Abstract:
A semiconductor device is provided in which a vertical NPN transistor and a vertical PNP transistor electrically isolated from each other are formed on a p-type semiconductor substrate. An n-type buried separating region of the vertical PNP transistor is formed by high-energy ion implantation prior to formation of the n +  type buried collector region of the vertical NPN transistor, and a p +  type buried collector region of the vertical PNP transistor is formed subsequently to formation of an n-type epitaxial layer and a device separating region is formed in the n-type epitaxial layer whereby the thickness of the n-type epitaxial layer is optimized to a required minimum value. A method for producing a semiconductor device is also provided in which a first vertical bipolar transistor of a first conductivity type and a second vertical bipolar transistor of a second conductivity type, electrically isolated from each other, are formed on a semiconductor substrate having a pre-set conductivity type. A buried collector region of the second vertical collector region is formed before formation of a buried collector region of the first vertical transistor.

Description:
This application is a divisional of application Ser. No. 08/529,213 filed Sep. 15, 1995, now U.S. Pat. No. 5,885,880. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a semiconductor device comprised of vertical NPN transistors and vertical PNP transistors formed on one and the same substrate for forming a complementary bipolar transistor, and a method for manufacturing the same. More particularly, it relates to a method for forming a high performance complementary bipolar transistor simply by supplementing a minimum number of steps to the conventional method for manufacturing bipolar transistors. 
     2. Description of the Related Art 
     A complementary bipolar transistor, which is a combination of a NPN transistor and a PNP transistor, has been employed up to now in a high-output amplifier stage of an audio equipment as a component of e.g., a push-pull circuit. In a amplifier/detector circuit for intermediate frequency for pictures for UHF television tuner or an LSI for high frequency represented by a signal processing circuit for high-speed communication or optical communication, the tendency is towards realization of a system-on-chip. In keeping up therewith, a there is a demand for a method for manufacturing a complementary bipolar transistor circuit of higher speed and higher integration degree with a smaller number of steps. 
     FIG. 1 shows a typical construction of a conventional representative complementary bipolar transistor. With the present bipolar transistor, there are formed a vertical NPN transistor (V-NPNTr) and a vertical PNP transistor (V-PNPTr) on one and the same substrate. With V-NPNTr and V-PNPTr, the emitter/base/collector junction is formed along the depth of the substrate, that is in the vertical direction. 
     In a V-NPNTr portion towards left in FIG. 1, a n +  type buried collector region  3  (n + -BL)is formed in a boundary region between a p-type substrate (p-Sub)  1  and a n-type epitaxial layer  5  (n-EPI) formed thereon. The n-type epitaxial layer  5  has its upper layer portion divided into plural island-like device-forming regions by device separating regions  7  formed by the LOCOS method (selective oxidization separation). A p-type base region  10  and a n +  type collector contact region  9  connecting to the buried collector region  3  are formed on an upper surface portion of the device forming region. 
     The upper surfaces of the device-forming regions are contacted by three different sorts of contact electrodes formed by polysilicon layers via an interlayer insulating layer  13 . That is, the portion of the upper surface facing the base region  10  is contacted by an emitter contact electrode  14 E n  and a base contact electrode  14 B n , where the suffix n refers to an NPN transistor. By impurity diffusion from these electrodes, n +  type emitter region  15 E n  and a p +  type base contact region  15 B n  are formed within the base region  10 . The portion of the upper surface facing the collector region  9  is contacted by a collector contact electrode  14 C n , and a n type collector contact region  15 C n  is formed by impurity diffusion from this electrode  14 C n.    
     To these contact electrodes  14 E n ,  14 B n  and  14 C n , there are connected, via openings formed in the SiO 2  interlayer insulating film  16 , an emitter electrode  17 E n , a base electrode  17 B n  and a collector electrode  17 C n , each of which is formed by an Al-based multi-layer film. 
     In a V-PNPTr portion towards right in FIG. 1, an n type buried separating region  2  (N-pocket) for electrically separating the transistor from the substrate and a p +  type buried collector region  4 C are formed in this order in a boundary region between the p-type substrate (p-Sub)  1  and the n-type epitaxial layer  5  (n-EPI) formed thereon. On the buried collector region  4 C is formed a p-type well  6  by ion implantation into the n-type epitaxial layer. This p-type well  6  has its upper surface layer divided into plural island-like device forming regions by the device separating regions  7  formed by LOCOS (selective oxidative separation). On the surface layer portion of the device forming region, there are formed an n-type base region  11  and a p +  type collector contact region  8 C connecting to the p +  type buried collector region  4 C. 
     The upper surface of the device forming region is contacted by three sorts of polysilicon layer contact electrodes via the SiO 2  interlayer insulating layer  13 . That is, the upper surface portion facing the base region  11  is contacted by an emitter contact electrode  14 E p  and a base contact electrode  14 B p , where the subscript p refers to the PNP transistor. By impurity diffusion or ion implantation from these electrodes, the p +  type emitter region  15 E p  and the n +  type base contact region  15 B p  are formed in the base region  11 . The upper surface portion facing the collector contact region  8 C is contacted by the collector contact electrode  14 C p , and a p +  type collector contact electrode  15 C p  is formed by impurity diffusion from this electrode  14 C p.    
     To these contact electrodes  14 E p ,  14 B p  and  14 C p  are connected the emitter electrode  17 E p , base electrode  17 B p  and the collector electrode  17 C p , each formed by Al-based multi-layer films, via openings formed in the SiO 2  interlayer insulating film  16 , respectively. 
     The V-NPNTr and the V-PNPTr are separated from each other, as are other devices, not shown, by a p +  type channel stop layer formed on the lower side of the device separating region  7 . The channel stop layer is made up of a lower layer side channel stop layer  4 ISO and an upper layer side channel stop layer  8 ISO stacked back-to-back as an upper tier and a lower tier. 
     The production process for the above-described complementary bipolar transistor is prolonged and complicated as compared to the production process for the usual bipolar transistor because of the necessity of forming the n-type buried separation layer  2  for electrically separating the p +  buried collector region  4 C of the V-PNPTr from the p-type substrate. Since this buried separating region  2  needs to be of the maximum thickness possible and formed at as deep a site in the substrate as possible, it is usually formed in the p-type substrate  1  at the outset by gasphase diffusion of n-type impurities. However, during the drivein of the n +  type buried contact region  3 , which represents the severest prolonged high-temperature heat-treatment process of the production process for the complementary bipolar transistor, the buried separating region  2  is diffused upwardly into the inside of the n-type epitaxial layer  5 . Consequently, the n-type epitaxial layer  5  needs to be of a certain thickness. 
     On the other hand, the p +  buried collector region  4 C of the V-PNPTr is also responsible for the increased thickness of the n-type epitaxial layer  5 . The p +  type buried collector region  4 C is usually formed in advance of the n-type epitaxial layer  5 . During the epitaxial growth carried out at a temperature of 1000° to 1100° C., the p +  type buried collector region  4 C is diffused upwardly by heat diffusion and auto-doping. In addition, the LOCOS step of forming the device separating region in the n-type epitaxial layer is the second severest prolonged high-temperature heat-treatment process of the production process of the complementary bipolar transistor. That is, the n-type epitaxial layer  5  needs to be increased in thickness in order to take into account the fact that the buried collector region  4 C undergoes upward diffusion in the course of the LOCOS process. 
     Thus the n-type epitaxial layer needs to be increased in thickness for improving characteristics of the V-PNPTr. However, this leads to increased size of the collector layer of the V-NPNTr and hence to base-widening effects of Kirk-effects, resulting in lowered cut-off frequency and lowered operating speed. 
     In addition, with the above-described production process, two ion implantation steps are employed for forming the channel stop layers. This is due to the fact that, since the n-type epitaxial layer  105  needs to be of an increased thickness for the above reason, the device separating region  7  and the single channel stop layer are not effective to separate the two bipolar transistors from each other. The lower layer side channel stop layer  4 ISO is formed by the ion implantation process common to that for forming the buried collector layer  4 C of the V-PNPTr, while the upper layer side channel stop layer  8 ISO is formed by the ion implantation process common to that for forming the collector contact region  8 C of the V-PNPTr. However, with the production process for the usual bipolar transistor in which a thin n-type epitaxial layer  5  suffices, there is no necessity of forming the collector contact region  8  of the V-PNPTr because only the collector contact electrode  15 C p  formed by impurity diffusion from the collector contact electrode suffices for providing connection between the buried collector region  4 C and the collector contact electrode  14 C p . In semiconductor industries, cost reduction is crucial and an increase in the number of steps needs to be avoided at any rate. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a semiconductor device comprised of a high performance complementary bipolar transistor in which an n-type epitaxial layer is prohibited from being increased in thickness and a method for producing the semiconductor device with a minimum increase in the number of process steps as compared to the conventional production process for bipolar transistors. 
     According to the present invention, there is provided a semiconductor device in which a vertical NPN transistor and a vertical PNP transistor electrically isolated from each other are formed on a p-type semiconductor substrate, wherein an n-type buried separating region of the vertical PNP transistor is formed by high-energy ion implantation prior to formation of the n +  type buried collector region of the vertical NPN transistor, and wherein a p +  type buried collector region of the vertical PNP transistor is formed subsequently to formation of an n-type epitaxial layer thereon and a device separating region formed in the n-type epitaxial layer whereby the thickness of the n-type epitaxial layer is optimized to a required minimum value. 
     According to the present invention, there is also provided a method for producing a semiconductor device in which a first vertical bipolar transistor of a first conductivity type and a second vertical bipolar transistor of a second conductivity type, electrically isolated from each other, are formed on a semiconductor substrate having a pre-set conductivity type, wherein a buried collector region of the second vertical collector region is formed before formation of a buried collector region of the first vertical transistor. This represents first means for prohibiting the n-type epitaxial layer from being increased in thickness. 
     The impurity may be introduced into the buried separating region of the second vertical transistor by high energy ion implantation. Such ion implantation is defined as being carried out at an ion accelerating energy of not less than 300 keV and being capable of achieving a projection range of not less than 0.4 μm, depending upon ion species. 
     Alternatively, the buried collector region of the second bipolar transistor may also be formed after forming the device separating region. This represents second means for prohibiting the n-type epitaxial layer from being increased in thickness. 
     If the buried collector region of the second vertical bipolar transistor is formed simultaneously during the impurity introducing step for forming a channel stop region of the first vertical bipolar transistor, it becomes possible to suppress the number of process steps to a minimum. 
     It is also possible to control the impurity profile during the common impurity introducing step by plural ion implantation steps under varying conditions of the ion accelerating energy. 
     If the first and second means are practiced simultaneously, instead of separately, the n-type epitaxial layer may be prohibited more effectively from being increased in thickness. 
     In addition, the graft base region of the vertical bipolar transistor and the emitter region and the collector contact region of the second vertical bipolar transistor may also be formed simultaneously by a common impurity diffusion step. 
     Since the bipolar transistor is usually fabricated on a p-type substrate, it is most preferred with the present invention that a V-NPNTr and a V-PNPTr be formed as the first vertical bipolar transistor and as the second vertical bipolar transistor, respectively. In such case, the n-type buried separating region is formed prior to formation of the n +  type buried collector region of the V-NPNTr. Also the p +  type channel stop region of V-NPNTr and the p +  type buried collector region of the V-PNPTr are formed simultaneously by a common impurity introducing step before or after formation of the n-type buried separating region of V-PNPTr. On the other hand, the p +  graft base region of the V-NPNTr and the p +  type collector contact region of the V-PNPTr are formed simultaneously by the common impurity introducing step. 
     According to the present invention, the step of forming buried regions of V-PNPTr, which are obstructive to reduction in thickness of the n-type epitaxial layer, is carried out at a stage as late as possible from process steps whose heat treatment conditions are generally thought to be severest in the production process of bipolar transistors, for the purpose of suppressing upward diffusion of the buried V-PNPTr region. Taking an example of a p-type buried semiconductor substrate, the n-type buried separating region of the V-PNPTr is formed on the substrate by high energy implantation technique at back of the n +  type buried collector region of the V-NPNTr, or in recessed parts of the substrate, while the p +  type buried collector region of the V-PNPTr is formed at back of the p +  type buried collector region of the V-PNPTr. However, even if the ion implantation is carried out after the n +  type buried collector region of V-NPNTr, the n-type buried separating region, which in particular needs to be increased in thickness, is preferably formed by introducing ntype impurity by high energy ion implantation with which it is possible to set the projection range in a recessed portion of the p-type semiconductor substrate. Since the buried regions are prohibited in this manner from being diffused to above the n-type epitaxial layer of the buried regions, it becomes unnecessary to set the thickness of the n-type epitaxial layer to a predetermined excess thickness. The result is that, with the semiconductor device produced by this method, the collector region of the V-NPNTr of the smallest possible thickness suffices to suppress the Kirk effect to expedite the operation. In addition, since there is no necessity of providing the channel stop region in an upper layer and a lower layer due to the reduced thickness of the n-type epitaxial layer, it becomes possible to eliminate one ion implantation process. 
     If the p +  type buried collector region of the V-NPNTr is formed simultaneously during the impurity introducing step for forming the channel stop region of the V-NPNTr, and the p +  graft base region of the V-NPNTr and the p +  collector contact region of V-PNPTr, are formed simultaneously by the common impurity introducing step, it becomes possible to suppress an increase in the number of process steps due to the constitution of the complementary structure to a minimum as compared to the production process for usual bipolar transistors. 
     Furthermore, if the p +  graft base region of the V-PNPTr and the p +  emitter and collector contact regions of the V-PNPTr are formed simultaneously by a common impurity introducing step, it becomes possible to suppress increase in the number of process steps. 
     According to the present invention, a complementary bipolar transistor having enclosed therein a V-NPNTr having an integration degree and a high-speed performance comparable to previous values and a V-PNPTr having high speed performance superior to a previous value may be fabricated by simply adding the minimum number of process steps to the conventional production process for bipolar transistors. Consequently, LSIs for high-frequency applications, typified by a picture amplifier/detector circuit for intermediate frequency of a UHF television tuner or a signal processing circuit for high-speed communication or optical communication, may be fabricated without significantly raising the production cost from the current level. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic cross-sectional view showing a typical construction of a complementary bipolar transistor produced by the conventional method. 
     FIG. 2 shows the profile of impurity in the V-PNPTr in the conventional complementary bipolar transistor. 
     FIGS. 3A to  3 N illustrate a first embodiment of the present invention, wherein FIG. 3A is a schematic cross-sectional view showing the state in which, in the production process for a complementary bipolar transistor according to the present invention, an n-type buried separation region of the V-PNPTr is being formed by ion implantation after forming an n +  type buried collector region of the V-NPNTr on the p-type Si substrate. 
     FIG. 3B is a schematic cross-sectional view showing the state in which an n-type epitaxial layer is grown on the Si substrate of FIG.  3 A and subsequently a device separating region is formed by the LOCOS method. 
     FIG. 3C is a schematic cross-sectional view showing the state in which a collector contact region of the V-NPNTr is formed on the n-type epitaxial layer of FIG.  3 B and the substrate surface is planarized. 
     FIG. 3D is a schematic cross-sectional view showing the state in which a channel stop layer of the V-NPNTr and the buried collector region of the V-PNPTr have been formed by ion implantation into the substrate. 
     FIG. 3E is a schematic cross-sectional view showing the state in which an SiO 2  interlayer insulating layer is being patterned, the first polysilicon layer is being deposited on the entire surface and p-type impurities are selectively introduced into the first polysilicon layer on the substrate of FIG.  3 D. 
     FIG. 3F is a schematic cross-sectional view showing the state in which n-type impurities are being selectively introduced into the remaining regions of the first polysilicon layer of FIG.  3 E. 
     FIG. 3G is a schematic cross-sectional view showing the state in which each contact electrode is being formed by patterning the first polysilicon layer, an SiO 2  interlayer insulating film is being deposited on the entire surface of the SiO 2  interlayer insulating film and a resist mask is being formed for forming an emitter window. 
     FIG. 3H is a schematic cross-sectional view showing the state in which the emitter window has been opened on the substrate and the base region and the pedestal region of the V-NPNTr have been formed by ion implantation. 
     FIG. 3I is a schematic cross-sectional view showing the state in which the base region of V-PNPTr and the pedestal region directly therebelow have been formed by ion implantation into the substrate of FIG.  3 H. 
     FIG. 3J is a schematic cross-sectional view showing the state in which a graft base region and a collector contact region have been formed by impurity diffusion from the polysilicon film of the respective contact electrodes of FIG.  3 I and the sidewall has been formed by etch-back. 
     FIG. 3K is a schematic cross-sectional view showing the state in which the second polysilicon layer is being deposited on the entire surface of the second polysilicon layer and n-type impurities are selectively implanted on the substrate of FIG.  3 J. 
     FIG. 3L is a schematic cross-sectional view showing the state in which, after selective ion implantation of n-type impurities into the second polysilicon layer of FIG. 3K, an emitter electrode is formed by patterning and an emitter region is formed by diffusion of impurities. 
     FIG. 3M is a schematic cross-sectional view showing the state in which the SiO 2  interlayer insulating film of FIG. 3L has been patterned and an upper metallization has been formed. 
     FIG. 3N shows the profile of impurity in the V-PNPTr in the complementary bipolar transistor IC. 
     FIGS. 4A to  4 F illustrate a second embodiment of the present invention, wherein FIG. 4A is a schematic cross-sectional view showing the state in the production process for a complementary bipolar transistor according to the present invention in which, in the production process of the complementary bipolar transistor according to the present invention, the n +  type buried collector region for the V-NPNTr and the n-type buried separating region for the V-PNPTr have been formed on the p-type Si substrate, the n-type epitaxial layer has been grown, the device separating region has been formed and the substrate has been planarized in this order. 
     FIG. 4B is a schematic cross-sectional view showing the state in which, after forming the channel stop region and the buried collector region in the substrate of FIG. 4A, the SiO 2  interlayer insulating film has been patterned, on the substrate and the first polysilicon layer has been deposited on the entire substrate surface, after which p-type impurities are being selectively introduced into the first polysilicon layer. 
     FIG. 4C is a schematic cross-sectional view showing the state in which n-type impurities are selectively introduced into remaining regions of the first polysilicon layer of FIG.  4 B. 
     FIG. 4D is a schematic cross-sectional view showing the state in which each contact electrode is formed by patterning the first polysilicon layer and coated by an SiO 2  interlayer insulating film and a resist mask for forming an emitter window has been formed. 
     FIG. 4E is a schematic cross-sectional view showing the state in which, in the substrate of FIG. 4D, a base region has been formed by ion implantation, an SiO 2  film for forming the sidewall has been coated on the entire substrate surface, a graft base region and a collector contact region have been formed by diffusion impurities from the respective contact electrodes and a sidewall has been formed by etch-back of the SiO 2  film. 
     FIG. 4F is a schematic cross-sectional view showing the state in which, on the substrate of FIG. 4E, a second polysilicon layer has been deposited on the entire substrate surface, an emitter region has been formed by diffusion of impurities from the second polysilicon layer, a contact hole has been formed by patterning the SiO 2  interlayer insulating film and an upper metallization has been formed. 
     FIGS. 5A to  5 H illustrate a third embodiment of the present invention, wherein FIG. 5A is a schematic cross-sectional view showing the state in the production process of the complementary bipolar transistor according to the present invention in which a base region is being formed by selective ion implantation into a V-PNPTr forming region of a substrate after formation of a channel stop region and the buried collector region of the V-PNPTr. 
     FIG. 5B is a schematic cross-sectional view showing the state in which, on the substrate of FIG. 5A, an SiO 2  interlayer insulating film is being patterned, a first polysilicon is being deposited on the entire substrate surface and p-type impurities are being introduced into the first polysilicon layer. 
     FIG. 5C is a schematic cross-sectional view showing the state in which, on the substrate of FIG. 5C, an emitter window for the V-NPNTr has been formed and an intrinsic base region and a pedestal region for the V-NPNTr have been formed by ion implantation. 
     FIG. 5D is a schematic cross-sectional view showing the state in which, after deposition on the substrate of FIG. 5D of a sidewall forming SiO 2  film, a graft base region and a collector contact region have been formed by diffusion of impurities from respective contact electrodes, a sidewall has been formed by etch-back of the SiO 2  film and a resist mask has been formed for forming an emitter/base window of the V-PNPTr. 
     FIG. 5E is a schematic cross-sectional view showing the state in which the emitter/base window is being formed by etching the SiO 2  interlayer insulating film of FIG. 5E, a second polysilicon layer is being deposited on the entire surface and p-type impurities are being selectively introduced into the V-PNPTr emitter forming region. 
     FIG. 5G is a schematic cross-sectional view showing the state in which n-type impurities are selectively introduced into remaining regions of the second polysilicon layer of FIG.  5 F. 
     FIG. 5H is a schematic cross-sectional view showing the state in which the second polysilicon layer of FIG. 5G has been patterned, an SiO 2  interlayer insulating film has been deposited on the entire substrate surface, and an emitter region of the V-NPNTr and an emitter region and a base region of the V-PNPTr have been formed by annealing. 
     FIG. 5I is a schematic cross-sectional view showing the state in which a contact hole has been formed by patterning the SiO interlayer insulating film of FIG.  5 H and an upper layer metallization has been formed. 
     FIGS. 6A to  6 H illustrate a fourth embodiment of the present invention, in which FIG. 6A is a schematic cross-sectional view showing the state in the production process of a complementary bipolar transistor according to the present invention in which, after formation of a channel stop region and a buried collector region on a substrate has been formed, a base region is being formed by selective ion implantation in the V-PNPTr forming region of the substrate. 
     FIG. 6B is a schematic cross-sectional view showing the state in which a graft base region is being formed by selective ion implantation into a V-PNPTr forming region of the substrate. 
     FIG. 6C is a schematic cross-sectional view showing the state in which, on the substrate of FIG. 6B, an SiO 2  interlayer insulating film is being patterned, a first polysilicon layer is being formed and n-type impurities are being introduced into the first polysilicon layer. 
     FIG. 6D is a schematic cross-sectional view showing the state in which each contact electrode has been formed by patterning the first polysilicon layer of FIG. 6C, the SiO 2  interlayer insulating film has been deposited on the entire substrate surface and a resist mask for forming an emitter window has been formed. 
     FIG. 6E is a schematic cross-sectional view showing the state in which an emitter window for the V-NPNTr has been formed on the substrate of FIG.  6 D and an intrinsic base region and a pedestal region for V-NPNTr have been formed by ion implantation. 
     FIG. 6F is a schematic cross-sectional view showing the state in which, after deposition on the entire substrate surface of FIG. 6E of an SiO 2  for sidewall formation, a graft base region, an emitter region and a collector contact region are being formed by diffusion of impurities from each contact electrode, a sidewall is being formed by etch-back of the SiO 2  film, a second polysilicon layer is being formed on the entire substrate surface and n-type impurities are being introduced into the entire surface. 
     FIG. 6G is a schematic cross-sectional view showing the state in which the second polysilicon layer has been patterned, an SiO 2  interlayer insulating film has been deposited and an emitter region of the V-NPNTr has been formed by annealing. 
     FIG. 6H is a schematic cross-sectional view showing the state in which a contact hole has been formed by patterning the SiO 2  interlayer insulating film and an upper layer metallization has been formed. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, preferred embodiments of the present invention will be explained in detail. 
     In the first embodiment, a production process for a two-layered silicon vertical bipolar transistor, in which a base region and an emitter region are formed in self-alignment, is utilized for producing a complementary bipolar transistor in which a V-NPNTr and a V-PNPTr are formed in adjacency to each other. 
     The production process is explained by referring to FIGS. 3A to  3 M. 
     On the surface of a p-type Si substrate  3  having the direction of crystal axes of &lt;111&gt; is formed an SiO 2  film, not shown, to a film thickness of approximately 300 nm by thermal oxidation. An opening is formed in a V-NPNTr forming region of the SiO 2  film, and antimony (Sb) is diffused via the opening by gas-phase diffusion of Sb 2 O 3  at approximately 1200° C. for 0.5 to 1 hour. A sheet resistance ρs of the buried collector region  32  was e.g., 20 to 50 Ω/□ and the depth of junction x j  was 1 to 2 μm. 
     A thin SiO 2  film  33 , with a thickness of approximately 10 nm, was formed by thermal oxidation on the entire substrate surface for prohibiting channelling, and a resist mask  34  is formed thereon. An opening  35  is formed in the V-PNPTr forming region of the resist mask  34 . 
     Phosphorus (P) was then introduced, with a projection range of not less than 0.4 μm, by high-energy ion implantation via the opening  35 , for forming an n-type buried separation region  36 . As the conditions for ion implantation, the ion accelerating energy and the dosage were set so as to be not less than 300 keV and equal to 1×10 13-15  cm −2 , respectively. 
     With the conventional production process for usual complementary bipolar transistor, this n-type buried separating region  36  is formed temporally ahead of the n +  type buried collector region  32 . This sequence is reversed in the present invention. It is feared that crystal defects may be produced by high energy ion implantation at the time of formation of the buried separating region  36 . However, since the crystal defects are generally incurred in the vicinity of the projection range in a concentrated manner, it is not obstructive to subsequent crystal growth. Conversely, the high energy ion implantation has a merit of reducing total dosage to suppress crystal defects as compared to the low-energy ion implantation onto the substrate surface. FIG. 3A shows the process up to this step. 
     Annealing at a temperature not lower than 800° C. was then carried out in order to relieve crystal defects caused by ion implantation. The n-type buried separating region  36  is expanded at this time due to upward impurity diffusion. However, since the impurity is introduced into deep sites of the substrate, the concentration of impurities in the vicinity of the substrate surface is suppressed to a lower value. This annealing may be omitted if hydrogen annealing is carried out for reducing native oxide film on the surface of the Si substrate  31  as a pre-process to growth of the n-type epitaxial layer  37  now to be explained. This hydrogen annealing is usually carried out in high concentration hydrogen for tens of minutes at 800 to 1100° C. 
     The n-type epitaxial layer  37  (n-Epi) was then grown after removal of the SiO 2  film  33 . This n-type epitaxial layer  37  had a resistivity of 1 to 5 Ω cm and a thickness of 0.8 to 2.5 μm. With the conventional production process for complementary bipolar transistors, since the p +  type buried collector region  43 C in FIG. 3D of the V-PNPTr or the channel stop region  43 ISO of V-NPNTr of FIG. 3D are formed at the time point of growing the n-type epitaxial layer  37 , it was necessary to form the n-type epitaxial layer  37  to a larger thickness in order to take account of upward diffusion therefrom and boron auto-doping. There has also been raised a problem that the concentration of the n-type epitaxial layer  37  cannot be controlled to a design value due to the auto-doping. According to the present invention, the thickness of the n-type epitaxial layer  37  can be approximately one-half the usual value while no problem is raised in connection with auto-doping. 
     The substrate was then oxidized by the LOCOS method in order to produce a device separating region  39 . With the LOCOS method, a pad oxide film was formed as conventionally to a thickness of 20 to 50 nm on the entire surface of the substrate by the thermal oxidation method, and subsequently a Si 3 N 4  film, not shown, was formed to a thickness of 50 to 100 nm by the reduced-pressure CVD method. These film thicknesses were optimized in consideration of controllability of stress or defect due to selective oxidation or bird&#39;s beak length. The Si 3 N 4  film and the pad oxide film were sequentially etched, using a resist mask, in order to form an oxide mask. The n-type epitaxial layer  37  exposed in the opening of the selectively oxidized mask was further etched for substantially planarizing the substrate surface following selective oxidization for producing a recess. The depth of the recess was set to approximately one-half the design film thickness of the device separating region  39 . 
     Under this condition, pyrogenic oxidation was carried out at 1000 to 1050° C. for 2 to 6 hours for forming the device separating region  39  having a thickness of 0.8 m to 1.5 μm. With the conventional production process for the complementary bipolar transistor, since ion implantation for forming the p +  buried collector of V-PNPTr is already carried out at the time point of oxidation by LOCOS, the impurity is diffused in a wide region under severe heat-treatment conditions. In this consideration, the n-type epitaxial layer  37  has to be formed to a larger thickness. Such precautions are unnecessary in the present invention. 
     The Si 3 N 4  was then removed using a hot phosphoric acid solution. FIG. 3B shows the process up to this step. 
     Then, for forming the n +  type collector contact region of V-NPNTr, phosphorus was ion implanted via a resist mask, not shown. As the conditions for ion implantation, the ion accelerating energy and the dosage were set to 40 to 100 keV and 1×10 15-16  cm 2 . 
     An SiO 2  film for planarization, not shown, was formed by CVD to a thickness of approximately 10 to 600 nm and annealed for about 30 minutes for impurity activation. By this annealing, an n type collector contact region  40 C connecting to the buried contact region  32  was formed. 
     The resist film, not shown, was coated for substantially planarizing the substrate surface, and the bird&#39;s beak and the pad oxide film were removed from the device separating region  39  by carrying out etch-back under the resist film to SiO 2  selection ratio of 1:1. FIG. 3C shows the process up to this step. 
     Then, a thin SiO 2  film, having a thickness of 10 to 30 nm, not shown, was formed on the substrate surface by thermal oxidation at 900° C. A resist mask  41  as shown in FIG. 3D was further formed and boron (BF 2   + ) was ion implanted via an opening  42  formed therein. As the conditions for ion implantation, the ion accelerating energy and the dosage were set to 200 to 500 kev and 1×10 13-14 /cm 2 , respectively. By this ion implantation, a p +  type channel stop region  43 ISO of V-NPNTr was formed below the device separating region  39 , at the same time as a p +  type buried collector region  43 C was formed in a region overlapped with the upper end of the buried separating region  36  of V-PNPTr. 
     If it is desired to optimize the impurity profile of the buried collector region  43 C of V-PNPTr for achieving high-speed operation, low-energy ion implantation with the ion accelerating energy on the order of 100 keV may be carried out before or after ion implantation for compensating the impurity concentration in the base/collector boundary region. The impurity at the time of low-energy ion implantation is captured by the device separating region  39  in the vicinity of the channel stop region  43 ISO  4  without affecting separating characteristics. FIG. 3D shows the process up to this step. 
     On the entire substrate surface, an SiO 2  interlayer insulating film  44  was deposited by CVD to a thickness of 50 to 200 nm and dry-etched via a resist mask, not shown, using e.g., a CHF 3 /O 2  mixed gas for forming an opening. This opening was formed in the base/emitter forming site of V-NPNTr and in the base/emitter forming site and collector forming site of V-PNPTr. 
     Then, a first polysilicon layer  45  was formed by CVD on the entire substrate surface to a thickness of 100 to 300 nm. 
     Then, in order for the p-type impurity to be contained in the portions of the first polysilicon layer  45  which later become the base contact electrode of V-NPNTr ( 45 B n  of FIG. 3G) and the collector contact electrode of V-PNPTr ( 45 C p  of FIG.  3 G), a resist mask  46  having an opening  47  for exposing a site slightly larger in area than these sites was formed and boron (BF 2   + ) was ion implanted via this opening  47 . As the conditions for ion implantation, the ion accelerating energy and the dosage were set to e.g., 30 to 70 keV and 1×10 14-16 /cm 2 , respectively. FIG. 3E shows the process up to this step. 
     Then, in order for n-type impurities to be contained in the portion of the first polysilicon layer  45  which later becomes the base contact electrode of V-PNPTr ( 45 B p  in FIG.  3 G), a resist mask  48  having an opening  49  for exposing a larger area inclusive of the V-PNPTr was formed and arsenic (As + ) was ion-implanted via this opening  49 . As the conditions for ion implantation, the ion accelerating energy and the dosage were set to e.g., 30 to 70 keV and 1×10 14-16 /cm 2 , respectively. 
     The first polysilicon layer  45  was then etched via a resist mask, not shown, using e.g., a C 2 Cl 3 F 3 /SF 6  mixed gas. In this manner, the base contact electrode  45 B n  of V-NPNTr and the base contact electrode  45 B p  and the collector contact electrode  45 C p  of V-PNPTr were formed, as shown in FIG.  3 G. The suffices n and p refer to V-NPNTr and V-PNPTr, respectively. 
     An interlayer insulating film  50  of SiO 2  was further formed on the entire substrate surface to a thickness of 300 to 500 nm for forming a resist mask  51  having openings  52  for forming emitter windows of V-NPNTr and V-PNPTr, respectively. 
     The SiO 2  interlayer insulating film  50  and the base contact electrode  45 B n  were sequentially etched via the resist mask  51  for forming emitter windows of V-NPNTr and V-PNPTr, as shown in FIG.  3 H. The resist mask was then removed and, after forming a thin SiO 2  film, not shown, by thermal oxidation, a resist mask  53  covering only the V-PNPTr forming region was newly formed. By ion-implanting boron (BF 2   + ) via an opening  54  in the resist mask  53 , an intrinsic base region  55 IB of V-NPNTr was formed. As the conditions for ion implantation, the ion accelerating energy and the dosage were set to e.g., 20 to 100 kev and 1×10 13-14 /cm 2 , respectively. 
     If it is desired to improve high frequency characteristics of V-NPNTr, it is preferred to introduce phosphorus by ion implantation for forming an n +  type pedestal region  56  adjacent to the upper end of the buried contact region  32 . As the conditions for ion implantation, the ion accelerating energy and the dosage were set to e.g., 300 to 500 keV and the order of 1×10 12 /cm 2 , respectively. 
     Then, as shown in FIG. 3I, a resist mask  57  covering the V-NPNTr forming region was formed and arsenic was ion-implanted via an opening  58  formed therein for forming an n-type intrinsic base region  59 IB of V-PNPTr. As the conditions for ion implantation, the ion accelerating energy and the dosage were set to e.g., 20 to 100 keV and 1×10 13-14 /cm 2 , respectively. 
     If it is desired to further improve high-frequency characteristics of V-PNPTr, or if the upper diffused end of the buried separation region  36  reaches the substrate surface beyond the p +  type buried collector region  43 C, it is preferred to introduce boron (B + ) by ion implantation in succession in order to form a p +  type pedestal region  60  reaching the upper end of the buried collector region  43 C. As the conditions for ion implantation, the ion accelerating energy and the dosage may be set to e.g., 300 to 500 keV and 1×10 12 /cm 2 , respectively. FIG. 3I shows the process up to this step. 
     An SiO 2  film for sidewall formation was then deposited by CVD on the entire substrate surface to a thickness of 300 to 600 nm and annealing was carried out at 800 to 950° C. for 10 to 60 minutes. By such annealing, the intrinsic base region  551 B was activated in the V-NPNTr forming region, while a p +  graft base region  62 GB n  was formed by impurity diffusion from the base contact electrode  45 B n . In the V-PNPTr forming region, the intrinsic base region  59 IB was activated, while an n +  type graft base region  62 GB p  and a p +  collector contact region  62 C were simultaneously formed by impurity diffusion from the base contact electrode  45 B p  and the collector contact electrode  45 C p , respectively. 
     By such annealing, the p +  type buried collector region  43 C of V-PNPTr was also activated and enlarged. However, the annealing conditions are more moderate than those used for previous oxidation by LOCOS, so that the buried collector region  43 C was not diffused upwardly excessively and hence there was no necessity of forming the n-type epitaxial layer  37  to an increased thickness. This represents a difference from the conventional production process for the usual complementary bipolar transistor in which the p +  type buried collector layer  43 C is formed prior to oxidation by LOCOS, and hence a merit of the present invention. 
     The SiO 2  film for sidewall formation was then etched back and a sidewall  61  was formed in the emitter window forming portions of V-NPNTr and V-PNPTr. FIG. 3J shows the process up to this step. 
     A second polysilicon layer  63  was then deposited by CVD on the entire substrate surface to a thickness of 50 to 200 nm. Then, boron (BF 2   + ) was ion-implanted via a resist mask, not shown, in a broader area inclusive of the portion of the second polysilicon layer  63  which later becomes an emitter contact electrode  63 E p  in FIG. 3L of V-PNPTr. As the conditions for ion implantation, the ion accelerating energy and the dosage were set to e.g., 30 to 100 keV and 10×10 15-16 /cm 2 , respectively. 
     Then, arsenic was ion-implanted via an opening  65  in a resist mask  64 , in a broader area inclusive of the portion of the second polysilicon layer  63  which later becomes an emitter contact electrode  63 E n  in FIG. 3L of V-NPNTr. As the conditions for ion implantation, the ion accelerating energy and the dosage were set to e.g., 30 to 100 keV and 1×10 15-16 /cm 2 , respectively. 
     The entire substrate surface was coated with an SiO 2  film, not shown, and annealing was carried out at 800 to 950° C. for tens of minutes or at 950 to 1100° C. for several seconds to tens of seconds. By such annealing, an n +  emitter region  66 E n  and a p +  type emitter region  66 E p  were formed by n-type impurity diffusion from the emitter contact region  63 E n  in the V-NPNTr forming region and by p-type impurity diffusion from the emitter contact region  63 E p  in the V-PNPTr forming region, respectively. In addition, by such annealing, the collector contact region  62 C of V-PNPTr could be enlarged and connected to the p +  type buried collector region  43 C. 
     The SiO 2  film was removed by wet etching and a resist mask  67  selectively covering the emitter window portions of both bipolar transistors was formed. The second polysilicon layer  50  was dry-etched via the resist mask  67  for forming the emitter contact electrode  63 E n  of V-NPNTr and the emitter contact electrode  63 E p  of V-PNPTr. 
     For contacting the electrodes other than the emitter contact electrodes  63 E n  and  63 E p , that is respective contact electrodes  45 B n ,  45 B p  and  45 G p , and the collector contact electrode  40 C of V-NPNTr, with the upper layer metallization, contact holes were formed in the SiO 2  interlayer insulating film  50  and optionally in the SiO 2  interlayer insulating film  44  by dry etching using a resist mask, not shown. This resist mask was then removed and a layered metallization film of barrier metal and Al-1% Si film were deposited by sputtering on the entire substrate surface. The metallization film was then patterned to form a base electrode  68 B n , an emitter electrode  68 E n  and a collector electrode  68 C n  of V-NPNTr and a base electrode  68 B p , an emitter electrode  68 E p  and a collector electrode  68 C p  of V-PNPTr. 
     A complementary bipolar transistor IC was then fabricated by carrying out usual process steps including multi-layer metallization and passivation. 
     FIG. 3N shows an impurity profile of the V-PNPTr portion of the IC produced as described above. For comparison sake, FIG. 2 shows an impurity profile of the V-PNPTr portion of the conventional complementary bipolar transistor shown in FIG.  1 . Heretofore, the total depth of the transistor, that is the depth as measured from the substrate surface (the surface of the n-type epitaxial layer) up to the lower end of the n-type buried separation region (n-pocket) indicated by an arrow is as large as 8.68 μm, whereas it is decreased with the present invention to approximately 2.50 μm which is less than 30% of the conventional value. The most outstanding contribution factor in this reduction is the reduction in the collector thickness. This is due to the fact that, since the p +  type buried collector region  43 C in the present invention is formed subsequently to the formation of the n-type epitaxial layer  37  and the device separating region  39  without undergoing severe heat treatment caused by epitaxial growth or oxidation by LOCOS thus suppressing upward diffusion towards the n-type epitaxial layer  37 . The next contributing factor is thickness of the substrate separation. This is due to the fact that the n-type buried separation region  36  in the present invention is formed subsequently to formation of the n +  type buried collector region  32  of V-NPNTr without undergoing severe drive-in process thus again suppressing upward diffusion towards the n-type epitaxial layer  37 . 
     By suppressing the upward diffusion, the thickness of the n-type epitaxial layer  37  is reduced to one half the conventional value for significantly improving high-frequency characteristics of the complementary bipolar transistor. 
     The second embodiment of the present invention is now explained. 
     In the present embodiment, the first polysilicon layer is left in the region of the substrate directly contacted by the upper layer metallization in the first embodiment, that is the collector contact region of V-NPNTr, for forming a collector contact region, while the phosphorus ion implantation step for forming the n +  type collector contact region is omitted. The production process for the complementary bipolar transistor IC of the present embodiment is now explained by referring to FIGS. 4A to  4 F. The parts in common with those of the previous embodiment are explained only briefly, while the substrate or layers which are the same as those of the previous embodiment are depicted by the same numerals. 
     With the present process, formation of the n +  buried collector region  32 , n-type buried separating region  36 , n-type epitaxial layer  37  and the device separating region  39  by the LOCOS method and substrate surface planarization were carried out in the same way as in the previous embodiment, as shown in FIG.  4 A. However, in the above-described process steps, the ion implantation step for forming the collector contact region of V-NPNTr, shown at  40 C in FIG. 3C, is omitted. 
     Then, as shown in FIG. 4B, the channel stop layer  43 ISO of V-NPNTr and the p +  buried collector region  43 C of V-PNPTr were formed by ion implantation of boron, and the SiO 2  interlayer insulating film  44  was deposited on the entire substrate surface and patterned. The first polysilicon layer  45  was deposited on the entire substrate surface and p-type impurities were introduced into the first polysilicon layer  45  via the opening  47  in the resist mask  46 , as in the first embodiment. During patterning of the SiO 2  interlayer insulating film, a window was also formed in the collector contact region of V-NPNTr for contacting the first polysilicon layer  45  with the n-type epitaxial layer  37 . 
     The, as shown in FIG. 4C, another resist mask  71  was formed and arsenic was ion-implanted via an opening  72  in a resist mask  71 . The n-type impurity was ion-implanted not only into the base-emitter forming region of V-PNPTr but also into the collector contact region of V-NPNTr, in a manner distinct from the previous embodiment. 
     The first polysilicon layer was then patterned for forming the base contact electrode  45 B n  and the collector contact electrode  45 C n  of V-NPNTr and the base contact electrode  45 B p  and the collector contact electrode  45 C p  of V-PNPTr as shown in FIG.  4 D. The collector contact electrode  45 C n  of V-NPNTr is a contact electrode not formed in the previous embodiment. 
     Then, as shown in FIG. 4E, an emitter window was opened by dry etching and the intrinsic base regions  55 IB,  59 IB and the pedestal regions  59 ,  60  were formed by ion implantation. The sidewall-forming SiO 2  film was applied to the entire substrate surface and graft base regions  62 GB n ,  62 GB p  and collector contact regions  73 C,  62 C were formed by annealing. Finally, the sidewall was formed by etch-back of the SiO 2  film. 
     Then, as shown in FIG. 4C, the second polysilicon layer was deposited on the entire substrate surface, and impurity was introduced into the second polysilicon layer. The emitter contact electrodes  63 E n  and  63 E p  were formed by patterning the second polysilicon layer and the contact hole was then formed by patterning the SiO 2  interlayer insulating film  50 . Finally, the respective electrodes were formed by an Al-l% Si based multi-layer film. 
     The usual multi-layer metallization and passivation were then carried out to complete an IC. 
     In the present embodiment, the n-type epitaxial layer  37  could be reduced in thickness by suppressing upward diffusion from the n-type buried separating region  36  and the p +  type buried collector region  43 C, as in the previous embodiment. The merit of the present second embodiment resides in the fact that, since the ion implantation step for forming the n +  type collector contact region of V-NPNTr can be omitted, it becomes possible to eliminate one photomask and the step of forming the resist mask for ion implantation. 
     A third embodiment of the present invention is now explained. 
     In the present embodiment, the so-called double polysilicon base/emitter self-alignment structure of fabricating the base region and the emitter region in self-alignment by impurity diffusion from the two polysilicon layers is adopted only for the V-NPNTr, while the emitter region and the base region of V-PNPTr are formed in a transverse array by impurity diffusion from the second polysilicon layer by the so-called single polysilicon structure. The production process for the complementary bipolar transistor IC of the present embodiment is explained by referring to FIGS. 5A to  5 I. The portions the present process has in common with the previous process are explained only briefly. The same numerals are used to depict the substrate and the films which are the same as those of the first embodiment. 
     In the present process, the process up to formation of the p +  channel stop layer  43 ISO and the buried collector region  43 C is carried out in the same way as the first embodiment and a resist mask  81  having an opening  82  in register with the base/emitter forming region of V-PNPTr was formed as shown in FIG.  5 A. Arsenic was then ion-implanted via the opening  82  for forming an n-type base region  83 B. As the ion implantation conditions, the ion accelerating energy and the dosage were set to 20 to 100 keV and 1×10 13-14 /cm 2 , respectively. 
     Then, as shown in FIG. 5B, the interlayer insulating film  44  was coated on the entire substrate surface and patterned and the first polysilicon layer  45  was coated on the entire substrate surface as in the first embodiment described above. Subsequently, boron (BF 2 ) was ion-implanted on the entire surface of the first polysilicon layer  45 . 
     Then, as shown in FIG. 5C, the SiO 2  interlayer insulating film  50  was deposited on the entire substrate surface and a resist mask  84  having an opening  85  in register with the base/emitter forming region of V-NPNTr was formed. 
     Then, as shown in FIG. 5D, a window was formed in the base/emitter forming region of V-NPNTr and boron was ion-implanted via the opening for forming the p-type intrinsic base region of V-NPNTr. In succession to this ion implantation, phosphorus ion implantation was carried out in a manner not shown for forming an n +  pedestal region  56 . 
     Then, as shown in FIG. 5E, a sidewall-forming SiO 2  was coated on the entire substrate surface and annealing was then carried out for forming a p +  type graft base region  62 GB n  of V-NPNTr and a p +  type collector contact region  62 C of V-PNPTr simultaneously. The SiO 2  was then etched back to form a sidewall  61 . 
     A resist mask  86  having an opening  87  was then formed in the SiO 2  interlayer insulating films  50 ,  44  for forming contact holes facing the emitter forming region and the base contact electrode forming region of V-PNPTr. 
     Then, as shown in FIG. 5F, the SiO 2  interlayer insulating films  50 ,  44  were dry-etched via the opening  87  for forming contact holes. 
     A second polysilicon layer  88  was then deposited on the entire substrate surface. Then, for introducing the p-type impurity into the region of the second polysilicon layer  88  which later becomes the emitter contact electrode of V-PNPTr, indicated by numeral  88 E p  of FIG. 5H, a resist mask  89  having an opening  90  was formed on the second polysilicon layer  88  for carrying out boron ion implantation. 
     Then, as shown in FIG. 5G, for introducing n-type impurities into the region of the second polysilicon layer  88  which later becomes the emitter contact region of V-NPNTr indicated by numeral  88 E p  of FIG. 5H, a resist mask  89  having an opening  90  was formed on the second polysilicon layer  88  for boron ion implantation. 
     Then, as shown in FIG. 5G, for introducing n-type impurity into a region of the second polysilicon layer  88  which later becomes the emitter contact electrode  88 E n  of FIG. 5H, and the base contact electrode of V-PNPTr indicated by  88 E p  of FIG. 5H, arsenic was ion-implanted into the second polysilicon layer  88 . 
     The, as shown in FIG. 5H, the second polysilicon layer  88  was patterned for forming an emitter contact electrode  88 E n  of V-NPNTr and an emitter contact electrode  88 E p  and a base contact electrode  88 E p  of V-PNPTr. The entire substrate surface was then coated with an SiO 2  interlayer insulating film  93  and annealing was then carried out for simultaneously forming an n +  type emitter region  66 E n  of V-PNPTR and a p emitter region  66 E p  and an n +  emitter electrode  66 E p  of V-NPNTr. 
     Then, as shown in FIG. 5I, contact holes were formed in the SiO 2  interlayer insulating films  93 ,  50 , at the same time as the respective electrodes were formed by Al-based layered films. 
     In the present embodiment, the n-type epitaxial layer  37  could similarly be reduced in thickness by suppressing the n-type buried separating region  36  and the p +  buried collector region  43 C. The merit of the present embodiment resides in that the self-alignment structure is not adopted in the base/emitter region of V-PNPTr for reducing the number of photomasks and the number of process steps. 
     Although the present invention has been described with reference to three embodiments, the present invention is not limited to these embodiments and may be suitably modified in connection with the design rule, process conditions and details of the IC structures. 
     A fourth embodiment of the present invention is explained. 
     In the present embodiment., the so-called double polysilicon base/emitter self-alignment structure of fabricating the base region and the emitter region in self-alignment by impurity diffusion from the two polysilicon layers is adopted only for the V-NPNTr, while the emitter region and the collector contact region of V-PNPTr are formed by impurity diffusion from the second polysilicon layer by so-called single polysilicon structure. The production process for the complementary bipolar transistor IC of the present embodiment is explained by referring to FIGS. 6A to  6 H. The portions the present process has in common with the previous process are explained only briefly. The same numerals are used to depict the substrate and the films which are the same as those of the first embodiment. 
     In the present process, the process up to formation of the p +  channel stop layer  43 ISO and the buried collector region  43 C was carried out in the same way as in the first embodiment and a resist mask  81  having an opening  82  in register with the base/emitter forming region of V-PNPTr was formed as shown in FIG.  6 A. Phosphorus was then ion-implanted via an opening  82  for forming an n-type base region  83 B. As the ion implantation conditions, the ion accelerating energy and the dosage were set to 100 to 200 keV and 1×10 13-14 /cm 2 , respectively. 
     Then, as shown in FIG. 6B, a resist mask  90  having an opening  91  in register with the base contact region of V-PNPTr was formed and arsenic was ion-implanted via the opening  91  for forming the n +  graft base region  66 GB. As the ion implantation conditions, the ion accelerating energy and the dosage were set to 20 to 100 keV and 1×10 15-16 /cm 2 , respectively. 
     Then, as shown in FIG. 6C, the SiO 2  interlayer insulating film  44  was deposited on the entire substrate surface and patterned and the first polysilicon layer  45  was deposited on the entire substrate surface, as in the first embodiment. Boron (BF 2   + ) was then ion-implanted on the entire surface of the first polysilicon layer  45 . 
     The first polysilicon layer  45  was then patterned for forming a base contact region  45 B n  of V-NPNTr and a collector contact electrode  45 C p  and an emitter contact electrode  45 E p  of V-PNPTr, as shown in FIG.  6 D. An SiO 2  interlayer insulating film  50  was then deposited on the entire substrate surface and a resist mask  84  having an opening  85  in register with the base-emitter forming region of V-NPNTr was formed. 
     Then, as shown in FIG. 6E, a window was formed in the base-emitter forming region of V-NPNTr, and boron ion implantation was carried out for forming a p-type intrinsic base region  55 IB of V-NPNTr. Phosphorus ions were implanted in succession for forming an n +  type pedestal region  56 . 
     Then, as shown in FIG. 6F, a-sidewall-forming SiO 2  film was deposited on the entire substrate and annealing was then carried out for simultaneously forming a p +  graft base region  62 GB n  of V-NPNTr and a p +  type collector contact region  62 C of V-PNPTr. The SiO 2  was also etched back for forming a sidewall  61 . 
     A second polysilicon layer  88  was then deposited on the entire substrate surface. Then, arsenic was ion-implanted into the entire surface of the second polysilicon layer  88  for forming the emitter region of V-NPNTr. 
     Then, as shown in FIG. 6G, the second polysilicon layer  88  was patterned for forming an emitter contact electrode  88 E n  of V-NPNTr. The entire substrate surface was then covered with an SiO 2  interlayer insulating film  93  and annealing was then carried out for forming an n +  emitter region  66 E n  of V-NPNTr. 
     Then, as shown in FIG. 6H, the SiO 2  interlayer insulating films  93 ,  50  were dry-etched for forming contact holes and respective electrodes were formed by Al-based layered films as in the first embodiment described above. 
     In the present embodiment, the n-type epitaxial layer  37  could similarly be reduced in thickness by suppressing upward diffusion from the n-type buried separating region  36  and the p +  buried collector region  43 C. The merit of the present embodiment resides in that the emitter region of the V-PNPTr and the base contact region of the V-NPNTr are formed simultaneously for reducing the number of photomasks and the number of process steps. 
     Although the present invention has been described with reference to four embodiments, the present invention is not limited to these embodiments and, as an example, the p +  type graft base region of the V-NPNTr and the emitter region of the V-PNPTr may be formed simultaneously by ion implantation. In addition, the present invention may be suitably modified in connection with the design rule, process conditions and details of the IC structures.