BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a method for manufacturing a bipolar transistor. 
   2. Description of the Related Art 
   Recent demand for a high speed signal processing device has rapidly increased. To meet such a demand, a bipolar transistor for high speed signal processing has been developed. The bipolar transistor may reduce a base resistance by reducing a distance between a base region and an emitter region. 
     FIG. 1  is a cross-sectional view showing a construction of a high speed bipolar transistor according to the related art. 
   As shown in  FIG. 1 , a buried layer  110  is formed on a substrate  10 , and a device isolation layer  140  is formed on the buried layer  110 . Here, the device isolation layer  140  is divided into a first well  120   a  and a second well  120   b . A first active region is formed at the first well  120   a  and a second active region is formed at the second well  120   b . An emitter region  150   b  and a base region  152   b  are formed inside the first active region of the first well  120   a . A collector region  156   a  is formed inside the second active region of the second well  120   b . An emitter electrode  150   a  is formed at the emitter region  150  to be connected to the first contact plug  150   c . A collector region  156   a  is connected to a second contact plug  156   c . A base electrode  152   a  is formed at the base region  152   b  to be connected to a third contact plug  152   c . A pad oxide layer  160  is formed between the base electrode  152   a  and the emitter electrode  150   a . The first, second, and third contact plugs  150   c ,  156   c , and  152   c  are connected to the emitter region  150   b , the collector region  156   a , and the base region  152   b  through the inter layer dielectric  170 , respectively. 
   On the other hand, in the bipolar transistor formed as mentioned above, the pad oxide layer  160  isolates the emitter electrode  150   a  and the base electrode  152   a . Ions doped in the emitter electrode  150   a  are diffused to form the emitter region  150   b , and ions doped into the base electrode  152   a  are diffused to form the base region  152   b.    
   However, when forming the aforementioned bipolar transistor, a height of the interlayer dielectric  170  including the emitter electrode  150   a  and the base electrode  152   a  may be relatively great in order to secure a CMP process margin during formation of the contact plugs to the electrodes. As a result, it becomes difficult to more highly integrate a device. 
   Moreover, two polysilicon layer formation and etching processes are performed to form the emitter electrode  150   a  and the base electrode  152   a , respectively. Thus, it may be difficult to simplify a process. During an etching process for forming the contact plugs, an overetching loss of the polysilicon layer constituting the electrodes can be incurred. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention is directed to a method for manufacturing a bipolar transistor that substantially obviates one or more problems due to limitations and disadvantages of the related art. 
   Accordingly, an object of the present invention is to provide a bipolar transistor. 
   Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure(s) particularly pointed out in the written description and claims hereof as well as the appended drawings. 
   To achieve these objects and other advantages, and in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided a method for manufacturing a bipolar transistor comprising: forming a device isolation layer in a device isolation region of a semiconductor substrate having first and second well regions having a first conductivity; implanting ions having a second conductivity in the first well to form a third well; forming and patterning a conductive layer on the semiconductor substrate to form an emitter electrode pattern on the third well region and a collector electrode pattern on the second well region; forming spacers at sidewalls of the emitter electrode pattern and the collector electrode pattern; performing a diffusion process to form an emitter region having a first conductivity in the third well region and to form a collector region having a first conductivity on the second well region; implanting ions having a second conductivity in the third well region to form a base region; and removing the emitter electrode pattern and the collector region pattern. 
   In another aspect of the present invention, there is provided a method for manufacturing a bipolar transistor comprising: forming a device isolation layer in a device isolation region of a semiconductor substrate having first and second well regions having a first conductivity therein; implanting ions having a second conductivity in the first well to form a third well; forming and patterning a conductive layer on the semiconductor substrate to form a base electrode pattern; forming a spacer at sidewalls of the base electrode pattern; implanting ions having a first conductivity in the semiconductor substrate to form an emitter region between base electrode pattern structures and form a collector region in the second well region; and performing a diffusion process on the semiconductor substrate to form base region(s) between the emitter region. 
   It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle(s) of the invention. In the drawings: 
       FIG. 1  is a cross-sectional view showing a construction of a high speed bipolar transistor according to the related art; 
       FIGS. 2 through 6  are cross-sectional views of a bipolar transistor for sequentially describing a method for manufacturing the bipolar transistor according to a first embodiment of the present invention; and 
       FIGS. 7 through 12  are cross-sectional views of a bipolar transistor for sequentially describing a method for manufacturing the bipolar transistor according to a second embodiment of the present invention. 
   


   DETAILED DESCRIPTION OF THE INVENTION 
   Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
   Hereinafter, the method for manufacturing the bipolar transistor according to the present invention with reference to the accompanying drawings in detail. 
     FIGS. 2 through 6  are cross-sectional views of a bipolar transistor for sequentially describing a method for manufacturing the bipolar transistor according to a first embodiment of the present invention. 
   First, as shown in  FIG. 2 , a substrate  10 , for example, a p-type (first conductivity) silicon substrate is prepared and/or provided. Here, an n-type (second conductivity, opposite or complementary to the first conductivity) buried layer  11  is on the substrate  10 , typically by epitaxial growth of silicon or a silicon-germanium alloy. A first well  12   a  and a second well  12   b  doped with n-type (second conductivity) ions are formed in the buried layer  11 , typically by ion implantation. 
   Next, for a device isolation of the bipolar transistor, a device isolation layer  14  can be formed in a field region of the substrate  10 . Typically, the device isolation layer  14  can be formed by conventional local oxidation of silicon or shallow trench isolation. 
   The device isolation layer  14  (which is formed in a field region of the substrate  10 ) functions to divide an active region of the substrate  10  into a first active region for an emitter region and a base region, and second active region for a collector region. 
   Then, a photolithography process and an ion implantation process are performed on the substrate on which the device isolation layer  14  is formed in order to form a third well  17  of a p-type in the first well  12   a  of the first active region. Here, a base and an emitter will be formed in the first well  12   a.    
   Thereafter, as shown in  FIG. 3 , a polysilicon layer doped with n-type ions is formed on the resulting object on which the third well  17  is formed, and a photoresist pattern (not shown) for defining an emitter electrode pattern and a collector electrode pattern are formed on the polysilicon layer. The poly silicon layer is etched using the photoresist pattern as an etch mask to form an emitter electrode pattern  18   a  on the third well  17  and a collector electrode pattern  18   b  on the second well  12   b.    
   After forming the emitter electrode pattern  18   a  and the collector electrode pattern  18   b , a process is executed for patterning a photoresist which is used for ion implantation. In detail, after patterning the photoresist, n+ ions are implanted in the emitter electrode pattern  18   a  and the collector electrode pattern  18   b  using the photoresist as a mask. Alternatively, a doped polysilicon layer (or other patternable source of diffusible dopant atoms) may be deposited directly (e.g., by chemical vapor deposition of silicon from a silane and a dopant source such as diborane, BF3, phosphine, etc.), then patterned, without need for the ion implantation step described in this paragraph. 
   Subsequently, a nitride layer is formed on the resulting object on which the emitter electrode pattern  18   a  and the collector electrode pattern  18   b  are formed. Further, an etching process such as a blanket etch is carried out to form spacers  20   a  and  20   b  at sidewalls of the emitter electrode pattern  20   a  and the collector electrode pattern  20   b.    
   Next, as shown in  FIG. 4 , a diffusion process is performed on the resulting object on which the spacers  20   a  and  20   b  are formed, so that n-type ions doped in the emitter electrode pattern  18   a  and the collector electrode pattern  18   b  are diffused to form an emitter region  22  and a collector region  24 . 
   Then, as shown in  FIG. 5 , a photoresist pattern  26  for defining a base region is formed on the resulting object. Next, p-type ions are implanted using the photoresist pattern  26  as a mask to form a base region  28  inside the third well  17 . 
   The base region  28  is spaced apart from the diffused emitter region  22  due to the spacer  20   a.    
   Finally, as shown in  FIG. 6 , the spacers  20   a  and  20   b , the emitter electrode pattern  22 , and the base electrode pattern  28  are respectively removed. A dielectric  30  (which may be referred to as an interlayer dielectric) is formed on an entire surface of the substrate from which the emitter electrode pattern  22  and the base electrode pattern  28  have been removed. Further, a photoresist pattern (not shown) is formed on the dielectric  27 . An etch process is performed using the photoresist pattern us a mask to form a plurality of contact holes, respectively exposing the base region  28 , the emitter region  22 , and the collector region  24 . 
   After a conductive layer has been formed or otherwise deposited in the contact hole, a planarization process is carried out until the dielectric  30  is exposed, in order to form contact plugs  32   a ,  32   b , and  32   c  contacting with the base region  28 , the emitter region  22 , and the collector region  24 , respectively. The contact plugs may comprise a metal such as tungsten (W) or copper (Cu) and may further comprise an adhesive liner on the sidewall of the contact holes, such as Ti or Ta, and/or a barrier layer between the metal and the contact hole sidewalls, such as TiN or TaN. Accordingly, the process is terminated. 
   On the other hand, after a polysilicon layer doped with n-type ions has been formed, the n-type ions are diffused to form an emitter region  22  and a collector region  24 . Next, by the emitter electrode pattern  18   a  and the spacer  20   a , a self-aligned base region  28  is formed. The spacer  20   a  secures a distance between the base region  28  and the emitter region  22  that allows a resistance of the base region to be reduced. 
   Furthermore, after the emitter electrode pattern  18   a  and the collector electrode pattern  18   b  have been formed, they are removed. Accordingly, in order to secure a CMP process margin required during a formation process of the contact plug, the dielectric layer can have a relatively small thickness which leads to or enables increased integration of a device. For example, the dielectric layer  30  may have a thickness of from 2500, 3000 or 4000 Å to 5000, 6000 or 7000 Å. 
   In addition, after the emitter electrode pattern  18   a  and the collector electrode pattern  18   b  have been formed, they are removed. Accordingly, a process may be simplified. Moreover, during an etch process for forming the contact plug, it can completely prevent a loss of the polysilicon layer. 
   In the first embodiment of the present invention, after a polysilicon layer doped with n-type ions has been formed, the n-type ions are diffused to form an emitter region and a collector region. Next, through the emitter electrode pattern  18   a  and the spacers, the self-aligned base region is formed. Accordingly, the spacers secure a distance between the base region and the emitter region that allows a resistance of the base region to be reduced. 
   Furthermore, after the emitter electrode pattern and the collector electrode pattern have been formed, they are removed. Accordingly, in order to secure a CMP process margin required during a formation process of the contact plug, the inter layer dielectric can be thinly formed which leads to an integration of a device. 
   In addition, after the emitter electrode pattern and the collector electrode pattern have been formed, they are removed. Accordingly, a process may be simplified. Moreover, during an etch process for forming the contact plug, it can prevent any loss of the polysilicon layer. 
     FIGS. 7 through 12  are cross-sectional views of a bipolar transistor for sequentially describing a method for manufacturing the bipolar transistor according to a second embodiment of the present invention. 
   First, as shown in  FIG. 7 , a substrate  10  (e.g., a p-type silicon substrate) is prepared and/or provided. Here, an n-type buried layer  11  is formed on the substrate  10 , as described above. A first well  12   a  and a second well  12   b  doped with n-type ions are formed in the buried layer  11 , as described above. 
   Next, a device isolation layer  14  for the bipolar transistor is formed in a field region of the substrate  10 . 
   As described above, the device isolation layer  14  functions to divide an active region of the substrate  10  into a first active region for an emitter region and a base region, and second active region for a collector region. 
   Then, a photolithography process and an ion implantation process are performed on the substrate on which the device isolation layer  14  is formed in order to form a third well  17  of a p-type in the first well  12   a  of the first active region. Here, a base region and an emitter will be formed in the first well  12   a.    
   Thereafter, as shown in  FIG. 8 , a p-type doped polysilicon layer  18  and an oxide layer  20  are formed on the resulting object on which the third well  17  is formed, and a photoresist pattern (not shown) for defining a base electrode pattern is formed on the oxide layer. The oxide layer  20  and the polysilicon layer  18  are etched using the photoresist pattern as an etch mask to form a base electrode pattern  21  (which comprises at least two parallel portions spaced apart from each other) on the third well  17 . 
   Subsequently, as shown in  FIG. 9 , after a nitride layer has been deposited on the resulting object on which the base electrode pattern  21  is formed, an etching process such as an etch back (or anisotropic etch process) is carried out to form spacers  19  at sidewalls of the base electrode pattern  21 . 
   As shown in  FIG. 10 , a photo resist pattern  22  is formed on the resulting object on which the base electrode pattern  21  is formed. Here, the spacer  19  is formed at the base electrode pattern  21 . Further, the photoresist pattern  22  functions to expose the third well  17  between the two parallel base electrode pattern portions  21  and the second well  12   b  of the second active region in which a collector region will be defined. Next, ions are implanted therein using the photoresist pattern  22  as a mask to form an emitter region  24  inside the third well  17  and a collector region  16  inside the second well  12   b.    
   The photoresist pattern  22  and the base electrode pattern in which the spacer is formed are used as a self-align ion implantation mask during an ion implantation process for forming the emitter region  24 . 
   Then, as shown in  FIG. 11 , a diffusion process is performed on the resulting object in which the emitter region  24  and the collector region  16  are formed by diffusion of p-type ions doped in the polysilicon layer  18  of the base electrode pattern  21 , so that a base region is formed. Moreover, the diffusion process diffuses and/or activates the n-type ions in the emitter region to form an emitter  24  having a similar depth to that of the base region  26 . 
   The diffusion process can form the emitter region  24  and the base region  26  to have a similar depth using a diffusion coefficient difference of the p-type ions doped in the poly silicon layer  18  of the base electrode pattern and the n-type ions defined in the emitter region  24 . 
   Finally, as shown in  FIG. 12 , a dielectric  27  is formed on an entire surface of the substrate in which the emitter region  24  and the base region  26  are defined. The dielectric  27  may comprise a silicon oxide (which may be undoped or doped with fluorine, boron and/or phosphorous, carbon, etc.). Further, a photoresist pattern (not shown) is formed on the dielectric  27 . An etch process is performed using the photoresist pattern us a mask to form a contact hole exposing the polysilicon layer  18 , the emitter region  24 , and the collector region  16 . 
   After a conductive layer has been formed in the contact hole as described above, a planarization process is carried out until the dielectric  27  is exposed, in order to form contact plugs  28   a ,  28   b , and  28   c  in contact with the polysilicon layer  18  of the base electrode pattern, the emitter region  24 , and the collector region  24 , respectively. 
   On the other hand, after the polysilicon layer doped with p-type ions has been formed, the p-type ions are diffused to form the base region  26 . Next, through the emitter electrode pattern  21  and the spacer  19 , the self-aligned emitter region  24  is formed. The spacer  19  secures a distance between the base region  26  and the emitter region  24  that allows a resistance of the base region to be reduced. 
   Furthermore, in order to secure a CMP process margin during formation of the contact plug using the base electrode pattern  21 , the interlayer dielectric can be thinly formed, which improves an integration of the device. 
   In addition, because the polysilicon layer may be patterned and etched to form only the emitter electrode, the process may be simplified. Moreover, since only the emitter electrode is formed from polysilicon or other patterned conductor, during an etch process for forming the contact plug, the loss of the polysilicon layer can be reduced in comparison with the case where the emitter electrode and the base electrode are formed from polysilicon. 
   In the second embodiment of the present invention, after the base electrode pattern has been formed of polysilicon layer doped with n-type ions, the n-type ions are diffused to form a base region. Next, through the base electrode pattern and the spacers, the self-aligned emitter region is formed. Accordingly, the spacers secure a distance between the base region  26  and the emitter region  24  that allows a resistance of the base region to be reduced. 
   So as to secure a CMP process margin during formation of the contact plug using only the base electrode pattern, the interlayer dielectric can be thinly formed which allows an integration of a device. 
   Because the polysilicon layer is patterned and etched to form only the emitter electrode, the process may be simplified. Moreover, since only the emitter electrode is formed, during an etch process for forming the contact plug, it can reduce the loss of the polysilicon layer constituting the electrodes in comparison with the case where the emitter electrode and the base electrode are formed. 
   It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.
A method for manufacturing a bipolar transistor includes: forming a device isolation layer on a semiconductor substrate having first and second well regions of a first conductivity therein; implanting ions of a second conductivity in the first well to form a third well; forming and patterning a conductive layer on the semiconductor substrate; forming an emitter electrode pattern on the third well region, and forming a collector electrode pattern on the second well region; forming spacers at sidewalls of the emitter and collector electrode patterns; performing a diffusion process to form an emitter region of a first conductivity on the third well region and to form a collector region of a first conductivity on the second well region; implanting ions of a second conductivity in the third well region to form a base region; and removing the emitter electrode and collector region patterns.