U.S. patent application number 13/050597 was filed with the patent office on 2011-10-20 for fluidized web polishing apparatus and method using contact pressure feedback.
This patent application is currently assigned to BOUTAGHOU LLC. Invention is credited to Zine-Eddine Boutaghou.
Application Number | 20110256803 13/050597 |
Document ID | / |
Family ID | 44788539 |
Filed Date | 2011-10-20 |
United States Patent
Application |
20110256803 |
Kind Code |
A1 |
Boutaghou; Zine-Eddine |
October 20, 2011 |
FLUIDIZED WEB POLISHING APPARATUS AND METHOD USING CONTACT PRESSURE
FEEDBACK
Abstract
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.
Inventors: |
Boutaghou; Zine-Eddine;
(North Oaks, MN) |
Assignee: |
BOUTAGHOU LLC
North Oaks
MN
|
Family ID: |
44788539 |
Appl. No.: |
13/050597 |
Filed: |
March 17, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61417708 |
Nov 29, 2010 |
|
|
|
61315259 |
Mar 18, 2010 |
|
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Current U.S.
Class: |
451/5 ; 451/490;
451/540 |
Current CPC
Class: |
B24B 37/10 20130101;
B24B 37/16 20130101; B24B 37/005 20130101; B24B 37/245
20130101 |
Class at
Publication: |
451/5 ; 451/540;
451/490 |
International
Class: |
B24B 49/00 20060101
B24B049/00; B24B 27/00 20060101 B24B027/00 |
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.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] 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
[0002] 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.
BACKGROUND
[0003] 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.
[0004] 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.
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] FIG. 3b shows hardness of diamond like carbons as a function
of deposition conditions and substrate adhesion of Ta--C on soft
polymers.
[0014] FIG. 4 shows a substrate 340 charged with abrasives 330. The
abrasives are adhered to the substrate with adhesives.
BRIEF SUMMARY OF THE INVENTION
[0015] 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.
[0016] 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
[0017] FIG. 1 depicts a servo pattern layout for a bit pattern
magnetic media.
[0018] FIG. 2 depicts a textured polishing substrate with a peak to
peak roughness.
[0019] FIG. 3a shows an example of a texture applied to the
polishing article.
[0020] FIG. 3b shows a graph of DLC hardness as a function of
deposition conditions.
[0021] FIG. 4 shows an example of an abrasive charged polishing
article.
[0022] FIG. 5a shows an example of a defect interacting with a
polishing article, according to an example embodiment.
[0023] FIG. 5a shows the removal of a defect interacting with a
polishing article, according to an example embodiment.
[0024] FIG. 6a shows an example of a defect interacting with a
flexible polishing article, according to an example embodiment.
[0025] FIG. 6a shows the removal of a defect interacting with a
flexible polishing article, according to an example embodiment.
[0026] FIG. 7 shows a polishing hydrostatic assembly with a
polishing pad, according to an example embodiment.
[0027] FIG. 8 shows a close up view of the polishing pad, according
to an example embodiment.
[0028] FIG. 9 shows a hydrostatic polishing pad attachment means,
according to an example embodiment.
[0029] FIG. 10 shows the polishing pad assembly which the polishing
pad holder the gas channels, according to an example
embodiment.
[0030] FIG. 11 depicts the exploded view of a circular polishing
pad, according to an example embodiment.
[0031] FIG. 12 shows an assembly of polishing pads supported by gel
like support, according to an example embodiment.
[0032] FIG. 13 shows a close up view assembly of polishing pads
supported by gel like support with gas supplies, according to an
example embodiment.
[0033] FIG. 14 shows a series of hydrostatic bearing structures
fabricated on a flexible substrate, according to an example
embodiment
[0034] FIG. 15 shows a single hydrostatic bearing structure,
according to an example embodiment.
[0035] FIG. 16A shows a foil bearing structure comprising a
multitude of hydrodynamic bearing structures, according to an
example embodiment.
[0036] FIG. 16B shows an exploded view of hydrodynamic bearing
structures fabricated onto the foil bearing structure, according to
an example embodiment.
[0037] 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.
[0038] FIG. 18 shows a foil bearing assembly with hydrodynamic
bearing structures applying a polishing pressure on a rotating
substrate, according to an example embodiment.
[0039] FIG. 19A shows a foil bearing assembly with hydrostatic
bearing structures applying a polishing pressure on a rotating
substrate, according to an example embodiment.
[0040] FIG. 19B shows a close up view of the hydrostatic bearing
fabricated onto a foil bearing, according to an example
embodiment.
[0041] 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.
[0042] FIG. 20B shows an externally pressurized bearing with
independent bearing structures separated by ambient pressure lines,
according to an example embodiment.
[0043] FIG. 20C shows a foil bearing with raised surfaces due to
pressure profile imparted by externally applied pressure, according
to an example embodiment.
[0044] 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.
[0045] 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.
[0046] 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.
[0047] FIG. 22A shows a suspended flexible foil hydrodynamic
bearing under tension, according to an example embodiment.
[0048] FIG. 22B shows a suspended flexible foil hydrodynamic
bearing under tension and suspended to a gimbal, according to an
example embodiment.
[0049] FIG. 23A shows a suspended flexible foil hydrodynamic
bearing under tension in a web configuration, according to an
example embodiment.
[0050] 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.
[0051] 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
[0052] 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.
[0053] 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.
[0054] 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.
[0055] 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.
[0056] 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.
[0057] 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.
[0058] 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.
[0059] 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.
[0060] 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.
[0061] 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.
[0062] 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.
[0063] 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.
[0064] 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.
[0065] 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.
[0066] 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.
[0067] 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.
[0068] 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.
[0069] 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.
[0070] 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.
[0071] 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.
[0072] 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.
[0073] 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.
[0074] 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.
[0075] 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.
[0076] 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.
[0077] 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.
[0078] 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.
[0079] 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.
[0080] 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.
[0081] 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.
[0082] 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.
[0083] 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.
[0084] 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.
[0085] 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.
[0086] 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
[0087] Goers et al. U.S. 2004/0033772A1 [0088] Albrecht U.S.
2009/0067082 A1 [0089] Meyer et al., IEEE Trans. On Mag. Vol. 33,
No. 1, Jan 97 [0090] Strom et al., IEEE Trans. On Mag. Vol. 40, No.
1, Jan 04 [0091] Basic Lubrication Theory, Cameron, Ellis Horwood
Series in Engineering Science, 1981 [0092] Azarian et al. (U.S.
Pat. No. 5,632,669)
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