Abstract:
A post-cleaning method of a via etching process in the present invention has the steps of: (a) performing a photoresist strip process to remove the photoresist layer; b) performing a dry cleaning process which uses CF 4  as the main reactive gas and is operated by dual powers; and (c) performing a water-rinsing process.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates in general to a cleaning method, in particular, the present invention relates to a post-cleaning method of a via etching process.  
           [0003]    2. Description of the Related Art  
           [0004]    In the semiconductor processing for pursuing the goal of minute line width and high integration, the product yield is greatly concerned with particles. In particular, during a via etching process, the residues remaining in the via will deteriorate the electrical-connecting property between metal layers.  
           [0005]    Please refer to FIG. 1 and FIG. 2. FIG. 1 is a cross-sectional schematic diagram of a via according to the prior art. FIG. 2 is a flow chart of a post-cleaning method of a via etching process according to the prior art. A wafer  10  comprises a substrate  12 , a metal layer  14  formed on the substrate  12 , an oxide layer  16  covered on the metal layer  14 , and a photoresist layer  18  coated on the oxide layer  16 . By using a dry etching process, a via  20  is patterned to pass through the photoresist layer  18  and the oxide layer  16  till exposing a predetermined area of the metal layer  14 . In a post-cleaning method of the via etching process, the step  22  of a photoresist strip process is firstly performed to remove the photoresist layer  18  by a dry etching process in a plasma reactor, wherein the hydrocarbon inside the photoresist layer  18  is reacted with oxygen plasma to be stripped off and the produced gases, such as CO, CO 2  and H 2 O are pumped by a vacuum system. However, the photoresist strip process also produces polymer residues and which greatly remain in the via  20 . For this reason, the step  24  of a wet cleaning process is performed for cleaning off the polymer residues. In general, the wafer  10  is dipped into sink filled with a specific etching solution, such as ACT, EKC or other alkaline compounds, on an appropriate condition of dipping time, temperature and solution concentration so as to make the polymer residues react with the etching solution to be removed off. Finally, at the step  26  of a water-rinsing process, the wafer  10  is turned vertically to ensure the fringe of the wafer  10  being cleaned off, and then the wafer  10  is dipped into deionized water to clean off the remaining etching solution.  
           [0006]    Nevertheless, the wet cleaning method that utilizes the chemicals such as ACT and EKC with high waste volume encounters problems in an increasing price of the chemicals and a shortage of the chemical resource. It does not conform to expectations for the cost considerations of mass production. Also, since dipping the wafer  10  into the etching solution consumes a period of time to make the polymer residues completely react with the etching solution, the overall via etching process period is increased.  
         SUMMARY OF THE INVENTION  
         [0007]    Therefore, the present invention provides a post-cleaning method of a via etching process, which substitutes a dry cleaning process for the wet cleaning process to solve the above-mentioned problems.  
           [0008]    The post-cleaning method of a via etching process in the present invention includes : (a) performing a photoresist strip process to remove the photoresist layer; b) performing a dry cleaning process which uses CF 4  as the main reactive gas and is operated by dual powers; and (c) performing a water-rinsing process.  
           [0009]    It is an advantage of the present invention that since the dry cleaning process substitutes the wet cleaning process to remove the polymer residues without using costly and rare alkaline compounds, the production cost is substantially decreased. Also, the dry cleaning process can quickly remove the polymer residues and the wafer needs not to be turned vertically before dipping into deionized water, so the overall post-clean process becomes more efficient. Furthermore, the photoresist strip process and the dry cleaning process can be in-situ performed; therefore this will facilitate the post-clean process.  
           [0010]    This and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The present invention can be more fully understood by reading the subsequent detailed description in conjunction with the examples and references made to the accompanying drawings, wherein:  
         [0012]    [0012]FIG. 1 is a cross-sectional schematic diagram of a via according to the prior art.  
         [0013]    [0013]FIG. 2 is a flow chart of a post-cleaning method of a via etching process according to the prior art.  
         [0014]    [0014]FIGS. 3A to  3 D are cross-sectional schematic diagrams of a cleaning method of a via etching process according to the first embodiment of the present invention.  
         [0015]    [0015]FIG. 4 is a flow chart of a post-cleaning method of the via etching process according to the present invention.  
         [0016]    [0016]FIGS. 5A to  5 C, which show cross-sectional schematic diagrams of another post-cleaning method of the via etching process according to the second embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]    [First Embodiment] 
         [0018]    Please refer to FIG. 3 and FIG. 4. FIGS. 3A to  3 D are cross-sectional schematic diagrams of a cleaning method of a via etching process according to the first embodiment of the present invention. FIG. 4 is a flow chart of a post-cleaning method of the via etching process according to the present invention. As shown in FIG. 3A, a wafer  30  comprises a substrate  32 , an aluminum (Al) layer  34  formed on the substrate  32 , a titanium nitride (TiN) layer  36  formed on the Al layer  34 , an oxide layer  38  covered on the TiN layer  36 , a photoresist layer  40  coated on the oxide layer  38 , and a via  42 . The oxide layer  38  is preferably made of TEOS-oxide. The via  42  is preferably fabricated by a dry etching process to pass through the photoresist layer  40 , the oxide layer  38  and the TiN layer  36  till exposing a predetermined area of the Al layer  34  that is used as an etch stop layer.  
         [0019]    As shown in FIG. 4, in the post-cleaning method of the present invention, the step  44  of a photoresist strip process is firstly performed to remove the photoresist layer  40  by a dry etching process in a plasma reactor, wherein the hydrocarbon inside the photoresist layer  40  is reacted with oxygen plasma to be stripped off, the produced gases, such as CO, CO 2  and H 2 O are pumped by a vacuum system, and the produced polymer residues  50  remain in the via  42 , as shown in FIG.3B. Then, the step  46  of a dry cleaning process is performed to remove the polymer residues  50  by a dry etching process, wherein the operation conditions are 15˜25 seconds, 60° C.˜80° C., 500 Mt, 700 W˜900 W of -wave power, 80 W˜120 W of RF power. As to the key point, it is preferred to use CF 4  as the main reactive gas combined with minor reactive gases, such as N 2  and H 2  wherein the proportion of CF 4  to the overall reactive gases is between ½ and ⅙. Besides, it is also preferred to use CF 4  and O 2  as the main reactive gases, wherein the flow rate of CF 4  is about 30 sccm and the flow rate of O 2  is about 500 sccm. Therefore, at the same time the polymer residues  50  are removed, CF 4  can react with TiN to form water-solutable TiF x  residues  52  and NF 3  gas, CF 4  also can react with the oxide layer  38  to form SiF 4 , SiF x , CO and CO 2  and CF 4  even can react with Al to form water-solutable AlF x  residues, as shown in FIG. 3C. Although those gases are pumped by a vacuum system, the water-solutable residues  52  still remain in the via  42 . Finally, at the step  48  of a water-rinsing process, the wafer  30  is directly dipped into deionized water to make the water-solutable residues  52  immediately dissolve in deionized water, and thereby all residues remaining in the via  42  are cleaned off, as shown in FIG. 3D.  
         [0020]    Compared with the prior post-cleaning method, in the post-cleaning method of the via etching process according to the present invention, the dry cleaning process substitutes the wet cleaning process to remove the polymer residues  50  without using costly and rare alkaline compounds, such as ACT and EKC. Hence, the production cost is substantially decreased. Also, the dry cleaning process can quickly remove the polymer residues  50  and the wafer  30  does not need to be turned vertically before dipping into deionized water, so the overall post-clean process becomes more efficient. Furthermore, the photoresist strip process and the dry cleaning process can be in-situ performed to remove the photoresist layer  40  and the polymer residues  50  in sequence by adjusting the operation factors of the plasma reactor to an appropriate condition. This will facilitate the post-clean process.  
         [0021]    [Second Embodiment] 
         [0022]    The above-mentioned post-cleaning method is applied to the case that employs the Al layer  34  as the etch stop layer. The present invention provides another cleaning method in the case that employs the TiN layer  36  as the etch stop layer. Please refer to Figs. 5A to  5 C, which show cross-sectional schematic diagrams of another post-cleaning method of the via etching process according to the second embodiment of the present invention. As shown in FIG. 5A, by using the TiN layer  36  as the etch stop layer, the via  42  passes through the photoresist layer  40  and the oxide layer  38  till exposing a predetermined area of the TiN layer  36 . In accordance with the steps  44 ˜ 46 , the polymer residues  50  can be removed. Compared with the first embodiment, since the polymer residues  50  are less produced during the photoresist strip process, as shown in FIG. 5B, the dry cleaning process only employs O 2  with a flow rate about 1000 sccm as the main reactive gas and the operation conditions that are similar to the first embodiment, and finally the polymer residues  50  are cleaned off, as shown in FIG. 5C.  
         [0023]    Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teaching of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.