Patent Publication Number: US-6043553-A

Title: Multi-emitter bipolar transistor of a self-align type

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a semiconductor device including a bipolar transistor, and particularly to a structure of a semiconductor device including a multi-emitter bipolar transistor of a self-align type. 
     Along with remarkable development of mobile communication equipment such as a mobile telephone or a PHS (Personal Handy-phone System) or computer networks, high-performance and inexpensive bipolar transistors are earnestly pursued for realizing high-speed and low-cost communication circuits. 
     An promising approach is application of a self-align type bipolar transistor having emitter and base leading electrodes formed of poly-Si (poly-crystalline silicon) such as described in &#34;Optimization of shallow and deep trench isolation structures for ultra-high-speed bipolar LSIs&#34; by Itoh et al., pp. 104-107, proceedings IEEE 1992 Bipolar Circuits and Technology Meeting. 
     FIG. 11A illustrates a plan layout of a conventional example (here-after called the first conventional example) of a bipolar transistor of this type, whereof a sectional view cut along a line F-F&#39; of FIG. 11A is illustrated in FIG. 11B. 
     In the first conventional example of FIGS. 11A and 11B, an n +  -type buried layer 202 is selectively formed on a p-type Si substrate 201 and an n-type epitaxial layer 203 is formed thereon, to configure a bipolar transistor in a region surrounded by a first element-isolation film 204. 
     An extrinsic base region 213, an intrinsic base region 214, and a collector leading region 206 for leading out the n +  -type buried layer 202 are formed in a region surrounded by a second element-isolation film 205. The extrinsic base region 213 is led out by a base leading electrode 209 made of poly-Si, and an emitter region 215 is led out by an emitter leading electrode 212 also made of poly-Si. The base leading electrode 209 and the emitter leading electrode 212 are isolated from each other by a first and a second insulation film 210 and 211. The collector leading region 206, the emitter leading electrode 212 and the base leading electrode 209 are connected to a collector wiring 219a, an emitter wiring 219b and a base wiring 219c, respectively, through respective one of contact plugs 218a, 218b and 218c which are formed penetrating through an inter-layer insulation film 217. 
     In FIG. 11B, the base diffusion width a, the collector-base isolation length b and the separation length c between two wirings are designed to be respective minimum values which process factors allow. 
     The above structure of the self-align type bipolar transistor is determined in consideration of following factors. 
     1) It is generally effective for performance improvement of a bipolar transistor to minimize an area size of its emitter/base formation region. For this purpose, the base diffusion width a of FIG. 11B should be made as narrow as possible for minimizing the size of the emitter/base formation region 208. 
     2) The collector-base isolation length b of FIG. 11B should be as small as possible for reducing parasitic capacitance of the bipolar transistor, provided that it is longer than an isolation length determined from the collector-base breakdown voltage, and usually designed to be a minimum value allowed by the process factors. 
     3) The wiring width of the emitter and the collector electrode should be as wide as possible, for improving wiring reliability of the self-align type bipolar transistor wherein on-current of several mA to several 10 mA flows. 
     It is from these reasons that the contact plug 218c of the base wiring 219c cannot be formed directly upon the extrinsic base region 213, when the separation between the emitter wiring 219b and the base wiring 219c is set to have the minimum length c, and should be positioned on the second element-isolation film 205 to be connected indirectly to the extrinsic base region 213 by way of the base leading electrode 209 formed along the surface of the second-element isolation film 205. 
     For improving high-frequency performance of the self-align type bipolar transistor, the maximum oscillation frequency fmax should be made high and the maximum oscillation frequency fmax is in inverse proportion to the base resistance. Therefore, a structure having two base electrodes at both sides of the emitter electrode is often applied for reducing the base resistance, instead of the basic structure having one electrode for each of the emitter, the collector and the base as illustrated in FIGS. 11A and 11B. Furthermore, a multi-emitter structure having more than one emitter/base formation regions is sometimes applied for increasing current capacity of the self-align type bipolar transistor. 
     As a second conventional example, a self-align type bipolar transistor having a multi-emitter structure provided with base electrodes ranged at both sides of each emitter is briefly described referring to FIGS. 12A and 12B. FIG. 12A illustrates a plan layout of the multi-emitter bipolar transistor of the second conventional example, whereof a sectional view cut along a line G-G&#39; is illustrated in FIG. 12B. 
     As shown in FIG. 12A, the contact holes for emitter, collector and base electrodes are arranged in an order of collector-base-emitter-base-collector-base-emitter-base-collector form left to right of the line G-G&#39;, and the contact plugs 218a, 218b and 218c of the respective electrodes are aligned straight. 
     Each element of the second conventional example of FIG. 12B is formed in a similar way with the corresponding element of the first conventional example of FIGS. 11A and 11B. However, the collector-base isolation length d of the second element-isolation film 205 is forced to be wider in FIG. 12B than the collector-base isolation length b of FIG. 11B, because of base wirings 219c each provided between a collector wiring 219a and an emitter wiring 219b provided upon the second element-isolation film 205 for reducing the base resistance, which were not provided there in the first conventional example of FIG. 11B. 
     Now, another example of the multi-emitter bipolar transistor is briefly described as a third conventional example referring to FIGS. 13A and 13B. FIG. 13A illustrates a plan layout of the multi-emitter bipolar transistor according to the third conventional example, and FIG. 13B is a sectional view cut along a line H-H&#39; of FIG. 13A. 
     The structure of the third conventional example of FIGS. 13A and 13B, wherein the central collector wiring and corresponding elements of the second conventional example of FIGS. 12A and 12B are omitted, is to be applied in a circuit where the collector resistance is not required to be so low, and a collector, a base, an emitter, a base, an emitter and a collector are arranged in this order from left to right of FIG. 13A. 
     Here also, the contact plugs 218a, 218b and 218c of the respective electrodes are aligned straight. 
     As the number of collector electrodes is reduced from three to two, the whole size of the multi-emitter bipolar transistor can be made smaller according to the third conventional example than the second conventional example. However, when each individual element has the same size, the collector-base isolation length d of FIG. 13B is the same to the collector-base isolation length d of FIG. 12B, remaining wider than the collector-base isolation length b of FIG. 11B. 
     As heretofore described, the multi-emitter structure is applied for improving transistor characteristics of the self-align type bipolar transistor. However, the multi-emitter structure of the self-align type bipolar transistor is conventionally accompanied with a problem that the collector-base isolation length d is forced to be wider as illustrated in FIGS. 12A and 12B or in FIGS. 13A and 13B than the minimum value b of the collector-base isolation length which can be achieved in the basic structure as illustrated in FIGS. 11A and 11B wherein only one electrode is provided for each of the emitter, the collector and the base. 
     This problem results in not only obstruction of high-integration and miniaturization of semiconductor integrated circuits but also degradation of high-frequency performance of the bipolar transistor, due to increase of collector resistance, collector-base capacitance and collector-substrate capacitance of the bipolar transistor. 
     SUMMARY OF THE INVENTION 
     Therefore, a primary object of the present invention is to resolve the above problem and provide a semiconductor device including a self-align type multi-emitter bipolar transistor wherein every collector-base isolation length can be reduced into a minimum value allowed in connection with the collector-base breakdown voltage. 
     In order to achieve the object, in a self-align type bipolar transistor having a multi-emitter structure included in a semiconductor device according to the invention, more than one emitter/base formation regions and at least one collector leading region are arranged in a single array, and extrinsic base regions are connected to at least one base electrode having a contact plug provided outside the single array by way of a base leading electrode. 
     Therefore, collector-base isolation lengths can be set to be a minimum length determined by the collector-base breakdown voltage, enabling to minimize the collector resistance, the collector-base capacitance and the collector-substrate capacitance, as well as to minimize the element size of the bipolar transistor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing, further objects, features, and advantages of this invention will become apparent from a consideration of the following description, the appended claims, and the accompanying drawings wherein the same numerals indicate the same or the corresponding parts. 
     In the drawings: 
     FIG. 1A shows a plan layout of a multi-emitter bipolar transistor according to a first embodiment of the invention; 
     FIG. 1B is a sectional view of the multi-emitter bipolar transistor of FIG. 1A cut along a line A-A&#39;; 
     FIG. 2A is a sectional view for illustrating fabrication processes of the multi-emitter bipolar transistor of FIG. 1A; 
     FIG. 2B is another sectional view for illustrating fabrication processes of the multi-emitter bipolar transistor of FIG. 1A; 
     FIG. 3A is another sectional view for illustrating fabrication processes of the multi-emitter bipolar transistor of FIG. 1A; 
     FIG. 3B is still another sectional view for illustrating fabrication processes of the multi-emitter bipolar transistor of FIG. 1A; 
     FIG. 4A shows a plan layout of a multi-emitter bipolar transistor according to a second embodiment of the invention; 
     FIG. 4B is a sectional view of the multi-emitter bipolar transistor of FIG. 4A cut along a line B-B&#39;; 
     FIG. 5A illustrates a plan layout of a multi-emitter bipolar transistor according to a third embodiment of the invention; 
     FIG. 5B is a sectional view of the multi-emitter bipolar transistor of FIG. 5A cut along a line C-C&#39;; 
     FIG. 6A is a sectional view for illustrating fabrication processes of the multi-emitter bipolar transistor of FIG. 5A; 
     FIG. 6B is another sectional view for illustrating fabrication processes of the multi-emitter bipolar transistor of FIG. 5A; 
     FIG. 7A is another sectional view for illustrating fabrication processes of the multi-emitter bipolar transistor of FIG. 5A; 
     FIG. 7B is still another sectional view for illustrating fabrication processes of the multi-emitter bipolar transistor of FIG. 5A; 
     FIG. 8A shows a plan layout of a multi-emitter bipolar transistor according to a fourth embodiment of the invention; 
     FIG. 8B is a sectional view of the multi-emitter bipolar transistor of FIG. 8A cut along a line D-D&#39;; 
     FIG. 9A is a sectional view for illustrating fabrication processes of the multi-emitter bipolar transistor of FIG. 8A; 
     FIG. 9B is another sectional view for illustrating fabrication processes of the multi-emitter bipolar transistor of FIG. 8A; 
     FIG. 10A is another sectional view for illustrating fabrication processes of the multi-emitter bipolar transistor of FIG. 8A; 
     FIG. 10B is still another sectional view for illustrating fabrication processes of the multi-emitter bipolar transistor of FIG. 8A; 
     FIG. 11A illustrates a plan layout of a first conventional example of a bipolar transistor of a self-align type; 
     FIG. 11B is a sectional view of the bipolar transistor of FIG. 11A cut along a line F-F&#39;; 
     FIG. 12A illustrates a plan layout of a multi-emitter bipolar transistor of a second conventional example; 
     FIG. 12B is a sectional view of the bipolar transistor of FIG. 12A cut along a line G-G&#39;; 
     FIG. 13A illustrates a plan layout of a multi-emitter bipolar transistor of a third conventional example; and 
     FIG. 13B is a sectional view of the bipolar transistor of FIG. 13A cut along a line H-H&#39;; 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now, embodiments of the present invention will be described in connection with the drawings. 
     FIG. 1A shows a plan layout of a multi-emitter bipolar transistor according to a first embodiment of the invention, and FIG. 1B is a sectional view thereof cut along a line A-A&#39; of FIG. 1A. 
     In the first embodiment, contact plugs 118a for collectors and contact plugs 118b for emitters are arranged alternately in an order of collector-emitter-collector-emitter-collector, from left to right on the line A-A&#39; of FIG. 1A, and contact plugs 118c for bases are not arranged on the line A-A&#39;. For each of the emitter contact plugs 118b, one base contact plug 118c is provided so that a line passing through centers of the base contact plug 118c and the emitter contact plug 118b falls at right angles with the line A--A&#39;, that is, a line passing through centers of two collector contact plugs 118a adjoining to the emitter contact plug 118b, both the separation between a collector wiring 119a and the emitter wiring 119b and the separation between the base wiring 119c and the emitter wiring 119b being set to be the minimum length c defined by the process factors as previously described. 
     In the first embodiment, each emitter leading electrode 112 is composed of a 2-layer film comprising an emitter leading poly-Si layer 112a and an emitter leading silicide layer 112b, and a main part of each base leading electrode 109 is also composed of a 2-layer film comprising a base leading poly-Si layer 109a and a base leading silicide layer 109b, as shown in FIG. 1B. Similarly, on each collector leading region 106, a collector leading silicide layer 116 is formed. For these emitter, base and collector silicide layers 112b, 109b and 116, silicide of Ti or Co is applied. 
     Here, it should be noted that the collector-base isolation length e can be minimized in the first embodiment to be the same with the collector-base isolation length b of the first conventional example of FIG. 11B, since no base wiring is provided upon the second element isolation film 105 between any pair of a collector wiring 119a and an emitter wiring 119b arranged along the line A-A&#39;. 
     Now, fabrication processes of the multi-emitter bipolar transistor of the first embodiment will be described referring to FIGS. 2A to 3B. 
     Referring to FIG. 2A, an n+ buried layer 102 is first formed selectively on a p-type Si substrate 101 making use of a mask, whereon an n-type epitaxial layer 103 of 0.4 μm to several μm thickness is grown. Then, wide and shallow trenches are formed so as not to attain to the n +   buried layer 102, for dividing emitter/base formation regions 108 and collector leading region 106 to be formed. Then, narrow and deep trenches of 0.4 μm to 2 μm width are formed so as to penetrate through the n +   buried layer 102 for sectioning a transistor formation region. By entirely filling the shallow and the deep trenches with insulation material such as an oxide film, a first and a second element-isolation film 104 and 105 are formed. Then, a first insulation film 107 of 5 to 30 nm thickness is formed by way of a thermal-oxidation method, for example, and the collector leading regions 106 doped into n +  -type are formed making use of selective ion-implantation technology. 
     Then, as shown in FIG. 2B, after partially removing the first insulation film 107 on the emitter/base formation regions 108 making use a photo-resist mask, for example, a poly-Si films having 10 to 40 nm thickness and doped into p-type are formed overall, through growth and ion-implantation or through deposition making use of a growth vapor added with impurities. Then, after covering the poly-Si film with a second insulation film 110 formed with an oxide or nitride film of 5 to 20 nm, the poly-Si film is masked with photo-resist, for example, and etched back through anisotropic etching in order to form the base leading poly-Si layers 109a each having an emitter opening 108a at its center part. 
     Then, as shown in FIG. 3A, intrinsic and extrinsic base regions 114 and 113 are formed through ion-implantation of B or BF 2 , or introduction of impurities through thermal diffusion from a gas. After forming the intrinsic base regions 114, a third insulation film 111 is formed and etched back by anisotropic etching for configuring side walls along side surfaces of the base leading poly-Si layers 109a. Then, n +   doped poly-Si film of 10 to 40 nm is formed through growth and ion-implantation, or deposition making use of a growth gas including impurities, which is masked with a photo-resist pattern 120 and processed by anisotropic etching for forming emitter leading poly-Si layers 112a. Then, the first insulation film 107 on the collector leading regions 106 is selectively removed by anisotropic etching using a photo-resist mask. 
     Then, as shown in FIG. 3B, Ti or Co of 10 to 50 nm thickness is depositted by sputtering, for example, and made to react with Si in a nitrogen or argon-nitrogen atmosphere into a silicide film, whereof useless parts are removed for forming base leading silicide layers 109b, collector leading silicide layers 116 and emitter leading silicide layers 112b on surfaces of the base leading poly-Si layers 109a, collector leading regions 106 and the emitter leading poly-Si layers 112a, respectively. 
     Then, an inter-layer insulation film 117 having a lamination of an oxide film and another oxide film including B and P is formed and contact plugs 118a to 118c including barrier metal are formed after digging contact holes at necessary positions of the inter-layer insulation film 117. Finally, a metal film of Al or Cu is formed and patterned by anisotropic etching for providing collector wirings 119a, emitter wirings 119b and base wirings 119c. 
     Thus, the multi-emitter bipolar transistor of FIGS. 1A and 1B is fabricated according to the first embodiment. 
     FIG. 4A shows a plan layout of a multi-emitter bipolar transistor according to a second embodiment of the invention, and FIG. 4B is a sectional view thereof cut along a line B-B&#39; of FIG. 4A. 
     A difference of the second embodiment from the first embodiment shown in FIGS. 1A to 3B lies in that the center collector electrode provided in the first embodiment between the two emitter electrodes is eliminated and the two base leading electrodes 109 and their wirings 119c of the first embodiment are united into one base leading electrode 109 and one base wiring 119c in the second embodiment. The structure according to the second embodiment is preferably applied where a little increase of collector resistance can be allowed, for enabling further reduction of the base resistance, the collector-base capacitance and the collector-substrate capacitance. 
     As a modification of the second embodiment, the two outer side collector electrodes of FIGS. 1A to 3B may be eliminated leaving the center collector electrode as it is, in turn, when further increase of the collector resistance is permissible. In this case too, it is preferable to form a base leading electrode from a single conductive film covering the transistor region to have two openings surrounding two emitter/base formation regions in contact with the extrinsic base regions and an opening surrounding the collector leading region with necessary isolation lengths. 
     FIG. 5A illustrates a plan layout of a multi-emitter bipolar transistor according to a third embodiment of the invention, whereof a sectional view cut along a line C-C&#39; is shown in FIG. 5B. 
     In the third embodiment, collector contact plugs 118a and emitter contact plugs 118b are arranged straight in a single array, and two base contact plugs 118c are provided adjoining to both ends of the array, as shown in FIG. 5A. 
     In the plan layout of FIG. 1A of the first embodiment, the base wirings 119c are connected to the base leading electrodes 109 through the base contact plugs 118c provided at one side of the array of the emitter and the collector contact plugs 118a and 118b. Therefore, potential drops may occur at farthest edges of the extrinsic base regions 113 from the base contact plugs 118c, when emitter length is increased in a direction perpendicular to the line A-A&#39;, even though resistivity of the silicide layer 116 is very low. 
     In the third embodiment, the two base contact plugs 118c are provided at both ends of the array of the collector and the emitter contact plugs 118a and 118b, in an order of base-collector-emitter-collector-emitter-collector-base, such as shown in FIG. 5A, from left to right of the line C-C&#39;, for resolving the above problem. 
     In the third embodiment, the collector-base isolation length e can be also minimized to be the same with the collector-base isolation length b of the first conventional example of FIG. 11B. 
     Now, fabrication processes of the multi-emitter bipolar transistor of the third embodiment is described referring to FIGS. 6A to 7B. 
     As shown in FIG. 6A, an n +   buried layer 102 is first formed selectively on a p-type Si substrate 101 making use of a mask, whereon an n-type epitaxial layer 103 of 0.4 μm to several μm thickness is grown. Then, wide and shallow trenches are formed so as not to attain to the n +   buried layer 102, for dividing emitter/base formation regions 108 and collector leading region 106 to be formed. Then, narrow and deep trenches of 0.4 μm to 2 μm width are formed so as to penetrate through the n +   buried layer 102 for sectioning a transistor formation region. By entirely filling the shallow and the deep trenches with insulation material such as an oxide film, a first and a second element-isolation film 104 and 105 are formed. Then, a first insulation film 107 of 5 to 30 nm thickness is formed by way of a thermal-oxidation method, for example, and the collector leading regions 106 doped into n +  -type are formed making use of selective ion-implantation technology. 
     Then, as shown in FIG. 6B, after partially removing the first insulation film 107 on the emitter/base formation regions 108 making use a photo-resist mask, for example, a poly-Si films having 10 to 40 nm thickness and doped into p-type are formed overall, through growth and ion-implantation or through deposition making use of a growth vapor added with impurities. Then, after covering the poly-Si film with a second insulation film 110 formed with an oxide or nitride film of 5 to 20 nm, the poly-Si film is masked with photo-resist, for example, and etched back through anisotropic etching in order to from a base leading poly-Si layer 109a having emitter openings 108a and collector openings 106a at its inner part. 
     Then, as shown in FIG. 7A, intrinsic and extrinsic base regions 114 and 113 are formed through ion-implantation of B or BF 2 , or introduction of impurities through thermal diffusion from a gas. After forming the intrinsic base regions 114, at third insulation film 111 is formed and etched back by anisotropic etching for configuring side walls along inner side surfaces of the base leading poly-Si layer 109a. Then, n +   doped poly-Si film of 10 to 40 nm is formed through growth and ion-implantation, or deposition making use of a growth gas including impurities, which is masked with a photo-resist pattern 120 and processed by anisotropic etching for forming emitter leading poly-Si layers 112a. Then, the first insulation film 107 on the collector leading regions 106 is selectively removed by anisotropic etching using a photo-resist mask. 
     Then, as shown in FIG. 7B, Ti or Co of 10 to 50 nm thickness is depositted by sputtering, for example, and made to react with Si in a nitrogen or argon-nitrogen atmosphere into a silicide film, whereof useless parts are removed for forming a base leading silicide layer 109b, collector leading silicide layers 116 and emitter leading silicide layers 112b on surfaces of the base leading poly-Si layer 109a, collector leading regions 106 and the emitter leading poly-Si layers 112a, respectively. 
     Then, an inter-layer insulation film 117 having a lamination of an oxide film and another oxide film including B and P is formed and contact plugs 118a to 118c including barrier metal are formed after digging contact holes at necessary positions of the inter-layer insulation film 117. Finally, a metal film of Al or Cu is formed and patterned by anisotropic etching for providing collector wirings 119a, emitter wirings 119b and base wirings 119c. 
     Thus, the multi-emitter bipolar transistor of FIGS. 5A and 5B of the third embodiment is fabricated in the same way with the first embodiment. 
     FIG. 8A shows a plan layout of a multi-emitter bipolar transistor according to a fourth embodiment of the invention, and FIG. 8B is a sectional view thereof cut along a line D-D&#39; of FIG. 8A. 
     A difference of the fourth embodiment from the third embodiment shown in FIGS. 5A to 7C lies in that the center collector electrode provided in the first embodiment between the two emitter electrodes is eliminated. The structure according to the fourth embodiment is preferably applied where a little increase of collector resistance can be allowed, for enabling further reduction of the base resistance, the collector-base capacitance and the collector-substrate capacitance. 
     As a modification of the fourth embodiment, the two outer side collector electrodes of FIGS. 5A to 7B may be eliminated leaving the center collector electrode as it is, when further increase of the collector resistance is permissible, for further reducing the base resistance, the collector-base capacitance and the collector-substrate capacitance. 
     Furthermore, the number of the base contact plugs 118c may be reduced to one by eliminating either of the two base wirings 119c, when resistivity of the base leading electrode can be made sufficiently low. 
     Now, a multi-emitter bipolar transistor according to a fifth embodiment of the invention will be described referring to FIGS. 9A to 10B. 
     The multi-emitter bipolar transistor of the fifth embodiment of FIG. 9A has a similar structure to the multi-emitter bipolar transistor of FIG. 1A according to the first embodiment. A difference of the fifth embodiment to the first embodiment is that the collector region composed of the n +  -type buried layer 102 and the n-type epitaxial layer 103 of the first embodiment is replaced with a single collector region 103a formed by ion-implantation as illustrated in FIG. 9B, and accordingly, there are formed collector leading regions 106a which are shallower than the collector leading regions 106 formed to contact with the n +  -type buried layer 102 in the first embodiment. 
     Recently, a technology to form collector regions directly on a p-type Si substrate by ion-implanting n-type impurities has become to be used for reducing the process cost. In the fifth embodiment, this technology is applied. According to this technology, there is formed no n +  -type buried layer, and therefore, collector resistance should inevitably become very high upto the order of 100 to 500 Ω, when a base contact plug is formed between the emitter and the collector contact plugs such as the second conventional example of FIGS. 12A and 12B. 
     This increase of collector resistance can be suppressed according to the fifth embodiment wherein the collector-base isolation length e can be set into the minimum isolation length b of FIG. 11B. 
     Now, fabrication processes of the multi-emitter bipolar transistor of the fifth embodiment is described referring to FIGS. 10A to 10B. 
     Referring to FIG. 10A, the collector region 103a is formed in a p-type Si substrate 101 by implanting P-ions of a dose amount of 5×10 13  to 5×10 14  with implantation energy of 500 KeV to 2 MeV. Then, wide and shallow trenches are formed so as not to attain to the bottom of the collector region 103a, for dividing emitter/base formation regions 108 and collector leading region 106a to be formed. Then, narrow and deep trenches of 0.4 μm to 2 μm width are formed so as to penetrate through the collector region 103a for sectioning a transistor formation region. By entirely filling the shallow and the deep trenches with insulation material such as an oxide film, a first and a second element-isolation film 104 and 105 are formed. Then, a first insulation film 107 of 5 to 30 nm thickness is formed by way of a thermal-oxidation method, for example. 
     Then, as shown in FIG. 10B, after partially removing the first insulation film 107 on the emitter/base formation regions 108 making use a photo-resist, mask, for example, a poly-Si films having 10 to 40 nm thickness and doped into p-type are formed overall, through growth and ion-implantation or through deposition making use of a growth vapor added with impurities. Then, after covering the poly-Si film with a second insulation film 110 formed with an oxide or nitride film of 5 to 20 nm, the poly-Si film is masked with photo-resist, for example, and etched back through anisotropic etching in order to from base leading poly-Si layers 109a shaped in strips each having an emitter opening 108a at its center part. 
     Then, intrinsic and extrinsic base regions 114 and 113 are formed a through ion-implantation of B or BF 2 , or introduction of impurities through thermal diffusion from a gas. After forming the intrinsic base regions 114, a third insulation film 111 is formed and etched back by anisotropic etching for configuring side walls of the base leading poly-Si layer 109a. Then, n +   doped poly-Si film of 10 to 40 nm is formed through growth and ion-implantation, or deposition making use of a growth gas including impurities, which is masked with a photo-resist pattern 120 and processed by anisotropic etching for forming emitter leading poly-Si layers 112a. Then, the first insulation film 107 on the collector leading regions 106 is selectively removed by anisotropic etching using a photo-resist mask. 
     Then, Ti or Co of 10 to 50 nm thickness is depositted by sputtering, for example, and made to react with Si in a nitrogen or argon-nitrogen atmosphere into a silicide film, whereof useless parts are removed for forming a base leading silicide layer 109b, collector leading silicide layers 116 and emitter leading silicide layers 112b on surfaces of the base leading poly-Si layer 109a, collector leading regions 106 and the emitter leading poly-Si layers 112a, respectively. 
     Then, an inter-layer insulation film 117 having a lamination of an oxide film and another oxide film including B and P is formed and contact plugs 118a to 118c including barrier metal are formed after digging contact holes at necessary positions of the inter-layer insulation film 117. Finally, a metal film of Al or Cu is formed and patterned by anisotropic etching for providing collector wirings 119a, emitter wirings 119b and base wirings 119c. 
     Thus, the multi-emitter bipolar transistor of FIGS. 9A and 9B of the fifth embodiment is fabricated. 
     As heretofore described, in a self-align type bipolar transistor having a multi-emitter structure included in a semiconductor device according to the invention, more than one emitter/base formation regions and at least one collector leading region are arranged in a single array, and extrinsic base regions are connected to at least one base electrode having a contact plug provided outside of the single array by way of a base leading electrode. Therefore, collector-base isolation lengths call be set to be a minimum length determined by a collector-base breakdown voltage, enabling to minimize the collector resistance, the collector-base capacitance and the collector-substrate capacitance, as well as to minimize the element size of the bipolar transistor. 
     According to concrete examples of the invention, the collector resistance, the collector-base capacitance and the collector-substrate capacitance can be reduced by 5 to 10%, about 10% and 35 to 45%, respectively, compared to a conventional example such as illustrated in FIGS. 12A and 12B.