Abstract:
The semiconductor component is fabricated on the basis of a semiconductor body with a first and a second surface. A multiplicity of pores are formed in the semiconductor body. The bores extend into the semiconductor body proceeding from the first surface and ending below the second surface. The electrical conductivity of the semiconductor body, that is of the component, is increased in the region of the pores. The corresponding semiconductor component has connection contacts on the first and second surfaces.

Description:
BACKGROUND OF THE INVENTION  
       FIELD OF THE INVENTION  
         [0001]    The invention lies in the semiconductor technology field. More specifically, the present invention relates to a semiconductor component which is integrated in a semiconductor body or chip having a first and a second surface. Connection contacts are arranged at the surfaces for making contact with the semiconductor component.  
           [0002]    Such a semiconductor component is, for example, a vertical transistor as it is described in Stengl/Tihanyi: “Leistungs-MOS-FET-Praxis” [Power MOSFETs in Practice], Pflaum Verlag, Munich 1992, page 37. That transistor has a heavily n-doped semiconductor substrate on which a more weakly n-doped epitaxial layer is applied. Arranged in the epitaxial layer are p-doped body zones wherein, in turn, n-doped source zones are arranged. In that component, contact is made with the source and body zones at a front side of the semiconductor body formed by the substrate and the epitaxial layer. The substrate forms a drain zone of the transistor, with which zone contact is made at a rear side of the semiconductor body.  
           [0003]    The thickness and the doping of the epitaxial layer which acts as drift zone crucially determine the electrical properties of the known component, in particular the reverse voltage thereof and the on resistance thereof. The substrate on which the epitaxial layer is applied is doped as highly as possible in order to influence the on resistance as little as possible.  
           [0004]    The heavily doped substrate essentially serves as a carrier and is required in order to be able to handle, during the fabrication method, a wafer wherein a multiplicity of such transistors are fabricated and from which the chips with the transistors are sawn at the-end of the fabrication method. A wafer having exclusively the thickness of the drift zone which determines the electrical properties is sufficient in theory, but in practice cannot be handled for the fabrication of the transistor since the thickness of the drift zone is usually so small that such a wafer would be completely unstable.  
           [0005]    Further generally known vertical semiconductor components with connections at opposite surfaces of a semiconductor body are diodes which, for stability reasons, usually likewise have a substrate which is a good electrical conductor and to which—for example by means of epitaxy—semiconductor layers are applied which form a pn junction and whose doping and dimensions determine the electrical properties of the diode.  
           [0006]    In order, on the one hand, to ensure sufficient mechanical stability of the wafer during fabrication, which can only be ensured by means of a certain thickness, and, on the other hand, to minimize the effects of this thickness required for fabrication on the component, further procedures are generally known in addition to the abovementioned possibility of applying epitaxial layers which determine the electrical properties to a substrate which is a good conductor.  
           [0007]    Thus, it is generally known to provide a wafer having a doping which satisfies the requirements made of the doping in regions of the semiconductor component, for example the drift zone, and subsequently to thin the wafer in the regions which influence the electrical properties of the component.  
           [0008]    Furthermore, it is generally known, if the intention is to dispense with an epitaxy, to use a more weakly doped wafer and to dope the wafer from a rear side by means of a deep diffusion, in order thus to produce a low resistance of the wafer in the regions which only contribute to the mechanical stability, and in order that contact can be made with semiconductor components formed above these regions from the rear side in a low-impedance manner.  
         SUMMARY OF THE INVENTION  
         [0009]    It is accordingly an object of the invention to provide a method of fabricating a semiconductor component, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which provides for a process wherein a wafer wherein a multiplicity of components are fabricated is permitted to have a thickness which suffices for handling the wafer during the fabrication method, and wherein that region of the wafer or of the later chip which does not form an active region of the component has a low electrical resistance.  
           [0010]    With the foregoing and other objects in view there is provided, in accordance with the invention, a method of fabricating a semiconductor component, which comprises the following steps:  
           [0011]    providing a semiconductor body having a first and a second surface;  
           [0012]    fabricating a multiplicity of pores in the semiconductor body, the pores proceeding from the first surface, extending into the semiconductor body, and ending below the second surface; and  
           [0013]    increasing an electrical conductivity of the semiconductor body in the region of the pores.  
           [0014]    In accordance with an added feature of the invention, regions of the semiconductor body that are uncovered in the pores are doped. In addition, diffusion may be carried out after the doping.  
           [0015]    In accordance with another feature of the invention, the pores are at least partly filled with an electrically conductive material, such as a metal or a polysilicon.  
           [0016]    With the above and other objects in view there is also provided, in accordance with the invention, a semiconductor component, comprising:  
           [0017]    a semiconductor body having a first surface and a second surface each having connection contacts;  
           [0018]    the semiconductor body having a multiplicity of pores formed therein extending into the semiconductor body, proceeding from the first surface and ending below the second surface, and wherein an electrical conductivity is increased in a region of the pores.  
           [0019]    In other words, the novel method for fabricating a semiconductor component provides for a semiconductor body having a first and a second surface to be provided and for a multiplicity of pores to be produced which extend into the semiconductor body proceeding from the first surface and which end below the second surface. The electrical conductivity of the semiconductor body is subsequently increased in the region of the pores. This is done, for example, by indiffusion of dopant atoms into regions of the semiconductor body which are uncovered in the pores, and/or by filling the pores with an electrically conductive material, in particular a metal or polysilicon.  
           [0020]    That region of the semiconductor body below the second surface which is not permeated by the pores can be utilized for realizing the active regions of the actual semiconductor components, for example a diode or a transistor. These active regions can be fabricated before the production of the pores or after the production of the pores. The depth to which the pores are introduced into the semiconductor body proceeding from the first surface is coordinated with the thickness of the semiconductor body or of the wafer which forms a multiplicity of the later semiconductor bodies/chips in such a way that a semiconductor layer having a thickness suitable for the realization of the desired component remains between that end of the pores which lies in the semiconductor body and the second surface. In this case, the method according to the invention is suitable in particular in the fabrication of PIN photodiodes.  
           [0021]    The values for the penetration of the pores into the semiconductor body lie, for example, in the range of between 50% and 95% of the total thickness of the semiconductor body in the direction of the pores.  
           [0022]    Electrically, the semiconductor body whose electrical conductivity has been increased in the region of the pores behaves approximately like a thin substrate which only has the thickness of that layer of the semiconductor body which is not permeated by pores, and with which contact can be made from the second surface of the semiconductor body via the porous region which is a good electrical conductor.  
           [0023]    Other features which are considered as characteristic for the invention are set forth in the appended claims.  
           [0024]    Although the invention is illustrated and described herein as embodied in a method for fabricating a semiconductor component and 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.  
           [0025]    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  
       [0026]    [0026]FIG. 1 (partial views FIG. 1A, FIG. 1B, and FIG. 1C) illustrates a detail from a semiconductor body/wafer during various method steps of a method according to the invention for fabricating a semiconductor component;  
         [0027]    [0027]FIG. 2 shows a detail from a semiconductor body/wafer wherein the electrical conductivity has been increased in the region of the pores by filling the pores with an electrically conductive material;  
         [0028]    [0028]FIG. 3 shows a semiconductor component according to the invention in accordance with a first embodiment of the invention; and  
         [0029]    [0029]FIG. 4 shows a semiconductor component according to the invention in accordance with a second embodiment of the invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]    Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown a detail that illustrates method steps according to the invention during the fabrication of a semiconductor component. The figure shows a detail from a semiconductor body or wafer from which a multiplicity of the later semiconductor bodies/chips are sawn, in cross section.  
         [0031]    In a first method step,-as illustrated in FIG. 1A, a semiconductor body  100  is provided which has a first surface  101  and a second surface  102 .  
         [0032]    Afterward, pores are produced in the semiconductor body  100  proceeding from the first surface  101 , which pores end below the second surface  102  of the semiconductor body, as is illustrated in FIG. 1B. By way of example, the electrochemical macroporous etching method described in U.S. Pat. No. 4,874,484 and European patent application EP 0 296 348 A1 is suitable for fabricating the pores  103 .  
         [0033]    In addition, as is illustrated in FIG. 1C, the electrical conductivity of the semiconductor body is increased in the region of the pores  103 . To that end, in accordance with a first embodiment of the method, it is provided that, proceeding from the first surface  101 , dopant atoms, in particular donor atoms, are doped into regions of the semiconductor body  100  which are uncovered in the pores, and the dopant atoms are subsequently caused to diffuse into the semiconductor body by means of a thermal processing step. The diffusion depth and the spacings of adjacent pores  103  are preferably coordinated with one another in such a way that the regions lying between the pores are completely doped and subsequently have a high doping. In the example, the semiconductor body  100  illustrated in FIG. 1A is weakly n-doped at the beginning of the process, a heavy n-doping being effected in order to increase the electrical conductivity in the region of the pores  103 .  
         [0034]    In order to increase the electrical conductivity in the region of the pores provision may be made, in addition or as an alternative, for filling the pores  103  with an electrically conductive material, in particular a metal, for example copper, or polysilicon. FIG. 2 shows a semiconductor body  100  whose pores  103  have been filled with a conductive material  106 .  
         [0035]    In the exemplary embodiments illustrated in FIGS. 1 and 2, the region with increased electrical conductivity occupies a region  105  with a thickness d. A region  104  with a thickness x above the region  105  having increased electrical conductivity remains for the realization of active regions of semiconductor components. The thickness d is preferably greater than the thickness x and is, for example, between 50% and 95% of the total thickness of the semiconductor body (d+x).  
         [0036]    The region  105  essentially contributes to the mechanical stability of a wafer during the fabrication of semiconductor components in the region  104 , the extent of the wafer in the lateral direction exceeding the thickness d, or the sum of the thicknesses d and x, by several orders of magnitude. Consequently, the region D essentially serves as carrier layer for the layer  104  wherein semiconductor components can be formed, as will be explained with reference to FIGS. 3 and 4. Furthermore, the region  105  serves as connection zone for said semiconductor components, the measure of increasing the electrical conductivity of the region  105  by doping and/or filling the pores  103  with a conductive material taking account of the endeavor having the intention that the connection zone  105  as far as possible dose not contribute to increasing the electrical resistance of the semiconductor component.  
         [0037]    The zone  104  of the semiconductor body acts like a thin substrate with which contact can be made in a low-impedance manner from the first surface  101  of the semiconductor body  100  via the zone  105 .  
         [0038]    In addition, this doping from the pores  103  has the effect that the lifetime for electron-hole pairs, generated by light for example, is very short in this region. As a result, very fast PIN diodes can be realized.  
         [0039]    [0039]FIG. 3 shows in side view in cross section a diode which is integrated in a semiconductor body processed by a method in accordance with FIGS.  1  or  2 . Contact is made with the region  105  with the pores  103  by means of a contact layer  110 , preferably a metal, applied to the first surface  101 . Proceeding from the second surface  102 , a p-doped zone  104 A has been produced in the region  104  by means of methods that are adequately known, contact being made with said zone by means of a contact layer  112 . The p-doped zone  104 A forms the anode zone and the n-doped zone  104 B forms the cathode zone of the diode. The original doping of the semiconductor body  100  is preferably chosen in such a way that it is suitable for forming the later cathode zone  104 B of the diode.  
         [0040]    [0040]FIG. 4 shows in side view in cross section a vertical MOS transistor which is integrated in a semiconductor body processed by means of a method in accordance with FIGS.  1  or  2 . In order to fabricate the transistor, p-doped body zones have been introduced into the n-doped zone  104 , heavily n-doped source zones  122  having been introduced, in turn, into said body zones. The source zones  122  and the body zones  120  are short-circuited by means of a source electrode  130  applied to the second surface  102  of the semiconductor body  100 . A section  120  of the zone  104  forms the drift zone of the MOS transistor, with which contact is made by a connection layer  110 , which is applied on the first surface  101  and forms the drain electrode, via the porous region  105 . Furthermore, gate electrodes  126  are provided above the second surface  102  of the semiconductor body  100  and are insulated from the semiconductor body  100  and the source electrode  130  by means of insulation layers  128 .  
         [0041]    In the case of the MOS transistor in accordance with FIG. 4, the semiconductor body is doped in the region of the pores  103  and the pores  103  are filled with an electrically conductive material. The original doping of the semiconductor body  100  is chosen in such a way that it is suitable for forming the drift zone  120 .  
         [0042]    Whereas it has been assumed in the above description that the active regions of the semiconductor components are produced after the fabrication of the pores  103 , it is also possible, of course, to fabricate the active regions of the semiconductor components before the production of the pores  103  in the semiconductor body  100 .  
         [0043]    The method according to the invention, wherein the conductivity of a semiconductor material is increased by fabricating pores and increasing the electrical conductivity in the region of the pores, is suitable for the fabrication of any desired vertical semiconductor components, the semiconductor body having the pores and having increased conductivity serving as replacement for known carrier materials, including epitaxial materials.