U.S. patent application number 12/766515 was filed with the patent office on 2011-05-05 for dressing bar for embedding abrasive particles into substrates.
This patent application is currently assigned to First Principles LLC. Invention is credited to Zine-Eddine Boutaghou, Karl G. Schwappach.
Application Number | 20110104989 12/766515 |
Document ID | / |
Family ID | 43925927 |
Filed Date | 2011-05-05 |
United States Patent
Application |
20110104989 |
Kind Code |
A1 |
Boutaghou; Zine-Eddine ; et
al. |
May 5, 2011 |
DRESSING BAR FOR EMBEDDING ABRASIVE PARTICLES INTO SUBSTRATES
Abstract
One or more individually gimballed dressing bars for embedding
abrasive particles into a substrate at a substantially uniform
height. A hydrostatic and/or hydrodynamic fluid bearing (air is the
typical fluid) is maintained between the dressing bar and the
substrate. The fluid bearing permits the dressing bar to follow
micrometer-scale and/or millimeter-scale wavelengths of waviness on
the substrate, while maintaining a constant clearance, to uniformly
embed the abrasive particle into the substrate.
Inventors: |
Boutaghou; Zine-Eddine;
(North Oaks, MN) ; Schwappach; Karl G.; (North
Oaks, MN) |
Assignee: |
First Principles LLC
|
Family ID: |
43925927 |
Appl. No.: |
12/766515 |
Filed: |
April 23, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61174472 |
Apr 30, 2009 |
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61187658 |
Jun 16, 2009 |
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61220149 |
Jun 24, 2009 |
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61221554 |
Jun 30, 2009 |
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61232425 |
Aug 8, 2009 |
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61232525 |
Aug 10, 2009 |
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61248194 |
Oct 2, 2009 |
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61267031 |
Dec 5, 2009 |
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61267030 |
Dec 5, 2009 |
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Current U.S.
Class: |
451/28 ; 451/443;
451/540; 51/307 |
Current CPC
Class: |
B24D 18/00 20130101;
B24B 53/12 20130101; B24B 53/017 20130101; B24B 37/14 20130101 |
Class at
Publication: |
451/28 ; 451/443;
451/540; 51/307 |
International
Class: |
B24B 1/00 20060101
B24B001/00; B24B 53/12 20060101 B24B053/12; B24B 37/00 20060101
B24B037/00; B24D 3/00 20060101 B24D003/00 |
Claims
1. A dressing bar assembly for embedding abrasive particles into a
surface of a substrate, the dressing bar assembly comprising: a
support structure; at least one gimbal assembly connecting at least
one dressing bar to the support structure, the gimbal assembly
permitting displacement of the dressing bar in at least pitch and
roll; a preload mechanism adapted to bias an active surface on the
dressing bar toward the substrate; and at least one gas conduit
adapted to deliver pressurized gas to one or more pressure ports
positioned opposite the substrate, the pressurized gas maintaining
a hydrostatic bearing between the active surface of the dressing
bar and the substrate while the active surface applies a
compressive forces sufficient to embed the abrasive particles into
the surface.
2. The dressing bar assembly of claim 1 comprising: a plurality of
gimbal assemblies arranged in an array; and a plurality of dressing
bars each engaged with one of the gimbal assemblies, the gimbal
assemblies permitting independent displacement of each dressing bar
in at least pitch and roll.
3. The dressing bar assembly of claim 1 wherein the hydrostatic
bearing generates moments on the dressing bar that are greater than
moments generated by interaction of the active surface with the
abrasive particles.
4. The dressing bar assembly of claim 1 wherein clearance between
the active surface and the substrate of the substrate is maintained
between about 25 nanometers to about 100 nanometers.
5. The dressing bar assembly of claim 1 wherein the hydrostatic
bearing permits the active surface to maintain a constant clearance
with the surface of the substrate.
6. The dressing bar assembly of claim 1 wherein the dressing bar
includes one or more fluid bearing features.
7. The dressing bar assembly of claim 6 wherein motion of the
dressing bar relative to the surface of the substrate generates a
hydrodynamic fluid bearing.
8. The dressing bar assembly of claim 1 wherein the active surface
comprises a plurality of spacer pads, the spacer pads have a height
generally corresponding to a target height of the abrasive
particles above the substrate.
9. The dressing bar assembly of claim 1 comprising three actuators
configured to alter the pitch and roll of the dressing bar relative
to the support structure.
10. The dressing bar assembly of claim 1 comprising one or more of
a rotary table, an X-Y stage, an orbital motion generator, or an
ultrasonic vibrator adapted to move the substrate relative to the
dressing bar.
11. An abrasive article comprising abrasive particles embedded into
a substrate at a substantially uniform height made with the
dressing bar of claim 1.
12. A dressing bar assembly for embedding abrasive particles into a
surface of a substrate, the dressing bar assembly comprising: a
support structure; at least one gimbal assembly connecting at least
one dressing bar to the support structure, the gimbal assembly
permitting displacement of the dressing bar in at least pitch and
roll; a preload mechanism adapted to bias an active surface on the
dressing bar toward the substrate; and one or more fluid bearing
features on the dressing bar configured to generate a hydrodynamic
bearing between the dressing bar and the substrate during motion of
the dressing bar relative to the substrate while the active surface
applies a compressive forces sufficient to embed the abrasive
particles into the surface.
13. The dressing bar assembly of claim 12 comprising: a plurality
of gimbal assemblies arranged in an array; and a plurality of
dressing bars each engaged with one of the gimbal assemblies, the
gimbal assemblies permitting independent displacement of each
dressing bar in at least pitch and roll.
14. The dressing bar assembly of claim 12 wherein the hydrodynamic
bearing generates moments on the dressing bar that are greater than
moments generated by interaction of the active surface with the
abrasive particles.
15. The dressing bar assembly of claim 12 wherein the active
surface comprises a plurality of spacer pads, the spacer pads have
a height generally corresponding to a target height of the abrasive
particles above the substrate.
16. A method of making an abrasive article comprising the steps of:
distributing a slurry including abrasive particles on a surface of
a substrate; connecting at least one dressing bar to the support
structure with a gimbal assembly, the gimbal assembly permitting
displacement of the dressing bar in at least pitch and roll;
biasing the dressing bar toward the substrate to engage an active
surface on the dressing bar with the slurry; creating a fluid
bearing between the dressing bar assembly and the substrate,
wherein the fluid bearing is one or more of a hydrostatic fluid
bearing or a hydrodynamic fluid bearing; adjusting the fluid
bearing to control spacing between the dressing bar assembly and
the substrate; and applying a compressive force sufficient for the
active surface to embed the abrasive particles into the surface at
a generally uniform height.
17. The method of claim 16 comprising the steps of: arranging a
plurality of gimbal assemblies in an array; and engaging a
plurality of dressing bars with each of the gimbal assemblies, the
gimbal assemblies permitting independent displacement of each
dressing bar in at least pitch and roll.
18. The method of claim 16 comprising generating moments on the
dressing bar with the fluid bearing that are greater than moments
generated by interaction of the active surface with the abrasive
particles.
19. The method of claim 16 comprising maintaining a constant
clearance between the active surface of the dressing bar and the
surface of the substrate.
20. The method of claim 16 comprising the steps of: delivering a
pressurized gas to one or more pressure ports positioned opposite
the substrate to create a hydrostatic fluid bearing during a
start-up phase; moving the dressing bar relative to the substrate
to create a hydrodynamic fluid bearings; and subsequently reducing
or terminating the flow of pressurized gas after the hydrodynamic
fluid bearing is formed.
21. The method of claim 16 comprising the steps of: preparing a
first abrasive article with abrasive particles at a first height
relative to the substrate for use with a first lubricant having a
first viscosity; and preparing a second abrasive article with
abrasive particles at a second height relative to the substrate for
use with a second lubricant having a second viscosity different
from the first viscosity.
22. A method of lapping a surface of a work piece comprising the
steps of: positioning an abrasive article made according to the
method of claim 16 opposite the surface of the work piece; engaging
the surface of the work piece with the abrasive particles; and
moving the work piece relative to the abrasive article.
Description
RELATED APPLICATIONS
[0001] The present application claims the benefit of U.S.
Provisional Patent Application Nos. 61/174,472 entitled Method and
Apparatus for Atomic Level Lapping, filed Apr. 30, 2009; 61/187,658
entitled Abrasive Member with Uniform Height Abrasive Particles,
filed Jun. 16, 2009; 61/220,149 entitled Constant Clearance Plate
for Embedding Diamonds into Lapping Plates, filed Jun. 24, 2009;
61/221,554 entitled Abrasive Article with Array of Gimballed
Abrasive Members and Method of Use, filed Jun. 30, 2009; 61/232,425
entitled Constant Clearance Plate for Embedding Abrasive Particles
into Substrates, filed Aug. 8, 2009; 61/232,525 entitled Method and
Apparatus for Ultrasonic Polishing, filed Aug. 10, 2009; 61/248,194
entitled Method and Apparatus for Nano-Scale Cleaning, filed Oct.
2, 2009; 61/267,031 entitled Abrasive Article with Array of
Gimballed Abrasive Members and Method of Use, entitled Dec. 5,
2009; and 61/267,030 entitled Dressing Bar for Embedding Abrasive
Particles into Substrates, filed Dec. 5, 2009, which are hereby
incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention is directed to one or more
individually gimballed dressing bars for embedding abrasive
particles into a substrate at a substantially uniform height. A
hydrostatic and/or hydrodynamic fluid bearing (air is the typical
fluid) is maintained between the dressing bar and the substrate.
The fluid bearing permits the dressing bar to follow
micrometer-scale and/or millimeter-scale wavelengths of waviness on
the substrate, while maintaining a constant clearance to uniformly
embed the abrasive particle into the substrate.
BACKGROUND OF THE INVENTION
[0003] Read-write heads for disk drives are formed at the wafer
level using a variety of deposition and photolithographic
techniques. Multiple sliders, up to as many as 40,000, may be
formed on one wafer. The wafer is then sliced into slider bars,
each having up to 60-70 sliders. The slider bars are lapped to
polish the surface that will eventually become the air bearing
surface. A carbon overcoat is then applied to the slider bars.
Finally, individual sliders are sliced from the bar and mounted on
gimbal assemblies for use in disk drives.
[0004] Slider bars are currently lapped using a tin plate charged
with small diamonds having an average diameter of about 250 nm FIG.
1A illustrates a conventional tin substrate 20 charged with
diamonds 22. Top surface 24 of the tin plate typically has a
certain amount of waviness. The height 26 of the diamonds 22 tends
to follow the contour of the top surface 24, even after the
substrate 20 is dressed. The waviness of the top surface 24 also
creates a non-uniform hydrostatic film 28 during lapping
operations, creating instability at the interface with the slider
bars.
[0005] Conventional tin substrate is prepared in several steps. The
first step is to machine a flat tin plate. The second step is to
machine grooves or geometrical features that promote lubricant
circulation and control the thickness of the hydrodynamic film
between the oil lubricant and the slider bars.
[0006] The third step is to charge the tin plate with diamonds,
such as illustrated in U.S. Pat. No. 6,953,385 (Singh, Jr.). Singh
teaches applying a ceramic impregnator downward on the substrate
surface with a controlled force while the diamond slurry is
supplied. The diamonds are impregnated into the relatively soft tin
layer of the substrate.
[0007] Fourth, the impregnated substrate is dressed with a dressing
bar. The dressing bar reduces the height variation by pressing the
larger diamonds further into the tin, producing a more uniform
height of the diamonds. Several runs of the dressing bar help
improve height uniformity of the abrasive diamonds impregnated into
the tin.
[0008] FIG. 1B illustrates a conventional dressing bar 30. The
leading edge 32 of the dressing bar 30 is designed with a sharp
ninety-degree angle interfacing with the diamonds during the
abrasive particles embedding process. The sharp leading edge 32
does not allow for efficient penetration of diamonds into the
interface defined by the dressing bar and the substrate. This
process generates a large amount of industrial waste. Current
processes are wasteful since over 90 percent of the diamonds are
lost and unrecoverable in the process.
[0009] During use, the substrate is flooded with a lubricant (oil
or water based). The viscosity of oil-based lubricants is about 4
orders of magnitude greater than the viscosity of air. The
lubricant causes a hydrodynamic film to be generated between the
slider bar and the substrate. The hydrodynamic film is critical in
establishing a stable interface during the lapping process and to
reduce vibrations and chatter. To overcome the hydrodynamic film, a
relatively large force is exerted onto the slider bar to cause
interference with the diamonds necessary to promote polishing. A
preload of about 10 kilograms is not uncommon to engage a single
slider bar with the lapping media.
[0010] FIG. 2 is a schematic side sectional view of a conventional
slider bar including a plurality of individual sliders before
lapping. Each slider in the slider bar typically includes
read-write transducers. As used herein, "read-write transducer"
refers to one or more of the return pole, the write pole, the read
sensor, magnetic shields, and any other components that are spacing
sensitive. Various methods and systems for finish lapping
read-write transducers are disclosed in U.S. Pat. Nos. 5,386,666
(Cole); 5,632,669 (Azarian et al.); 5,885,131 (Azarian et al.);
6,568,992 (Angelo et al.); and 6,857,937 Bajorek), which are hereby
incorporated by reference.
[0011] Variables such as lapping media speed, preload on the slider
bar load, nominal diamond size, and lubricant type must be balanced
to yield a desirable material removal rate and finish. A balance is
also required between the hydrodynamic film and the height of the
embedded diamonds to achieve an interference level between the
slider bar and the diamonds.
[0012] The preload applied to the slider bar is typically
determined by the density of the diamonds and the diamond height
variation. As the industry moves to nano-diamonds smaller than 250
nm, the preload will need to be increased to reduce the fluid film
thickness a sufficient amount so the diamonds contact the slider
bars. Nano-diamonds are difficult to embed in the tin plate. The
risk of free diamonds damaging the slider bar increases.
[0013] Slider bars with trailing edges composed of metallic layers
and ceramic layers present very severe challenges during lapping.
Composite structures of hard and soft layers present differential
lapping rates when lapped using conventional abrasive substrates.
The variable polishing rates of the metallic and ceramic materials
lead to severe recessions, sensor damage, and other problems. FIG.
3 illustrates the bar of FIG. 2 after lapping with a conventional
diamond-charged substrate. The diamond-charged plates cause large
transducer protrusion and recession variations, contact detection
area variation, substrate recession, microscopic substrate
fractures leading to particle release during operation of the disk
drive, scratches from free diamonds, and transducer damage.
[0014] The realization of a data density of 1 Terabyte/inch.sup.2
(1 Tbit/in.sup.2) or higher depends, in part, on designing a
head-disk interface (HDI) with the smallest possible head-media
spacing ("HMS"). Head-media spacing refers to the distance between
a read or write sensor and a surface of a magnetic media. A
discussion of head-media spacing is found in U.S. patent
application Ser. No. 12/424,441, entitled Method and Apparatus for
Reducing Head Media Spacing in a Disk Drive, filed Apr. 15, 2009,
which is hereby incorporated by reference. Conventional diamond
charged plates used to lap slider bars are an impediment to
achieving data densities on the order of 1 Tbit/in.sup.2.
[0015] U.S. Pat. Nos. 7,198,533 and 6,123,612 disclose an abrasive
article including a plurality of abrasive particles securely
affixed to a substrate with a corrosion resistant matrix material.
The matrix material includes a sintered corrosion resistant powder
and a brazing alloy. The brazing alloy includes an element which
reacts with and forms a chemical bond with the abrasive particles,
thereby securely holding the abrasive particles in place. A method
of forming the abrasive article includes arranging the abrasive
particles in the matrix material, and applying sufficient heat and
pressure to the mixture of abrasive particles and matrix material
to cause the corrosion resistant powder to sinter, the brazing
alloy flows around, react with, and forms chemical bonds with the
abrasive particles, and allows the brazing alloy to flow through
the interstices of the sintered corrosion resistant powder and
fauns an inter-metallic compound therewith.
[0016] U.S. Pat. Publication No. 2009/0038234 (Yin) discloses a
method for making a conditioning pad using a plastic substrate
having a plurality of recesses. The abrasive grains are secured in
the recesses by adhesive. The second substrate is formed around the
exposed portions of the abrasive grains. After the second substrate
hardens, the first substrate is removed, exposing the cutting
surfaces of the abrasive grains.
[0017] Example 1 of Yin teaches recesses are about 225 micrometers
deep and about 450 micrometers wide, with a maximum height
difference between the highest and lowest peak of about 25
micrometers. Example 3 of Yin discloses a maximum height difference
between the highest and lowest peak of about 15 micrometers. Yin
discloses diamond abrasive grains with particle diameters ranging
from 10 mesh to 140 mesh. Applicants believe these mesh sizes
correspond generally to abrasive particles with a major diameter of
about 2 millimeters to about 0.1 millimeters. The large size of the
diamonds of Yin allows for insertion into the recesses. Forming the
first substrate with sub-micron sized recesses and then inserting
sub-micron sized abrasive grains, however, is not currently
commercially viable. Sorting sub-micron sized abrasive grains is
also problematic.
[0018] Other methods for orienting and positioning discrete
abrasive particles are disclosed in U.S. Pat. Nos. 6,669,745
(Prichard et al.) and 6,769,975 (Sagawa), and U.S. Pat. Publication
No. 2008/0053000 (Palmgren), which are hereby incorporated by
reference.
BRIEF SUMMARY OF THE INVENTION
[0019] The present invention is directed to one or more
individually gimballed dressing bars for embedding abrasive
particles into a substrate at a substantially uniform height. The
present invention is also directed to an abrasive article with
abrasive particles embedded in a substrate at a substantially
uniform height, including a method of making and use the abrasive
article. The abrasive article is typically nano-scale diamonds
embedded in a Tin lapping plate. The present method and abrasive
article can be used with the current infrastructure for lapping and
polishing.
[0020] A hydrodynamic and/or hydrostatic fluid bearing (air is the
typical fluid) is maintained between the dressing bar and the
substrate. The fluid bearing permits the dressing bar to follow
micrometer-scale and/or millimeter-scale wavelengths of waviness on
the substrate, while maintaining a constant clearance, to uniformly
embed the abrasive particle into the substrate. The abrasive
particles are preferably partially embedded in the substrate before
application of the dressing bar. The fluid can be gas, liquid, or a
combination thereof. As used herein, "topography following" refers
to a gimbaled dressing bar that generally follows millimeter-scale
and/or micrometer-scale wavelengths of waviness at a generally
uniform clearance above a substrate to reduce nanometer-scale
height variations of abrasive particles on the surface.
[0021] The gimbal mechanism permits the dressing bar to move
vertically, and in pitch and roll relative to the substrate. The
fluid bearing provides vertical stiffness, and pitch and roll
stiffness to the dressing bar, while controlling the spacing and
pressure distribution across the fluid bearing features on the
dressing bar. The high stiffness of the dressing bar reduces
clearance loss and chatter emanating from particle interaction
during embedding of the abrasive particles. Adjustments to certain
variables, such as for example, the spacing, pitch and roll
stiffness, and/or preload can be used to modify the force applied
to the abrasive particles.
[0022] The primary forces involved in a given fluid bearing are the
gimbal structure and the preload. The gimbal structure applies both
pitch and roll moments to the dressing bar. If the gimbal is
extremely stiff, the fluid bearing may not be able to form a pitch
or roll angle. The preload and preload offset (location where the
preload is applied) bias the dressing bar toward the substrate. The
preload is typically applied by a different structure than the
gimbal structure.
[0023] In hydrodynamic applications, fluid bearing surface
geometries play a role in pressurization of fluid bearing surfaces,
particularly on hydrodynamic fluid bearings. Possible geometries
include tapers, steps, trenches, crowns, cross curves, twists, wall
profile, and cavities. Finally, external factors such as viscosity
of the bearing fluid and linear velocity play an extremely
important role in pressurizing bearing structures.
[0024] In one embodiment, the spacing profile is achieved with a
fluid bearing configured to achieve a pitch and roll stiffness
capable of countering the forces emanating between the abrasive
particles and the dressing bar during the charging process. In
another embodiment, the spacing profile is achieved with the aid of
actuators causing the dressing bar to maintain a desired spacing
profile with respect to the substrate. The present systems and
methods can be used with or without lubricants.
[0025] In one embodiment, the dressing bar includes a leading edge
taper causing progressive interference with the embedded abrasive
particles. In a second embodiment, the interference with the
abrasive particles is controlled by pitch of the dressing bar. The
pitch of the dressing bar can be achieved with a hydrostatic
clearance profile or by appropriately controlling actuators acting
on the dressing bar. Pads are optionally added to a tapered
dressing bar to allow for a low frictional interface and a
clearance setting between the dressing bar and the substrate.
[0026] Large forces are expected to incur during the process of
embedding abrasives. The fluid bearing stiffness is designed to
counter the cutting forces and moments emanating from the embedding
process. The gimbal assembly allows the dressing bar to react to
these cutting forces. The spacing control between the dressing bar
and the substrate is crucial to controlling the height of the final
embedded abrasives. The spacing control can be achieved by
hydrostatic and/or hydrodynamic fluid bearings, with or without
actuators.
[0027] The method of making an abrasive article in accordance with
the present invention includes the steps of distributing a slurry
including abrasive particles on a surface of a substrate. At least
one dressing bar is connected to the support structure with a
gimbal assembly. The gimbal assembly permits displacement of the
dressing bar in at least pitch and roll. The dressing bar is biased
toward the substrate to engage an active surface on the dressing
bar with the slurry. A fluid bearing is generated between the
dressing bar assembly and the substrate. The fluid bearing can be
adjusted to control spacing between the dressing bar assembly and
the substrate. The active surface of the dressing bar applies a
compressive force sufficient to embed the abrasive particles into
the surface.
[0028] The present method and apparatus permits the height of the
abrasive particles relative to the substrate to be precisely
controlled. Consequently, abrasive articles made using the present
method and apparatus can be tailored for particular applications
and process parameters, such as for example the customers preferred
lubricant. In one embodiment, a first abrasive article is prepared
for use with a first lubricant having a first viscosity and a
second abrasive article is prepared for use with a second lubricant
having a second viscosity different from the first viscosity.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0029] FIG. 1A is a schematic sectional view of a prior art
diamond-charged substrate.
[0030] FIG. 1B is a perspective view of a prior art dressing
bar.
[0031] FIG. 2 is a schematic side sectional view of a conventional
slider bar before lapping.
[0032] FIG. 3 illustrates the bar of FIG. 2 after lapping with a
conventional diamond-charged substrate.
[0033] FIG. 4 is a schematic illustration of a method and apparatus
for progressively embedding abrasive particles in accordance with
an embodiment of the present invention.
[0034] FIG. 5A is a perspective view of a tapered dressing bar in
accordance with an embodiment of the present invention.
[0035] FIG. 5B is a side view of the tapered dressing bar of FIG.
5A engaged with an abrasive article in accordance with an
embodiment of the present invention.
[0036] FIG. 6 is a perspective view of a circular tapered dressing
bar in accordance with an embodiment of the present invention.
[0037] FIG. 7 is a perspective view of a grooved and tapered
dressing bar in accordance with an embodiment of the present
invention.
[0038] FIG. 8 is a perspective view of an alternate grooved and
tapered dressing bar in accordance with an embodiment of the
present invention.
[0039] FIG. 9 is a perspective view of a dressing bar with spacers
in accordance with an embodiment of the present invention.
[0040] FIG. 10 is a perspective view of a circular dressing bar
with spacers in accordance with an embodiment of the present
invention.
[0041] FIG. 11 is an exploded view of a gimballed dressing bar
holder in accordance with an embodiment of the present
invention.
[0042] FIG. 12A is a side view of the gimballed dressing bar holder
of FIG. 11.
[0043] FIG. 12B is a conceptual view of a dressing bar interacting
with a substrate in accordance with an embodiment of the present
invention.
[0044] FIGS. 13A and 13B illustrate the gimballed dressing bar
holder of FIG. 11 before and after engagement with a substrate in
accordance with an embodiment of the present invention.
[0045] FIG. 14 is an exploded view of an alternate gimballed
dressing bar holder in accordance with an embodiment of the present
invention.
[0046] FIG. 15 is a sectional view of the gimballed dressing bar
holder of FIG. 14.
[0047] FIGS. 16 and 17 are perspective views of the gimballed
dressing bar holder of FIG. 14.
[0048] FIG. 18 is a perspective view of a gimbal assembly for the
dressing bar holder of FIG. 14.
[0049] FIG. 19 is a perspective view of a dressing bar assembly
with a hydrostatic fluid bearing in accordance with an embodiment
of the present invention.
[0050] FIG. 20 is a perspective view of the dressing bar assembly
of FIG. 19 engaged with an abrasive article in accordance with an
embodiment of the present invention.
[0051] FIG. 21 is a perspective view of the dressing bar assembly
of FIG. 19.
[0052] FIG. 22 is a perspective view of a dressing bar assembly
with mechanical actuators in accordance with an embodiment of the
present invention.
[0053] FIG. 23 is a perspective view of the dressing bar assembly
of FIG. 22.
[0054] FIG. 24 is a perspective view of a dressing bar assembly of
FIG. 22 engaged with an abrasive article in accordance with an
embodiment of the present invention.
[0055] FIG. 25 is a perspective view of a dressing bar assembly of
FIG. 22.
[0056] FIG. 26 is an exploded view of an alternate dressing bar
assembly with mechanical actuators in accordance with an embodiment
of the present invention.
[0057] FIG. 27 is a plan view of a gimbal assembly for the dressing
bar assembly of FIG. 26.
[0058] FIG. 28 is a perspective view of an alternate dressing bar
assembly with mechanical actuators in accordance with an embodiment
of the present invention.
[0059] FIG. 29 is a perspective view of the dressing bar and
mechanical actuators of FIG. 28.
[0060] FIG. 30 is an enlarged view of an interface between the
dressing bar and the mechanical actuators of FIG. 28.
[0061] FIG. 31 is a perspective view of a resilient interface
between the dressing bar and the mechanical actuators in accordance
with an embodiment of the present invention.
[0062] FIG. 32 is a perspective view of the dressing bar assembly
and mechanical actuators of FIG. 31.
[0063] FIG. 33 is a perspective view of the dressing bar assembly
and mechanical actuators of FIG. 31.
[0064] FIG. 34 is a perspective view of an alternate button
bearings in accordance with an embodiment of the present
invention.
[0065] FIG. 35 is a perspective view of a dressing bar with the
button bearings of FIG. 34 in accordance with an embodiment of the
present invention.
[0066] FIG. 36 is a side view of the dressing bar of FIG. 35.
[0067] FIG. 37 is a pressure profile for the button bearing of FIG.
34.
[0068] FIGS. 38A and 38B illustrate a multi-layered gimbal assembly
in accordance with an embodiment of the present invention.
[0069] FIGS. 39 and 40 are perspective views of a dressing bar
assembly in accordance with an embodiment of the present
invention.
[0070] FIGS. 41A and 41B are perspective views of a dressing bar
with an array of the hydrostatic ports in accordance with an
embodiment of the present invention.
[0071] FIG. 42 is a perspective view of an alternate dressing bar
with a plurality of active surfaces surrounded by hydrostatic ports
in accordance with an embodiment of the present invention.
[0072] FIG. 43 is a perspective view of a dressing bar assembly
with an array of individually gimballed hydrostatic dressing bars
in accordance with an embodiment of the present invention.
[0073] FIG. 44 is an exploded view of the dressing bar assembly of
FIG. 43.
[0074] FIG. 45A is a rear view of an individual dressing bar for
the dressing bar assembly of FIG. 43.
[0075] FIG. 45B is a front view of the dressing bar assembly of
FIG. 43 in accordance with one embodiment of the present
invention.
[0076] FIG. 46 is a top view of a gimbal assembly for the dressing
bar assembly of FIG. 43.
[0077] FIG. 47 is a perspective view the dressing bar assembly of
FIG. 43.
[0078] FIG. 48 is a perspective view of a dressing bar assembly
with an array of individually gimballed dressing bars in accordance
with an embodiment of the present invention.
[0079] FIG. 49 is an exploded view of the dressing bar assembly of
FIG. 48.
DETAILED DESCRIPTION OF THE INVENTION
[0080] The entire content of U.S. Provisional Patent Application
Nos. 61/174,472, filed Apr. 30, 2009; 61/187,658, filed Jun. 16,
2009; 61/220,149, filed Jun. 24, 2009; 61/221,554, filed Jun. 30,
2009; 61/232,425, filed Aug. 8, 2009; 61/232,525, filed Aug. 10,
2009; 61/248,194, filed Oct. 2, 2009; 61/267,031, entitled Dec. 5,
2009; and 61/267,030, filed Dec. 5, 2009, is hereby incorporated by
reference.
[0081] FIG. 4 is a schematic illustration of dressing bar 40 using
progressive interference to embed abrasive particles 42 into
substrate 44. Progressive interference refers to a tapering gap
interface 48 between active surface 45 of the dressing bar 40 and
the substrate 44. In the illustrated embodiment, the dressing bar
40 is at an angle with respect to the substrate 44 to progressively
embed the abrasive particles 42 into the substrate 44, resulting in
a constant clearance 47 of the abrasive particles 42 relative to
the substrate 44. The interference can be adjusted by changing the
clearance 47, the slope of the active surface 45 relative to the
substrate 44, adding a taper to the dressing bar (see FIG. 5A), or
a combination thereof. Preload 46 may be in the range of about 1
kilogram, depending on a number of variables, such as for example,
the size of the abrasive particles 42, the material of the
substrate 44, and the like. As used herein, "clearance" refers to a
distance between an active surface of a dressing bar and a
substrate.
[0082] In one embodiment, the abrasive particles 42 are partially
embedded in the substrate 44 before application of the dressing bar
40. As used herein, "embed" or "embedding" refers generically to
pressing free and/or partially embedded abrasive particles into a
substrate. The substrate is preferably plastically deformable to
receive the abrasive particles.
[0083] FIGS. 5A and 5B illustrate dressing bar 50 equipped with a
tapered leading edge 52 in accordance with an embodiment of the
present invention. The tapered leading edge 52 promotes progressive
interference and facilitates entry of abrasive particles 54 into
interface 56 between the dressing bar 50 and the substrate 58. The
taper leading edge 52 applies a downward force 60 onto the abrasive
particles 54 entrained by the relative motion imparted to the
substrate 58. The abrasive particles 54 progressively penetrate the
soft substrate 58. Methods of uniformly dispersing nanometer size
abrasive grains are disclosed in U.S. Pat. Pub. No. 2007/0107317
(Takahagi et al.) which is hereby incorporated by reference.
[0084] A fluid bearing at the interface 56 controls the stiffness
of the dressing bar 50 in the normal direction, pitch direction,
and roll direction. Active surface 62 of the dressing bar 50
imparts a generally constant downward load 64 embedding the
abrasive particles 54 further into the substrate 58. The spacing
control between the dressing bar 50 and the substrate 58 assure a
constant height 66 of the abrasive particles 54 above reference
plane 68.
[0085] In the load dominated approach, once the load carried by the
embedded diamonds 54 equals the applied load 64, the diamond
embedding reaches equilibrium. The active surface 62 optionally
includes hydrostatic ports 70, that will be discussed further
below.
[0086] In a clearance dominated approach, the clearance between the
diamond plate and the dressing bar is controlled via a hydrodynamic
film or hydrostatic film. The stiffness of the hydrodynamic film is
designed to be substantially higher than the countering stiffness
emanating from the embedded diamond into the substrate. Upon
interference of the dressing bar with respect to the abrasive
particles, the later will offer little resistance to the force
applied by the dressing bar.
[0087] The substrate 58 can be made from a variety of materials,
such as for example, tin, a variety of other metals, polymeric
materials, copper, ceramics, or composites thereof. The substrate
58 can also be flexible, rigid, or semi-rigid.
[0088] A hard coat is preferably applied to protect the surfaces
52, 62 of the dressing bar 50. The desired thickness of the hard
coat can be in the range of about 100 nanometers or greater. In one
embodiment, the hard coat is diamond-like carbon ("DLC") with a
thickness of about 100 nanometers to about 200 nanometers. It is
highly desirable to generate DLC hardness in the range of 70-90
giga-Pascals ("GPa"). In other embodiments, the hard coat is TiC,
SiC, AlTiC.
[0089] In one embodiment the DLC is applied by chemical vapor
deposition. As used herein, the term "chemically vapor deposited"
or "CVD" refer to materials deposited by vacuum deposition
processes, including, but not limited to, thermally activated
deposition from reactive gaseous precursor materials, as well as
plasma, microwave, DC, or RF plasma arc jet deposition from gaseous
precursor materials. Various methods of applying a hard coat to a
substrate are disclosed in U.S. Pat. Nos. 6,821,189 (Coad et al.);
6,872,127 (Lin et al.); 7,367,875 (Slutz et al.); and 7,189,333
(Henderson), which are hereby incorporated by reference.
[0090] Abrasive particles of any composition and size can be used
with the method and apparatus of the present invention. The
preferred abrasive particles 54 are diamonds with primary diameters
less than about 1 micrometer, also referred to as nano-scale. For
some applications, however, the diamonds can have a primary
diameter of about 100 nanometers to about 20 micrometers. The
abrasive particles may also be present in the form of an abrasive
agglomerate. The abrasive particles in each agglomeration may be
held together by an agglomerate binder. Alternatively, the abrasive
particles may bond together by inter-particle attraction forces.
Examples of suitable abrasive particles include fused aluminum
oxide, heat treated aluminum oxide, white fused aluminum oxide,
porous aluminas, transition aluminas, zirconia, tin oxide, ceria,
fused alumina zirconia, or alumina-based sol gel derived abrasive
particles.
[0091] FIG. 6 illustrates a circular dressing bar 80 with a tapered
edge 82 extending substantially around perimeter 84 in accordance
with an embodiment of the present invention. The dressing bar 80
optionally includes hydrostatic ports 86, that are discussed
below.
[0092] FIG. 7 illustrates an alternate dressing bar 90 with slots
or grooves 92 in accordance with an embodiment of the present
invention. During the embedding process, the abrasive particles are
displaced into the grooves 92, simulating grooves on the resulting
substrate, without the need for a machining step.
[0093] FIG. 7 illustrates an alternate dressing bar 90 with slots
or grooves 92 in accordance with an embodiment of the present
invention. The grooves 92 are fabricated to reduce the magnitude of
the hydrodynamic fluid bearing. The grooves are recessed with
respect to land 94 and do not participate in embedding the abrasive
particle into the substrate. The grooves 92 also control the amount
of abrasive particles being embedded at any giving time, reducing
the required preload. The grooves 92 can also be used for form a
patterns of abrasive particles in the substrate.
[0094] FIG. 8 is a circular dressing bar 100 with slots 102 that
permit the abrasive slurry to circulate during the embedding
process in accordance with an embodiment of the present
invention.
[0095] FIG. 9 is a perspective view of an alternate dressing bar
110 with low friction pads 112 in accordance with an embodiment of
the present invention. The low friction pads 112 control spacing
between the dressing bar 110 and the substrate. The low friction
pads 112 include a pre-defined height 114 that corresponds to the
target height the abrasive particles extend above the substrate.
The pads 112 assure a constant height during the entire dressing
operation. It is envisioned that the low friction pads displace the
abrasive particles during the embedding process and engage with the
substrate.
[0096] In one embodiment, the pads 112 have heights of about 100
nanometers for use with abrasive particles having major diameters
of about 200 nanometers to about 400 nanometers. The tapered region
116 forms an angle with respect to the flat region 118 of about 0.4
milli-radians.
[0097] FIG. 10 is a perspective view of a circular dressing bar 120
with low friction pads 122, as discussed above.
[0098] FIGS. 11 and 12A illustrate a gimballed dressing bar
assembly 130 in accordance with an embodiment of the present
invention. Gimbal mechanism 132 allows the dressing bar 134 to be
topography following with respect to the substrate 136 (see FIG.
13A). The gimbal mechanism 132 and preload structure 140 allows the
dressing bar 134 to form a fluid bearing with a clearance
determined by the system parameters. Once the clearance desired
between the substrate 136 and the dressing bar 134 is achieved,
abrasive particles are introduced at the interface. As used herein,
"fluid bearing" refers generically to a fluid (i.e., liquid or gas)
present at an interface between a dressing bar and a substrate that
applies a lift force on the dressing bar. Fluid bearings can be
generated hydrostatically, hydrodynamically, or a combination
thereof.
[0099] Fluid bearings are fairly complex with a substantial number
of variables involved in their design. The primary forces involved
in a given fluid bearing are the gimbal structure 132 and the
preload 148. The gimbal structure 132 applies both pitch and roll
moments to the dressing bar 134. If the gimbal 132 is extremely
stiff, the fluid bearing may not be able to form a pitch angle or a
roll angle. The preload 148 and preload offset (location where the
preload is applied) bias the fluid bearing toward the
substrate.
[0100] Fluid bearing geometries on the active surface 133 of the
dressing bar play a role in pressurization of a fluid bearing.
Possible geometries include tapers, steps, trenches, crowns, cross
curves, twists, wall profile, and cavities. Finally, external
factors such as viscosity of the bearing fluid and linear velocity
play an extremely important role in pressurizing bearing
structures.
[0101] The dressing bar 134 is attached to bar holder 138. Bar
holder 138 is engaged with preload fixture 140 by a series of
springs 142. The bar holder 138 is captured between base plate 146
and a preload structure 140. Spacers 144 assure that the springs
142 are preloaded prior to engaging the dressing bar 134 with the
plate 136. The springs 142 are preloaded to closely match the
externally applied load 148. The springs 142 permit the bar holder
to gimbal with respect to the preload structure 140.
[0102] In the preferred embodiment, externally applied load 148 is
higher than the preload applied by the spring 142 on the gimbaled
bar holder 138. The gimbaled bar holder 138 is suspended and free
to gimbal and follow the run out and curvature of the substrate
136.
[0103] FIG. 12B is a schematic illustration of the engagement
between the dressing bar 134 with substrate 136 in the topography
following mode in accordance with an embodiment of the present
invention. The dressing bar 134 is illustrated following the
micrometer-scale and/or millimeter-scale wavelength 135 of the
waviness on the substrate 136.
[0104] The leading edge 149 of the dressing bar 134 is raised above
the substrate 136 due to hydrostatic and/or hydrodynamic lift
force. In some embodiments, lubricant on the substrate 136 may
contribute to the lift force. Discussion of hydrodynamic lift is
provided in U.S. Pat. Nos. 7,93,805 and 7,218,478, which are hereby
incorporated by reference.
[0105] Engagement of the dressing bar 134 with the substrate 136 is
defined by pitch angle 134A and roll angle 134B of the dressing bar
134, and clearance 141 with the substrate 136. The gimbal 132 (see
FIG. 11) provides the dressing bar 134 with roll and pitch
stiffness that balance by the roll and pitch moments 143 generated
by the hydrostatic and/or hydrodynamic lift.
[0106] The frictional forces 145 generated during interference
embedding of the abrasive particles 139 cause a tipping moment 147
opposite to the moment 143, causing the leading edges 149 of the
dressing bar 134 to move toward the substrate 136. The moment 143
generated by the lift is preferably greater than the moment 147
generated by frictional forces 145 at the interface with the
abrasive particles 139, causing the abrasive particles to be
embedded in the substrate 136 with a uniform height.
[0107] FIGS. 13A and 13B illustrate the gimballed dressing bar
assembly 130 before and after engagement with substrate 136. As
illustrated in FIG. 13A, the springs 142 bias the bar holder 138
into engagement with the base 146. The dressing bar 134 is at it
maximum extension beyond the base 146.
[0108] As illustrated in FIG. 13B, the dressing bar 134 is engaged
with the substrate 136. This engagement acts in opposition of the
force of the springs 142, creating clearance 150 between shoulder
152 on the bar holder 138 and the base 146. The clearance 150 is
preferably less than the diameter of the abrasive particles
139.
[0109] FIGS. 14 through 17 illustrate an alternate gimballed
dressing bar assembly 170 in accordance with an embodiment of the
present invention. Dressing bar 172 is attached to gimbal assembly
174, which is attached to preload structure 176 by fasteners 178
and spacers 180. The gimbal assembly 174 is captured between base
plate 175 and the spacers 180.
[0110] Spring assembly 182 transfers preload P from the preload
structure 176 to the gimbal assembly 174. As best illustrated in
FIG. 15, dimple 184 on spring assembly 182 applies a point load on
the gimbal assembly 174. The dimple 184 decouples the preload from
the roll and pitch stiffness of the dressing bar 172. The spring
assembly 182 is maintained in compression between the preload
structure 176 and the base plate 175. The gimbal assembly 174
allows the dressing bar 172 to move vertically, and in pitch and
roll around the dimple 184. The dressing bar 172 meets all the
conditions for establishing a fluid bearing with the substrate 192.
The fluid bearing must be smaller than the diamonds in order to
permit interference embedding of the diamonds into the plate
192.
[0111] FIG. 18 is a perspective view of the gimbal assembly 174. A
series of arms or segments 186 connect frame portion 188 to center
portion 190. The dressing bar 172 can be integrally formed with the
gimbal assembly 174 or can be a separate component attached
thereto. The configuration of the segments 186 is well suited for
in-plane deformation due to external load application. The
displacement of the attached dressing bar 172 is substantially
normal to the applied load with minimal twist, roll, or pitch,
which is very desirable in order to cause the dressing bar 172 to
rest substantially flat with respect to the substrate. In
particular, the dressing bar 172 moves parallel to a plane defined
by the applied load.
[0112] FIGS. 19-21 illustrate an embodiment of a dressing bar
assembly 301 with a hydrostatic fluid bearing 302 in accordance
with an embodiment of the present invention. The dressing bar 300
includes tapered leading edge 304 progressively interfering with
abrasive particles 306 on substrate 308 (see FIG. 20).
[0113] As the abrasive particles 306 enter interface region 310
with the tapered leading edge 304 downward force 312 progressively
increases, thus embedding the abrasive particles 306 into the
substrate 308. The shape of the leading edge 304 can be linear or
curvilinear depending on the clearance embedding force relationship
desired during the abrasive embedding process.
[0114] As the substrate 308 rotates, the abrasive particles 306 are
progressively driven downward as a function of the interference
level with active surface 301. In an alternate embodiment, the
substrate 308 is translated relative to the dressing bar 300 by an
X-Y stage. The substrate 308 is optionally vibrated ultrasonically
to facilitate penetration of the abrasive particles 306 into the
plate 308.
[0115] The dressing bar 300 is suspended by a spring gimballing
system 320 attached to support structure 321. Gimbal mechanism 324
includes a series of springs 326 that provide preload roll torque
and pitch torque to buffer bar 328. The buffer bar 328 includes
hydrostatic ports 330 in fluid communication with hydrostatic ports
322 on the dressing bar 300. The dressing bar 300 is attached to
the buffer bar 328 to transfer the preload from the gimbal
mechanism 324 to the hydrostatic fluid bearing 302.
[0116] Hydrostatic bearing system 320 includes a series of
hydrostatic ports 322 formed in surface 332 of the dressing bar
300. The ports 322 are in fluid communication with delivery tubes
334 providing a source of compressed air. The hydrostatic lift
system 320 provides the dressing bar 300 with roll, pitch and
vertical stiffness, as well as controlling the spacing with the
substrate 308.
[0117] A controller monitors gas pressure delivered to the slider
dressing bar 300. Gas pressure to each of the four ports 322 is
preferably independently controlled so that the pitch and roll of
the slider dressing bar 300 can be adjusted. In another embodiment,
the same gas pressure is delivered to each of the ports 322. While
clean air is the preferred gas, other gases, such as for example,
argon may also be used. The gas pressure is typically in the range
of about 2 atmospheres to about 4 atmospheres. Once calibrated, the
spacing between the dressing bar 300 and the substrate 308 can be
precisely controlled, even while the dressing bar 300 follows the
millimeter-scale and/or micrometer-scale waviness on the substrate
308.
[0118] The height of the abrasive particles 306 is determined by a
spacing profile established by the active surface 301 of the
dressing bar 300. The hydrostatic forces 302 supporting the
dressing bar 300 counter the forces generated during embedding
abrasive particles 306 as the substrate 308 is moved relative to
the dressing bar 300.
[0119] The stiffness of the dressing bar 300 is determined by the
relationship:
K=.DELTA.F/.DELTA.h
where .DELTA.F is the change of load caused by a change in spacing
.DELTA.h between the dressing bar and the substrate.
[0120] It is important to match the stiffness of the hydrostatic
fluid bearing 302 to the change in spacing .DELTA.h. Note also that
such relationship is generally nonlinear. The desired height of the
diamonds 306 embedded in the substrate 308 is achieved by assuring
a minimum clearance .DELTA.h between the plate and the dressing
bar. The minimum clearance of the dressing bar 300 is set equal to
the desired height 338 of the diamonds 306. The desired height 338
of the dressing bar 300 is adjusted by controlling the hydrostatic
pressure, Ps, leading to a desired spacing 338 between the dressing
bar and the plate. A similar relationship can be drawn for pitch
and roll stiffness.
[0121] Multiple design configurations can be envisioned for the
dressing bar 300. Hydrostatic ports 322 can be machined into the
dressing bar 300 or attached to the dressing bar 300 via a
fixture.
[0122] A fly height tester can be used to determine the
relationship between the applied load on the dressing bar and the
spacing between the dressing bar and the substrate. By varying the
external pressure on the hydrostatic ports fabricated onto the
dressing bar, a desired minimal clearance matching the desired
abrasive height and pitch and roll angles can be established for
each dressing bar.
[0123] Alternate hydrostatic slider height control devices are
disclosed in commonly assigned U.S. Provisional Patent Application
Ser. No. 61/220,149 entitled Constant Clearance Plate for Embedding
Diamonds into Substrates, filed Jun. 24, 2009 and Ser. No.
61/232,425 entitled Dressing bar for Embedding Abrasive Particles
into Substrates, which are hereby incorporated by reference. A
mechanism for creating a hydrostatic air bearing for a gimbaled
structure is disclosed in commonly assigned U.S. Provisional Patent
Application Ser. No. 61/172,685 entitled Plasmon Head with
Hydrostatic Gas Bearing for Near Field Photolithography, filed Apr.
24, 2009, which is hereby incorporated by reference.
[0124] FIGS. 22 through 25 illustrate a mechanically actuated
dressing bar assembly 351 attached to a hydrostatic bearing
mechanism 358 in accordance with an embodiment of the present
invention. The hydrostatic bearing mechanism 358 permits dressing
bar 350 to be topography following with respect to the substrate
354 (see FIG. 24) to achieve a constant spacing 356. Spacing 370
between dressing bar 350 and substrate 354 can be controlled
independently from spacing 356 with the hydrostatic bearing
mechanism 358. As best illustrated in FIG. 25, the dressing bar 350
includes taper 351.
[0125] The hydrostatic bearing mechanism 358 includes a series of
hydrostatic ports 360 in fluid communication with delivery tubes
362 connected to a source of compressed air. The hydrostatic ports
360 maintain the spacing 356 between the hydrostatic bearing
mechanism 358 and the substrate 354.
[0126] Gimbal mechanism 364 includes a rigid support structure 365
that supports springs 368 providing preload force 366 with pitch
and roll movement to the hydrostatic bearing mechanism 358. The
springs 368 are organized to minimize the distortion of the
hydrostatic bearing mechanism 358.
[0127] The dressing bar 350 is attached to a hydrostatic bearing
mechanism 358 by actuators 352. The attachment between the dressing
bar 350 and the actuators 352 is critical for advancing the
dressing bar 350 to the substrate 354 and achieving a desired
spacing profile 370. The actuators 352 can be controlled
independently to adjust clearance, pitch, roll, and yaw of the
dressing bar 350 relative to the hydrostatic bearing mechanism
358.
[0128] In operation, the actuators 352 advance the dressing bar 350
toward the substrate 354, while the hydrostatic bearing mechanism
358 maintains a constant spacing 356. The end effectors of the
actuators 352 control push/pull the gimballing mechanism 364. As
the actuators 352 are pushing and pulling the attitude including
pitch, roll, and vertical location of the dressing bar 350 is
mechanically controlled to a desired value. A prescribed height 370
of the dressing bar 350 with respect to the substrate 354 is
controlled via the actuators 352.
[0129] Motion of the dressing bar 350 relative to the substrate 354
is controlled by translation mechanism 371. Translation mechanism
371 can be a rotary table, an X-Y stage, an orbital motion
generator, an ultrasonic vibrator, or some combination thereof.
[0130] FIGS. 26 and 27 illustrate an alternate mechanically
actuated dressing bar assembly 400 attached to a hydrostatic
bearing mechanism 402 in accordance with an embodiment of the
present invention. The hydrostatic bearing mechanism 402 operates
as discussed in connection with FIGS. 21-25.
[0131] The dressing bar 404 is attached to a gimbal assembly 406.
Gimbal assembly 406 includes a series of spring arms 408A, 408B,
408C (collectively "408") that permit the dressing bar 404 to move
through pitch, roll, and yaw. The spring arms 408 minimize twist of
the hydrostatic bearing mechanism 402, while allowing for a
substantially linear axial motion during axial motion of actuators
410.
[0132] The gimbal assembly 406 is attached to the hydrostatic
bearing mechanism 402. The actuators 410 are interposed between the
hydrostatic bearing mechanism 402 and pad 412 on the gimbal
assembly 406. The actuators 410 advance the dressing bar 404 toward
the substrate as discussed in connection with FIG. 24.
[0133] FIGS. 28-30 illustrate an alternate mechanically actuated
dressing bar assembly 450 attached to a hydrostatic bearing
mechanism 452 in accordance with an embodiment of the present
invention. The hydrostatic bearing mechanism 452 operates as
discussed in connection with FIGS. 21-25.
[0134] Dressing bar 454 is attached to the hydrostatic bearing
mechanism 452 using three actuators 456 arranged in a three-point
push configuration. Ball and socket mechanism 460 is provided at
the interface between micro-actuators 456 and the dressing bar 454.
The micro-actuators may be piezoelectric, heaters to create thermal
deformation, or a variety of other micro-actuators known in the
art.
[0135] The ball and socket mechanism 460 minimizes vibrations and
stresses transferred to the hydrostatic bearing mechanism 452. The
ball and socket mechanism 460 allows the hydrostatic bearing
mechanism 452 to rotate freely while being attached to the
micro-actuators 456. The ball and socket mechanism 460 allow for a
true planar relationship between the micro-actuators 456 and the
hydrostatic bearing mechanism 452.
[0136] The ball socket mechanism 460 preferably introduces minimal
slack to avoid any undesired motion. The interference fit generates
frictional forces enhancing the stability of the dressing bar 454
under external excitations.
[0137] FIGS. 31-33 illustrate an alternate mechanically actuated
dressing bar assembly 500 attached to a hydrostatic bearing
mechanism 502 in accordance with an embodiment of the present
invention. The hydrostatic bearing mechanism 502 operates as
discussed in connection with FIGS. 21-25.
[0138] Dressing bar 504 is attached to the hydrostatic bearing
mechanism 502 using three actuators 506 arranged in a three-point
push configuration. An elastic member 508 is located at interface
510 between the actuators 506 and the dressing bar 504. The elastic
members 508 permit the dressing bar 504 to rotate relative to the
actuators 506.
[0139] A fly height tester can be used to determine the
relationship between the applied load on the dressing bar and the
spacing between the dressing bar and the substrate. By varying the
external pressure on the hydrostatic ports in the hydrostatic
bearing mechanism, a desired minimal clearance matching the desired
abrasive height and pitch and roll angles can be established for
each dressing bar.
[0140] Acoustic emission can also be used to determine contact
between the dressing bar and the substrate by energizing the
actuators. A transfer function between the actuators and the
gimballing mechanism can be established numerically or empirically
to determine the displacement actuation relationship.
[0141] FIG. 34 illustrates a hydrostatic button bearing 550 with
cavity 552 having port 554 and an outer annular active surface 556
in accordance with an embodiment of the present invention. In one
embodiment, R0 is about 2 millimeters and the ratio of R1/R0 is
about 0.87. The preload on the hydrostatic bearing is about 8.8
Newtons.
[0142] FIG. 35 is a perspective view of dressing bar 560
incorporating four of the button bearings 550A, 550B, 550C, 550D
("550") of FIG. 34, in accordance with an embodiment of the present
invention. Assuming a flow rate of about 10 milliliters/minute is
delivered to the port 554, the pressure regulators generate a
hydrostatic pressure about 0.8 Mega Pascals (MPa) in order to
maximize the load carrying capacity. The resulting hydrostatic
bearing has a clearance of about 1 micrometers measured between the
active surfaces 556 and the substrate.
[0143] As best illustrated in FIG. 36, the active surface 562 of
dressing bar 560 extends a distance 564 of about 800 nanometers to
about 900 nanometers above the active surfaces 556 of the button
bearings 550, resulting in a spacing of the active surface 562
above the substrate of about 100 nanometers to about 200
nanometers. The pressure at leading edge button bearings 550A, 550B
is preferably greater than at trailing edge button bearings 550C,
550D in order to pitch the dressing bar 560.
[0144] FIG. 37 shows a shape of the pressure distribution with a
flat top pressure corresponding to the externally delivered
pressure in the cavity 552 and the decaying pressure distribution
along the bearing surface 554.
[0145] FIG. 38A illustrates a multi-layered gimbal assembly 570 in
accordance with an embodiment of the present invention. In the
illustrated embodiment, center layer 572 includes traces 574 that
deliver compressed air from inlet ports 576 in the top layer 578 to
exit ports 580 on the bottom layer 582. The exit ports 580 are
fluidly coupled to the ports 554 on the button bearings 550. As
best illustrated in FIG. 38B, the inlet ports 576 are offset and
mechanically decoupled from the gimbal mechanism 590.
[0146] FIGS. 39 and 40 are perspective views of a dressing bar
assembly 600 in accordance with an embodiment of the present
invention. Spring load mechanism 602 delivers a preload of about 40
Newtons from the preload structure 604 to bar holder 608 and
dressing bar 560. Tubes 606 deliver compressed air to each of the
inlet ports 576 of the gimbal assembly 570.
[0147] FIGS. 41A and 41B are front and rear perspective views of an
alternate dressing bar 650 in accordance with an embodiment of the
present invention. A first set of hydrostatic ports 652 are located
adjacent to leading edge 654 of active surface 656. A second set of
hydrostatic ports 658 are located adjacent to trailing edge 660 of
active surface 656. The plurality of hydrostatic ports 652, 658
allows for a better averaging of the substrate waviness and a
better overall topography following. The plurality of ports 652,
658 results in lower flow per port and allows for more accurate
clearance control.
[0148] The hydrostatic ports in the first set 652 are optionally
smaller than the hydrostatic ports in the second set 658 so leading
edge 662 can be positioned higher above the surface than trailing
edge 664. The pressure in cavity 664 is generally uniform so the
flow is delivered uniformly to each of the ports 666 and 668.
Variations in incoming flow is seen by all the bearings 652, 658
causing minimal change in pitch and roll of the dressing bar 650,
although the overall spacing of the dressing bar 650 will be
effected by the changes in the flow. In an alternate embodiment,
the cavity 664 is divided so one flow controller supplies the ports
652 and another flow controller supplies the ports 658.
[0149] FIG. 42 is a perspective view of an alternate dressing bar
700 in accordance with an embodiment of the present invention. A
plurality of hydrostatic ports 702 surround the plurality of active
surfaces 704A-704G ("704") on the dressing bar 700. The plurality
of hydrostatic ports 702 reduce the flow per port and compensate
for the incoming flow variations. The configuration of the ports
702 around the active surfaces 704 averages the response of the
dressing bar 700 to variations in micrometer-scale and
millimeter-scale topography of the substrate. In essence, the
dressing bar 700 acts as a mechanical filter reducing clearance
variations due to changes in the topography of the substrate.
Manufacturing tolerances and variations in the dressing bar 700 are
also averaged and randomized leading to less spacing variations.
Flow variation causes a proportional change of spacing at the
leading edge 706 and the trailing edge 708, serving to maintain the
pitch or attitude of the dressing bar 700.
[0150] FIG. 43 is a bottom perspective view of dressing bar
assembly 750 with an array of dressing bar 752 in accordance with
an embodiment of the present invention. FIG. 44 is an exploded view
of the dressing bar assembly of FIG. 43. Alternatively, the
dressing bars can be arranged in a circular array, an off-set
pattern, or a random pattern.
[0151] Abrasive particle embedding is accomplished by relative
motion between the dressing bar assembly 750 and the substrate 754,
such as linear, rotational, orbital, ultrasonic, and the like. In
one embodiment, that relative motion is accomplished with an
ultrasonic actuator such as disclosed in commonly assigned U.S.
Provisional Patent Application Ser. No. 61/232,525, entitled Method
and Apparatus for Ultrasonic Polishing, filed Aug. 10, 2009, which
is hereby incorporated by reference.
[0152] In the illustrated embodiment, each dressing bar 752 is
hydrostatically controlled. FIG. 45A illustrates a top view of an
individual dressing bar 752. Pressure cavity 756 is fabricated on
the back surface 758 of the dressing bar 752 that acts as a plenum
for the delivery of pressurized gas out through the hydrostatic
pressure ports 760.
[0153] FIG. 45B illustrates an embodiment of dressing bar 752 with
both hydrostatic and hydrodynamic fluid bearing capabilities
designed into bottom surface 773 in accordance with an embodiment
of the present invention. Leading edge 774 of the dressing bar 752
includes a pair of fluid bearing features 775A, 775B (collectively
"775") each with at least one associated pressure port 760A, 760B.
Trailing edge 776 also includes fluid bearing features 777A, 777B
(collectively "777") and associated hydrostatic pressure ports
760C, 760D. Active surface 778 on the trailing edge 776 enhance the
stability of the dressing bar 752 at the interface with a abrasive
particles.
[0154] The fluid bearing features 777 on the trailing edge 776 have
less surface area than the fluid bearing features 775 at the
leading edge 774. Consequently, the leading edge 774 typically
flies higher than the trailing edge 776, which sets the pitch of
the dressing bar 752 relative to the substrate 754 (see, e.g., FIG.
43). The trailing edge 776 is typically designed to be in
interference with the abrasive particles on the substrate 754. Both
leading edge and trailing edge fluid bearing features 775, 777
contribute to holding the dressing bar 752 at a desired clearance
796 from the substrate 754 and controlling the amount of
interference with abrasive particles. It is also possible to
control the pressure applied to the hydrostatic pressure ports 760
to increase or decrease the pitch of the dressing bar 752.
[0155] The hybrid dressing bar 752 can operate with a hydrostatic
fluid bearing and/or a hydrodynamic fluid bearing. The hydrostatic
pressure ports 760 apply lift to the dressing bar 752 prior to
movement of the substrate 754. The lift permits clearance 796 to be
set before the substrate 754 starts to move. Consequently, the high
preload 794 does not damage the substrate 754 during start-up. Once
the substrate 754 reaches its safe speed and the hydrodynamic fluid
bearing is fully formed, the hydrostatic fluid bearing can be
reduced or terminated. The procedure can also be reversed at the
end of the embedding process. The hybrid dressing bar 752 is
particularly well suited to prevent damage to Tin substrates. Tin
is a very soft metal and precautions are needed to avoid damage and
tear out of the Tin coating during start-up and wind-down.
[0156] In another embodiment, both the hydrostatic and hydrodynamic
fluid bearings are maintained during at least a portion of the
embedding process. The pressure ports 760 can be used to supplement
the hydrodynamic bearing during the embedding process. For example,
the pressure ports 760 may be activated to add stiffness to the
fluid bearing during initial passes of the dressing bar 752 over
the substrate 754. After the abrasive particles are substantially
uniformly embedded, the hydrostatic portion of the fluid bearing
may be reduced or terminated to reduce the stiffness. The pressure
ports 760 can also be used to adjust or fine tune the attitude or
clearance of the dressing bar 752 relative to the substrate 754.
Hybrid dressing bars can be used alone or in an array. A single
hybrid dressing bar 50 is illustrated in FIG. 5A.
[0157] As best illustrated in FIG. 44, the dressing bars 752 are
preferably formed in an array separated by spacing structures 762.
In one embodiment, the dressing bars 752 and spacing structures 762
are injection molded from a polymeric material to form an integral
structure. Alternatively, discrete dressing bars 752 can be bonded
or attached to the gimbal mechanisms 764 on the gimbal assembly
766. The dressing bars 752 can be arranged in a regular or random
pattern.
[0158] As illustrated in FIG. 46, gimbal assembly 766 includes an
array of the gimbal mechanisms 764. Each gimbal mechanism 764
includes four L-shaped springs 768A, 768B, 768C, 768D (collectively
"768") that suspend the dressing bars 752 above the substrate 754
in accordance with an embodiment of the present invention. Box-like
structure 770 is optionally fabricated on each gimbal mechanism 764
to help align the dressing bars 752. The box-like structure 770
also includes a port 772 that delivers the pressurized gas to the
cavity 756 in the dressing bars 752 and out the hydrostatic
pressure ports 760.
[0159] As best illustrated in FIG. 44, external pressure source 780
delivers pressurized gas (e.g., air) to plenum 782 in preload
structure 784. Cover 786 is provided to enclose the plenum 782. A
plurality of hydrostatic pressure ports 788 in the plenum 782 are
fluidly coupled to the hydrostatic pressure ports 772 on the gimbal
mechanism 764 by bellows couplings 790. An adhesive layer (not
shown) attaches the dressing bars 752 to the gimbal box-like
structure 770.
[0160] Springs 792 transfer the preload 794 from the preload
structure 784 to each of the gimbal mechanisms 764. The externally
applied load 794 and the external pressure control the desired
spacing 796 between the dressing bars 752 and the substrate 754
(see FIG. 43).
[0161] As best illustrated in FIG. 47, dimple structures 804 are
interposed between springs 806 and the gimbal mechanisms 764. The
dimple structure 804 delivers preload 810 as a point source.
Adjacent to the springs 806 and the dimples 804 are the flexible
bellows 790 that deliver the external pressure to each individual
dressing bar 752 via the gimbal mechanisms 764.
[0162] Holder structure 800 is attached to the preload structure
784 by stand-offs 802. The holder structure 800 sets the preload
810 applied on each dressing bar 752 and limits the deformation of
the gimbal mechanisms 764 in order to avoid damage. The gimbal
mechanisms 764, preload structure 784, and holder structure 800 can
also be used in a hydrodynamic application without the hydrostatic
pressure ports 760 and bellows couplings 790.
[0163] FIGS. 48 and 49 illustrate an alternate dressing bar
assembly 820 substantially as shown in FIG. 43, without the
hydrostatic control, in accordance with an embodiment of the
present invention. An array of dressing bars 822 is attached to
preload structure 824 by an array of gimbal mechanisms 826. Preload
828 is transmitted to the gimbal mechanisms 826 by dimpled springs
830, generally as discussed above. The suspended dressing bars 822
have a static pitch and roll stiffness through the hydrodynamic
fluid bearing and a z-axis stiffness through the gimbal mechanisms
826. Bottom surfaces of the dressing bars 822 preferably have fluid
bearing features, such as illustrated in FIG. 45B.
[0164] Where a range of values is provided, it is understood that
each intervening value, to the tenth of the unit of the lower limit
unless the context clearly dictates otherwise, between the upper
and lower limit of that range and any other stated or intervening
value in that stated range is encompassed within the inventions.
The upper and lower limits of these smaller ranges which may
independently be included in the smaller ranges is also encompassed
within the inventions, subject to any specifically excluded limit
in the stated range. Where the stated range includes one or both of
the limits, ranges excluding either both of those included limits
are also included in the inventions.
[0165] 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 described the methods
and/or materials in connection with which the publications are
cited.
[0166] 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.
[0167] 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.
[0168] 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.
* * * * *