Abstract:
Field effect transistors include a semiconductor substrate having a channel region of first conductivity type therein extending adjacent a surface thereof. Source and drain regions of second conductivity type are also provided at opposite ends of the channel region. The source and drain regions extend in the semiconductor substrate and form P-N rectifying junctions with the channel region. A gate electrode extends on the channel region and comprises a first electrically conductive material having a first work function. A first sub-gate electrode extends on the channel region and comprises a second electrically conductive material having a second work function that is unequal to the first work function. The second electrically conductive material is preferably selected so that a difference between the second work function and a work function of the channel region is sufficient to form an inversion-layer in a portion of the channel region extending opposite the first sub-gate electrode when the first sub-gate electrode is at a zero potential bias relative to the channel region.

Description:
REFERENCE TO PRIORITY APPLICATION  
       [0001]    This application is a divisional of U.S. application Ser. No. 09/654,859, filed Sep. 5, 2000, the disclosure of which is hereby incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to a semiconductor device and a fabricating method thereof, and more particularly, to a submicron channel MOSFET and a fabricating method thereof.  
         BACKGROUND OF THE INVENTION  
         [0003]    In general, the length of a channel must be shortened to reduce the size of a MOSFET. Hence, various approaches have been conducted to develop MOSFETs having a submicron channel. However, when a MOSFET becomes a submicron channel, that is, a short channel, the unit devices (unit MOSFETs) of a highly-integrated circuit have different distributions of impurities in a channel region, leading to a problem in which the unit devices have different threshold voltages. Also, the junction depth of a source/drain region must be thin while a MOSFET becomes a short channel.  
           [0004]    The problem in which the unit devices of a highly-integrated circuit have different threshold voltages has been solved to some extent by adopting a double-sided gate or a back plane gate. This problem would not be solved completely as far as there are impurities in a channel region, since the difference in threshold voltage between unit devices is caused by the impurities in the channel region.  
           [0005]    The problem in that a thin source/drain region must be formed has been solved by using a thin electrically-formed inversion layer as a source/drain region, since a thin source/drain region cannot be not formed when ion implantation is used.  
           [0006]    [0006]FIG. 1 is a cross-sectional view of a conventional submicron channel MOSFET. To be more specific, a thin oxide film  107   a  and a thick oxide film  107   b  are formed on a P-type substrate  101  on which a source region  103  and a drain region  105  have been formed. A main gate  109  is formed on the thin oxide film  107   a , and sub-gates  111  are formed on the thick oxide film  107   b . In the conventional submicron channel MOSFET using the main gate  109  and the sub-gates  111  as described above, inversion layers  113  are formed under the sub-gates  111  by applying voltage to the main gate  109  and the sub-gates  111 , and the formed inversion layers  113  are used as a thin source/drain.  
           [0007]    However, the conventional submicron channel MOSFET of FIG. 1 has a problem associated with a process, in that a special pad must be made to apply voltage to the sub-gates  111 .  
           [0008]    Also, in the conventional extra-small channel MOSFET of FIG. 1, a high voltage must be applied to the sub-gates to form inversion layers  113 , that is, the thin source and drain.  
         SUMMARY OF THE INVENTION  
         [0009]    An object of the present invention is to provide a submicron channel metal oxide semiconductor field effect transistor (MOSFET) in which a thin source/drain region can be formed under sub-gates without formation of a special pad, and by which non-uniformity of threshold voltage between the unit devices of a highly-integrated circuit can be solved.  
           [0010]    Another object of the present invention is to provide a method of fabricating the submicron channel MOSFET.  
           [0011]    The first object of the present invention is achieved by a submicron channel metal oxide semiconductor field effect transistor (MOSFET) according to an embodiment of the present invention, wherein N +  source/drain regions are formed near the surface of a P −  silicon substrate, having a channel therebetween, a gate dielectric film is formed on the channel, a main gate is formed on the gate dielectric film on the channel, and sub-gates having a smaller work function than the main gate are formed on the gate dielectric film and on the sidewalls of the main gate covered with a dielectric film.  
           [0012]    The main gate can be formed of P +  polycrystalline silicon, and the sub-gates can be formed of N +  polycrystalline silicon. The main gate can be formed of SiGe or a metal having a work function that is smaller than that of P +  polycrystalline silicon and greater than that of N +  polycrystalline silicon, and the sub-gates can be formed of N +  polycrystalline silicon. The sub-gates can be formed of a conductive material having a work function that is equal to or smaller than that of N +  polycrystalline silicon, and the main gate can be formed of P +  polycrystalline silicon.  
           [0013]    In the submicron channel MOSFET of the present invention as described above, there is a difference in work function between a main gate and sub-gates, and the main gate is formed of P +  polycrystalline silicon on a P −  substrate, so that the concentration of impurities for controlling a threshold voltage implanted into a channel region under the main gate can be reduced as much as possible. This leads to a minimization of the difference in threshold voltage between the unit devices of a highly-integrated circuit due to the non-uniformity of the impurities for controlling a threshold voltage.  
           [0014]    Also, in the submicron channel MOSFET of the present invention, thin inversion layers used as source/drain regions under the sub-gates are formed because of the difference in work function between the main gate and the sub-gates. Furthermore, in the submicron channel MOSFET of the present invention, the sub-gates are formed of N +  polycrystalline silicon, and a P −  silicon substrate having a low concentration is used, so that thin inversion layers are formed under the sub-gates. Hence, voltage does not need to be applied to the sub-gates, so that a special metal pad does not need to be formed.  
           [0015]    The submicron channel MOSFET described above denotes an N-MOSFET. However, the contents described above can be applied to P-MOSFETs.  
           [0016]    In a submicron channel MOSFET according to another embodiment of the present invention to achieve the first object of the present invention, P +  source/drain regions are formed near the surface of an N −  silicon substrate, having a channel therebetween. A gate dielectric film is formed on the channel, and a main gate is formed on the gate dielectric film on the channel. Sub-gates having a greater work function than the main gate are formed on the gate dielectric film and on the sidewalls of the main gate covered with a dielectric film. Here, inversion layers formed under the sub-gates act as thin source/drain regions.  
           [0017]    The main gate can be formed of N +  polycrystalline silicon, and the sub-gates can be formed of P +  polycrystalline silicon. The main gate can be formed of SiGe or a metal having a work function that is smaller than that of P +  polycrystalline silicon and greater than that of N +  polycrystalline silicon, and the sub-gates can be formed of P +  polycrystalline silicon. The sub-gates can be formed of a conductive material having a work function that is equal to or smaller than that of P +  polycrystalline silicon, and the main gate can be formed of N +  polycrystalline silicon.  
           [0018]    The second object of the present invention is achieved by a method of fabricating a submicron channel MOSFET, wherein a gate dielectric film is formed on a P −  silicon substrate, a main gate is formed on the gate dielectric film, a dielectric film is formed to surround the main gate, sub-gates having a smaller work function than the main gate are formed on the dielectric film on the sidewalls of the main gate, and N +  source/drain regions are formed by implanting N-type impurities into the entire surface of the P −  silicon substrate on which the main gate, the dielectric film and the sub-gates are formed. Here, inversion layers formed under the sub-gates act as thin source/drain regions.  
           [0019]    The main gate can be formed of P +  polycrystalline silicon, and the sub-gates can be formed of N +  polycrystalline silicon. After the sub-gates are formed, a P 0  region can be formed near the N +  source/drain regions under the sub-gates by tilt ion implanting P-type impurities toward the sidewalls of the sub-gates. Before the gate dielectric film is formed, a P 0  region having a higher doping concentration than the P −  silicon substrate can be formed within the P −  silicon substrate.  
           [0020]    The second object of the present invention is also achieved by a method of fabricating a submicron channel MOSFET, wherein a gate dielectric film is formed on an N −  silicon substrate, a main gate is formed on the gate dielectric film, a dielectric film is formed to surround the main gate, sub-gates having a greater work function than the main gate are formed on the dielectric film on the sidewalls of the main gate, and P +  source/drain regions are formed by implanting P-type impurities into the entire surface of the N −  silicon substrate on which the main gate, the dielectric film and the sub-gates are formed. Here, inversion layers formed under the sub-gates act as thin source/drain regions.  
           [0021]    Before the gate dielectric film is formed, an N 0  region having a higher doping concentration than the N −  silicon substrate can be formed within the N −  silicon substrate. The main gate can be formed of N +  polycrystalline silicon, and the sub-gates can be formed of P +  polycrystalline silicon. After the sub-gates are formed, an N 0  region can be formed near the P +  source/drain regions under the sub-gates by tilt ion implanting N-type impurities toward the sidewalls of the sub-gates. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    The above objects and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which:  
         [0023]    [0023]FIG. 1 is a cross-sectional view of a conventional submicron channel metal oxide semiconductor field effect transistor (MOSFET);  
         [0024]    [0024]FIG. 2 is a cross-sectional view of a submicron channel MOSFET according to a first embodiment of the present invention;  
         [0025]    [0025]FIG. 3 is a cross-sectional view of a submicron channel MOSFET according to a second embodiment of the present invention;  
         [0026]    [0026]FIGS. 4 through 7 are cross-sectional views illustrating a method of fabricating the submicron channel MOSFET of FIG. 2; and  
         [0027]    [0027]FIGS. 8 through 11 are cross-sectional views illustrating a method of fabricating the submicron channel MOSFET of FIG. 3. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0028]    The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the thickness of layers and regions are exaggerated for clarity. It will also be understood that when a layer is referred to as being “on” another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may also be present. Moreover, the terms “first conductivity type” and “second conductivity type” refer to opposite conductivity types such as N or P-type, however, each embodiment described and illustrated herein includes its complementary embodiment as well. Like numbers refer to like elements throughout.  
         [0029]    A submicron channel MOSFET according to a first embodiment of the present invention shown in FIG. 2 is an N-MOSFET. To be more specific, a P 0  region  503  is formed on a P −  silicon substrate  501  to have a higher doping concentration than the P −  silicon substrate  501 . The P 0  region  503  is formed to prevent a short channel effect by improving drain induced barrier lowering (DIBL).  
         [0030]    N +  source/drain regions  505  are formed near the surface of the P silicon substrate  501 , and a P 0  halo ion implantation region  507  is formed below one side of each of the N +  source/drain regions  505 . The P 0  halo ion implantation region  507  is formed to suppress punch through between the two N +  source/drain regions  505 .  
         [0031]    A gate dielectric film  509 , for example, a silicon oxide film, is formed on the entire surface of the P −  silicon substrate  501  on which the N +  source/drain regions  505  are formed. A main gate  511  is formed on the gate dielectric film  509  between the N +  source/drain regions  505 . A thin dielectric film  513 , for example, a silicon oxide film, which covers the main gate  511 , is formed on the gate dielectric film  509  to a thickness of 600 Å. Sub-gates  515  having a smaller work function than the main gate  511  are formed in spacer shapes on the thin dielectric film  513  on the sidewalls of the main gate  511 . The main gate  511  can be formed of P +  polycrystalline silicon, and the sub-gates  515  can be formed of N +  polycrystalline silicon.  
         [0032]    In the submicron channel N-MOSFET of the present invention having such a structure, there is a difference in a work function between the main gate  511  and the sub-gates  515 , and the main gate  511  is formed of P +  polycrystalline silicon on the P −  substrate  501 , so that the concentration of impurities for controlling a threshold voltage implanted into a channel region under the main gate  511  can be reduced as much as possible. The reduction of the concentration of impurities for controlling a threshold voltage implanted into a channel region can increase the mobility of a carrier and can minimize a change in the threshold voltage between the unit devices of a highly-integrated circuit due to the non-uniformity of the impurities for controlling a threshold voltage. The main gate  511  can be formed of P +  polycrystalline silicon in this embodiment, but can be formed of silicon germanium (SiGe) or a metal having a work function that is smaller than that of P +  polycrystalline silicon and greater than that of N +  polycrystalline silicon, for example, Ag or Au.  
         [0033]    Also, in the submicron channel N-MOSFET of the present invention, the main gate  511  and the sub-gates  515  have different work functions, so that the threshold voltage under the main gate  511  is different from the threshold voltage under the sub-gates  515 . Because of the difference in work function between the main gate  511  and the sub-gates  515 , the thin inversion layers  517  formed under the sub-gates  515  are used as a source/drain region.  
         [0034]    Furthermore, in the submicron channel N-MOSFET of the present invention, the sub-gate  515  is formed of N +  polycrystalline silicon, and the P −  silicon substrate  501  having a low concentration is used, so that thin inversion layers  517  are formed under the sub-gates  515 . Accordingly, voltage does not need to be applied to the sub-gates  515 , so that the sub-gates  515  can be formed by a general sidewall process without the formation of a special metal pad.  
         [0035]    Also, when voltage is applied to the main gate  511 , the sub-gates  515  are floated, and thus the electrostatic potential of the sub-gates  515  (floating gates) is increased due to electrostatic capacity coupling, resulting in the smooth formation of the thin inversion layers  517 . The thin inversion layers  517  smoothly formed in this way can be used as source drain regions. The sub-gates  515  are formed of N +  polycrystalline silicon in this embodiment, but can be formed of a conductive material having a work function that is equal to or smaller than that of N +  polycrystalline silicon.  
         [0036]    Also, in the submicron channel MOSFET of the present invention, the thin dielectric film  513  is provided between the main gate  511  and the sub-gates  515  to distinguish between the two gates, so that the main gate  511  and the sub-gates  515  can be formed of various materials.  
         [0037]    Also, the resistance under the sub-gates  515  can be reduced by forming an N region (not shown), that is too thin to affect DIBL, under the sub-gates  515 .  
         [0038]    [0038]FIG. 3 is a cross-sectional view of a submicron channel MOSFET according to a second embodiment of the present invention. The submicron channel MOSFET of FIG. 3 is a P-MOSFET.  
         [0039]    To be more specific, an N 0  region  703  is formed on an N −  silicon substrate  701  to have a higher doping concentration than the N −  silicon substrate  701 . The N 0  region  703  is formed to prevent a short channel effect by improving DIBL. P +  source/drain regions  705  are formed near the surface of the N −  silicon substrate  701 , and an N 0  halo ion implantation region  707  is formed below one side of each of the P +  source/drain regions  705 . The N 0  halo ion implantation region  707  is formed to suppress punch through between the two P +  source/drain regions  705 .  
         [0040]    A gate dielectric film  709  is formed on the entire surface of the N −  silicon substrate  701  on which the P +  source/drain regions  705  are formed. A main gate  711  is formed on the gate dielectric film  709 , for example, a silicon oxide film, between the P +  source/drain regions  705 . A thin dielectric film  713 , for example, a silicon oxide film, which covers the main gate  711 , is formed on the gate dielectric film  709  to a thickness of 600 Å.  
         [0041]    In contrast to FIG. 2, sub-gates  715  having a greater work function than the main gate  711  are formed in spacer shapes on the thin dielectric film  713  on the sidewalls of the main gate  711 , in order to manufacture the P-channel MOSFET. The main gate  711  can be formed of N +  polycrystalline silicon, and the sub-gates  715  can be formed of P +  polycrystalline silicon.  
         [0042]    In the submicron channel P-MOSFET of the present invention having such a structure, there is a difference in a work function between the main gate  711  and the sub-gates  715 , and the main gate  711  can be formed of N +  polycrystalline silicon on the N −  substrate  701 , so that the concentration of impurities for controlling a threshold voltage implanted into a channel region under the main gate  711  can be reduced as much as possible. The reduction of the concentration of impurities for controlling a threshold voltage implanted into a channel region can increase the mobility of a carrier and can minimize a change in the threshold voltage between the unit devices of a highly-integrated circuit due to the non-uniformity of the impurities for controlling a threshold voltage. The main gate  711  can be formed of N +  polycrystalline silicon in this embodiment, but can be formed of silicon germanium (SiGe) or a metal having an work function that is smaller than that of P +  polycrystalline silicon and greater than that of N +  polycrystalline silicon, for example, Al or Mg.  
         [0043]    Also, in the submicron channel P-MOSFET of the present invention, the main gate  711  and the sub-gates  715  have different work functions, so that the threshold voltage under the main gate  711  is different from the threshold voltage under the sub-gates  715 . Because of the difference in work function between the main gate  711  and the sub-gates  715 , the thin inversion layers  717  formed under the sub-gates  715  are used as a source/drain region.  
         [0044]    Furthermore, in the submicron channel P-MOSFET of the present invention, the sub-gate  715  is formed of P +  polycrystalline silicon, and the N −  silicon substrate  701  having a low concentration is used, so that the thin inversion layers  717  are formed under the sub-gates  715 . Accordingly, voltage does not need to be applied to the sub-gates  715 , so that the sub-gates  715  can be formed by a general sidewall process without the formation of a special metal pad.  
         [0045]    Also, when voltage is applied to the main gate  711 , the sub-gates  715  are floated, and thus the electrostatic potential of the sub-gates  715  (floating gates) is increased due to electrostatic capacity coupling, resulting in the smooth formation of the thin inversion layers  717 . The thin inversion layers  717  smoothly formed in this way can be used as source/drain regions. The sub-gates  715  are formed of P +  polycrystalline silicon in this embodiment, but can be formed of a conductive material having a work function that is equal to or smaller than that of P +  polycrystalline silicon.  
         [0046]    Also, in the submicron channel MOSFET of the present invention, the thin dielectric film  713  is provided between the main gate  711  and the sub-gates  715  to distinguish between the two gates, so that the main gate  711  and the sub-gates  715  can be formed of various materials.  
         [0047]    Also, the resistance under the sub-gates  715  can be reduced by forming a P region (not shown), that is too thin to affect DIBL, under the sub-gates.  
         [0048]    In a process for fabricating a conventional P-MOSFET, boron ions are implanted to adjust a threshold voltage to a desired value, leading to easy occurrence of punch through in the P-MOSFET. However, in the P-MOSFET of the present invention, additional ion implantation for adjusting a threshold voltage is not required since a low concentration substrate is used, so that punch through is prevented.  
         [0049]    [0049]FIGS. 4 through 7 are cross-sectional views illustrating a method of fabricating the submicron channel MOSFET of FIG. 2. Referring to FIG. 4, a P 0  region  503  having a higher doping concentration than a P −  silicon substrate  501  is formed on the P −  silicon substrate  501  to suppress a short channel effect by improving DIBL. A gate dielectric film  509  is formed on the P −  silicon substrate  501 . Then, a main gate  511  is formed of P +  polycrystalline silicon to a thickness of 1100 Å on the gate dielectric film  509  by a photo-etching process. P +  polycrystalline silicon forming the main gate  511  is formed by forming a polycrystalline silicon film on the P −  silicon substrate  501  and then implanting boron at a 1.0×10 15  cm −2  dose with 10 KeV energy. Since the main gate  511  is formed of P +  polycrystalline silicon and the P −  silicon substrate  501  is used, channel doping can be reduced as much as possible, and thus the mobility of a carrier can be significantly increased. The main gate  511  can be formed of SiGe or a metal having a work function that is smaller than that of P +  polycrystalline silicon and greater than that of N +  polycrystalline silicon, for example, Ag or Au.  
         [0050]    Referring to FIG. 5, a thin dielectric film  513 , for example, a silicon oxide film, which surrounds the main gate  511 , is formed to a thickness of 600 Å. Then, sub-gates  515  are formed of N +  polycrystalline silicon having a smaller work function than the main gate  511 , on the sidewalls of thin dielectric film  513 . The sub-gates  515  are formed to a thickness of 500 to 1500 Å. N +  polycrystalline silicon forming the sub-gates  515  is formed by implanting a 1.0×10 15  cm −2  dose of arsenic (As) with 10 KeV energy into a polycrystalline silicon film. The sub-gates  515  and the main gate  511  have different work functions, so that the threshold voltage under the sub-gates  515  is different from that under the main gate  511 .  
         [0051]    In particular, since the sub-gates  515  are formed of N +  polycrystalline silicon, and a P −  silicon substrate having a low concentration is used, inversion layers are formed under the sub-gates  515 . Accordingly, the inversion layers are formed without applying voltage to the sub-gates  515 , so that the sub-gates  515  can be formed by an existing sidewall process without formation of a special metal pad.  
         [0052]    When voltage is applied to the main gate  511 , the sub-gates  515  are floated, and thus the electrostatic potential of the floating gates is increased due to electrostatic capacity coupling, leading to smoother formation of inversion layers. The sub-gates  515  can be formed of a conductive material having a work function that is equal to or smaller than that of N +  polycrystalline silicon.  
         [0053]    Referring to FIG. 6, P-type impurities  516  are tilt ion implanted into the sidewalls of the sub-gates  515  to form the P 0  halo ion regions  507  (FIG. 2) under the sub-gates  515 . The P 0  halo ion implantation is performed to prevent a short channel effect by improving the punch through characteristics.  
         [0054]    Referring to FIG. 7, N-type impurities, for example, arsenic (As), are implanted at a 1×10 20  cm −2  dose on the entire surface of the P −  silicon substrate  501  on which the main gate  511 , the thin dielectric film  513  and the sub-gates  515  are formed. Continuously, the P 0  halo ion regions  507  (FIG. 2) and the N +  source/drain regions  505  (FIG. 2) are formed through thermal treatment, thereby completing the formation of the N-MOSFET.  
         [0055]    [0055]FIGS. 8 through 11 are cross-sectional views illustrating a method of fabricating the submicron channel MOSFET of FIG. 3. Referring to FIG. 8, an N 0  region  703  having a higher doping concentration than an N-type substrate  701  is formed on the N −  silicon substrate  701  to suppress a short channel effect by improving DIBL. A gate dielectric film  709  is formed on the N-type substrate  701 . Then, a main gate  711  is formed of N +  polycrystalline silicon to a thickness of 1100 Å on the gate dielectric film  709  by a photo-etching process. N +  polycrystalline silicon forming the main gate  711  is formed by forming a polycrystalline silicon film on the N −  silicon substrate  701  and then implanting arsenic into the polycrystalline silicon film at a 1.0×10 15  cm −2  dose with 5 KeV energy. Since the N −  silicon substrate  701  is used, and the main gate  711  is formed of N +  polycrystalline silicon, channel doping can be reduced as much as possible, and thus the mobility of a carrier can be significantly increased. The main gate  711  can be formed of SiGe or a metal having a work function that is smaller than that of P +  polycrystalline silicon and greater than that of N +  polycrystalline silicon, for example, Al or Mg.  
         [0056]    Referring to FIG. 9, a thin dielectric film  713 , for example, a silicon oxide film, which surrounds the main gate  711 , is formed to a thickness of 600 Å. Then, sub-gates  715  are formed of P +  polycrystalline silicon having a greater work function than the main gate  711 , on the sidewalls of the thin dielectric film  713 . The sub-gates  715  are formed to a thickness of 500 to 1500 Å. P +  polycrystalline silicon forming the sub-gates  715  is formed by implanting a 1.0×10 15  cm −2  dose of boron (B) into a polycrystalline silicon film with 10 KeV energy. The sub-gates  715  and the main gate  711  have different work functions, so that the threshold voltage under the sub-gates  715  is different from that under the main gate  711 .  
         [0057]    In particular, since the sub-gates  715  are formed of P +  polycrystalline silicon, and an N −  silicon substrate having a low concentration is used, inversion layers are formed under the sub-gates  715 . Accordingly, the inversion layers are formed without applying voltage to the sub-gates  715 , so that the sub-gates  715  can be formed by an existing sidewall process without formation of a special metal pad.  
         [0058]    When voltage is applied to the main gate  711 , the sub-gates  715  are floated, and thus the electrostatic potential of the floating gates is increased due to electrostatic capacity coupling, leading to smoother formation of inversion layers. The sub-gates  715  can be formed of a conductive material having a work function that is equal to or greater than that of P +  polycrystalline silicon.  
         [0059]    Referring to FIG. 10, N-type impurities  716  are tilt ion implanted into the sidewalls of the sub-gates  715  to form the P 0  halo ion regions  707  (FIG. 3) under the sub-gates  715 . The P 0  halo ion implantation is performed to prevent a short channel effect by improving the punch through characteristics.  
         [0060]    Referring to FIG. 11, P-type impurities, for example, boron, are implanted into the entire surface of the N −  silicon substrate  701  on which the main gate  711 , the thin dielectric film  713  and the sub-gates  715  are formed. Continuously, the P 0  halo ion regions  707  (FIG. 3) and the P+source/drain regions  705  (FIG. 3) are formed through thermal treatment, thereby completing the formation of the P-MOSFET.  
         [0061]    In an submicron channel MOSFET of the present invention as described above, the mobility of a carrier can be increased by reducing the concentration of impurities for controlling a threshold voltage as much as possible, and can minimize a change in threshold voltage due to the non-uniformity of the impurities for controlling a threshold voltage.  
         [0062]    Also, the submicron channel MOSFET of the present invention includes a main gate and sub-gates and uses inversion layers formed under the sub-gates as a thin source/drain region, thus reducing a short channel effect. Furthermore, in the submicron channel MOSFET of the present invention, the inversion layers can be formed more smoothly because of electrostatic capacity coupling without separate application of voltage to the sub-gates.  
         [0063]    Also, in the submicron channel MOSFET of the present invention, a thin dielectric film is provided between the main gate and the sub-gates to distinguish between the two gates, so that the main gate and the sub-gates can be formed of various materials.  
         [0064]    In the drawings and specification, there have been disclosed typical preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.