance between the main area and the connection region remote from the main area. If, in the same depth as the already mentioned connection region remote from the main area, a further connection region remote from the main area is present, as far as which a further isolating trench extends, which has the same depth as the auxiliary trench, then an ESD protection element (electrostatic discharge) can be produced in the region of the shortened isolating trench in a simple manner, said protection element avoiding damage to the other component by means of its own early breakdown. 
   In another development, the auxiliary trench has the same trench filling as the isolating trench. Consequently, measures for introducing different trench fillings are not necessary. In an alternative configuration, by contrast, the auxiliary trench has a different trench filling than the isolating trench. In particular, the auxiliary trench is filled with an electrically conductive material, e.g. with doped polycrystalline silicon or with a metal, which is electrically conductively connected to the connection region remote from the main area. Different trench fillings can be achieved in a simple manner by the covering or the later formation of the other type of trench. 
   In a next development, a doping of the basic doping type with a higher dopant concentration than in the drift region is present between the isolating trench and the auxiliary trench, the doping filling the region between the isolating trench and the auxiliary trench completely—for example in the case of a vertical diffusion delimited by the two trenches—or only in the vicinity of the auxiliary trench and not in the vicinity of the isolating trench—for example in the case of a diffusion proceeding from the auxiliary trench. 
   In another development, the auxiliary trench is electrically insulating. The auxiliary trench extends into the substrate main region more deeply than the connection region remote from the main area and is arranged at the edge of an electronic component, so that it insulates the component from other components into the depth as well. 
   In a next development, a substrate main region is doped in accordance with the reverse doping type. A substrate trench extends from the main area as far as the substrate main region and serves for connection of the substrate main region. Consequently, three types of trench are present, namely the isolating trench, the auxiliary trench and the substrate trench. The substrate trench enables a simple and area-saving connection of the substrate, for example as access for a doping material that is introduced into the surroundings of the substrate trench, or as a lateral boundary of a diffusion process. 
   The technical effects discussed above for the auxiliary trench and the isolating trench also apply to the formation of the substrate trench, in particular with regard to the same depth of trenches and with regard to the same trench filling of trenches. 
   In a next development, a connection of the transistor is electrically conductively connected to the reverse doping region, so that the transistor is a bipolar transistor having a pnp layer sequence or an npn layer sequence. As an alternative, an insulating layer is present that is electrically insulating, adjoins the reverse doping region and isolates the reverse doping region from an electrically conductive control electrode of the transistor, so that a field effect transistor is formed which operates as an n-channel transistor or as a p-channel transistor. 
   The invention additionally relates to a method having the steps specified in the independent or coordinate method claim, the order in which the steps are specified not constituting any restriction. In the case of the method, similarly, a transistor with a multiple trench arises, so that the technical effects specified above also apply to the method. 
   Further objects, features and advantages of this invention will become readily apparent to persons skilled in the art after a review of the following description, with reference to the drawings and claims that are appended to and form a part of this specification. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows two bipolar transistors each having two trenches, a substrate connection being produced with the aid of a substrate trench; 
       FIG. 2  shows a bipolar transistor having two trenches, a substrate connection being produced by means of a large-area diffusion; 
       FIG. 3  shows a bipolar transistor having two trenches, a substrate connection being delimited by two substrate trenches; 
       FIG. 4  shows a field effect transistor having two trenches; and 
       FIG. 5  shows a bipolar transistor having two trenches with different lengths. 
   

   DETAILED DESCRIPTION 
   Exemplary embodiments are explained below which apply in principle both to bipolar transistors and to field effect transistors. In the exemplary embodiments, only one emitter or source connection and one base or gate connection are provided per component. In order to increase the switching current, other exemplary embodiments use, in one component, a sequence of emitter-base pairs which are respectively assigned a collector region, or source-gate pairs which are respectively assigned a drain region. By way of example, the collector or drain connection and/or the substrate connection encloses the emitter-base pairs or the source-gate pairs, respectively, of a component. 
     FIG. 1  shows two bipolar transistors T 1  and T 2 , a substrate connection of a substrate main part  10  being produced with the aid of a substrate trench  12 . The substrate main part  10  contains lightly p-doped silicon and is contained in a commercially available wafer, by way of example. Buried doping regions  14  and  16  have been introduced into the wafer, said doping regions being heavily n-doped and belonging to a buried layer  18 . A lightly n-doped epitaxial layer  20  has a layer thickness D 1  of twenty micrometers in the exemplary embodiment. The epitaxial layer  20  is adjacent to the substrate main area  10  and contains an upper layer part of the buried layer  18 . 
   The substrate trench  12  penetrates through the epitaxial layer  20  and ends in the substrate main part  10 . The substrate trench  12  is surrounded at its sidewalls  22  and at the trench bottom  24  by a substrate connection doping  26 , e.g. a high p-type doping, which surrounds the substrate trench  12  with a layer thickness of e.g. greater than 500 nanometers or of one micrometer. In particular, the layer thickness of the substrate connection doping  26  is less than three micrometers. 
   Heavily p-doped doping regions  32  and  34  extend from the surface  30  of the epitaxial layer  20  on both sides of the substrate trench  12 , said doping regions being electrically conductively connected to a metallic or polycrystalline substrate connection  36 . The doping regions  32  and  34  in each case have e.g. a depth of one micrometer and a width of one micrometer. 
   The two transistors T 1  and T 2  lie e.g. on both sides of the substrate trench  12 . The transistor T 1  contains a collector connection  40 , a base connection  42 , and an emitter connection  44 . 
   In another exemplary embodiment, further base connection-emitter connection pairs  45  of the transistor T 1  are present, indicated by dots. The collector connection  40 , the base connection  42  and the emitter connection  44  are electrically conductive and contain e.g. a metal or highly doped polycrystalline silicon. 
   In the transistor T 1 , there is an auxiliary trench  46 . The auxiliary trench  46  encloses an isolating trench  48 , which laterally isolates a drift zone  50  formed in the epitaxial layer  20 . 
   The auxiliary trench  46  penetrates through the epitaxial layer  20  and ends in the doping region  14  of the buried layer  18 . The auxiliary trench  46  is surrounded at its sidewalls and at the trench bottom by a collector connection doping  52 , for example a high n-type doping, which surrounds the auxiliary trench  46  with a layer thickness of e.g. 500 nanometers or of one micrometer. In particular, the layer thickness of the collector connection doping  52  is less than three micrometers. 
   A heavily n-doped doping region  54  extends from the surface  30  of the epitaxial layer  20  at the inner trench edge of the substrate trench  12 , said doping region being electrically conductively connected to the collector connection  40 . The doping region  54  has e.g. a depth of one micrometer and a width of e.g. greater than three micrometers, e.g. five micrometers. In another exemplary embodiment, there are doping regions for the collector connection  40  on both sides of the auxiliary trench  46  along the peripheral trench edge. As an alternative, there is only one outer doping region for the collector connection  40  on the right-hand side of the auxiliary trench  46  relative to the trench section illustrated in  FIG. 1 . 
   A region of the epitaxial layer  20  lies between the substrate connection doping  26  and the collector connection doping  52 . By way of example, the minimum distance between the substrate connection doping  26  and the collector connection doping  52  is greater than ten micrometers, e.g. twenty micrometers. 
   The isolating trench  48  likewise penetrates through the epitaxial layer  20  and ends in the doping region  14  of the buried layer  18 . The isolating trench  48  is not surrounded by a doping region introduced with the aid of the isolating trench  48 . 
   A p-doped base region  56  extends from the surface  30  of the epitaxial layer  20  within the zone enclosed by the isolating trench  48 , said base region being electrically conductively connected to the base connection  42 . The base region  56  has e.g. a depth in the range of one micrometer up to three micrometers, e.g. of two micrometers, and a width of e.g. greater than four micrometers, e.g. ten micrometers. 
   The base region  56  encloses an n-doped emitter region  58 , which likewise extends from the surface  30  of the epitaxial layer  20  in the direction of the doping region  14 . The emitter region  58  is electrically conductively connected to the emitter connection  44 . 
   In the exemplary embodiment, the substrate trench  12 , the auxiliary trench  46  and the isolating trench  48  are completely filled with an electrically insulating material, namely with silicon dioxide. In the exemplary embodiment, the trench width B of the substrate trench  12 , of the auxiliary trench  46  and of the isolating trench  48  is 1.5 micrometers in each case. The trench depth is identical for all three trenches  12 ,  46  and  48  and is 21 micrometers, by way of example. 
   The transistor T 2  is constructed like the transistor T 1 , so that reference is made to the explanations above. Elements of the transistor T 2  having the same construction and the same function as elements in the transistor T 1  bear the same reference symbol in  FIG. 1 , but followed by the lower-case letter b, see e.g. a base region  56   b  corresponding to the base region  56 , an auxiliary trench  46   b  and an isolating trench  48   b.    
   By virtue of the construction of the transistors T 1  and T 2  that is illustrated in  FIG. 1 , only a small chip area is required because the connection of the doping region  14  and  16  via the collector connection doping  52  and  52   b , respectively, lies very near to the base region  56  and  56   b , respectively, on account of the isolating trench  48  and  48   b , respectively.  FIG. 2  shows a bipolar transistor T 3 , which is constructed like the bipolar transistor T 1  apart from the deviations explained below, so that like elements are designated by the same reference symbols but followed by the lower-case letter c, see:
         Substrate main region  10   c,      Doping region  14   c  in a buried layer  18   c,      Epitaxial layer  20   c,      Surface  30   c,      Collector connection  40   c,      Base connection  42   c,      Emitter connection  44   c,      Auxiliary trench  46   c,      Isolating trench  48   c,      Drift region  50   c,      Collector connection doping  52   c,      Doping region  54   c,      Base region  56   c,  and   Emitter region  58   c.          

   In the case of the bipolar transistor T 3 , in contrast to the transistor T 1  and T 2 , the substrate connection was produced by means of a high p-type doping and a subsequent large-area diffusion in relation to the required chip area as far as the substrate main part  10   c.  A smallest lateral dimensioning L 1  of a substrate connection doping  26   c  is approximately equal to the diffusion depth at the surface  30   c,  that is to say that the dimensioning L 1  is more than twenty micrometers in the exemplary embodiment. The required chip area is nevertheless smaller than in the case of previously known transistors on account of the use of the trenches  46   c  and  48   c.  Moreover, the large-area substrate connection does not have to be embodied separately for each transistor. 
   The substrate connection doping  26   c  is electrically conductively connected via a p-type doping region  32   c  to a substrate connection  36   c  corresponding to the substrate connection  36 . The substrate connection doping  26   c  is again separated from the collector connection doping  52   c  by a zone of the epitaxial layer  20   c  in which the original dopant concentration of the epitaxial layer is present. 
     FIG. 3  shows a bipolar transistor T 5 , which is constructed like the bipolar transistor T 1  apart from the deviations explained below, so that identical elements are designated by the same reference symbols but followed by the lower-case letter d, see:
         Substrate main region  10   d,      Doping region  14   d  in a buried layer  18   d,      Epitaxial layer  20   d,      Surface  30   d,      Collector connection  40   d,      Base connection  42   d,      Emitter connection  44   d,      Auxiliary trench  46   d,      Isolating trench  48   d,      Drift region  50   d,      Collector connection doping  52   d,      Doping region  54   d,      Base region  56   d , and   Emitter region  58   d.          
   In the case of the bipolar transistor T 5 , in contrast to the transistors T 1 , T 2  and T 3 , a substrate connection doping  26   d  was produced by a diffusion that was laterally delimited by two substrate trenches  60  and  62 . The substrate trenches  60  and  62  have the width B, that is to say the same width as the auxiliary trench  46   d  and the isolating trench  48   d.  The depth of the substrate trenches  60 ,  62  also matches the depth of the auxiliary trench  46   d  and the isolating trench  48   d,  that is to say that the depth is 21 micrometers in the exemplary embodiment. The substrate trenches  60  and  62  contain the same filling material as the auxiliary trench  46   d  and the isolating trench  48   d.    
   Although the substrate connection doping  26   d  has been outdiffused into the depth over ten micrometers as far as the substrate main region  10   d,  the smallest lateral dimensioning L 2  or the width of the substrate connection doping  26   d  is less than five micrometers. The lateral dimensioning L 2  is prescribed by the distance between the walls of the substrate trenches  60  and  62  bearing against the substrate connection doping  26   d  and is three micrometers in the exemplary embodiment. 
   The substrate connection doping  26   d  is electrically conductively connected via a p-doped doping region  32   d  to a substrate connection  36   d  corresponding to the substrate connection  36 . A region in which the original doping of the epitaxial layer  20   d  is retained lies between that wall of the substrate trench  60  which faces the auxiliary trench  46   d  and the collector connection doping region  52   d.  By way of example, a distance A between the collector connection doping region  52   d  and the trench wall of the substrate trench  60  is less than five micrometers, one micrometer in the exemplary embodiment. 
   The connection variant of the substrate main region  10   d  illustrated in  FIG. 3  is thus space-saving and has very low impedance. On account of the good connection of the substrate main region  10   d,  the high-voltage transistor T 5  also has good switching properties. 
     FIG. 4  shows a field effect transistor T 6 , a substrate connection of a substrate main part  110  being produced with the aid of a substrate trench  112 . The substrate main part  110  contains lightly p-doped silicon and is originally contained in a commercially available wafer, by way of example. Doping regions have been introduced into the wafer, e.g. a doping region  114 , said doping regions being heavily n-doped and belonging to a buried layer  118 . In the exemplary embodiment, a lightly n-doped epitaxial layer  120  has a layer thickness D 2  of twenty micrometers. The epitaxial layer  120  is adjacent to the substrate main region  110  and contains an upper layer part of the buried layer  118 . 
   The substrate main region  110  is connected like the substrate main region  10 , that is to say by the substrate trench  112 , which is formed like the substrate trench  12 , a substrate connection doping  126  corresponding to the substrate connection doping  26 , heavily p-doped doping regions  132  and  134  corresponding to the doping regions  32  and  34 , respectively, and by a substrate connection  136  having the same construction and the same function as the substrate connection  36 . 
   The transistor T 6  contains a drain connection  40 , a gate connection  42 , and a source connection  44 . 
   The drain connection  40 , the gate connection  42  and the source connection  44  are electrically conductive and contain e.g. a metal of highly doped polycrystalline silicon. 
   In the transistor T 6 , there is an auxiliary trench  146  enclosed by the substrate trench  112 , for example. The auxiliary trench  146 , for its part, encloses an isolating trench  148 , which laterally isolates a drift zone  150  formed in the epitaxial layer  120 . 
   The buried doping region  114  is connected like the doping region  14 , that is to say by the auxiliary trench  146 , which is formed like the auxiliary trench  46 , a drain connection doping  152  corresponding to the collector connection doping  52 , and a heavily n-doped doping region  154 , which is formed like the doping region  54 . 
   A region of the epitaxial layer  120  lies between the substrate connection doping  126  and the drain connection doping  152 . By way of example, the minimum distance between the substrate connection doping  126  and the drain connection doping  152  is greater than ten micrometers, typically equal to the thickness of the epitaxial layer  120 . 
   The isolating trench  148  likewise penetrates through the epitaxial layer  120  and ends in the doping region  114  of the buried layer  118 . The isolating trench  148  is not surrounded by a doping region introduced with the aid of the isolating trench  148 , but rather directly adjoins the epitaxial layer  120 . 
   A p-doped channel doping region  156  extends from the surface  130  of the epitaxial layer  120  within the zone enclosed by the isolating trench  148 , said channel doping region serving for forming an inversion channel. The channel doping region  156  has e.g. a depth in the range of one micrometer up to three micrometers, e.g. of two micrometers, and a width greater than four micrometers, e.g. ten micrometers. 
   The channel doping region  156  encloses an n-doped source region  158  which likewise extends from the surface  130  of the epitaxial layer  120  in the direction of the buried doping region  114 . The source region  158  is electrically conductively connected to the source connection  144 . A lightly n-doped extension region  160  of the source region  158  is optionally situated between the channel doping region  156  and the source region  160 . 
   A dielectric  162  made of silicon dioxide, for example, is situated on the surface of the channel doping region  156  that lies between the source region  158  and the isolating trench  148 . The thickness of the dielectric  162  is more than 10 nanometers, in particular 15 nanometers. A gate region  164  made e.g. of a metal or highly doped polycrystalline silicon is arranged on that side of the dielectric  162  which is remote from the epitaxial layer  120 . The gate region  164  is electrically conductively connected to the gate connection  142 . 
   In the exemplary embodiment, the substrate trench  112 , the auxiliary trench  146  and the isolating trench  148  are completely filled with electrically insulating material, namely with silicon dioxide. In the exemplary embodiment, the trench width B of the substrate trench  112 , of the auxiliary trench  146  and of the isolating trench  148  is 1.5 micrometers in each case. The trench depth is identical for all three trenches  112 ,  146  and  148  and is 21 micrometers, by way of example. 
   The field effect transistor T 6  is a field effect transistor in which the channel length is determined by the dimensions of the gate. In an alternative exemplary embodiment, the field effect transistor T 6  is a doubly diffused field effect transistor in which the channel length is set by way of a diffusion length. The field effect transistor T 6  can also be produced on a small chip area and is nevertheless suitable for switching voltages of greater than 40 volts, greater than 50 volts or even greater than 100 volts. 
     FIG. 5  shows a bipolar transistor T 8 , which is constructed like the bipolar transistor T 1  apart from the deviations explained below, so that identical elements are designated by the same reference symbols but followed by the lower-case letter e, see:
         Substrate main region  10   e,      Doping region  14   e  in a buried layer  18   e,      Epitaxial layer  20   e,      Surface  30   e,      Collector connection  40   e,      Base connection  42   e,      Emitter connection  44   e,      Auxiliary trench  46   e,      Isolating trench  48   e,      Drift region  50   e,      Doping region  54   e,      Base region  56   e , and   Emitter region  58   e.          
   The substrate trench  12   e  and the isolating trench  48   e  have the same depth of e.g. 21 micrometers. By contrast, the auxiliary trench  46   e  is made deeper, e.g. by more than three micrometers, in comparison with the substrate trench  12   e  or isolating trench  48   e.  The trench bottom of the auxiliary trench  52   e  is situated more deeply than that interface of the doping region  14   e  which is furthest away from the surface  30   e,  for example by more than one micrometer, see overhang dimension U. 
   The auxiliary trench  46   e  preferably adjoins the doping region  14   e.  The auxiliary trench  46   e  is preferably arranged in such a way that the doping region  14   e  is completely enclosed laterally by the auxiliary trench  46   e.  In another exemplary embodiment, the auxiliary trench  46   e  subdivides the doping region  14   e  into an inner region, which is electrically conductively connected to the collector connection  40   e,  and into an outer doping region, which is electrically insulated from the inner doping region and does not belong to a component. 
   The auxiliary trench  46   e  is not surrounded by a doping region introduced with the aid of the auxiliary trench  46   e.  A trench intermediate region  98  between the auxiliary trench  46   e  and the isolating trench  48   e  was heavily n-doped in its entirety, for example by an implantation with subsequent outdiffusion. The distance between the auxiliary trench  46   e  and the isolating trench  48   e  is e.g. less than five micrometers or even less than three micrometers. Despite a diffusion depth of more than ten micrometers, the lateral diffusion during the doping of the trench intermediate region  98  is effectively delimited by the auxiliary trench  46   e  and the isolating trench  48   e,  thereby likewise giving rise to a transistor which requires only a small chip area and is nevertheless suitable for switching voltages of greater than 40 volts. 
   In other exemplary embodiments, the isolating trench  48 ,  48   c,    48   d,    148  or  48   e  is embodied in a shortened manner, so that it does not reach as far as the buried doping region  14 ,  14   c ,  14   d,    114  or  14   e,  respectively, see dashed lines  170  to  178 . By way of example, the distance between the trench bottom of the isolating trench and the buried doping region is greater than one micrometer or greater than three micrometers. The breakdown voltage U CE  of the transistor T 1 , T 3 , T 5 , T 8  or the breakdown voltage U DS  of the transistor T 6  is thereby reduced. By way of example, the transistor T 1 , given a shortened isolating trench  48 , can be used as an ESD protection element for the transistor T 2  with an unshortened isolating trench  48   b  if the isolating trench  48   b  has the depth illustrated in  FIG. 1 , that is to say reaches as far as the buried doping region  16 . The breakdown voltage of the ESD protection element can be set by way of the distance between the trench bottom of the isolating trench  48  and the surface  30 , see arrow  180  in  FIG. 1 . Particularly in the case of a bipolar transistor, an ESD protection effect can be achieved even if, in the transistor to be protected, the isolating trench is shortened only in one section. 
   In other exemplary embodiments, field effect transistors constructed like the field effect transistor T 6  are used instead of the bipolar transistors T 1 , T 2 , T 3 , T 5  and T 8  elucidated in  FIGS. 1 ,  2 ,  3  and  5 . 
   To summarize, it holds true that a vertical drift path that saves chip area arises as a result of the introduction of the isolating trench. The drift path runs firstly into the depth along the isolating trench and then on the other side of the isolating trench vertically to the surface along the isolating trench. The required chip area can thereby be drastically reduced compared with transistors with a lateral drift path. 
   Moreover, the possibility is afforded of setting, by way of the depth of the trench, the collector-emitter breakdown voltage U CE  in the case of bipolar transistors or the drain-source breakdown voltage U DS  in the case of MOS transistors (metal oxide semiconductor) in a targeted manner in conjunction with laterally unchanged dimensions. 
   The doping of the trench walls for the collector connection or drain connection and also for the substrate connection may be effected e.g. by implantation with subsequent outdiffusion or by coating. The trenches are etched e.g. by means of a trench etching process, e.g. in dry-chemical fashion. 
   The isolating trench, the auxiliary trench and, if appropriate, also the substrate trench are produced simultaneously in one exemplary embodiment. Different depths can also be achieved during simultaneous etching if different trench widths are chosen. At least one of the following steps is also performed simultaneously and thus in a simple manner: filling of the trenches of the two or three types of trench, doping of the sidewalls of an auxiliary trench and of a substrate trench. 
   As a person skilled in the art will readily appreciate, the above description is meant as an illustration of implementation of the principles this invention. This description is not intended to limit the scope or application of this invention in that the invention is susceptible to modification, variation and change, without departing from the spirit of this invention, as defined in the following claims.