Abstract:
An apparatus and method of conditioning a CMP polishing pad to ensure consistent polishing throughout the polishing process. In particular, the apparatus consists of a translatable wedge-shaped conditioning plate, having a three point adjustable contact to ensure proper alignment with the polishing pad; a high pressure conditioning spray nozzle to clean the polishing pad and conditioning assembly throughout polishing; and a slurry dispensing nozzle to enhance planarization of the wafer. Further, the frequency of oscillation may be varied by the operator to prevent grooves from forming in the polishing pad.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates generally to semiconductor processing and, more particularly, to chemical-mechanical polishing used to planarize a semiconductor substrate. 
     2. Related Art 
     Chemical-mechanical polishing (hereinafter “CMP”), is a common method of planarization used in semiconductor manufacture. CMP typically involves the use of a circular polishing pad, mounted to a polishing table or platen, which is transported and held in contact with the surface of the semiconductor wafer via a carrier. An abrasive slurry, typically water-based, is applied to the surface of the polishing pad to facilitate and enhance polishing of the wafer. During polishing both polishing pad and wafer are rotated relative to one another. As a result, unwanted material is removed from the surface of the wafer, producing a planarized surface. 
     However, during polishing the surface of the polishing pad becomes matted and unevenly worn. This occurs for several reasons. For example, the pores in the surface of the pad which deliver slurry to the wafer become clogged with slurry and particulate material removed from the wafer. Further, the frictional polishing action designed to planarize the wafer also begins to planarize or wear the pad surface over time. Therefore, one key to effectively employing CMP methods is maintaining the consistency and integrity of the polishing pad surface throughout polishing. This necessitates conditioning the pad surface at frequent intervals to prevent degradation of the polishing pad surface. 
     Although typical devices used in the industry condition the polishing pad both before and after each wafer polishing cycle, non-uniformities occur within each cycle as a result of the wear discussed above. In addition, the majority of these conditioning techniques and devices are very time consuming, difficult to use and therefore, not cost effective. 
     In an attempt to remedy the defect, a prior art technique described in U.S. Pat. No. 5,785,585 to Manfredi et al., provides an in-situ conditioning method. Specifically, a stationary wedge-shaped conditioning plate, having a roughened bottom surface, rests flat on the polishing pad surface. Throughout polishing the pad is abraded by the wedge conditioner, thereby providing a consistent and reliable polish for the entirety of each wafer polishing cycle. 
     Although the method described in Manfredi et al. is quite effective when used with soft pads, such as suba-4, manufactured by Rodel Corporation, it is less effective when used with harder pads, such as IC-1000, by the same manufacturer. In particular, grooves often form in the pad surface, producing reservoirs in which the slurry collects, thereby preventing slurry from reaching the wafer surface. Further, particulate material removed from both the polishing pad and the wafer builds up at the edge of the conditioning plate, thereby interfering with effectiveness of the polishing. 
     Accordingly, there exists a need in the industry for a simpler, more cost effective apparatus for, and method of, maintaining a consistent polishing surface, for both hard and soft pads, by conditioning the pad throughout the polishing process. 
     SUMMARY OF THE INVENTION 
     The present invention provides an automated in-situ CMP pad conditioner for, and method of, cost effectively maintaining pad surface consistency throughout the duration of the polishing process, thereby producing consistent polishing over time. 
     A first general aspect of the present invention provides an apparatus for conditioning a polishing pad, comprising: a translatable plate positioned above the polishing pad; an elongated conduit having a plurality of outlets which deliver fluid to the polishing pad surface; and a translating means to move the translatable plate relative to the polishing pad. This aspect allows for the automatic conditioning of a polishing pad to ensure polishing pad consistency throughout the polishing process. Further, this aspect prevents the build-up of excess slurry and particulate material on the polishing pad surface, as well as at the edge of the conditioning plate. 
     A second general aspect of the present invention provides a method for conditioning a polishing pad surface throughout a polishing process, comprising the steps of: providing a translatable conditioning plate in contact with the polishing pad surface; oscillating the translatable conditioning plate relative to the rotating polishing pad surface; and dispensing a high pressure spray conditioning fluid over the polishing pad surface. This aspect provides for a method of maintaining polishing pad surface consistency throughout polishing, and provides similar advantages as those mentioned with respect to the first aspect. 
     A third general aspect of the present invention provides an apparatus for conditioning a polishing pad, comprising: a translatable conditioning plate positioned above the polishing pad; a translating means to move the translatable conditioning plate; and a fluid delivery mechanism affixed to the translatable conditioning plate. This aspect allows for similar advantages as those discussed with respect to the first aspect. 
     The foregoing and other features and advantages of the present invention will be apparent from the following more particular description of preferred embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The preferred embodiments of this invention will be described in detail, with reference to the following figures, wherein like designations denote like elements, and wherein: 
     FIG. 1 depicts a CMP polishing unit in accordance with the present invention; 
     FIG. 2 depicts the three segments of the wedge conditioning assembly in accordance with the present invention; and 
     FIG. 3 depicts the lower conditioning plate of the wedge conditioning assembly in accordance with the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Although certain preferred embodiments of the present invention will be shown and described in detail, it should be understood that various changes and modifications may be made without departing from the scope of the appended claims. The scope of the present invention will in no way be limited to the number of constituting components, the materials thereof, the shapes thereof, the relative arrangement thereof, etc., and are disclosed simply as an example of the preferred embodiments. 
     FIG. 1 depicts the components of CMP polishing unit  10  in accordance with the present invention. In particular, polishing unit  10  includes a frame  12 , comprising a vertical back  14 , a bottom  16 , a top  18 , and a circular retaining ring  20  affixed to and extending outwardly from top  18 . A power unit  22 , containing the typical necessary components, i.e., a motor, cam, etc. (individual components not shown) is mounted on bottom  16  of frame  12  to supply the requisite power to unit  10 . Power unit  22  receives a vertical shaft  24 , extending upwardly and protruding through top  18 . Lifting mechanism  26  is mounted to the portion of vertical shaft  24  that protrudes through top  18 . Vertical shaft  24  and lifting mechanism  26  work in conjunction to control movement of wedge conditioning assembly  28 , which is mounted to the under side of lifting mechanism  26  via bolts, screws, etc. In particular, vertical shaft  24  provides conditioning assembly  28  with oscillatory movement, and lifting mechanism  26  provides wedge conditioning assembly  28  with vertical movement with respect to polishing pad  30 . Wedge conditioning assembly  28  fits within and abuts circular retaining ring  20 . 
     A polishing pad  30  is mounted on a circular platen or table (not shown), and positioned within circular retaining ring  20 . Polishing pad  30  rotates about shaft  31  in the direction indicated by directional arrow  31 A, at a speed between 0 and 100 rpm, and engages the underside of wedge conditioning assembly  28 . At a location apart from wedge conditioning assembly  28  on polishing pad  30 , a wafer carrier  32 , rotating about shaft  33 , typically in the same direction as polishing pad  30 , illustrated by directional arrow  33 A, at between 0 and 100 rpm, forcibly holds a wafer (located at the underside of carrier  32 , but not shown) face down on polishing pad  30 . 
     As depicted in FIG. 2, wedge conditioning assembly  28  comprises three wedge-shaped segments, including an upper plate  34 , a retaining frame  36 , and a lower conditioning plate  38 . Retaining frame  36  fits loosely around the outside of both upper plate  34  and lower conditioning plate  38 , and functions to hold and guide upper plate  34  and lower conditioning plate  38 . Pipe  42  is mounted along the side of retaining frame  36 , ending in a nozzle  44 . Pipe  42  contains two internal chambers (not shown), one containing an abrasive slurry, such as silica, etc., and the other containing pressurized air. Both slurry and pressurized air exit nozzle  44  simultaneously, thereby uniformly dispensing atomized slurry over the surface of polishing pad  30 . This fine spray of slurry facilitates and enhances mechanical etching of the wafer. Similarly, pipe  46  is fastened along the back edge  37  and outside of retaining frame  36  ending in a high pressure nozzle  48 , which dispenses conditioning solution onto polishing pad  30 . The high pressure nozzle  48  is mounted on the up-stream side of wedge conditioning assembly  28 . In other words, high pressure nozzle  48  dispenses conditioning fluid onto the surface of polishing pad  30  before polishing pad  30  contacts lower conditioning plate  38 . This ensures that polishing pad  30  is cleaned of debris, such as excess slurry and particulate material, before conditioning to prevent build-up of excess slurry and particulate material at the edge of wedge conditioning assembly  28 , as discussed with the prior art. Upper plate  34 , held within retaining frame  36 , is mounted to the under side of lifting mechanism  26 , via bolts, or other conventional means. Lower conditioning plate  38 , typically having the same dimensions as upper plate  34  and held within retaining frame  36 , has cylindrical pins or posts  40  extending upwardly, which slidably engage holes  41  of upper plate  34 . This “three point contact” allows lower conditioning plate  38  to move relative to upper plate  34 , thereby ensuring wedge conditioning assembly  28  is in parallel with polishing pad  30 . 
     FIG. 3 shows lower conditioning plate  38 , having a roughened sheet  50  mounted on the bottom face  39 , via glueing or other means. Roughened sheet  50  contacts polishing pad  30 , thereby abrading and conditioning the surface of polishing pad  30 . Roughened sheet  50  may be made of a metal-bonded diamond grinding disc, i.e., nickel-bonded diamond, etc. 
     Directing attention again to FIG.  1  and the operation of CMP unit  10 , rotation of polishing pad  30  about shaft  31  is maintained throughout the polishing process. Lifting mechanism  26  raises wedge conditioning assembly  28  off polishing pad  30 , thereby allowing wafer carrier  32  to transport a wafer (not shown) to the surface of polishing pad  30 . Lifting mechanism  26  then lowers wedge conditioning assembly  28  into contact with polishing pad  30 . Since wedge conditioning assembly  28  contains the three point contact, thereby facilitating slidable adjustability, lower conditioning plate  38  (in FIG. 2) moves vertically with respect to upper plate  34 , within retaining frame  36 , and ensures parallel contact with polishing pad  30 . This is important because tolerances vary between different polishing pads used in CMP polishing units, and a parallel contact is vital to uniform conditioning. 
     Once wedge conditioning assembly  28  is parallel with polishing pad  30 , a pneumatic cylinder or air cushion system, applies a downward force on wedge conditioning assembly  28  to enhance the abrading effects of roughened sheet  50 . Simultaneously, a force is applied to counteract the downward force, thereby allowing the operator to control the amount of force applied (from between 0 psi to full static weight) at any given time. 
     Slurry, such as silica, or other water-based slurry, is delivered to the surface of polishing pad  30  via pipe  42  and nozzle  44  (refer to FIG. 2) throughout the wafer polishing cycle to enhance planarization. Spray conditioner is also delivered to the surface of polishing pad  30  throughout the wafer polishing cycle, via pipe  46  and high pressure nozzle  48 . The conditioner delivered by high pressure nozzle  48  forces the excess expended slurry and particulate material off the surface of polishing pad  30 , effectively cleaning the polishing pad  30  before it contacts lower conditioning plate  38  (refer to FIG.  2 ). The conditioner supplied by high pressure nozzle  48  also forces any debris attached to the leading edge of wedge conditioning assembly  28  off polishing pad  30 , which may interfere with conditioning. 
     Dictated by the cam profile (within power unit  22 ) which is selected by the operator, wedge conditioning assembly  28  oscillates, thereby abrading an arc within the surface of polishing pad  30 . The arc produced is typically, but not limited to, a sin wave. The oscillatory motion prevents grooves from forming within the pad surface caused by the repeated abrading by roughened sheet  50  affixed to lower conditioning plate  38  (refer to FIG.  3 ). It is important to note that the cam profile may be altered by the operator, thereby changing the arc produced within the pad surface. In other words, by changing the cam profile, the frequency of oscillation of wedge conditioning assembly  28  may be varied, thereby altering the pad conditioning characteristics. It should be appreciated that the oscillation of wedge conditioning assembly is not restricted to movement in merely two directions. 
     When the polishing cycle is completed for a single wafer, lifting mechanism  26  raises wedge conditioning. assembly  28  off of polishing pad  30 , thereby allowing carrier  32  to lift the wafer from the surface of polishing pad  30 . Another wafer within carrier  32  may be placed on polishing surface  30  and the process repeated. 
     While this invention has been described in conjunction with the specific embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the preferred embodiments of the invention set forth above are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention as defined in the following claims.