Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
  • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
  • H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
  • H01L21/302—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to change their surface-physical characteristics or shape, e.g. etching, polishing, cutting
  • H01L21/304—Mechanical treatment, e.g. grinding, polishing, cutting
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
  • B24B37/00—Lapping machines or devices; Accessories
  • B24B37/11—Lapping tools
  • B24B37/20—Lapping pads for working plane surfaces
  • B24B37/26—Lapping pads for working plane surfaces characterised by the shape of the lapping pad surface, e.g. grooved
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
  • B24B37/00—Lapping machines or devices; Accessories
  • B24B37/04—Lapping machines or devices; Accessories designed for working plane surfaces
  • B24B37/042—Lapping machines or devices; Accessories designed for working plane surfaces operating processes therefor
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24D—TOOLS FOR GRINDING, BUFFING OR SHARPENING
  • B24D3/00—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents
  • B24D3/02—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents the constituent being used as bonding agent
  • B24D3/20—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents the constituent being used as bonding agent and being essentially organic
  • B24D3/28—Resins or natural or synthetic macromolecular compounds
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
  • Y02P70/10—Greenhouse gas [GHG] capture, material saving, heat recovery or other energy efficient measures, e.g. motor control, characterised by manufacturing processes, e.g. for rolling metal or metal working

Definitions

• the present invention relates generally to polishing pads used to polish and/or planarize substrates, particularly metal or metal-containing substrates during the manufacture of a semiconductor device.
• CMP Chemical-mechanical planarization
• metal layers such as tungsten, aluminum, or copper.
• CMP must generally meet more demanding performance standards.
• a relatively recent CMP process has been the fabrication of metal interconnects by the metal damascene process (see for example, S. P. Murarka, J. Steigerwald, and R. J. Gutmann, "Inlaid Copper Multilevel Interconnections Using Planarization by Chemical Mechanical Polishing", MRS Bulletin, pp. 46-51, June 1993, which is hereby incorporated by reference in its entirety for all useful purposes).
• the polished substrate is generally a composite rather than a homogenous layer and generally comprises the following basic steps: i. a series of metal conductor areas (plugs and lines) are photolithographically defined on an insulator surface; ii. the exposed insulator surface is then etched away to a desired depth; iii. after removal of the photoresist, adhesion layers and diffusion barrier layers are applied; iv. thereafter, a thick layer of conductive metal is deposited, extending above the surface of the insulator material of the plugs and lines; and v. the metal surface is then polished down to the underlying insulator surface to thereby produce discrete conductive plugs and lines separated by insulator material.
• the conductive plugs and lines are perfectly planar and are of equal cross-sectional thickness in all cases.
• significant differences in thickness across the width of the metal structure can occur, with the center of the feature often having less thickness than the edges.
• This effect commonly referred to as “dishing” is generally undesirable as the variation in cross-sectional area of the conductive structures can lead to variations in electrical resistance. Dishing arises because the harder insulating layer (surrounding the softer metal conductor features) polishes at a slower rate than the metal features. Therefore, as the insulating region is polished flat, the polishing pad tends to erode away conductor material, predominantly from the center of the metal feature, which in turn can harm the performance of the final semiconductor device.
• Grooves are typically added to polishing pads used for CMP for several reasons:
• polishing pad 1. To prevent hydroplaning of the wafer being polished across the surface of the polishing pad. If the pad is either ungrooved or unperforated, a continuous layer of polishing fluid can exist between the wafer and pad, preventing uniform intimate contact and significantly reducing removal rate.
• the invention relates to polishing pads with low elastic recovery and grooves. Embodiments of the invention will now be described, by way of example, with reference to the following detailed description.
• GSQ Geographical Stiffness Quotient
• the present invention is directed to polishing pads for CMP having low elastic recovery during polishing, while also exhibiting significant anelastic properties relative to many known polishing pads, and with defined groove patterns having specific relationships between groove depth and overall pad thickness and groove area and land area.
• the pads of the present invention further define: i. an average surface roughness of about 1 to about 9 micrometers; ii. a hardness of about 40 to about 70 Shore D; and iii. a tensile Modulus up to about 2000 MPa at 40°C.
• the polishing pads of the present invention define a ratio of Elastic Storage Modulus (E') at 30° and 90°C being 5 or less, more appropriately less than about 4.6 and more appropriately less than about 3.6.
• the polishing pad defines a ratio of E' at 30°C and 90°C from about 1.0 to about 5.0 and an Energy Loss Factor (KEL) from about 100 to about 1000 (1/Pa) (40°C).
• the polishing pad has an average surface roughness of about 2 to about 7 micrometers, a hardness of about 45 to about 65 Shore D, a Modulus E' of about 150 to about 1500 MPa at 40°C, a KEL of about 125 to about 850 (1/Pa at 40°C) and a ratio of E' at 30°C and 90°C of about 1.0 to about 4.0.
• the polishing pads of the present invention have an average surface roughness of about 3 to about 5 micrometers, a hardness of about 55 to about 63 Shore D, a Modulus E' of 200 to 800 MPa at 40°C, KEL of 150 to 400 (1/Pa at 40°C) and a ratio of E' at 30°C and 90°C of 1.0 to 3.6.
• the present invention is directed to polishing pads having a groove pattern with a groove depth in a range of about 75 to about 2,540 micrometers (more appropriately about 375 to about 1 ,270 micrometers, and most appropriately about 635 to about
• a groove width in a range of about 125 to about 1 ,270 micrometers (more appropriately about 250 to about 760 micrometers, and most appropriately about 375 to about 635 micrometers) and a groove pitch in a range of about 500 to about 3,600 micrometers (more appropriately about 760 to about 2,280 micrometers, and most appropriately about 2,000 to about
• a pattern with this configuration of grooves further provides a Groove
• GSQ Stiffness Quotient
• GFQ Groove Flow Quotient
• the pads of the present invention may be filled or unfilled and porous or non-porous.
• Appropriate fillers include, but are not limited to, micro-elements (e.g., micro-balloons), abrasive particles, gases, fluids, and any fillers commonly used in polymer chemistry, provided they do not unduly interfere negatively with polishing performance.
• abrasive particles include, but are not limited to, alumina, ceria, silica, titania, germania, diamond, silicon carbide or mixtures thereof, either alone or interspersed in a friable matrix which is separate from the continuous phase of pad material.
• the pads of this invention can be used in combination with polishing fluids to perform CMP upon any one of a number of substrates, such as, semiconductor device (or precursor thereto), a silicon wafer, a glass (or nickel) memory disk or the like. More detail may be found in
• the pad formulation may be modified to optimize pad properties for specific types of polishing. For example, for polishing softer metals, such as aluminum or copper, softer pads are sometimes required to prevent scratches and other defects during polishing. However, if the pads are too soft, the pad can exhibit a decreased ability to planarize and minimize dishing of features. For polishing oxide and harder metals such as tungsten, harder pads are generally required to achieve acceptable removal rates.
• the present invention is directed to a process for polishing metal damascene structures on a semiconductor wafer by: i. pressing the wafer against the surface of a pad in combination with an aqueous-based liquid that optionally contains sub-micron particles; and ii. providing mechanical or similar-type movement for relative motion of wafer and polishing pad under pressure so that the moving pressurized contact results in planar removal of the surface of said wafer.
• the appropriate pads of*the present invention have high-energy dissipation, particularly during compression, coupled with high pad stiffness.
• the pad exhibits a stable morphology that can be reproduced easily and consistently.
• the pad surface has macro-texture. This macro-texture can be either perforations through the pad thickness or surface groove designs.
• Such surface groove designs include, but are not limited to, circular grooves which may be concentric or spiral grooves, cross-hatched patterns arranged as an X-Y grid across the pad surface, other regular designs such as hexagons, triangles and tire-tread type patterns, or irregular designs such as fractal patterns, or combinations thereof.
• the groove profile may be rectangular with straight side-walls or the groove cross-section may be "V"-shaped, "U”-shaped, triangular, saw-tooth, etc.
• the geometric center of circular designs may coincide with the geometric center of the pad or may be offset.
• the groove design may change across the pad surface. The choice of design depends on the material being polished and the type of polisher, since different polishers use different size and shape pads (i.e. circular versus belt).
• Groove designs may be engineered for specific applications. Typically, these groove designs comprise one or more grooves. Further, groove dimensions in a specific design may be varied across the pad surface to produce regions of different groove densities either to enhance slurry flow or pad stiffness or both. The optimum macro-texture design will depend on the material being polished (i.e. oxide or metal, copper or Tungsten) and the type of polisher (e.g. IPEC 676, AMAT Mirra, Westech 472, or other commercially available polishing tools ). The following drawings are provided: Figure 1 illustrates pad and groove dimensions.
• Figure 2 illustrates GSQ versus Groove Depth at constant Pad Thicknesses.
• Figure 3 illustrates GSQ versus Pad Thickness at constant Groove Depths.
• Figure 4 illustrates GFQ versus Groove Width at constant Groove Pitches.
• Figure 5 illustrates GFQ versus Groove Pitch at constant Groove Widths.
• Commercially available pads used for CMP are typically about 1 ,300 micrometers thick.
• Pad thickness can contribute to the stiffness of the pad, which in turn, can determine the ability of the pad to planarize a semiconductor device.
• Pad stiffness is proportional to the product of pad modulus and cube of the thickness, and this is discussed in Machinery's Handbook, 23 rd edition, which is incorporated by reference in its entirety for all useful purposes (see in particular page 297).
• doubling the pad thickness can theoretically increase stiffness eight-fold.
• pad thickness in excess of 250 micrometers is typically required.
• pad thickness greater than 1 ,300 micrometers may be required.
• Appropriate pad thickness is in the range of about 250 to about 5,100 micrometers. At a pad thickness above 5,100 micrometers, polishing uniformity may suffer because of the inability of the pad to conform to variations in global wafer flatness.
• stiffness is proportional to the cube of thickness compared to only the single power of modulus, so that changing pad thickness can have a more significant impact than changing pad modulus.
• Figure 1 defines the critical dimensions of the grooved pad and shows GSQ relating groove depth to pad thickness, such that:
• GSQ Groove Depth (D)/Pad Thickness (T) If no grooves are present, GSQ is zero and, at the other extreme, if the grooves go all the way through the pad, GSQ is unity.
• a second parameter may be used to relate the groove area to the land area of the design. This is also shown in Figure 1.
• a convenient method of showing this parameter is by calculating the ratio of the groove cross-sectional area to the total cross-sectional area of the groove repeat area (i.e. the pitch cross-sectional area), such that GFQ is defined as:
• GFQ Groove Cross-Sectional Area (Ga)/Pitch Cross-Sectional Area (Pa) where
• D is the groove depth
• W is the groove width
• L is the width of the land area
• P is the pitch. Since D is a constant for a particular groove design, GFQ may also be expressed as the ratio of groove width to pitch:
• GFQ Groove Width (W)/Groove Pitch (P)
• W Pad Width
• P Gap Pitch
• the GSQ value generally affects pad stiffness, slurry distribution across the wafer, removal of waste polishing debris, and hydroplaning of the wafer over the pad. At high GSQ values the greatest effect is generally on pad stiffness. In the extreme case, where the groove depth is the same as the pad thickness, the pad comprises discrete islands which are able to flex independently of neighboring islands. Secondly, above a certain groove depth, the channel volume of the grooves will generally be sufficiently large to distribute slurry and remove waste independent of their depth. By contrast, at low GSQ values slurry and waste transport typically becomes the primary concern. At even lower GSQ values, or in the extreme case of no grooves, a thin layer of liquid can prevent pad and wafer from making intimate contact, resulting in hydroplaning and ineffective polishing.
• the grooves In order to avoid hydroplaning of the wafer over the pad surface, the grooves must generally be deeper than a critical minimum value. This value will depend on the micro-texture of the pad surface. Typically, micro-texture comprises a plurality of protrusions with an average protrusion length of less than 0.5 micrometers. In some commercially available pads, polymeric microspheres add porosity to the pad and increase surface roughness, thereby reducing the tendency of hydroplaning and the need for aggressive pad conditioning. For filled pads, the minimum groove depth to prevent hydroplaning is about 75 micrometers and for unfilled pads about 125 micrometers. Thus assuming a reasonable pad thickness of say 2,540 micrometers, the minimum values of GSQ for filled and unfilled pads are 0.03 and 0.05 respectively.
• a high initial pad thickness can be advantageous, as the change in stiffness with polishing time will be relatively less for a thicker pad.
• high thickness for the underlying ungrooved layer and for the overall pad are appropriate, since stiffness can be less dependent on the groove depth in this case.
• Pad stiffness is important, because it controls several important polishing parameters, including uniformity of removal rate across the wafer, die level planarity, and to a lesser extent dishing and erosion of features within a die. Ideally for uniform polishing, removal rate should be the same at all points on the wafer surface. This would suggest that the pad needs to be in contact with the whole wafer surface with the same contact pressure and relative velocity between pad and wafer at all points. Unfortunately, wafers are not perfectly flat and typically have some degree of curvature resulting from the stresses of manufacture and differing coefficients of thermal expansion of the various deposited oxide and metal layers. This requires the polishing pad to have sufficient flexibility to conform to wafer-scale flatness variability.
• One solution to this problem is to laminate a stiff polishing pad to a flexible underlying base pad, which is typically a more compressive, foam-type polymeric material. This improves polishing uniformity across the wafer without unduly compromising the stiffness of the polishing top pad.
• Edge effects can also arise during polishing. This phenomenon manifests as non- uniformity in removal across the wafer surface, such that less material is removed near the wafer edge. The problem becomes worse as the stiffness of the top pad increases and the compressibility of the base pad increases. The phenomenon has been discussed by A. R. Baker in “The Origin of the Edge Effect in CMP', Electrochemical Society Proceedings, Volume 96-22, 228, (1996) which is incorporated by reference in its entirety for all useful purposes. By grooving the top pad, it is possible to reduce its stiffness and hence reduce edge effects. Top pad stiffness is important because it governs the ability of the pad to planarize die level features. This is an important characteristic of a pad for chemical mechanical planarization and is the very reason that the CMP process is used. This is described in “Chemical Mechanical Planarization of Microelectronic Materials", J. M. Steigerwald, S. P. Murarka, R. J. Gutman, Wiley, (1997) which is incorporated by reference in its entirety for all useful purposes.
• a typical integrated circuit die contains features, such as conductor lines and vias between layers, of different sizes and pattern densities. Ideally, it is required that as polishing proceeds, these features reach planarity independent of feature size and pattern density. This requires a stiff pad which will first remove high spots and continue to preferentially remove those high spots until the die surface is perfectly flat.
• pad stiffness is dependent on groove depth which may be adequately described by GSQ. It is also somewhat dependent on GFQ which encompasses the other groove dimensions. This dependency comes more from the groove pitch rather than the groove width. A razor thin groove will reduce stiffness almost as much as wider groove and the more grooves (lower pitch) in a pad, the lower the stiffness. Stiffness will therefore decrease as GFQ increases.
• the table below shows modulus data measured parallel and perpendicular to circular grooves of a thin pad and a thick pad manufactured by Rodel Inc., which are otherwise substantially identical.
• the groove dimensions have been previously shown in the earlier table above. Also shown are values of pad thickness, calculated GSQ and GFQ parameters, and stiffness values normalized to the thin pad.
• the pad properties depend on the measurement direction. Both modulus and stiffness values are anisotropic and depend on whether measurements are made parallel or perpendicular to the groove direction. The pad is more flexible if the groove direction is perpendicular to the direction of curvature. This is an important consideration when designing pads for belt or roll type polishers, in which the pads have to move repetitively and rapidly around low radius drive cylinders. Anisotropy is greater for the thick pad relative to the thin pad. Secondly, it is apparent that the stiffness of the thick pad is higher than that of the thin pad. The factor driving the higher value is the greater thickness of the thick pad.
• Optimum groove design depends on many factors. These include pad size, polishing tool, and material being polished. Although most polishers use circular pads and are based on planetary motion of pad and wafer, a newer generation of polishers is emerging based on linear pads. For this type of polisher, the pad can be either in the form of a continuous belt or in the form of a roll which moves incrementally under the wafer. As shown in the table below different polishers use pads of different sizes and geometry:
• slurry is typically introduced at the pad center and centrifugally transported to the pad edge.
• slurry transport becomes more challenging and may be enhanced by grooving the pad surface.
• Concentric grooves can trap slurry on the pad surface and radial grooves or cross-hatch designs can facilitate flow across the pad surface.
• a denser groove design or, in other words, a higher GFQ ratio.
• the IPEC 676 polisher uses small pads but slurry is introduced through the pad to the wafer surface. A grid of X-Y grooves is therefore required to transport the slurry from the feed holes across the pad surface.
• grooves not only facilitate slurry flow, they are also needed to make the pad more flexible so that it can repetitively bend around the drive mechanism.
• pads for linear polishers tend to be fairly thin with deep grooves and high GSQ ratios.
• grooves are appropriately cut perpendicular rather than parallel to the length of the pad.
• CMP polishing is a process which involves both mechanical and chemical components.
• the relative importance of each of these depends on the material being polished.
• hard materials such as oxide dielectrics and tungsten
• softer pads are appropriate and the chemical component becomes more important.
• stiffer pads are appropriate with lower GSQ and GFQ ratios.
• slurry transport across the pad surface is critical, which is favored by higher GSQ and GFQ values.
• polishing removal rate is determined by Preston's equation described in F. W. Preston, J. Soc. Glass Tech., XI, 214,(1927) which is incorporated by reference in its entirety for all useful purposes which states that removal rate is proportional to the product of polishing down-force and relative velocity between wafer and pad.
• polishing down-force and relative velocity between wafer and pad.
• the problem can be rectified by varying groove density across the pad surface, in other words, by changing either groove width, pitch or depth from the center to the edge of the pad.
• groove depth i.e. GSQ
• the groove configuration circular versus X-Y versus both, etc.
• the local stiffness of the pad can be controlled, and by changing groove versus land area (i.e.
• the slurry distribution and area of the pad in contact with the wafer can be manipulated.
• the pads of the present invention can be made in any one of a number of different ways. Indeed, the exact composition generally is not important so long as the pads exhibit low elastic recovery during polishing. Although urethanes are appropriate pad material, the present invention is not limited to polyurethanes and can comprise virtually any chemistry capable of providing the low elastic recovery described herein.
• the pads can be, but are not limited to, thermoplastics or thermosets and can also be filled or unfilled.
• the pads of the present invention can be made by any one of a number of polymer processing methods, such as but not limited to, casting, compression, injection molding (including reaction injection molding), extruding, web-coating, photopolymerizing, extruding, printing (including ink-jet and screen printing), sintering, and the like. In an exemplary embodiment, the pads of the present invention have one or more of the following attributes:
• the above attributes can be influenced and sometimes controlled through the physical properties of the polishing pad, although pad performance is also dependent on all aspects of the polishing process and the interactions between pad, slurry, polishing tool, and polishing conditions, etc.
• the pads of the present invention define a polishing surface which is smooth, while still maintaining micro-channels for slurry flow and nano-asperities to promote polishing.
• One way to minimize pad roughness is to construct an unfilled pad, since filler particles tend to increase pad roughness.
• Pad conditioning can also be important. Sufficient conditioning is generally required to create micro-channels in the pad surface and to increase the hydrophilicity of the pad surface, but over-conditioning can roughen the surface excessively, which in turn can lead to an increase in unwanted dishing.
• the pads of the present invention appropriately have low elastic rebound. Such rebound can often be quantified by any one of several metrics. Perhaps the simplest such metric involves the application of a static compressive load and the measurement of the percent compressibility and the percent elastic recovery. Percent compressibility is defined as the compressive deformation of the material under a given load, expressed as a percentage of the pad's original thickness. Percent elastic recovery is defined as the fraction of the compressive deformation that recovers when the load is removed from the pad surface.
• Percent compressibility is defined as the compressive deformation of the material under a given load, expressed as a percentage of the pad's original thickness.
• Percent elastic recovery is defined as the fraction of the compressive deformation that recovers when the load is removed from the pad surface.
• polishing pads tend to be polymeric exhibiting viscoelastic behavior; therefore, perhaps a better method is to use the techniques of dynamic mechanical analysis (see J. D. Ferry, "Viscoelastic Properties of Polymers", New York, Wiley, 1961. Viscoelastic materials exhibit both viscous and elastic behavior in response to an applied deformation.
• the resulting stress signal can be separated into two components: an elastic stress which is in phase with the strain, and a viscous stress which is in phase with the strain rate but 90 degrees out of phase with the strain.
• the elastic stress is a measure of the degree to which a material behaves as an elastic solid; the viscous stress measures the degree to which the material behaves as an ideal fluid.
• the elastic and viscous stresses are related to material properties through the ratio of stress to strain (this ratio can be defined as the modulus).
• the ratio of elastic stress to strain is the storage (or elastic) modulus and the ratio of the viscous stress to strain is the loss (or viscous) modulus.
• E' and E" designate the storage and loss modulus, respectively.
• the ratio of the loss modulus to the storage modulus is the tangent of the phase angle shift ( ⁇ ) between the stress and the strain.
• E7E' Tan ⁇ and is a measure of the damping ability of the material.
• Polishing is a dynamic process involving cyclic motion of both the polishing pad and the wafer. Energy is generally transmitted to the pad during the polishing cycle. A portion of this energy is dissipated inside the pad as heat, and the remaining portion of this energy is stored in the pad and subsequently released as elastic energy during the polishing cycle. The latter is believed to contribute to the phenomenon of dishing.
• KEL tan ⁇ * 10 12 / [E'*(1 +tan ⁇ 2 )]
• One method to increase the KEL value for a pad is to make it softer. However, along with increasing the KEL of the pad, this method tends to also reduce the stiffness of the pad. This can reduce the pad's planarization efficiency which is generally undesirable.
• An approach to increase a pad's KEL value is to alter its physical composition in such a way that KEL is increased without reducing stiffness. This can be achieved by altering the composition of the hard segments (or phases) and the soft segments (or phases) in the pad and/or the ratio of the hard to soft segments (or phases) in the pad. This results in a pad that has a suitably high hardness with an acceptably high stiffness to thereby deliver excellent planarization efficiency.
• the morphology of a polymer blend can dictate its final properties and thus can affect the end-use performance of the polymer in different applications.
• the polymer morphology can be affected by the manufacturing process and the properties of the ingredients used to prepare the polymer.
• the components of the polymer used to make the polishing pad should appropriately be chosen so that the resulting pad morphology is stable and easily reproducible.
• the glass transition temperature of the polymer used to make the polishing pad is shifted to sub-ambient temperatures without impacting the stiffness of the pad appreciably.
• Lowering the glass transition temperature (Tg) of the pad increases the KEL of the pad and also creates a pad whose stiffness changes very little between the normal polishing temperature range of 20°C and 100°C.
• changes in polishing temperature have minimal effect on pad physical properties, especially stiffness. This can result in more predictable and consistent performance.
• a feature of an embodiment of this invention is the ability to shift the glass transition temperature to below room temperature and to design a formulation which results in the modulus above Tg being constant with increasing temperature and of sufficiently high value to achieve polishing planarity.
• Modulus consistency can often be improved through either crosslinking, phase separation of a "hard”, higher softening temperature phase, or by the addition of inorganic fillers (alumina, silica, ceria, calcium carbonate, etc.).
• inorganic fillers alumina, silica, ceria, calcium carbonate, etc.
• Another advantage of shifting the Tg (glass transition temperature) of the polymer to sub-ambient temperatures is that in some embodiments of the invention, the resulting pad surface can be more resistant to glazing.
• the polishing surface between pad grooves is a hydrophilic porous or non-porous material which is not supported or otherwise reinforced by a non- woven fiber-based material.
• Pads of the present invention can be made by any one of a number of polymer processing methods, such as but not limited to, casting, compression, injection molding (including reaction injection molding), extruding, web-coating, photopolymerizing, extruding, printing (including ink-jet and screen printing), sintering, and the like.
• the pads may also be unfilled or optionally filled with materials such as polymeric microballoons, gases, fluids or inorganic fillers such as silica, alumina and calcium carbonate.
• Appropriate abrasive particles include, but are not limited to, alumina, ceria, silica, titania, germanium, diamond, silicon carbide or mixtures thereof.
• Pads of the present invention can be designed to be useful for both conventional rotary and for next generation linear polishers (roll or belt pads).
• pads of the present invention can be designed to be used for polishing with conventional abrasive containing slurries, or alternatively, the abrasive may be incorporated into the pad and the pad used with a particle free reactive liquid, or in yet another embodiment, a pad of the present invention without any added abrasives may be used with a particle free reactive liquid (this combination is particularly useful for polishing materials such as copper).
• Appropriate abrasive particles include, but are not limited to, alumina, ceria, silica, titania, germania, diamond, silicon carbide or mixtures thereof.
• the reactive liquid may also contain oxidizers, chemicals enhancing metal solubility (chelating agents or complexing agents), and surfactants.
• Slurries containing abrasives also have additives such as organic polymers which keep the abrasive particles in suspension.
• Complexing agents used in abrasive-free slurries typically comprise two or more polar moieties and have average molecular weights greater than 1000.
• the pads of this invention also have a small portion constructed of a polymer that is transparent to electromagnetic radiation with a wavelength of about 190 to about 3,500 nanometers. This portion allows for optical detection of the wafer surface condition as the wafer is being polished. More detail may be found in U.S. patent 5605760 which is incorporated here in all its entirety for all useful purposes.
• Attributes of the pad of the present invention include: 1. High pad stiffness and pad surface hardness; 2. High energy dissipation (high KEL);
• Pad chemistry can be easily altered to make it suitable for polishing a wide variety of wafers.
• Pads for metal CMP generally have an optimized combination of one or more of the following: stiffness (modulus and thickness), groove design (impacting groove width, groove depth, and groove pitch), Groove Stiffness Quotient, Groove Flow Quotient, Energy Loss Factor (KEL), modulus-temperature ratio, hardness, and surface roughness: by varying the pad composition, these can be somewhat independently controlled;
• Pads with low elastic recovery generally produce low dishing of features during metal CMP polishing
• KEL Ernergy Loss Factor
• the last row defines the ratio of the modulus measured at 30°C and 90°C. This represents the useful temperature range for polishing. Ideally, modulus will change as little as possible and in a linear trend with increasing temperature (i.e. ratio approaches unity). Surface roughness values are after conditioning.
• pads of this invention will generally have a flat modulus - temperature response, a high KEL value in combination with a high modulus value, low surface roughness after conditioning, and optimized GSQ and GFQ values corresponding to the groove design chosen for a specific polishing application.
• Examples 1 and 2 represent comparative pads. Comparative Example 1
• a polymeric matrix was prepared by mixing 2997 grams of polyether-based liquid urethane (Uniroyal ADIPRENE® L325) with 768 grams of 4,4-methylene-bis-chloroaniline (MBCA) at about 65°C. At this temperature, the urethane/polyfunctional amine mixture has a pot life of about 2.5 minutes; during this time, about 69 grams of hollow elastic polymeric microspheres (EXPANCEL® 551 DE) were blended at 3450 rpm using a high shear mixer to evenly distribute the microspheres in the mixture. The final mixture was transferred to a mold and permitted to gel for about 15 minutes.
• polyether-based liquid urethane Uniroyal ADIPRENE® L325
• MBCA 4,4-methylene-bis-chloroaniline
• the mold was then placed in a curing oven and cured for about 5 hours at about 93°C.
• the mixture was then cooled for about 4-6 hours, until the mold temperature was about 21 °C.
• the molded article was then "skived” into thin sheets and macro-channels mechanically machined into the surface ("Pad A").
• Pad 2A a pad made by a molding process disclosed in US
• Patent 6022268 In order to form the polishing pad, two liquid streams were mixed together and injected into a closed mold, having the shape of the required pad. The surface of the mold is typically grooved so that the resulting molded pad also has a grooved macro-texture to facilitate slurry transport.
• the first stream comprised a mixture of a polymeric diol and a polymeric diamine, together with an amine catalyst.
• the second stream comprised diphenylmethanediisocyanate (MDI). The amount of diisocyanate used was such as to give a slight excess after complete reaction with diol and diamine groups.
• the mixed streams were injected into a heated mold at about 70°C to form a phase separated polyurethane-urea polymeric material. After the required polymerization time had elapsed, the now solid part, in the form of a net-shape pad, was subsequently demolded.
• Table 1 shows key physical properties for the pads described in Examples 1 and 2:
• Example 3 illustrates the making of filled and unfilled pads, according to the present invention, using a casting process analogous to that described in Example 1.
• ADIPRENES shown in Table 2 cured with 95% of the theoretical amount of MBCA curing agent.
• Preparation consisted of thoroughly mixing together ADIPRENE and MBCA ingredients and pouring the intimate mixture into a circular mold to form a casting. Mold temperature was 100°C and the castings were subsequently post-cured for 16 hours at 100°C. After post-curing, the circular castings were "skived” into thin 50 mil thick sheets and macro-channels were mechanically machined into the surface. Channels were typically 15 mil deep, 10 mil wide, with a pitch of 30 mil. Properties of the castings are shown in Table 2 and illustrate the favorable combination of key physical properties required for polishing of metal layers in a CMP process:
• Example 3D contains 2wt% EXPANCEL® 551 DE and is made as described in Example 1.
• Table 2 Properties of Cast Pads
• ADIPRENE® LF products are Toluene Diisocyanate based prepolymers manufactured by
• Example 4 illustrates making pads of the present invention using a molding process analogous to that described in Example 2.
• Table 3 shows the composition and key physical properties of typical pads made by a molding process. Molding conditions are as described in
• Both pads were polished using an Applied Materials' MIRRA polisher using a platen speed of 141 rpm, a carrier speed of 139 rpm, and a down-force of 4 psi.
• the pads were both preconditioned before use using an ABT conditioner. Post conditioning was used between wafers. Sematech pattern wafer 931 test masks containing copper features of different dimensions were polished using the pads in conjunction with an experimental copper slurry (CUS3116) from Rodel.
• the copper features were measured for dishing using atomic force microscopy. Defects were measured using an Orbot Instruments Ltd. wafer inspection system. Table 4 summarizes dishing and defect data for the pads polished.
• Example 5 illustrates making pads of the present invention from thermoplastic polymers using an extrusion process.
• a polyether type thermoplastic polyurethane was blended with 20 wt% of either 4 micron or 10 micron calcium carbonate filler using a Haake mixer.
• the resulting blend, together with the unfilled polymer was extruded into a 50 mil sheet using a twin-screw extruder manufactured by American Leistritz.
• Additional formulations were prepared by blending together the above polyether based TPU with a softer polyester based TPU. These were again filled with calcium carbonate.
• Table 5 Table 5: Composition and Properties of Extruded Pads
• thermoplastic polyurethane (TPU's) examples are used to illustrate the invention, the invention is not limited to TPU's.
• Other thermoplastic or thermoset polymers such as nylons, polyesters, polycarbonates, polymethacrylates, etc. are also applicable, so long as the key property criteria are achieved.
• the properties may be realized by modifying the base polymer properties by filling with organic or inorganic fillers or reinforcements, blending with other polymers, copolymerization, plasticization, or by other formulation techniques known to those skilled in the art of polymer formulation.
• a typical pad formulation from Table 5 was used to polish copper patterned wafers in order to measure dishing of fine copper features. Polishing performance was compared to that of a pad as prepared in Example 1.
• Both pads were polished using an Applied Materials' MIRRA polisher using a platen speed of 141 rpm, a carrier speed of 139 rpm, and a down-force of 4 psi.
• the pads were both preconditioned before use using an ABT conditioner. Post conditioning was used between wafers.
• Sematech pattern wafer 931 test masks containing copper features of different dimensions were polished using the pads in conjunction with slurry.
• Figures 2 through 5 graphically show the relationships between GSQ and GFQ ratios and groove dimensions for the pad of this invention.
• Figures 2 and 3 show ranges for Groove Depth and Pad Thickness respectively. From these values of Groove Depth and Pad Thickness, it is possible to calculate appropriate ranges for GSQ.
• Figures 4 and 5 show ranges for Groove Width and Groove Pitch respectively. From these values of Groove Width and Groove Pitch, it is possible to calculate appropriate ranges for GFQ.
• the Table below summarizes the ranges of groove dimensions and specific values for an "optimized" pad:
• polishing pad's groove design may be optimized to achieve optimal polishing results. This optimization may be achieved by varying the groove design across the pad surface to tune the slurry flow across the pad-wafer interface during CMP polishing.
• the number of grooves at the center of the wafer track on the pad may be reduced while increasing or maintaining the number of grooves elsewhere on the pad. This increases the pad area in contact with the center of the wafer and helps to increase the removal rate at the center of the wafer.
• Another technique to increase the removal rate at the center of the wafer is to reduce the groove depth at the center of the wafer track on the pad. This is especially effective when polishing copper substrates using an abrasive containing slurry. These shallow grooves increase the amount of abrasive trapped between the wafer surface and the pad thereby increasing the removal rate at the center of the wafer.
• the groove design may also be utilized to change the residence time of the slurry across the wafer surface.
• the residence time of the slurry at the pad-wafer interface may be increased by increasing the groove depth uniformly across the pad.
• the residence time of the slurry at the pad-wafer interface may be reduced by changing the groove pattern on the pad.
• An X-Y pattern may be superimposed on top of a circular pattern to channel slurry quickly across the wafer surface. Further the pitch of the circular grooves or the X-Y grooves may be altered to fine tune the slurry flow across the pad.

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• Condensed Matter Physics & Semiconductors (AREA)
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• Manufacturing & Machinery (AREA)
• Computer Hardware Design (AREA)
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• Mechanical Treatment Of Semiconductor (AREA)
• Finish Polishing, Edge Sharpening, And Grinding By Specific Grinding Devices (AREA)

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