Patent application title: FLUIDIZED WEB POLISHING APPARATUS AND METHOD USING CONTACT PRESSURE FEEDBACK
Zine-Eddine Boutaghou (North Oaks, MN, US)
IPC8 Class: AB24B4900FI
Class name: Abrading precision device or process - or with condition responsive control computer controlled
Publication date: 2011-10-20
Patent application number: 20110256803
An abrasive article with an abrasive element fabricated on a flexible
foil suspended by a hydrostatic preloader, a gimball mechanism or a soft
pad capable of selectively engaging with substrate to remove material
while monitoring the contact pressure. A hydrostatic pressure bed is
applied to the non-abrasive surface of the tensioned flexible foil to
provide a contact pressure to the abrasive surface against the substrate.
A series of fluid bearing surfaces are fabricated or imparted onto the
abrasive side of the flexible foil to cause controlled interference and
pressure with the substrate. A hydrostatic pressure emanating from the
preloader supports the non-abrasive side of the flexible foil under
tension while the abrasive side of the flexible foil engages a substrate.
Alternatively the flexible foil web is constructed of a series of
individual flexible foil bearings connected by non-straight links and
housed in flexible holder pads capable of deforming and conforming to the
substrate and wafer topography under applied externally applied load and
1. An abrasive article for polishing a substrate surface, the abrasive
article comprising: a holder pad assembly; an abrasive member held in
place with respect to a holder pad, the abrasive member further
comprising: a first surface engaged with the holder pad assembly, and a
second surface including an abrasive; a preload mechanism positioned to
biases the second surfaces of the abrasive member toward the substrate
surface; and one or more fluid bearing features on the second surface of
the abrasive member configured to generate lift forces during relative
motion between the abrasive article and the substrate surface.
2. The abrasive article of claim 1 further comprising at least one abrasive features located on the second surface of the abrasive member, the at least one abrasive feature applying a cutting force to the substrate surface during relative motion between the abrasive article and the substrate surface.
3. The abrasive article of claim 2 wherein the fluid bearing is a hydrostatic bearing.
4. The abrasive article of claim 3 wherein the fluid bearing is a hydrodynamic bearing.
5. The abrasive article of claim 2 wherein the at least one abrasive feature of claim 2 includes diamond like carbon.
6. The abrasive article of claim 2 wherein the at least one abrasive feature of claim 2 includes aluminum oxide.
7. The abrasive article of claim 2 wherein the at least one abrasive feature of claim 2 includes a shaped abrasive feature.
8. A flexible foil bearing abrasive article for polishing a substrate surface, the abrasive article comprising: a preloader assembly; a flexible foil web held over the preloader assembly, the flexible foil web further comprising: a first surface comprising one or more fluid bearings fabricated on the flexible foil web to generate lift forces during motion of the abrasive article relative to the substrate surface; a second surface engaging the preloader assembly; and a mechanism that biases the second surface of the abrasive members toward the substrate surface.
9. The flexible foil bearing abrasive article of claim 8 further comprising at least one abrasive feature located on the first surface of the flexible foil web, the at least one abrasive feature applying cutting forces to the substrate surface during relative motion of the abrasive article and the substrate surface.
10. The flexible foil bearing abrasive article of claim 8 wherein the preloader assembly is a hydrostatic pressure bed fabricated on a curved contactor.
11. The flexible foil bearing abrasive article of claim 8 wherein the preloader assembly is a gimbal assembly with a negative suction cup.
12. The flexible foil bearing abrasive article of claim 8 wherein the fluid bearing is a hydrostatic bearing.
13. The flexible foil bearing abrasive article of claim 8 wherein the fluid bearing is a hydrodynamic bearing.
14. The flexible foil bearing abrasive article of claim 10 wherein the preloader further comprises pressure contact sensors located on a hydrostatic bed.
15. A flexible foil bearing abrasive article for polishing a substrate surface, the abrasive article comprising: a flexible foil web under tension; a hydrostatic preloader comprising a plurality of closed form hydrostatic beds separated by grooves connected to ambient pressure; a first non abrasive foil surface associated with the flexible foil web; a second abrasive foil surface associated with the flexible foil web; the first non abrasive foil surface engaging the hydrostatic preloader to impart bearing surfaces on the abrasive second flexible foil bearing surface; a mechanism that biases the second abrasive surface toward the substrate surface; and an abrasive feature located on the second surface of the flexible foil web, the abrasive feature applying cutting forces to the substrate surface during motion of the abrasive article relative to the substrate surface.
16. The flexible foil bearing abrasive article of claim 15 wherein the hydrostatic preloader further comprises pressure contact sensors located at a closed form hydrostatic bed.
17. The flexible foil bearing abrasive article of claim 15 wherein the second abrasive surface includes a hydrostatic bearing.
18. The flexible foil bearing abrasive article of claim 15 wherein the second abrasive surface comprises a hydrodynamic bearing.
19. The flexible foil bearing abrasive article of claim 15 wherein the second abrasive surface includes diamond like carbon.
20. The flexible foil bearing abrasive article of claim 15 wherein the second abrasive surface includes alumina.
21. A flexible foil bearing abrasive article for polishing a substrate surface, the abrasive article comprising: a foil hydrodynamic bearing suspended with non straight links between two tensioned tapes; a mechanism that biases the second surfaces of the abrasive members toward the substrate surface; and abrasive features located on a surface of the flexible foil nearest the substrate surface, the abrasive features applying cutting forces to the substrate during motion of the abrasive article relative to the substrate.
22. The flexible foil bearing abrasive article of claim 21, the foil hydrodynamic bearing suspended with a gimballing mechanism.
23. The flexible foil bearing abrasive article of claim 21, the foil hydrodynamic bearing suspended with a hydrostatic preloader.
24. A method of polishing a surface of a substrate, the method comprising: biasing a flexible foil web under tension wrapped around a hydrostatic preloader toward the surface of the substrate; pressurizing an abrasive surface of the flexible foil web to provide a contact pressure for the abrasive surface; and monitoring the pressure between the substrate and the abrasive with a pressure opening in the hydrostatic preloader.
CROSS-REFERENCE TO RELATED APPLICATIONS
 This application claims the benefits of the filing date of U.S. Provisional Patent Application Ser. No. 61/417,708 filed Nov. 29, 2010, which is entitled "Compliant Polishing Pad II" and U.S. Provisional Patent Application Ser. No. 61/315,259 filed Mar. 18, 2010, which is entitled "Compliant Polishing Pad" which are hereby incorporated herein in their entirety by reference.
FIELD OF THE INVENTION
 The present application is directed to an abrasive article fabricated on a tensioned flexible foil bearing wherein the non-abrasive side is supported by a hydrostatic pressure bed capable of engaging the abrasive side with the workpiece while monitoring the contact pressure to adjust the magnitude of the pressure acting on the hydrostatic pressure bed and the amount of engagement. Each abrasive member maintains a fluid bearing (air is the typical fluid) with the substrate. The abrasive member includes bearing surfaces and abrasive features to engage with the substrate. Alternatively a gimballing mechanism or a soft compliant pad provides the restoring moments and forces supporting the tensioned foil bearing.
 Fine polishing relies on removal of a uniform amount of material across the entire substrate area. Substrate refers to magnetic substrate media, semi conductor wafers, optical lenses, etc. Soft pad polishing also known as chemical mechanical polishing is the method of choice using free slurries to interact and removal controlled amounts of material from substrates. Residues of the process causes defects especially while polishing soft substrates. The free abrasives get implanted into the substrate and become lodged into the substrate and are chemically inert. These defects are virtually impossible to remove with current cleaning methods. Experimental methods using soft abrasives to polish soft materials such as glass, copper, etc. are not economical due throughput time.
 Defect removal has long been relinquished to cleaning using contact methods such as brushes and non-contact methods such as mega sonic cleaning to remove debris. Such methods cannot deal with embedded particles and chemically bonded nano height defects. Alternative methods must be found.
 A popular approach method to polish a substrate using an substrate charged with abrasive as shown in U.S. 2004/0033772 A1 with diamonds or hard abrasives. Slurry is typically used in concert with the polishing pad to remove the photo resist, the re-deposited etched material from the media, and the fill material. Empirical data related to plate speed, load, abrasive size, and lubricant type is established to yield a desirable material removal rate. A balance is achieved between the slurry type, abrasive size, and the polishing conditions to achieve a desired finish. Typical results from the polishing of filled back patterned media include defects, media scratches, media smears, and dishing. Instead of relying on the current polishing process to complete the polishing process, an additional kiss polish process is to remove media defects, media smears and media defects.
 Azarian et al. (U.S. Pat. No. 5,632,669) disclosed a textured lapping plate with diamond like carbon coating to polish head level sliders suspended to head gimbal assemblies. The head gimball suspended slider provides a stable base for polishing one slider at a time.
 Baraj et al. (2009). Monitoring the pressures detected by the pressure sensing elements 301 and comparing that information to an established pressure model apply a predetermined pressure profile. Differences between the actual pressures and the pressure model may then be used to alter the polishing operations to affect the desired pressure profile. This approach is effective for long-range waviness. The size of the sensing device is substantially larger than the die size leading to average pressure detection not an instantaneous pressure detection as required to compensate for dishing and over polishing for small wafer features. In addition short-range wavelength pressure fluctuations cannot be readily detected.
 In one embodiment a continuous contact pressure monitoring is disclosed. A curved preloader is equipped with a series of openings arranged in a closed form structure. Air pressure is externally supplied to the openings contained in the curved preloader to form a hydrostatic pressure bed. A flexible foil bearing is tensioned over the curved preloader. The spacing between the curved preloader and the flexible foil bearing is related to the externally applied pressure, the foil tension and the radius of the curved preloader. The mean pressure at the center of the hydrostatic bed monitored via a center opening at the curved preloader is referred to as contact pressure. As the abrasive side of the flexible foil bearing is engaged with a workpiece, the contact pressure is monitored and a relationship between the amount of engagement with the workpiece (interference) and the contact pressure is established herein. A large number of discrete closed form structures are added to the curved preloader separated by deep grooves connected to ambient pressure. Such discrete structures are referred to as isolated hydrostatic pressure beds. Isolated hydrostatic pressure beds are formed between the tensioned flexible foil and the curved preloader. The isolated hydrostatic pressure beds cause the flexible foil to experience localized deformations resulting in fluid bearing like surfaces forming on the abrasive side. Upon engagement of the abrasive article into the workpiece, a tailored hydrodynamic film is formed between the workpiece and the abrasive side of the flexible foil bearing. The contact pressure at each discrete pressure bed can be monitored and adjusted for tailoring a desired contact pressure.
 In another embodiment a continuous polishing contact pressure-monitoring device is disclosed herein. A rectangular preloader is equipped with a series of openings arranged in a closed form structure referred as hydrostatic pressure bed. An external air pressure is supplied to the openings contained in the preloader. A foil hydrodynamic bearing suspended between two tensioned tapes with non-straight links is wrapped around the preloader floats on a hydrostatic pressure bed. The foil hydrodynamic bearing suspended by the non-straight links is capable of freely complying with the preloader to match its orientation referred to herein as attitude. The contact pressure at the center of the hydrostatic pressure bed is monitoring via a center opening at the preloader. As the abrasive side of the flexible foil bearing is engaged with a workpiece, the contact pressure is monitored and a relationship between interference and contact pressure is established.
 Applications such as hard disk drives and semiconductor wafer polishing rely on fabricating nano size features as shown in FIG. 1. For economical reasons a polymer is desirable to use as a substrate as shown in FIGS. 2 and 3a. Diamond like carbons adhere readily to polymers. Modern Ta--C filtered ion source diamond like carbon deposition tools are capable of generating films with a hardness in the range of 20-90 GPa would be required to provide a burnish amount of 1-5 nm for material removal operation as shown in FIG. 4. Combinations of lower burnish levels and substantially harder materials look promising at reducing the burnish time to practical ranges.
 Diamond like carbon with high hardness is known as tetrahedral carbon (Ta--C) is substantially harder than amorphous carbon (a-C). Ta--C is ideal for protecting against high wear application. a-C is well suited for low friction applications where wear is not a concern. However, Ta--C is known to transform to a-C in the presence of high flash temperatures are expected to be present during the polishing process. So the transformation of Ta--C to a-C promote low frictional contact and promotes lubricity of the interactions, thus requiring minimum fluid based lubrication. Another unique property of Ta--C is the roughness imparted to the film during the deposition. The rule is that the roughness of the film is about 10 percent of the thickness promotes additional burnishing.
 Slutz et al. (U.S. Pat. No. 7,367,875 B2) proposes a CVD diamond coating to adhere diamonds to a substrate. Protruding large diamonds are responsible for material removal. Diamond abrasives with variable height and protrusions are too aggressive to provide atomic level burnishing. Henderson (U.S. Pat. No. 7,189,333 B2) and Lin et al. (U.S. Pat. No. 6,872,127 B2) proposes coating lapping end effectors and chemical mechanical polishing pads with diamond like carbon over engineered surfaces. The patterned geometrical features require large stress to initiate material removal, such action is not desirable for atomic level material removal. Ideally we would require two orders of magnitude increase in asperity density for fast and economical mechanical polishing.
 FIG. 3b shows hardness of diamond like carbons as a function of deposition conditions and substrate adhesion of Ta--C on soft polymers.
 FIG. 4 shows a substrate 340 charged with abrasives 330. The abrasives are adhered to the substrate with adhesives.
BRIEF SUMMARY OF THE INVENTION
 Maintaining a stable interface between the polished surface or substrate and the polishing pad or abrasive charged pad to achieve a desired level of interference is achieved by hydrodynamic or hydrostatic lift. A large number of high stress points at the onset of contact between the abrasive elements and the polished substrate is attained at the interface. The interface formed between the polishing pad and the substrate contains a gas bearing surface and a large number of stress contact points between the substrate and the polishing pad.
 To achieve a stable interface one can take advantage of the inherent stability of a hydrostatic or hydrodynamic bearing structures to provide a stabilizing force countering the cutting forces generated during the material removal process. Hydrostatic or hydrodynamic bearings balance a set of forces including a preload and moments generated from the mechanical assembly.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
 FIG. 1 depicts a servo pattern layout for a bit pattern magnetic media.
 FIG. 2 depicts a textured polishing substrate with a peak to peak roughness.
 FIG. 3a shows an example of a texture applied to the polishing article.
 FIG. 3b shows a graph of DLC hardness as a function of deposition conditions.
 FIG. 4 shows an example of an abrasive charged polishing article.
 FIG. 5a shows an example of a defect interacting with a polishing article, according to an example embodiment.
 FIG. 5a shows the removal of a defect interacting with a polishing article, according to an example embodiment.
 FIG. 6a shows an example of a defect interacting with a flexible polishing article, according to an example embodiment.
 FIG. 6a shows the removal of a defect interacting with a flexible polishing article, according to an example embodiment.
 FIG. 7 shows a polishing hydrostatic assembly with a polishing pad, according to an example embodiment.
 FIG. 8 shows a close up view of the polishing pad, according to an example embodiment.
 FIG. 9 shows a hydrostatic polishing pad attachment means, according to an example embodiment.
 FIG. 10 shows the polishing pad assembly which the polishing pad holder the gas channels, according to an example embodiment.
 FIG. 11 depicts the exploded view of a circular polishing pad, according to an example embodiment.
 FIG. 12 shows an assembly of polishing pads supported by gel like support, according to an example embodiment.
 FIG. 13 shows a close up view assembly of polishing pads supported by gel like support with gas supplies, according to an example embodiment.
 FIG. 14 shows a series of hydrostatic bearing structures fabricated on a flexible substrate, according to an example embodiment
 FIG. 15 shows a single hydrostatic bearing structure, according to an example embodiment.
 FIG. 16A shows a foil bearing structure comprising a multitude of hydrodynamic bearing structures, according to an example embodiment.
 FIG. 16B shows an exploded view of hydrodynamic bearing structures fabricated onto the foil bearing structure, according to an example embodiment.
 FIG. 17 shows an externally pressurized foil bearing assembly applying a pressure profile onto the foil patterned with hydrodynamic bearing structures, according to an example embodiment.
 FIG. 18 shows a foil bearing assembly with hydrodynamic bearing structures applying a polishing pressure on a rotating substrate, according to an example embodiment.
 FIG. 19A shows a foil bearing assembly with hydrostatic bearing structures applying a polishing pressure on a rotating substrate, according to an example embodiment.
 FIG. 19B shows a close up view of the hydrostatic bearing fabricated onto a foil bearing, according to an example embodiment.
 FIG. 20A shows a bearing structure applying tailored pressure profile at multi sites onto the foil bearing to form desired pressure pattern onto the foil bearing, according to an example embodiment.
 FIG. 20B shows an externally pressurized bearing with independent bearing structures separated by ambient pressure lines, according to an example embodiment.
 FIG. 20C shows a foil bearing with raised surfaces due to pressure profile imparted by externally applied pressure, according to an example embodiment.
 FIG. 21A shows an example with a constant pressure inlet, a pressure monitoring at the center of the, a foil bearing applying a polishing pressure, according to an example embodiment.
 FIG. 21B shows a polishing example with a polishing pressure profile measured at the center of the foil during the polishing pressure, according to an example embodiment.
 FIG. 21c shows a constant polishing pressure measured at the center of the foil with intermittent pressure drops due to substrate runnout, according to an example embodiment.
 FIG. 22A shows a suspended flexible foil hydrodynamic bearing under tension, according to an example embodiment.
 FIG. 22B shows a suspended flexible foil hydrodynamic bearing under tension and suspended to a gimbal, according to an example embodiment.
 FIG. 23A shows a suspended flexible foil hydrodynamic bearing under tension in a web configuration, according to an example embodiment.
 FIG. 23B shows a suspended flexible foil hydrodynamic bearing under tension in a web configuration suspended by a gimbal mechanism, according to an example embodiment.
 FIG. 23C shows a suspended flexible foil hydrodynamic bearing under tension in a web configuration supported by a hydrostatic pressure bed, according to an example embodiment.
DETAILED DESCRIPTION OF THE INVENTION
 Web based fluid bearing surfaces can be classified into two major types. First, bearings in which members are coated with a low modulus of elasticity material, providing a flexible surface. Second, foil bearings in which at least one of the bearing surfaces is flexible and subjected to a tensile stress in order to support a load. Both types are known as web based fluid bearings. Such bearing configurations rely on a hydrodynamic or hydrostatic effect to generate lift and are widely used in magnetic tape retrieval systems.
 In one embodiment, a hydrostatic pressure bed is disclosed to form between a flexible foil under tension stored in a web and a curved surface under externally supplied pressure. The hydrostatic pressure bed is formed between the curved surface and the non-abrasive side of the flexible foil via externally applied pressure known as hydrostatic lift or due to the relative motion of the flexible web with respect to the curved surface forming a hydrodynamic lift. The flexible foil has typically one surface containing abrasives and a surface containing no abrasives supported by a preloader. The curved surface contains a series of opening configured in a closed form shape to form a hydrostatic pressure bed. An opening at the center of the hydrostatic pressure bed monitors pressure changes during the normal approach of the abrasive surface with the polishing substrate or workpiece. The normal approach of the abrasive surface with the polishing substrate is referred to as interference. An increase in pressure is observed during the contact between the workpiece and the foil abrasive surface. The flexible foil is capable of complying with the substrate waviness and causes a substantially constant cutting pressure to be generated leading to uniform material removal.
 Three types of suspension mechanisms are disclosed herein, a hydrostatic pressure bed to support the non-abrasive side of a flexible foil on a preloader, a moment and force restoring system referred to as a gimbal mechanism, and a soft supporting pad. The hydrostatic pressure bed is achieved by supplying a pressure to a series of closed form openings to form a uniform pressure bed supporting the non-abrasive side of the flexible foil. A gimbal mechanism typically comprises a series of spring arranged to provide a restoring roll and pitch moments to support the hydrodynamic or hydrostatic film formation between the abrasive side of the flexible foil and the workpiece. A soft pad is typically a gel like or sponge like preloader pad providing both preload and a restoring moment to support hydrodynamic film formation.
 In this patent application we will disclose a novel type of web based foil bearing structure capable of following the topography of a wafer or substrate under an externally applied load by generating a bearing surface between the wafer or substrate and the flexible foil. FIGS. 6a and 6b show a conceptual design of a hydrostatic flexible foil bearing following the topography of a wafer substrate during polishing. The surface of the flexible foil in contact with the wafer or substrate forms a fluid bearing surface.
 FIG. 5a shows a rigid bearing surface 350 supported by fluid bearings 353 and 354 formed on a relatively flat substrate surface or wafer 370. Inlet fluid openings 351 and 352 supply the fluid bearings 353 and 354. An abrasive element 380 such as hard coatings or abrasive particles is applied to the flexible foil bearing. A relative motion 390 between the substrate and the flexible foil bearing engages defect 360. The engagement of the rigid bearing surface charged with abrasives 380 with the defect 360 subjects the defect to large stresses causing burnishing of the defect with minimal material removal from the substrate surface 370. FIG. 5b shows defect 370 removed after several interactions between the rigid bearing surface and the substrate or wafer. A rigid bearing surface suffers from the inability to follow substrate waviness in the range of the bearing surface dimensions.
 An embodiment of the present invention is shown in FIGS. 6a and 6b. Example portrayed in FIG. 6a shows a flexible polishing article 420 that includes a flexible foil bearing 430 supported by a hydrostatic bearing, a gimbal mechanism or a soft pad such as a sponge like or gel like pad 410 carrying air conducts 405 to the flexible foil bearing 430. The surface of the flexible foil bearing facing the substrate or wafer contains abrasive elements 435. The example shows that the substantial compliance of the flexible foil bearing follows the counter topography 450 of the substrate or wafer. Multiple inlet ports 405 create a hydrostatic bearing uniformly distributed over the surface of the flexible foil bearing surface 430. The fluid bearing formed between the substrate and the foil bearing causes localized compliance to take place between the polishing abrasives and the topography of the substrate or wafer. The localized deformation is tailored to minimize the amount of interactions with the substrate waviness for example. As the substrate moves relative to the flexible foil, as depicted by arrow 460, an interaction between the defect 440 and the abrasive surface causes removal of the defect 440 as shown in FIG. 6b. Note that rigid bearing 350 is incapable of following the topography of the substrate leading to indiscriminate removal of peaks 450.
 The examples shown in FIG. 5a-b and 6a-b demonstrate that there are several strategies; a rigid polishing pad with the inability to follow substrate topography and a flexible foil with the ability to follow the substrate topography within very short wavelength.
 For a rigid polishing pad a priori care must be taken to produce a substantially flat mold with desired microwaviness, roughness, and overall flatness. The polishing substrate can be fabricated from a molding process or a polymer substrate diamond charged process.
 The polishing substrate is fabricated from a mold with a mechanical texture established using a pressure tape applied over the flat mold filled with diamonds slurry. Button hydrostatic bearings are shown to depict a simple bearing structure. Once the mold is fabricated the media is fabricated with the desired mechanical roughness and a series of patterned grooves to enable the polishing pad to form an air film. The desired peak to peak roughness varies from 10-100 nm to provide an effective cutting surface according to Meyer et al. (1997). Filtered cathodic arc carbon is deposited onto the polishing pad to provide a hard protective coating. Diamond Like Carbon ("DLC") films adhere well on polycarbonate substrate without the need of an adhesion layer. DLC thickness varies from 20-300 nm to provide a hard surface capable of burnishing. DLC hardness must be greater than 5 GPa to meet the required lapping rates; it is highly desirable to generate DLC hardness in the range of 20-90 GPa to further improve the burnishing process.
 A rotating textured polycarbonate DLC coated pad as described earlier is equipped with hydrostatic bearing structures as shown in FIG. 5a. The simplest hydrostatic bearing is a button bearing (Cameron 1981) that can be adapted into the polishing pad. The hydrostatic pressure causes a predictable clearance to be achieved between the polishing pad and the substrate or wafer.
 Several manufacturing methods can be used to form the bearings. The polishing pad is fabricated with the same process discussed earlier with the integration of cutting asperities with a height of 5-50 nanometers to provide high stress sites, a DLC film with a thickness of 50-200 nm to provide a hard burnishing surface, and a thin film lubricant to provide boundary lubrication.
 FIG. 7 shows a polishing hydrostatic assembly with a polishing pad, according to an example embodiment. A polishing pad contains two elements, a polishing pad 500 with hydrostatic bearing structure containing an abrasive surface, a hydrostatic bearing surface and a soft support pad, a supporting soft holder pad 600 containing the fluid ports, and a fluid supply source 650 and load plate 700.
 FIG. 8 is a close up view of the polishing pad containing a series of individually connected polishing pads 510 connected by a series of non-straight links 520. Each individual polishing surface contains a series of hydrostatic bearing surfaces 530 and an abrasive surface 511 interacting with wafer topography or defects. An externally supplied pressurized gas passes through the conduits fabricated into the soft support pad 600 form a hydrodynamic bearing surface.
 FIG. 9 gives a close up view of an individual polishing structures 590 containing at least one hydrostatic bearing surface 530. As shown in FIG. 9, there are a plurality of hydrostatic bearing surfaces. An opening 532 around the bearing surface 530 is fabricated to insure ambient atmospheric pressure surrounds the bearing surface 530. The fluid supply is provided via a through opening 531 to the bearing surface 530. The polishing surface 511 contains abrasive material responsible for material removal such as abrasives or hard coatings such as diamond like carbon. A series of non straight links 520 with substantial out of plane flexibility connect the individual polishing pads 590. The low out of plane flexibility attained by the non-straight links assist the individual polishing pads to move independently of each other's to minimize the effect of membrane forces.
 In another embodiment, hydrostatic bearing surfaces 530 can be added to a flexible polishing island fabricated from a thin substrate of polymer, for example, to allow for better topography and substrate counter following during the polishing process.
 FIG. 10 shows the soft holder pad 600 containing the fluid inlets 601 supplying the polishing pads 590. A series of individual soft holder pads 602 are fabricated into the soft holder pad 600. The soft holder pads generally house a polishing pad 590. The individual soft holder pads 602 transfer the generalized loads from the load plate 700 to individual polishing structures. The generalized loads include preload and moments exerted on the load plate which, in turn, are transferred to the soft holder pads 602. A rectangular soft holder pad is used for illustrative purposes; other shapes such as links, crosses, bars, openings, etc can be used to further reduce the stiffness of the soft holder pad 602 to allow compliance of the polishing islands to the surface of the substrate or wafer.
 FIG. 11 shows a circular polishing assembly configuration with a polishing pad 800, a soft holder pad assembly 900 and a preload plate 950. The polishing pad contains a series of independent polishing islands connected via non-straight links. The soft holder pad assembly 900 is fabricated from a series of independent holder pads housing each polishing island.
 FIGS. 12 and 13 give a close up view of the polishing pad containing a series of individually connected polishing pads 810 connected by a series of non-straight links 820. Each individual polishing surface contains a series of hydrostatic bearing surfaces 830 and an abrasive surface 811 interacting with wafer topography or defects. An externally supplied fluid is passed through the conduits fabricated into the soft support pad 910 to pressurize the hydrodynamic bearing surface. A series of individual soft holder pads 920 are fabricated into the soft holder pad to house each polishing pad 900. The individual soft holder pads 920 transfer the generalized loads from the load plate 950 to the individual polishing pads 810. The generalized loads include a preload exerted by the load plate and moments exerted by the load plate.
 FIG. 14 is a perspective view of a flexible foil bearing 880 with a plurality of hydrostatic bearing surfaces 882 connected by a constant boundary pressure line (atmospheric pressure) 883. A plurality of non-straight links connect the polishing island, represented by the flexible foil bearing 880 shown, to other polishing islands (not shown in FIG. 14) to form a polishing pad. The polishing islands are fabricated from a very thin polymeric material with a low modulus of elasticity to allow for compliance. The spacing between the polishing pad and the wafer or substrate is controlled by the flexibility of the compliant polishing island, the local topography, and the lift from the bearing structure. It is expected that the spacing within the polishing island vary as a function of the substrate or wafer topography. It should be noted that although the flexible foil bearing 880 includes a rectangular array or pattern of hydrostatic bearing surfaces 882, other patterns of hydrostatic bearing surfaces are also contemplated. In addition, some arrays might not include a pattern of hydrostatic bearing surfaces 882. In other words, the hydrostatic bearing surfaces 882 could be random over the island.
 FIG. 15 shows a single hydrostatic bearing structure with an opening 885 and specifically the inlet of that opening 885 supplying externally pressurized gas to the bearing land 884. A leakage path formed by openings 883 into the substrate provides atmospheric pressure boundary conditions for escape of the pressurized gas.
 FIG. 16A shows a flexible foil substrate patterned with hydrodynamic bearing structures. The hydrodynamic structures are coated with abrasives or fabricated out of abrasive. The various features of the hydrodynamic structures apply desirable clearance or interference between the work piece and the flexible foil polishing substrate. Hydrodynamic bearing structures 201 are replicated or mold injected onto the flexible foil bearing 200. Tension 202 is applied onto the flexible foil. FIG. 16B gives an exploded view of hydrodynamic bearing structures fabricated onto the flexible foil 200. Bearing surfaces include a leading edge 205 and a leading edge 204, a rail, 206, and a contacting pad 203 and a contacting pad 207 which are fabricated onto a single hydrodynamic cell 201. The contacting pad 207 and the contacting pads 203 are positioned near a trailing edge of the hydrodynamic cell 201.
 FIG. 17 gives a simplified hydrodynamic structure fabricated onto substrate formed by the foil bearing 200. A hydrodynamic bearing cell including 201 including leading edge 210, cavity 213, and contacting pad 211 are manufactured onto the flexible foil 200. A tension force, depicted by arrows 202, wraps the foil bearing onto a semi circular hydrostatic pressure bed structure 214 with pressure inlets 215. The pressure inlets 215 provide a substantially constant pressure profile for lifting the foil bearing off the semi circular hydrostatic bearing. FIG. 18 shows a hydrodynamic bearing structure fabricated onto a flexible foil tape supported by a hydrostatic bearing bed 201 contacting a rotating substrate 220. The hydrostatic pressure applied by 214 pushes the abrasive coated side of the flexible foil, i.e. the hydrodynamic bearing surfaces 201, to contact the substrate 220. The hydrodynamic structures 201 engage the substrate 220. Note that substrate 220 is in relative motion with respect to the polishing flexible foil 200, as depicted by arrow. The relative motion between the substrate 220 and the foil 200 generates a lift between the hydrodynamic bearing 201 and the substrate 220. The compliance of the flexible foil permits the hydrodynamic surface to comply with the waviness features on the substrate as depicted in FIGS. 6a and 6b. The topography following ability of the flexible foil with hydrodynamic abrasive surfaces supported by a hydrostatic bed provides an ideal structure for polishing wavy surfaces and removing nanometer size defects. The hydrodynamic abrasive surfaces form a predictable spacing between the substrate surface 220 and the foil 200.
 FIG. 19A provides another example of an abrasive hyrodstatic bearing fabricated with a flexible substrate, such as foil. The abrasive hydrostatic bearing includes land 231 and boundary contours 230 fabricated onto the flexible foil. A semi circular hydrostatic pressure bed 214 supports the flexible foil. The semi circular hydrostatic bearing 214 has a series of openings 215 machined therein which transfer a pressurized fluid, such as pressurized air, onto the flexible foil. A series of abrasive hydrostatic structures are in proximity to the substrate 220. The spacing between the substrate and the abrasive hydrostatic structures 230 is maintained by external pressure entering the inlet 232. FIG. 19B is a close up view of the abrasive hydrostatic bearing with openings 230 connected to atmospheric pressure, land 231 containing the abrasive structures, and inlet 232. The incoming air pressure for example enters opening 232, generates lift between the substrate 220 and land 232 and dissipates in the openings 231. The compliance of the flexible foil allows the abrasive hydrostatic surface to comply with the waviness features on the substrate, as depicted in FIGS. 6a and 6b. The topography following ability of the flexible foil with hydrostatic abrasive surfaces supported by a hydrostatic bed, provides an ideal structure for polishing wavy surfaces and removing nanometer size defects. The abrasive hydrostatic surfaces form a predictable spacing between the substrate surface 200 and the foil.
 The polishing flexible foil integrates a series or plurality of bearing structures allowing a cushioning bearing to form between the polishing pad and the substrate or semi-conductor wafer. The fluid bearings are tuned to generate a desired interference between the polishing pad and the wafer. Note that the contact forces between the wafer and the asperities of the polishing pad are countered by the stiffness generated by the air bearing to provide a stable burnishing operation with minimal oscillations.
 FIGS. 20A-20C show another embodiment of a flexible foil bearing. Now turning to FIGS. 20A-20C, the other embodiment will be detailed. A flexible foil bearing is under tension, as represented by arrows 202, with a first surface containing an abrasive surface 270A and a second surface with a non-abrasive surface 270B, as shown in FIG. 20A. A pressure emanating from a curved hydrostatic preloader 214 from a series of pressure openings 215 applies a desired pressure onto the non-abrasive surface 270B. FIG. 20B shows a detailed view of the hydrostatic preloader 214. Three closed form pressure profiles are formed by pressure openings 242A, 242B, and 242C separated by atmospheric channels 241A, 241B and 241C. Three closed form pressure loops 240A, 240B, 240C are formed by the pressure openings 242A, 242B, 242C respectively. A series of deep grooves 241A, 241B, and 241C are formed between the various closed form pressure loops to contain three distinct pressure profiles. FIG. 20C gives a deformed profile of the flexible foil 200 under the three closed form pressure loops leading to surfaces 250A, 250B, 250C. A cross section is performed on the deformed foil surface 250B. The proposed approach uses a flexible foil with abrasive structures on one surface. The hydrostatic preloader features multiple independent pressure channels and closed form pressure profiles. The pressure profiles are imparted to the non-abrasive side of the flexible foil causing protruding surfaces to form on the surface with abrasive structures of the flexible foil. A multitude of pressure profiles can be tailored to cause tailoring protrusions such as herringbone and chevron surfaces suitable for sweeping action or diamond shapes suitable for burnishing and cleaning.
 The relative motion of the substrate 220 with respect to the flexible foil 202 causes a hydrodynamic lift between the foil protruding features and the substrate. The relative motion promotes the formation of pressure profiles on the protruding surfaces leading to desired contact force between the substrate and the abrasive surfaces.
 In another embodiment, FIG. 21A shows a polishing flexible foil 200 under tension 202 wrapped around a semi circular hydrostatic preloader with pressure openings 215 controlling the inlet pressure at approximately 2 pounds per square inch (psi), as an illustrative example. An opening 260 monitors the contact pressure formed between the non-abrasive surface of the foil and the hydrostatic preloader. The inlet pressure openings 215 form a rectangular air bed with a uniform hydrostatic pressure of 2 psi. FIG. 21B monitors the pressure at opening 260. The graph shows a sudden increase in pressure due to an increase in interference between the substrate 220 and the foil bearing 200 while maintaining a constant inlet pressure of 2 psi. Upon removing the interference, the contact pressure drops to its original value. A feedback mechanism monitors the contact pressure change between the abrasive flexible foil bearing and the workpiece. FIG. 21c captures the event of a shock causing a separation between the substrate and the flexible foil. Monitoring the contact pressure in opening 260 captures an instantaneous contact pressure drop due to shock and physical separation of the work piece from the flexible polishing foil.
 The radius of curvature of the hydrostatic preloader plays an important role in controlling the contacting area between the foil bearing 200 and the substrate 220. A large radius of the hydrodynamic bearing is desirable in many cases where a large contact area is desired requires a very small inlet pressure at ports 215 to be delivered to support the required tension 202 leading to small perturbations in pressures causing large spacing changes at the interface between the foil 200 and the curvilinear contactor 214.
 Another embodiment is proposed where the contact area of the hydrodynamic foil bearing with the substrate is maximized. FIG. 22A shows another embodiment of the present invention. A foil hydrodynamic web 700 is shown. The foil hydrodynamic bearing structures 750 are suspended to a tensioned tape 760A and 760B via S-shaped links 730A and 730B. Tension, depicted by arrows 720, applies a constant stretch on the tape 760A and 760B to aid in material handling. The hydrodynamic bearing structures experience no stretching or tensioning from the stretched tape 760A-B. Rib stiffener 770 aids in providing a relatively rigid link between the tensioned tapes 760A and 760B during the tensioning and web handling processes. The suspended hydrodynamic bearing structures located between the tensioned tapes which are linked through a semi rigid rib is referred to as flexible foil.
 FIG. 22B provides a suction mechanism to grab the flexible foil hydrodynamic bearing 750 prior to engaging the substrate for polishing. An external pressure outlet 740 is connected to a vacuum pump to cause a negative suction force transferred through the closed channel 742 to the pressure suction cup 741 to cause an intimate contact with the foil hydrodynamic bearing 750. The vacuum channel structures 742 are integral part of the gimbal mechanism 743 providing a restoring spring to the foil hydrodynamic bearing 750.
 The present foil hydrodynamic bearing is attached to a web handling system in FIG. 23A. Foil hydrodynamic bearing surfaces 751, 752, and 753 are shown for illustrative purposes. A multitude of hydrodynamic bearing features adapted for burnishing (753), for cleaning (751) and for polishing (752) can be designed in the same flexible foil. The foil hydrodynamic is wound around rollers 780 under tension 720. FIG. 23B illustrates a top view of the foil hydrodynamic 700 under tension 720. A suction cup 741 integrated into the gimbal 743 captures the foil hydrodynamic bearing 750 prior to engaging with the substrate 790 while tension is still applied. In this embodiment, a tensioned web with a flat polishing surface has been disclosed. FIG. 23C substitutes the gimball mechanism with a hydrostatic pressure bed 214 with a series of pressure inlet openings 215 and a pressure feedback opening 260 to monitor the contact pressure.
 Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which these inventions belong. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present inventions, the preferred methods and materials are now described. All patents and publications mentioned herein, including those cited in the Background of the application, are hereby incorporated by reference to disclose and describe the methods and/or materials in connection with which the publications are cited.
 The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present inventions are not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed.
 Other embodiments of the invention are possible. Although the description above contains much specificity, these should not be construed as limiting the scope of the invention, but as merely providing illustrations of some of the presently preferred embodiments of this invention. It is also contemplated that various combinations or sub-combinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the inventions. It should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the disclosed inventions. Thus, it is intended that the scope of at least some of the present inventions herein disclosed should not be limited by the particular disclosed embodiments described above.
 Thus the scope of this invention should be determined by the appended claims and their legal equivalents. Therefore, it will be appreciated that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean "one and only one" unless explicitly so stated, but rather "one or more." All structural, chemical, and functional equivalents to the elements of the above-described preferred embodiment that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims.
 Goers et al. U.S. 2004/0033772A1  Albrecht U.S. 2009/0067082 A1  Meyer et al., IEEE Trans. On Mag. Vol. 33, No. 1, Jan 97  Strom et al., IEEE Trans. On Mag. Vol. 40, No. 1, Jan 04  Basic Lubrication Theory, Cameron, Ellis Horwood Series in Engineering Science, 1981  Azarian et al. (U.S. Pat. No. 5,632,669)
Patent applications by Zine-Eddine Boutaghou, North Oaks, MN US
Patent applications by BOUTAGHOU LLC
Patent applications in class Computer controlled
Patent applications in all subclasses Computer controlled