Patent Publication Number: US-6702654-B2

Title: Conditioning wheel for conditioning a semiconductor wafer polishing pad and method of manufacture thereof

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention is directed, in general, to a conditioning wheel for a semiconductor wafer polishing pad and, more specifically, to a conditioning wheel that has a retainer coating deposited over the abrasive particles that inhibit the abrasive particles from dislodging from a surface of the conditioning wheel during a conditioning process. 
     BACKGROUND OF THE INVENTION 
     In the manufacture of the integrated circuits (ICs) derived from semiconductor wafers, chemical-mechanical planarization (CMP) is used to provide smooth topographies of the wafer substrates on which ICs are formed for subsequent lithography and material deposition. 
     Unfortunately, during the CMP process the polishing pad often collects particulate material from the slurry, as well as byproducts from the polishing process. Over time, this material begins to clog the pad, inhibiting the CMP process. When the pad becomes clogged, it becomes necessary to condition the pad in order to restore its original shape and properties. That is, the material must be removed before it completely clogs the pad and results in a surface that does not effectively polish the semiconductor wafer, or a surface that scratches or otherwise damages the wafer. In short, to properly polish a semiconductor wafer, the performance of the polishing pad should not be compromised. 
     In conventional processes, to condition the polishing pad, a conditioning wheel with a surface of diamond abrasives embedded in a nickel/stainless steel alloy setting is used. Referring initially to FIG. 1, illustrated is a polishing pad conditioning wheel  100  found in the prior art. The conditioning wheel  100  includes a planar body  110  and an upper surface  120 , typically composed of metal or a metal alloy, for conditioning a semiconductor wafer polishing pad (not illustrated). 
     The upper surface  120  of the conditioning wheel  100  includes abrasive particles, one of which is designated  140 , that are embedded in the upper surface  120 . The abrasive particles  140  are typically diamond crystals. These diamond crystals are well suited for conditioning the polishing surface of a polishing pad, which must be done periodically to keep the polishing pad at optimum polishing efficiency. 
     As the conditioning wheel  100  is repeatedly used, its effectiveness at reconditioning the surface of a polishing pad decreases. Perhaps the most common reason for this decrease may be that the abrasive particles  140  become worn and rounded, losing their polishing effectiveness. However, a more pressing concern for this degradation may be that the abrasive particles  140  in the upper surface  120  become lose and fall out of the upper surface  120  of the conditioning wheel  100 , as illustrated by arrow  150 . Of course, this reduces the effective surface area of the conditioning wheel  100  and slows the conditioning process. Moreover, this condition becomes even more pressing if many abrasive particles  140  are lost from a single area of the upper surface  120 . In such a case, the conditioning wheel  100  may begin to condition a polishing pad unevenly, which may translate into damaging or unevenly polishing a semiconductor wafer undergoing the CMP process. Once dislodged, the abrasive particles  140  that fall from the conditioning wheel  100  cannot be replaced with new particles. In time, when a substantial number of abrasive particles  140  have been lost, the capabilities of the conditioning wheel  100  are so lost that it must be replaced with a new one, usually at significant costs. 
     Perhaps more importantly, the loss of abrasive particles  140  during the conditioning process is not only undesirable from a cost standpoint, but also from a quality standpoint as the abrasive particles  140  can become embedded in the polishing pad just conditioned. Once embedded in the polishing pad, the abrasive particles  140  will easily scratch a semiconductor wafer undergoing CMP, in some cases damaging it beyond repair. With the high cost of semiconductor materials, manufacturers are understandably eager to avoid damaging, and thus, discarding wafers during the CMP process. 
     Accordingly, what is needed in the art is an improved conditioning wheel for conditioning a semiconductor wafer polishing pad that does not suffer from the deficiencies found in the prior art. 
     SUMMARY OF THE INVENTION 
     To address the above-discussed deficiencies of the prior art, the present invention provides an improved polishing pad conditioning wheel. In one embodiment, the conditioning wheel includes a planar body having a metal surface located thereon. The metal surface has abrasive particles embedded therein, and a retainer coating deposited over the metal surface and the abrasive particles. The retainer coating inhibits the abrasive particles from dislodging during a conditioning process. The retainer coating includes a wide range of coatings that would inhibit the abrasive particles from dislodging from the condition wheel. 
     The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the scope of the invention in its broadest form. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 illustrates a sectional view of a polishing pad conditioning wheel found in the prior art; 
     FIG. 2 illustrates a sectional view of a polishing pad conditioning wheel manufactured according to the principles of the present invention; and 
     FIG. 3 illustrates a sectional view of the polishing pad conditioning wheel of FIG. 2 having a worn retainer coating; 
     FIG. 4A illustrates a sectional view of a conventional polishing apparatus polishing a semiconductor wafer; and 
     FIG. 4B illustrates a sectional view of the conventional polishing apparatus of FIG. 4A incorporating a conditioning wheel according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring now to FIG. 2, there is illustrated an advantageous embodiment of a polishing pad conditioning wheel  200  as covered by the present invention. The conditioning wheel  200  includes a planar body  210  and an upper surface  220 . In a particularly advantageous embodiment, the planar body  210  has an annular configuration, however the present invention is broad enough to encompasses other geometric configurations. In such an embodiment, the conditioning wheel  200  conditions a polishing pad (not illustrated) by rotating against and across the pad&#39;s polishing surface. 
     In the illustrated embodiment, the upper surface  220  is a metal surface, and in an advantageous embodiment is composed of a nickel-chrome alloy. In an alternative embodiment, the upper surface  220  may be composed of stainless steel, however a conditioning wheel  200  according to the present invention is broad enough to encompass any material suitable for use in the upper surface  220  of the planar body  210  that is capable of retaining abrasive particles. 
     The upper surface  220  of the conditioning wheel  200  also includes abrasive particles, one of which is designated  240 , that are embedded in the upper surface  220 . In an exemplary embodiment, the abrasive particles  240  are diamond particles, however, other abrasive particles capable of conditioning a polishing pad, such as silicon carbide particles, may be used as the abrasive particles  240 . 
     The conditioning wheel  200  of the present invention further includes a retainer coating  250  that is located over the upper surface  220  and the abrasive particles  240 . The retainer coating  250  secures the abrasive particles  240  to the upper surface  220  and may, depending on the material, also provide an abrasive component. The retainer coating  250  also inhibits the abrasive particles  240  from becoming dislodged during conditioning of a polishing pad. Since the retainer coating  250  inhibits the abrasive particles  240  from falling from the upper surface  220 , the conditioning effectiveness of the conditioning wheel  200  remains high and the conditioning wheel  220  need only be replaced when the abrasive particles  240  are so worn they can no longer effectively condition a polishing pad. In a particularly advantageous embodiment of the conditioning wheel  200 , diamond particles are used as the abrasive particles  240  because of the superior wear-resistance. Because of this superior wear-resistance, the diamond particles could effectively condition substantially more polishing pads than conditioning wheels found in the prior art before the need to be replaced since the abrasive particles  240  would be securely held in place by the retainer coating  250 . 
     In one aspect of the conditioning wheel  200 , the retainer coating  250  is also composed of diamond. In this embodiment, the diamond coating  250  not only inhibits the abrasive particles  240  from becoming dislodged from the upper surface  220 , but also provides another abrasive surface for use in conditioning polishing pads. In fact, in a related embodiment the retainer coating  250  composed of diamond may even replace the abrasive particles  240  as the abrasive used to condition a polishing pad. This diamond coating may be deposited by a chemical vapor process. In such embodiments, the retainer coating  250  is a chemical vapor deposition diamond (CVD diamond) coating. As used with regard to the present invention, CVD diamond is defined as the deposition or growth of diamond crystals on a surface, through a chemical vapor deposition (CVD) process, which results in a microcrystalline diamond film forming on the surface. In this embodiment, to create the CVD diamond coating, CVD diamond is deposited onto the upper surface  220  of the conditioning wheel  200  through a CVD process. Those skilled in the art are familiar with such CVD process, as well as the tendency of the CVD process to create an ultra-thin film that closely follows the topography of the deposition surface. A conditioning wheel  200  having a CVD diamond coating as the retainer coating  250  also provides an additional abrasive surface, or, alternatively, a replacement abrasive surface, similar to the exemplary embodiment discussed above. 
     In yet another advantageous embodiment, the retainer coating  250  may be composed of silicon carbide. In this particular embodiment, the silicon carbide retainer coating  250  still inhibits the abrasive particles  240  from becoming dislodged from the upper surface  220 , and those skilled in the art are familiar with the advantages associated with the use of silicon carbide, such as increased wear-resistance and increased heat resistance. In one aspect of this particular embodiment, the silicon carbide coating may be a chemical vapor deposition silicon carbide (CVD silicon carbide) coating. As used with regard to the present invention, CVD silicon carbide is defined as the deposition or growth of silicon carbide on a surface, through a CVD process, which results in a silicon carbide film forming on the surface. Like the diamond coatings discussed above, the CVD silicon carbide coating also inhibits the abrasive particles  240  from becoming dislodged from the upper surface  220 , thus significantly extending the useful life of the conditioning wheel  200  above that of the prior art, and it also provides another abrasive surface that can be used to condition a polishing pad. 
     In view of the disclosed embodiments, one skilled in the art can see that a conditioning wheel  200  having a retainer coating  250  according to the principles of the present invention provides numerous advantages over wheels found in the prior art. Among the most significant advantages is preventing the contamination of polishing pads by inhibiting dislodging of the abrasive particles  240  during polishing pad conditioning. By inhibiting dislodging of the abrasive particles  240 , the conditioning wheel  200  provides the protection against scratching or otherwise damaging semiconductor wafers undergoing CMP unavailable in the prior art. Of course, the present invention also provides other important advantages including incorporating known CVD processes that result in a retainer coating  250  that will closely follow the surface topography, thus substantially maintaining the original abrasiveness of the upper surface  220 . In addition, the retainer coating  250  further provides an increased wear-resistance of its own. Specifically, the hardness of the retainer coating  250 , especially in embodiments using CVD diamond, provides extra life for the conditioning wheel  200  since the retainer coating  250  must first be worn before the abrasive particles  240  begin to wear. Furthermore, where conditioning wheels in the prior art cannot be repaired and reused once the abrasive particles are lost, the conditioning wheel  200  of the present invention may easily have a new retainer coating  250  replace a prior coating when it has excessively worn. Yet another advantage of the retainer coating  250  of the present invention is its ability to continue to provide support for the abrasive particles  240 , even after the retainer coating  250  becomes worn by repeated conditioning operations. This benefit will be described in greater detail with reference to FIG.  3 . 
     Referring now to FIG. 3, there is illustrated the polishing pad conditioning wheel  200  of FIG. 2 having a worn retainer coating  250 . The conditioning wheel  200  still includes the planar body  210  and upper surface  220  in which the abrasive particles  240  are embedded. The retainer coating  250  is again illustrated as deposited over the abrasive particles  240  and the upper surface  220  of the conditioning wheel  200 . 
     As illustrated, the retainer coating  250  of the conditioning wheel  200  has been worn away at the crests  310  of the abrasive particles  240 . These worn portions of the retainer coating  250  leave the crests  310  of the abrasive particles  240  exposed, and thus become the only portions of the conditioning wheel  200  used to condition a polishing pad (not illustrated). However, although the crests  310  of the retainer coating  250  are worn away, the retainer coating  250  still forms support walls  320  on each side of the abrasive particles  240 . As a result, the support walls  320  continue to secure the abrasive particles  240  in the upper surface  220 , thus continuing to inhibit them from becoming dislodged and possibly contaminating the CMP process of a semiconductor wafer. 
     In a particularly advantageous embodiment of the conditioning wheel  200 , the support walls  320  are capable of securing the abrasive particles  240  in the upper surface  220  until the abrasive particles  240  become too worn to effectively condition a polishing pad. In such an embodiment, the life of the conditioning wheel  200  is greatly extended, with a substantially reduced risk of contaminating the CMP process with loose abrasive particles  240 . 
     Referring now to FIGS. 4A and 4B, concurrently, illustrated is an example of a conventional polishing apparatus  400  that can be used to polish a semiconductor wafer  405 , and that can be used in conjunction with the present invention. Those who are skilled in the art understand how to make and use the polishing apparatus  400 , as well as how to condition a polishing pad. Basically, the polishing apparatus  400  includes a polishing platen  410  and a polishing pad  420  attached to the polishing platen  410  that is used to polish the semiconductor wafer  405 , perhaps during a CMP process. 
     The polishing apparatus  400  further includes a carrier head  430 . As illustrated in FIG. 4B, removably mounted to the carrier head  430  is the conditioning wheel  200  illustrated in FIGS. 2 and 3. The conditioning wheel  200  is removable so that the carrier head  430  may accommodate the semiconductor wafer  405 , as shown in FIG.  4 A. When the polishing effectiveness of the polishing pad  420  is lost or has diminished, the conditioning wheel  200 , with the abrasive particles  240  and the retainer coating  250  of the present invention, is mounted to the carrier head  430  and used to condition the polishing pad  420 . In such instances, the full polishing potential of the polishing pad  420  is realized for each wafer undergoing the CMP process. In other embodiments, the conditioning wheel  200  is a complete assembly, incorporating the carrier head  430  as part of a single assembly. In addition, other assemblies incorporating the conditioning wheel  200  are also encompassed by the present invention. 
     After the polishing pad  420  has been used to polish numerous semiconductor wafers  405 , its polishing surface will eventually degrade to the point of requiring conditioning to return its polishing efficiency. In such instances, the conditioning wheel  200  as covered by the present invention is attached to the carrier head  430  and used to condition the polishing pad  420 . 
     When conditioning of the polishing pad  420  is completed, the conditioning wheel  200  is removed from the carrier head  430  and a carrier ring  440  is reattached to the carrier head  430  and the polishing process on the semiconductor wafer  405  is resumed. This conditioning procedure is, of course, repeated whenever necessary. However, as discussed above, the retainer coating  250  continues to inhibit the abrasive particles  240  from becoming dislodged and falling away from the upper surface  220  of the conditioning wheel  200 , even when the conditioning process is repeated a significant number to times. As a result, the conditioning wheel  200 , according to the principles of the present invention, prevents the abrasive particles  240  from becoming embedded in the polishing pad  420  and contaminating the future polishing of other semiconductor wafers  405 . 
     Thus, with the durability of the retainer coating  250  securing the abrasive particles  240  in the upper surface  220 , the conditioning wheel  200  of the present invention may be used to condition significantly more polishing pads  420  than conditioning wheels found in the prior art. This conditioning can be done without the risk of contaminating those polishing pads  420  and damaging the semiconductor wafers  405  with dislodged abrasive particles  240 , as typically occurs with prior art conditioning wheels. 
     Although the present invention has been described in detail, referring to several embodiments, those skilled in the art should understand that they can make various changes, substitutions and alterations herein without departing from the spirit and scope of the invention in its broadest form.