Abstract:
A super self-aligned heterojunction bipolar semiconductor device and its manufacturing method are disclosed. The present invention provides a super self-aligned heterojunction bipolar transistor that may maintain the operational stability and the uniformity of a device, facilitate the manufacturing process, and reduce manufacturing time by employing a highly concentrated thick polysilicon film; and its manufacturing method. Also, the present invention provides a super self-aligned heterojunction bipolar transistor that may reduce noise by making the base resistance reduced by a highly concentrated thick polysilicon film, and may minimize the parasitic capacitance between a collector and a base and between a base and an emitter, and the parasitic resistance of a base, so as to realize high-speed operation of a device; and its manufacturing method.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims priority to Korean patent Application No. 2001/77723, filed Dec. 10, 2001.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a super self-aligned heterojunction bipolar transistor (hereinafter “HBT”) including a Si/SiGe heterojunction base layer and its manufacturing method.  
           [0004]    2. Description of the Related Art  
           [0005]    In the communication technology field, semiconductor devices that can operate at high frequency are needed to achieve high-speed communications. To meet these needs, compound semiconductors such as GaAs, InP and SiGe have been developed and employed in high-speed communication devices. Among these compound semiconductors, devices using SiGe may be preferred to GaAs and InP for the capacity of SiGe for very large scale integration and high-speed performance.  
           [0006]    SiGe devices have a hetero structure of Si, whose energy gap is 1.12 eV, and Ge, whose energy gap is 0.66 eV. Such a combination of different energy gaps may provide fast transition speed of electrons and a high efficiency of operation.  
           [0007]    Further, by using SiGe for a base of a transistor, the injection efficiency of carrier into emitter may be improved such that high current gain is achieved. Since the doping level of a base is sufficiently improved and the width of the base may be narrowed, a device with better performance at high frequencies may be achieved. Moreover, cut-off frequency can be increased by reducing emitter-to-base diffusion time. In addition, by gradually increasing the concentration of Ge within a base, a device can be fabricated to have a much higher cut-off frequency.  
           [0008]    Because the SiGe device has several advantages with respect to increasing the concentration of Ge within a base, several techniques to evaporate a high density SiGe layer have been developed. In particular, as is well known, since the lattice constant of Ge is larger than that of Si by 4%, when SiGe is grown on a semiconductor substrate, a lattice mismatch occurs between the substrate and SiGe, and consequently a compressive strain occurs. If a SiGe layer becomes thicker than a certain thickness, which is may be referred to as a “critical thickness,” the misfit energy increases such that the energy state reaches the point where dislocation of the alloy film can easily occur. This dislocation may adversely affect the performance of a device, and may cause leakage current and low breakdown voltage, particularly in a bipolar transistor.  
           [0009]    As the concentration of Ge increases in a SiGe device, the critical thickness decreases due to a greater mismatch. For example, if the concentration of Ge is 50%, the critical thickness may be about 10 nm, which may be too thin a layer for a layer of a heterojunction bipolar transistor. By comparison, if the concentration of Ge is 10%, the critical thickness may be about 100 nm.  
           [0010]    If the thickness of a base is about 100 nm, the concentration of Ge may be up to 15-20%. However, if the concentration of Ge is further increased, a misfit strain may occur at the base of SiGe device, and the performance of an HBT may fall off.  
           [0011]    Therefore, an HBT is required that has a high Ge concentration, but in which substantially no misfit dislocation occurs.  
           [0012]    Several methods have been filed or patented based on the heterojunction bipolar transistor (SiGe HBT) techniques described above. These may include methods by IBM in the U.S., NEC and HITACHI in Japan, Temic in Germany, and ETRI in Korea. With regard to the structural characteristics of a SiGe HBT, a method used by NEC may be representative. In the NEC method, a SiGe base layer is formed using a selective crystal growth process. By contrast, a prior art method of ASB Inc. uses a conventional crystal growth process.  
           [0013]    The method of NEC in Japan is described below and represented in FIG. 1.  
           [0014]    [0014]FIG. 1 shows a heterojunction bipolar transistor that selectively grows a base layer containing SiGe at a device active region, and thereby self-aligns collector-base and emitter-base, respectively. The manufacturing process is as follows:  
           [0015]    An implanted n+ type collector  2  is formed by ion-implanting n+ type dopant into a p− type semiconductor substrate  1 . Collector layer  3  is evaporated on the front surface of substrate  1 , on which the implanted collector  2  is to be formed. n+ type dopant is ion-implanted into a portion of collector layer  3  on which a collector semiconductor electrode will later be formed, so that collector sinker  4  is formed. Collector sinker  4  may connect the implanted collector  2  to the collector semiconductor electrode.  
           [0016]    Subsequently, in order to electrically separate the transistor from neighboring transistors, collector layer  3  and substrate  1  are etched to form a trench. Then, device isolating trench  5  is formed by filling an insulator such as boron phosphorus silica glass (BPSG) into the etched trench. The BPSG insulator is made flat by chemical-mechanical polishing (CMP) so that the surface of isolating trench  5  becomes the same level as that of collector layer  3 . On substrate  1 , whereon the collector layer  3  and the isolating trench  5  are formed, a silicon oxide film is evaporated to form collector insulating film  6 . A p+ type polycrystalline silicon is evaporated to form base semiconductor electrode  7 . A silicon nitride film is evaporated to form emitter insulating film  8 . Emitter insulating film  8  and base semiconductor electrode  7  are together etched so that collector insulating film  6  is exposed.  
           [0017]    Thereafter, by means of evaporation of an insulating material and anisotropic etching, the exposed portion of collector insulating film  6 , masked by first sidewall insulating film  9  that is on the sidewall of emitter insulating film  8  and base semiconductor electrode  7 , is removed by a wet-etching process, and a portion of collector layer  3  thereunder is exposed. After the portion of collector layer  3  is exposed, the wet-etching continues for some time so that undercut  6   a  is formed to reach a predetermined region under p+ type polycrystalline base semiconductor electrode  7 . n type intrinsic collector region  10  is formed by further ion-implanting n type dopant into a portion of collector layer  3  in the active device region (which is exposed through first insulation film  9 ) so that the cut-off frequency of the device increases in a high-current state. (See FIG. 1 a .)  
           [0018]    An extrinsic collector region of collector layer  3  is exposed by undercutting n type intrinsic collector region  10  and collector insulating film  6 . Only on the extrinsic collector region, an intrinsic SiGe layer, a p+ type SiGe layer, and an intrinsic Si layer (that later forms emitter  13 ) are sequentially piled up to selectively grow single crystalline base layer  11 . Under base semiconductor electrode  7 , which is exposed due to the undercut collector insulating film  6 , base connector  12  is grown of the same polycrystalline layer as base layer  11 .  
           [0019]    After base layer  11  is formed to a predetermined thickness, in order to ensure connection between base layer  11  and base connector  12 , a silicon film is filled in between. The growth rate of a single crystalline silicon layer is controlled to be minimized, while the growth rate of a polycrystalline silicon layer is controlled to be maximized, so as to minimize excessive growth on the intrinsic silicon layer of base layer  11  (which will later form emitter  13 ).  
           [0020]    Subsequently, an insulating material such as silicon nitride is evaporated and etched anisotropically so that a second sidewall insulating film  14  that extends from the first insulating film  9  to the inner region of the opening and contacts with a part of base layer  11  (specifically, emitter  13 ) is formed. Thereafter, a part of collector insulating film  6  covering collector sinker  4  is etched to expose collector sinker  4 .  
           [0021]    On part of base layer  11  (specifically, emitter  13 ), an emitter semiconductor electrode  15  is formed comprising n type polycrystalline silicon. On the region around the opening where the implanted collector  2  is connected, collector semiconductor electrode  16  is formed. Collector semiconductor electrode  16  is made out of the same n type polycrystalline silicon as emitter semiconductor electrode  15 . Thereafter, dopant within emitter semiconductor electrode  15  is heat-treated and diffused so that an intrinsic Si layer of top of base layer  11  forms an n type emitter  13 .  
           [0022]    Using the above process, a super self-aligned transistor is formed. In this transistor, the collector-base region is proximate to the undercut and the selective base layer growth. The emitter-base region is proximate to first sidewall insulating film  9  and second sidewall insulating film  14 , respectively self-aligned without using any extra mask. (See FIG. 1. b .)  
           [0023]    In the case of the above-described NEC device, an undercut  6   a  is made at the collector insulating film beneath base semiconductor electrode  7  by wet-etching. The procedural stability and uniformity of this process may be extremely difficult to control. The collector-base parasitic junction capacitance may be greatly influenced by the length of the undercut. Therefore, the stability and the uniformity of performance of the device may suffer.  
           [0024]    Moreover, because the base layer is grown by means of a selective crystal growth process only on the surface of the silicon collector layer, the doping concentration, the amount of Ge, and the thickness of the layer may vary greatly due to the loading effect, influenced by the concentration and the size of the collector layer exposed on the wafer. The pressure during the growth process may be lowered to reduce the influences of the loading effect. However, a lower pressure may slow the growth rate to an extent that throughput decreases.  
           [0025]    Further, because base semiconductor electrode  7  (employing polycrystalline silicon) has a large resistance itself and because of parasitic resistance, there may be a limit to improvement in the operating speed (f max ) of the device.  
           [0026]    The technique of ASB Inc. is described below and represented in FIG. 2. FIG. 2 shows a heterojunction bipolar transistor employing a base ohmic electrode of titanium silicide on a selective crystal growth film and employing SiGe as a base.  
           [0027]    Implanted collector  22  is formed by ion-implanting and diffusing n+ type dopant such as arsenic (As) or phosphorus (P) on a p− type semiconductor substrate  21 . Silicon is grown on the substrate whereon the implanted collector has been formed to form a collector layer.  
           [0028]    In the collector layer, collector insulating film (field oxide film)  23  is formed, by means of thermal oxidation process (LOCOS) except at the regions that will later be active collector region  25  and collector sinker  24 . Using a photo mask that is open only at the region corresponding to the collector sinker  24 , n+ type dopant, such as As or P, is doped and diffused by a heat treatment.  
           [0029]    Base layer  26  is formed on the entire front side of substrate  21  whereon the active collector region  25 , collector sinker  24 , and collector insulating film  23  are formed. For a heterojunction bipolar transistor, base layer  26  is grown comprising a SiGe layer without dopant and a p+ type SiGe layer. When base layer  26  is grown out of SiGe, it is desirable that a Si seed layer is formed first and the base layer  26  next, so that the thickness of base layer  26  and the distribution and the doping concentration of Ge is uniform. Thus, base layer  26  has a multilayer structure of an intrinsic silicon layer (which is a seed layer), a base layer (comprising intrinsic SiGe and p+ type SiGe), and an intrinsic silicon layer (which will later be an emitter), which are grown upward in serial order. Base layer  26  is patterned employing a photomask that defines a base electrode region.  
           [0030]    After base layer  26  is formed, a masking film that covers an active base region of base layer  26  and collector sinker  24  is formed. The masking film comprises at least one of silicon oxide and silicon nitride. While the masking film is in place the portion of base layer  26  outside the active base region is processed to form a first base semiconductor electrode  28   a.    
           [0031]    Second base semiconductor electrode  28   b  is selectively grown only on the exposed first base semiconductor electrode  28   a . Second base semiconductor electrode  28   b  is doped with boron by an in-situ process. Thereafter, Ti and TiN are sequentially sputtered, heat treated and wet-etched to selectively form base ohmic electrode  29  only on the second base semiconductor electrode  28   b . Base ohmic electrode  29  may comprise titanium silicide (TiSi 2 ). Insulator  27  may divide intrinsic base region from first base semiconductor electrode  28   a.    
           [0032]    If ohmic electrode  29  were formed directly on a thin base layer, agglomeration of the silicide might penetrate the thin base layer and contact active collector region  25  such that a Schottky junction would be formed between the base and the collector.  
           [0033]    However, in the case of the ASB Inc. device, because the ohmic electrode  29  is not formed on the active base region (which is covered with the masking film), but is instead formed on the second base semiconductor electrode  28   b , the thickness of the base layer  26  can be kept thin so that a high-speed operation can be realized.  
           [0034]    Emitter insulating film  30  is formed by evaporating silicon oxide or silicon nitride on the entire surface of the substrate whereon base ohmic electrode  29  is formed. Then, using a photomask that defines an emitter region, emitter insulating film  30  and masking film covering the base beneath emitter insulating film  30  are etched so that an opening is made at the emitter region. Polycrystalline n+ type silicon is formed and patterned using a photo mask defining emitter semiconductor electrode  31 . Thereafter, heat treatment is performed, during which n+ type dopant inside emitter semiconductor electrode  31  is diffused into the intrinsic layer on top of base layer  26  so as to produce emitter  32 .  
           [0035]    Protection film  33  is evaporated on the entire surface of the resulting substrate. Protection film  33  is an insulating material such as silicon oxide or silicon nitride. Protection film  33 , emitter insulating film  30  and masking film may be etched as required to form a base contact window, an emitter contact window and a collector contact window.  
           [0036]    After washing the surface using a standard washing process, a barrier metal comprising titanium (Ti) and titanium nitride (TiN) is formed, and aluminum (Al) or Al-1%Si metal is evaporated. A heat treatment and a patterning are performed to form base terminal  34 , emitter terminal  35 , and collector terminal  36 .  
           [0037]    The above-described method used for the ASB device differs from the selective crystal growth method used for the NEC device in that when the SiGe base layer is formed, the base layer is formed on the entire substrate, rather than a selective region. For this reason, the thickness of the base layer and the distribution and doping concentration of Ge can be uniformly maintained, and base layer  26  is formed regardless of irregularities in the silicon area that is exposed.  
           [0038]    However, insulating material  27  and emitter  32  are not self-aligned structures. Because of the misalignment, parasitic resistance and parasitic capacitance may exist between the base and the collector. To inhibit such misalignment, some space margin is required. To secure the space margin, the area is enlarged, increasing base resistance. As a consequence, the noise characteristic may be degraded. In addition, a stable device may not be achieved because of the difficulty in setting up the process condition in view of the loading effect.  
         SUMMARY OF THE INVENTION  
         [0039]    It is, therefore, a primary object of the present invention to provide a super self-aligned heterojunction bipolar transistor and its manufacturing method that provides high speed operation with less noise, improved operational stability, and uniformity of devices.  
           [0040]    In accordance with the present invention, there is provided a method of manufacturing a heterojunction bipolar transistor comprising: a) forming a sub-collector by ion-implanting dopant into a portion of a semiconductor substrate and diffusing it; b) forming a field insulating film by forming a collector layer on the entire surface of the semiconductor substrate and oxidizing a region except a active collector region and a collector sinker by a LOCOS method; c) ion-implanting dopant into the collector sinker using a photo mask, heat-treating; diffusing; and removing the collector sinker to have a predetermined thickness; d) forming a base electrode by evaporating a thermal oxidation film, a base electrode and a base electrode protection film on the entire surface of the field insulating film, the active collector region and the sinker protection film; e) exposing the active collector region and the sinker protection film by etching the base electrode, the base electrode protection film, and the thermal oxidation film in a predetermined pattern; f) forming an intrinsic collector by ion-implanting dopant into the active collector region and heat-treating; g) forming a SiGe base layer on the entire surface of the protection film, the intrinsic collector and the sinker protection film; h) forming a masking film by evaporating a buffer protection film on the entire surface of the SiGe base layer and dry-etching the buffer protection film; i) separating the base and the emitter by removing the masking film by wet-etching and forming a first sidewall film and a second sidewall film; j) forming an emitter electrode by removing the second sidewall film and the first insulating film by etching and evaporating polysilicon on the base layer; k) removing the base electrode protection film by dry-etching so as to expose the base electrode and evaporating a silicon oxide film so as to protect the emitter electrode from the damage by dry-etching when the emitter sidewall film is formed; l) forming an emitter sidewall film by evaporating a silicon nitride film or a silicon oxide film and dry-etching in a predetermined pattern; m) forming an ohmic electrode only on the emitter electrode and the base electrode by exposing the emitter electrode and the base electrode by wet-etching, heat-treating, sputtering titanium (Ti) and titanium nitride (TiN) and wet-etching; n) forming an emitter contact window, a base contact window and a collector contact window by evaporating silicon oxide or silicon nitride on the entire surface of the semiconductor substrate whereon the ohmic electrode is formed to form an insulating film and patterning the insulating film and the sinker protection film using a photo mask; and o) forming a base terminal, an emitter terminal and a collector terminal by cleaning the surface of the semiconductor substrate according to the standard cleaning process, forming barrier metal by sputtering titanium (Ti) and titanium nitride (TiN), evaporating a conductive metal, heat-treating and patterning.  
           [0041]    In accordance with this present invention, there is provided a super self-aligned heterojunction bipolar transistor comprising: a) a sub-collector formed by ion-implanting dopant into a portion of a semiconductor substrate and diffusing it; b) a field insulating film formed by forming a collector layer on the entire surface of the semiconductor substrate and oxidizing the a region except the active collector region and the collector sinker, wherein dopant is ion-implanted into the collector sinker, and wherein the collector layer is heat-treated and the ions are diffused in the collector sinker; c) a sinker protection film formed by removing the collector sinker to a predetermined thickness and forming a film on the collection sinker; d) a thermal oxidation film formed on the entire surface of the field insulating film, the active collector region and the sinker-protection film; e) a base electrode formed on the entire surface of the thermal oxidation film with a predetermined thickness by in-situ method; wherein a base electrode protection film is formed on the base electrode with a predetermined thickness so as to protect the base electrode; f) an intrinsic collector formed by dry-etching the base electrode and the base electrode protection film in a predetermined pattern; wet-etching the thermal oxidation film so as to expose the active collector region and the sinker protection film; ion-implanting dopant into the active collector region; and heat-treating; g) a SiGe base layer formed by forming a silicon film on the entire surface of the base electrode protection film, the intrinsic collector and the sinker protection film h) a first sidewall film and a second sidewall film formed by removing a masking film by wet-etching, wherein the masking film is formed by dry-etching a buffer protection film formed on the entire surface of the SiGe base layer; and evaporating a silicon oxide film or a silicon nitride film to a predetermined thickness; i) an emitter electrode formed by removing the second sidewall film and the first sidewall film respectively by etching; evaporating polysilicon on the base layer; heat-treating; and patterning; j) an emitter sidewall film formed by exposing the base electrode by dry-etching; evaporating a film on the base electrode; heat-treating; and wet-etching; k) an ohmic electrode formed on the emitter electrode and the base electrode by sputtering titanium (Ti) and titanium nitride (TiN) in order on the emitter electrode and the base electrode, heat-treating, and wet-etching; l) an insulating film formed by evaporating silicon oxide or silicon nitride on the entire surface of the semiconductor substrate whereon the ohmic electrode is formed; m) a barrier metal formed by forming an emitter contact window, a base contact window and a collector contact window by patterning the insulating film and the sinker protection film using a photo mask; cleaning the surface of the semiconductor substrate; and sputtering titanium (Ti) and titanium nitride (TiN); and n) a base terminal, an emitter terminal, and a collector terminal provided by evaporating a conductive metal on the barrier metal, heat-treating and patterning.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0042]    These and other features, aspects, and advantages of preferred embodiments of the present invention will be more fully described in the following detailed description and the accompanying drawings, in which:  
         [0043]    [0043]FIGS. 1 a  and  1   b  show cross-sectional views of a super self-aligned heterojunction bipolar transistor manufactured by prior art techniques;  
         [0044]    [0044]FIG. 2 shows a cross-sectional view of another super self-aligned heterojunction bipolar transistor manufactured by prior art techniques; and  
         [0045]    [0045]FIG. 3 a  to FIG. 3 j  show cross-sectional views representing the manufacturing process of a super self-aligned heterojunction bipolar transistor-in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0046]    A heterojunction bipolar transistor and its manufacturing method according to this invention are further described herein.  
         [0047]    One embodiment of a manufacturing method according to this invention is discussed with reference to FIG. 3. First, a semiconductor substrate  100  may be prepared. Semiconductor substrate  100  may be a p-type semiconductor substrate. The resistivity of semiconductor substrate  100  may be over 50 Ω-cm. n+ type dopant such as arsenic (As) or stibium (antimony) (Sb) may be ion-implanted with a concentration of about 5×10 19  cm −3  to about 1×10 20  cm −3  into a part of semiconductor substrate  100  and diffused so that sub-collector  101  is formed. Thereafter, collector layer  102  may be formed on the entire surface of semiconductor substrate  100 . Collector layer  102  may be, for example, a silicon layer with a thickness of about 500 nm to about 1200 nm. Collector layer  102  may be formed by means of a thermal oxidation method.  
         [0048]    Field insulating film  103  may be formed by employing a LOCOS method to collector layer  102  except at active collector region  104  and the region of collector sinker  105 . Thereafter, n+ type dopant such as arsenic (As) or phosphorus (P) may be ion-implanted into said collector sinker  105  with a concentration of about 5×10 19  cm −3  to about 1×10 20  cm −3 . Collector layer  102  may be heat-treated and the implanted ions diffused. Subsequently, a part of the upper surface of collector sinker  105  may be removed by employing photoresist. (FIG. 3 a )  
         [0049]    Sinker protection film  106  may be formed on collector sinker  105  where the part of the upper surface of collector sinker  105  was removed. Thermal oxidation film  107 , which may comprise a silicon oxide film, may be formed on the entire surface of field insulation film  103 , active collector region  104 , and sinker protection film  106  at a temperature of between about 900-1000° C. and heat treated. Thermal oxidation film  107  may have a thickness of about 20 nm to about 100 nm. Thereafter, base electrode  108 , which may comprise polysilicon, may be evaporated by an in-situ process in which p+ type dopant such as boron (B) is doped into the entire surface of thermal oxidation film  107 . Base electrode  108  may have a thickness of about 200 nm to about 600 nm. The concentration of dopant may be over 1×10 19  cm −3 . Base electrode protection film  109 , which may comprise silicon nitride film or silicon oxide film, may be evaporated so as to protect base electrode  108 . Base electrode protection film  109  may have a thickness of about 200 nm to about 600 nm. Subsequently, to expose a base and emitter region, thermal oxidation film  107  may be exposed by sequentially dry-etching base electrode  108  and base electrode protection film  109  using a photomask. (FIG. 3 b )  
         [0050]    Subsequently, thermal oxidation film  107  may be wet-etched by HF, NH 4 F, or a mixture thereof. Active collector region  104  and sinker protection film  106  may be exposed. Thereafter, intrinsic collector  110  may be formed by ion-implanting n+ type dopant such as arsenic (As) or phosphorus (P) into active collector region  104  with a concentration of 1×10 16  cm −3  to about 5×10 18  cm −3 . Active collector region  104  may be heat treated so that the cut-off frequency of the device increases. (FIG. 3 c )  
         [0051]    A silicon film, which may have a thickness of 10 nm to about 60 nm, may be formed on the entire surface of base electrode protection film  109 , intrinsic collector  110 , and sinker protection film  106 . An intrinsic SiGe film, a p+ type extrinsic SiGe, and an intrinsic silicon film may be sequentially grown so that the SiGe base layer  111  is formed. Base layer  111  may have a thickness of about 50 nm to about 100 nm in total. The concentration of Ge may be in the range of 1 to about 20%. The doping concentration of p+ type dopant such as boron (B) may be in the range of 10 19  cm −3  to about 3×10 20  cm −3 . (FIG. 3 d )  
         [0052]    Subsequently, buffer protection film  112  may be evaporated on the entire surface of SiGe base layer  111  by a low pressure chemical vapor deposition (LPCVD) method. (FIG. 3 e ) Buffer protection film  112  may be dry-etched until the upper surface of base electrode  108  is reached so that masking film  112 A is formed. (FIG. 3 f )  
         [0053]    The portion of base layer  111  that is not masked by masking film  112 A may be removed by dry-etching. Then, masking film  112 A may be removed by wet-etching, thereby exposing the remaining portion of base layer  111 . Thereafter, by employing a low pressure chemical vapor deposition method (LPCVD), first sidewall film  113 , which may comprise a silicon oxide film or a silicon nitride film with a thickness of about 50 nm about 300 nm, may be formed to separate base and emitter. Second sidewall film  114  may be formed by thickly evaporating a silicon oxide film or a silicon nitride film. The thickness of second sidewall film  114  may be about 200 nm to about 800 nm. First sidewall film  113  may inhibit damage to the surface of the emitter when the emitter is exposed.  
         [0054]    Subsequently, second sidewall film  114  may be removed by dry-etching. First sidewall film  113  may be removed by wet-etching. Simultaneously, base electrode protection film  109  and sinker protection film  106  may be exposed.  
         [0055]    Thereafter, emitter electrode  115  may be formed by evaporating n+ type polysilicon on the exposed portion of base layer  111 . The junction between the base and the emitter may be formed by diffusing the n+ type dopant contained in emitter electrode  115  into base layer  111 . Emitter electrode  115  may be patterned by using a photomask which defines the emitter electrode. Base electrode protection film  109  may be removed by dry-etching so that base electrode  108  is exposed. (FIG. 3 h )  
         [0056]    To form silicide ohmic electrode  117  on the electrodes of the emitter and the base, emitter sidewall film  116  may first be formed by evaporating a silicon nitride film or a silicon oxide film and dry-etching. Emitter sidewall film  116  may have a thickness of about 200 to about 1000 nm. Emitter sidewall film  116  may prevent the emitter electrode  115  from being damaged during dry-etching. The thickness of the silicon nitride film or silicon oxide film may vary according to the area of the exposed emitter so that the exposed emitter region is fully refilled. Emitter electrode  115  and base electrode  108  may be exposed by wet-etching.  
         [0057]    Subsequently, ohmic electrode  117 , which may comprise titanium silicide (TiSi 2 ), may be formed only on emitter electrode  115  and base electrode  108 . Ohmic electrode  117  may be formed by sequentially sputtering titanium (Ti) and titanium nitride (TiN), heat-treating and wet-etching. The thickness of ohmic electrode  117  may be about 40 nm to about 60 nm. (FIG. 3 i )  
         [0058]    Insulating film  118  may be formed by evaporating silicon oxide or silicon nitride on the entire surface of the semiconductor substrate  100  whereon ohmic electrodes  117  of the base and the emitter are formed. Emitter contact window, base contact window, and collector contact window may be sequentially formed by patterning insulating film  118  and sinker protection film  106  using a photo mask. Thereafter, semiconductor substrate  100  may be washed according to a standard washing process. Base terminal  119 , emitter terminal  120 , and collector terminal  121  may be formed by evaporating a metal, heat-treating and patterning. In one embodiment, the metal of the terminals may be selected from a group consisting of aluminum (Al), aluminum-silicon (Al—Si), copper (Cu), and gold (Au). (FIG. 3 j )  
         [0059]    While the present invention has been described with reference to the illustrative embodiments, this description is not intended to be construed in a limiting sense. Numerous other arrangements may be readily devised by those skilled in the art that embody the principles of the invention and fall within its spirit and scope.  
         [0060]    For example, in the above embodiment, the description of a p type semiconductor substrate and an n type dopant is not intended to be construed in a limiting sense, and numerous other arrangements are possible, for example, an n type semiconductor and a p type dopant.  
         [0061]    While the present invention has been described in the above description the heterojunction bipolar transistor and its manufacturing method, in particular, an NPN type junction device and its manufacturing method, the description is not intended to be construed in a limiting sense. For example, the present invention can be applied to a PNP type junction device and its manufacturing method, or a BiCMOS (Bipolar CMOS) device and its manufacturing method, and so on.  
         [0062]    Advantages of the present invention may include:  
         [0063]    (1) According to the present invention, since the SiGe heterojunction bipolar transistor may be realized with a super self-aligned structure and a base layer may be formed by means of the entire surface crystal growth process, there may be an advantage that the uniformity of the device performance can be maintained.  
         [0064]    (2) According to the present invention, since the process may be shortened by streamlining the mask alignment process, etc., there may be an advantage that manufacturing cost can be reduced.  
         [0065]    (3) According to the present invention, since the base electrode may be formed using highly concentrated thick polysilicon, there may be advantages that the process condition can be easily set up and the time required for manufacturing can be shortened.  
         [0066]    (4) According to the present invention, since the base electrode may be formed using highly concentrated thick polysilicon, and the noise may be reduced by reducing the space of the sidewall, thereby reducing the base resistance, and a titanium silicide film may also be applied to a base electrode and an emitter electrode, there may be an advantage that parasitic resistance and parasitic capacitance can be minimized, which may facilitate high speed operation of a device.