Abstract:
A vertical-type semiconductor device for controlling a current flowing between electrodes opposed against each other across a semiconductor substrate, including: a semiconductor substrate having first and second surfaces opposed against each other; a first electrode formed in the first surface; a second electrode formed in the second surface through a high-resistance electrode whose resistance is Rs; and a third electrode formed along at least a part of the outer periphery of the second surface, wherein a potential difference Vs between the second and third electrodes is measured with a current I flowing between the first and second electrodes, and the current I is detected from the resistance Rs and the potential difference Vs.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     The disclosure of Japanese Patent Application No. 2005-299574 filed on Oct. 14, 2005 including specification, drawings and claims is incorporated herein by reference in its entirely.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention is related to a semiconductor device having a current detecting function, and more particularly, to a power semiconductor device in which a current detecting function is deployed in an outer peripheral portion of an electrode.  
         [0004]     2. Description of the Related Art  
         [0005]     The recent years have seen an increasing demand for a power semiconductor module to have a structure which realizes detection of a current. To meet the demand, detection of a current may be attained for example by means of separate disposition of a resistor element from a power semiconductor element within a power semiconductor module and through measurement of a potential difference between the both ends of the resistor element (JP, 04-93033, A).  
         [0006]     However, a structure in which a resistor element is disposed separately from a power semiconductor element has a problem that it requires a space for disposing the resistor element and that the layout of the power semiconductor element and the like must be changed. Further, the newly added resistor element gives rise to a problem that the manufacturing process becomes complex and the manufacturing cost becomes more expensive.  
       SUMMARY OF THE INVENTION  
       [0007]     Accordingly, an object of the present invention is to provide a semiconductor device which is capable of detecting a current without using any newly added resistor element.  
         [0008]     The present invention is directed to a vertical-type semiconductor device for controlling a current flowing between electrodes opposed against each other across a semiconductor substrate, including: a semiconductor substrate having first and second surfaces opposed against each other; a first electrode formed in the first surface; a second electrode formed in the second surface through a high-resistance electrode whose resistance is Rs; and a third electrode formed along at least a part of the outer periphery of the second surface, wherein a potential difference Vs between the second and third electrodes is measured with a current I flowing between the first and second electrodes, and the current I is detected from the resistance Rs and the potential difference Vs.  
         [0009]     As described above, effectively using the outer peripheral portion in which a current density is small, the semiconductor device according to the present invention can detect a current without increasing the element area size or changing the layout. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a bottom view of an IGBT according to an embodiment 1 of the present invention;  
         [0011]      FIGS. 2A and 2B  are a cross sectional view of the IGBT according to the embodiment 1 of the present invention;  
         [0012]      FIG. 3  is a cross sectional view of the IGBT according to the embodiment 1 of the present invention;  
         [0013]      FIG. 4  is a bottom view of the IGBT according to the embodiment 1 of the present invention;  
         [0014]      FIG. 5  shows an inverter circuit contained in a power semiconductor module according to the embodiment 1 of the present invention;  
         [0015]      FIG. 6  shows an inverter circuit contained in a conventional power semiconductor module;  
         [0016]      FIG. 7  is a layout diagram of the power semiconductor module according to the embodiment 1 of the present invention;  
         [0017]      FIG. 8  is a layout diagram of the conventional power semiconductor module;  
         [0018]      FIG. 9  is a layout diagram of other power semiconductor module according to the embodiment 1 of the present invention;  
         [0019]      FIG. 10  is a bottom view of a vertical-type MOSFET according to an embodiment 2 of the present invention;  
         [0020]      FIGS. 11A and 11B  are a cross sectional view of the vertical-type MOSFET according to the embodiment 2 of the present invention;  
         [0021]      FIG. 12  is a bottom view of a vertical-type diode according to an embodiment 3 of the present invention; and  
         [0022]      FIGS. 13A and 13B  are a cross sectional view of the vertical-type diode according to the embodiment 3 of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]     Preferred embodiments of the present invention will now be described with reference to the associated drawings. While the expressions like “above”, “below”, “left” and “right” and phrases containing these expressions will be used below in describing the embodiments, the directions indicated by these expressions are referred to merely for easy understanding of the invention based on the drawings: The technical scope of the present invention includes any examples which are the vertically reversed version of the embodiments or which are the embodiments rotated along any desired direction.  
       Embodiment 1  
       [0024]      FIG. 1  is a bottom view of an insulated gate bipolar transistor (hereinafter referred to as an “IGBT”) generally denoted at  100  according to the embodiment 1, and  FIGS. 2A and 2B  are a cross sectional view of the IGBT  100  shown in  FIG. 1  taken along the direction which is parallel to the plane of the drawing (the direction A in  FIG. 1 ).  FIG. 2A  is the cross sectional view taken in the region of a collector electrode (region (a)) denoted at  10  in  FIG. 1 , while  FIG. 2B  is the cross sectional view taken in the region of a ring-like sense collector electrode (region (b)) denoted at  13  in  FIG. 1 .  
         [0025]     As shown in  FIGS. 1, 2A  and  2 B, the IGBT  100  includes a silicon substrate  1  which contains an n− base layer  5  and a p+ collector layer  8 .  
         [0026]     In the region (a), there is a resistor layer  14  under the collector layer  8 , and there is a collector electrode  10  under the resistor layer  14 . The top surface of the base layer  5  includes a p base layer  6 , and an n− emitter layer  7  is formed in the base layer  6 . Further, an insulation film  9  containing a gate electrode  4  is disposed on the base layer  5 , and an emitter electrode  2  is disposed such that it partially contacts the p base layer  6  and the n− emitter layer  7  and it covers the insulation film  9 .  
         [0027]     In the region (b), there is a sense collector electrode  13  under the collector layer  8 . Meanwhile, the top of the base layer  5  is coated with the insulation film  9 .  
         [0028]      FIG. 3  is a cross sectional view of  FIG. 1  taken along the A-A direction, where the numerals which are identical with those of  FIG. 2  denote identical components. As shown in  FIG. 3 , the collector electrode  10  and the sense collector electrode  13  do not contact with each other at the boundary between the region (a) and the region (b).  
         [0029]     In the structure in  FIG. 3 , the resistor layer  14  is formed thicker than the sense collector electrode  13 , thereby creating a step between the collector electrode  10  and the sense collector electrode  13 , and patterning which creates a clearance between the electrodes ensures no contact between the electrodes.  
         [0030]     For instance, the collector electrode  10 , the sense collector electrode  13  and the emitter electrode  2  are made of aluminum, while the gate electrode  4  is made of polycrystalline silicon. The resistor layer  14  whose resistance is higher than those of the collector electrode  10  and the sense collector electrode  13  is made of nickel for example. The insulation film  9  is made of silicon oxide for example.  
         [0031]     Although the foregoing is directed to an example that nickel is used for the resistor layer  14 , a similar function can be realized by a resistor layer which is obtained by forming a p− layer inside the p+ collector layer  8  of the silicon substrate  1 .  
         [0032]     An operation of the IGBT  100  will now be described. In general, as a voltage is applied between the gate electrode  4  and the emitter electrode  2  with a voltage applied between the collector electrode  10  and the emitter electrode  2 , a current I flows between the collector electrode  10  and the emitter electrode  2  in the IGBT  100 .  
         [0033]     In the IGBT  100 , the resistor layer  14  is located between the collector layer  8  and the collector electrode  10 . Hence, as the current I flows between the collector electrode  10  and the emitter electrode  2 , the existence of the resistor layer  14  (having the resistance Rs) develops a potential difference Vs between the collector electrode  10  and the sense collector electrode  13 .  
         [0034]     The resistance Rs of the resistor layer  14  can be set to a desired design value by means of adjustment of the material, the film thickness of the like of the resistor layer  14 . The potential difference Vs between the collector electrode  10  and the sense collector electrode  13  roughly corresponds to a voltage drop at the resistor layer  14 .  
         [0035]     Measurement of the potential difference Vs therefore makes it possible to calculate, from the potential difference Vs and the resistance Rs, the current I which is carried by the collector electrode  10 .  
         [0036]     Generally used techniques such as photolithography, ion implantation and thermal diffusion may be applied to manufacturing of the IGBT  100 . The collector electrode  10  and the sense collector electrode  13  are formed as follows: After forming a nickel layer, i.e., the material of the resistor layer  14  on the bottom surface of the collector layer  8 , the nickel layer is selectively removed only in the region of the sense collector electrode  13  (peripheral portion) so that the remaining nickel layer will serve as the resistor layer  14 , an aluminum layer is formed by sputtering or the like all over the surface so that the aluminum layer on the resistor layer  14  will serve as the collector electrode  10  and the aluminum layer around this on the collector layer  8  will serve as the sense collector electrode  13 . It is ensured during this process that the collector electrode  10  and the sense collector electrode  13  will not be connected directly with each other.  
         [0037]     In the event that a p layer rather than a nickel layer is used as the resistor layer  14 , within a region to form the collector electrode in the p+ collector layer, a p− layer is formed through injection and diffusion of n-type impurities or otherwise appropriately.  
         [0038]     A vertical-type MOSFET and a diode according to embodiments described below can be fabricated similarly, using these generally used manufacturing techniques.  
         [0039]     In the IGBT  100  according to the embodiment 1, the sense collector electrode  13  which is used for measurement of the potential difference Vs is formed in the outer peripheral portion within the back surface of the IGBT  100 . Since a current density is low in such an outer peripheral portion inside a high breakdown voltage semiconductor element such as an IGBT, the outer peripheral portion is not used to make the semiconductor element operate and a terminating structure such as a guard ring is disposed in the outer peripheral portion.  
         [0040]     In the IGBT  100  according to the embodiment 1, since the sense collector electrode  13  is formed in the outer peripheral portion, it is possible to make an effective use of the outer peripheral portion in which a current density is low, and the disposition of the sense collector electrode  13  does not enlarge the element area size. Further, it is not necessary to change the emitter electrode side layout.  
         [0041]     Although the structure in  FIG. 1  is such a structure that the sense collector electrode  13  completely surrounds the collector electrode  10 , the sense collector electrode  13  may surround the collector electrode  10  partially. One example is a structure as that shown in  FIG. 4  that a sense collector electrode is disposed on two sides of the collector electrode  10 . This similarly applies also to the embodiments described below.  
         [0042]      FIG. 5  shows an inverter circuit contained in a power semiconductor module which uses the IGBT according to the embodiment 1 of the present invention. In the inverter circuit, two transistors Tr 1  and Tr 2  are connected in series and diodes D 1  and D 2  are connected in anti-parallel respectively to the transistors Tr 1  and Tr 2 , thereby constituting a half-bridge circuit. Further, for detection of a current which flows between terminals U and N, a resistor Rs is formed inside the transistor Tr 2 . Measurement of the potential difference Vs across the resistor Rs attains detection of the current I.  
         [0043]      FIG. 6  shows an inverter circuit which is contained in a conventional power semiconductor module. In this inverter circuit, a resistor Rs is disposed separately from transistors Tr 1  and Tr 2 , and as a potential difference Vs across the resistor Rs is measured, a current I is detected.  
         [0044]      FIGS. 7 and 8  are layout diagrams of power semiconductor modules which correspond to  FIGS. 5 and 6 , of which  FIG. 7  shows a power semiconductor module which uses the IGBT according to the embodiment 1 while  FIG. 8  shows a conventional power semiconductor module.  
         [0045]     Comparison of  FIGS. 7 and 8  against each other makes it clear that the conventional power semiconductor module must secure a region for disposing the resistor Rs as the resistor Rs needs be disposed separately from the transistors Tr 1  and Tr 2 . In contrast, in the power semiconductor module according to the embodiment 1, it is not necessary to separately dispose the resistor Rs since a collector electrode (not shown) of the transistor Tr 2  has a resistor component, which permits reducing the size of the power semiconductor module.  
         [0046]     While the sense collector electrode  13  completely surrounds the collector electrode  10  ( FIG. 1 ) in this structure illustrated in this drawing and it is therefore necessary that the circuit board has a multi-layer interconnection structure and an insulation film is disposed on interconnections, use of the structure shown as other example of the embodiment 1 that the sense collector electrode  13  partially surrounds ( FIG. 4 ) permits use of a circuit board having a conventional interconnection layer structure as that shown in  FIG. 9 .  
       Embodiment 2  
       [0047]      FIG. 10  is a bottom view of a vertical-type MOSFET generally denoted at  110  according to the embodiment  2 , and  FIGS. 11A and 11B  are a cross sectional view of the MOSFET  110  shown in  FIG. 10  taken along the direction which is parallel to the plane of the drawing.  FIG. 11A  is the cross sectional view taken in the region of a drain electrode (region (a)) denoted at  30  in  FIG. 10 , while  FIG. 11B  is the cross sectional view taken in the region of a ring-like sense drain electrode (region (b)) denoted at  33  in  FIG. 10  and surrounding the drain electrode  30 .  
         [0048]     In  FIGS. 10, 11A  and  11 B, components denoted at the same numerals as those used in  FIGS. 1, 2A  and  2 B are the same or corresponding components. The fact that the structures of the emitter electrode  2 , the n− emitter layer  7  and the collector layer  8  shown in  FIGS. 1, 2A  and  2 B serve respectively as a source electrode  22 , a source layer  27  and a drain layer  28  in  FIGS. 10, 11A  and  11 B because of a difference between an IGBT and a MOSFET is well known to those skilled in the art, and therefore, details of this will not be described here.  
         [0049]     The resistor layer  14  may be a resistor layer which is obtained by forming an n− layer within the n+ drain layer  28  of the silicon substrate  1 , as such a resistor layer functions similarly.  
         [0050]     As in the IGBT  100  described above, the MOSFET  110  according to the embodiment 2 permits making an effective use of an outer peripheral portion in which a current density is low and which is within the back surface of the MOSFET  110 , as the sense drain electrode  33  which is used for measurement of the potential difference Vs is formed in the outer peripheral portion. Hence, even despite the sense drain electrode  33 , the element area size does not increase, and further, it is not necessary to change the source electrode side layout.  
       Embodiment 3  
       [0051]      FIG. 12  is a bottom view of a vertical-type diode generally denoted at  120  according to the embodiment 3, and  FIGS. 13A and 13B  are a cross sectional view of the diode  120  shown in  FIG. 12  taken along the direction which is parallel to the plane of the drawing.  FIG. 13A  is the cross sectional view taken in the region of a cathode electrode denoted at  40  in  FIG. 12 , while  FIG. 13B  is the cross sectional view taken in the region of a ring-like sense cathode electrode (region (b)) denoted at the  43  in  FIG. 12  and surrounding the cathode electrode  40 .  
         [0052]     In  FIGS. 12, 13A  and  13 B, components denoted at the same numerals as those used in  FIGS. 1, 2A  and  2 B are the same or corresponding components.  
         [0053]     The resistor layer  14  may be a resistor layer which is obtained by forming an n− layer within the n+ cathode layer  48  of the silicon substrate  1 , as such a resistor layer functions similarly.  
         [0054]     As shown in  FIGS. 12, 13A  and  13 B, the diode  120  includes the silicon substrate  1  which contains the n− base layer  5  and the n+ cathode layer  48 .  
         [0055]     In the region (a), there is the resistor layer  14  under the cathode layer  48 , and there is the cathode electrode  40  under the resistor layer  14 . Meanwhile, there are a p anode layer  46  and an anode electrode  42  formed on the base layer  5 .  
         [0056]     In the region (b), there is the sense cathode electrode  43  under the cathode layer  48 . The top of the base layer  5  is coated with the insulation film  9 . The cathode electrode  40  and the sense cathode electrode  43  are formed such that they do not contact with each other.  
         [0057]     In the diode  120 , when a voltage is applied between the cathode electrode  40  and the anode electrode  42 , the current I flows between these two electrodes. This develops the potential difference Vs attributable to the resistor layer  14 , between the cathode electrode  40  and the sense cathode electrode  43 .  
         [0058]     Hence, measurement of the potential difference Vs permits calculating the current I from the potential difference Vs and the resistor Rs of the resistor layer  14 , which is similar in the embodiment 1.  
         [0059]     As in the MOSFET  110  described above, in the diode  120  according to the embodiment 3, since the sense cathode electrode  43  which is used for measurement of the potential difference Vs is formed in an outer peripheral portion within the back surface of the diode  120 , it is possible to effective utilize the outer peripheral portion in which a current density is low, and therefore, even despite the sense cathode electrode  43 , the element area size does not increase. Further, it is not necessary to change the anode electrode side layout.