U.S. patent application number 13/701744 was filed with the patent office on 2013-10-03 for processing substrates using a temporary carrier.
This patent application is currently assigned to PLASTIC LOGIC LIMITED. The applicant listed for this patent is James Watts. Invention is credited to James Watts.
Application Number | 20130255873 13/701744 |
Document ID | / |
Family ID | 42471187 |
Filed Date | 2013-10-03 |
United States Patent
Application |
20130255873 |
Kind Code |
A1 |
Watts; James |
October 3, 2013 |
PROCESSING SUBSTRATES USING A TEMPORARY CARRIER
Abstract
A technique comprising: securing a device substrate (8) to a
carrier (1) using one or more adhesive elements (6); forming
electronic elements (10) on the device substrate with the device
substrate thus secured to the carrier; and thereafter reducing the
adhesion strength of at least one of the one or more adhesive
elements to facilitate the release of the substrate from the
carrier.
Inventors: |
Watts; James; (Ely,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Watts; James |
Ely |
|
GB |
|
|
Assignee: |
PLASTIC LOGIC LIMITED
Cambridge
GB
|
Family ID: |
42471187 |
Appl. No.: |
13/701744 |
Filed: |
June 3, 2011 |
PCT Filed: |
June 3, 2011 |
PCT NO: |
PCT/EP2011/059220 |
371 Date: |
February 15, 2013 |
Current U.S.
Class: |
156/247 |
Current CPC
Class: |
H01L 21/67 20130101;
H01L 29/78603 20130101; B32B 2307/748 20130101; H01L 23/32
20130101; H05K 13/00 20130101; B32B 37/12 20130101; H01L 21/50
20130101; Y02E 10/549 20130101; H01L 21/78 20130101; H01L 21/304
20130101; H01L 21/70 20130101; H01L 2221/6835 20130101; H01L
21/6835 20130101; H01L 21/02 20130101; H01L 21/68 20130101; B32B
2309/02 20130101; H01L 21/20 20130101; H01L 2221/68381 20130101;
H01L 27/1266 20130101; H01L 23/12 20130101; B32B 7/06 20130101;
H01L 2221/68318 20130101 |
Class at
Publication: |
156/247 |
International
Class: |
H05K 13/00 20060101
H05K013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 4, 2010 |
GB |
1009401.9 |
Claims
1. A method, comprising: securing a device substrate to a carrier
using one or more adhesive elements; forming electronic elements on
the device substrate with the device substrate thus secured to the
carrier; and thereafter reducing the adhesion strength of at least
one of the one or more adhesive elements to facilitate the release
of the substrate from the carrier.
2. A method, comprising: securing a substrate to a carrier using
one or more adhesive elements; processing the substrate with the
substrate thus secured to the carrier; and thereafter reducing the
adhesion strength of at least one of the one or more adhesive
elements to facilitate the release of the substrate from the
carrier, wherein the substrate is secured to the carrier using an
adhesive unit comprising adhesive layers supported on opposite
sides of a support element; and comprising preferentially reducing
the adhesion strength of the adhesive layer between the support
element and one of the substrate and carrier, and removing said one
of the substrate and carrier from the adhesive unit without
removing the other of the substrate and the carrier from the
adhesive unit.
3. The method according to claim 2, comprising: comprising
preferentially reducing the adhesion strength of the adhesive layer
between the support element and the substrate, and removing the
substrate from the adhesive unit without removing the adhesive unit
from the carrier.
4. The method according to claim 3, comprising: thereafter reducing
the adhesion strength of the adhesive layer between the support
element and the carrier, and removing the adhesive unit from the
carrier.
5. The method according to claim 2, comprising: reducing the
adhesion strength of the adhesive layer between the support element
and said one of the substrate and the carrier by heating the
adhesive unit to a first temperature, and reducing the adhesion
strength of the adhesive layer between the support element and the
other of the substrate and the carrier by heating the adhesive unit
to a second temperature higher than the first temperature.
6. The method according to claim 5, wherein the second temperature
is higher than the first temperature by at least about 20 degrees
C.
7. The method according to claim 6, wherein the second temperature
is higher than the first temperature by at least about 40 degrees
C.
8. The method according to claim 5, wherein the first temperature
is in the range of 85 to 95 degrees C.
9. The method according to claim 5, wherein the second temperature
is in the range of 130 to 170 degrees C.
10. The method according to claim 5, wherein the adhesive layers
exhibit an adhesion strength of at least 3 Newtons/20 mm before the
heating.
11. The method according to claim 2, wherein processing the
substrate comprises forming one or more electronic elements on the
device substrate.
12. The method according to claim 1, comprising: reducing the
adhesion strength of at least one of the adhesive elements or at
least one of the adhesive layers by heating or by irradiation.
13. The method according to claim 1, wherein the substrate or
device substrate is a flexible substrate, and the carrier is a
glass carrier.
14. The method according to claim 1, wherein the substrate or
device substrate exhibits a co-efficient of thermal expansion of
greater than about 10 ppm of expansion per degree C.
15. The method according to claim 1, wherein the substrate or
device substrate is more flexible than the carrier.
Description
[0001] The present invention relates to a method of processing
substrates. In one embodiment, it relates to a method of processing
flexible substrates in the production of flexible electronic
devices.
[0002] Some electronic devices such as flexible displays use
flexible polymer substrates as the support for electronic elements
such as an array of TFTs.
[0003] One challenge with the production of such devices is to
prevent misalignment of electronic elements caused by distortion of
the substrate during processing. One technique aimed at reducing
such misalignments is to subject the plastic (polymer) substrate to
a prolonged bake before processing.
[0004] It is an aim of the present invention to provide an improved
technique for reducing such misalignments.
[0005] The present invention provides a method, comprising:
securing a device substrate to a carrier using one or more adhesive
elements; forming electronic elements on the device substrate with
the device substrate thus secured to the carrier; and thereafter
reducing the adhesion strength of at least one of the one or more
adhesive elements to facilitate the release of the substrate from
the carrier.
[0006] In one embodiment, the method further comprises: securing a
substrate to a carrier using one or more adhesive elements;
processing the substrate with the substrate thus secured to the
carrier; and thereafter reducing the adhesion strength of at least
one of the one or more adhesive elements to facilitate the release
of the substrate from the carrier, wherein the substrate is secured
to the carrier using an adhesive unit comprising adhesive layers
supported on opposite sides of a support element; and comprising
preferentially reducing the adhesion strength of the adhesive layer
between the support element and one of the substrate and carrier,
and removing said one of the substrate and carrier from the
adhesive unit without removing the other of the substrate and the
carrier from the adhesive unit.
[0007] In one embodiment, the method further comprises:
preferentially reducing the adhesion strength of the adhesive layer
between the support element and the substrate, and removing the
substrate from the adhesive unit without removing the adhesive unit
from the carrier.
[0008] In one embodiment, the method further comprises: thereafter
reducing the adhesion strength of the adhesive layer between the
support element and the carrier, and removing the adhesive unit
from the carrier.
[0009] In one embodiment, the method further comprises: reducing
the adhesion strength of the adhesive layer between the support
element and said one of the substrate and the carrier by heating
the adhesive unit to a first temperature, and reducing the adhesion
strength of the adhesive layer between the support element and the
other of the substrate and the carrier by heating the adhesive unit
to a second temperature higher than the first temperature.
[0010] In one embodiment, the second temperature is higher than the
first temperature by at least about 20 degrees C.
[0011] In one embodiment, the second temperature is higher than the
first temperature by at least about 40 degrees C.
[0012] In one embodiment, the first temperature is in the range of
85 to 95 degrees C.
[0013] In one embodiment, the second temperature is in the range of
130 to 170 degrees C.
[0014] In one embodiment, the adhesive layers exhibit an adhesion
strength of at least 3 Newtons/20 mm before the heating.
[0015] In one embodiment, processing the substrate comprises
forming one or more electronic elements on the device
substrate.
[0016] In one embodiment, the method further comprises: reducing
the adhesion strength of at least one of the adhesive elements or
at least one of the adhesive layers by heating or by
irradiation.
[0017] In one embodiment, the substrate or device substrate is a
flexible substrate, and the carrier is a glass carrier.
[0018] In one embodiment, the substrate or device substrate
exhibits a co-efficient of thermal expansion of greater than about
10 ppm of expansion per degree C.
[0019] In one embodiment, the substrate or device substrate is more
flexible than the carrier.
[0020] In one embodiment, the substrate or device substrate has a
co-efficient of thermal expansion greater than that of the
carrier.
[0021] In one embodiment, the substrate or device substrate is
secured to the carrier as part of a sheet of substrate or device
substrate material providing a plurality of substrates or device
substrates.
[0022] According to one embodiment, a dual adhesive element is
provided that is able to adhere the substrate to the carrier during
processing of the device, but then is able to release the substrate
from the carrier when required, during a single step, while
avoiding both distortion and damage to the substrate during
processing, and further allows the carrier to be reused.
[0023] According to one embodiment, the tackiness of an upper
adhesive layer is able to be reduced when required, allowing the
substrate to be released from the carrier, without any effects of
degradation to the substrate. The dual adhesive element remains on
the carrier, until a further increase in temperature is used to
reduce the tackiness of a lower adhesive layer of the dual adhesive
element and facilitate the release of the dual adhesive element
from the carrier.
[0024] A specific embodiment thereof will now be described by way
of example and with reference to the accompanying drawings, in
which:
[0025] FIG. 1 illustrates the securing a device substrate to a
carrier in accordance with an embodiment of the present invention
using an adhesive element;
[0026] FIG. 2 illustrates pre-use protection of the adhesive
element used in FIG. 1; and
[0027] FIG. 3 illustrates securing a plurality of device substrates
to a carrier in accordance with an embodiment of the present
invention using an adhesive element.
[0028] In accordance with a first embodiment of the invention as
illustrated in FIG. 1, a plurality of flexible device substrates 8
(only one is shown in FIG. 1) are secured to a rigid glass carrier
1 via an adhesive element 6. As discussed in more detail below, the
electronic elements 10 (such as the TFT array) are formed on the
device substrate 8 after the device substrate 8 has been secured to
the rigid glass carrier 1. After processing, the device substrate 8
is removed from the carrier 1. The electronic elements 10 are
formed on the device substrate 8 via a planarisation layer 9
deposited on the device substrate 8 after securing the device
substrate 10 to the carrier 1.
[0029] The processing of the device substrate includes a sequence
of steps including depositing material and removing deposited
material. Such deposition and removal steps are controlled
automatically on the basis of the expected position and
configuration of the device substrate 8 on the carrier 1. If the
position of the device substrate 8 relative to the carrier 1 and/or
the configuration of the device substrate 8 on the carrier 1 does
not remain substantially constant for each of the sequence of
steps, this can lead to misalignments and device failures.
[0030] The device substrate 8 may be a flexible substrate, such as
an organic polymer substrate, for supporting a TFT array 10 to
serve as the backplane of an LCD or electrophoretic display device.
Examples of plastic substrates for this use are organic polymer
films such as films of heat-stabilised polyethyleneterephtalate
(HS-PET) and films of heat-stabilised polyethylenenaphtalene
(HS-PEN).
[0031] The adhesive element 6 comprises a central polyester film
support element 3 supporting two adhesive layers 2, 4. For the
adhesive layers 2 and 4 are used materials whose strength of
adhesion for the carrier 1 and device substrate 8 can be reduced by
an external stimulus such as heating or UV irradiation. Under the
conditions at which the device substrate is processed in position
on the carrier, the adhesive layers exhibit an adhesion strength
sufficiently high to securely hold the device substrate 8 on the
carrier during the processing of the substrate on the carrier.
[0032] The processing of the device substrate includes exposing the
device substrate to low pressure/vacuum conditions as part of the
production of the TFT array 10, and the adhesion strength exhibited
by the adhesive layers for the carrier, support element and device
substrate is sufficiently high to prevent the device substrate 8
from bubbling up (lifting) under such low pressure/vacuum
conditions. Bubbling-up of the substrate is undesirable because it
can cause distortion in the z-axis (i.e. an axis perpendicular to
the plane of the device substrate) during processing, and can also
cause distortion in the x-y axis (i.e. in a direction parallel to
the plane of the device substrate 8) after a return to normal
pressure conditions, as the device substrate relaxes back down.
[0033] The processing of the device substrate 8 on the carrier also
includes subjecting the device substrate to rises in temperature.
Flexible plastic substrates have a relatively high co-efficient of
thermal expansion (CTE), and rises in temperature during processing
cause expansion of the device substrate. The internal cohesive
strength of the adhesive layers (and also the other layers/elements
in the stack) are sufficiently high to return the device substrate
8 to substantially the same X-Y position relative to the glass
carrier upon a return to normal temperature conditions in
preparation for another processing step. This further helps to
reduce or eliminate the misalignment of layers/elements/components
applied to or deposited on the device substrate 8 as part of said
another processing step.
[0034] After processing of the device substrate 8 on the carrier 1
is completed, the adhesive element 6 is subjected to the necessary
external stimulus to trigger a reduction in the adhesion strength
of the adhesive layers.
[0035] In accordance with this embodiment of the invention, the
adhesive materials for the two adhesive layers 2 and 4 are selected
such that a significant reduction in the adhesion strength can be
triggered in the adhesive layer 4 adjacent to the device substrate
8 without triggering a significant reduction in the adhesion
strength of the adhesive layer 2 adjacent to the carrier 1. It is
found that this is advantageous for ensuring complete and reliable
removal of adhesive material from the undersurface of the device
substrate 8.
[0036] Further in accordance with this embodiment of the invention,
the adhesive material for the adhesive layer 2 adjacent to carrier
1 is further selected such that its adhesion strength can be
significantly reduced by the application of a further external
stimulus. For example, the adhesive material for the adhesive layer
4 adjacent to the device substrate 8 is one at which a significant
reduction in adhesion strength is first achieved in a short period
(e.g. 3 seconds) at a relatively low temperature (e.g. between 85
and 95 degrees C. or about 90 degrees C.), and the adhesive
material for the adhesive layer 2 adjacent to the carrier 1 is one
at which a significant reduction in adhesion strength is first
achieved in a short period (e.g. 3 seconds) at a higher temperature
(e.g. between 130 and 170 degrees C. or about 150 degrees C.).
[0037] The selection of appropriate trigger temperatures will
depend on the temperatures that are reached during the processing
of the device substrate 8 on the carrier 1, and the amount of heat
that the device substrate 8 and the TFT array 7 formed thereon can
withstand without suffering a degradation of those elements and a
deterioration in device performance. It has been found that a
temperature of between 85 to 95 degrees C. or about 90 degrees C.
is a suitable trigger temperature for the adhesive layer 4 adjacent
to the device substrate 8 for the case of a TFT array including
organic polymer materials for the semiconducting channel and gate
dielectric. An appropriate trigger temperature for the adhesive
layer 2 adjacent to the carrier 1 is the lowest temperature at
which it can be sure that the adhesive layer 2 adjacent to the
carrier 1 will not undergo a significant degree in adhesion
strength at the time of heating the adhesive layer 4 adjacent to
the device substrate 8 to trigger a reduction in the adhesion
strength of that adhesive layer. It has been found that a
temperature of between 130 and 170 degrees C. or about 150 degrees
C. is a suitable trigger temperature for the adhesive layer 2
adjacent to the carrier 1. In order to prevent a significant
reduction in the adhesion strength of the adhesive layer adjacent
to the carrier 1 at the time of reducing the strength of the
adhesive layer adjacent to the device substrate 8, the trigger
temperature for the adhesive layer adjacent to the carrier 1 should
be sufficiently higher than the trigger temperature for the
adhesive layer adjacent to the device substrate 8. A trigger
temperature difference of least about 20 degrees C., and more
preferably at least about 40 degrees C. is found to be effective
for this purpose.
[0038] It has been found that this embodiment of the present
invention can be implemented by making the adhesive element using,
for example, adhesive tapes commercially available from Nitto Denko
under the product name REVALPHA.RTM.. These tapes are found to
exhibit an adhesion strength of at least 3 N/20 mm (as measured in
accordance with the JIS Z-0237 standard (Surface material: S/S
board, Peeling speed: 300 mm/min, Peeling angle: 180.degree.) for
the glass carrier 1 and a PET device substrate 8 at the
temperatures under processing of the device substrate 8 to form the
TFT array 10 takes place. This level of adhesion strength is found
to be sufficient to reliably hold the device substrate 8 in place
on the carrier 1 and substantially prevent distortions of the kind
that might cause misalignments of the various elements deposited on
the device substrate 8 to form the TFT array 10. These tapes are
available in different types exhibiting a reduction in adhesion
strength at different temperatures. It has been found that the 90
degree C. type is suitable for the adhesive layer 4 adjacent to the
device substrate 8 and that the 150 degree C. type is suitable for
the adhesive layer 2 adjacent to the carrier 1.
[0039] As shown in FIG. 2, the tapes are provided with upper and
lower liners 5a, 5b that provide pre-use protection for the
adhesives layer 2 and 4. These liners 5a, 5b are removed from the
adhesive element 6 before the adhesive element 6 is used to secure
the device substrate 8 to the carrier 1.
[0040] To secure the device substrate 8 to the carrier 1: firstly,
the lower liner (5a) is first removed from the adhesive element 6,
and the exposed lower adhesive layer 2 is pressed onto the carrier
1 to secure the adhesive element 6 to the carrier 1; and, the upper
liner 5b is then removed from the adhesive element 6, and the
device substrate 8 is pressed down onto the exposed upper adhesive
layer 4.
[0041] Processing of the device substrate 8 then takes place. For
the example of an organic polymer TFT array, this includes the
sputter deposition and patterning of upper and lower metal layers
to define the source, drain and gate electrodes and addressing
lines/interconnects; and the deposition from solution of an organic
polymeric semiconductor material to form the semiconducting channel
between the source and drain electrodes of each TFT and the
deposition from solution of an organic polymeric dielectric
material to form the gate dielectric between the semiconducting
channel and gate electrode of each TFT.
[0042] After the processing of the device substrate on the carrier
is completed (and the TFT array 10 is formed on the device
substrate 8), the device substrate 8 is released from the adhesive
element by mounting the rigid glass carrier 1 on a hot plate at an
appropriate temperature to trigger a reduction in the adhesion
strength of the adhesive layer 4 adjacent to the device substrate 8
without triggering a significant reduction in the adhesion strength
of the adhesive layer 2 adjacent to the carrier 1. After removal of
the device substrate 8 from the carrier 1, the carrier 1 is heated
to a higher temperature to reduce the adhesion strength of the
adhesive layer 2 adjacent to the carrier 1 and release the carrier
1 from the adhesive element 6, thereby facilitating reuse of the
carrier 1.
[0043] The time that it takes to heat the adhesive layers to the
release temperature will depend on the speed at which the heat can
be transferred to the adhesive layer. Because of the thermal lag
caused by the assembly in which the adhesive layers reside, it may
take significantly longer to heat the adhesive layer to the
respective release temperature, For example, it may take about 30
seconds, or as much as 105 seconds or 180 seconds.
[0044] According to one variation of the above-mentioned technique,
adhesive materials are used for which a reduction in adhesion
strength can be achieved by UV irradiation. This alternative
technique is of particular use where the device substrate 8 or the
TFTs 10 formed thereon are not degraded or damaged by exposure to
UV radiation, and/or where the elements formed on the device
substrate by processing on the carrier include heat-sensitive
elements. For example, one or both of the adhesive layers 2, 4 in
the technique described above could be replaced with a UV peeling
tape such as those commercially available from Nitto Denko.
Replacing only one of the adhesive layers 2, 4 with a UV peeling
tape facilitates the selective removal of one of the carrier 1 and
the device substrate 8 from the adhesive element 6. For example, if
only the adhesive layer 2 adjacent to the carrier 1 is replaced
with a UV peeling tape, the device substrate could be removed from
the adhesive element by heating as described above, and exposure of
UV irradiation from the bottom would allow the carrier 1 to be
removed from the adhesive element without damage. Alternatively, a
UV peeling tape could be used selectively adjacent to the device
substrate 8 to facilitate removal of the device substrate 8 from
the adhesive element 6 by exposure to UV radiation, and heating
could be used as described above to subsequently release the
adhesive element 6 from the carrier 1.
[0045] With the above-described technique, it is possible to
suppress the effect of linear expansion changes in the plastic
device substrate 8 during processing, as well as resist non-linear
(random) distortions in the plastic device substrate 8 during
processing, which non-linear distortions can arise because of
defects or abnormalities in the structure of the plastic substrate.
As mentioned above, the high adhesion strength and cohesive
strength of the adhesive layers serve to prevent undesirable
changes in the position of the device substrate 8 relative to the
glass carrier 1, which itself has a very low co-efficient of
thermal expansion in the range of 3 to 5 ppm expansion per degree
C.
[0046] The above-described technique makes it possible to: (a)
improve yields by reducing misalignments; (b) facilitate the
production of high resolution displays; and (c) reduce
manufacturing costs because less distortion implies less critical
alignment (e.g., less local alignment steps).
[0047] We have chosen the example of producing an organic polymer
TFT array to describe techniques in accordance with embodiments of
the invention, but the same kind of techniques are also applicable
to the production of other kinds of devices including a flexible
plastic support substrate.
[0048] Also, we have chosen to illustrate the invention in FIG. 1
with reference to the securing and processing of an individual
device substrate to a rigid carrier. However, the techniques
described above are equally applicable to the securing and
processing of a plurality of device substrates on a common rigid
carrier. For example, according to one variation illustrated in
FIG. 3, the adhesive element 6 is used in the form of a relatively
large area sheet to secure a sheet of device substrate material to
a carrier 1. The sheet of device substrate material provides a
plurality of device substrates (two are shown in FIG. 3). A
planarisation layer 9 is formed over the entire surface of the
device substrate material sheet 2, and then a plurality of display
device products are formed on respective regions of the sheet of
device substrate material 2. After the processing is completed, the
device substrate material sheet and underlying adhesive element
sheet 6 is cut in a region between the device substrate regions,
and the plurality of individual device substrates are removed from
the respective adhesive element patches in the same way as
described above in relation to FIG. 1; and the adhesive element
patches left adhered to the carrier 1 are also removed from the
carrier in the same way as described above in relation to FIG.
1.
[0049] The invention is not limited to the above-described examples
and embodiments. It will be evident to a person skilled in the art
that various modifications may be made within the scope of the
invention.
[0050] The applicant hereby discloses in isolation each individual
feature described herein and any combination of two or more such
features, to the extent that such features or combinations are
capable of being carried out based on the present specification as
a whole in the light of the common general knowledge of a person
skilled in the art, irrespective of whether such features or
combinations of features solve any problems disclosed herein, and
without limitation to the scope of the claims. The applicant
indicates that aspects of the present invention may consist of any
such individual feature or combination of features.
* * * * *