Abstract:
A method for cleaning suicide includes providing a substrate having at least an intergraded silicide and residues, sequentially performing an ammonia hydrogen peroxide (APM) mixture cleaning process and a vaporized hydrochloric acid-hydrogen peroxide mixture (HPM) cleaning process to remove the residues, and performing a sulfuric acid-hydrogen peroxide mixture (SPM) cleaning process to remove residuals of the vaporized HPM cleaning process.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to methods for cleaning self-aligned silicidation (salicide), and more particularly, to methods for cleaning salicide capable of preventing the salicide from further contamination. 
         [0003]    2. Description of the Prior Art 
         [0004]    In semiconductor manufacturing processes, a wafer undergoes several deposition, photolithography, etching, and transporting processes to obtain designed integrated circuit patterns. Therefore a great deal of particles, such as metals, inorganics, and organics, together with native oxide or other contaminants generated by artificial or environmental factors remain on, and contaminate the wafer. Thus, for maintaining the surface cleanliness of the wafer and improving reliability and yield of the wafer, a variety of cleaning methods are conducted in the manufacturing processes. 
         [0005]    Please refer to  FIGS. 1-2 , which are drawings illustrating a conventional method for forming salicide. As shown in  FIG. 1 , a wafer  10  having a substrate  12  and a transistor  14  formed thereon is provided. The transistor  14  comprises a gate dielectric layer  16 , a gate  18 , and lightly doped drains (LDDs)  20  formed in the substrate  12  adjacent to two sides of the gate  18 , spacers  22  formed on sidewalls of the gate  18 , and a source/drain  24 . The salicide is formed after forming the source/drain  24 . A metal layer such as a nickel layer  26  and a TiN layer  28  are deposited on the substrate  12  by thin film deposition. Please refer to  FIG. 2 . Then, a first rapid thermal process (RTP) is performed to make parts of the nickel layer  26  react with silicon of the gate  18  and the source/drain  24  underneath and form intergraded salicide  30 . Following the first RTP, an SPM cleaning process is performed to remove the TiN layer  28  and unreacted nickel. A second RTP is then performed to transform the intergraded salicide into salicide having a lower resistance. 
         [0006]    In the conventional salicide process, a metal such as platinum (Pt) is added with a low concentration ranging from 3-8% to the nickel layer  26  to prevent nickel silicide (NiSi) from agglomeration, which causes junction leakage, during the first RTP. The added Pt improves thermal stability of the NiSi and prevents agglomeration at a relatively higher temperature. To remove the added Pt, an HPM cleaning process is added after the SPM cleaning process to remove the unreacted Pt. The added HPM reacts with the unreacted Pt above the intergraded silicide  30  to form soluble complex ions. 
         [0007]    It should be noted that the HPM, which comprises hydrogen peroxide, vaporized hydrochloric acid, and vaporized chlorine often damages the intergraded salicide  30 , and even erodes and strips the intergraded salicide  30 . Chloride ions and hydrochloric acid of the HPM may react with the remaining agents of the former processes and form salts. The salts remaining on the surface of the wafer and in the wet bench are harmful to the surface cleanliness and cause contamination in the wet bench. In addition, the extremely corrosive and toxic HPM pollutes the environment and endangers operators. 
         [0008]    Therefore, a method that can effectively remove residuals of the HPM cleaning process, improve surface cleanliness of the wafer, and further prevent the cleaned wafer from further contamination is still needed. 
       SUMMARY OF THE INVENTION 
       [0009]    Therefore the present invention provides methods for cleaning salicide for preventing surface cleanliness of the wafer from being influenced by the second contamination. 
         [0010]    According to the claimed invention, a method for cleaning salicide is provided. The method comprises providing a substrate having at least an intergraded silicide and residues formed thereon, performing an ammonia hydrogen peroxide mixture (APM) cleaning process to clean the substrate, performing a vaporized hydrochloric acid-hydrogen peroxide mixture (HPM) cleaning process to clean the substrate again, and performing a sulfuric acid-hydrogen peroxide mixture (SPM) cleaning process to remove residuals of the vaporized HPM cleaning process. 
         [0011]    According to the claimed invention, another method for cleaning salicide is provided. The method comprises providing a substrate having at least an intergraded silicide and remnant metals formed thereon, performing an vaporized HPM cleaning process to remove the remnant metals from the substrate, and performing an SPM cleaning process to remove residuals of the vaporized HPM cleaning process. 
         [0012]    According to the claimed invention, a wet cleaning process is provided. The method comprises performing a vaporized HPM cleaning process, and performing an SPM cleaning process to remove residuals of the vaporized HPM cleaning process. 
         [0013]    According to the present invention, the SPM cleaning process is added after the vaporized HPM cleaning process, the active residuals of the vaporized HPM will be completely removed from the wafer in the SPM cleaning process, therefore the surface cleanliness of the wafer is improved. 
         [0014]    These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIGS. 1-2  are drawings illustrating a conventional method for forming salicide. 
           [0016]      FIGS. 3-5  are drawings illustrating a first preferred embodiment provided by the present invention. 
           [0017]      FIG. 6  is a drawing illustrating remaining particle amounts on a cleaned wafer according to the first preferred embodiment. 
           [0018]      FIG. 7  is a drawing illustrating a second preferred embodiment provided by the present invention. 
           [0019]      FIG. 8  is a drawing illustrating remaining particle amounts on a cleaned wafer according to the second preferred embodiment. 
           [0020]      FIG. 9  is a drawing illustrating steps for forming a salicide. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Please refer to  FIGS. 3-5 , which are drawings illustrating a first preferred embodiment provided by the present invention. As shown in  FIG. 3 , a wafer  50  having a substrate  52  is provided. The substrate  52  has completely undergone a shallow trench isolation (STI) process and a well formation process, and at least a transistor  54  having a gate dielectric layer  56  and a gate  58  is formed in the substrate  52 . The gate dielectric layer  56  comprises a nitric oxide layer, a nitride layer, an oxide layer, or another dielectric layer; the gate  58  comprises conductive material such as doped polycrystalline silicon. The transistor  54  also comprises lightly doped drains (LDDs)  60  formed in the substrate  52  adjacent to two sides of the gate  58 , spacers  62  formed on sidewalls of the gate  58 , and a source/drain  64  formed in the substrate  52  adjacent to the spacers  62 . 
         [0022]    Please refer to  FIGS. 3-4 . A thin film deposition process is performed to form a metal layer  66  and a TiN layer  68  used as a barrier layer on the substrate  52  and the transistor  54 . The metal layer  66  comprises a first metal comprising platinum (Pt), nickel (Ni), cobalt (Co), titanium (Ti) or alloys of the aforementioned metals used to form silicide and, a second metal comprising Pt, Co, palladium (Pd), manganese (Mn), tantalum (Ta), ruthenium (Ru) or alloys of the aforementioned metals in a low concentration. The second metal is in a concentration of 3-8% (wt %) and is used to improve a thermal stability of the salicide and to prevent the salicide from agglomeration which increases contact resistance and junction leakage. In the first preferred embodiment, the first metal is Ni and the second metal is Pt. However, in a modification of the first preferred embodiment, the first metal is not limited to Ni, but can be Co or Pt; and, the second metal used to improve thermal stability is not limited to Pt, but can also be Pd, Mo, Ta, or Ru. Then, a first rapid thermal process (RTP) is performed to make the nickel layer  66  react with silicon of the gate  58  and the source/drain  64  and to form intergraded salicides  70 . These processes are well known to those skilled in the art and further detailed description is therefore omitted here for brevity. 
         [0023]    Please refer to  FIG. 5 . For removing unreacted Ni and other residues, the wafer  50  is positioned in a wet cleaning apparatus and undergoes a vaporized HPM cleaning process  120  for a duration of 4-5 minutes to remove residues such as remnant metals: Pt, Co, Pd, Mn, Ta, Ru, or alloys of the aforementioned metals from the wafer  50 . In addition, as shown in  FIG. 5 , to further remove the residues, a pre-SPM cleaning process  110  is added before performing the vaporized HPM cleaning process  120 . 
         [0024]    Please refer to  FIG. 5  again. To remove the residuals of the vaporized HPM cleaning process  120 , the wafer undergoes an SPM cleaning process  130  in the wet cleaning apparatus. The SPM cleaning process  130  is performed at a temperature between 95-120° C. for a duration of 4-5 minutes. It is noteworthy that the SPM cleaning processes  130  are performed after the vaporized HPM cleaning processes  120  to remove residuals, such as chlorine, hydrochloric acid, and salts from the wafer  50  and to improve surface cleanliness of the wafer  50 . 
         [0025]    Please refer to  FIG. 6  which is a drawing illustrating remaining particle amounts on the cleaned wafer according to the first embodiment provided by the present invention. As shown in  FIG. 6 , the remaining particles on the cleaned wafer  50  are reduced to under 40. Therefore, the method for cleaning salicide provided by the first preferred embodiment indeed improves surface cleanliness of the wafer. 
         [0026]    Please refer to  FIG. 7 , which is a drawing illustrating a second preferred embodiment provided by the present invention. As shown in  FIG. 7 , for removing the unreacted Ni and other residues from the intergraded salicide  70 , the wafer  50  is positioned in a wet cleaning apparatus. Then, an APM cleaning process  200  is performed at a temperature between 30-70° C. to remove residues from the substrate  52 . Following the APM cleaning process  200 , an vaporized HPM cleaning process  220  is performed for a duration of 4-5 minutes to remove residues such as remnant metals: Pt, Co, Pd, Mn, Ta, Ru, or alloys of the aforementioned metals. In addition, as shown in  FIG. 7 , for further removing the remnant metals such as Pt or Co, a pre-SPM cleaning process  210  is added before the vaporized HPM cleaning process  220 . 
         [0027]    Please refer to  FIG. 7  again. For removing residuals of the vaporized HPM cleaning process  220 , an SPM cleaning process  230  is performed in the wet cleaning apparatus. The SPM cleaning process  230  is performed at a temperature between 90-120° C. for a duration of 4-5 minutes. Please note that the SPM cleaning processes  230  are performed after the vaporized HPM cleaning processes  220  to remove residuals, such as chlorine, hydrochloric acid, and salts from the wafer  50  and to improve surface cleanliness of the wafer  50 . 
         [0028]    Please refer to  FIG. 8 , which is a drawing illustrating remaining particle amounts on the cleaned wafer. As shown in  FIG. 8 , the remaining particles on the cleaned wafer  50  are reduced to 20, which is much lower than the desired standard of 30. Therefore, the method for cleaning salicide provided by the second preferred embodiment indeed improves surface cleanliness of the wafer. 
         [0029]    Please refer to  FIG. 9  which is a drawing illustrating steps for forming the salicide. As shown in  FIG. 9 , a second RTP is performed on the wafer  50  to transform the intergraded salicides  70  into salicides  90 . The salicides  90  can be nickel salicide, cobalt salicide, titanium salicide, or a combination of the aforementioned metals. For example, in the first and second preferred embodiments, the salicide comprises nickel salicide. 
         [0030]    According to the first and second preferred embodiments provided by the present invention, the SPM cleaning processes  130 ,  230  are performed after the vaporized HPM cleaning processes  120 ,  220  to remove residuals, such as chlorine, hydrochloric acid, and salts to improve surface cleanliness of the wafer  50 . 
         [0031]    As mentioned above, the present invention actually provides a wet cleaning method which can be applied to a method for cleaning salicide. Because hydrogen peroxide, hydrochloric acid, and chlorine used in the vaporized HPM cleaning process are vaporized and often remain on the cleaning objects and in the wet cleaning apparatus, even reacting with agents used in preceding processes and forming salts. Those particles and residuals remaining on the object will contaminate the wafer again. Therefore, an SPM cleaning process is performed after the vaporized HPM cleaning process at a temperature between 90-120° C. for a duration of 4-5 minutes to remove those residuals. Furthermore, the SPM cleaning process and the vaporized HPM cleaning process are performed in the same wet cleaning apparatus. 
         [0032]    When the wet cleaning method provided by the invention is applied to a method for cleaning salicide, the SPM cleaning process added after the vaporized HPM cleaning process will remove the active residuals of the vaporized HPM process from the wafer, therefore surface cleanliness of the wafer is improved and the pollution to the environment and danger to the operator are reduced. 
         [0033]    Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.