U.S. patent application number 14/456401 was filed with the patent office on 2015-01-15 for apparatus and method for heat treating a glass substrate.
The applicant listed for this patent is Corning Incorporated. Invention is credited to Frank Coppola, Monica Jo Mashewske.
Application Number | 20150013392 14/456401 |
Document ID | / |
Family ID | 45695331 |
Filed Date | 2015-01-15 |
United States Patent
Application |
20150013392 |
Kind Code |
A1 |
Coppola; Frank ; et
al. |
January 15, 2015 |
APPARATUS AND METHOD FOR HEAT TREATING A GLASS SUBSTRATE
Abstract
An apparatus and method for heat treating a plurality of glass
substrates. The glass substrates are supported on support platform
and housed in a heat treating furnace. The substrates are supported
in a substantially vertical orientation by restraining pins
extending through walls of the furnace, and are separated from each
other by frame-shaped spacing members. The spacing members reduce
convection currents between the substrates and reduce or eliminate
the post-heat treating distortion of each glass substrate to less
than 100 .mu.m over the entire surface of the substrate.
Inventors: |
Coppola; Frank; (Horseheads,
NY) ; Mashewske; Monica Jo; (Horseheads, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Corning Incorporated |
Corning |
NY |
US |
|
|
Family ID: |
45695331 |
Appl. No.: |
14/456401 |
Filed: |
August 11, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12871204 |
Aug 30, 2010 |
8826693 |
|
|
14456401 |
|
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|
Current U.S.
Class: |
65/160 ;
65/355 |
Current CPC
Class: |
C03B 23/02 20130101;
C03B 25/025 20130101; C03B 32/00 20130101; C03B 35/205 20130101;
C03B 23/0093 20130101; C03B 29/025 20130101; C03B 2225/02
20130101 |
Class at
Publication: |
65/160 ;
65/355 |
International
Class: |
C03B 32/00 20060101
C03B032/00; C03B 35/20 20060101 C03B035/20; C03B 25/02 20060101
C03B025/02 |
Claims
1-10. (canceled)
11. An apparatus for heat treating a plurality of glass substrates
comprising: a furnace comprising an outer enclosure wall, an inner
enclosure wall, a first side and a second side; a first plurality
of restraining pins extending through the first side of the furnace
into an interior volume defined by the furnace inner enclosure
wall, the first plurality of restraining pins being rigidly fixed;
and a second plurality of restraining pins extending through the
second side of the furnace, each restraining pin of the second
plurality of restraining pins being movable along a longitudinal
axis of the restraining pin, and wherein each restraining pin of
the second plurality of restraining pins comprises a biasing
assembly configured to apply a force against the plurality of glass
substrates.
12. The apparatus according to claim 11, wherein the inner
enclosure wall is corrugated.
13. The apparatus according to claim 11, wherein each restraining
pin of the first plurality of restraining pins comprises a contact
member that configured to contacts a glass substrate of the
plurality of glass substrates and an extension member coupled to
the biasing assembly, and wherein a joint movably connects the
contact member and the extension member.
14. The apparatus according to claim 11, wherein each restraining
pin of the second plurality of restraining pins comprises a contact
member that-configured to contacts a glass substrate of the
plurality of glass substrates and an extension member coupled to
the biasing assembly, and wherein a joint movably connects the
contact member and the extension member.
15. The apparatus according to claim 11, wherein the biasing
assembly comprises a pneumatic cylinders.
16. The apparatus according to claim 11, wherein the biasing
assembly comprises a springs.
17.-18. (canceled)
19. The apparatus according to claim 11, wherein a position sensor
is coupled to each biasing assembly.
20. The apparatus according to claim 11, further comprising a
computer in electrical communication with each biasing assembly,
and wherein the computer is configured to controls a position of
each biasing assembly individually.
21. The apparatus according to claim 11, wherein a force sensor is
coupled to each biasing assembly.
22. The apparatus according to claim 11, wherein a floor of the
furnace is movable from a position outside the furnace to a
position within the furnace.
23. The apparatus according to claim 22, wherein the floor of the
furnace comprises wheels.
24. An apparatus for heat treating a plurality of glass substrates
comprising: a furnace comprising a first side and a second side; a
first plurality of rigidly fixed restraining pins extending through
the first side of the furnace into an interior volume of the the
furnace; and a second plurality of restraining pins extending
through the second side of the furnace into the interior volume of
the furnace, each restraining pin of the second plurality of
restraining pins being movable along a longitudinal axis of the
restraining pin, and wherein each restraining pin of the second
plurality of restraining pins comprises a biasing assembly
configured to apply a force against the plurality of glass
substrates.
25. The apparatus according to claim 24, wherein a floor of the
furnace is movable from a position inside the furnace to a position
outside the furnace.
26. The apparatus according to claim 25, wherein the floor
comprises wheels configured to engage with one or more rails.
27. The apparatus according to claim 25, wherein the floor
comprises a substrate support member that is a wall of the
furnace.
28. The apparatus according to claim 25, wherein the floor
comprises heating elements.
29. The apparatus according to claim 27, wherein the substrate
support comprises heating elements.
30. The apparatus according to claim 24, further comprising a guide
member extending from a location outside the furnace to a location
within the furnace and configured to support the glass substrates
in a vertical orientation.
31. The apparatus according to claim 30, wherein the guide member
is a cable extending along a rail.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 12/871204 filed on Aug. 30, 2010, the content of which is
relied upon and incorporated herein by reference in its entirety,
and the benefit of priority under 35 U.S.C. .sctn.120 is hereby
claimed.
FIELD
[0002] This invention relates to a method and apparatus for heat
treating a glass substrate, and more particularly to a method and
apparatus for simultaneously compacting a plurality of glass
substrates.
BACKGROUND
[0003] Liquid crystal displays (LCDs) are typically comprised of
two flat glass substrates that encapsulate a thin layer of liquid
crystal material. Arrays of transparent thin-film electrodes on one
of the substrates modulate the light transmission properties of the
liquid crystal material, thereby creating the image. By
incorporating an active device such as a diode or thin film
transistor (TFT) at each pixel, high contrast and response speed
can be achieved to produce high-resolution displays. Such flat
panel displays, commonly referred to as active matrix LCDs (AMLCD),
have become the predominant technology for high performance
displays such as computers and televisions.
[0004] The fabrication process for LCDs, and especially those used
in the manufacture of poly-crystalline silicon (poly-Si) displays,
typically consists of successive deposition and patterning of thin
films using elevated temperature processes which result in
substrate heating. Because of the high registration requirement
between patterning steps for these thin films, the glass substrates
often require dimensional stability (low shrinkage) in the 5-20
parts per million (ppm) range throughout the process. Five to
twenty parts per million shrinkage means, for example, 2.5-10
microns shrinkage over a substrate length of 500 mm. When greater
than 5-20 ppm shrinkage occurs, registration errors will accrue
between components subsequently applied.
[0005] Poly-Si is conventionally made by depositing amorphous
silicon (a-Si) onto a glass substrate using chemical vapor
deposition (CVD) techniques, and subsequently exposing the coated
glass to high temperatures for a sufficient period of time to
crystallize the a-Si to poly-Si. This crystallization step is
typically done at about 600.degree. C. for several tens of hours.
In addition, several other high temperature processes may follow
the crystallization step. Such process steps include deposition and
annealing of the gate oxide, and source/drain annealing.
[0006] The relatively high temperatures of the crystallization and
subsequent processing steps encountered during poly-Si TFT
manufacturing greatly increases the potential for glass substrate
shrinkage.
[0007] Manufacturers of glass substrates (e.g., liquid crystal
display, or "LCD", glass substrates) often heat treat the glass
substrates to pre-shrink or compact the glass prior to shipping.
Compacting glass substrates can be performed at various
temperatures below the glass substrate strain point. Compaction or
densification is performed to minimize dimensional changes of the
glass during the customer's processing of the glass substrate. If
the glass substrates are not pre-shrunk, the substrates can undergo
contour changes that may negatively affect the finished display
quality. Compaction must be performed without creating glass chips
that can contaminate the glass surfaces, or distorting the glass
substrate surfaces through spatially non-uniform heating and/or
cooling patterns.
[0008] Conventionally, a closed cassette has been used to support
glass substrates during heat treatment. An open cassette is also
utilized in some applications. In a closed cassette support method,
multiple glass substrates are held in a vertical orientation within
enclosed sections of a cassette. The glass substrates are supported
with horizontal and vertical supports (such as those made of
stainless steel). In practice, the glass substrates are supported
around their perimeters to maintain surface quality and prevent
warp. The glass substrates are typically captured along the full
length of all four edges.
[0009] In an open cassette support method, multiple glass sheets
are held in a vertical orientation within a cassette. The glass
sheet is supported at its edges with vertical and horizontal
supports. As in the closed cassette support method, the glass
substrate is supported around the perimeter to maintain its
physical attributes. Both the open and closed cassette methods
generally minimize the gravity effect on the glass during heat
treatment.
[0010] In both the closed and open cassette support designs, the
glass substrates are contacted along substantially all of at least
three edges. This contact often causes substrate damage or loss.
The full-contact supports also have an impact on the thermal
characteristics of the system. As may be appreciated, the metal
mass of the supports concentrated along each substrate edge impacts
the temperature profile at the edges due to the heat having to
travel through metal before reaching the glass along the edges and
corners. Additionally, in both support designs, debris (including
glass particles and chips) builds up in the bottom-edge support and
is difficult to clean out; as a result, these support designs can
cause significant debris contamination of glass substrates.
Moreover, the large differences in coefficient of thermal expansion
between the metal supports and the glass substrates result in a
large movement of the substrates relative to the supports and
potential damage to the substrates.
[0011] Both of the aforementioned support designs are manufactured
by bending and forming sheet material (such as stainless steel)
into the required assembly. By nature, these procedures are not
precise, difficult to produce, and costly to manufacture.
SUMMARY
[0012] In accordance with one embodiment, a method of heat treating
a plurality of glass substrates in a furnace is disclosed
comprising positioning at least one spacing member between pairs of
adjacent glass substrates of the plurality of glass substrates, the
at least one spacing member comprising a closed outer frame portion
bounding an open interior, and wherein a difference between a CTE
of the one or more spacing members and a CTE of the plurality of
glass substrates is less than 10.times.10.sup.-7/.degree. C. In
some embodiments, the glass substrates may have a dimension such
that a major surface of each glass substrate of the plurality of
glass substrates has a surface area of at least 5 m.sup.2.
[0013] Adjacent glass substrates and the at least one spacing
member form an enclosed space bounded by the adjacent glass
substrates and the at least one spacing member.
[0014] The plurality of glass substrates are supported in a
substantially vertical orientation wherein the plurality of glass
substrates and the one or more spacing members positioned between
adjacent glass substrates are biased together in a contacting
relationship with a biasing force and heated in the furnace. After
the heating process, the glass substrates are allowed to cool. An
out-of-plane distortion of the plurality of glass substrates after
cooling does not exceed 100 .mu.m.
[0015] A plurality of spacing members may be employed between
adjacent glass substrates, arranged in a vertical and/or horizontal
array. Preferably, adjacent spacing members positioned between the
same pair of adjacent glass substrates contact each other at
outside non-quality edge portions of each adjacent spacing
member.
[0016] The plurality of glass substrates are preferably heated to a
temperature greater than an annealing point of the plurality of
glass substrates and less than a softening temperature of the
plurality of glass substrates. In some embodiments, depending on
glass composition, the plurality of glass substrates is heated to a
temperature greater than 700.degree. C.
[0017] The at least one spacing member may be composed of glass.
Preferably a composition of the glass of the at least one spacing
member is the same glass composition as a glass composition of the
plurality of glass substrates.
[0018] In some embodiments, the furnace comprises an outer
enclosure wall and an inner enclosure wall and a first side and a
second side. A first plurality of restraining pins extend through
the inner enclosure wall and the outer enclosure wall on the first
side of the furnace, the first plurality of restraining pins being
rigidly mounted to a support structure. A second plurality of
restraining pins extend through the inner enclosure wall and the
outer enclosure wall on the second side of the furnace, wherein
each restraining pin of the second set of restraining pins movable
along a longitudinal axis of the restraining pin. The bias force is
applied against the plurality of glass substrates with the second
plurality of restraining pins. In another embodiment, an apparatus
for heat treating a plurality of glass substrates is described
comprising a furnace comprising an outer enclosure wall, an inner
enclosure wall, a first side and a second side, a first plurality
of restraining pins extending through the outer enclosure wall and
the inner enclosure wall on the first side of the furnace into an
interior volume defined by the furnace, the first plurality of
restraining pins being constrained such that movement of the pins
relative to the inner enclosure wall is prevented. A second
plurality of restraining pins extends through the outer enclosure
wall and the inner enclosure wall on the second side of the furnace
and each restraining pin of the second plurality of restraining
pins is movable along a longitudinal axis of the restraining pin.
The second plurality of restraining pins comprises biasing
assemblies to apply a bias force against the plurality of glass
substrates. The biasing assembly may comprise, for example,
pneumatic cylinders and/or springs. A position sensor may be
coupled to each restraining pin of the second plurality of
restraining pins. The position sensor relays information about the
position of the restraining pin to a computer in electrical
communication with each biasing assembly of the second plurality of
restraining pins. The computer controls the position of the
restraining pins individually, based on the received position
information.
[0019] To accommodate expansion and contraction of the inner wall,
for example during heat up and cool down, the inner furnace wall
may be corrugated.
[0020] Each restraining pin of the first plurality of restraining
pins comprises a contact member that contacts a glass substrate of
the plurality of glass substrates and an extension member coupled
to the biasing assembly, and wherein a joint movably connects the
contact member and the extension member.
[0021] Similarly, each restraining pin of the second plurality of
restraining pins may also comprise a contact member that contacts a
glass substrate of the plurality of glass substrates and an
extension member coupled to the biasing assembly, and wherein a
joint movably connects the contact member and the extension member.
In some instances, movement of the second set of restraining pins
is controlled such that contact between the second plurality of
restraining pins and an outermost glass substrate of the plurality
of glass substrates is coplanar during the heating process.
[0022] The apparatus may include one or more guide members
extending into the furnace that support the plurality of glass
substrates in a vertical orientation, wherein a glass substrate of
the plurality of glass substrates makes sliding contact with the
one or more guide members while the plurality of glass substrates
are moved from a position outside the furnace to a position inside
the furnace.
[0023] Additional features and advantages of the invention are set
forth in the detailed description which follows, and in part will
be readily apparent to those skilled in the art from that
description or recognized by practicing the invention as described
herein. The accompanying drawings are included to provide a further
understanding of the invention, and are incorporated in and
constitute a part of this specification. It is to be understood
that the various features of the invention disclosed in this
specification and in the drawings can be used in any and all
combinations.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a cross sectional end view of an apparatus for
compacting a plurality of glass substrates in a vertical
orientation.
[0025] FIG. 2 is a side view of an articulated restraining pin.
[0026] FIG. 3 is a side elevated view of a cart for supporting and
transporting a plurality of glass substrates in an upright (i.e.
vertical) orientation.
[0027] FIG. 4 is a perspective view of a spacing member used to
separate adjacent glass substrates.
[0028] FIG. 5 is a cross sectional view of a stack of glass
substrates seen from the edges of the substrates, wherein the
substrates are separated by spacing members.
[0029] FIG. 6 is a side elevational view of the stack of glass
substrates of FIG. 5 showing the spacing members.
[0030] FIG. 7 is a cross sectional edge view of the stack of glass
substrates of FIG. 5 showing compartments between the glass
substrates formed by the spacing members.
DETAILED DESCRIPTION
[0031] In the following detailed description, for purposes of
explanation and not limitation, example embodiments disclosing
specific details are set forth to provide a thorough understanding
of the present invention. However, it will be apparent to one
having ordinary skill in the art, having had the benefit of the
present disclosure, that the present invention may be practiced in
other embodiments that depart from the specific details disclosed
herein. Moreover, descriptions of well-known devices, methods and
materials may be omitted so as not to obscure the description of
the present invention. Finally, wherever applicable, like reference
numerals refer to like elements.
[0032] Shown in FIG. 1 is a perspective view of an apparatus 10 for
simultaneously heat treating a plurality of vertically oriented
glass substrates 12 in a compaction process. Apparatus 10 comprises
furnace 14 including inner furnace wall 16 and outer furnace wall
18, the inner and outer furnace walls being separated by insulating
material 20. Heating elements 22 are positioned within interior
volume 23 defined by furnace 14, and are generally arranged
adjacent to inner furnace wall 16. Furnace 14 further includes a
first side 24 and a second side 26, which, when the plurality of
glass substrates are loaded into the furnace, are generally
parallel to the glass substrates. The first and second sides are
comprised of portions of the inner and outer furnace walls. When
furnace 14 is in operation, a plurality of glass substrates 12 are
arranged vertically on a movable cart 28 within interior volume 13
and separated from each other by spacing members 30. These and
other components of apparatus 10 will be described in more detail
below.
[0033] Referring still to FIG. 1, inner furnace wall 16 may be
constructed to accommodate thermal expansion of the inner wall. For
example, the inner furnace wall shown in FIG. 1 is formed from a
metal selected to minimize corrosion (e.g. stainless steel or
Inconel.RTM.), and is corrugated to accommodate thermal expansion
of the wall.
[0034] Heating elements 22 are disposed within interior volume 23
and arranged to flank, or be adjacent to, the outer-most glass
substrates of the plurality of glass substrates arranged on cart
28. Heating elements 22 can be, for example, electrical resistance
heaters. In some embodiments, multiple individually controlled
heating elements can be employed along each side of the assembled
glass substrates so the heating elements can be used to produce a
differential temperature profile across the plurality of glass
substrates if needed. That is, so that the temperature radiated
against a surface of an outermost glass substrate can be varied
across that surface if desired. Additional heating elements 22 may
also be arranged in an upper portion of furnace 14 and at an end of
furnace 14 to ensure the edge portions of the glass substrates are
also heated.
[0035] Also shown in FIG. 1 are pluralities of restraining pins 34
that extend from outside the furnace to inside the furnace through
outer furnace wall 18 and inner furnace wall 16 along the first and
second sides of the furnace. Restraining pins 34 are positioned to
contact the outermost glass substrates of the plurality of glass
substrates and stabilize the vertically standing substrates. In
some embodiments, a first plurality or set 36 of restraining pins
extend through first side 24 of the furnace (e.g. through the outer
and inner enclosure walls), are configured to contact an outer-most
glass substrate of the plurality of glass substrates, and are
rigidly fixed so that there is no movement of each restraining pin
along a corresponding longitudinal axis of the restraining pin. For
example, first restraining pin set 36 can be rigidly coupled to the
furnace as shown in FIG. 1. Alternatively, first restraining pin
set 36 can be coupled to a support structure outside and separated
from the furnace.
[0036] A second plurality or set 38 of restraining pins on
opposite, second side 26 of the furnace are configured to contact
the other outermost glass substrate and are biased against the
other outermost glass substrate by biasing assemblies 40 when the
plurality of glass substrates are positioned within the furnace.
Biasing assemblies 40 can comprise springs and/or pistons (e.g.
pneumatically or hydraulically-operated pistons) coupled to the
individual restraining pins of second restraining pin set 38. As
shown in FIG. 1, biasing assemblies 40 may be connected through
individual pneumatic control valves 42 and gas supply lines 44 to
pressurized gas source 46 and may be individually controlled by a
computer 48 through control lines 52. Position information from
individual biasing assemblies may be collected by position sensors
(not shown) comprising the biasing assemblies, and communicated to
computer 48 through data lines 54. The biasing assemblies may also
include force sensors, i.e. load cells (not shown) that provide
information to the computer about the force applied to the glass
substrates by the individual restraining pins. Computer 48 utilizes
the position and/or force information from each position and/or
force sensor to maintain each restraining pin in registration such
that the distal ends of each pin (i.e. the contact surfaces of each
restraining pin that contact the glass substrates) are coplanar and
apply sufficient force to ensuring the glass substrates are held
flat.
[0037] Restraining pins 34 may further include jointed distal
contact members that contact the outer-most glass substrates.
During temperature changes in the heat treating furnace (e.g. heat
up and cool down), the glass substrates may expand or contract a
sufficient amount that relative motion between un-jointed
restraining pins and the outermost glass substrates occurs, leading
to potential damage to the glass substrates. Consequently, as shown
in FIG. 2, each restraining pin 34 may include an end portion, or
contact foot 56, that is coupled to an extension member 58 via one
or more joints 60 such as ball joints. This articulated (jointed)
construction allows the contact foot portion of the restraining pin
to move relative to the extension member portion, such as during
expansion and contraction of the plurality of glass substrates.
[0038] As may be appreciated, contact between the restraining pins
and the glass substrates has the potential for damaging the two,
outer-most glass substrates of the plurality of assembled
substrates. This can be avoided by arranging the restraining pins
so that each restraining pin contact foot contacts the outermost
glass substrates only in areas of the substrate that will not later
be used in a device--so-called non-quality areas. However, as the
restraining pins are generally not easily repositionable along each
side of the furnace, an arrangement of restraining pins that works
for one glass substrate size will likely not accommodate another
size. An alternative approach is to employ sacrificial glass
substrates as the outer-most glass substrates. Thus, surface damage
resulting from contact between the restraining pins and the
sacrificial glass substrates will not affect the interior glass
substrates positioned between the sacrificial glass substrates. The
sacrificial glass substrates can be cleaned and re-used, or
discarded.
[0039] The plurality of glass substrates are assembled on top of
cart 28. The cart also may serve as the bottom of the furnace. Cart
28 preferably comprises an insulated top portion 61 upon which the
glass substrates rest. The insulated portion of the cart can be
encased in alloy steel for example. The cart supports the weight of
the glass substrates, and is movable between a position outside the
furnace to a position inside the furnace to transport the glass
substrates into and out of the furnace. The cart can include
heating elements 22 located on or in the top portion of the cart
and under the glass substrates to heat the bottom of the glass
substrates and improve temperature uniformity. An upright support
member 62 is positioned at one end of the cart (FIG. 3), and can be
used to support the glass substrates on the cart as the substrates
are loaded. For example, the car can be tilted backward so that
edges of the glass substrates are supported by support member 62
during the loading. Support member 62 can form a closure for the
furnace (e.g. door) when the cart is positioned within the furnace.
That is, support member 62 can form a wall of the furnace. Support
62 may also include heating elements 22. Thus, a combination of
heating elements 22, either forming a part of the furnace or cart
28, and positioned along the edges of the glass substrates when the
substrates are positioned within furnace 14, ensure even heating of
the glass substrates and reduced stresses.
[0040] Preferably, cart 28 comprises wheels 63 for facilitating
transport of the glass substrates into and out of the heat treating
furnace. For example, the wheels may be configured to ride on one
or more rails 64. In some embodiments, wheels may be included on
one side of the cart, while legs are provided on the other side.
The legs facilitate tilting of the platform, which can be
advantageous when loading the platform with glass substrates.
[0041] In addition, at least one guide member 66 extends from a
location outside the furnace into the furnace, such that, as cart
28 is moved into the furnace, the plurality of glass substrates are
contacted and supported by the at least one guide member as the
platform traverses the distance into the furnace. For example, in
certain embodiments, the guide member is a cable that extends into
the furnace along cart rail 64. As cart 28 is moved into furnace 14
with the plurality of glass substrates positioned atop the cart, at
least one glass substrate of the plurality of glass substrates
contacts guide member 66, preventing the plurality of glass
substrates from leaning away from a vertical orientation. In
certain other embodiments, multiple guide members can be used, for
example, two guide cables, one arranged on each side of the
plurality of glass substrates to prevent leaning to either side of
the glass substrates. Preferably, the contacted glass substrates
are sacrificial glass substrates.
[0042] Shown in FIG. 4 is a perspective view of a single spacing
member 30. As illustrated, spacing member 30 comprises an outer
wall portion 68 that is a closed loop shaped like a picture frame,
and thus has an open interior 70 circumscribed by the spacing
member outer wall portion. Each spacing member should be
constructed of a material having a coefficient of thermal expansion
(CTE) that substantially matches the CTE of the glass substrates to
minimize relative motion between the spacing members and the glass
substrates during heat up and cool down cycles. The CTE difference
between the spacing members and the glass substrates should not
exceed 10.times.10.sup.-7/.degree. C. For example, the spacing
member may be formed from the same glass that forms the glass
substrate. That is, the spacing member and the glass substrates
preferably have the same glass composition. The spacing member can
alternatively be made from a glass ceramic material as long as the
CTE difference between glass ceramic material and the glass of the
glass substrates does not exceed 10.times.10.sup.-7/.degree. C.
[0043] The spacing members can be formed, for example, by casting.
A single slab of glass can be cast, ground and polished to ensure
the surfaces of the spacing member will be flat and parallel, and a
center portion of each slab cut away, such as by water jet cutting.
Alternatively, a slab or plate can be formed by other processes
(e.g. drawing), after which cutting, grinding and polishing can be
performed.
[0044] In accordance with embodiments of the present invention, at
least one spacing member 30 is positioned between adjacent glass
substrates of the plurality of glass substrates to form a stack 72
consisting of alternating glass substrates and spacing members
(FIG. 5).
[0045] For large glass substrates (or small sized spacing members),
such as glass substrates having a one-side surface area equal to or
greater than 5 m.sup.2, a plurality of spacing members 30 may be
deployed between adjacent glass substrates of the plurality of
glass substrates, with the spacing members arranged in a horizontal
and vertical arrays such as illustrated in FIG. 6. For example,
four spacing members 30 can be arranged in a 2.times.2 array
arranged edge-to-edge. Preferably, the plurality of spacing members
is positioned with at least some of their outer edges in contact to
minimize the creation of unusable (contacted) glass surface area.
The number of spacing members positioned between adjacent glass
substrates, and the dimensions of the array, depend on the size and
shape of the glass substrates to be separated.
[0046] With one or more spacing members 30 positioned between
adjacent glass substrates 12, narrow pockets or compartments 74 are
created between adjacent glass substrates 12, each glass substrate
having first and second parallel major surfaces 76 and 78. FIG. 7
depicts a cross sectional edge view of the stack of glass
substrates and spacing members of FIG. 6, and shows a plurality of
compartments 74 located between and in contact with adjacent major
surfaces of adjacent glass substrates of the stack This
compartmentalization between adjacent glass substrates minimizes
gas flow between the glass substrates, and thereby temperature
differentials on the glass substrate that can produce stress are
also minimized. For example, a plurality of glass substrates can be
arranged such that four spacing members are disposed between each
adjacent pair of glass substrates. If there are eight square glass
substrates each having a dimension of 2 meters by 2 meters (2
m.times.2 m), 7 sets of spacing members are employed, one set
between each pair of adjacent glass substrates, and each set
consisting of four one-meter square spacing members arranged in a
contacting relationship in a 2.times.2 array. Because the spacing
members have frame shaped walls, there is no contact with the glass
substrates within the central open area of the frame-shaped spacing
members. When the spacing members are sandwiched between adjacent
glass substrates, four compartments are created between each pair
of adjacent glass substrates, each compartment bounded by the glass
substrates and the walls of the spacing members. The walls of the
spacing members prevent gas flow between compartments and
effectively prevent significant convection currents to move over
the glass surface that might otherwise create unwanted temperature
differentials in the glass.
[0047] Because in certain industries, such as the LCD display
industry, contact with the glass substrates creates areas of the
substrate that are no longer useable (e.g. due to potential contact
damage), it is preferably that contact between the spacing members
occurs only in the non-quality regions of the glass substrate. For
example, glass substrates are typically supplied to equipment
manufacturers (e.g. those making the display units) in large master
glass substrates that are later sectioned into a plurality of
smaller substrates. Cutting the master substrate to size is usually
performed by the equipment manufacturer. Prior knowledge by the
glass manufacturer of the number of sections to be created from an
original master by the equipment manufacturer allows arrangement of
the spacing members during the heat treating according to the
intended cut pattern. Continuing with the previous example of a 2
m.times.2 m glass substrate, if it is known the original, master
glass substrate is to be divided into 4 equal-sized segments of 1
square meter, the "seams" between four 1 meter spacing members
arranged in a 2.times.2 array between adjacent glass
substrates--the line where each spacing member contacts an adjacent
spacing member--coincides with the cut line that separates the
glass substrate into separate sections. Thus, the plurality of
spacing members forms a grid of glass walls disposed between
adjacent glass substrates. If the width of the wall forming each
spacing member is minimized, the amount of surface area on each of
the resultant separate substrate sections contacted by any given
spacing member is minimized. For example, if the wall of each
spacing member is 1 cm wide, the perimeter area of each cut or
sectioned substrate contacted by a spacing member is only 1 cm,
even though the combined wall width of two adjacent spacing members
is 2 cm in this example.
[0048] Alternatively, to reduce the contact area of the spacing
members against the glass substrates still further, those portions
of the spacing member wall that contact other spacing members can
be made thinner than the portions of the spacing member that do not
contact other spacing members. Using the example above, if the
sides of rectangular spacing member that contact other spacing
members are made to have a width of only 0.5 cm rather than the 1
cm described above, the combined width of adjacent walls of
adjacent spacing members is only 1 cm rather than the 2 cm
previously obtained. Thus, one or more spacing members may be used
wherein a width of the wall of the spacing member varies. That is,
one side wall of the spacing member can have one width and another
side wall of the spacing member can have a different width.
[0049] In some embodiments, the plurality of glass substrates may
be divided into two stacks, each stack comprising a plurality of
glass substrates. Furnace 14 may then include an additional set of
heating elements 22 that is centrally and vertically disposed in
the furnace such that the centrally disposed heating elements are
positioned between the first and second assemblies of glass
substrates when the glass substrates are positioned within the
furnace by cart 28.
[0050] The process of heat treating the plurality of glass
substrates can proceed as follows. In a first step, a first glass
substrate is loaded onto cart 28. To facilitate loading, the cart
can be tilted to one side, and may further be raised at one end so
that the glass substrates are supported simultaneously by top
portion 61 and support member 62 of cart 28. The first loaded glass
substrate becomes one of the outer-most glass substrates, and
because it will be contacted by a set of restraining pins, a
sacrificial glass substrate may be used.
[0051] Next, at least one spacing member is positioned adjacent to
the first glass substrate. If the glass substrate is large enough,
a plurality of spacing members can be positioned adjacent to the
first glass substrate. Then, one the one or more spacing members
are appropriately arranged, a second glass substrate is positioned
adjacent to the previously deployed spacing members, and another
set of one or more spacing members are positioned adjacent to the
second glass substrate. This process, positioning alternating
layers of glass substrates and one or more spacing members,
continues until the desired number of glass substrates are
assembled into the stack. The last loaded glass substrate becomes
the other, opposite outer-most glass substrate, and may also be a
sacrificial glass substrate.
[0052] When the final glass substrate has been positioned, cart 28
with assembled stack 72 of glass substrates can be righted, and the
stack of glass substrates clamped at the edges thereof, such as by
U-clamps. Cart 28 is then moved into furnace 14, with the stack of
glass substrates in contact with the at least one guide member
66.
[0053] In the furnace, one side of the stacked assembly 72 of glass
substrates is contacted by the first set 36 of the fixed
restraining pins extending through a first wall of the furnace,
while the second set 38 of movable restraining pins are biased
against the opposite side of the stacked assembly of glass
substrates, effectively clamping the assembly of glass substrates
between the two groups of restraining pins in a substantially
vertical orientation. Stacked assembly 72 is preferably maintained
within 10 degrees of vertical, within 5 degrees of vertical, within
3 degrees of vertical and preferably within 1 degree of vertical as
heat is applied during the heat treating process. The furnace heats
the stacked glass substrates to an appropriate heat treating
temperature for an appropriate amount of time. Because the combined
weight of the substantially vertically oriented stacked assembly 72
bears downward against cart 28 during the heat treating there is
less likelihood that out of plane distortion of the glass
substrates can occur. By out of plane distortion what is meant is a
gravity-free shape change in a glass substrate that extends out of
the plane represented by a surface of a given glass substrate. That
is, in the absence of gravity, the opposing major surfaces of a
glass substrate should be substantially planar (i.e. having a
deviation from planar no more than 100 .mu.m over an entire major
surface of the substrate), and maintain this planarity after the
heat treating. More simply put, out of plane distortion results in
a glass substrate that is not flat.
[0054] It should be emphasized that the above-described embodiments
of the present invention, particularly any "preferred" embodiments,
are merely possible examples of implementations, merely set forth
for a clear understanding of the principles of the invention. Many
variations and modifications may be made to the above-described
embodiments of the invention without departing substantially from
the spirit and principles of the invention. All such modifications
and variations are intended to be included herein within the scope
of this disclosure and the present invention and protected by the
following claims.
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