Abstract:
The present invention relates to a dressing apparatus for conditioning and regenerating a chemical mechanical polishing (CMP) pad. More specifically, the invention relates to a diamond disc dresser that employs an air spraying assembly and radially arranged dressing tools to clean, flatten, and roughen the polishing pad. Each of the dressing tools points at a same radial angle but are not necessarily equidistantly separated. Furthermore, a debris collector is used to collect the micro-particles and other types of contamination after they are swept off the working surface of the polishing pad.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a dressing apparatus for conditioning and regenerating a chemical mechanical polishing (referred to as CMP hereafter) pad; more specifically, the invention relates to a diamond disc dresser that cleans, flattens, and roughens the polishing pad. 
     2. Description of Related Art 
     A CMP device for polishing the surface of a semiconductor wafer includes a carrier for holding the semiconductor wafer and a polishing pad made of porous material polishes the wafer while retaining polishing slurry. The polishing slurry is a polishing fluid of certain grainy property. The carrier and pad are positioned such that the surface of the semiconductor wafer to be polished faces upward. The slurry is fed to the rear of the pad such that the porosity of the polishing pad allows the slurry to penetrate from the rear to the front of the pad. 
     Conventionally, two types of diamond disc dressers for conditioning the CMP pad are utilized by industry: annular disc type and spiky disc type. 
     An annular disc type dresser is a ring-shaped dressing apparatus with embedded synthetic diamond tool bits on its working surface. The main functions of the annular disc type dresser are to clean, roughen, and flatten the polishing pad of a CMP device. Nevertheless, it is extremely difficult to control the quality of the annular disc type dresser when it is being manufactured since the tiny diamond tool bits have to be permanently grafted to the working surface of the dresser with extreme evenness and tightness. 
     A spiky disc type dresser, on the other hand, is a disc dresser with a plurality of replaceable cylindrical spikes, wherein synthetic diamond bits are embedded on the tip portion of the cylindrical spikes. Since only a small area of the spiky type dresser is embedded with synthetic diamond bits, it is much simpler to manufacture the spiky disc type dresser compared with that of the annular disc type dresser. However, the spiky disc type dresser is less effective in cleaning, flattening, and roughening the pad. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to improve on a dressing apparatus for the conditioning and regeneration of a CMP pad which is simple to manufacture and provides effective cleaning, flattening, and roughening of the CMP pad. 
     The present invention meets this object by providing a dressing apparatus comprising: a rotatable inner shaft defining a first axis; an outer sleeve shaft disposed around the inner shaft; an air cap comprising a bottomless air chamber and at least one opening penetrating its upper surface for receiving compressed air; an air cap support connected to the outer sleeve shaft and supporting the curved air cap; a carrier plate disposed beneath the air cap and having an upper surface, a lower surface, and a plurality of through holes communicating the upper surface and the lower surface, wherein the upper surface is coupled to the inner shaft so as to rotate the carrier plate about the first axis, and the through holes receive compressed air from the air cap when the rotation of the carrier plate brings them under the air cap; and a plurality of dressing tools, each having a mounting surface and a dressing surface, wherein the mounting surfaces of the dressing tools are mounted to the lower surface of the carrier plate with the dressing surfaces facing the working surface of the CMP pad; wherein, the rotation of carrier plate conditions and regenerates the working surface of the CMP pad by action of the dressing surfaces of the dressing tools, and compressed air provided through the air cap is forced through the plurality of through holes in the carrier plate, thereby forcing micro-particles and other types of contamination off the working surface of the CMP pad. 
     The air cap can be curved, wherein the center of the curvature of the air cap is the first axis, and the air cap spans a spanning angle no greater than 180° and preferably no greater than 120°. A plurality of tiny synthetic diamond bits can permanently grafted onto the dressing surfaces of the dressing tools to enhance the conditioning and regenerating action. A debris collector can be provided for collecting the micro-particles and other types of contamination swept of the working surface of the CMP pad. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features, and advantages of the present invention will become apparent from the following detailed description of the preferred but non-limiting embodiment. The description is made with reference to the accompanying drawings in which: 
     FIG. 1A is a top view of a the dressing apparatus of this invention positioned on top of a CMP machine; 
     FIG. 1B is a perspective view of the drawing shown in FIG. 1A; 
     FIG. 2A is a detailed perspective drawing of the dressing apparatus of the present invention; 
     FIG. 2B shows an exploded view of the dressing apparatus of the present invention; 
     FIG. 3 is a perspective view of a curved air cap component for trapping compressed air according to the present invention; 
     FIG. 4A is a perspective drawing of one of the dressing tools shown in FIGS. 2A and 2B; 
     FIG. 4B is a perspective drawing depicting the dressing tool of FIG. 4A from an opposing angle. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1A shows a top view of a dressing apparatus  1  of the preferred embodiment of the present invention, illustrating how it is integrated into a CMP device for wafer processes. FIG. 1B is a perspective view of FIG.  1 A. 
     As shown in FIGS. 1A and 1B, the dressing apparatus  1  includes a sleeve bearing mechanism, wherein a rotatable inner shaft  100  supports the weight of the carrier plate  15  and the dressing tools  17 , while a non-rotating outer sleeve shaft  10  supports the weight of the air spraying assembly, which includes an air cap support  11  and an air cap  13 . Viewed from the top, the inner shaft  100  rotates in a clockwise direction with the first axis I—I as its rotating axis, whereby the carrier plate  15  and its dressing tools  17  carried thereunder are also driven to rotate. A manipulator (not shown) is adopted for moving of the dressing apparatus  1  to a specified location on the polishing pad  20 . Furthermore, the polishing pad  20  comprises a layer of microporous polyurethane material having an upward working surface  200  and operating on top of a rotating platform  21 , wherein the upward working surface  200  and rotating platform  21  are concentric and rotate clockwise about a second axis II—II. A wafer carrier  23 , rotates about a third axis III—III, a wafer  3  being carried on its underside (for example, by suction or vacuum actuated mechanism) to be polished by the working surface  200  of the polishing pad  20  and a polishing slurry  50 . The dressing apparatus  1  is positioned on top of the polishing pad  20  and aside from the second axis II—II, and the polishing slurry is delivered onto the working surface  200  via a nozzle slurry distribution system  5 , whereby the porous polishing pad  20  is permeated with the polishing slurry  50 . 
     Please refer to FIGS. 2A,  2 B, and  3 . FIG. 2A depicts the perspective view of the dressing apparatus  1  as a unit, FIG. 2B shows an exploded view of the dressing apparatus  1  in perspective view, and FIG. 3 is a perspective view of a curved air cap  13  which traps compressed air. 
     As shown in FIG. 2B, the dressing apparatus  1 , according to a preferred embodiment of the present invention, comprises an air cap support  11 , a curved air cap  13 , a carrier plate  15 , and a plurality of dressing tools  17 . 
     The air cap support  11  is a saucer-like supporting structure with a center hole portion  110  and an outer rim member  111  separated by an annular slot opening  112  that is configured for the insertion of the curved air cap  13 . The annular slot opening  112  communicates the top and bottom surfaces  113  and  115  of the air cap support  11 , and the center hole portion  110  is centered at point C, wherein C is on the first axis I—I. The air cap support  11  is coupled to the sleeve shaft  10  by fitting its center hole portion  110  to the outside circumference of the sleeve shaft  10 . Note that the inner shaft  100  rotates while the outer sleeve  10  and components coupled thereto (the air cap support  11  and the air cap  13 ) remain stationary. 
     The curved air cap  13 , comprises a curved bottomless air chamber  130  having its curvature centered at point C, and at least one opening  135  communicating the chamber  130  to the outer surface  133  of the curved air cap  13  (two openings  135  are illustrated). The curved air cap  13  can be provided with sidewalls  131  and  132  extending parallel to the sides of the curved air chamber  130  to be received in concentric annular recesses formed in the bottom surfaces of the center hole portion  110  and the outer rim portion  111 . Please refer to FIG.  3 . The curved air cap  13 , centered at point C, spans an angle of θ=120° according to a preferred embodiment of the present invention. However, it can also span any angle up to θ=180°. The curved air cap  13  is assembled to the air cap support  11  by inserting the air chamber  130  of the curved air cap  13  into and through the annular slot opening  112  of the air cap support  11  from underneath. When the two parts are thus mated, as shown in FIG. 2A, the air cap  13  fits tightly in the annular slot opening  112 , with the multiplicity of openings  135  of the air chamber  130  on top. 
     The carrier plate  15  is a circular plate having a upper surface  151  and a lower surface  152 , wherein the upper surface  151  of the carrier plate  15  is coupled to the inner shaft  100  with the first axis I—I being their common center axis. The inner shaft  100  drives the carrier plate  15  to rotate immediately beneath the curved air cap  13 . A plurality of dressing tools  17  are mounted on the lower surface  152  facing towards the working surface  200  of the polishing pad  20 . In addition, a multiplicity of through holes  153  symmetrical to the first axis I—I are arranged and positioned on the carrier plate  15  in such fashion that the inlet openings  153   i  are located on the upper surface  151  while the outlet openings  153   e  are to be located on lower surface  152 . Each of the through holes  153  is an air passageway having a deflected angle halfway between the air inlet opening  153   i  and the outlet opening  153   e;  the deflected angle in each of the through holes  153  is designed with the intention to force the pressurized air out at a direction away from the axis of the dressing apparatus  1  so that debris, or micro-particles generated by the CMP process, can by pushed off the working surface  200  of the polishing pad  20 . 
     As shown by FIG. 2B, a plurality of dressing tools  17 , each with curved surface outlines, are radially installed onto the lower surface  152  of the carrier plate  15  with the first axis I—I as their common center point. Also referring to FIGS. 4A and 4B, each of the dressing tools  17  has a mounting surface  171  and a dressing surface  173 , wherein the mounting surface  171  is for mounting the dressing tool  17  onto the lower surface  152  of the carrier plate  15  and the dressing surface  173  for conditioning and regeneration of the working surface  200  of the polishing pad  20 . Furthermore, a plurality of tiny synthetic diamond bits  175  are permanently grafted onto the dressing surface  173  of the dressing tool  17 , which provides the needed dressing effect. 
     Referring back to FIG. 1A, each of the dressing tools  17  located on the lower surface  152  of the carrier plate  15  is pointing in the same radial angle. In this embodiment, they are equidistant. 
     Referring to FIG. 2A, a detailed perspective drawing of the dressing apparatus with air cap support  11 , carrier plate  15 , a plurality of dressing tools  17 , inner shaft  100 , outer sleeve  10 , and curved air cap  13  assembled together as a whole. Referring again to FIG. 1A, in operation, compressed nitrogen (N 2 ) from a compressed nitrogen source  4  would enter the air chamber  130  by the multiplicity of openings  135  on top of the air cap  13 . When part of the rotating carrier plate  15  with the through holes  153  is directly under and exposed to the bottomless air chamber  130 , the compressed air inside the air chamber  130  will be forced out via the through holes  153  of the carrier plate  15  and exit said outlet opening  153   e  at a deflected angle. 
     Referring to FIGS. 1A and 1B again, the working surface  200  of the polishing pad  20  rotates in clockwise direction A as shown. While the dressing apparatus  1 , rotating swiftly in clockwise direction as well, brushes over the working surface  200  of the polishing pad  20 , the synthetic diamond bits  175  roughen the working surface  200  and remove the adhered micro-particle debris. The polishing pad  20  is reconditioned and regenerated to provide a smoother and more consistent polishing finish for wafers  3  since the working surface  200  of the polishing pad  20  is constantly being cleaned, roughened, and flattened by means of the diamond bits  175  and said air spraying assembly. A debris collector (not shown) can be provided to collect the micro-particles and other types of contamination after they are swept off the working surface  200  of the polishing pad  20 . 
     Therefore, the CMP dressing apparatus according to the preferred embodiments of the present invention can effectively cleans, roughens, and flattens the polishing pad  20 , which in turn improves the yield and reliability of wafer-making process. 
     Although the present invention has been explained by the embodiments shown in the drawings described above, it should be understood to the ordinary skilled person in the art that the invention is not limited to the embodiments, but rather that various changes or modifications thereof are possible without departing from the spirit of the invention. Accordingly, the scope of the invention shall be determined only by the appended claims and their equivalents.