FLUIDIZED WEB POLISHING APPARATUS AND METHOD USING CONTACT PRESSURE FEEDBACK
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 moments.
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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 INVENTIONThe 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.
BACKGROUNDFine 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
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.
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.
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.
An embodiment of the present invention is shown in
The examples shown in
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
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.
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.
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.
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,
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.
The present foil hydrodynamic bearing is attached to a web handling system in
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.
REFERENCES
- 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)
Claims
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.
Type: Application
Filed: Mar 17, 2011
Publication Date: Oct 20, 2011
Applicant: BOUTAGHOU LLC (North Oaks, MN)
Inventor: Zine-Eddine Boutaghou (North Oaks, MN)
Application Number: 13/050,597
International Classification: B24B 49/00 (20060101); B24B 27/00 (20060101);