Patent Publication Number: US-6220936-B1

Title: In-site roller dresser

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to the field of Chemical Mechanical Polishing (CMP). More particularly, the present invention relates to methods and apparatus for chemical mechanical polishing of substrates, such as semiconductor substrates, on a rotating polishing pad in the presence of chemically and/or physically abrasive slurry. The present invention provides a pad profile conditioning apparatus to condition the polishing pad while the polishing pad is being used to polish semiconductor substrates. 
     (2) Description of the Prior Art 
     Chemical Mechanical Polishing is a method of polishing materials, such as semiconductor substrates, to a high degree of planarity and uniformity. The process is used to planarize semiconductor slices prior to the fabrication of semiconductor circuitry thereon, and is also used to remove high elevation features created during the fabrication of the microelectronic circuitry on the substrate. One typical chemical mechanical polishing process uses a large polishing pad that is located on a rotating platen against which a substrate is positioned for polishing, and a positioning member which positions and biases the substrate on the rotating polishing pad. Chemical slurry, which may also include abrasive materials therein, is maintained on the polishing pad to modify the polishing characteristics of the polishing pad in order to enhance the polishing of the substrate. 
     The use of chemical mechanical polishing to planarize semiconductor substrates has not met with universal acceptance, particularly where the process is used to remove high elevation features created during the fabrication of microelectronic circuitry on the substrate. One primary problem which has limited the used of chemical mechanical polishing in the semiconductor industry is the limited ability to predict, much less control, the rate and uniformity at which the process will remove material from the substrate. As a result, CMP is a labor intensive process because the thickness and uniformity of the substrate must be constantly monitored to prevent overpolishing or inconsistent polishing of the substrate surface. 
     The profile of the polishing pad plays an important role in determining good overall polishing results. The polishing pad can, for instance, be profiled thick at the inner diameter of the polishing pad as compared to the outer diameter of the polishing pad and visa versa. The profile of the polishing pad is typically achieved by trial and error and by adjusting the position of a diamond dresser (see following paragraph). This method of profiling the polishing pad is destructive, time consuming and causes the loss of the polishing pad. Since this measure of the polishing pad profile can only be performed at the end of the useful life of the polishing pad, the wrong profile can only be detected after the polishing pad has served its useful life. 
     The function of the diamond dresser is to maintain and/or restore the polishing characteristics of the polishing pad to the maximum extent possible during the polishing operation and in doing so to extend the useful life or the operating characteristics of the polishing pad. The diamond dresser performs this function by influencing the polishing action of the polishing pad during its operation. This influencing can take the form of exerting pressure on the polishing pad and in so doing influencing the polishing characteristics of the polishing pad. 
     The polishing process is carried out until the surface of the wafer is ground to a highly planar state. During the polishing process, both the wafer surface and the polishing pad become abraded. After numerous wafers have been polished, the polishing pad becomes worn to the point where the efficiency of the polishing process is diminished and the rate of removal of material from the wafer surface is significantly decreased. It is usually at this point that the polishing pad is treated and restored to its initial state so that a high rate of uniform polishing can once again be obtained. 
     FIG. 1 shows a Prior Art CMP apparatus. A polishing pad  20  is affixed to a circular polishing table  22  that rotates in a direction indicated by arrow  24  at a rate in the order of 1 to 100 RPM. A wafer carrier  26  is used to hold wafer  18  face down against the polishing pad  20 . The wafer  18  is held in place by applying a vacuum to the backside of the wafer (not shown). The wafer  18  can also be attached to the wafer carrier  26  by the application of a substrate attachment film (not shown) to the lower surface of the wafer carrier  26 . The wafer carrier  26  also rotates as indicated by arrow  32 , usually in the same direction as the polishing table  22 , at a rate on the order of 1 to 100 RPM. Due to the rotation of the polishing table  22 , the wafer  18  traverses a circular polishing path over the polishing pad  20 . A force  28  is also applied in the downward vertical direction against wafer  18  and presses the wafer  18  against the polishing pad  20  as it is being polished. The force  28  is typically in the order of 0 to 15 pounds per square inch and is applied by means of a shaft  30  that is attached to the back of wafer carrier  26 . 
     Accordingly, the subject surface (that is the lower surface) of the substrate  18  is polished by the combination of a chemical polishing action of alkali contained in the polishing agent or slurry  21  and a mechanical polishing action by silica contained in the polishing slurry  21 . 
     U.S. Pat. No. 5,775,983 (Shendon et al.) shows a conical roller for conditioning a pad. 
     U.S. Pat. No. 5,779,526 (Gill) show a polishing pad conditioning roller. 
     U.S. Pat. No. 5,681,212 (Hayakawa) shows a disk dresser. 
     U.S. Pat. No. 5,421,768 (Fijiwara et al.) shows a brush to clean a polishing pad. 
     U.S. Pat. No. 5,688,360 (Jairath) shows cylindrical and conical polishing pads. 
     SUMMARY OF THE INVENTION 
     It is therefore the primary objective of the present invention to provide a polishing device that can realize a high semiconductor wafer throughput and that exhibits uniformity and planarity or evenness of surface in the plane of the surface of the substrate that is to be polished. 
     The in-site roller dresser that is the subject of the present invention allows for the profile of the pad to be monitored while the roller is dressed or refurbished. This eliminates the need for destructive testing of the polishing pad. The in-site roller dresser at the same time eliminates the need for machine downtime for polishing pad profile determination since the polishing pad profile is dynamically tested and monitored during polishing operations. In conventional arrangements, the dresser is a disk, in the arrangement of the present invention the dresser is a roller type that can rotate around its axis in either direction. A sensor is provided with the diamond dresser that monitors the surface or profile of the polishing pad. Based on the data obtained by the sensor, the diamond dresser can be adjusted, which directly controls the polishing pad refurbishing action provided by the dresser. 
     In the first embodiment of the present invention the in-site roller dresser is manually controlled and adjusted for desired polishing pad profile and in accordance with a visually observed profile of the polishing pad as observed via an electronic display. 
     In the second embodiment of the present invention the in-site roller dresser is automatically controlled and adjusted for desired polishing pad profile. This adjustment is in accordance with a desired and predetermined polishing pad profile that is contained within the controlling mechanism of the polishing pad dresser. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a Prior Art polishing pad apparatus. 
     FIG. 2 shows an overview of the mounting of the present invention diamond dresser with respect to the polishing pad and the polishing table. 
     FIG. 3 shows the mounting of the sensor of the present invention with respect to the polishing pad and the polishing table. 
     FIG. 4 shows the profile of a polishing pad as can be obtained within the scope of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now more specifically to FIG. 2, there is shown a rotating around its axis  27  that is mounted in a suspended manner and in such a manner that the diamond dresser  20  is above the polishing pad  22  and can be brought into physical contact with polishing pad  22 . Polishing pad  22  is mounted on top of the polishing table  21 . The mounting or suspension of dresser  20  is such that either of the two extremities of the dresser  20  can move in the Z direction, that is the direction perpendicular to the plane of the polishing pad  22 . This movement or rotation is indicated by rotations  16  and  18 . The two forces  12  and  14  that are exerted in the Z direction cause this movement. The circular polishing table  21  rotates around its axis  23  in a direction indicated by arrow  25  at a rate in the order of 1 to 100 RPM. 
     It must be noted at this time that the operation of the diamond dresser  20  is an operation that may or may not take place concurrent with the polishing action of the polishing pad. The action of the diamond dresser is invoked at the time that it is considered necessary to refurbish or ‘dress’ the polishing pad. That is the profile of the polishing pad must, after the pad has been used for a period of time, be restored to a new or corrected profile that is required for further and continued polishing operation. 
     FIG. 3 shows the mounting of the sensor  28  with respect to the polishing pad  22  and the polishing table  21 . The sensor  28  slides along the sensor guide  35  in a plane that is parallel with the plane of the surface of polishing pad  22 . The sensor  28  can be of a variety of types, for instance a capacitive sensor. The sensor position can be varied in a direction  26 , that is parallel to the polishing pad  22 . This motion  26  enables the sensor  28  to measure or track the profile of the polishing pad  22  across the entire surface of the polishing pad  22 . These measurements provide a direct feedback of the condition of the profile or surface condition of the polishing pad  22 . By increasing force  12  (FIG. 2) with respect to force  14  (FIG.  2 ), the diamond dresser  20  will exert more pressure on the polishing pad in the center of the polishing pad  22 . Inversely, by increasing the pressure of force  14  (FIG. 2) with respect to force  12  (FIG.  2 ), the diamond dresser  20  will exert more pressure on the polishing pad  22  in the periphery or outer edges of the polishing pad  22 . It is thus clear that the diamond dresser  20  has direct control over the shaping of the profile or top surface of the polishing pad  22  in a closed loop control system. 
     The parameters required to determine the position of the sensor  28  above the polishing pad  22  are the angle of rotation of the polishing pad  22  combined with the position of the movement  26  of the detector  28  along its axis of motion. Since the measurements obtained by the sensor  28  are a direct indication of the profile or top surface of the polishing pad  22  and since this information can be compared directly with a desired profile or top surface of the polishing pad, it is apparent that the information which directs forces  12  and  14  in FIG. 2 is available which in turn allows for either manual or automatic control or adjustment of the profile or top surface of the polishing pad  22 . 
     FIG. 4 shows how the profile can be displayed and monitored by using an electronic display or monitor. This does allow for human intervention and adjustment. This human intervention however is not in conflict with a completely automatic control system of the profile  29  of the polishing pad where measured (by the sensor) data is compared with stored or required profile data. The adjustment parameters, if any, can automatically adjust the two polishing pad profile control parameters  12  and  14  of FIG.  2 . 
     From the foregoing it will be clear that, although a specific embodiment of the present invention has been described herein for purposes of illustration, various modifications to the present invention may be made without deviating from the spirit and scope of the present invention. Accordingly, the present invention is not limited except as by the appended claims.