Patent Application
20110306276
The present invention is related generally to the field of chemical mechanical planarization (CMP). In particular, the present invention is a technique for simulating a splice for edges of fixed abrasives for use in a CMP process.
Fixed abrasives are commonly used in chemical mechanical planarization (CMP) processes because they provide consistent planarity, high substrate removal rates, and low levels of nonuniformity and defects. In the field of semiconductors, it is well known that polishing a wafer, for example, over the edges of a fixed abrasive article may result in high defect levels on the wafer being polished. These defects can occur when the diameter of the fixed abrasive article is smaller than the diameter of the platen that the fixed abrasive article is positioned on. The defects can be in the form of scratches caused by the relatively rough and uneven edges of the fixed abrasive article contacting the wafer. Conventional solutions include either splicing the edges of two separate, fixed abrasive articles together or splicing two edges of a single fixed abrasive article together in order to cover the entire platen.
In one embodiment, the present invention is an abrasive article including a support pad, a first abrasive element, a second abrasive element and a fixation mechanism. The support pad has a first major surface, a second major surface, a first edge, a second edge and a channel. The channel is formed within the first major surface and extends from the first edge to the second edge. The first and second abrasive elements are each positionable over a portion of the support pad. The fixation mechanism is positioned within the channel and secures an edge of the first abrasive element and an edge of the second abrasive element to the support pad.
In another embodiment, the present invention is a fixed abrasive article including a pad, a first abrasive element, a second abrasive element and a fixation mechanism. The pad has a first major surface and a second major surface. The first and second abrasive elements are each positionable over a portion of the first major surface. The fixation mechanism is located below a plane defined by the first major surface and attaches an edge of the first abrasive element and an edge of the second abrasive element to the pad.
In yet another embodiment, the present invention is a method of polishing a surface of a workpiece. The method includes providing a support pad having a first major surface, a first edge, a second edge, and a channel located within the first major surface extending from the first edge to the second edge, covering the first major surface of the support pad with a first abrasive element and a second abrasive element, positioning an edge of each of the first and second abrasive elements within the channel of the support pad, maintaining the edges of the first and second abrasive elements within the channel, contacting the first and second abrasive elements with the surface of the workpiece and moving the workpiece and the fixed abrasive elements with respect to each other.
The invention will be more readily understood and other features and advantages thereof will appear more clearly with reference to the accompanying drawings, given solely by way of example, in which:
The support pad 10 has a first major surface 14, a second major surface 16 and a channel 18 extending from a first edge 20 to a second edge 22 opposite the first edge 20. The channel 18 is formed within the first major surface 14 and includes a floor 24, a first side wall 26 and second side wall 28. The channel 18 results in the support pad 10 having a first height H1 and a second height H2. The first height H1 is measured from a plane of the second major surface 16 to a plane of the first major surface 14. The second height H2 is measured from a plane of the second major surface 16 to a plane of the floor 24 of the channel 18. The second height H2 is thus shorter than the first height H1. In one embodiment, the first height H1 is about 90 micrometers and the second height H2 is about 60 micrometers. Although
The hardness and/or compressibility of the support pad elements 36 and 38 are selected to provide the desired grinding characteristics (i.e., cut rate, product life, wafer uniformity and workpiece surface finish) for the particular process. The choice of materials for the resilient and rigid elements 36 and 38 will thus vary depending on the compositions of the workpiece surface (i.e. wafer surface) and fixed abrasive elements 30 and 32, the shape and initial flatness of the workpiece surface, the type of apparatus used for modifying the workpiece surface (e.g., planarizing the surface), the pressures used in the modification process, etc. In addition, the materials for use in the resilient and rigid elements 36 and 38 are selected such that the fixed abrasive article 12 provides uniform material removal across the workpiece surface (i.e., uniformity), and good planarity on patterned wafers, which includes flatness (measured in terms of the Total Indicated Runout (TIR)), and dishing (measured in terms of the planarization ratio). The particular planarity values depend on the individual workpiece and the application for which it is intended, as well as the nature of subsequent processing steps to which the workpiece may be subjected.
The primary purpose of the resilient element 36 is to allow the fixed abrasive article 12 to substantially conform to the global topography of the surface of the workpiece while maintaining a uniform pressure on the workpiece. For example, a semiconductor wafer may have an overall shape with relatively large undulations or variations in thickness, which the fixed abrasive article 12 should substantially match. It is desirable to provide substantial conformance of the fixed abrasive article 12 to the global topography of the workpiece so as to achieve the desired level of uniformity after modification of the workpiece surface. Because the resilient element 36 undergoes compression during a surface modification process, its resiliency when compressed in the thickness direction is an important characteristic for achieving this purpose. The resiliency (i.e., the stiffness in compression and elastic rebound) of the resilient element is related to the modulus of the material in the thickness direction, and is also affected by its thickness.
The resilient materials suitable for use in the fixed abrasive article 12 can be selected from a wide variety of materials. Typically, the resilient material is an organic polymer, which can be thermoplastic or thermoset and may or may not be inherently elastomeric. The materials generally found to be useful resilient materials are organic polymers that are foamed or blown to produce porous organic structures, which are typically referred to as foams. Such foams may be prepared from natural or synthetic rubber or other thermoplastic elastomers such as polyolefins, polyesters, polyamides, polyurethanes, and copolymers thereof, for example. Suitable synthetic thermoplastic elastomers include, but are not limited to, chloroprene rubbers, ethylene/propylene rubbers, butyl rubbers, polybutadienes, polyisoprenes, EPDM polymers, polyvinyl chlorides, polychloroprenes, or styrene/butadiene copolymers. An example of a particularly suitable resilient material is a copolymer of polyethylene and ethyl vinyl acetate in the form of a foam. Resilient materials may also be of other constructions if the appropriate mechanical properties (e.g., Young's Modulus and remaining stress in compression) are attained. Polyurethane impregnated felt-based materials used in conventional polishing pads can be used, for example. The resilient material may also be a nonwoven or woven fiber mat of, for example, polyolefin, polyester, or polyamide fibers, which has been impregnated by a resin (e.g. polyurethane). The fibers may be of finite length (i.e., staple) or substantially continuous in the fiber mat. Specific resilient materials that are suitable in the fixed abrasive articles of the present invention include, but are not limited to, poly(ethylene-co-vinyl acetate) foams available under the trade designations CELLFLEX 1200, CELLFLEX 1800, CELLFLEX 2200, CELLFLEX 2200 XF (Dertex Corp., Lawrence, Mass.); 3M SCOTCH brand CUSHION-MOUNT Plate Mounting Tape 949 (a double-coated high density elastomeric foam tape available from 3M Company, St. Paul, Minn.); EMR 1025 polyethylene foam (available from Sentinel Products, Hyannis, N.J.); HD200 polyurethane foam (available from Illbruck, Inc., Minneapolis, Minn.); MC8000 and MC8000EVA foams (available from Sentinel Products); and SUBA IV Impregnated Nonwoven (available from Rodel, Inc., Newark, Del.).
The primary purpose of the rigid element 38 is to limit the ability of the fixed abrasive article 12 to substantially conform to the local features of the surface of the workpiece. For example, a semiconductor wafer typically has adjacent features of the same or different heights with valleys between, the topography to which the abrasive construction should not substantially conform. It is desirable to attenuate conformance of the fixed abrasive article 12 to the local topography of the workpiece so as to achieve the desired level of planarity of the workpiece (e.g., avoid dishing). The bending stiffness (i.e., resistance to deformation by bending) of the rigid element 38 is an important characteristic for achieving this purpose. The bending stiffness of the rigid element 38 is directly related to the in-plane modulus of the material and is affected by its thickness. For example, for a homogeneous material, the bending stiffness is directly proportional to its Young's Modulus times the thickness of the material raised to the third power.
Exemplary rigid materials include, but are not limited to: organic polymers, inorganic polymers, ceramics, metals, composites of organic polymers, and combinations thereof. Suitable organic polymers can be thermoplastic or thermoset. Suitable thermoplastic materials include, but are not limited to: polycarbonates, polyesters, polyurethanes, polystyrenes, polyolefins, polyperfluoroolefins, polyvinyl chlorides, and copolymers thereof. Suitable thermosetting polymers include, but are not limited to: epoxies, polyimides, polyesters, and copolymers thereof. As used herein, copolymers include polymers containing two or more different monomers (e.g., terpolymers, tetrapolymers, etc.). The organic polymers may or may not be reinforced. The reinforcement can be in the form of fibers or particulate material. Suitable materials for use as reinforcement include, but are not limited to, organic or inorganic fibers (continuous or staple), silicates such as mica or talc, silica-based materials such as sand and quartz, metal particulates, glass, metallic oxides, and calcium carbonate.
Metal sheets can also be used as the rigid element 38. Typically, because metals have a relatively high Young's Modulus (e.g., greater than about 50 GPa), very thin sheets are used (typically about 0.075-0.25 mm). Suitable metals include, but are not limited to, aluminum, stainless steel, and copper. Particularly suitable rigid materials include, but are not limited to:
poly(ethylene terephthalate), polycarbonate, glass fiber reinforced epoxy boards (e.g., FR4, available from Minnesota Plastics, Minneapolis, Minn.), aluminum, stainless steel, and IC1000 (available from Rodel, Inc., Newark, Del.).
The resilient and rigid elements 36 and 38 of the abrasive constructions are typically separate layers of different materials. Each portion is typically one element of a material;
however, each element 36 and 38 can include more than one layer of the same or different materials provided that the mechanical behavior of the layer is acceptable for the desired application. For example, the rigid element 38 can include elements of resilient and rigid materials arranged so as to give the required bending stiffness. Similarly, the resilient element 36 can include elements of resilient and rigid materials as long as the overall laminate has sufficient resiliency.
There may also be intervening layers of adhesive or other attachment means between the various components of the fixed abrasive article construction 12. For example, an adhesive element (e.g., a pressure sensitive adhesive) may be interposed between the rigid element 38 and the backings of the fixed abrasive elements 30 and 32. Although not shown in
The fixed abrasive elements 30 and 32 include a plurality of abrasive particles affixed to a backing In general, the abrasive particles are dispersed in a binder to form an abrasive coating and/or abrasive composites bonded to the backing “Abrasive composite” refers to one of a plurality of shaped bodies which collectively provide a textured, three-dimensional abrasive element comprising abrasive particles and binder. “Textured” when used to describe a fixed abrasive element refers to a fixed abrasive element having raised portions and recessed portions. The abrasive particles may be homogeneously dispersed in the binder or alternatively the abrasive particles may be non-homogeneously dispersed. Generally, the abrasive particles are homogeneously dispersed so that the resulting abrasive coating provides a more consistent cutting ability. The first and second fixed abrasive elements 30 and 32 may include the same abrasive particles.
For semiconductor wafer planarization, fine abrasive particles are typically used. The average particle size of the abrasive particles can range from about 0.001 to 50 micrometers, typically between 0.01 to 10 micrometers. The particle size of the abrasive particle is typically measured by the longest dimension of the abrasive particle. In almost all cases there will be a range or distribution of particle sizes. In some instances the particle size distribution is tightly controlled such that the resulting abrasive article 12 provides a very consistent surface finish on the wafer after planarization.
The abrasive particles may also be in the form of an abrasive agglomerate which includes a plurality of individual abrasive particles bonded together to form a unitary particulate mass. The abrasive agglomerates may be irregularly shaped or have a predetermined shape. The abrasive agglomerates may utilize an organic binder or an inorganic binder to bond the abrasive particles together.
Examples of suitable abrasive particles include ceria (cerium oxide). fused aluminum oxide, heat treated aluminum oxide, white fused aluminum oxide, black silicon carbide, green silicon carbide, titanium diboride, boron carbide, silicon nitride, tungsten carbide, titanium carbide, diamond, cubic boron nitride, hexagonal boron nitride, garnet, fused alumina zirconia, alumina-based sol gel derived abrasive particles and the like. The alumina abrasive particle may contain a metal oxide modifier. Examples of alumina-based sol gel derived abrasive particles can be found in U.S. Pat. Nos. 4,314,827; 4,623,364; 4,744,802; 4,770,671; and 4,881,951, all incorporated herein by reference. The diamond and cubic boron nitride abrasive particles may be mono crystalline or polycrystal line. In the case of metal oxide-containing wafer surfaces (e.g., silicon dioxide-containing surfaces), ceria abrasive particles are useful. Ceria abrasive particles may be purchased from Rhone Poulenc; Shelton, Conn.; Transelco, N.Y.; Fujimi, Japan; Molycorp, Fairfield, N.J.; American Rar Ox, Chaveton City, Mass.; and Nanophase, Burr Ridge, Ill.
The fixed abrasive elements 30 and 32 may also contain a mixture of two or more different types of abrasive particles. For example, the mixture may include a mixture of “hard” inorganic abrasive particles and “soft” inorganic abrasive particles, or a mixture of two “soft” abrasive particles. “Hard” inorganic abrasive particles generally have a Mohs hardness of about 8 or greater and “soft” inorganic abrasive particles generally have a Mohs hardness less than about 8. In the mixture of two or more different abrasive particles, the individual abrasive particles may have the same average particle sizes, or may have different average particle sizes.
The binders for the fixed abrasive elements 30 and 32 of the present invention may be formed from an organic binder precursor. The binder precursor has a phase that is capable of flowing sufficiently so as to be coatable, and then solidifying. The solidification can be achieved by curing (e.g., polymerizing and/or crosslinking) and/or by drying (e.g., driving off a liquid), or simply upon cooling. The precursor can be an organic solvent-borne, water-borne, or 100% solids (i.e., a substantially solvent-free) composition. Both thermoplastic and thermosetting materials, as well as combinations thereof, can be used as the binder precursor.
The binder precursor is particularly a curable organic material (i.e., a material capable of polymerizing and/or crosslinking upon exposure to heat and/or other sources of energy, such as E-beam, ultraviolet, visible, etc., or with time upon the addition of a chemical catalyst, moisture, and the like). Binder precursor examples include amino resins (e.g., aminoplast resins) such as alkylated urea-formaldehyde resins, melamine-formaldehyde resins, and alkylated benzoguanamine-formaldehyde resin, acrylate resins (including acrylates and methacrylates) such as vinyl acrylates, acrylated epoxies, acrylated urethanes, acrylated polyesters, acrylated acrylics, acrylated polyethers, vinyl ethers, acrylated oils, and acrylated silicones, alkyd resins such as urethane alkyd resins, polyester resins, reactive urethane resins, phenolic resins such as resole and novolac resins, phenolic/latex resins, epoxy resins such as bisphenol epoxy resins, isocyanates, isocyanurates, polysiloxane resins (including alkylalkoxysilane resins), reactive vinyl resins, and the like. The resins may be in the form of monomers, oligomers, polymers, or combinations thereof.
In one embodiment, the abrasive article may comprise pre-determined pattern of a plurality of precisely shaped abrasive composites comprising abrasive particles dispersed in a binder. “Precisely shaped abrasive composite” refers to an abrasive composite having a molded shape that is the inverse of the mold cavity which is retained after the composite has been removed from the mold; preferably, the composite is substantially free of abrasive particles protruding beyond the exposed surfaces of the shape before the abrasive article has been used, as described in U.S. Pat. No. 5,152,917 (Pieper et al.).
Suitable backings for the abasive articles include both flexible backings and backings that are more rigid. The backing may be selected from a group of materials which have been used previously for abrasive articles, for example paper, nonwoven materials, cloth, treated cloth, polymeric film, primed polymeric film, metal foil, treated versions thereof, and combinations thereof. One preferred type of backing may be a polymeric film. Examples of such polymeric films include polyester films, co-polyester films, microvoided polyester films, polyimide films, polyamide films, polyvinyl alcohol films, polypropylene film, polyethylene film, and the like.
The thickness of the polymeric film backing generally may be from about 20 micrometers, preferably from about 50 micrometers, most preferably from about 60 micrometers; and may range to about 1,000 micrometers, more preferably to about 500 micrometers, and most preferably to about 200 micrometers. At least one surface of the backing may be coated with a matrix material and abrasive particles. In certain embodiments, the backing may be uniform in thickness. If the backing is not sufficiently uniform in thickness, greater variability in wafer polishing uniformity may result in the CMP process.
In practice, the backings of the first and second fixed abrasive elements 30 and 32 are generally coextensive with the first major surface 14 of the support pad 10 and are permanently attached to the support pad 10. The first abrasive element 30 is positioned over a first portion of the first major surface 14 of the support pad 10 created by the channel 18 such that an edge 40 of the first abrasive element 30 is positioned within the channel 18. Similarly, the second abrasive element 32 is positioned over a second portion of the first major surface 14 of the support pad 10 created by the channel 18 such that an edge 42 of the second abrasive element 32 is positioned within the channel 18. The fixed abrasive elements 30 and 32 can be attached to the support pad 10 by any means known in the art, including, but not limited to: adhesives, co-extrusion, thermal bonding, mechanical fastening devices, etc. Optionally, the fixed abrasive elements 30 and 32 do not need to be attached to the first major surface 14, but are at least maintained in a position immediately adjacent to it and coextensive with it. In this case some mechanical means of holding the fixed abrasive elements 30 and 32 in place during use will be required, such as placement pins, retaining ring, tension, vacuum, etc.
As can be seen in
Although the edges 40 and 42 of the fixed abrasive elements 30 and 32 are depicted in
During use, the surfaces of the fixed abrasive elements 30 and 32 contact the workpiece to modify the surface of the workpiece to achieve a surface that is more planar and/or more uniform and/or less rough than the surface prior to treatment. The underlying combination of the resilient and rigid elements 36 and 38 of the support pad 10 provides an abrasive construction that substantially conforms to the global topography of the surface of the workpiece (e.g., the overall surface of a semiconductor wafer) while not substantially conforming to the local topography of the surface of the workpiece (e.g., the spacing between adjacent features on the surface of a semiconductor wafer) during surface modification. As a result, the fixed abrasive article 12 will modify the surface of the workpiece in order to achieve the desired level of planarity, uniformity, and/or roughness. The particular degree of planarity, uniformity, and/or roughness desired will vary depending upon the individual workpiece and the application for which it is intended, as well as the nature of any subsequent processing steps to which the wafer may be subjected.
As previously mentioned, although the edges 40 and 42 of the first and second abrasive elements 30 and 32 are depicted as being affixed to the floor 24 of the channel 18, the edges 40 and 42 may be affixed anywhere within the channel 18 without departing from the intended scope of the present invention as long as the edges 40 and 42 are attached below the plane of polishing P.
In general, the abrasive rolls will be indexed to achieve the desired planarization criteria. Indexing may occur between the planarization of two separate workpieces. Alternatively, indexing may occur during the planarization of one workpiece. If the latter occurs, the indexing speed will be set to achieve the desired planarization criteria. Indexing of conventional abrasive rolls is well known in the art. Thus, the abrasive roll is not attached to the support pad 10 and is designed to move incrementally along the first major surface 14 of the support pad 10 in the direction of the channel 18 from the first edge 20 of the support pad 10 to the second edge 22 of the support pad 10 (shown in
The support pad 10 and the fixed abrasive elements 30 and 32 of the fixed abrasive article 12c depicted in
When the edges 40 and 42 are positioned within the slits 46 and 48, the edges 40 and 42 of the abrasive elements 30 and 32 are maintained below the plane of polishing P while the workpiece is being polished. To help maintain the remainder of the fixed abrasive elements 30 and 32 against the first major surface 14 of the support pad 10 during polishing, a vacuum, as is well known in the art, is applied. In configurations in which a vacuum is used, the platen surface is typically designed with holes, ports and/or channels to facilitate communication between the vacuum and the fixed abrasive article 12c. The vacuum is applied within the channel 18 as well as under the fixed abrasive elements 30 and 32 in order to ensure that the fixed abrasive elements 30 and 32 are being held down tightly, even in the area of the simulated splice. Upon completion of the polishing operation, the vacuum may be removed and the abrasive elements 30 and 32 can be moved forward, i.e., incremented a set amount, exposing a fresh region of abrasive. Optionally, any means known in the art of temporarily maintaining the fixed abrasive elements 30 and 32 against the support pad 10 during polishing can be used without departing from the intended scope of the present invention.
When the workpiece is not being polished, the vacuum is removed and the fixed abrasive elements 30 and 32 are advanced. The slits 46 and 48 allow the edges 40 and 42 of the fixed abrasive elements 30 and 32 to slide within the slits 46 and 48 such that the incrementing web can be advanced in the direction of the channel 18 and travel from the first edge 20 of the support pad 10 towards the second edge 22 of the support pad 10. When the fixed abrasive elements 30 and 32 have been advanced to the desired positions, the vacuum is reapplied to temporarily secure the fixed abrasive elements 30 and 32 to the support pad 10.
In one embodiment, the fixed abrasive elements 30 and 32 are maintained against the support pad 10 by a vacuum during polishing as described in the embodiment of
The fixed abrasive articles of the present invention can be used to polish or planarize a workpiece, such as a semiconductor wafer for example, during chemical mechanical planarization. The fixed abrasive articles minimize defects on the surface of the workpiece caused by contact with the rough edges of the fixed abrasive elements.
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
