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  Cmp polishing pad having grooves arranged to improve polishing medium utilizationUSPTO Application #: 20060128291Title: Cmp polishing pad having grooves arranged to improve polishing medium utilization Abstract: A polishing pad (104, 304, 404, 504) having an annular polishing track (152, 312, 412, 512) for polishing a wafer (120, 316, 416, 516). A plurality of grooves (112, 320, 420, 520) are arranged within the wafer track so that they are spaced from one another both radially and circumferentially relative to the rotational nature of pad and are at least partially non-circumferential relative to the pad. (end of abstract) Agent: Rohm And Haas Electronic Materials Cmp Holdings, Inc. - Wilmington, DE, US Inventor: Gregory P. Muldowney USPTO Applicaton #: 20060128291 - Class: 451527000 (USPTO) Related Patent Categories: Abrading, Flexible-member Tool, Per Se, Interrupted Or Composite Work Face (e.g., Cracked, Nonplanar, Etc.) The Patent Description & Claims data below is from USPTO Patent Application 20060128291. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] The present invention generally relates to the field of chemical mechanical polishing (CMP). More particularly, the present invention is directed to a polishing CMP pad having grooves arranged to improve polishing medium utilization. [0002] In the fabrication of integrated circuits and other electronic devices, multiple layers of conducting, semiconducting and dielectric materials are deposited onto and removed from a surface of a semiconductor wafer. Thin layers of conducting, semiconducting and dielectric materials may be deposited using a number of deposition techniques. Common deposition techniques in modem wafer processing include physical vapor deposition (PVD), also known as sputtering, chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD) and electrochemical plating, among others. Common removal techniques include wet and dry isotropic and anisotropic etching, among others. [0003] As layers of materials are sequentially deposited and removed, the uppermost surface of the wafer becomes non-planar. Because subsequent semiconductor processing (e.g., metallization) requires the wafer to have a flat surface, the wafer needs to be planarized. Planarization is useful for removing undesired surface topography and surface defects, such as rough surfaces, agglomerated materials, crystal lattice damage, scratches and contaminated layers or materials. [0004] Chemical mechanical planarization, or chemical mechanical polishing (CMP), is a common technique used to planarize workpieces such as semiconductor wafers. In conventional CMP, a wafer carrier, or polishing head, is mounted on a carrier assembly. The polishing head holds the wafer and positions the wafer in contact with a polishing layer of a polishing pad within a CMP apparatus. The carrier assembly provides a controllable pressure between the wafer and polishing pad. Simultaneously therewith, a slurry, or other polishing medium, is flowed onto the polishing pad and into the gap between the wafer and polishing layer. To effect polishing, the polishing pad and wafer are moved, typically rotated, relative to one another. The wafer surface is polished and made planar by chemical and mechanical action of the polishing layer and polishing medium on the surface. As the polishing pad rotates beneath the wafer, the wafer sweeps out a typically annular polishing track, or polishing region, wherein the wafer surface directly confronts the polishing layer. [0005] Important considerations in designing a polishing layer include the distribution of polishing medium across the face of the polishing layer, the flow of fresh polishing medium into the polishing track, the flow of used polishing medium from the polishing track and the amount of polishing medium that flows through the polishing zone essentially unutilized, among others. One way to address these considerations is to provide the polishing layer with grooves. Over the years, quite a few different groove patterns and configurations have been implemented. Prior art groove patterns include radial, concentric-circular, Cartesian-grid and spiral, among others. Prior art groove configurations include configurations wherein the depth of all the grooves are uniform among all grooves and configurations wherein the depth of the grooves varies from one groove to another. [0006] It is generally acknowledged among CMP practitioners that certain groove patterns result in higher slurry consumption than others to achieve comparable material removal rates. Circular grooves, which do not connect to the outer periphery of the polishing layer, tend to consume less slurry than radial grooves, which provide the shortest possible path for slurry to reach the pad perimeter under the forces resulting from the rotation of the pad. Cartesian grids of grooves, which provide paths of various lengths to the outer periphery of the polishing layer, hold an intermediate position. [0007] Various groove patterns have been disclosed in the prior art that attempt to reduce slurry consumption and maximize slurry retention time on the polishing layer. For example, U.S. Pat. No. 6,241,596 to Osterheld et al. discloses a rotational-type polishing pad having grooves defining zigzag channels that generally radiate outward from the center of the pad. In one embodiment, the Osterheld et al. pad includes a rectangular "x-y" grid of grooves. The zigzag channels are defined by blocking selected ones of the intersections between the x- and y-direction grooves, while leaving other intersections unblocked. In another embodiment, the Osterheld et al. pad includes a plurality of discrete, generally radial zigzag grooves. Generally, the zigzag channels defined within the x-y grid of grooves or by the discrete zigzag grooves inhibit the flow of slurry through the corresponding grooves, at least relative to an unobstructed rectangular x-y grid of grooves and straight radial grooves. Another prior art groove pattern that has been described as providing increased slurry retention time is a spiral groove pattern that is assumed to push slurry toward the center of the polishing layer under the force of pad rotation. [0008] Research and modeling of CMP to date, including state-of-the-art computational fluid dynamics simulations, have revealed that in networks of grooves having fixed or gradually changing depth, a significant amount of polishing slurry may not contact the wafer because the slurry in the deepest portion of each groove flows under the wafer without contact. While grooves must be provided with a minimum depth to reliably convey slurry as the surface of the polishing layer wears down, any excess depth will result in some of the slurry provided to polishing layer not being utilized, since in conventional polishing layers an unbroken flow path exists beneath the workpiece wherein the slurry flows without participating in polishing. Accordingly, there is a need for a polishing layer having grooves arranged in a manner that reduces the amount of underutilization of slurry provided to the polishing layer and, consequently, reduces the waste of slurry. STATEMENT OF THE INVENTION [0009] In one aspect of the invention, a polishing pad, comprising: a) a polishing layer configured to polish a surface of at least one of a magnetic, optical or semiconductor substrate in the presence of a polishing medium, the polishing layer including a rotational axis, an outer periphery and an annular polishing track concentric with the rotational axis; and a plurality of grooves formed in the polishing layer and comprising a first set of grooves located entirely within the annular polishing track, each groove in the first set of grooves: i) being spaced from other grooves in the first set of grooves in a radial direction relative to the rotational axis; ii) being spaced from other grooves in the first set of grooves in a circumferential direction relative to the polishing pad; and iii) having a longitudinal axis at least a portion of which is oriented non-circumferentially relative to the polishing pad forming a discontinuous flow for the polishing medium where land regions interrupt flow to the outer periphery. [0010] In another aspect of the invention, a polishing pad, comprising: a) a polishing layer configured to polish a surface of at least one of a magnetic, optical or semiconductor substrate in the presence of a polishing medium, the polishing layer including: i) a rotational axis; ii) an outer periphery; iii) an annular polishing track concentric with the rotational axis; and iv) a peripheral region located between the annular polishing track and the outer periphery; and b) a plurality of grooves formed in the polishing layer and comprising: i) a first set of grooves located entirely within the annular polishing track, each of at least some of the grooves in the first set of grooves: A) spaced from others of the grooves in the first set of grooves in a radial direction relative to the rotational axis of the polishing layer; and B) spaced from others of the grooves in the first set of grooves in a circumferential direction relative to the polishing pad; and ii) a second set of grooves each located only in the annular polishing track and the peripheral region forming a discontinuous flow for the polishing medium where land regions interrupt flow to the outer periphery. BRIEF DESCRIPTION OF THE DRAWINGS [0011] FIG. 1 is a partial perspective view of a chemical mechanical polishing (CMP) system of the present invention; [0012] FIG. 2 is a plan view of the polishing pad of FIG. 1; and [0013] FIG. 3 is a plan view of a composite of three alternative polishing pads of the present invention illustrating three different groove arrangements. DETAILED DESCRIPTION OF THE INVENTION [0014] Referring now to the drawings, FIG. 1 shows in accordance with the present invention a chemical mechanical polishing (CMP) system, which is generally denoted by the numeral 100. CMP system 100 includes a polishing pad 104 having a polishing layer 108 that includes a plurality of grooves 112 arranged and configured for improving the utilization of a polishing medium 116 applied to the polishing pad during polishing of a semiconductor wafer 120 or other workpiece, such as glass, silicon wafers and magnetic information storage disks, among others. For convenience, the term "wafer" is used in the description below. However, those skilled in the art will appreciate that workpieces other than wafers are within the scope of the present invention. Polishing pad 104 and its unique features are described in detail below. [0015] CMP system 100 may include a polishing platen 124 rotatable about an axis 128 by a platen driver (not shown). Platen 124 may have an upper surface on which polishing pad 104 is mounted. A wafer carrier 132 rotatable about an axis 136 may be supported above polishing layer 108. Wafer carrier 132 may have a lower surface that engages wafer 120. Wafer 120 has a surface 140 that confronts polishing layer 108 and is planarized during polishing. Wafer carrier 132 may be supported by a carrier support assembly (not shown) adapted to rotate wafer 120 and provide a downward force F to press wafer surface 140 against polishing layer 108 so that a desired pressure exists between the wafer surface and the polishing layer during polishing. [0016] CMP system 100 may also include a supply system 144 for supplying polishing medium 116 to polishing layer 108. Supply system 144 may include a reservoir (not shown), e.g., a temperature controlled reservoir, that holds polishing medium 116. A conduit 148 may carry polishing medium 116 from the reservoir to a location adjacent polishing pad 104 where the polishing medium is dispensed onto polishing layer 108. A flow control valve (not shown) may be used to control the dispensing of polishing medium 116 onto pad 104. [0017] During the polishing operation, the platen driver rotates platen 124 and polishing pad 104 and the supply system 144 is activated to dispense polishing medium 116 onto the rotating polishing pad. Polishing medium 116 spreads out over polishing layer 108 due to the rotation of polishing pad 104, including the gap between wafer 120 and polishing pad 104. The wafer carrier 132 may be rotated at a selected speed, e.g., 0 rpm to 150 rpm, so that wafer surface 140 moves relative to the polishing layer 108. The wafer carrier 132 may also be controlled to provide a downward force F so as to induce a desired pressure, e.g., 0 psi to 15 psi, between wafer 120 and polishing pad 104. Polishing platen 124 is typically rotated at a speed of 0 to 150 rpm. As polishing pad 104 is rotated beneath wafer 120, surface 140 of the wafer sweeps out a typically annular wafer track, or polishing track 152 on polishing layer 108. [0018] It is noted that under certain circumstances polishing track 152 may not be strictly annular. For example, if surface 140 of wafer 120 is longer in one dimension than another and the wafer and polishing pad 104 are rotated at particular speeds such that these dimensions are always oriented the same way at the same locations on polishing layer 108, polishing track 152 would be generally annular, but have a width that varies from the longer dimension to the shorter dimension. A similar effect would occur at certain rotational speeds if surface 140 of wafer 120 were bi-axially symmetric, as with a circular or square shape, but the wafer is mounted off-center relative to the rotational center of that surface. Yet another example of when polishing track 152 would not be entirely annular is when wafer 120 is oscillated in a plane parallel to polishing layer 108 and polishing pad 104 is rotated at a speed such that the location of the wafer due to the oscillation relative to the polishing layer is the same on each revolution of the pad. In all of these cases, which are typically exceptional, polishing track 152 is still annular in nature, such that they are considered to fall within the coverage of the term "annular" as this term is used in the appended claims. [0019] FIG. 2 illustrates polishing pad 104 of FIG. 1 in more detail. Grooves 112 are arranged within polishing track 152 so that they are spaced from one another in both a radial direction 156 and a circumferential direction relative to the rotational nature of polishing pad 104. During polishing, the polishing medium, e.g., polishing medium 116 of FIG. 1, moves from groove 112 to groove 112 within polishing track 152 (as illustrated by arrows 164) primarily only under the influence of wafer 120 as the wafer is rotated in confronting relationship with polishing pad 104, e.g., in rotational direction 166. Since the polishing medium generally moves only when wafer 120 is present, the polishing medium tends to be utilized more efficiently than with conventional pads (not shown) having grooves that extend uninterrupted through the polishing track. This is so because a polishing medium often flows through the polishing track in these uninterrupted grooves under the influence of the rotation of the pad regardless of whether or not the wafer is present. Consequently, under these circumstances a polishing medium will often be used more rapidly with a conventional polishing pad than with a polishing pad, such as pad 104, of the present invention. This more rapid usage of a polishing medium by conventional polishing pads can have a number of drawbacks, including consumption of more polishing medium than optimally necessary and, for polishing that is enhanced by polishing byproducts, the level of byproducts being lower than optimal. [0020] In addition to grooves 112 being spaced from one another radially and circumferentially, it is desirable that at least a portion of the longitudinal axis 168 of each groove be oriented non-circumferentially relative to polishing pad 104. In other words, it is desirable that longitudinal axes 168 of grooves 112 not be merely arcs of circles concentric with rotational axis 128 of polishing pad 104. Providing such grooves 112 can facilitate the flow of a polishing medium as polishing pad 104 is rotated due to the effects of centrifugal forces caused by the rotation. In the present example, grooves 112 are generally arcs of spirals and, therefore, are non-circumferential along their entire lengths. In some, but not necessarily all, groove arrangements of the present invention, it is desirable that the distance between endpoints of each groove along a straight line connecting the endpoints be less than the least dimension of the surface of the substrate being polished that extends through the rotational center of that surface. For example, for a circular surface rotated about its concentric center, the straight-line distance between the endpoints of each groove using this criterion would be a value less than the diameter of the surface. On the other hand, for a rectangle having long sides of length L and short sides of length S, under this criterion the straight line distance between the endpoints of a groove would be a value less than the short side length S. Continue reading... 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