Abstract:
In order to reduce a device area, a bipolar transistor using temperature characteristics of a forward voltage generated between an emitter and a base has a structure in which a high concentration second conductivity type impurity region for a base electrode and a high concentration first conductivity type impurity region for a collector electrode are brought into direct contact with each other to prevent formation of an unnecessary isolation region. Further, an emitter region is disposed to self-align with a device isolation insulating film or a polycrystalline silicon arranged on a surface of a semiconductor substrate.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a semiconductor device using a bipolar transistor. 
         [0003]    2. Description of the Related Art 
         [0004]    In recent years, the application fields of power devices have expanded dramatically. The power devices are increasingly applied to wide ranges of fields such as consumer products, transportation, and information in addition to the industrial use. Along with the progress toward high frequency and high efficiency in application, large current capability is required to the power devices, and at the same time various peripheral circuits such as protection circuits and drive circuits are indispensable. Accordingly, the development of products having higher functions and higher reliability is advancing through incorporation of those circuits into a single module. 
         [0005]    An example of the protection circuits is an overheat protection circuit. The overheat protection circuit has a function of preventing breakage or deterioration of internal parts due to overheat caused by extraordinary rise in the temperature within the semiconductor integrated circuit. The overheat protection circuit includes a part that works as a temperature sensor which sends a signal thereof when the temperature reaches a certain value, and a part that works to receive the signal to make the circuit off. 
         [0006]    Various elements are used as the temperature sensor portion. And, examples in which a bipolar transistor is used are disclosed in the following documents. 
         [0007]    Patent Document 1: JP 2004-294322A 
         [0008]    Patent Document 2: JP 10-122976A 
       Problem to be Solved by the Invention 
       [0009]    However, the inventions disclosed in JP 2004-294322A and JP 10-122976A each employs a bipolar transistor which is generally used, and hence those inventions are not considered from the viewpoint of reducing the area to lower its cost. For example, as shown in  FIG. 6 , a field oxide film  109  is arranged between an emitter region  104  and a base high concentration impurity region  103 , and between the base high concentration impurity region  103  and a collector high concentration impurity region  105 , preventing reduction in area. 
       SUMMARY OF THE INVENTION 
       [0010]    Considering the above-mentioned problem of area reduction, which has been out of examination, the present invention has been made, and has an object to reduce a device size compared to the conventional structure, thereby reducing the area of a semiconductor integrated circuit, and to lower its manufacturing cost. Meanwhile, the present invention has another object to form the emitter region in a self-aligning manner to reduce variation in the device characteristics by suppressing variation in the size of the emitter region since the size of the emitter region contributes to the bipolar device characteristics. 
       Measure to Solve the Problem 
       [0011]    In order to solve the above-mentioned problem, the present invention employs a bipolar transistor in which temperature characteristics of a forward voltage generated between an emitter and a base is used. More specifically, the present invention employs the following structures. 
         [0012]    (1) A semiconductor device including a bipolar transistor, the bipolar transistor including: a collector region having a first conductivity type formed on a surface of a semiconductor substrate having a first conductivity type; a base region having a second conductivity type formed in the collector region; and an emitter region having a first conductivity type formed in the base region, the collector region including a high concentration first conductivity type region for a collector electrode, the base region including a high concentration second conductivity type region for a base electrode, in which the high concentration first conductivity type region for a collector electrode and the high concentration second conductivity type region for a base electrode are brought into direct contact with each other so that the collector region and the base region have an equal potential. 
         [0013]    (2) A semiconductor device according to Item (1), in which the high concentration first conductivity type region for a collector electrode and the high concentration second conductivity type region for a base electrode are connected to each other at the same contact with the same metal electrode to have the equal potential. 
         [0014]    (3) A semiconductor device, which is different in configuration from the semiconductor device according to Item (2), in which the high concentration first conductivity type region for a collector electrode and the high concentration second conductivity type region for a base electrode are connected to each other with the same metal electrode through different contacts and to have the equal potential. 
         [0015]    (4) A semiconductor device according to Item (1), (2), or (3), in which the emitter region is formed in a self-aligning manner through a sheet of polycrystalline silicon arranged above the surface of the semiconductor substrate. 
         [0016]    (5) A semiconductor device according to Item (4), in which the polycrystalline silicon has a second conductivity type. 
         [0017]    (6) A semiconductor device according to Item (4) or (5), in which the polycrystalline silicon has a potential equal to a potential of the base region and the collector region. 
         [0018]    (7) A semiconductor device according to Item (4) or (5), in which the polycrystalline silicon has a potential equal to a potential of the emitter region. 
         [0019]    (8) A semiconductor device according to Item (1), (2), or (3), in which the emitter region is formed in a self-aligning manner with a device isolation insulating film. 
       BENEFIT OF THE INVENTION 
       [0020]    In the bipolar transistor in which the temperature characteristics of the forward voltage generated between the emitter and the base is used, the high concentration impurity region for the base and the high concentration impurity region for the collector are brought into contact with each other to have an equal potential, permitting elimination of the device isolation region between the base and the collector, which enables reduction in the device size and the cost. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    In the accompanying drawings: 
           [0022]      FIG. 1  is a sectional view of a bipolar transistor according to a first embodiment of the present invention; 
           [0023]      FIG. 2  is a plan view showing a main portion of the bipolar transistor according to the first embodiment of the present invention; 
           [0024]      FIGS. 3A to 3E  are sectional views taken along the line A-A′ of  FIG. 2 , showing processes for a main portion of a semiconductor device according to the first embodiment of the present invention; 
           [0025]      FIG. 4  is a sectional view of a bipolar transistor according to a second embodiment of the present invention; 
           [0026]      FIG. 5  is a sectional view of a bipolar transistor according to a third embodiment of the present invention; and 
           [0027]      FIG. 6  is a sectional view showing an example of a conventional bipolar transistor. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    A semiconductor device according to the present invention is a bipolar transistor in which temperature characteristics of a forward voltage generated between an emitter and a base is used. And in particular, the semiconductor device can be used for a temperature sensor or the like. A number of bipolar transistors have been proposed to use in this way, but the conventional bipolar transistors are not designed from the viewpoint of reduction in area. The present invention thus discloses a method of reducing area of a bipolar transistor in which the temperature characteristics of the forward voltage generated between the emitter and the base is used. The method of reducing area is described below. 
         [0029]    First, because this bipolar transistor only needs the forward voltage, the base and the collector do not need to be reverse-biased and can have an equal potential. Then, consideration of breakdown voltage between the base and the collector, which has been necessary in a normal bipolar transistor, can be eliminated. Accordingly, device isolation provided between a high concentration region for a base electrode and a high concentration region for a collector electrode, which has been necessary to secure the breakdown voltage therebetween, can be eliminated, permitting reduction in device area. At the same time, the present invention proposes a manufacturing method in which suppression of the variation of the emitter region and reduction of variation in device characteristics are considered through formation of an emitter region in a self-aligning manner. Hereinafter, details of the present invention are described by using embodiments of a PNP bipolar transistor with reference to the drawings. 
       First Embodiment 
       [0030]      FIG. 1  shows a sectional view of a bipolar transistor according to a first embodiment of the present invention. The sectional view is taken along the line A-A′ of a plan view shown in  FIG. 2 . The bipolar transistor is described. A semiconductor substrate  101  is a p-type substrate and serves as a collector region. An n-type impurity region  102  serving as a base region is provided in the semiconductor substrate  101 . In the n-type impurity region  102  serving as the base region, a high concentration n-type impurity region for a base electrode  103  is provided so as to come into contact with the collector region. Further, in the n-type impurity region  102 , a high concentration p-type impurity region  104  is provided as an emitter region, and an emitter metal electrode  107  is in contact with it. A high concentration p-type impurity region for a collector electrode  105  is provided outside the n-type impurity region  102  so as to be in contact with the high concentration n-type impurity region  103 . The base and the collector are used in the same potential, and thus a base/collector metal electrode  108  is brought into contact with the high concentration n-type impurity region for a base electrode  103  and the high concentration p-type impurity region for a collector electrode  105 . An area between the emitter region  104  and the high concentration n-type impurity region for a base electrode  103  is separated by a polycrystalline silicon  106  so that the emitter region  104  is formed in the self-aligning manner. 
         [0031]      FIG. 2  is a plan view of the bipolar transistor according to the first embodiment of the present invention. A portion surrounded by the polycrystalline silicon  106  is the high concentration p-type impurity region  104  serving as the emitter region, and the high concentration n-type impurity region for a base electrode  103  is provided so at to surround the polycrystalline silicon. The high concentration p-type impurity region for a collector electrode  105  is provided so as to surround the high concentration n-type impurity region for a base electrode  103 , and a field insulating film  109  is provided outside thereof. 
         [0032]    Next, an embodiment of a method of manufacturing the bipolar transistor shown in  FIGS. 1 and 2  is described with reference to  FIGS. 3A to 3E .  FIG. 3A  is a view showing that the n-type impurity region  102  to become the base region is manufactured in the p-type substrate  101  to become the collector region. The p-type substrate  101  is generally formed with a concentration of about 1×10 14  to 1×10 15  cm −3 . The n-type impurity region  102  is doped with n-type impurities, for example, phosphorus with the concentration of about 1×10 12  to 1×10 13  cm −2  by ion implantation, and is thermally diffused, to thereby manufacture the n-type impurity region  102  with the concentration of about 1×10 16  to 5×10 16  cm −3 . Subsequently, a field insulating film  109  is formed by local oxidation of silicon (LOCOS) with a thickness of about 500 to 1,000 nm to become a device isolation region. 
         [0033]      FIG. 3B  is a view showing that, in order to form the emitter region  104  in the self-aligning manner, the polycrystalline silicon  106  is deposited on a gate insulating film  110  to be patterned by etching. In this case, it is assumed that the polycrystalline silicon  106  having an n-type conductivity is used, and a threshold value thereof may be raised so that a parasitic MOS transistor does not operate under the polycrystalline silicon  106 . In order to obtain the n-type conductivity, n-type impurities, for example, arsenic is injected by ion implantation with the concentration of about 5×10 15  cm −2 , and thereafter the semiconductor substrate  101  thus obtained is subjected to heat treatment at a temperature of about 850 degrees to diffuse the impurities injected in the polycrystalline silicon  106 . For reduction in sheet resistance, a refractory metal silicide  111  is deposited with a thickness of about 100 nm. Patterning is performed by photoresist and etching is performed, whereby the refractory metal silicide  111  can be formed. Note that the ion implantation is employed in this embodiment when the polycrystalline silicon  106  is made to have the n-type conductivity, but predeposition of phosphorus or arsenic may be performed. Further, in order to raise the threshold value, impurities may be doped under the polycrystalline silicon  106 . 
         [0034]      FIG. 3C  is a view showing that patterning is performed with a photoresist  113 , and high concentration p-type impurities are doped by ion implantation to form the emitter region and the high concentration impurity region for a collector electrode. In this case, the high concentration p-type impurity region is formed by doping high concentration p-type impurities, for example, BF2 with the concentration of about 5×10 15  cm −2  to obtain the concentration of about 5×119 cm −1  to 1×10 21  cm −1 . 
         [0035]      FIG. 3D  is a view showing that pattering is performed with the photoresist  113 , and high concentration n-type impurities are doped by ion implantation to form the high concentration impurity region for a base electrode. In this case, the high concentration n-type impurity region is formed by doping high concentration n-type impurities, for example, arsenic with the concentration of about 5×10 15  cm −2  to obtain the concentration of about 5×10 19  cm −3  to 1×10 21  cm −3 . 
         [0036]    Next, an interlayer insulating film (not shown) is deposited, and the photoresist is patterned and etching is performed to obtain a common contact with the high concentration n-type impurity region for a base electrode  103  and the high concentration p-type impurity region for a collector electrode  105 . After that, as shown in  FIG. 3E , the emitter metal electrode, the base-collector metal electrode, and a polycrystalline silicon metal electrode  108 . In this case, the polycrystalline silicon metal electrode  108  has an equal potential to the base-collector metal electrode, but the polycrystalline silicon metal electrode  108  can have an equal potential to the emitter. 
       Second Embodiment 
       [0037]      FIG. 4  shows a bipolar transistor according to a second embodiment of the present invention. The emitter region  104  is formed so as to be self-aligned with the device isolation insulating film. When variation in the shape of the polycrystalline silicon is large, the device isolation insulating film may be used to form the bipolar transistor as in the second embodiment of the present invention. 
       Third Embodiment 
       [0038]      FIG. 5  shows a bipolar transistor according to a third embodiment of the present invention. The emitter region  104  is formed to be self-aligned with the polycrystalline silicon  106 , and the high concentration n-type impurity region for a base electrode  103  and the high concentration p-type impurity region for a collector electrode  105  are provided with separate contacts. In this case, the polycrystalline silicon metal electrode has the same potential to the base-collector metal electrode. 
         [0039]    Note that the description has been made on the PNP bipolar transistor in the embodiments. The similar structure can be applied to an NPN bipolar transistor using an n-type substrate.