Abstract:
A single-wafer dry cleaning procedure. First, an etched wafer having a photo resist pattern thereon is provided. Then, an ashing process is performed to remove the photo resist pattern. Finally, the etched wafer is hoisted and maintained in a suspended condition, a dry cleaning process then being performed upon the etched wafer.

Description:
BACKGROUND OF INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a single-wafer cleaning procedure, and more particularly, to a single-wafer dry cleaning procedure performed when the wafer is in a hoisted condition.  
         [0003]     2. Description of the Prior Art  
         [0004]     The manufacturing of VLSI, ULSI, and MEMS are based on a substrate, e.g. a silicon wafer, and are successively implemented by performing hundreds of processes including thin film deposition, oxidization, photolithography, etching, implantation, etc. An example of forming a gate structure of an MOS element is described as follows. First of all, a gate insulating layer, a polysilicon layer, and a polycide layer are consecutively formed on a wafer. Then, a photolithography process is utilized to form a photo resist pattern on the wafer surface to define the position of the gate structure. Following that, an etching process is performed to remove the gate insulating layer, the polysilicon layer, and the polycide layer thus forming the gate structure. As known in the art, however, polymer particles, which are the products of the etching reaction, would adhere to the wafer surface, and thus a cleaning process must be performed to remove the polymer products. In such a case, the electrical performance of the MOS element can be ensured, and subsequent processes can be continued successfully.  
         [0005]     Please refer to  FIG. 1 .  FIG. 1  is a flow chart illustrating a conventional wafer cleaning procedure. As shown in  FIG. 1 , the conventional wafer cleaning procedure includes the following steps:  
         [0006]     Step  10 : utilizing a photolithography process to form a photo resist pattern on a thin film positioned on a wafer surface;  
         [0007]     Step  20 : performing an ashing process by introducing oxygen at a high temperature to remove the photo resist pattern; and  
         [0008]     Step  30 : performing a wet cleaning process by immerse the wafer into at least a cleaning solution tank to remove the polymer particles adhered to the wafer surface (including front surface, back surface, and bevel surface), and rinsing the wafer with deionized (DI) water.  
         [0009]     The aforementioned wafer cleaning procedure is a common way to clean wafers. However, the concentration of the cleaning solution varies with the quantity of wafers processed. That is, considering wafers of different batches, the cleaning effect of the solution on wafers of any given batch is inevitably poorer compared to the cleaning effect on wafers of a previous batch. Consequently, the quality of subsequent processes is more difficult to control. In the mass production of small-sized wafers, since the critical dimensions are larger and the integration is not high, the conventional cleaning procedure by performing a wet cleaning process is an acceptable solution. However, because critical dimensions are reduced and integration is improved in the fabrication of 12-inch wafers, a single-wafer cleaning procedure is necessary to ensure effective cleaning.  
         [0010]     As described above, the process precision involved in the fabrication of large-sized wafers requires strict cleanliness controls, and hence a single-wafer cleaning procedure must be adopted. In addition, if the single-wafer cleaning procedure is implemented by a wet cleaning process in a spinning manner, particles such as polymer particles or organic components would remain on the back surface and the bevel surface of the wafers. These remaining polymer particles become the source of contamination in the chambers of subsequent processes, and therefore affect the quality and yield of these processes.  
       SUMMARY OF INVENTION  
       [0011]     It is therefore a primary object to provide a single-wafer dry cleaning procedure to overcome the aforementioned problem.  
         [0012]     According to a preferred embodiment of the present invention, a single-wafer dry cleaning procedure is disclosed. First, an etched wafer including a photo resist pattern thereon is provided. An ashing process is thereafter performed to remove the photo resist pattern. Finally, the etched wafer is hoisted up, and a dry cleaning process is performed upon the etched wafer.  
         [0013]     Since the dry cleaning process, e.g. oxygen plasma bombardment, is performed when the etched wafer is in a hoisted condition according to the present invention, polymer particles adhering to the back surface and the bezel surface of the etched wafer are easily removed.  
         [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 DRAWINGS  
       [0015]      FIG. 1  is a flow chart illustrating a conventional wafer cleaning procedure.  
         [0016]      FIG. 2  and  FIG. 3  are schematic diagrams illustrating a dry cleaning procedure according to a preferred embodiment of the present invention.  
         [0017]      FIG. 4  is a schematic diagram illustrating a dry cleaning procedure according to another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0018]     Please refer to  FIG. 2  and  FIG. 3 .  FIG. 2  and  FIG. 3  are schematic diagrams illustrating a dry cleaning procedure according to a preferred embodiment of the present invention. As shown in  FIG. 2 , a wafer which has just been etched (hereinafter referred to as etched wafer  40 ) is loaded into a reaction chamber  42 , and supported by a carrier  42 . The etched wafer  40  includes a thin film pattern  46 , and a photo resist pattern  48  on the front surface for defining the thin film pattern  46 . In addition, the etched wafer  40  randomly includes a plurality of polymer particles  50  (or organic components), generated during the etching process, on the front surface, the back surface, and the bevel surface. Following that, an ashing process is performed by, such as introducing oxygen, ozone, or utilizing oxygen-carbon tetrafluoride (O 2 —CF 4 ) plasma, nitrogen oxygen (N 2 —O 2 ) plasma, at a temperature within 100° C. to 300° C. to remove the photo resist pattern  48 .  
         [0019]     As shown in  FIG. 3 , after the photo resist pattern  48  positioned on the front surface of the etched wafer  40  is removed in the ashing process, the etched wafer  40  is then hoisted up by pins  52  of the carrier  44  and undergoes a dry cleaning process in an in-situ manner. In this embodiment, the process temperature is maintained under a low pressure and within 100° C. to 300° C. In addition, a plasma, e.g. an oxygen plasma  54 , is utilized to bombard the etched wafer  40  when the etched wafer  40  is in a hoisted condition. Accordingly, the oxygen plasma  54  is capable of removing the polymer particles on the front surface, and the polymer particles  50  adhered to the back surface and the bevel surface of the etched wafer  40  as well.  
         [0020]     Since the main characteristic of the present invention is to perform a dry cleaning process upon the etched wafer  40 , the etched wafer  40  being hoisted, other suitable cleaning methods can also be adopted to remove the polymer particles  50 . For example, the polymer particles  50  on the front surface, back surface, and bevel surface can be burned away by introducing at least a gas (e.g. oxygen or ozone) at a high temperature. In addition, since the plasma substantially consists of charged ions, radicals, molecules, and electrons, a certain portion of the plasma can be selected to bombard the etched wafer  40  so as to improve the cleaning effect of the dry cleaning process.  
         [0021]     Please refer to  FIG. 4 .  FIG. 4  is a schematic diagram illustrating a dry cleaning procedure according to another embodiment of the present invention. It is appreciated that like numerals represent like components in  FIG. 3  and  FIG. 4 . As shown in  FIG. 4 , what is different from the previous embodiment is that in this embodiment the radicals  58  of the oxygen plasma  54  are select to bombard the etched wafer  40 . Consequently, a filter  56  is installed over the etched wafer  40  for only allowing the radicals  58  of the oxygen plasma  54  to pass through. Accordingly, the radicals  58  can remove the polymer particles  50  adhered to the front surface, the back surface, and the bevel surface of the etched wafer  40 .  
         [0022]     It is to be appreciated that the dry cleaning process aims to remove the polymer particles adhered to the front surface, the back surface, and the bevel surface of the etched wafer when the etched wafer is in a hoisted condition. On the other hand, the ashing process is also a dry process, which works to remove the photo resist pattern positioned on the front surface of the etched wafer. However, the dry cleaning process of the present invention can be implemented in a low pressure reaction chamber, in which the wafer is hoisted, by performing a single plasma process to remove the photo resist pattern and the polymer particles simultaneously. In addition, to ensure the cleanness of the etched wafer, a wet cleaning process can also be performed on the etched wafer after the dry cleaning process. Since the etched wafer may include only a small amount of polymer particles, the concentration of the cleaning solution is not altered dramatically.  
         [0023]     In conclusion, the prior art utilizes a wet cleaning process to remove the polymer particles adhered to the etched wafer, and thus suffers from variations in the concentration of the cleaning solution. For large-sized wafers, the above-mentioned wet cleaning process is not an acceptable solution in the removal of polymer particles. In comparison with the prior art, the present invention utilizes a dry cleaning process to remove the polymer particles adhered to the front surface, the back surface, and the bevel surface of the etched wafer, and thus has a stable cleaning ability to remove the polymer particles effectively.  
         [0024]     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.