Abstract:
A chemical mechanical polishing (CMP) system includes a wafer polishing unit comprising a waste liquid sink for receiving a used slurry and a waste slurry drain piping for draining the used slurry; and a post-CMP cleaning unit coupled to the wafer polishing unit such that a used base chemical such as tetramethyl ammonium hydroxide (TMAH) produced from the post-CMP cleaning unit flows toward the wafer polishing unit to frequently wash at least the waste slurry drain piping in a real time fashion on a wafer by wafer basis.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to a wafer processing system. More particularly, the present invention relates to an integrated chemical mechanical polishing (CMP) system including a CMP wafer polishing unit and a post-CMP cleaning unit coupled to the CMP wafer polishing unit. The inventive CMP system is capable of preventing clogs in the drain piping of the CMP wafer polishing unit. 
         [0003]    2. Description of the Prior Art 
         [0004]    Chemical mechanical polishing (CMP) techniques are used for planarizing material layers on a wafer in semiconductor industry. In chemical mechanical polishing, slurry is dispensed onto a polishing surface of a polishing pad. Relative movement between the polishing surface and the wafer produces a combined mechanical and chemical effect on the surface of the wafer. This process creates a highly level surface on the wafer. After CMP, the wafer is transferred to a cleaning unit and scrubbed with roller-shaped PVA brushes. During scrubbing of the wafer, a base chemical such as tetramethyl ammonium hydroxide (TMAH) is simultaneously applied onto the surface of the wafer to be cleaned. 
         [0005]    One of the major problems facing the CMP process is the clogging in the waste slurry drain piping. It is believed that the agglomeration of abrasive particles, the base chemical crystals from the slurry and/or the polishing pad debris cause clogs in the drain pipe. The cleaning of the clogged drain pipe is time-consuming because the substances that clog the drain pipe are difficult to be removed. Extended maintenance hours may be required in order to ensure that the drain pipe is clean, which increase the down time of the CMP tool as well as the manufacture cost. Moreover, many clogs reside in remote locations in the drain pipe and it is difficult or impossible to find the clogged sites at remote locations in the drain pipe. Sometime, leakage may occur even though the CMP tool is just maintained and the drain pipe is cleaned lately. 
         [0006]    Accordingly, there is a need in this industry to provide an improved CMP system and method that better addresses the issues of clogs in the waste slurry drain piping and leakage in the CMP tool. 
       SUMMARY OF THE INVENTION 
       [0007]    It is one object of the present invention to provide an improved CMP system including a CMP wafer polishing unit and a post-CMP cleaning unit coupled to the CMP wafer polishing unit in order to solve the above-mentioned prior art problems. 
         [0008]    To these ends, according to one aspect of the present invention, there is provided a chemical mechanical polishing (CMP) system comprising a wafer polishing unit comprising a waste liquid sink for receiving a used slurry and a waste slurry drain piping for draining the used slurry; and a post-CMP cleaning unit coupled to the wafer polishing unit such that a used base chemical such as tetramethyl ammonium hydroxide (TMAH) produced from the post-CMP cleaning unit flows toward the wafer polishing unit to frequently wash at least the waste slurry drain piping in a real time fashion on a wafer by wafer basis. In one aspect, the wafer polishing unit may comprise a platen, a polishing pad mounted on the platen, a carrier for holding and rotating a wafer, and a slurry feeding device. The post-CMP cleaning unit may comprise a plurality of rollers for supporting and rotating a wafer, a brush for scrubbing the wafer, and a spray bar disposed in proximity to the brush. 
         [0009]    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 
         [0010]    The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings: 
           [0011]      FIG. 1  is a schematic diagram showing germane parts of a CMP system in accordance with the first embodiment of the present invention; 
           [0012]      FIG. 2  is a schematic diagram showing germane parts of a CMP system in accordance with the second embodiment of the present invention; and 
           [0013]      FIG. 3  is a schematic diagram showing germane parts of a CMP system in accordance with the third embodiment of the present invention. 
       
    
    
       [0014]    It should be noted that all the figures are diagrammatic. Relative dimensions and proportions of parts of the drawings have been shown exaggerated or reduced in size, for the sake of clarity and convenience in the drawings. The same reference signs are generally used to refer to corresponding or similar features in modified and different embodiments. 
       DETAILED DESCRIPTION 
       [0015]    In the following description, numerous specific details are given to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the invention may be practiced without these specific details. In order to avoid obscuring the present invention, some well-known system configurations and process steps are not disclosed in detail. 
         [0016]    The drawings showing embodiments of the apparatus are semi-diagrammatic and not to scale and, particularly, some of the dimensions are for the clarity of presentation and are shown exaggerated in the figures. Also, where multiple embodiments are disclosed and described having some features in common, for clarity and ease of illustration and description thereof like or similar features one to another will ordinarily be described with like reference numerals. 
         [0017]      FIG. 1  depicts a CMP system  1  in accordance with the first embodiment of the present invention. As shown in  FIG. 1 , the CMP system  1  comprises at least a CMP wafer polishing unit  10  and a post-CMP cleaning unit  20 , which may be configured together inside a cluster CMP tool, but not limited thereto. In general, the CMP wafer polishing unit  10  may comprise a platen  100  connected to a shaft  101  for rotating the platen  100  about its central axis during CMP process. A polishing pad  110  is mounted on the platen  100 . A wafer  122  is held and rotated by a carrier  120 . In polishing, a slurry feeding device  130  may spray slurry S onto the polishing pad  110 . The rotating wafer  122  is pressed against the polishing pad  110  by the carrier  120  to cause relative movement between the polishing surface of the polishing pad  110  and the wafer  122 , thereby producing a combined mechanical and chemical effect on the surface of the wafer. The once-used slurry S′ may be received by a waste liquid sink  140  and then stored in a waste liquid tank  150  through the waste slurry drain piping  144 . 
         [0018]    As previously mentioned, the agglomeration or precipitation of abrasive particles and base chemical crystals originated from the slurry S and the polishing pad debris causes clogs in the waste slurry drain piping  144  or clogs near the drain outlet  142 . The cleaning of the clogged waste slurry drain piping  144  is time-consuming because the substances that clog the waste slurry drain piping  144  are difficult to be removed. Extended maintenance hours may be required in order to ensure that the waste slurry drain piping  144  is clean, which increase the down time of the CMP tool as well as the manufacture cost. Moreover, many clogs reside in remote locations in the waste slurry drain piping  144  and it is difficult or impossible to find the clogged sites at remote locations therein. Sometime, leakage may occur even though the CMP tool is just maintained and the waste slurry drain piping  144  is cleaned lately. The present invention addresses this issue. 
         [0019]    Still referring to  FIG. 1 , the post-CMP cleaning unit  20  may be a single-sided or double-sided scrubber cleaner. After polishing, the wafer  122  is transferred to the post-CMP cleaning unit  20 . In the post-CMP cleaning unit  20 , the wafer  122  may be held and rotated by a plurality of rollers  252  with its surface to be cleaned facing the roller-shaped brush  210 . The wafer  122  is scrubbed by the brush  210  to remove the slurry residues from the wafer surface. During the scrubbing and cleaning process, a base chemical B such as tetramethyl ammonium hydroxide (TMAH) is simultaneously applied onto the surface of the wafer to be cleaned. The base chemical B enhances the cleaning ability and helps remove the slurry abrasives or particles adhered or adsorbed to the wafer surface. Typically, the base chemical B is sprayed by a spray bar  220  that is disposed in proximity to the brush  210 . The once-used base chemical B′ is received by the waste liquid sink  240 . 
         [0020]    According to the first embodiment of the invention, the waste liquid sink  240  of the post-CMP cleaning unit  20  communicates with the waste liquid sink  140  of the CMP wafer polishing unit  10  via a conduit  310  such that the once-used base chemical B′ can be drained by gravity from the waste liquid sink  240  of the post-CMP cleaning unit  20  to the waste liquid sink  140  of the CMP wafer polishing unit  10  when scrubbing the wafer  122 . By providing such configuration, the waste liquid sink  140  and the waste slurry drain piping  144  of the CMP wafer polishing unit  10  can be washed by the once-used base chemical B′ every time the post-CMP cleaning unit  20  is operated, thereby preventing agglomeration or precipitation of abrasive particles and base chemical crystals and the polishing pad debris in the waste slurry drain piping  144  or clogs near the drain outlet  142 . 
         [0021]    It is advantageous to use the present invention because the cleaning of the waste liquid sink  140  and the waste slurry drain piping  144  of the CMP wafer polishing unit  10  is performed in a real time fashion and is frequently performed on a wafer by wafer basis without the need to halt the CMP process. In addition, since the waste slurry drain piping  144  is regularly maintained in a clean condition, the down time for the CMP system due to preventative maintenance (PM) can be significantly reduced and also the risk of leakage can be avoided. 
         [0022]      FIG. 2  is a schematic diagram showing germane parts of a CMP system in accordance with the second embodiment of the present invention. As shown in  FIG. 2 , likewise, the CMP system  1   a  comprises at least a CMP wafer polishing unit  10  and a post-CMP cleaning unit  20 , which may be configured together inside a cluster CMP tool, but not limited thereto. In general, the CMP wafer polishing unit  10  may comprise a platen  100  connected to a shaft  101  for rotating the platen  100  about its central axis during CMP process. A polishing pad  110  is mounted on the platen  100 . A wafer  122  is held and rotated by a carrier  120 . In polishing, a slurry feeding device  130  may spray slurry S onto the polishing pad  110 . The rotating wafer  122  is pressed against the polishing pad  110  by the carrier  120  to cause relative movement between the polishing surface of the polishing pad  110  and the wafer  122 , thereby producing a combined mechanical and chemical effect on the surface of the wafer. The once-used slurry S′ may be received by a waste liquid sink  140  and then stored in a waste liquid tank  150  through the waste slurry drain piping  144 . 
         [0023]    After polishing, the wafer  122  is transferred to the post-CMP cleaning unit  20 . In the post-CMP cleaning unit  20 , the wafer  122  may be held and rotated by a plurality of rollers  252  with its surface to be cleaned facing the roller-shaped brush  210 . The wafer  122  is scrubbed by the brush  210  to remove the slurry residues from the wafer surface. During the scrubbing and cleaning process, a base chemical B such as TMAH is simultaneously applied onto the surface of the wafer to be cleaned. Typically, the base chemical B is sprayed by a spray bar  220  that is disposed in proximity to the brush  210 . According to the second embodiment of the invention, the once-used base chemical B′ is received by the waste liquid sink  240  and stored in the collection tank  250  through the drain pipe  244 . The collection tank  250  communicates with the waste liquid sink  140  of the CMP wafer polishing unit  10  via a connection conduit  410 . A pump  420  is disposed in the connection conduit  410  to pump the once-used base chemical B′ from the collection tank  250  to the waste liquid sink  140  of the CMP wafer polishing unit  10 . Optionally, a control valve  402  may be disposed in the connection conduit  410  to control the entrance of the once-used base chemical B′. The waste liquid sink  140  and the waste slurry drain piping  144  of the CMP wafer polishing unit  10  can be washed by the once-used base chemical B′, thereby preventing agglomeration or precipitation of abrasive particles and base chemical crystals and the polishing pad debris in the waste slurry drain piping  144  or clogs near the drain outlet  142 . 
         [0024]      FIG. 3  is a schematic diagram showing germane parts of a CMP system in accordance with the third embodiment of the present invention. As shown in  FIG. 3 , likewise, the CMP system  1   b  comprises at least a CMP wafer polishing unit  10  and a post-CMP cleaning unit  20 , which may be configured together inside a cluster CMP tool, but not limited thereto. In general, the CMP wafer polishing unit  10  may comprise a platen  100  connected to a shaft  101  for rotating the platen  100  about its central axis during CMP process. A polishing pad  110  is mounted on the platen  100 . A wafer  122  is held and rotated by a carrier  120 . In polishing, a slurry feeding device  130  may spray slurry S onto the polishing pad  110 . The rotating wafer  122  is pressed against the polishing pad  110  by the carrier  120  to cause relative movement between the polishing surface of the polishing pad  110  and the wafer  122 , thereby producing a combined mechanical and chemical effect on the surface of the wafer. The once-used slurry S′ may be received by a waste liquid sink  140  and then stored in a waste liquid tank  150  through the waste slurry drain piping  144 . 
         [0025]    After polishing, the wafer  122  is transferred to the post-CMP cleaning unit  20 . In the post-CMP cleaning unit  20 , the wafer  122  may be held and rotated by a plurality of rollers  252  with its surface to be cleaned facing the roller-shaped brush  210 . The wafer  122  is scrubbed by the brush  210  to remove the slurry residues from the wafer surface. During the scrubbing and cleaning process, a base chemical B such as TMAH is simultaneously applied onto the surface of the wafer to be cleaned. Typically, the base chemical B is sprayed by a spray bar  220  that is disposed in proximity to the brush  210 . According to the third embodiment of the invention, the waste liquid sink  240  of the post-CMP cleaning unit  20  does not directly communicates with the waste liquid sink  140  of the CMP wafer polishing unit  10 . Instead, the once-used base chemical B′ is drained by gravity from the waste liquid sink  240  of the post-CMP cleaning unit  20  to the waste slurry drain piping  144  of the CMP wafer polishing unit  10  via the conduit  510 . In this case, only the waste slurry drain piping  144  of the CMP wafer polishing unit  10  is washed by the once-used base chemical B′ every time the post-CMP cleaning unit  20  is operated. 
         [0026]    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.