Abstract:
A chemical mechanical polishing (CMP) system includes a wafer polishing unit producing a used slurry; a slurry treatment system for receiving and treating the used slurry to thereby produce an extracted basic solution; and a post-CMP cleaning unit utilizing the extracted basic solution to wash a polished wafer surface. The post-CMP cleaning unit includes 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 for spraying the extracted basic solution onto the polished wafer surface.

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. 
         [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. 
         [0005]    Polishing slurry or slurry is the main component used in the CMP process. Typically, the slurry used in the CMP process consists mainly of colloidal silica suspended in deionized water or KOH solution. The slurry is frequently fed by an automatic slurry feeding system in order to ensure uniform wetting of the polishing pad and proper delivery of the slurry. Conventionally, the once-used slurry is received by a waste liquid receiver in the CMP tool, stored in a waste liquid tank, and then completely disposed of. 
         [0006]    After CMP, the wafer is transferred to a cleaning unit and scrubbed with roller-shaped PVA (polyvinyl acetate) 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. However, the amount of usage of TMAH is huge and accounts for about 1.3˜1.5 USD per wafer. This makes it one of the major consumable cost factors in a CMP process. It would be advantageous to have an improved CMP system that is capable of reducing the cost of polishing each wafer. 
       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, which is capable of reducing the cost of polishing each wafer. 
         [0008]    According to one aspect of the present invention, there is provided a chemical mechanical polishing (CMP) system comprising a wafer polishing unit producing a used slurry; a slurry treatment system for receiving and treating the used slurry to thereby produce an extracted basic solution; and a post-CMP cleaning unit utilizing the extracted basic solution to wash a polished wafer surface. The post-CMP cleaning unit comprises 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 for spraying the extracted basic solution onto the polished wafer surface. 
         [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 one embodiment of the present invention; 
           [0012]      FIG. 2  schematically shows an exemplary CMP unit in accordance with one embodiment of the present invention; and 
           [0013]      FIG. 3  schematically shows an exemplary post-CMP cleaning unit in accordance with one 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. 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. 
         [0016]      FIG. 1  depicts a CMP system  1  in accordance with one embodiment of the present invention. As shown in  FIG. 1 , the CMP system  1  comprises at least a CMP wafer polishing unit or CMP unit  10  and a post-CMP cleaning unit  20 , which may be configured together inside a cluster CMP tool, but not limited thereto. An exemplary CMP unit  10  is shown schematically in  FIG. 2 . 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. The shaft  101  may be driven by a motor (not shown). 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 aqueous slurry S onto the polishing pad  110 . The rotating wafer  122  is pressed against the wetted polishing pad  110  by the carrier  120  to cause relative movement between the polishing surface of the polishing pad  110  and the wafer  122 . 
         [0017]    The aqueous slurry, which is preferably basic, may include abrasive particles, a reactive chemical agent such as a transition metal chelated salt or an oxidizer, and adjuvants such as solvents, buffers, and passivating agents. Within the slurry, the salt or other agent provides the chemical etching action, with the abrasive particles, in cooperation with the polishing pad, providing the mechanical polishing action. According to the embodiment of the invention, the aqueous slurry may be of either an oxide, i.e., ceramic, or metal abrasive particle type. For example, the oxide-type particles may include silica (SiO2), ceria (CeO2), silicon carbide (SiC), silicon nitride (Si3N4), iron oxide (Fe2O3), alumina (Al2O3), and the like. The metal particles may include tungsten and copper. The slurry may be formulated to have a relatively high solids level which may be about 40% or more by weight, with a mean average abrasive particle size, which typically is given as a distribution range, of limits between about 0.05˜5.0 μm for oxide slurries and about 20˜35 μm for tungsten slurries. 
         [0018]    Still referring to  FIG. 1 , 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 . The once-used slurry S′ stored in the waste liquid tank  150  may be pumped to a slurry treatment system  30  by using a pump P 1 . In another case, the pump P 1  may be omitted and the once-used slurry S′ flows to the slurry treatment system  30  by gravity. According to the embodiment of the invention, the slurry treatment system  30  is used to separate the suspended particles such as abrasive particles or pad debris from the aqueous basic solution such as KOH or NH4OH of the once-used slurry S′. 
         [0019]    According to the embodiment of the invention, by way of example, the slurry treatment system  30  may comprise a centrifugal separation device  302  and a filter  304 . First, the once-used slurry S′ is pumped into the centrifugal separation device  302  and most of the suspended particles in the once-used slurry S′ can be separated by the centrifugal separation device  302  using centrifugal force, thereby forming clarified, aqueous slurry S″ with very low content of suspended solid. The clarified slurry S″ is then pumped into a filter  304  by a pump P 2  via a conduit  312 . The rest of the suspended particles can be completely removed by the filter  304  to form an extracted basic solution S′″. According to the embodiment of the invention, the filter  304  may be of surface-type filtration or tortuous path, depth-type filtration. For example, the filter  34  may contain membranes or fibrous media capable of filtering the smallest particle size in the once-used slurry S′. The extracted basic solution S′″, which is an extracted and clarified aqueous basic solution containing substantially no solid content, is then distributed into the subsequent post-CMP cleaning unit  20  via a conduit  322  for cleaning the wafer surface. Optionally, a valve  342  and a valve  344  may be disposed in the conduit  312  and in the conduit  322  respectively for flow control or maintenance purposes. It is to be understood that other clarifier or filter components may be used in the slurry treatment system  30 . 
         [0020]    An exemplary post-CMP cleaning unit  20  is shown schematically in  FIG. 3 . The post-CMP cleaning unit  20  may be a single-sided or double-sided scrubber cleaner for removing slurry residues from the polished wafer surfaces. As shown in  FIG. 3 , after polishing, the wafer  122  is transferred to the post-CMP cleaning unit  20  by robot. 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  212 , which are configured together within an enclosure  202 . The wafer  122  is scrubbed by the brush  212  to remove the slurry residues from the wafer surface. During the scrubbing and cleaning process, the extracted basic solution S′″ is simultaneously applied onto the surface of the wafer to be cleaned (the spouts indicated by arrows). Typically, the extracted basic solution S′″ is sprayed by a spray bar  214  that is disposed in proximity to the brush  212 . An inlet  214   a  of the spray bar  214  is connected to the conduit  322  that is connected to the outlet of the filter  304  in  FIG. 2 . 
         [0021]    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.