Abstract:
This invention relates to a method for forming a metal oxide semiconductor type field effect transistor (MOSFET), more particularly, to the method for forming the MOSFET by forming a gate and a spacer in a trench. The present invention is used to form the gate and the spacer of the MOSFET in the trench which is preformed in the substrate to reduce the junction depth of the source/drain region. The present invention also can reduce the defects in the drain induced barrier lowering and the punch-through leakage to avoid the spiking leakage defects in the back-end process.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to a method for forming a metal oxide semiconductor type field effect transistor (MOSFET), more particularly, to the method for forming the MOSFET by forming a gate and a spacer in a trench. The present invention uses the gate and the spacer, which are formed in the trench of the substrate, of the MOSFET to reduce the junction depth of the source/drain region. The present invention also can reduce the defects in the drain induced barrier lowering (DIBL) and the punch-through leakage to avoid the spiking leakage defects in the back-end process.  
           [0003]    2. Description of the Prior Art  
           [0004]    In the continual improvement of semiconductor integrated circuit fabrication techniques, the number of devices that can be packed onto a semiconductor chip has increased greatly, while the geometric dimensions of the individual device has been markedly reduced. In today&#39;s fabricating process, the feature size has shrunk into the sub-micron range. In such high-density chips, each of the elements&#39; volume must be reduced suitably to decrease the defects of the semiconductor elements, whose volume is reduced.  
           [0005]    Referring to FIG. 1, the traditional method for forming the MOSET is to form a gate  20  on a substrate  10 . The gate  20  comprises a gate oxide layer  22 . Referring to FIG. 2, the N type ions or the P type ions, which are needed in the process, are implanted into the substrate which is on both sides of the gate by using the ions implantation method to form the lightly doped drain (LDD)  30  region. Referring to FIG. 3, the spacer  40  is formed on sidewalls of the gate  20 . The material of the spacer  40  is most the insulating material, such as silicon nitride. The main function of the spacer  40  is to reduce the leakage defect of the gate  20 . Referring to FIG. 4, the N type ions or the P type ions, which are needed in the process, are implanted into the substrate by using the ions implantation method to form the source/drain  50  region. The source/drain region is located on both sides of the LDD  30  region. Referring to FIG. 5, a silicide layer  60  is formed on the gate  20  and the source/drain region  50  by using the salicide process. Then the traditional MOSFET process is finished.  
           [0006]    When the volume of the semiconductor is reduced, the volume of each element is following reduced. When the volume of the MOSFET is reduced, the volume of each element of MOSFET, such as the gate, the spacer or the source/drain region, is also following reduced. When the source/drain region is reduced, the junction depth of the source/drain region is also following reduced. But in the traditional MOSFET structure, the spiking leakage defect and the trade off defect will be caused in the following process after forming the silicide layer if the junction depth of the source/drain region is too shallow. The DIBL defect and the punch-through leakage defect will be caused if the junction depth of the source/drain region is too deep. Therefore, when the volume of the semiconductor element is smaller and smaller, the qualities and yields of the semiconductor elements will be reduced and the production costs will be increased if the traditional method is still used to form the MOSFET.  
         SUMMARY OF THE INVENTION  
         [0007]    In accordance with the above-mentioned invention backgrounds, the traditional method can not form the MOSFET which has the smaller volume and the better efficacy. The present invention provides a method for forming the MOSFET by forming the gate and the spacer in the trench which is in the substrate to reduce the DIBL defect.  
           [0008]    The second objective of this invention is to reduce the punch-through defect by forming the gate and the spacer in the trench which is in the substrate to form the MOSFET.  
           [0009]    The third objective of this invention is to reduce the spiking leakage defect by forming the gate and the spacer in the trench which is in the substrate to form the MOSFET.  
           [0010]    The fourth objective of this invention is to reduce the trade off defect by forming the gate and the spacer in the trench which is in the substrate to form the MOSFET.  
           [0011]    It is a further objective of this invention is to increase the qualities and the yields of the semiconductor elements by forming the gate and the spacer in the trench which is in the substrate to form the MOSFET.  
           [0012]    In according to the foregoing objectives, the present invention provides a method for forming the MOSFET by forming the gate and the spacer in the trench which is in the substrate to avoid the DIBL defects and the punch-through leakage defects being caused in the MOSFET, whose volume is reduced, as a result of the too shallow or the too deep junction depth. The present invention can also avoid the spiking leakage defect and trade off defect as a result of the too shallow or the too deep junction depth. The present invention can further increase the qualities and the yields of the semiconductor elements. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    In the accompanying drawing forming a material part of this description, there is shown:  
         [0014]    [0014]FIG. 1 shows a diagram in forming a gate on a substrate of a wafer;  
         [0015]    [0015]FIG. 2 shows a diagram in forming the lightly doped drain region in the substrate;  
         [0016]    [0016]FIG. 3 shows a diagram in forming the spacers on the sidewalls of the gate;  
         [0017]    [0017]FIG. 4 shows a diagram in forming the source/drain region in the substrate;  
         [0018]    [0018]FIG. 5 shows a diagram in forming the silicide layers on the gate and source/drain region;  
         [0019]    [0019]FIG. 6 shows a diagram in forming a trench in the substrate;  
         [0020]    [0020]FIG. 7 shows a diagram in forming a gate on the bottom of the trench;  
         [0021]    [0021]FIG. 8 shows a diagram in forming a spacer layer on the gate and the substrate and filling of the trench;  
         [0022]    [0022]FIG. 9 shows a diagram in forming the spacers on the sidewalls of the gate and filling of the trench;  
         [0023]    [0023]FIG. 10 shows a diagram in forming the source/drain region and the source/drain extended region in the substrate;  
         [0024]    [0024]FIG. 11 shows a diagram in forming a metal layer on the gate, the spacers, and the source/drain region; and  
         [0025]    [0025]FIG. 12 shows a diagram in forming the silicide layers on the gate and the source/drain region.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0026]    The foregoing aspects and many of the intended advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:  
         [0027]    The present invention is to form the MOSFET by forming the gate and the spacer on a trench of the substrate. Referring to FIG. 6, a wafer, which comprises a substrate  100 , is provided at first. Then the partial substrate  100  is removed to form a trench  120  in the substrate  100 . The width and the depth of the trench  120  are different following the needs of the process. The etching process is most used to remove the partial substrate  100 . The silicon substrate is most used to be the material of the substrate  100 . Referring to FIG. 7, a gate  200  is formed on the bottom of the trench  120 . The gate  200  comprises a gate oxide layer  220 . The depth range of the trench is about 50% to 80% of the thickness of the gate. The width range of the trench is about 0.2 μm to 0.35 μm. Following the volume of the semiconductor elements being reduced, the depth and the width of the trench are smaller and smaller. The volume of the gate  200  is reduced following the volume of the MOSFET being reduced. Referring to FIG. 8, then a spacer layer  300  is formed on the gate  200  and the substrate  100  and is filled of the trench. the insulating material is most used to be the material of the spacer layer  300 , such as silicon nitride.  
         [0028]    Referring to FIG. 9, the partial spacer layer  300  is removed to form the spacer  310  on the sidewalls of the gate  200 . The main function of the spacer  310  is to reduce the leakage defect of the gate  200  and is located on the sidewalls of the gate  200 . The spacer  300  is filled of the trench  120 . The etching method is most used to remove the partial spacer layer  300 . Referring to FIG. 10, then the N type ions or the P type ions, which are needed in the process, are implanted into the substrate, which is on both sides of the spacer, by using the ions implantation method to form the source/drain  400  region. In the traditional method to form the MOSFET, the lightly doped drain region process is most used to avoid the MOSFET having the short channel effects. But after the volume of the MOSFET is reduced, the lightly doped drain region is also following reduced. In the lightly doped drain region process, the range of the lightly doped drain region can be controlled. But in the following high temperature process, the ions, which are in the lightly doped drain region, will move to other regions by the ways of diffusion and permeation to increase the range of the lightly doped drain region and to cause the short channel effect. Therefore, the ions, which are needed in the process, are implanted directly to form the source/drain region  400  in the present invention. Then the first rapid thermal process (RTP) is proceed to be the anneal process. The depth of the ions and the temperature of the RTP process are controlled to make the ions, which are implanted, move to the suitable place by the ways of diffusion and permeation to form the source/drain extended region  420 . The function of the source/drain extended region  420  can replace the lightly doped drain region. The temperature of the first rapid thermal process is about 950° C. to 1050° C.  
         [0029]    Referring to FIG. 1  1 , a metal layer  500  is formed on the gate  200 , spacer  310 , and the source/drain region  400 . The chemical vapor deposition method or the direct current magnetron sputtering method is most used to form the metal layer  500 . Then the wafer is placed into the chamber to proceed the second rapid thermal process. The metal layer  500  will react with the silicon, which is at the contact region, to form the silicide layer. The using temperature of the silicide process is about 500 to 700° C. The structure of the metal silicide which is formed in the second rapid thermal process is a metastable C-49 phase structure with higher resistivity. Referring to FIG. 12, the unreacted and the remained metal layer  500  is removed by applying the RCA cleaning method. Therefore, the silicide layers  510  are existed on the top of the gate  200  and the source/drain region  400 . Finally, the third rapid thermal process is performed to transform higher resistivity of the C-49 phase silicide structure into lower resistivity of the C-54 phase silicide structure. The using temperature of the third rapid thermal process is about 750 to 850° C. The material of the metal layer  500  can be titanium, cobalt, and platinum. Titanium is usually used to be the material of the metal layer  500 .  
         [0030]    Titanium is the most common used metallic material for the current salicide process. Basically, titanium is a fine oxygen gettering material, where under an appropriate temperature titanium and silicon at MOSFET device source/drain and gate regions are easily mutually diffused to form a titanium silicide with very low resistance.  
         [0031]    The MOSFET, which is formed by using the present invention method, can control the junction depth of the source/drain more accurately and the error in range of the junction depth is greater. Therefore, the spiking leakage defect and the trade off defect will not be caused in the following process after forming the silicide layer if the junction depth of the source/drain region is too shallow. The DIBL defect and the punch-through leakage defect will also not be caused if the junction depth of the source/drain region is too deep. The present invention method can reduce the volume of the semiconductor elements successfully and also can not affect the efficiency of the semiconductor elements. Therefore, the present invention method can increase the qualities and the yields of the semiconductor elements.  
         [0032]    In accordance with the present invention, the present invention provides a method for forming the MOSFET by forming the gate and the spacer in the trench which is in the substrate to avoid the DIBL defects and the punch-through leakage defects being caused in the MOSFET, whose volume is reduced, as a result of the too shallow or the too deep junction depth. The present invention can also avoid the spiking leakage defect and trade off defect as a result of the too shallow or the too deep junction depth. The present invention can further increase the qualities and the yields of the semiconductor elements.  
         [0033]    Although specific embodiments have been illustrated and described, it will be obvious to those skilled in the art that various modifications may be made without departing from what is intended to be limited solely by the appended claims.