Abstract:
A method of depositing thin films has steps of: providing a physical vapor deposition (PVD) vacuum reactor to deposit a first layer; providing at least a metal-organic chemical vapor deposition (MOCVD) vacuum reactor to deposit a second layer on the first layer; and providing a radio frequency (RF) plasma treatment reactor to perform plasma treatment on the second layer.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a method of depositing a Ti/TiN thin film and an apparatus for forming the same and, more particularly, to an apparatus comprising a plasma treatment reactor for depositing a TiN thin film.  
           [0003]    2. Description of the Related Art  
           [0004]    Titanium (Ti) and titanium nitride (TiN) are refractory materials with metallic conductivity and characteristics of thermal stability, excellent mechanical strength and good resistance to corrosion. In the manufacture of very large scale integrated (VLSI) circuitry, Ti and TiN function as, for example, adhesion layers and diffusion barriers. In addition, Ti/TiN bilayers can be formed on a silicon substrate, where the Ti functions as a getter for oxygen at the silicon interface so as to provide a lower and more stable contact resistance. Conventionally, TiN thin film is mainly prepared by physical vapor deposition (PVD) that uses reactive sputtering to form the TiN thin film on the silicon substrate or on the sidewall of a contact hole. However, sputtering produces film with poor step coverage and having columnar structures. In order to solve the problems associated with PVD, chemical vapor deposition (CVD) is employed to deposit the TiN thin film. Generally, CVD for forming Ti-based materials is classified into two types. One type is a method of using inorganic metal-halogen compounds, for example, TiCl 4 /NH 3  as the precursor. This method may, however, form corroded impurities and particles in the thin film. The other method uses organic metal compounds as the precursor, for example, TDMAT and TDEAT, referred to as metal-organic CVD (MOCVD).  
           [0005]    At present, in fabricating the Ti/TiN thin film, a Ti thin film is sputtered and a TiN thin film is then deposited on the TiN thin film by MOCVD. Thereafter, plasma treatment is required to remove carbon and hydrogen impurities existing in the organic precursor. This also reduces the thickness of the TiN thin film and decreases the resistance of the TiN thin film. FIG. 1 is a schematic diagram showing an apparatus  10  for depositing the Ti/TiN thin film according to the prior art. The apparatus  10  comprises a plurality of wafer-loading/wafer-unloading chambers  12 , a PVD vacuum reactor  14 , a first MOCVD vacuum reactor  161 , a second MOCVD vacuum reactor  162 , a cooling chamber  18  and a robotic transporting  20 . In depositing the Ti/TiN thin film in the apparatus  10 , a prepared wafer is loaded in the wafer-loading chamber  12 , and then the prepared wafer is transported to the PVD vacuum reactor  14  by the robotic transporting  20  to deposit a Ti thin film on the prepared wafer. Next, the prepared wafer is transported to the first MOCVD vacuum reactor  161  by the robotic transporting  20  to deposit a first TiN thin film on the Ti thin film, and then a first plasma treatment is performed on the first TiN thin film. Thereafter, the prepared wafer is transported to the second MOCVD vacuum reactor  162  by the robotic transporting  20  to deposit a second TiN thin film on the first TiN thin film, and then a second plasma treatment is performed on the second TiN thin film. Finally, using the robotic transporting  20 , the prepared wafer is transported to the cooling chamber  18  to cool the prepared wafer, and then transported to the wafer-unloading chamber  12 .  
           [0006]    However, two steps of depositing TiN thin film and two steps of plasma treatments are required in the two MOCVD vacuum reactors  161  and  162  respectively, thus pipes of organic precursors and pipes of plasma reacting gases are necessarily disposed in the two MOCVD vacuum reactors  161  and  162  respectively. This makes the MOCVD vacuum reactors  161  and  162  more complicated and expensive. Also, since the plasma treatment is very time-consuming, two steps of plasma treatment prolong the process time of depositing the TiN thin film, resulting in a decrease in the yield of the apparatus  10 . Thus, a novel method and a corresponding apparatus solving the aforementioned problems are called for.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention provides a method of depositing Ti/TiN thin film by using an apparatus that uses a radio frequency (RF) treatment reactor to replace the plasma treatment in the MOCVD vacuum reactor.  
           [0008]    The method of depositing thin films has steps of: providing a physical vapor deposition (PVD) vacuum reactor to deposit a first layer; providing at least a metal-organic chemical vapor deposition (MOCVD) vacuum reactor to deposit a second layer on the first layer; and providing a radio frequency (RF) plasma treatment reactor to perform plasma treatment on the second layer.  
           [0009]    Accordingly, it is an object of the invention to provide the RF plasma treatment reactor to reduce the time that the prepared wafer stays in the MOCVD vacuum reactor.  
           [0010]    It is another object of the invention to increase the throughput of the Ti/TiN thin film.  
           [0011]    Yet another object of the invention is to selectively use equipment relating to plasma treatment in the MOCVD vacuum reactor to decrease the equipment cost.  
           [0012]    These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a schematic diagram showing an apparatus for depositing the Ti/TiN thin film according to the prior art.  
         [0014]    [0014]FIG. 2A is a sectional diagram showing the Ti/TiN thin film in a contact hole structure.  
         [0015]    [0015]FIG. 2B is a sectional diagram showing the Ti/TiN thin film in a via structure  
         [0016]    [0016]FIG. 3 is a schematic diagram showing an apparatus for depositing the Ti/TiN thin film according to the present invention. 
     
    
       [0017]    Similar reference characters denote corresponding features consistently throughout the attached drawings.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]    The present invention provides a method of depositing Ti/TiN thin film and a corresponding apparatus for forming the same, in which a radio frequency (RF) reactor is disposed to function as a plasma treatment to replace the step of plasma treatment in the conventional MOCVD vacuum reactor. In the preferred embodiment, the apparatus is used to deposit a Ti/TiN thin film that may serve as an adhesion layer and a diffusion barrier layer. FIG. 2A is a sectional diagram showing the Ti/TiN thin film in a contact hole structure. A semiconductor silicon substrate  22  comprises a gate electrode  24 , a source/drain region  26 , an inter-metal dielectric (IMD) layer  28 , and a contact hole  30  passing through the ILD layer  28  to expose the source/drain region  26 . In addition, a Ti thin film  32  is deposited on the bottom and sidewall of the contact hole  30 , a TiN thin film  34  is deposited on the Ti thin film  32 , and a metal wiring layer  36  is formed on the TiN thin film to fill the contact hole  30 . The Ti/TiN thin film  32  and  34  are used as adhesion layers to reduce the contact resistance, and also used as diffusion barrier layers to prevent inter diffusion between the metal wiring layer  36  and the silicon substrate  22 .  
         [0019]    [0019]FIG. 2B is a sectional diagram showing the Ti/TiN thin film in a via structure. The semiconductor substrate  22  has a first metal wiring layer  361 , an IMD layer  28 , and a plurality of vias  31  passing through the IMD layer  28  to expose the first metal wiring layer  361 . A Ti thin film  32  is deposited on the bottom and sidewall of the via  31 , a TiN thin film  34  is deposited on the Ti thin film  32 , and a second metal wiring layer  362  is deposited on the TiN thin film to fill the via  31 .  
         [0020]    [0020]FIG. 3 is a schematic diagram showing an apparatus  40  for depositing the Ti/TiN thin film  32  and  34  according to the present invention. In the deposition of the Ti/TiN thin film  32  and  34 , sputtering is used to deposit the Ti thin film  32 , and then MOCVD is used to deposit the TiN thin film  34 , and thereafter plasma treatment is employed to remove the carbon/hydrogen impurities existing in the organic precursors. The plasma treatment also reduces the thickness of the TiN thin film  34 , increases the density of the TiN thin film  34  and decreases the resistivity of the TiN thin film  34 . Accordingly, the apparatus  40  comprises a wafer-loading chamber  42 , a wafer-unloading chamber  42 , a PVD vacuum reactor  44 , a first MOCVD vacuum reactor  461 , a second MOCVD vacuum reactor  462 , an RF plasma treatment reactor  48 , a cooling chamber  52 , and a robotic transporting system  50 .  
         [0021]    In depositing the Ti/TiN thin film  32  and  34 , a prepared wafer is loaded in the wafer-loading chamber  42 , and then the prepared wafer is transported to the PVD vacuum reactor  44  by the robotic transporting system  50  to deposit a Ti thin film  32  on the prepared wafer. Next, the prepared wafer is transported to the first MOCVD vacuum reactor  461  by the robotic transporting system  50  to perform a first-step deposition of the TiN thin film  34  on the Ti tin film  32 , and then a first plasma treatment can be selectively performed on the TiN thin film  34 . Thereafter, the prepared wafer is transported to the second MOCVD vacuum reactor  462  by the robotic transporting system  50  to perform a second-step deposition of the TiN thin film  34 , and then a second plasma treatment can be selectively performed on the TiN thin film  34 . Finally, using the robotic transporting system  50 , the prepared wafer is transported to the cooling chamber  52  to cool down the prepared wafer, and then transported to the wafer-unloading chamber  42 .  
         [0022]    In order to promote the depositing efficiency, the RF plasma treatment reactor  48  is selectively employed to replace the first/second plasma treatments in the first/second MOCVD vacuum reactors  461  and  462 . For example, when the first-step deposition of the TiN thin film  34  is completed in the first MOCVD vacuum reactor  461 , the prepared wafer can be transported to the RF plasma treatment reactor  48  to perform the first plasma treatment. Also, at the same time, another prepared wafer can be transported to the first MOCVD vacuum reactor  461  to perform the first-step deposition of the TiN thin film  34 . Similarly, the RF plasma treatment reactor  48  is provided when the second-step deposition of the TiN thin film  34  is completed in the second MOCVD vacuum reactor  462 . It is noted that the operational sequence between the RF plasma treatment reactor  48 , the first MOCVD vacuum reactor  461  and the second MOCVD reactor  462  depends on process requirements.  
         [0023]    Compared with the prior art, in the apparatus  40  of the present invention, the time-consuming plasma treatment is performed in the RF plasma treatment reactor  48  to reduce the time that the prepared wafer stays in the first MOCVD vacuum reactor  461  and the second MOCVD reactor  462 . Thus, the throughput of the Ti/TiN thin film is increased in the apparatus  40 . Also, since the RF plasma treatment reactor  48 , having a simple structure, replaces the plasma treatment equipment relating to plasma treatment in the MOCVD vacuum reactors  461  and  462  can be omitted to decrease the equipment cost of the MOCVD vacuum reactors  461  and  462 .  
         [0024]    In another preferred embodiment, the apparatus  40  can be applied to the deposition of Ta/TaN thin film. The Ta thin film is deposited in the PVD vacuum reactor  44 , the first-step deposition of the TaN thin film is performed in the first MOCVD vacuum reactor  461 , and the second-step deposition of the TaN thin film is performed in the second MOCVD vacuum reactor  462 .  
         [0025]    It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.