Background of the Invention The production of integrated circuits began with the creation of high-quality semiconductor wafers. During the wafer fabrication process, the wafers may undergo multiple masking, etching and dielectric and conductor deposition processes. Because of the high-precision required in the production of these integrated circuits, an extremely flat surface is generally needed on at least one side of the semiconductor wafer to ensure proper accuracy and performance of the microelectronic structures being created on the wafer surface. As the size of the integrated circuits continues to decrease and the density of the microstructures per integrated circuit increases, the need for precise wafer surfaces becomes more important. Therefore, between each processing step, it is usually necessary to polish or planarize the surface of the wafer to obtain the flattest surface possible.

For a discussion of chemical mechanical planarization (CMP) processes and apparatus, see, for example, Arai, et al., U. S. Patent No. 4,805,348, issued February, 1989; Arai, et al., U. S.

Patent No. 5,099,614, issued March, 1992; Karlsrud et al., U. S. Patent No. 5,329,732, issued July, 1994; Karlsrud, U. S. Patent No. 5,498,196, issued March, 1996; and Karlsrud et al., U. S.

Patent No. 5,498,199, issued March, 1996.

Such polishing is well known in the art and generally includes attaching one side of the wafer to a flat surface of a wafer carrier or chuck and pressing the other side of the wafer against a flat polishing surface. In general, the polishing surface comprises a horizontal polishing pad onto which is applied a slurry. Polishing slurries may include abrasives of, for example, cerium oxide, aluminum oxide, fumed/precipitated silica or other particulate abrasives. Polishing pads can be formed of various materials, as is known in the art, and which are available commercially.

Typically, the polishing pad may be a blown polyurethane, such as the IC and GS series of polishing pads available from Rodel Products Corporation in Scottsdale, Arizona. The hardness

and density of the polishing pad depends on the material that is to be polished.

The wafer carrier is rotated around the periphery of the polishing machine while the wafer carrier itself is rotated. A fine particle sized abrasive slurry is used in conjunction with the movement of the wafer against the polishing pad in order to achieve the desired smoothness in polishing the wafer. Oftentimes, uneven or nonflat polishing occurs because some areas of the wafer receive more polishing than others despite control factors for alleviating this problem. As a result, several polishing pads have been designed to minimize non-planarity of the wafer surface during polishing. For example, U. S. Patent No. 5,177,908 issued to Tuttle discloses a polishing pad for semiconductor wafers which comprises a face for providing a constant surface contact rate to a semiconductor wafer in order to effect improved planarity of the wafer. The face pattern comprises a sunburst pattern having nontapered rays that are coaxial with the pad's rotation.

Another patent, U. S. Patent No. 5,394,655 issued to Allan et al. describes a semiconductor polishing pad having portions of the polishing surface removed by reducing the pad thickness so that parts of the wafer surface passing over the reduced thickness portions of the polishing pad are not polished as much as other parts of the wafer surface. A polishing pad formed from a mold is disclosed in U. S. Patent No. 5,441,598 issued to Yu et al. The Yu et al. polishing pad has a polishing side which can take several different shapes depending upon the primary surface of the mold. Channels may be formed along the polishing side of the pad in order to allow a smaller pore size to be used or a plurality of features having a specified height may be formed on the polishing side of the pad. As a result, the mold allows for more control over the surface of the polishing side of the pad.

Further, U. S. Patent No. 5,605,760 issued to Roberts discloses a polishing pad comprised of a solid uniform polymer sheet with no ability to absorb or transport slurry particles. This polishing pad allows for the use of optical detection to detect the condition of the wafer surface as the wafer is being polished. This allows one to monitor the planarity of the wafer. U. S. Patent No. 5,645,469 issued to Burke et al. describes a polishing pad having radially extending tapered channels in its polishing surface. The channels are configured to direct slurry from the inner radius of the polishing surface to the outer radius of the polishing surface. The channels can further be shaped to form a sunburst or starfish pattern.

Although all of the above described prior art polishing pads are designed to improve the planarity of the wafer surface being polished, none of the prior art polishing pads addresses the

principle of designing or configuring a polishing pad used in chemical mechanical polishing of semiconductor wafers which would improve the polishing pad maintenance (removal and replacement of the polishing pads) and storage. In addition, none of the prior art polishing pads overcomes the problems and disadvantages associated with the use of large diameter polishing pads which will become necessary to overcome with the trends toward larger wafer diameters.

At the same time, it is still important to monitor and achieve planarity in the wafer surfaces.

Accordingly, there is a need for a polishing pad which provides for the easy removal and replacement of polishing pads, including very large polishing pads, which also assists in providing for, or improving, the planarity of the wafer surface.

Summarv of the Invention It is a principle object of the present invention to provide an improved polishing pad for use in the chemical-mechanical polishing of workpieces, particularly semiconductor wafers.

It is another object of the present invention to provide an improved polishing pad for use in the chemical-mechanical polishing of semiconductor wafers which improves the planarity of the wafer surface by facilitating and improving slurry distribution of the slurry used during polishing.

It is still another object of the present invention to provide a segmented polishing pad which facilitates the removal, replacement, and storage of the polishing pads used in association with chemical-mechanical polishing machines.

It is yet another object of the present invention to provide a polishing pad which can be produced to accommodate large polish table platforms which will be manufactured and used to accommodate the larger wafer diameter trends in the semiconductor industry.

Briefly, the present invention is directed to a polishing pad comprising individual pieshaped segments. The individual pie shaped segments can be removed and replaced one at a time at different times throughout the life of the polishing pad, or alternatively, more than one individual segment or all of the individual segments can be removed and replaced at the same time. The segmented polishing pad of the present invention provides for the easy removal and replacement of the polishing pad regardless of the diameter of the polishing pad because the single pie-shaped pieces are much easier to handle and manipulate. Further, in that current polishing pads are stored flat in a stack and therefore occupy a large amount of floor space, the

segmented polishing pad of the present invention facilitates the storage of polishing pads because the individual segments of the pad when stored flat require less floor space. Also, the individual segmented pieces of the polishing pad of the present invention facilitate disposal of the polishing pads for chemical-mechanical polishing machines in that the machines are located in clean rooms and the current large diameter polishing pads are awkward to dispose of in a clean room environment. The individual segmented pieces of the polishing pad of the present invention can be easily removed from the lap wheel of the chemical-mechanical polishing machine and immediately placed in disposal bags.

Brief Description of the Drawings The present invention will hereinafter be described in conjunction with the appended drawing figures, wherein like numerals denote like elements, and: Figure 1 is a perspective schematic view of a semiconductor wafer polishing and planarization machine currently known in the art; Figures 2 and 3 are top cross-sectional views of the wafer polishing machine shown in Figure 1 illustrating different parts of the machine at different times in the polishing process; Figure 4 is a side cross-sectional view of a semiconductor wafer carrier element with an in-situ polishing pad conditioning ring connected thereto; Figure 5 is a top plan view of a prior art polishing pad used in conjunction with a chemical-mechanical polishing machine; Figure 6 is a top plan view of a first preferred embodiment of the segmented polishing pad of the present invention used in conjunction with a chemical-mechanical polishing machine; Figure 7 is a perspective view of the individual pie shaped segments of the segmented polishing pad shown in Figure 6 formed in a stack for storing; Figure 8 is a top plan view of a second embodiment of the segmented polishing pad of the present invention used in conjunction with a chemical-mechanical polishing machine; Figure 9 is a top plan view of a third embodiment of the segmented polishing pad of the present invention used in conjunction with a chemical-mechanical polishing machine; and Figure 10 is a top plan view of a fourth embodiment of the segmented polishing pad of the present invention used in conjunction with a chemical-mechanical polishing machine.

Detailed Description of the Preferred Embodiments The present invention relates to an improved polishing pad for use with a chemical- mechanical polishing machine for polishing workpieces, particularly semiconductor wafers. The improved polishing machine comprises pie-shaped segments which are completely separated from one another such that the individual segments can be easily removed one at a time. In order to more fully appreciate the advantages of the segmented polishing pad of the present invention, a description of the chemical-mechanical polishing machine used in conjunction with the segmented polishing pad along with the polishing process are described.

Referring now to Figures 1-3, a wafer polishing apparatus 100 is shown embodying the present invention. Wafer polishing apparatus 100 suitably comprises a comprehensive wafer polishing machine which accepts wafers from a previous processing step, polishes and rinses the wafers, and reloads the wafers back into wafer cassettes for subsequent processing. Discussing now the polishing apparatus 100 in more detail, apparatus 100 comprises an unload station 102, a wafer transition station 104, a polishing station 106, and a wafer rinse and load station 108.

In accordance with a preferred embodiment of the invention, cassettes 110, each holding a plurality of wafers, are loaded into the machine at load station 102. Next, a robotic wafer carrier arm 112 removes the wafers from cassettes 110 and places them, one at a time, on centering fixture 113. Wafer transfer arm 114 then lifts and moves the wafer into wafer transition section 104. That is, transfer arm 114 suitably places an individual wafer on one of a plurality of wafer pick-up stations 116 which reside on a rotatable table 120 within wafer transition section 104. Rotatable table 120 also suitably includes a plurality of wafer drop-off stations 118 which alternate with pick-up stations 116. After a wafer is deposited on one of the plurality of pick-up stations 116, table 120 will rotate so that a new station 116 aligns with transfer arm 114. Transfer arm 114 then places the next wafer on the new empty pick-up station 116. This process continues until all pick-up stations 116 are filled with wafers. In the preferred embodiment of the invention, table 120 will include five pick-up stations 116 and five drop-off stations 118.

Next, a wafer carrier apparatus 122, comprising individual wafer carrier elements 124, suitably aligns itself over table 120 so that respective carrier elements 124 are positioned directly above the wafers which reside in respective pick-up stations 116. Pickup stations 116 then move up and load wafers into the carrier apparatus 122, and the carrier apparatus 122 moves the wafers

laterally such that the wafers are positioned above polishing station 106. Once above polishing station 106, carrier apparatus 122 suitably lowers the wafers, which are held by individual elements 124, into operative engagement with a polishing pad 126 which sits atop a lap wheel 128. During operation, lap wheel 128 causes polishing pad 126 to rotate about its vertical axis.

At the same time, individual carrier elements 124 spin the wafers about their respective vertical axis and oscillate the wafers back and forth across pad 126 (substantially along arrow 133) as they press against the polishing pad. In this manner, the surface of the wafer will be polished or planarized.

After an appropriate period of time, the wafers are removed from polishing pad 126, and carrier apparatus 122 transports the wafers back to transition station 104. Dropoff stations 118 rise up to the carrier apparatus 122, which receives wafers which are ejected using water and/or air blowoff. The wains are then removed from drop-off stations 118 by a second transfer arm 130. Transfer arm 130 suitably lifts each wafer out of transition station 104 and transfers them into wafer rinse and load station 108. In the load station 108, transfer arm 130 holds the wafers while they are rinsed. After a thorough rinsing, the wafers are reloaded into cassettes 132, which then transport the subsequent stations for further processing or packaging.

During this polishing and planarization process, the polishing pad will wear and thus become less effective. Therefore, it is important to buff or condition polishing pad 126 to remove any surface irregularities that may develop during polishing. Generally, there are two ways to condition the polishing pad; in-situ and ex-situ conditioning. In-situ conditioning takes place during the wafer polishing process, while ex-situ conditioning occurs in between polishing steps.

Referring now to Figures 2-4, in-situ conditioning will first be discussed. In accordance with a preferred embodiment of the present invention, in-situ conditioning generally occurs by connecting an in-situ conditioning element 200 to each individual carrier element 124.

Therefore, as carrier elements 124 rotate and move the wafers over the polishing pad, conditioning elements 200 will also contact the polishing pad, thus conditioning the pad while the wafers are being polished.

Referring now to Figure 4, the configuration of conditioning element 200 and carrier element 124 will now be discussed. As previously mentioned, carrier element 124 holds and presses the wafers against the polishing pad during the polishing operation. As is well known in the art, carrier element 124 may comprise a number of different embodiments. However, for

purposes of discussing the present invention, carrier element 124 will be discussed in accordance with the embodiment shown in Figure 4.

Carrier element 124 preferably comprises a pressure plate 142, a carrier housing 140, a retaining ring 144, and a rotation drive shaft 146. Pressure plate 142 applies an equally distributed downward pressure against the backside of a wafer 10 as it is pressed against polishing pad 126. Protective layer 11 will preferably reside between pressure plate 142 and wafer 10 to protect the wafer during the polishing process. Protective layer 11 may be any type of semi-rigid material that will not damage the wafer as pressure is applied; for example, a urethane-type material. Wafer 10 may be held against protective layer 11 by any convenient mechanism, such as, for example, by vacuum or by wet surface tension. Circular retaining ring 144 preferably is connected around the periphery of protective layer 142 and prevents wafer 10 from slipping laterally from beneath the protective layer as the wafer is polished. Retaining ring 144 is generally connected to carrier housing 140 by bolts 148.

Also connected to carrier housing 140 is conditioning element 200 which is a ring formed of a rigid material, such as metal. As shown in Figures 4, conditioning element 200 preferably includes a downwardly extending flange 202 which terminates in a substantially flat bottom surface 204 having cutting elements attached thereto. The flange 202 is of sufficient length so that bottom surface 204 with attached cutting elements will contact the polishing pad during processing. Further, conditioning element 200 preferably will be loosely connected to carrier housing 140 by bolts 206. This relatively loose connection between pressure plate 140 and conditioning element 200 allows limited vertical movement but restricts lateral movement of conditioning element 200. The vertical movement of the conditioning element 200, which occurs between nuts 208 and 210 (Figure 4), is permitted so that the cutting elements contact pad 126 by virtue of the weight of conditioning element 200, rather than by pressure applied by carrier element 124. if needed, additional weighted rings 212 may be added to conditioning element 200 to increase the weight of the ring and thus the conditioning pressure on the pad.

During operation of apparatus 100, wafer 10 held by carrier element 124 is brought into contact with polishing pad 126 which is secured to lap wheel 128. Preferably, to maximize polishing, an abrasive slurry is introduced between polishing pad 126 and wafer 10. Various types of abrasive slurries can be used, as is known in the art. As wafer 10 contacts pad 126, both lap wheel 128 and carrier element 124 rotate, thus facilitating the polishing and planarization of the wafer. In addition, as carrier element 124 lowers wafer 10 onto the pad, conditioning element

200, which is connected to carrier element 124, will be lowered into contact with the pad. As lap wheel 128 and carrier element 124 rotate, cutting elements on the bottom surface 204 of flange 202 will rough-up and, thus, condition polishing pad 126 at the same time the wafers are being polished.

Turning now to Figure 5, a prior art polishing pad 146 is shown wherein the polishing pad 146 is comprised of a single circular layer 147 of polyurethane material having an inner diameter 148 and an outer diameter 150. Currently, all chemical-mechanical polishing pads are single sheets that are cut to the diameter of the polish table of the chemical-mechanical polishing machine. Current larger diameter pads have an outer diameter of 32 inches. Further, the circular single piece polishing pads are stacked and stored flat. Accordingly, it is easy to see how a stack of single piece 32 inch diameter polishing pads can occupy a substantial amount of floor space.

The segmented polishing pad of the present invention facilitates the storage of the polishing pads in that the individual segments of the pad can be stacked and stored thereby reducing the amount of storage space required.

A first preferred embodiment of the segmented polishing pad 156 of the present invention is shown in Figure 6. The segmented polishing pad 156 comprises a single layer of six pie-shaped segments 158 each having an outer edge 160 and an inner edge 162. Channels 164 are formed between the individual pie-shaped segments 158 when all of the pie-shaped segments 158 are properly positioned. The channels 164 allow for improved slurry distribution of the abrasive slurries that are introduced between the polishing pad and the wafer in order to maximize polishing. This first preferred embodiment may be formed from an existing 32 inch outer diameter polishing pad such as the IC 100/Suba IV pad manufactured by Rodel. The 32 inch diameter pad is cut into six pie-shaped segments 158 at approximately 60 degree angles with the segments being cut narrow enough to leave a very slight gap, i. e. less than 1/16 of an inch, between segments 158. These gaps form channels 164. Alternatively, the polishing pad can be cut into segments without leaving a gap between the segments.

The segmented polishing pad of the present invention is easier to store, easier to apply, easier to remove, and easier to dispose of than the traditional single piece polishing pads. For example, it is much easier for a worker in the clean room to remove and replace a single pie-shaped segment which is smaller and less cumbersome than the 32 inch diameter single piece polishing pad shown in Figure 5. Further, as evidenced in Figure 7, storage of the pie-shaped segments in stacks would require less floor space than the traditional single piece polishing pads.

Also, the large single piece polishing pads are often difficult to dispose of in a clean room environment. The smaller, pie-shaped segments of the polishing pad of the present invention can be easily placed in disposal bags for clean room removal. The channels 164 that may be created between segments 158 may also provide the extra benefit of improving slurry distribution during polishing thereby resulting in improved planarity of the wafer surface and the channel themselves may actually improve polishing of the wafer surface. However, extra care needs to be taken to correct for any possible thickness variation between the pad segments 158. Still, the individual pad segments 158 may be designed to vary in thickness in order to maximize planarity of the wafer surface if it is found that certain areas of the wafer are being polished more than others by coming into contact with the polishing pad.

Figures 8,9 and 10 show top planar views of additional embodiments of the segmented polishing pad of the present invention. Depending upon the desired outer diameter of the polishing pad the number of pie-shaped segments which comprise the segmented polishing pad of the present invention may vary. For example, a second embodiment of the segmented polishing pad 166 shown in Figure 8 comprises sixteen pieshaped segments 168 each having an outer edge 170 and an inner edge 172 with channels 174 created between the segments 168. A third embodiment of the segmented polishing pad 176 shown in Figure 9 comprises four pie-shaped segments 178 each having an outer edge 180, an inner edge 182 and channels 184 created between the segments 178. Finally, a fourth embodiment of the segmented polishing pad 186 shown in Figure 10 comprises eight pieshaped segments 188 each having an outer edge 190, an inner edge 192 and channels 194 created between the segments 188.

It will be understood that the foregoing description is of preferred exemplary embodiments of the invention and that the invention is not limited to the specific forms shown or described herein. Various modifications may be made in the design, arrangement, and type of elements disclosed herein, as well as the steps of making and using the invention without departing from the scope of the invention as expressed in the appended claims.