Abstract:
A CMP slurry mix and delivery system includes at least one container for holding a polishing agent; a pump connected to the container for pumping the polishing agent to a point of use; and a slurry dispersion unit installed between the pump and the point of use, wherein slurry dispersion unit provides megasonic energy that is capable of dispersing the polishing agent flowing through the slurry dispersion unit.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to the field of chemical mechanical polishing or chemical mechanical planarization (CMP) techniques. More particularly, the present invention relates to a slurry mix and delivery system for a CMP apparatus. 
         [0003]    2. Description of the Prior Art 
         [0004]    As known in the art, mechanical polishing or chemical mechanical planarization (CMP) is essential to the semiconductor fabrication to achieve a high degree of planarity on the surface of a semiconductor wafer. In a CMP process, the wafer is typically pressed against a rotating polishing pad. The wafer may rotate and oscillate over the surface of the polishing pad to improve polishing effectiveness. During the CMP process, aqueous slurry is provided to facilitate the polishing process. 
         [0005]    Typically, the aqueous slurry is introduced from a slurry reservoir through a piping system to a nozzle or sprayer where it is applied to the polishing pad to subsequently contact the wafer polishing surface. Alternatively, the slurry may be fed through a feed system directly through the lower portion of the polishing pad. The aqueous slurry 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. 
         [0006]    One problem associated with the conventional CMP techniques is the agglomeration of the slurry particles. Micro-scratching or other damage occurs to the wafer surface during polishing when the slurry particles or agglomerate exceed a given size. Therefore, a need exists in the industry to provide an improved slurry mix and delivery system for a CMP apparatus, which is capable of avoiding agglomeration of the slurry particles or dispersing agglomerated particles, thereby maintaining good particle dispersion in the slurry stream. 
       SUMMARY OF THE INVENTION 
       [0007]    It is one object of the present invention to provide an improved slurry mix and delivery system for a CMP apparatus in order to solve the above-described problems. 
         [0008]    To these ends, according to one aspect of the present invention, there is provided a CMP slurry mix and delivery system including at least one container for holding a polishing agent; a pump connected to the container for pumping the polishing agent to a point of use; and a slurry dispersion unit installed between the pump and the point of use, wherein slurry dispersion unit provides megasonic energy that is capable of dispersing the polishing agent flowing through the slurry dispersion unit. 
         [0009]    According to one aspect of the claimed invention, the slurry dispersion unit comprises a megasonic tank that is filled with a fluid, and a spiral tube installed within the megasonic tank and is dipped into the fluid. The polishing agent flows through the spiral tube. The number of turns of the spiral tube can be determined by the retention time of the polishing agent flowing through the spiral tube within the megasonic tank. The slurry dispersion unit may further comprise a transducer coupled to the fluid held by the megasonic tank and the polishing agent flowing through the spiral tube. 
         [0010]    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 
         [0011]    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: 
           [0012]      FIG. 1  is a schematic diagram illustrating a CMP slurry mix and delivery system in accordance with one embodiment of this invention; 
           [0013]      FIG. 2  is a schematic, perspective view showing an exemplary megasonic tank of the CMP slurry mix and delivery system in accordance with one embodiment of this invention; and 
           [0014]      FIG. 3  is a schematic, cross-sectional diagram illustrating an exemplary CMP station or CMP polishing unit in accordance with one embodiment of this invention. 
       
    
    
       [0015]    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 
       [0016]    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. 
         [0017]    Likewise, 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. 
         [0018]      FIG. 1  is a schematic diagram illustrating a CMP slurry mix and delivery system in accordance with one embodiment of this invention. As shown in  FIG. 1 , the CMP slurry mix and delivery system  10  comprises a plurality of container  12  and  14  each of which can hold a fluid constituent used for the slurry. Although two containers  12  and  14  for two-liquid mixed type slurry are shown, fewer or more containers can be provided depending on the composition of the slurry to be used in the CMP process. For example, in a case that the slurry is pre-mixed, only one container is needed. 
         [0019]    According to the embodiment of this invention, the first container  12 , which holds a first polishing agent S 1 , is connected to a first pump P 1  via a conduit  101 . The second container  14 , which holds a second polishing agent S 2 , is connected to a second pump P 2  via a conduit  102 . The first polishing agent S 1  is pumped to a main slurry conduit  105  via a conduit  103  and mixed with the second polishing agent S 2  pumped by the second pump P 2  via the conduit  104 . The mixed slurry S 3  then flows through a slurry dispersion unit  20  and is well dispersed therein. The dispersed slurry S 4  is then pumped into a CMP station  30  via a conduit  106  and is sprayed onto a polishing pad by a slurry feeding device. 
         [0020]    As used herein, the term “polishing agent” may include one or more fluids that are used during a CMP or other wafer polishing process. Examples of polishing agents include but not limited to slurries, buffing agents, and cleansing agents, among others. A polishing agent may include one or more constituents. 
         [0021]      FIG. 2  is a schematic, perspective view showing an exemplary slurry dispersion unit of the CMP slurry mix and delivery system in accordance with one embodiment of this invention. As shown in  FIG. 2 , the slurry dispersion unit  20  comprises a megasonic tank  201  that is filled with fluid  202  such as water or pure water. A spiral tube  210  is disposed within the megasonic tank  201  and is dipped into the fluid  202 . The number of turns of the spiral tube  210  can be determined by the retention time of the mixed slurry S 3  flowing through the spiral tube  210  within the megasonic tank  201 . One end of the spiral tube  210  may be coupled to a sidewall of the megasonic tank  201  via an inlet joint  205  that is connected to the main slurry conduit  105 . The other end of the spiral tube  210  may be coupled to an opposite sidewall of the megasonic tank  201  via an outlet joint  206  that is connected to the conduit  106 . The spiral tube  210  may be made of plastic materials such as polyvinyl chloride (PVC), metal such as copper, silicone or any suitable materials. 
         [0022]    According to the embodiment of this invention, the megasonic tank  201  may be equipped with a transducer  230 , which may be coupled to the fluid  202  held by the megasonic tank  201  and the slurry flowing through the spiral tube  210 . For example, the transducer  230  may oscillate between compressed and strained states at a near 1 MHz rate. The megasonic oscillation output by the transducer  230  causes a megasonic pressure oscillation within the megasonic tank  201 , thereby dispersing the slurry flowing through the spiral tube  210 . Optionally, a heater such as a thermal couple may be installed within the megasonic tank  201  to alter the temperature of the fluid  202  as well as the temperature of the slurry flowing through the spiral tube  210 . The transducer  230  and the heater  240  may be connected to a controller (not shown). The agglomerated particles in the slurry stream can be effectively dispersed by megasonic energy provided by the slurry dispersion unit  20 . 
         [0023]    As previously described, the dispersed slurry S 4  is then pumped into the CMP station  30  and is sprayed onto a polishing pad by a slurry feeding device. As shown in  FIG. 3 , the CMP station  30  may comprise a platen  300  connected to a shaft  301  for rotating the platen  300  about its central axis during polishing. A polishing pad  310  is mounted on the platen  300 . A wafer  322  is held and rotated by a carrier  320 . In polishing, a slurry feeding device  330  receives the dispersed slurry S 4  and sprays slurry S 4  onto the polishing pad  310 . The rotating wafer  322  is pressed against the polishing pad  310  by the carrier  320  to cause relative movement between the polishing surface of the polishing pad  310  and the wafer  322 , thereby producing a combined mechanical and chemical effect on the surface of the wafer. 
         [0024]    According to another embodiment of this invention, the first polishing agent S 1  and the second polishing agent S 2  may be mixed and dispersed within the megasonic tank  201  by megasonic energy. In such case, the fluid  202  and the spiral tube  210  are omitted. Further, the megasonic tank  201  may be hermetic or airtight. An additional pump (not shown) may be disposed in the conduit  106  to control the flow rate of the slurry S 4 . 
         [0025]    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.