Abstract:
Provided are bipolar transistor, BiCMOS device and method of fabricating thereof, in which an existing sub-collector disposed beneath a collector of a SiGe HBT is removed and a collector plug disposed at a lateral side of the collector is approached to a base when fabricating a Si-based very high-speed device, whereby it is possible to fabricate the SiGe HBT and an SOI CMOS on a single substrate, reduce the size of the device and the number of masks to be used, and implement the device of high density, low power consumption, and wideband performance.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the invention  
         [0002]     The present invention relates to a bipolar transistor and a method for fabricating the same and, specifically, a SiGe bipolar complementary metal oxide semiconductor (BiCMOS) device integrated on a silicon on insulator (SOI) and a method for fabricating the same.  
         [0003]     2. Description of the Prior Art  
         [0004]     In the past days, gallium arsenide (GaAs) compound semiconductors have been widely used in the fabrication of radio frequency (RF) devices for information communications, and CMOS devices have been widely used in the fabrication of analog/digital circuits. In the recent days, an RF/analog/digital integration chip (SoC: system on chip) has been widely used, and silicon germanium (SiGe) BiCMOS devices are most suitable for it&#39;s manufacturing purpose and thus widely used.  
         [0005]     SiGe BiCMOS technology is that a SiGe heterojunction bipolar transistor (HBT) suitable for RF/analog circuits and a CMOS device suitable for digital circuits are both integrated on a single substrate, nowadays the SiGe BiCMOS technology has been employed for the integration chip fabrication of an information communication apparatus such as a portable mobile phone, and then the SiGe BiCMOS is a widespread technology.  
         [0006]     The SiGe HBT is a technology that has been improved from a conventional bipolar transistor, and makes use of not silicon (Si) but a SiGe alloy material that Si is intermixed with Ge of about 20%, as a base. The SiGe HBT, as compared with a conventional bipolar transistor, has advantages that large current gain can be obtained, and its base can be formed thin by increasing the impurity concentration thereof by about 100 times, thus it is possible to operate at a high speed and a high frequency. However, a SiGe BiCMOS device fabricated in accordance with the conventional art, as compared with a CMOS device, has problems that the process is more complex and the production cost is higher because of requiring 10 or more sheets of mask additionally, and that the integration capability of the SiGe BiCMOS device is not as high as that of the CMOS device because devices of the HBT are not downsized. To overcome these problems, an integration chip composed of either only a CMOS device or only a silicon on insulator (SOI) CMOS device having low power consumption among CMOS devices, has been developed by a number of universities, etc. However, the integration chip has a problem that its performance is insufficient due to the restricted properties of the CMOS devices.  
       SUMMARY OF THE INVENTION  
       [0007]     Accordingly, the present invention is contrived to solve the above-mentioned problems, and the present invention is directed to a SiGe BiCMOS device that the number of masks to be used is reduced and a method for fabricating the same.  
         [0008]     Further, the present invention is directed to a SiGe BiCMOS device that a size of a SiGe HBT device is reduced and a method for fabricating the same.  
         [0009]     Still further, the present invention is directed to a SiGe BiCMOS device capable of realizing high density, low power consumption, and wideband performances.  
         [0010]     One aspect of the present invention is to provide a bipolar transistor, comprising: a first insulating film; a collector formed on the first insulating film, the collector being made of any one of N-type and P-type semiconductors; a collector plug formed on the first insulating film, the collector plug being contacted with the collector, made of the same type of semiconductor as the collector, and more highly doped than the collector; a second insulating film disposed on a portion where the collector and the collector plug are contacted to each other; a base formed on the collector, the base being contacted with the second insulating film and made of a different type of semiconductor from the collector; and an emitter formed on the base, the emitter being made of the same type of semiconductor as the collector.  
         [0011]     A second aspect of the present invention is to provide a BiCMOS device, comprising: a first insulating film; a bipolar transistor, including: a collector formed on the first insulating film, the collector being made of any one of N-type and P-type semiconductors; a collector plug formed on the first insulating film, the collector plug being contacted with the collector, made of the same type of semiconductor as the collector, and more highly doped than the collector; a second insulating film disposed on a portion where the collector and the collector plug are contacted to each other; a base formed on the collector, the base being made of a different type of semiconductor from the collector; and an emitter formed on the base, the emitter being made of the same type of semiconductor as the collector; an NMOS device, including: a P-well disposed on the first insulating film and made of the P-type semiconductor; a first source and a first drain respectively disposed on a left side and a right side of a top the P-well and made of the N-type semiconductor; a first gate insulating film disposed on the P-well; and a first gate disposed on the first gate insulating film; and a PMOS device, including: an N-well disposed on the first insulating film and made of the N-type semiconductor; a second source and a second drain respectively disposed on a left side and a right side of a top the N-well and made of the P-type semiconductor; a second gate insulating film disposed on the N-well; and a second gate disposed on the second gate insulating film.  
         [0012]     A third aspect of the present invention is to provide a method for manufacturing a bipolar transistor, comprising the steps of: forming a collector plug, in an SOI substrate having a first insulating film and a first semiconductor that is made of any one of N-type and P-type semiconductors and disposed on the first insulating film, the collector plug being made of the same type as the first semiconductor and more highly doped than the first semiconductor on a portion of the first semiconductor; forming a buffer oxide film and a nitride film; forming any one of a single open slit and a plurality of open slits by patterning the nitride film, and removing the nitride film disposed on a portion where a field oxide film is to be formed; forming a field oxide film, a collector made of the first semiconductor surrounded with the field oxide film and the collector plug, and an oxide film disposed on a portion where the collector and the collector plug are contacted to each other and having a thickness thinner than that of the field oxide film, by performing a thermal oxidation process; removing the nitride film; forming a base on the collector, the base being made of a different type of semiconductor from the first semiconductor; forming a second insulating film; and forming an emitter connected to the base through a contact hole of the second insulating film, the emitter being made of the same type of semiconductor as the first semiconductor.  
         [0013]     A fourth aspect of the present invention is to provide a method for manufacturing a BiCMOS device, comprising the steps of: forming a collector plug, a P-well doped with P-type impurities, and an N-well doped with N-type impurities, in an SOI substrate having a first insulating film and a first semiconductor that is made of any one of N-type and P-type semiconductors and disposed on the first insulating film, the collector plug being made of the same type as the first semiconductor and more highly doped than the first semiconductor on a portion of the first semiconductor; forming a buffer oxide film and a nitride film; forming any one of a single open slit and a plurality of open slits by patterning the nitride film, and removing the nitride film disposed on a portion where a field oxide film is to be formed; forming a field oxide film, a collector made of the first semiconductor surrounded with the field oxide film and the collector plug, and an oxide film disposed on a portion where the collector and the collector plug are contacted to each other and having a thickness thinner than that of the field oxide film, by performing a thermal oxidation process; removing the nitride film; forming a gate oxide film; depositing a base epitaxial layer made of a different type of semiconductor from the first semiconductor; forming a second insulating film; forming an emitter and a gate of a CMOS device by etching the gate oxide film and the second insulating film, after depositing and patterning a semiconductor of the same type as the first semiconductor; forming a base by patterning the base epitaxial layer; performing N-type doping with a low concentration into a source/drain region of the P-well, and P-type doping with a low concentration into a source/drain region of the N-well; forming a spacer in a sidewall of the emitter and a sidewall of the gate of the CMOS device; and performing N-type doping with a high concentration into a source/drain region of the NMOS device, and P-type doping with a high concentration into a source/drain region of the PMOS device. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     The above and other objectives, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0015]      FIG. 1  is a schematic cross-sectional view of a SiGe BiCMOS device according to a preferred embodiment of the present invention; and  
         [0016]     FIGS.  2  to  18  illustrate cross-sectional views showing a sequence of fabrication processes for a SiGe BiCMOS device according to a preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     Hereinafter, the present invention will be described with reference to the accompanying drawings. As many apparently widely different embodiments of the present invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the below specific embodiments thereof. Embodiments of the present invention are to provide to more fully explain the present invention to those skilled in the art.  
         [0018]      FIG. 1  is a schematic cross-sectional view of a SiGe BiCMOS device according to a preferred embodiment of the present invention.  
         [0019]     In  FIG. 1 , the SiGe BiCMOS device comprises a substrate  10 , an insulating film  20 , a SiGe HBT  30 , an NMOS device  40 , a PMOS device  50 , and a field insulating film  60 .  
         [0020]     The substrate  10  is, for example, composed of a p-type material with resistivity of about 6 to 100 ohm centimeter (Ω·cm). A high resistance substrate is a substrate doped with a low concentration, and thus, substrate performances become higher due to the lower substrate capacitance, but there is a disadvantage that the substrate cost is expensive.  
         [0021]     The insulating film  20  is, for example, an oxide film with a thickness of 0.3 to 2 μm, and preferably, a thick insulating film. However, there is a disadvantage that the SOI having the thick insulating film is expensive.  
         [0022]     The SiGe HBT  30  comprises a collector  130 , a collector plug  140 , a collector insulating film  150 , a base  120 , and an emitter  110 . The collector  130  and the collector plug  140  are disposed on the insulating film  20  and contacted to each other. The collector insulating film  150  is disposed on a portion where the collector  130  and the collector plug  140  are contacted to each other. The base  120  is disposed on the collector, and the emitter  110  is disposed on the base.  
         [0023]     The collector  130  and the collector plug  140  are, for example, N −  and N + doped silicon with a thickness of 250 to 700 nm, respectively. The collector insulating film  150  has a thickness less than that of the field insulating film  60 . The base  120  is, for example, P-type silicon with a thickness of 120 nm. The base  120  can be comprised of multiple layers including a buffer layer made of silicon with a thickness of 40 nm, a SiGe layer that the Si is intermixed with Ge of 20%, with a thickness of 40 nm, and a cap layer made of silicon with a thickness of 40 nm. The emitter  110  is, for example, N-type polysilicon with a thickness of 350 nm.  
         [0024]     There are several advantages to the SiGe HBT configured by the above-described manner, as compared with the prior art. In the SiGe HBT according to the conventional art, the connection between the collector and the collector plug was implemented with a sub-collector disposed below the collector. However, according to the present invention, it is possible to considerably decrease the power loss by removing the sub-collector and directly connecting the collector and the collector plug, and also by eliminating leak currents of capacitor components, which flow from the sub-collector to the substrate. In addition, the leveling dimension and integration capability of the device can be increased by reducing the dimension of the collector insulating film  150 , and a resistance value between the base  120  and a base metal wiring  200  can be minimized by shortening the distance between the devices, and thus noise removal can be improved. Further, it is possible to improve the current driving forces, if a high concentration arsenic (As) layer having a thickness of  100  nm around the bottom interface of the collector  130  is formed, or a high concentration shallow N + layer which is doped with phosphorus into the collector  130  and thermal-treated to pile-up the phosphorus (P) around the bottom interface is formed.  
         [0025]     The SiGe HBT  30  can further comprise a base protective layer  160  disposed at an edge of a portion where the base  120  and the collector  130  are contacted to each other. The base protective layer  160 , when formed of P + -type silicon, serves to increase the current gain by preventing the recombination-extinction of an electron that is injected from the emitter into the base. The collector plug  140  should appropriately keep a distance with the base protective layer  160 . The reasons are that the current driving force may be limited in case where the distance between the collector plug and the base protective layer is too much apart from, and the breakdown withstanding voltage may be lowered in case where the distance is too much close.  
         [0026]     The SiGe HBT  30  can further comprise metal wirings  200 ,  210  and  220  for external connection of the emitter  110 , the base  120 , and the collector plug  140 . Also, the SiGe HBT  30  can further comprise silicide layers  170 ,  180  and  190  to improve the contact properties of the metal wirings  200 ,  210  and  220 , with the emitter  110 , the base  120  and the collector plug  140 , respectively. The metal wirings  200 ,  210  and  220  are disposed in the corresponding contact holes of the insulating film  70 , respectively.  
         [0027]     The NMOS device  40  comprises a P-well  330 , source/drain  340  and  350 , a gate  310 , and a gate insulating film  320 . The P-well  330  is disposed on the oxide film  20 , and it has an example configuration of P-type silicon with a thickness in the range of 250 nm to 700 nm. The source/drain  340  and  350  may be N-type silicon, for example. The gate  310  is, for example, N-type polysilicon with a thickness of  350  nm. The gate insulating film  320  is, for example, an oxide layer with a thickness in the range of 15 nm to 2 nm. The NMOS device  40  can further comprise metal wirings  390 ,  410  and  400  for external connection between the source/drain  340  and  350 , and the gate  310 . Also, the NMOS device  40  can further comprise silicide layers  360 ,  380  and  370  to improve the contact properties of the metal wirings  390 ,  410  and  400 , with the source/drain  340  and  350 , and the gate  310 , respectively. The metal wirings  390 ,  410  and  400  are disposed in the corresponding contact holes of the insulating film  70 , respectively.  
         [0028]     The PMOS device  50  comprises an N-well  530 , source/drain  540  and  550 , a gate  510 , and a gate insulating film  520 . The N-well  530  is disposed on the oxide film  20 , and it has an example configuration of N-type silicon with a thickness of 250 nm to 700 nm. The source/drain  540  and  550  are, for example, P-type silicon. The gate  510  is, for example, N-type polysilicon with a thickness of 350 nm. The gate insulating film  520  is, for example, an oxide film with a thickness of 15 nm to 2 nm. The PMOS device  50  can further comprise metal wirings  590 ,  610  and  600  for external connection between the source/drain  540  and  550 , and the gate  510 . Also the PMOS device  50  can further comprise silicide layers  560 ,  580  and  570  to improve the contact properties of the metal wirings  590 ,  610  and  600 , with the source/drain  540  and  550 , and the gate  510 , respectively. The metal wirings  590 ,  610  and  600  are disposed in the corresponding contact holes of the insulating film  70 , respectively.  
         [0029]     The configuration as described above has advantages that an HBT having excellent RF and analog performances can be mounted on a substrate such as an SOI CMOS device which has been widely employed for low power consumption, downsizing and high density of the device are possible by leveling the HBT device configuration along with the CMOS device, and the number of masks can be reduced by two sheet (for device isolation and sub-collector), as compared with the prior art.  
         [0030]     FIGS.  2  to  18  illustrate cross-sectional views showing a sequence of fabrication processes for a SiGe BiCMOS device according to a preferred embodiment of the present invention.  
         [0031]     Referring to  FIG. 2 , an SOI substrate is prepared. In the SOI substrate, a silicon  1010  on the bottom may have, for example, P-type silicon with resistivity in the range of 6 to 100 ohm centimeter (Ω·cm). As an insulting film  1020 , an oxide film with a thickness of about 0.3 to 2 μm is preferable. Preferably, the insulting film  1020  may be a thick film, but a thick insulating film would be expensive. Preferably, a silicon  1030  disposed on the insulating film may have a thickness of 50 to 100 nm. If the silicon  1030  has a thickness in the range of 250 nm to 700 nm, the process shown in  FIG. 3  can be omitted. In this step, the silicon  1030  may be doped with arsenic (As) having ineffective thermal diffusion by 10 18 /cm 3 , thereby an N + layer can be formed. When the N + layer is formed, the limiting value of the current driving force is improved. Subsequently, a collector may be doped with phosphorus (P) and the doped phosphorus (P) is piled up at an interface of the lower oxide film when a field oxide film of  FIG. 6  is grown, thereby the N + layer also can be formed.  
         [0032]     Referring to  FIG. 3 , a collector epitaxial layer  1040  is grown on the SOI substrate. This epitaxial growth can be performed by a reduced pressure chemical vapor deposition method at a pressure of several torr and a temperature of 1,100° C. At this time, the gases to be used are SiH 2 Cl 2 , GeH 4 , PH 3 , and H 2 . The collector epitaxial layer  1040  has a thickness of 200 nm to 600 nm. If the layer is thin, it is suitable for high frequency circuits since the operation speed is fast, and if this layer is thick, it is suitable for power circuits since the breakdown withstanding voltage is high although the operation speed becomes slow. The epitaxial layer has a concentration of the phosphorus (P) in the range of 5×10 16  to 2×10 17  to achieve the optimization of the operation speed and the breakdown withstanding voltage, and as the thinner the thickness of the layer is, the higher concentration in phosphorus (P) of the epitaxial layer should be required. On the other hand, the low concentration in phosphorus (P) of the epitaxial layer should be required if the layer becomes thicker.  
         [0033]     Referring to  FIG. 4 , a protective oxide film  1050  is formed on the collector epitaxial layer  1040 , and then an ion implantation process is performed into a collector plug  1060  of the SiGe HBT with a high concentration, performed into a P-well  1070  of the NMOS device and an N-well  1080  of the PMOS device, and then, the protective oxide film  1050  is removed. The protective film is performed by using a low temperature oxide deposition (LTO) method at a temperature of 400° C. with a thickness of 120 nm. The conditions of the ion implantation process are P, 80 KeV, and 4×10 15 /cm 2  for the collector plug  1060 , BF 2 , 60 KeV, and 7.0×10 12 /cm 2  for the P-well  1070  of the CMOS device, and P, 125 KeV, and 1.1×10 13  cm 2  for the N-well  1080 .  
         [0034]     Referring to  FIG. 5 , a buffer oxide film  1090  and a nitride film (Si 3 N 4 )  1100  is formed, and then the nitride film  1100  is patterned to divide into an active region and an inactive region that is a field region. The nitride film  1100  is about 160 nm in thickness and grown by using a low pressure chemical vapor deposition (LPCVD) method. The nitride film  1100  serves to prevent oxidation of the active region. In the subsequent processes, the nitride film in a region  1110  of the field oxide film to be grown is removed for a wide region. However, in the subsequent processes, the nitride film in a region  1120  of the oxide film to be disposed between the collector and collector plug of the SiGe HBT is removed for a narrow region. This is to suppress the growth of the oxide film by reducing the contact area that the oxygen to be supplied contacts to the region  1120 , and by decreasing the amount of oxygen to be supplied. Also, this region  1120  can be composed of a single open slit or a plurality of open slits. When the region  1120  is composed of the plurality of open slits, it means that the nitride film of the open slit is removed and the nitride film interposed between the open slits is not removed. The thickness of the oxide film to be formed in the subsequent process is controlled by the width and space of the open slit, and the width and space may be, for example, 0.2 to 0.5 μm.  
         [0035]     Referring to  FIG. 6 , after a thick field oxide film  1130  and an oxide film  1140  disposed on the junction between the collector  1150  and the  20  collector plug  1060  of the SiGe HBT are grown, and then the nitride film is removed. In order to realize extremely high device isolation before the growth of the oxide film, the ion implantation process is performed into a region in which the field oxide film  1130  is formed, under conditions of BF 2 , 70 KeV, and 5×10 13 /cm 2 . The growth of the oxide films  1130  and  1140  is performed in a thermal oxidation furnace of 1000° C. for about 4 hours by a thermal oxidation process, and the thickness of the oxide film is 650 nm. After the oxide film is grown, the nitride film is etched using a heated phosphoric acid as an etchant.  
         [0036]     Referring to  FIG. 7 , the ion implantation process is performed into the collector  1150  and the collector plug  1060  of the SiGe HBT, or performed into the P-well  1070  and the N-well  1080  to finely adjust threshold voltages of the NMOS device and the PMOS device. The breakdown withstanding voltage is reduced to 3 V or less but an operation speed is more improved, by performing the ion implantation process into the collector  1150  and the collector plug  1060  of the SiGe HBT. Therefore, the aforementioned ion implantation process is performed only for the SiGe HBT to be used for very high speed digital or high speed analog. The conditions of the ion implantation are P, 180 KeV, and 2×10 13 /cm 2  for the HBT collector  1150  and the collector plug  1060 , BF 2 , 80 KeV, and 7.7×10 12 /cm 2  for the P-well  1070 , and P, 125 KeV, and 5.5×10 11 /cm 2  for the N-well  1080 .  
         [0037]     Referring to  FIG. 8 , a gate oxide film  1160  of the CMOS device is grown, and then the grown gate oxide film on the collector  1150  of the SiGe HBT is removed. The gate oxidation is performed in a thermal oxidation furnace of 850° C. for about 1 hour by a thermal oxidation process. Preferably, the thickness of the gate oxide film is about 15 nm in case where a line width of the gate is about 0.5 μm, and is about 2 nm in the case of several tens of nano.  
         [0038]     Referring to  FIG. 9 , a base epitaxial layer  1170  having a thickness of 120 nm to be served as a base of the SiGe HBT is grown, and then a protective oxide film  1180  is deposited thereon, and then high concentration ion implantation is performed into the base epitaxial layer  1170  which is disposed on the field oxide film  1130  and the oxide film  1140  between the collector  1150  and the collector plug  1060 . The base epitaxial layer  1170  is grown by the steps of growing a buffer layer made of silicon with a thickness of 40 nm; growing a SiGe layer made by intermixing the silicon with 20% Ge with a thickness of 40 nm; and growing a cap layer made of the silicon with a thickness of 40 nm. The buffer layer and the cap layer are undoped silicon layers. A P +  layer doped with boron (B) substantially serving as a base is disposed within the SiGe layer, and the thickness and the concentration thereof is about 15 nm and 5×10 19 /cm 3 , respectively. Accordingly, it is possible for high speed operations while maintaining a withstanding voltage of the collector since the P +  layer is doped with high concentration. The base epitaxial layer  1170  is grown at a pressure of several tens of torr and a temperature in the range of 650 to 700° C. by a reduced pressure chemical vapor deposition method using gases including SiH 4 , GeH 4 , B 2 G 6 , and H 2 . The protective oxide film  1180  is grown by using a low temperature oxide deposition (LTO) method at a temperature of 400° C., and the thickness thereof is about 400 nm. In addition, high concentration ion implantation is performed into the base epitaxial layer  1170  which is disposed on the field oxide film  1130  and the oxide film  1140  disposed on the junction between the collector  1150  and the collector plug  1060 , to reduce the resistance of a base external connection layer and ensure a stable resistance value for a base resistor that is a resistor having a high resistance value to be served as a passive device when it is manufactured.  
         [0039]     Referring to  FIG. 10 , oxide films are further formed to form the base epitaxial layer  1170  of the SiGe HTB and an interlayer insulating film  1190  between the emitters. In the oxide films, an oxide film disposed at the CMOS device region is removed because it is unnecessary, and a portion for the contact hole between the base epitaxial layer  1170  and the emitter is removed. The interlayer insulating film  1190  is formed by using the low temperature oxide deposition (LTO) method at a temperature of 400° C., and the thickness thereof is about 80 nm.  
         [0040]     Referring to  FIG. 11 , a polysilicon layer is deposited, an emitter  1200  of the HBT and a gate  1210  of the CMOS device are formed by patterning the polysilicon layer, and then the oxide film is etched to form the oxide film  1190  disposed beneath the gate  1210  of the CMOS device. The polysilicon layer is formed by using a low pressure chemical vapor deposition (LPCVD) method at a temperature of 625° C., and the thickness thereof is about 350 nm.  
         [0041]     Referring to  FIG. 12 , a lightly doped drain (LLD) that is a shallow source/drain expansion region is formed by performing the ion implantation process into a source/drain region  1220  of the NMOS device and a source/drain region  1230  of the PMOS device, and then a base protective layer  1240  is formed by performing the ion implantation process into the edge of the active region of the SiGe HBT. The lightly doped drain serves to improve the operation withstanding voltage of the CMOS device, and to suppress the occurrence of hot carriers. The base protective layer  1240  serves to increase the current gain by prohibiting the recombination-extinction of an electron that is injected from the emitter into the base. The conditions of the ion implantation are P, 60 KeV, and 2.2×10 13 /cm 2  for the N-LLD, BF 2 , 100 KeV, and 9.0×10 12 /cm 2  for the P-LDD, and BF 2 , 40 KeV, and 4.0×10 14 /cm 2  for the base protective layer  1240 .  
         [0042]     Referring to  FIG. 13 , there is shown a process for forming a spacer  1250  with a thickness of 200 nm at an emitter sidewall of the HBT and gate sidewalls of the NMOS device and PMOS device. The spacer  1250  serves to improve isolations between the emitter  1200  of the HBT and the base epitaxial layer  1170  and between the gate  1210  of the CMOS device and the source/drain regions  1220  and  1230 , and to increase the breakdown voltage. The spacer  1250  is easily implemented by using a low temperature oxide deposition (LTO) method and a reactive ion etching (RIE) method.  
         [0043]     Referring to  FIG. 14 , a base  1170  is formed by pattering the base epitaxial layer  1170  of the HBT, the oxide film on the collector plug  1060  is removed, and then a selective epitaxial growth (SEG) is performed on an exposed portion of the base  1170  and the source/drain regions  1220  and  1230 . The patterning of the base epitaxial layer  1170  can be optionally formed immediately after forming of the base epitaxial layer  1170  shown in  FIG. 10 . The selective epitaxial growth means that the epitaxial layer is grown on an exposed portion of the polysilicon or silicon layer, i.e. the emitter  1200  and the base layer  1180 , the gate  1210  and the source/drain layers  1220  and  1230 , but the epitaxial layer is not grown on a portion covered with the oxide film. Furthermore, a silicon epitaxial layer is grown in case that an epitaxial layer is grown on a silicon layer, and the polysilicon epitaxial layer is grown in case where an epitaxial layer is grown on a polysilicon layer. With the selective epitaxial growth, a subsequent metal silicide forming process can be performed in a stable fashion since the thickness of the exposed portion of the base  1170  becomes thick, and thus, to reduce the electric resistance of the portion. In addition, it is possible to protect a shallow injunction of the source/drain  1220  and  1230  of the CMOS device. The selective epitaxial growth is performed by using SiH 2 Cl 2 , HCl, and H 2  gases at a pressure of several tens of torr and a temperature of approximately 700° C., and the grown thickness is about 50 nm.  
         [0044]     Referring to  FIG. 15 , high concentration ion implantation is performed into the source/drain  1220  and  1230  of the CMOS device. The conditions of the ion implantation are P, 80 KeV, and 8.0×10 15 /cm 2  for the source/drain region  1220  of the NMOS device, and BF 2 , 80 KeV, and 3.7×10 15 /cm 2  for the source/drain region  1230  of the PMOS device.  
         [0045]     Referring to  FIG. 16 , a silicide layer  1260 , which is a compound of silicon and metal, is formed. The silicide layer  1260  is formed by depositing Ti and TiN, which are metals for silicide, with a thickness of about 23 nm, respectively, using a sputtering apparatus; siliciding (TiSi 2 ) by means of a first heat treatment at a temperature of 650° C.; etching the portions where the silicide is not formed with a chemical etchant; and performing a second heat treatment at a temperature of 850° C. The resulting electric resistivity of the silicide layer  1260  is in the range of about 5 to 20 ohm centimeter (Ω·cm). The silicide layer  1260  is formed at a point where the selective epitaxial growth occurs, i.e. the exposed region of the silicon or polysilicon layer. On the other hand, the silicide layer is not formed in the regions covered with the oxide film. Since the silicide has properties as mentioned above, it is referred to as a salicide (self aligned silicidation).  
         [0046]     Referring to  FIG. 17 , an interlayer insulating film  1270  is deposited for external metal wirings and a contact hole is formed using an etching process. The interlayer insulating film is formed by using the low temperature oxide deposition (LTO) method at a temperature of 400° C., and the thickness thereof may be about 600 nm.  
         [0047]     Referring to  FIG. 18 , a metal layer of Ti/TiN/Al is deposited by means of a sputter and patterned to form a metal wiring layer  1280 , and then an alloying process is performed at a temperature of 450° C. in N 2 /H 2  environment for 30 minutes. With this process, the resultant SiGe BiCMOS device is formed.  
         [0048]     As described above, the configuration has advantages that an HBT having excellent RF and analog performances can be mounted on a substrate such as an SOI CMOS device, which has been widely employed for low power consumption, a size reduction and a high density of the device are possible by leveling the HBT device configuration along with the CMOS device, and the number of masks can be reduced to two sheet (for device isolation and sub-collector), as compared with the prior art.  
         [0049]     A SiGe BiCMOS device according to the present invention has an advantage that power consumption is lowered.  
         [0050]     In addition, the SiGe BiCMOS device according to the present invention has an advantage that it requires low costs for processes by reducing the number of masks being needed.  
         [0051]     Further, the SiGe BiCMOS device according to the present invention has an advantage that the HBT can be fabricated together with the SOI CMOS device, thereby reducing the power consumption.  
         [0052]     Still further, the SiGe BiCMOS device according to the present invention has an advantage that it is possible to increase the device density by reducing the horizontal dimension and vertical height of the HBT.  
         [0053]     Although a preferred embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.