U.S. patent application number 11/619484 was filed with the patent office on 2007-05-10 for automated process and apparatus for planarization of topographical surfaces.
Invention is credited to James E. III Lamb, Jeremy McCutcheon.
Application Number | 20070105384 11/619484 |
Document ID | / |
Family ID | 36994626 |
Filed Date | 2007-05-10 |
United States Patent
Application |
20070105384 |
Kind Code |
A1 |
McCutcheon; Jeremy ; et
al. |
May 10, 2007 |
AUTOMATED PROCESS AND APPARATUS FOR PLANARIZATION OF TOPOGRAPHICAL
SURFACES
Abstract
An improved apparatus (20) and method are provided for
effective, high speed contact planarization of coated curable
substrates such as microelectronic devices to achieve very high
degrees of planarization. The apparatus (20) includes a planarizing
unit (28) preferably having an optical flat flexible sheet (88) and
a backup optical flat body (82), and a curing assembly (30). In
operation, a substrate (78) having a planarizable coating (76) is
placed within a vacuum chamber (26) beneath sheet (88) and body
(82). A pressure differential is created across sheet (88) so as to
deflect the sheet into contact with a central region C of the
coating (76), whereupon the coating (76) is brought into full
planarizing contact with sheet (88) and body (82) by means of a
support (114) and vacuum chuck (120); at this point the coating
(76) is cured using assembly (30). After curing, a pressure
differential is established across sheet (88) for sequentially
separating the sheet from the peripheral portion P of the coating,
and then full separation of the sheet (88) and coating (76).
Inventors: |
McCutcheon; Jeremy; (Rolla,
MO) ; Lamb; James E. III; (Rolla, MO) |
Correspondence
Address: |
HOVEY WILLIAMS LLP
2405 GRAND BLVD., SUITE 400
KANSAS CITY
MO
64108
US
|
Family ID: |
36994626 |
Appl. No.: |
11/619484 |
Filed: |
January 3, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10887530 |
Jul 8, 2004 |
|
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11619484 |
Jan 3, 2007 |
|
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60486021 |
Jul 10, 2003 |
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Current U.S.
Class: |
438/692 |
Current CPC
Class: |
H01L 21/31058 20130101;
H01L 21/67092 20130101; H01L 21/6719 20130101 |
Class at
Publication: |
438/692 |
International
Class: |
H01L 21/461 20060101
H01L021/461 |
Goverment Interests
[0002] This invention was made with the U.S. Government support
under ATP #70NANB1H3019 awarded by the National Institute of
Standards and Technology (NIST). The Government has certain rights
in the invention.
Claims
1. Apparatus for planarizing a curable coating applied to a
substrate, said coating having a surface presenting a surface area
with a central region and a surrounding peripheral region, said
apparatus comprising: a support operable to support and hold a
thin, flexible sheet of material; a support assembly operable to
support and hold said substrate with said coating proximal to said
sheet; a differential pressure assembly operable to create a
pressure differential across said sheet of sufficient magnitude to
deflect the sheet so that the sheet contacts the central region of
said surface area but is spaced from said peripheral region, said
support assembly shiftable to move said substrate into face-to-face
planarizing contact with said sheet throughout substantially all of
said surface area; and a device for curing said coating during said
planarizing contact.
2. The apparatus of claim 1, said support comprising a pair of
annular clamping rings operable to cooperatively clamp and hold the
margin of said sheet.
3. The apparatus of claim 1, said mounting assembly comprising a
ring-like body sized to engage the periphery of a face of said
substrate remote from said coating, and a piston and cylinder
assembly operably coupled with the body for selective shifting
thereof toward and away from said sheet.
4. The apparatus of claim 3, said mounting assembly further
including a shiftable compression member operable to press said
coating into said planarizing contact with said sheet.
5. The apparatus of claim 4, said compression member comprising a
vacuum chuck, said chuck operably coupled with a vacuum source.
6. The apparatus of claim 1, said differential pressure assembly
including wall structure defining a first chamber in communication
with the face of said sheet remote from said coating, and a second
chamber in communication with the face of said sheet adjacent said
coating.
7. The apparatus of claim 6, including structure defining a vacuum
port in communication with said first chamber in order to create
vacuum conditions therein.
8. The apparatus of claim 6, including structure defining a port in
communication with said second chamber for selectively drawing a
vacuum or establishing a positive pressure therein.
9. The apparatus of claim 1, said mounting assembly also shiftable
to move said substrate out of contact with said sheet after said
curing of said coating.
10. The apparatus of claim 1, including an optical flat body
positioned adjacent the face of said sheet remote from said
substrate, said sheet engageable with said optical flat body during
said planarizing contact between said coating and said sheet.
11. The apparatus of claim 10, said optical flat body operable to
transmit said UV radiation therethrough.
12. The apparatus of claim 1, including a resilient platen adjacent
the face of said substrate remote from said coating, said platen
being shiftable with said mounting assembly.
13. The apparatus of claim 1, wherein said apparatus does not
include an optical flat body.
14. Apparatus for planarizing a curable coating applied to a
substrates said coating having a surface presenting a surface area
with a central region and a surrounding peripheral region, said
apparatus comprising: means for positioning a thin, flexible sheet
of material in proximal spaced relationship to said surface; means
for causing said sheet to deflect so that the sheet contacts the
central region of said surface area but is spaced from said
peripheral region; means for effecting relative movement between
the substrate and sheet until the sheet is in face-to-face
planarizing contact with substantially all of said surface area;
and means for curing said surface coating while maintaining said
planarizing contact.
15. The apparatus of claim 14, wherein said apparatus does not
include an optical flat body.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of nonprovisional
application Ser. No. 10/887,530, filed Jul. 8, 2004, which claims
the benefit of provisional application Ser. No. 60/486,021 filed
Jul. 10, 2003. These applications are incorporated by reference
herein.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention is broadly concerned with the improved
methods and apparatus for the contact planarization of surfaces
such as those developed during the manufacture of advanced
integrated circuit and other devices. More particularly, the
invention is concerned with such methods and apparatus wherein a
coated substrate is placed adjacent an optical flat flexible sheet,
and the latter is first deflected to contact a central region of
the coating, followed by full, pressurized planarizing contact
between the sheet and coating; during such pressurized planarizing
contact, the coating is cured. Post-curing separation of the sheet
and coating preferably involves generating a pressure differential
between the sheet and coating which creates a smooth edge-to-center
separation.
[0005] 2. Description of the Prior Art
[0006] Advanced integrated circuit (IC) designs are highly
dependent on increasingly complex device-layering techniques to
produce semiconductor devices that are more powerful, have lower
profiles, and require less energy to operate. To make these
qualities possible, more circuits with much finer structures must
be integrated into a microchip by constructing multiple layers of
interconnects and dielectrics on a semiconductor substrate in an
appropriate sequence. To construct an IC, many layers containing
ultra-fine structures must be patterned onto a semiconductor
surface. Currently, photolithography is the predominant technique
used to pattern these ultra-fine structures. This technique
requires materials to be deposited and removed from the surface to
construct such ultra-fine structures.
[0007] Photolithography involves depositing a photosensitive
material, known as a photoresist, onto a semiconductor substrate
surface. An optical transparent object, known as the photomask or
reticle, with pre-defined images of the structures to be built on
the semiconductor surface is placed above the photoresist-coated
substrate. An appropriate wavelength of light is illuminated
through the optical object. The light either decomposes or cures
the exposed area of the photoresist, depending on the nature of the
photoresist and the process. The semiconductor surface is then
developed to produce the patterned image on the substrate surface,
and the device is ready for subsequent processing.
[0008] Materials can be applied in a uniform thickness if the
surface to be coated is entirely planar. However, if the surface is
not planar, that is, it has topographic features, materials may not
coat with a uniform thickness, which may greatly affect the final
yield or performance of the device. A coating deposited on top of a
topographic surface tends to contour the topography of the
underlying surface, thus producing a non-planar surface.
[0009] Fabricating one layer on top of another produces the
multi-layer structure of an IC. The first layer of the structure is
built on a totally planar semiconductor surface. As a result, a
topographic surface is introduced onto the semiconductor substrate
surface. The second layer is built on top of the topographic
surface of the first structural layer. As more layers are built on
the substrate, the severity of the surface topography increases.
The non-planar surface is no longer suitable for constructing the
next structural layer. Therefore, the topographic surface needs to
be planarized, or flattened, prior to the construction of the next
layer. To planarize the topographic surface, techniques such as
plasma etch-back, chemical mechanical polishing (CMP), and contact
planarization can be used.
[0010] The plasma etch-back technique involves the deposition of a
thick film to smooth the underlying topographic surface to some
extent. As the thickness of the film increases, surface planarity
is improved. However, a longer plasma etch time is needed to etch
the thicker films.
[0011] The deposited film is required to have a matched plasma etch
rate to that of the underlying topographic layer material under
specific etch parameters. Subsequently, the thick film is etched in
a plasma etcher to the underneath topographic layer to improve the
surface planarity. This planarization technique has been used and
known to those skilled in the art.
[0012] The CMP technique uses a slurry solution to mechanically
polish the surface against a pad with the assistance of chemical
reactions that occur between the substrate material and the slurry
solution. A slurry solution containing abrasive particles and
certain chemicals is dispensed on the pad surface. The topographic
substrate surface is pressed against the pad. The substrate is then
polished with a circular motion against the pad to remove the
topography of the surface. CMP is currently used in IC fabrication.
The specific requirements and processing conditions for certain
materials that need to be planarized are known to those skilled in
the art.
[0013] Contact planarization, in theory, provides an alternative to
plasma etch-back and CMP techniques to planarize topographic
surfaces. the topographic surface is first deposited with a
flowable planarization material. Subsequently, the surface is
pressed against an optical flat surface, which allows the material
to flow around the topographic structures under certain conditions.
The material is then hardened by either photo-irradiation or heat
to replicate the planarity of the optical flat surface onto the
planarized material surface. The planarized material surface is
then released from the optical flat object surface. To facilitate
the separation, the optical flat object surface can be treated with
a known art to lower its surface energy. This can be achieved by
depositing a thin film or low surface energy material, such as a
fluoropolymer or a fluorinated compound, onto the optical flat
object surface. Another approach is to put a low surface energy
material with comparable surface planarity, such as a disk or film,
between the planarization material and optical flat object surface.
Examples of low surface energy materials are Teflon.RTM. materials,
fluorocarbon polymers, or the like. The planarized material surface
then undergoes plasma etch to the underlying topographic layer. The
planarity of the optical flat surface is transferred to the
underlying topographic layer. The topographic surface is then
planarized. One requirement of the planarized material is that it
needs to possess a plasma etch ratio of 1 in relation to that of
the underlying topographic layer material. The plasma etch
parameters required to reach a 1:1 etch rate ratio are known to
those skilled in the art.
[0014] U.S. Pat. No. 6,048,799 to Prybyla et al. described the use
of an optical flat surface in contact with a material that can be
solidified by heat or ultraviolet (UV) irradiation to planarize
topographical surfaces. The Prybyla patent does not provide the
details associated with reducing the technology to practice.
Specifically the separation of the coated wafer from the optical
flat surface and the optimal range of process parameters required
to perform fully automated contact planarization are not
discussed.
[0015] Blalock et al. (U.S. Pat. No. 6,062,133) describes method
and apparatus for achieving a global planarization of a surface of
a deformable layer of a wafer using a curable planarization
material. A deformable material is deposited onto a substrate
surface. This substrate is then placed in to the apparatus with the
deformable material-coated surface facing toward and pressing
against an optical flat object surface under certain press force
and time. The deformable material is then cured while still in
contact with the optical flat object surface. The planarity of the
optical flat object surface is replicated to the coated substrate
surface. Like the Prybyla et al. patent, this process and apparatus
does not cover the separation of the coated wafer from the optical
flat surface and the optimal range of process parameters required
to perform fully automated contact planarization.
[0016] In U.S. Pat. No. 6,331,488 B1, Doan et al. describes a
planarization process for semiconductor substrates. This process
uses an optical flat surface to press against a nonplanar
insulating material-coated substrate surface onto which a
deformable material is coated. The deformable material is cured
while still in contact with the optical flat surface. The planarity
of the optical flat surface is replicated to the planarized
deformable material surface. The planarized surface then undergoes
the CMP process to transfer the planarity of the planarized surface
to the underlying insulating layer. This patent also fails to
include the process for separating the coated wafer from the
optical flat surface and the optimal range of process parameters to
perform contact planarization fully automated.
SUMMARY OF THE INVENTION
[0017] The present invention overcomes the problems outlined above
and provides improved contact planarizing apparatus and
corresponding methods, which are capable of quickly and efficiently
planarizing various coated substrates, while achieving very high
planarization ratios. Broadly speaking, the apparatus of the
invention includes a support operable to engage and hold a thin
flexible sheet of material (which is preferably an optically flat
material fabricated from Teflon, other fluorocarbon polymers, or
silicones) with an assembly operable to support and hold a
substrate with the coating thereof proximal to the sheet. A
differential pressure assembly is also provided to create a
pressure differential across the sheet of sufficient magnitude to
deflect the sheet so that the latter contacts the central region of
the surface of the coating, but is spaced from the periphery
thereof. The support assembly is also shiftable for moving the
substrate into face-to-face planarizing contact with the sheet
throughout substantially the entirety of the surface area of the
coating. Finally, the apparatus includes a device for curing the
coating during the course of such full planarizing contact.
[0018] In its method aspects, the invention includes the steps of
first locating a thin, flexible sheet of material in proximal
spaced relationship to the surface of a planarizable coating on a
substrate, and then causing the sheet to deflect so that the sheet
contacts a central region of the coating surface but is spaced from
the periphery thereof. Next, relative movement is effected between
the substrate and sheet until the latter is in full face-to-face
planarizing contact with the entirety of the surface area of the
coating. In this condition, the coating is cured, usually by using
UV radiation or heat. Preferably, during separation of the cured
coating and the flexible sheet, a pressure differential is created
across the latter to first separate the sheet from the periphery of
the cured coating, followed by full separation thereof.
[0019] In one embodiment, a solid planarizing body is provided
having a planarizing surface which mates with the flexible sheet.
Alternately, appropriate levels of air pressure and vacuum are used
for manipulation of the flexible planarizing sheet without the need
for a solid backup planarizing body.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a perspective view of a preferred planarizing
apparatus in accordance with the invention, illustrated with a
robotic arm of the apparatus supporting a resilient platen used in
the preferred planarizing method, prior to insertion of the platen
into the primary vacuumization chamber of the apparatus;
[0021] FIG. 2 is a view similar to that of FIG. 1, but illustrating
the apparatus during use thereof with the resilient platen inserted
into the primary vacuumization chamber, the latter being
closed;
[0022] FIG. 3 is an exploded perspective view illustrating the
operative components of the preferred planarizing apparatus;
[0023] FIG. 4 is a fragmentary vertical sectional view of the
planarizing apparatus, with a coated substrate therein and prior to
initiation of the planarizing process;
[0024] FIG. 5 is a vertical sectional view taken along line 5-5 of
FIG. 4 and further illustrating the configuration of the
planarizing apparatus;
[0025] FIG. 6 is a fragmentary vertical sectional view similar to
that of FIG. 4, but depicting the apparatus during planarizing
contact between the coated substrate and an optical flat body and
sheet;
[0026] FIG. 7 is a view similar to that of FIG. 6, but depicting
the apparatus after planarization of the coated substrate;
[0027] FIG. 8 is a view similar to that of FIG. 7, but showing the
apparatus during the separation sequence between the planarized
substrate coating and optical flat body and sheet;
[0028] FIG. 9 is a view similar to that of FIG. 8, but showing the
apparatus upon full separation between the planarized substrate
coating and the optical flat body and sheet;
[0029] FIG. 10 is a schematic illustration depicting the initial
step in the planarizing process wherein the preferred optical flat
sheet is deflected;
[0030] FIG. 11 is another schematic illustration showing the next
step in the planarizing process wherein full planarizing contact is
established between the coated substrate and the optical flat body
and sheet;
[0031] FIG. 12 is a schematic illustration showing the initial
stage of the separation sequence between the planarized substrate
coating and the optical flat body and sheet;
[0032] FIG. 13 is a view similar to that of FIG. 12, but showing
the next step in the separation sequence;
[0033] FIG. 14 is a schematic view similar to that of FIG. 13 and
showing the final step in the separation sequence;
[0034] FIG. 15 is a schematic view similar to that of FIG. 10, but
illustrating a method and apparatus wherein the optical flat body
is eliminated, during the initial deflection of the optical flat
sheet;
[0035] FIG. 16 is a view similar to that if FIG. 15, but depicting
the method and apparatus during full planarizing contact between
the substrate coating and optical flat sheet;
[0036] FIG. 17 is a schematic view similar to that of FIG. 16, but
showing the initial step in the separation sequence between the
planarized substrate coating and the optical flat sheet; and
[0037] FIG. 18 is a schematic view similar to that of FIG. 17,
illustrating the final step in the separation sequence.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Embodiment of FIGS. 1-14
[0038] Turning now to the drawings, FIG. 1 illustrates a preferred
planarization apparatus 20 in accordance with the invention. The
apparatus 20 broadly includes a support flame 22, and a planarizing
assembly 24 atop the latter. The planarizing assembly 24 includes a
lower vacuum chamber 26 together with an upper planarizing unit 28
and a UV light curing assembly 30. The overall apparatus 20 is
designed to efficiently contact planarize coatings applied to
individual substrates, such as microelectronic, optoelectronics,
photonic, optical, flat panel display, microelectromechanical
systems (MEMS), biochips and sensor devices.
[0039] In more detail, the support frame 22 includes a base 32 with
four upstanding, rigid support legs 34 secured thereto. A base
plate 36 is affixed to the upper ends of the legs 34, and has a
pair of opposed tubular guides 38 and a further pair of laterally
spaced apart, forward tubular guides 40. A conventional robotic arm
assembly 42 is also secured to base plate 36 via coupler 44. The
assembly 42 has a pivotally mounted arm 46 terminating in a pair of
opposed, arcuate support segments 48. The base plate 36 also
supports superposed piston and cylinder assemblies 50, 134.
Finally, a dual piston and cylinder assembly 52 is secured to the
underside of base plate 36 with the piston rods 54 thereof
extending upwardly through the forward guides 40 for purposes which
will be explained.
[0040] The vacuum chamber 26 includes an annular, upstanding outer
chamber wall 56 presenting a lower surface 58 resting atop plate 36
and secured thereto by peripheral clamps 37; a circular O-ring 60
(see FIG. 5) serves to effect a vacuum seal between the wall 56 and
base plate 36. The wall 56 is equipped with an elongated,
transverse entryway 62 adjacent the upper margin thereof, leading
to the interior of the chamber 26. The upper margin of the wall 56
is of stepped configuration in section, and is equipped with a
sealing O-ring 64. The chamber 26 also has a door 66 designed to
selectively cover entryway in order to permit establishment of a
vacuum condition within the chamber, and allow for insertion and
removal of substrates. In particular, the door 66 includes a
pneumatic actuator 68, coupler 70 and arcuate segment 72 which
conforms to the shape of sidewall 56. A peripheral gasket 74 (see
FIG. 5) is provided on the inner face of segment 72 for sealing
purposes. As best seen in FIGS. 1, 2 and 5, the door 66 is
supported for selective vertical shifting movement by the piston
rods 54, so that upon actuation of the assembly 57, the door 66 is
moved from the FIG. 1 position to the FIG. 2 position, thereby
sealing entryway 62. Door 66 moves vertically upon actuation of
assembly 52, then horizontally upon actuation of assembly 68.
Alternately, when the assembly 52 is actuated to lower the door 66,
the entryway 62 is open (see FIG. 1).
[0041] The planarizing unit 28 includes the components operable for
contact planarizing a coating 76 on one surface of a substrate 78
(see FIG. 10). The unit 28 operates in conjunction with the vacuum
chamber 26 to effect this planarization. Broadly speaking, the
planarizing unit 28 includes an optical flat assembly 80 made up of
a UV-transparent optical flat block or body 82 presenting a lower
optically flat surface 84, as well as a thin, flexible sheet 86 of
optically flat material, the latter being supported by a sheet
support 88; and a support assembly 90 beneath the assembly 88 and
operable to support and hold the substrate 78 with coating 76
proximal to sheet 86.
[0042] In greater detail, the body 82 is of circular configuration,
having an upper, radially enlarged section 92 and a depending
section 94 terminating in optical flat surface 84. The body 82 is
supported within a complemental annular head 96 which also has a
threaded port 98 and a sealing ring 99. A retainer ring 100 having
a pair of outwardly projecting, opposed ears 102 is positioned atop
body 82 and is connected to head 96 via screws 104, thereby
securing the body 82 in place. The sheet support 88 includes a pair
of opposed upper and lower clamping rings 106, 108 which receive
and support the sheet 86. In detail (see FIG. 5), the upper ring
106 includes an annular, depending rib 110 whereas the second or
lower ring 108 has a mating groove 112 which receives rib 110. The
sheet support 88 and sheet 86 are positioned within the stepped
upper margin of wall 56, with the lower ring 108 in engagement with
sealing O-ring 64.
[0043] Considering FIG. 5 for example, it will be appreciated that
the chamber 26 communicates with one face of the sheet 88 whereas
wall 56 defines the chamber 26 which is adjacent to and
communicates with the lower face of sheet 88. However, another
chamber 113 is created between the inner surface of head 96 and
body 82 below O-ring 99. The port 98 is in communication with this
chamber 113 as shown.
[0044] The support assembly 90 within chamber 26 includes an
arcuate, generally C-shaped ring-like body 114 which is sized to
support the substrate 76. The body 114 is selectively moveable
through the medium of two pneumatic piston and cylinder assemblies
116 each having the rod 118 thereof coupled to the underside of
body 114. As illustrated in FIG. 5, each assembly 116 is secured to
the upper face of base plate 36.
[0045] In addition, the assembly 90 includes a circular vacuum
chuck 120 which includes an upper, ringed vacuum surface 122 and a
central, hollow vacuumizing screw 124 communicating with surface
122. The chuck 120 is supported on a bored block 126 which receives
the lower end of screw 124. Block 126 includes an L-shaped vacuum
passageway 128 terminating in a fitting 130. A flexible pneumatic
hose 132 is secured to fitting 130 and passes through base plate 36
as shown for connection to a vacuum source (not shown). The block
126 and chuck 120 are vertically moveable within chamber 26 by
means of piston and cylinder assembly 134, operably secured to the
lower end of block 126 through coupler 127. Reciprocation of the
block 126 and chuck 120 is guided by a pair of spaced, upright rods
136 secured to base plate 36. As best shown in FIG. 4, the block
126 has laterally extending sections 138 each equipped with a slide
bushing 140 to ensure smooth up and down reciprocation of the block
126.
[0046] In the preferred practice of the invention, use is made of a
resilient platen 142 which is of circular configuration and is
adapted to overlie surface 122 of chuck 120. The platen 142
includes a lowermost bottom plate 144 having a depending peripheral
lip 146, together with an upper resilient pad 148. As best seen in
FIG. 5, the platen 142 is sized to complementally fit on the
surface 122 of chuck 120.
[0047] A threaded port 150 is provided through base plate 36. A
vacuum pump (not shown) is operably coupled with the port 150 and
with hose 132 for purposes to be described. In addition, another
pneumatic hose (not shown) is secured to port 98 provided in head
96 for alternate drawing of a vacuum and injection of positive
pressure air.
[0048] In order to permit opening of apparatus 20, upper
planarizing unit 28, UV light carrying assembly 30, and the
stricture carried thereby, are selectively vertically shiftable;
this permits changeout of the sheet support 88. To this end, a pair
of elongated, vertically oriented rods 152 are provided which are
coupled to the ears 102 of retainer 100 via fasteners 154; the rods
152 extend downwardly through the corresponding guides 38 to a
point beneath piston and cylinder assembly 50. A crossbar 156
extends between and interconnects the rods 152 at their lower ends.
A piston rod 158 forming a part of assembly 50 is secured to
crossbar 156. The assembly 50 may be selectively actuated for
raising and lowering of the retainer 100. The open and closed
positions of the apparatus 20 are shown in FIGS. 1 and 2,
respectively.
[0049] The light curing assembly 30 is positioned above retainer
100 and includes a spacer 160 affixed to retainer 100 by screws
162. Finally, a UV light box 164 is connected to the spacer 160.
The light box 164 has a selectively operable UV light source which
directs UV light downwardly through optical flat body 82 and sheet
86 as will be described.
[0050] The overall apparatus 20 is also provided with conventional
control circuitry for monitoring and controlling the planarizing
operations. Such control circuitry includes a vacuum sensor,
pressure sensor and a gas supply (not shown) secured in threaded
port 166 (see FIG. 5) of base plate 36, various other position and
condition sensors, and programmable microprocessor controllers.
This equipment and the use/programming thereof is well within the
skill of the art.
Operation
[0051] The planarizing operation of apparatus 20 will now be
described. It will be first assumed that the apparatus is in the
FIG. 1 position thereof, i.e., the assembly 50 has been actuated to
open apparatus 20 so that head 96 and the structure carried thereby
is spaced above chamber 26. Also, the support 114 and chuck 120 are
in their lowered positions. In this orientation of apparatus 20, a
sheet support assembly 88 carrying flexible sheet 86 is positioned
atop chamber wall 56 with ring 108 engaging seal 64. The assembly
50 is then actuated to lower head 96 until the underside thereof
carrying seal 97 comes into direct engagement with the upper ring
support 106. Next, a fresh substrate 78 having a coating 76 thereon
is placed upon C-shaped body 114, with the coating 76 facing
upwardly. The arm assembly 42 is then actuated to rotate arm 46 so
that the support segments 48 carrying platen 142 enter chamber 26
through entryway 62. The platen is thus placed upon the surface 122
of vacuum chuck 120.
[0052] Next, the door 66 is closed by operation of the piston and
cylinder assembly 52 to extend the rods 54 and operation of
pneumatic actuator assembly 68 respectively until gasket 74 comes
into circumscribing and sealing relationship with the wall
structure about entryway 62, thus establishing a closed chamber 26.
A vacuum is then drawn through hose 132 (normally from about 685 to
750 torr) in order to hold the platen 142 in place on the chuck
120. At this point a vacuum is drawn within chamber 26 through port
150, and through port 98 of head 96, sufficient to create a
pressure differential across sheet 86 sufficient to deflect the
sheet sufficient to deflect the sheet towards region C of substrate
coating 76 while the sheet remains spaced from the peripheral
region P thereof. Generally, with the preferred apparatus 20, a
vacuum of from about 685 to 750 torr is drawn through port 150,
whereas a lesser vacuum of from about 635 to 710 torr is drawn
through port 98.
[0053] In the next step, the assembly 134 is actuated so as to move
chuck 120 carrying platen 142 into the position of FIGS. 6 and 11,
i.e., in the planarizing position where the coating 76 is fully in
contact with sheet 86, the latter fully engaged with the surface 84
of body 82. In order to establish the appropriate planarizing
contact, the chuck 120 should exert a pressure of from about 1 to
90 lb/square inch against the substrate 78. Next, the vacuum, drawn
through port 150 and chamber 26 is relieved, and the latter is
allowed to return to atmospheric pressure, to release the sheet 86
from its deflected condition.
[0054] During such movement of the chuck 120 to the frill
planarizing position, any entrained air bubbles between the sheet
86 and surface 84 and/or platen 142 are eliminated. Moreover, the
sequential movement toward the full planarizing position, involving
the initial defection of sheet 86 followed by movement of the chuck
120, has been found to materially expedite the planarizing
operation while giving superior end products.
[0055] The light assembly 30 is then actuated to cure the coating
76 during the above-described planarizing contact. The wave length
of UV light selected for this purpose, and the duration of the
light-on condition, is dictated by the nature of the coating to be
cured, and these parameters are within the skill of the art.
[0056] Once the coating 76 is properly cured and planarized, the
apparatus 20 is operated to detach the substrate 78 and coating 76
from sheet 86 and to permit retrieval of the cured substrate and
insertion of a fresh coated substrate. In particular, in the next
step depicted in FIG. 7, the piston and cylinder assemblies 116 are
actuated to move the support 114 to come into contact with the
substrate 178 to secure it while the platen 142 is removed. Next,
the piston and cylinder assembly 134 is actuated to withdraw chuck
120 and platen 142 from the substrate 78, the vacuum drawn through
hose 132 is relieved. The door 66 is then opened and robotic arm
assembly 42 is used to retrieve platen 142. The door 66 is then
moved back to its chamber-closing position relative to entryway 62,
so that the apparatus assumes the FIG. 7 position. Next, the
assembly 134 is again actuated to elevate chuck 120 until the
vacuum surface 122 thereof comes into direct contact with the
substrate 78. This orientation is shown in FIG. 8. Next the piston
and cylinder assemblies 116 are actuated to move the support 114 to
its lower position away from substrate 78. At this point, the
vacuum is drawn through hose 132. An appropriate pressure
differential is created across sheet 86 by directing positive
pressure air through port 98 of head 96. Normally, a vacuum of from
about 685 to 750 torr is drawn through hose 132, while air at a
positive pressure of from about 0.5 to 50 psi is directed through
port 98. As best seen in FIG. 12, this combination creates a
situation where the sheet 86 is cleanly drawn away from surface 84
of body 82 while the sheet remains adhered to coating 76 of
substrate 78.
[0057] The next step is depicted in FIG. 13, where it will be seen
that a pressure differential is created across sheet 86 sufficient
to separate the sheet 86 from the coating 78 at the peripheral
region P, while maintaining such contact at the central region C.
This is accomplished by slightly shifting the chuck 120 downwardly,
while maintaining the vacuum through hose 132 with a corresponding
positive pressure delivered through port 98.
[0058] The final removal step involves a further shifting of chuck
120 away from body 82. The drawing of the vacuum through port 98
ensures that the sheet 86 moves back into full planarizing contact
with the surface 84 of body 82, so that the apparatus 20 is ready
to begin the planarization process again.
Embodiment of FIGS. 15-18
[0059] The apparatus 20 in preferred forms includes the use of the
solid planarized body 82 with lower planarizing surface 84.
However, the invention is not so limited. That is, the same
improved operational characteristics can be achieved using positive
air pressure and vacuum alone, without a solid planarizing body. In
FIG. 15-18 this apparatus and method are shown in schematic format.
A flexible planarizing sheet 88a is provided with adjacent
stationary support 114a and chuck 120a. As shown, the chuck 120a
holds a substrate 78a having a coating 76a to be planarized.
[0060] In the first step of the planarizing operation depicted in
FIG. 15, a pressure differential is created to bow the central
region C towards the coating 76a and substrate 78a. The central
region C of the sheet 88a comes into contact with the corresponding
region of the coating, as described in connection with the first
embodiment. At this point positive pressure air indicated by arrows
168 is directed against the upper face of sheet 88a, while
(optionally) a vacuum may be drawn though chuck 120a. Next, the
chuck 120a is moved to the full planarizing position, and
additional positive pressure air is directed against the upper face
of sheet 88a. This ensures the desired full planarizing contact
between the sheet 88a and coating 76a. Of course, during such
contact the coating 76a is cured, typically by application of UV
radiation or heat.
[0061] FIG. 17 illustrates the first step in the detachment of
sheet 88a from the now-cured coating 76a. This involves creation of
a differential pressure across the sheet 88a, by application of
positive pressure air above the sheet 88a and/or drawing a vacuum
below sheet 88a. In either instance the central region of the sheet
88a remains in contact with the coating 76a at central region C,
whereas the peripheral region P of the coating is spaced from the
sheet. In the final step (FIG. 18), a negative pressure is drawn
against the face of sheet 88a remote from the coating 76a thereby
fully separating the sheet 88a from coating 76a, and thereby
positioning the apparatus for the next planarizing operation.
EXAMPLE I
[0062] In this example, a trench wafer having a photocurable
material was planarized using apparatus 20. In particular, a
silicon wafer having trench structures about 1 .mu.m was used as
the substrate. The featured density of the wafer ranged from about
4-96%. A photocurable material was prepared by thoroughly mixing 20
grams of epoxy (D.E.R. 354LV, Dow Chemical Co.), 80 grams of
propylene glycol monomethyl ether (PGME, Aldrich Chemical Co.), and
1.2 grams of Sarcat KI-85 (Sartomer Chemical) in a yellow-lighted
laboratory. The material was then filtered using a 0.2 .mu.m filter
and stored in a clean brown bottle. A film of the photocurable
planarization material less than 0.5 .mu.m thickness was
spin-coated onto the silicon trench wafer.
[0063] During processing, the closed apparatus chamber was
evacuated to less than 20 torr for about 30 seconds to remove
residual solvent. During planarization, the substrate was pressed
against the Teflon optical flat surface using a force of about 68
psi for 300 seconds. During this time, UV light was used to cure
the coating. After UV exposure, the chamber was pressurized to
atmospheric, the substrate was separated from the optical flat
surface, and the substrate was removed from the chamber.
[0064] As a comparison, another similar trench wafer was coated
with the same material under identical conditions. This reference
product was cured in the same manner, except that there was no
press step used. The comparative wafers were characterized using a
Tencor Alphastep Profilometer. A surface topography of about 250
.ANG. was measured across the structure produce in accordance with
the invention. The reference wafer exhibited a measured surface
topography of about 7000 .ANG.. The planarization film thickness
within different feature-density areas of the pressure-planarized
wafer was measured using a scanning electron microscope. Film
thicknesses over feature-density areas, representing a maximum of
about 40% difference feature density, were measured. Film
thicknesses on top of the structures, not over the trenches, in two
feature-density areas were about 0.45 .mu.m, with a thickness
difference of about 0.012 .mu.m (120 .ANG.).
EXAMPLE II
[0065] In this example a thermocurable material was applied to a
silicon wafer. The wafer was prepared by first coating it with a
silicon dioxide film having a thickness of about 1 .mu.m. A pattern
containing vias of 0.2 to 1 .mu.m in diameter and having various
feature density areas was patterned into the silicon dioxide film.
The depth of the vias was about 1 .mu.m. A thermocurable material
was prepared as set forth in Example I, except that 1.0 grams of
Nacure.RTM. Super XC-A 230 catalyst (King Industries) was used in
lieu of the Sarcat product. The material was spin-coated to a
thickness of about 0.2 .mu.m onto the silicon via wafer.
[0066] The coated wafer was transferred to the apparatus 20 which,
after sealing, was evacuated to less than about 20 torr for about
180 seconds to remove residual solvent. The coated substrate was
pressed against the optical flat surface using a force of 68 psi
for 60 seconds. During this time a pulsing UV/infrared heating
light was illuminated through the optical flat surface to cure the
planarization material (120 seconds at a curing temperature of at
least about 130.degree. C.). After curing, the chamber was vented
to atmospheric, the substrate stage was lowered, the chamber door
was opened, and the substrate was removed for characterization.
[0067] The planarized via wafer surface was characterized with a
Tencor Alphastep profilometer. A surface topography over planarized
structures of less than 100 .ANG. and less than about 300 .ANG.
across adjacent feature density areas was measured. The
planarization film thickness over structures in different
feature-density areas was measured using a scanning electron
microscope. Two feature-density areas were measured. Film thickness
on top of the structures in an area having about 0.3 .mu.m diameter
vias with a pitch of about 0.5 .mu.m was measured. Film thickness
was also measured on top of the structures in an area having about
0.3 .mu.m-vias with a pitch of about 1.75 .mu.m. The film thickness
measured were about 0.19 .mu.m and 0.21 .mu.m, respectively.
EXAMPLE III
[0068] In this example, photocurable planarization material
consisting of 5 grams of Novolac epoxy resin (D.E.R..TM. 354LV, The
Dow Chemical Company), 5 grams oft-butyl glycidyl ether (Aldrich),
and 0.6 grams of 500% triarylsulfonium hexafluorophosphate (a photo
acid generator) solution (Aldrich) was formulated and mixed
thoroughly. The solvent used in the photo acid generator solution
was a reactive solvent. The material was filtered with 0.2 .mu.m
filter.
[0069] A 1.7 .mu.m thick layer of the planarization material was
coated onto a 6-inch silicon wafer surface that had been treated
with an adhesion promoter APX-K1 (Brewer Science, Inc.) using the
vendor's recommended process. A standard edge bead removal process
was conducted that removed about 5 mm of edge bead.
[0070] The substrate was placed within the apparatus 20 as
described in previous examples, and pressed against the optical
flat surface using a pressure of 68 psi for 30 seconds. During this
contact, a continuous UV light from a mercury-xenon lamp was
illuminated through the optical flat surface for 10 seconds to cure
the planarization material. The pressure was then released and the
wafer was removed from the apparatus. A Dektak 8 (Veeco Metrology
Group) was used to characterize the planarized surface roughness
and the degree of planarization. A step height of approximately 200
.ANG. was found on the 1 .mu.m tall portions of the original
substrate structures. A degree of planarization of about 98% was
achieved, and no voids were found in the planarized material.
EXAMPLE IV
[0071] In this example, a curable material was planarized using air
pressure in lieu of the optical flat body 82. The photocurable
material and wafers of Example I were used. The coated substrate
was placed in the apparatus 20, and the chamber was evacuated to
less than 20 torr for about 30 seconds for residual solvent
removal. The substrate was then pressed against the optical flat
sheet. After such contact, air pressure was applied to the opposite
side of the film at a pressure of about 20 psi for 300 seconds.
While the surface was thus maintained in contact with the optical
flat film, UV light was illuminated through the film for 10 seconds
to cure the planarization material. After planarization, the
pressure within the chamber was relieved to atmospheric, and the
substrate was separated from the film and removed for
characterization.
[0072] A reference wafer was prepared in the same fashion, except
that it was not subjected to the air pressure pressing step. The
wafer surface produced according to the invention, and the
reference surface were characterized using a Tencor Alphastep
Profilometer. A surface topography of about 350 .ANG. was measured
across the structures and across adjacent feature density areas in
the substrate produce din accordance with the invention.
Planarization film thickness within different feature-density areas
was measured using a scanning electron microscope. Film thicknesses
over feature-density areas, representing a maximum of about 40%
difference over feature-density, were measured. Film thicknesses on
top of the structures, not over the trenches, into feature-density
areas were about 0.45 .mu.m with a thickness difference of about
0.014 .mu.m (140 .ANG.). The reference wafer exhibited a surface
topography of about 7000 .ANG. across the topographic
structures.
* * * * *