Abstract:
A semiconductor device is composed a semiconductor substrate having a first conducting-type first semiconductor layer, a second conducting-type second semiconductor layer, a first conducting-type third semiconductor layer, a second conducting-type fourth semiconductor layer and a first conducting-type fifth semiconductor layer, a first main electrode for short-circuiting the first semiconductor layer and the second semiconductor layer, a second main electrode for short-circuiting the fourth semiconductor layer and the fifth semiconductor layer, and a control electrode provided on the third semiconductor layer. The first semiconductor layer and the second semiconductor layer form a joint. The second semiconductor layer and the third semiconductor layer form a joint. The third semiconductor layer and the fourth semiconductor layer form a joint. The fourth semiconductor layer and the fifth semiconductor layer form a joint.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a semiconductor device having switching function such as IGBT (Insulated Gate Bipolar Transistor), GCT (Gate Commutated Turn-off Thyristor) or GTO (Gate Turn-off Thyristor).  
           [0003]    2. Description of the Background Art  
           [0004]    [0004]FIG. 8 is a cross section showing a structure of a conventional reverse conducting GTO. Here, there will be explained below GTO as an example of a semiconductor device having a switching function. Normally, the reverse conductive GTO is constituted so that a GTO area is connected to a free wheeling diode area in antiparallel and these areas are integrated in one semiconductor substrate.  
           [0005]    In the conventional reverse conducting GTO, a P layer  602 , and an N E  layer  603  are diffused on a semiconductor substrate N-layer  601  made of silicon or the like in order from a cathode side in a GTO area  620 . Similarly an N +  layer  604  and a P E  layer  605  are diffused in order from an anode side. In a diode area  621 , the P layer  602  is diffused on the semiconductor substrate N −  layer  601  made of silicon or the like from the cathode side, and the N +  layer  604  and an N ++  layer  606  are diffused in order from the anode side.  
           [0006]    In addition, this reverse conducting GTO has a cathode electrode  607  and a gate electrode  608  in the GTO area, a cathode electrode  609  in the diode area and an anode electrode  610  in the whole area. In a separating area which separates the GTO area  620  from the diode area  621 , an etching section  611  is provided on a portion of the P layer  602  which remains on the N −  layer  601  after a diffusion area of the P layer  602  of about 90 μm is etched down by about 60 μm, and the width A of the etching portion is about 5 mm. Resistance of 300 to 500 Ω is provided between the GTO area  620  and the diode area  621  and they are separated by the etching area with the width A of about 5 mm. Paying attention to thermal resistance, thermal resistance is generated on the surface of the GTO area  620  at the time of operating GTO, and on the surface of the diode area  621  at the time of operating diode.  
           [0007]    Further, relating techniques are disclosed in Japanese Patent Application Laid-Open Nos. 9-191110 (1997) and 2-309676 (1990). Japanese Patent Application No. 9-191110 (1997) discloses an insulating gate bipolar transistor containing a diode. In this transistor, a cathode electrode and a collector electrode are integrated, and an anode electrode and an emitter electrode are integrated so that a size of the whole transistor is reduced.  
           [0008]    Japanese Patent Application Laid-Open No. 2-309676 (1990) discloses a reverse conducting-type insulated gate bipolar transistor. In this transistor, a source of IGBT and an anode of a diode are formed by one electrode, and a collector of IGBT and a cathode of the diode are formed by one electrode.  
           [0009]    In the conventional reverse conducting GTO (FIG. 8), since the GTO area  620  and the diode area  621  are separated by high resistance, the separating area is required. Moreover, in this reverse conducting GTO, since thermal resistance is generated on the surface of the GTO area  620  and on the surface of the diode area  621 , there arises a problem that the thermal resistance in the reverse conducting GTO is high. Further, as for both the diodes disclosed in Japanese Patent Application Laid-Open Nos. 9-191110 (1997) and 2-309676 (1990), a switching element and the diode use one electrode so that the whole diode becomes compact. However, a separating area which separates the switching element area from the diode area is required. There arises a problem that an actual operating area is reduced due to this separating area and thus a performance of a semiconductor device is deteriorated.  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention is devised in order to solve the above problems, and it is an object of the present invention to provide a semiconductor device in which a switching ability and a diode ability can be used properly in a regular direction and a reverse direction in one structure, thereby increasing a surface area of a chip and reducing thermal resistance, and a separating area is eliminated, thereby increasing an actual operating area.  
           [0011]    In order to achieve the above objects, a first aspect of the invention provides a semiconductor device characterized by including: a semiconductor substrate; wherein the semiconductor includes: a first conducting-type first semiconductor layer; a second conducting-type second semiconductor layer; a first conducting-type third semiconductor layer; a second conducting-type fourth semiconductor layer; and a first conducting-type fifth semiconductor layer; a first main electrode for short-circuiting the first semiconductor layer and the second semiconductor layer; a second main electrode for short-circuit the fourth semiconductor layer and the fifth semiconductor layer; and a control electrode provided on the third semiconductor layer. The semiconductor device is characterized in that the first semiconductor layer and the second semiconductor layer form a joint, the second semiconductor layer and the third semiconductor layer forms a joint, the third semiconductor layer and the fourth semiconductor layer form a joint, and the fourth semiconductor layer and the fifth semiconductor layer form a joint.  
           [0012]    In accordance with the semiconductor device of the first aspect of the present invention, the area having the switching ability and the area having the diode ability are provided and they commonly have the PN joint so that the surface area is increased and the thermal resistance can be reduced. Further, since an area which separates the area having the switching ability from the area having the diode ability is not provided, the actual operating area can be increased.  
           [0013]    The semiconductor device of the second aspect of the invention, which relates to the semiconductor device of the first aspect, is characterized in that the first semiconductor layer and the third semiconductor layer are separated by the second semiconductor layer, and the third semiconductor layer and the fifth semiconductor layer are separated by the fourth semiconductor layer.  
           [0014]    In accordance with the semiconductor device of the second aspect of the present invention, the area having the switching ability and the area having the diode ability are provided and they commonly have the PN joint so that the surface area is increased and the thermal resistance can be reduced. Further, since an area which separates the area having the switching ability from the area having the diode ability is not provided, the actual operating area can be increased.  
           [0015]    The semiconductor device of the third aspect of the invention, which relates to the semiconductor device of the first aspect, is characterized in that the first semiconductor layer and the second semiconductor layer are exposed from a first main surface of the semiconductor substrate, and the first semiconductor layer is surrounded by the second semiconductor layer.  
           [0016]    In accordance with the semiconductor device of the third aspect of the present invention, the area having the switching ability and the area having the diode ability are provided and they commonly have the PN joint so that the surface area is increased and the thermal resistance can be reduced. Further, since an area which separates the area having the switching ability from the area having the diode ability is not provided, the actual operating area can be increased.  
           [0017]    The semiconductor device of the fourth aspect of the invention, which relates to the semiconductor device of the first aspect, is characterized in that the fourth semiconductor layer and the fifth semiconductor layer are exposed from a second main surface of the semiconductor substrate, and the fifth semiconductor layer is surrounded by the fourth semiconductor layer.  
           [0018]    In accordance with the semiconductor device of the fourth aspect of the present invention, the area having the switching ability and the area having the diode ability are provided and they commonly have the PN joint so that the surface area is increased and the thermal resistance can be reduced. Further, since an area which separates the area having the switching ability from the area having the diode ability is not provided, the actual operating area can be increased.  
           [0019]    The semiconductor device of the fifth aspect of the invention, which relates to the semiconductor device of the first aspect, is characterized in that the first conducting type is p type.  
           [0020]    In accordance with the semiconductor device of the fifth aspect of the present invention, the area having the switching ability and the area having the diode ability are provided and they commonly have the PN joint so that the surface area is increased and the thermal resistance can be reduced. Further, since an area which separates the area having the switching ability from the area having the diode ability is not provided, the actual operating area can be increased.  
           [0021]    The semiconductor device of the sixth aspect of the invention, which relates to the semiconductor device of the first aspect, is characterized in that the first semiconductor layer is exposed from a first main surface of the semiconductor substrate and a maximum width in a short-length direction of the exposed surface of the first semiconductor layer is not more than 100 μm.  
           [0022]    In accordance with the semiconductor device of the sixth aspect of the present invention, the effect which is similar to that of the semiconductor device of the first aspect of the invention can be obtained. Further, the maximum width in the short-length direction of the exposed surface of the first semiconductor layer is set to not more than 100 μm so that the semiconductor device can be prevented from being broken due to the spike voltage at the time of the switching operation.  
           [0023]    The semiconductor device of the seventh aspect of the invention, which relates to the semiconductor device of the first aspect, is characterized in that the first main electrode is a cathode and the control electrode is provided only on the third semiconductor layer.  
           [0024]    In accordance with the semiconductor device of the seventh aspect of the present invention, the effect which is similar to that of the semiconductor device of the first aspect of the present invention can be obtained. Further, the area having the switching ability can be formed as GCT, GTO or the like.  
           [0025]    The semiconductor device of the eighth aspect of the invention, which relates to the semiconductor device of the first aspect, characterized in that the first and second main electrodes are pressed by a metal plate.  
           [0026]    In accordance with the semiconductor device of the eighth aspect of the present invention, the effect which is similar to that of the semiconductor device of the first aspect of the present invention can be obtained. Further, the structure which can be used more easily can be obtained.  
           [0027]    The semiconductor device of the ninth aspect of the invention, which relates to the semiconductor device of the first aspect, is characterized in that a dielectric layer is provided between the control electrode and the third semiconductor layer.  
           [0028]    In accordance with the semiconductor device of the ninth aspect of the present invention, the effect which is similar to that of the semiconductor device of the first aspect of the present invention can be obtained. Further, the area having the switching ability can be formed as IGBT or the like.  
           [0029]    The semiconductor device of the tenth aspect of the invention, which relates to the semiconductor device of the ninth aspect, is characterized in that a portion of the control electrode is positioned on the second semiconductor layer or on the second semiconductor layer and the first semiconductor layer.  
           [0030]    In accordance with the semiconductor device of the tenth aspect of the present invention, the effect which is similar to that of the semiconductor device of the ninth aspect of the present invention can be obtained. Further, the area having the switching ability can be formed as IGBT or the like.  
           [0031]    The semiconductor device of the eleventh aspect of the invention, which relates to the semiconductor device of the ninth aspect, is characterized in that the first main electrode is an anode.  
           [0032]    In accordance with the semiconductor device of the eleventh aspect of the present invention, the effect which is similar to that of the semiconductor device of the ninth aspect of the present invention can be obtained. Further, the area having the switching ability can be formed as IGBT or the like.  
           [0033]    The semiconductor device of the twelfth aspect of the invention, which relates to the semiconductor device of the ninth aspect, is characterized in that in the case where an electric potential of the first main electrode is higher than an electric potential of the second main electrode, an electric potential of the control electrode is controlled to not more than the electric potential of the first main electrode.  
           [0034]    In accordance with the semiconductor device of the twelfth aspect of the present invention, the effect which is similar to that of the semiconductor device of the ninth aspect of the present invention can be obtained. Further, the structural breakdown of the PN joint can be prevented in the case where a reverse voltage is applied. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0035]    [0035]FIG. 1 is a cross section showing a structure of a semiconductor device in a first embodiment;  
         [0036]    [0036]FIG. 2 is a graph showing a relationship between a width W of a P layer  106  or an interval W of a P E  layer  105  and a spike voltage;  
         [0037]    [0037]FIGS. 3A through 3C are cross sections showing the steps of manufacturing the semiconductor device in the first embodiment;  
         [0038]    [0038]FIGS. 4A and 4B are cross sections showing the steps of manufacturing the semiconductor device in the first embodiment;  
         [0039]    [0039]FIG. 5 is a cross section showing a structure of the semiconductor device in the first embodiment;  
         [0040]    [0040]FIG. 6 is a cross section showing a structure of the semiconductor device in a second embodiment;  
         [0041]    [0041]FIG. 7 is an explanatory diagram for explaining an off state of the semiconductor device in the second embodiment; and  
         [0042]    [0042]FIG. 8 is a cross section showing a structure of a conventional reverse conducting GTO. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0043]    There will be described below embodiments of the present invention with reference to the drawings.  
         [0044]    First Embodiment  
         [0045]    [0045]FIG. 1 is a cross section showing a structure of a semiconductor device in a first embodiment. As shown in FIG. 1, a semiconductor device is composed of a semiconductor substrate having an N −  layer  101 , a P B  layer  102 , an N E  layer  103 , an N +  layer  104 , a P E  layer  105  and a P layer  106 , a cathode electrode  107 , an anode electrode  108  and a control (gate) electrode  109  in the P B  layer  102 . The N −  layer  101  and the P B  layer  102  form a PN joint. The P B  layer  102  and the N E  layer  103  form a PN joint. The N E  layer  103  and the P layer  106  form a PN joint. The N +  layer  104  and the P E  layer  105  form a PN joint.  
         [0046]    In addition, the N E  layer  103  and the P layer  106  are exposed from a surface where the semiconductor substrate contacts with the cathode electrode  107 , and the N E  layer  103  surrounds the P layer  106 . Here, the cathode electrode  107  short-circuits the N E  layer  103  and the P layer  106 . The exposed surface of the P layer  106  is rectangular, oval or the like, and it is preferable its maximum length of a short-length direction is not more than 100 μm. In FIG. 1, the maximum length in the short-length direction of the exposed surface of the P layer  106  corresponds to a width W of the P layer  106  or an interval W of the P E  layer  105 . The N +  layer  104  and the P E  layer  105  are exposed from a surface where the semiconductor substrate contacts with the anode electrode  108 , and the P E  layer  105  surrounds the N +  layer  104 . The anode electrode  108  short-circuits the N +  layer  104  and the P E  layer  105 .  
         [0047]    In addition, the P B  layer  102  and the P layer  106  are separated by the N E  layer  103 . The P B  layer  102  and the P E  layer  105  are separated by the N −  layer  101  and the N +  layer  104 .  
         [0048]    With the above structure, this semiconductor device is composed so that the diode area  120  and the GTO area  121  which serves as a switching element are provided in same structure. In the semiconductor device, the diode area  120  and the GTO area  121  are connected in antiparallel so as to compose a circuit. In this structure, an area which separates the diode area  120  from the GTO area  121  is not provided.  
         [0049]    Next, there will be explained below as to that the width W of the P layer  106  or the interval W of the P E  layer  105  is preferably not more than 100 μm. FIG. 2 is a graph showing a relationship between the width W of the P layer  106  or the interval W of the P E  layer  105  and a spike voltage. The width W of P layer  106  strongly relates to the interval of the P E  layer  105 , and they influence rising or the like at the time of switching operation.  
         [0050]    As shown in FIG. 2, as the width W of the P layer  106  or the interval W of the P E  layer  105  becomes wider, a spike voltage V sp  becomes larger. When the width W of the P layer  106  or the interval W of the P E  layer  105  exceeds 100 μm, the spike voltage V sp  exceeds a value of absolute withstand voltage ×0.8. In order to prevent the semiconductor device from being broken due to the spike voltage V sp , the width W of the P layer  105  or the interval W of the P E  layer  105  is set to no more than 100 μm. Here, the absolute withstand voltage is a limit value which causes breakdown of the semiconductor device under any conditions.  
         [0051]    Next, there will be explained below a semiconductor device manufacturing method with reference to FIGS. 3A through 3C and FIGS. 4A and 4B.  
         [0052]    [0052]FIGS. 3A through 3C and FIGS. 4A and 4B are cross sections showing the steps of manufacturing the semiconductor device.  
         [0053]    At first, boron which is a dopant as impurity is injected from a cathode side (upper side of the drawing) into the semiconductor substrate N −  layer  101  made of silicon or the like by using an ion injecting method so that the dopant is introduced. Thereafter, the substrate is heated for a long time at a temperature of not less than 1200° C. and the impurity is diffused so that the P B  layer  102  is formed (FIG. 3A). Next, phosphorus which is a dopant as impurity is injected from the cathode side by using the ion injecting method and is diffused similarly so that the N E  layer  103  is formed (FIG. 3B). Next, boron with high density is injected from the cathode side and partially diffused so that the P layer  106  with high density is formed (FIG. 3C). At this time, a conventional method of forming a mask and injecting boron into an unnecessary portion is not needed.  
         [0054]    Next, phosphorus with high density is injected from an anode side (lower side of the drawing) and is diffused so that the N −  layer  104  is formed. Further, boron is injected from the anode side and is partially diffused so that the P E  layer  105  is formed (FIG. 4A). At this time, a conventional method of forming a mask and injecting boron into an unnecessary portion is not needed. Moreover, the P E  layer  105  which is diffused from the anode side forms an anode short structure partially. Next, the cathode electrode  107  is provided so as to short-circuit the N E  layer  103  and the P layer  106 , and the anode electrode  108  is provided so as to short-circuit the N +  layer  104  and the P E  layer  105 . Further, a control electrode  109  is taken out from the P E  layer  102  (FIG. 4B).  
         [0055]    Next, there will be explained below another structure of the semiconductor device.  
         [0056]    [0056]FIG. 5 is a cross section of the semiconductor device in the first embodiment.  
         [0057]    As shown in FIG. 5, the semiconductor device has a cold welding structure in which the cathode electrode  107  and the anode electrode  108  of the semiconductor device shown in FIG. 1 are pressed by a metal plate made of, for example, molybdenum or the like. With this structure, the semiconductor device can be used easily.  
         [0058]    In the semiconductor device according to the first embodiment of the present invention, the GTO area  121  having the switching ability and the diode area  120  having the diode ability coexist in the one structure, thereby increasing the area of the chip and reducing the thermal resistance. Further, the semiconductor device in the first embodiment does not require a conventional separating area, and the GTO area  121  and the diode area  120  commonly have the PN joint so that the actual operating area can be enlarged.  
         [0059]    Second Embodiment  
         [0060]    [0060]FIG. 6 is a cross section showing a structure of the semiconductor device in a second embodiment. As shown in FIG. 6, the semiconductor device is composed of a semiconductor substrate having an N −  layer  301 , a P +  layer  302 , a P B  layer  303 , N +  layers  304  and an N layer  305 , an emitter electrode  306 , a collector electrode  307 , control electrodes  308  and oxide films  309  which serves as a dielectric. The N −  layer  301  and the P +  layer  302  form a PN joint. The P +  layer  302  and the N layer  305  form a PN joint. The N −  layer  301  and the P B  layer  303  form a PN joint. The N +  layers  304  and the P E  layer  303  form PN joints.  
         [0061]    In addition, the P B  layer  303  and the N +  layers  304  are exposed from a surface where the semiconductor substrate contacts with the emitter electrode  306 , and the P B  layer  303  surrounds the N +  layers  304 . Here, the emitter electrode  306  short-circuits the N +  layers  304  and the P B  layer  303 , and serves also as an anode electrode. The N layer  305  and the P +  layer  302  are exposed from a surface where the semiconductor substrate contacts with the collector electrode  307 , and the P +  layer  302  surrounds the N layer  305 . The collector electrode  307  short-circuits the P +  layer  302  and the N layer  305 , and serves also as a cathode electrode.  
         [0062]    In addition, the N +  layers  304  and the N −  layer  301  are separated by the P B  layer  303 . The N layer  305  and the N −  layer  301  are separated by the P +  layer  302 . Further, the oxide films  309  as insulators are provided on the N −  layer  301  and the P B  layer  303  and the N +  layers  304  so as to contact with the N −  layer  301  and the P B  layer  303  and the N +  layers  304 . The control electrodes  308  are provided on the oxide films  309 .  
         [0063]    According to the above structure, in the semiconductor device, the diode area  120  and IGBT area  122  which serves as a switching element are provided in the same structure. In the semiconductor device, the diode area  120  and the IGBT area  122  are connected in antiparallel so as to form a circuit. In this structure, an area which separates the diode area  120  from the IGBT area  122  is not provided.  
         [0064]    Next, there will be explained below an off state of the semiconductor device.  
         [0065]    [0065]FIG. 7 is an explanatory diagram for explaining the off state of the semiconductor device in the second embodiment.  
         [0066]    As shown in FIG. 7, an electric potential of the collector (cathode) electrode  307  is higher than an electric potential of the emitter (anode) electrode  306 . When a difference in the electric potential between the collector electrode  307  and the emitter electrode  306  is small, an electric current does not flow. However, the difference in the electric potential is large, a breakdown phenomenon that an electric current abruptly flows occurs. When the difference in the electric potential becomes larger, there is a possibility that the PN joint is structurally broken. In order to prevent the structural breakdown of the PN joint, an electric potential of the control electrodes  308  is set to be lower than the electric potential of the emitter electrode  306 .  
         [0067]    This is because when the electric potential of the control electrodes  308  is set to be lower than the electric potential of the emitter electrode  306 , surface density of the N −  layer  301  and the N +  layers  304  just below the control electrodes  308  via the oxide films  309  is inverted so that the P B  layer  303  can be thick. When the P B  layer  303  is thick, a flow of the electric current from the N −  layer  301  to the N +  layer  303  can be prevented, and the structural breakdown of the PN joint between the P B  layer  303  and the N −  layer  301  can be prevented. Therefore, in the case where a reverse voltage is applied to the semiconductor device, the electric potential of the control electrodes  308  is controlled so as to be not more than the electric potential of the emitter electrode  306 .  
         [0068]    Next, there will be explained below the semiconductor device manufacturing method according to the second embodiment. Similarly to the semiconductor device manufacturing method in the first embodiment, a dopant as impurity is injected by the ion injecting method and after the dopant is introduced, the substrate is heated for a long time at a temperature of not less than 1200° C. and impurity is diffused so that the respective semiconductor layers are formed. Needless to say, in order not to inject the dopant into an unnecessary portion, a mask is formed by the conventional method.  
         [0069]    At first, boron is injected from a first surface side of the semiconductor substrate into the semiconductor substrate N −  layer  301  made of silicon or the like and is diffused so that the P B  layer  303  is formed. Here, a first surface means upper side of FIG. 7. Next, phosphorus with high density is injected from the first surface side and is diffused similarly so that the N +  layers  304  are formed. At this time, a plurality of the diffused N +  layers  304  is formed partially.  
         [0070]    Next, boron with high density is injected from a second surface side and is diffused so that the P +  layer  302  is formed. Here, a second surface means lower side of FIG. 7. Next, phosphorus is injected from the second surface side and is diffused so that the N layer  305  is formed. Next, the oxide films  309  are formed on the N −  layer  301  and the P B  layer  303  and the N +  layers  304  of the first surface. Next, the control electrodes  308  are provided on the oxide films  309 , and the emitter electrode  306  is provided so as to short-circuit the P B  layer  303  and the N +  layers  304 . The collector electrode  307  is provided so as to short-circuit the P +  layer  302  and the N layer  305 .  
         [0071]    In the semiconductor device in the second embodiment, the IGBT area  122  having the switching ability and the diode area  120  having the diode ability coexist in the one structure, thereby increasing the area of the chip, and reducing the thermal resistance. Further, the semiconductor device in the second embodiment does not require the conventional separating area, and the IGBT area  122  and the diode area  120  commonly have the PN joint so that the actual operating area can be enlarged.