Abstract:
An embodiment relates generally to a chemical mechanical polishing apparatus. The apparatus includes a platen adapted to receive a wafer to be chemical-mechanically polished and a polishing pad configured to polish the wafer. The apparatus also includes a slurry feed line configured to provide slurry to the polishing pad and at least one slurry dispensing outlet coupled to the slurry feed line and configured to dispense slurry as a mist of small droplets ranging from submicron to about 500 microns.

Description:
FIELD 
       [0001]    This invention relates generally to chemical-mechanical polishing, more particularly, to systems and methods for efficient slurry application for chemical-mechanical polishing. 
       DESCRIPTION OF THE RELATED ART 
       [0002]    A flat disk or “wafer” of single crystal silicon is the basic substrate material in the semiconductor industry for the manufacture of integrated circuits. Semiconductor wafers are typically created by growing an elongated cylinder or boule of single crystal silicon and then slicing individual wafers from the cylinder. The slicing causes both faces of the wafer to be extremely rough. The front face of the wafer on which integrated circuitry is to be constructed must be extremely flat in order to facilitate reliable semiconductor junctions with subsequent layers of material applied to the wafer. Also, the material layers (deposited thin film layers usually made of metals for conductors or oxides for insulators) applied to the wafer while building interconnects for the integrated circuitry must also be made a uniform thickness. 
         [0003]    Planarization is the process of removing projections and other imperfections to create a flat planar surface, both locally and globally, and/or the removal of material to create a uniform thickness for a deposited thin film layer on a wafer. Semiconductor wafers are planarized or polished to achieve a smooth, flat finish before performing process steps that create the integrated circuitry or interconnects on the wafer. A considerable amount of effort in the manufacturing of modern complex, high density multilevel interconnects is devoted to the planarization of the individual layers of the interconnect structure. Nonplanar surfaces create poor optical resolution of subsequent photolithography processing steps. Poor optical resolution prohibits the printing of high-density lines. Another problem with nonplanar surface topography is the step coverage of subsequent metalization layers. If a step height is too large there is a serious danger that open circuits will be created. Planar interconnect surface layers are required in the fabrication of modern high-density integrated circuits. To this end, chemical-mechanical polishing (“CMP”) tools have been developed to provide controlled planarization of both structured and unstructured wafers. 
         [0004]    CMP consists of a chemical process and mechanical process acting together, for example, to reduce height variations across a dielectric region, clear metal deposits in damascene processes or remove excess oxide in shallow trench isolation fabrication. The chemical-mechanical process is achieved with a liquid medium containing chemicals and abrasive particles (commonly referred to as slurry) that react with the front surface of the wafer while it is mechanically stressed during the planarization process. 
         [0005]    In a conventional CMP tool for planarizing a wafer, a wafer is secured in a carrier connected to a shaft. Pressure is exerted on the back surface of the wafer by the carrier in order to press the front surface of the wafer against the polishing pad in the presence of slurry. The wafer and/or polishing pad are then moved in relation to each other via motor(s) connected to the shaft and/or platen in order to remove material in a planar manner from the front surface of the wafer. Various combinations of motions are known for moving the wafer and polishing pad in relation to each other. For example, the wafer is commonly rotated or held stationary and the polishing pad is moved in either a linear, rotational or orbital manner. 
         [0006]    The slurry used in CMP may represent a significantly large portion of the cost to manufacture a semiconductor wafer. The current CMP tools distribute the slurry through tubing in large droplet form to one or more sites on the polishing plate. The large droplets of slurry tend to spin quickly off of the pad by centrifugal forces. This results in a much smaller portion of the dispensed slurry reaching the polishing pad/wafer interface at a high slurry cost. 
       SUMMARY 
       [0007]    An embodiment relates generally to a chemical mechanical polishing apparatus. The apparatus includes a platen adapted to receive a wafer to be chemical-mechanically polished and a polishing pad configured to polish the wafer. The apparatus also includes a slurry feed line configured to provide slurry to the polishing pad and at least one slurry dispensing outlet coupled to the slurry feed line and configured to dispense slurry as a mist of small droplets ranging from submicron to about 500 microns. 
         [0008]    Another embodiment pertains generally to a chemical mechanical polishing apparatus. The apparatus includes a platen adapted to receive a wafer to be chemical-mechanically polished and a polishing pad configured to polish the wafer. The apparatus also includes a slurry feeder configured to dispense slurry onto the polishing pad and multiple slurry outlets. Each slurry outlet is configured to spread slurry to a uniform coat on the polishing pad. 
         [0009]    Yet another embodiment relates generally to a method of chemical mechanical polishing. The method includes providing slurry to a polishing pad and applying the polishing pad to a wafer. The method also includes dispensing the slurry to the polishing pad as a mist of small droplets, where each droplet ranging from substantially submicron to 500 microns. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Various features of the embodiments can be more fully appreciated, as the same become better understood with reference to the following detailed description of the embodiments when considered in connection with the accompanying figures, in which: 
           [0011]      FIG. 1  illustrates an exemplary rotary polisher with an efficient slurry outlet in accordance with an embodiment; and 
           [0012]      FIG. 2  illustrates a more detailed view of the efficient slurry outlet. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0013]    For simplicity and illustrative purposes, the principles of the present invention are described by referring mainly to exemplary embodiments thereof. However, one of ordinary skill in the art would readily recognize that the same principles are equally applicable to, and can be implemented in, all types of chemical-mechanical polishing devices, and that any such variations do not depart from the true spirit and scope of the present invention. Moreover, in the following detailed description, references are made to the accompanying figures, which illustrate specific embodiments. Electrical, mechanical, logical and structural changes may be made to the embodiments without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense and the scope of the present invention is defined by the appended claims and their equivalents. 
         [0014]    Embodiments relate generally to methods and systems for efficient application of slurry for chemical-mechanical polishing (“CMP”) machines. More particularly, conventional CMP machines typically dispense slurry from at least one outlet onto a polishing pad of a CMP machine. These outlets may dispense the slurry as large droplets (&gt;1 mm) or streams. Since the polishing pad is rotating, a significant amount of the dispensed slurry tends to rotate off the polishing pad due to the centrifugal forces. In some embodiments, the outlets can dispense a liquid or chemical mixture absent of abrasives found in slurries. 
         [0015]    Embodiments reduce the amount of the dispensed slurry by applying the slurry as a fine mist, i.e., droplets (less than about 500 micrometers) to provide a uniform coating on the pad-wafer interface. Some embodiments may use outlets configured with an atomizer (air or ultrasonic) to dispense the slurry. Several outlets may be arranged to provide a uniform coating over the length of the wafer-polishing pad interface. An outlet may contain a slit/gap which controls the droplet size from submicron to hundreds of microns. 
         [0016]      FIG. 1  illustrates an exemplary rotary polisher  100  with an efficient slurry dispenser  125  in accordance with an embodiment. It should be readily apparent to those of ordinary skill in the art that the elements depicted in  FIG. 1  represents a generalized schematic illustration and that other components may be added or existing components may be removed or modified. 
         [0017]    As shown in  FIG. 1 , the rotary polisher  100  may include a polisher platen  105  coupled to a spindle  110 . The polisher platen  105  may provide a surface to polish a wafer  130  being attached to a movable structure  135 . The polisher platen  105  may also include a polishing pad (not shown). The spindle  110  may rotate the polisher platen  105  at various user-determined speeds. 
         [0018]    The rotary polisher may also include a slurry delivery (or supply) arm  115 . The slurry delivery arm  115  may be coupled to a slurry supply  120 . Slurry from the slurry supply  120  may be delivered through a channel (not shown) within the slurry delivery arm  115  as known to those skilled in the art. The slurry delivery arm  115  may also be configured to move the outlet of the slurry from the outer edge to the center of the polisher platen  105  to dispense slurry at the interface between a lowered wafer  130  and the polisher platen  105 . 
         [0019]    Unlike conventional slurry delivery arms which dispense slurry in large (&gt;˜1 mm) droplets or streams, the efficient slurry dispenses  125  may be configured to deliver slurry as a fine mist and/or droplet to provide a uniform coating of slurry to the polisher platen-wafer interface while minimizing the influence of centrifugal forces. Accordingly, the surface tension effects due to the thin uniform coat (or film) of slurry counteract the centrifugal force, thus reducing waste. In some embodiments, the efficient slurry dispenser  125  may be implemented as an atomizer to dispense the slurry. The atomizer can be an air or an ultrasonic type as known to those skilled in the art that can be configured to dispense the slurry from sub-micron to hundreds of microns, e.g., 500 microns, sized droplets or thickness of film. 
         [0020]      FIG. 2  depicts a more detailed view of the efficient slurry dispenser  125 . It should be readily apparent to those of ordinary skill in the art that the efficient slurry dispenser  125  depicted in  FIG. 2  represents a generalized schematic illustration and that other components may be added or existing components may be removed or modified. 
         [0021]    As shown in  FIG. 2 , the efficient slurry dispenser  125  comprises a housing  205  which provides a support structure for the atomizer  210 . The housing  205  can also be configured to interface with the slurry supply lines. More particularly, the housing  205  can be configured with a fitting to connect with slurry supply line of the rotary polisher  100  and retrofitting to the rotary dispensing arms of existing rotary polishing devices. 
         [0022]    The atomizer  210  may be configured to dispense slurry as droplets from about 500 microns or smaller in order to build a thin film of slurry in the range from submicron to hundreds of microns. The atomizer  210  may be an air atomizer which uses air to create the pressure to atomize the slurry. In other embodiments, the atomizer  210  may be an ultrasound atomizer which uses ultrasound frequencies to atomize the slurry. In some embodiments, the atomizer  210  can be configured to dispense other liquids or chemical mixtures. 
         [0023]    Although  FIGS. 1 and 2  depict a single efficient slurry dispenser  125 , it should be readily obvious that any number of efficient slurry dispensers may be used without departing from the spirit and scope of the present embodiments. For example, the number of efficient slurry dispensers on a slurry delivery arms may depend on the diameter of the mist/droplets. More particularly, the number of efficient slurry dispensers used in a configuration of the rotary polisher can be equivalent to the length of the slurry delivery arm divided by the diameter of the mist/droplets plus or minus a tolerance. Some embodiments of the efficient slurry dispenser  125  can limit the number of slurry dispensers to about twenty. 
         [0024]    While the invention has been described with reference to the exemplary embodiments thereof, those skilled in the art will be able to make various modifications to the described embodiments without departing from the true spirit and scope. The terms and descriptions used herein are set forth by way of illustration only and are not meant as limitations. In particular, although the method has been described by examples, the steps of the method may be performed in a different order than illustrated or simultaneously. Those skilled in the art will recognize that these and other variations are possible within the spirit and scope as defined in the following claims and their equivalents.