U.S. patent application number 13/861954 was filed with the patent office on 2014-05-15 for led light source, its manufacturing method, and led-based photolithography apparatus and method.
This patent application is currently assigned to Hitachi High-Technologies Corporation. The applicant listed for this patent is Hitachi High-Technologies Corporation. Invention is credited to Shohei HATA, Susumu ISHIDA.
Application Number | 20140134767 13/861954 |
Document ID | / |
Family ID | 43380353 |
Filed Date | 2014-05-15 |
United States Patent
Application |
20140134767 |
Kind Code |
A1 |
ISHIDA; Susumu ; et
al. |
May 15, 2014 |
LED LIGHT SOURCE, ITS MANUFACTURING METHOD, AND LED-BASED
PHOTOLITHOGRAPHY APPARATUS AND METHOD
Abstract
Structurally-simple LED light source preventing temperature
variations among multiple LED elements arranged densely on
LED-mounting substrate is described. LED light source includes a
plurality of LED elements each of which is formed by connecting an
LED chip to electrodes formed on a ceramic substrate; LED-mounting
substrate on which to mount the plurality of LED elements, the
LED-mounting substrate having through holes therein; and heat sink
plate for releasing heat from the LED-mounting substrate, wherein a
thermally conductive resin is present between the LED-mounting
substrate and the heat sink plate and wherein part of the thermally
conductive resin protrudes from the through holes of the
LED-mounting substrate and covers the top surface of the
LED-mounting substrate on which the plurality of LED elements are
mounted, so thermally conductive resin is in contact with the
plurality of LED elements.
Inventors: |
ISHIDA; Susumu; (Yokohama,
JP) ; HATA; Shohei; (Yokohama, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hitachi High-Technologies Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
Hitachi High-Technologies
Corporation
Tokyo
JP
|
Family ID: |
43380353 |
Appl. No.: |
13/861954 |
Filed: |
April 12, 2013 |
Current U.S.
Class: |
438/28 |
Current CPC
Class: |
G03F 7/7005 20130101;
H05K 2201/0209 20130101; H05B 3/0038 20130101; H05K 3/0061
20130101; G03F 7/70858 20130101; H05K 1/0206 20130101; H01L
2224/48091 20130101; H01L 2224/48091 20130101; H01L 33/64 20130101;
H05K 2201/09063 20130101; H01L 33/641 20130101; H05K 2201/10977
20130101; H05K 2201/10106 20130101; H01L 25/13 20130101; H01L
2924/00014 20130101; H05K 1/0204 20130101 |
Class at
Publication: |
438/28 |
International
Class: |
H01L 33/64 20060101
H01L033/64 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 2009 |
JP |
2009-155179 |
Claims
1. A method for manufacturing an LED light source, the method
comprising the steps of: applying a thermally conductive resin on a
heat sink plate; pressing a bottom surface of an LED-mounting
substrate, on a top surface of which a plurality of LED elements
are mounted and through holes are formed on the LED-mounting
substrate, against the heat sink plate on which the thermally
conductive resin has been applied until the distance between the
heat sink plate and the LED-mounting substrate becomes a particular
value, so that the thermally conductive resin can spread between
the heat sink plate and the LED-mounting substrate and so that part
of the thermally conductive resin flows the through holes from the
bottom surface to the top surface of the LED-mounting substrate and
spread out on the top surface of the LED-mounting substrate so as
to fill spaces between the plurality of LED elements; and heating
the thermally conductive resin for solidification after the
pressing step.
2. The method of claim 1, wherein the plurality of LED elements are
each formed by wiring an LED chip to electrodes formed on a ceramic
substrate.
3. The method of claim 1, wherein the thermally conductive resin is
higher in thermal conductivity than the LED-mounting substrate.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] Japan Priority Application 2009-155179, filed Jun. 30, 2009
including the specification, drawings, claims and abstract, is
incorporated herein by reference in its entirety. This application
is a Divisional of U.S. application Ser. No. 12/815,222, filed Jun.
14, 2010, incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] As an example of a conventional LED (light-emitting diode)
substrate, Japanese Unexamined Patent Application Publication No.
2004-311791 (Patent Document 1) discloses such an LED substrate as
illustrated in FIG. 5.
[0003] The LED substrate 10 of FIG. 5 has a concave portion 11a
formed on the top surface of its ceramic substrate 11. Conductive
wiring patterns 12 are formed on the concave portion 11a, and a
single LED chip 13 is glued to the conductive wiring patterns 12
with its bottom surface facing the concave portion 11a (the bottom
surface of the LED chip 13 is the surface through which light is
not emitted). The electrodes on the light-emitting-surface side of
the LED chip 13 are connected by wires 14, made of gold or the
like, to particular locations of the conductive wiring patterns 12
on the concave portion 11a of the ceramic substrate 11. The concave
portion 11a is sealed with resin 15 (e.g., silicone resin), or
inert gas such as nitrogen or the like is sealed inside the concave
portion 11a. Part of the side faces and part of the bottom face of
the ceramic substrate 11 are covered with outer terminals 16 so
that the LED substrate 10 can be electrically connected to other
external devices. Note that multiple LED chips 13 with different
luminescent colors can also be mounted on the concave portion 11a
in place of the single LED chip 13.
[0004] As illustrated in FIG. 6, Patent Document 1 also discloses
an LED light source that involves the use of multiple LED
substrates 10, each of which is the one shown in FIG. 5. In this
LED light source, the multiple LED substrates 10 are attached by
solder 17a to the top surface of a substrate 17, made of glass
epoxy resin or the like, in the form of a single or multiple rows.
Also, an LED chip 13 (13a-13c) is mounted on each of the concave
portions 11a-11c the LED substrates 10 with the bottom surfaces of
the LED chips 13 facing the LED substrates 10.
[0005] When the LED light source of Patent Document 1 is used for a
photolithography apparatus or an illumination device, sufficient
heat release is required because the LED light source is driven by
a high electric current. Thus, as illustrated in FIG. 6, a heat
sink plate 18 is attached to the bottom surface of the substrate
17, i.e., the surface opposite the surface to which the substrates
10 are attached. This LED light source is arranged, as illustrated
in FIG. 7, across from a light guide plate 19 of a backlight so
that the light from the LED substrates 10 can travel into the light
guide plate 19.
[0006] As another heat release structure, Patent Document 1 also
discloses such an LED light source structure as illustrated in FIG.
8. In this LED light source, an LED chip 13 is glued to the
conductive wiring patterns on each of concave portions 11a of
ceramic substrates 11, with the bottom surfaces of the LED chips 13
facing the concave portions 11a. Also, a heat sink plate 18 is
glued directly to the bottom faces of the ceramic substrates 11,
i.e., the surface opposite the light emitting surface of the
ceramic substrate. This LED light source also has a substrate 17
placed on the ceramic substrates 11. The substrate 17 has windows
21 so that the light emitted from the ceramic substrates 11 can
travel there through. The conductive wiring patterns on the
substrate 17 (not illustrated) which are used for power supply to
the LED chips 13 are connected by solder 20 to the conductive
wiring patterns on the top surfaces of the ceramic substrates 11
(not illustrated).
[0007] The LED display device of Patent Document 1 that involves
the use of such LED light sources as above is capable of releasing
the heat of the LED chips 13 efficiently because the heat can be
transferred to the heat sink plate 18 only through the ceramic
substrates 11 and the adhesive that glues the LED chips 13 to the
ceramic substrates 11.
[0008] As a modification example of the LED substrate 10 of FIG. 5,
Japanese Unexamined Patent Application Publication No. 2008-172177
(Patent Document 2) discloses, as illustrated in FIG. 9, a heat
release structure in which a metal housing 22 the houses a
liquid-to-vapor heat release device 23 is attached to the bottom
surface of an LED chip 13, i.e., the surface opposite the light
emitting surface of the chip 13.
[0009] In the heat release structure of Patent Document 2, the heat
of the LED chip 13 can be quickly released through the metal
housing 22 and the liquid-to-vapor heat release device 23, which is
high in thermal conductivity. Thus, temperature rises of the LED
chip 13 can be prevented.
[0010] Further, Japanese Unexamined Patent Application Publication
No. 2006-250982 (Patent Document 3) discloses a maskless
photolithography apparatus.
SUMMARY OF THE INVENTION
[0011] As stated above, in the LED light source of Patent Document
1 as illustrated in FIG. 5, the heat sink plate 18 is attached to
the bottom surface of the substrate 17 on the top surface of which
are mounted the multiple LED substrates 10. Thus, the heat of the
LED chips 13 is transferred to the heat sink plate 18 through the
ceramic substrates 11 of the LED substrates 10 and through the
substrate 17.
[0012] If multiple LED substrates 10a, 10b, and 10c are closely
arranged on the substrate 17 as illustrated in FIG. 10, the heat of
an LED element of the LED substrate 10a located adjacent to the LED
substrate 10b is transferred to the heat sink plate 18 through the
solder 17a and through the substrate 17. This increases the
temperature of a portion of the heat sink plate 18 which is located
right below the LED substrate 10a, and that temperature is thus
higher than those at the periphery of the heat sink plate 18.
[0013] The heat of the LED substrate 10b is also transferred to the
heat sink plate 18 through the solder 17a and through the substrate
17. However, if the heat sink plate 18 is already raised in its
temperature, the heat of the LED substrate 10b cannot be dispersed
inside the heat sink plate 18 as with the heat of the LED substrate
10a. This will increase the temperatures of a substrate area 17b
and a heat sink plate area 18b that are located below the LED
substrate 10b. As a result, the temperature of the LED substrate
10b will also increase because the heat of the LED substrate 10b
cannot be transferred sufficiently to the substrate 17. This
results in the temperature difference between the LED substrates
10a and 10b as well as the temperature variations among the LED
substrates 10a to 10c.
[0014] The LED temperature variations will increase as the heat of
the LED chips 13 increases (e.g., when the LED light source is used
for a photolithography apparatus or an illumination device which
consumes a large amount of electric power). The LED temperature
variations will also increase when the LED substrates 10a to 10c
are more closely arranged on the substrate 17. When the temperature
of the LED substrate 10a increases, the temperature of its LED chip
13a will also increase. A temperature increase of an LED chip
causes its illumination efficiency and light intensity to decrease.
When the LED chip is constantly subjected to a high-temperature
environment, the LEC chip will deteriorate faster, shortening its
mechanical life. For these reasons, increased temperature
variations among LED chips lead to adverse consequences such as
light intensity decreases, light intensity variations, and
shortened LED life.
[0015] While the LED display device of Patent Document 1 has the
improved capabilities of transferring heat from its LED-mounting
substrate to its heat sink plate, no consideration is given to LED
temperature variations, making the LED display device susceptible
to the LED temperature variations.
[0016] Those disclosed in Patent Document 2 are also susceptible to
the LED temperature variations.
[0017] Patent Document 3 relates to a maskless photolithography
apparatus that involves the use of a semiconductor laser or a
discharge lamp such as a mercury lamp and a xenon lamp as its light
source, but no mention is made of an LED light source.
[0018] To address the above problems, an object of the present
invention is thus to provide a structurally-simple or
easily-manufacturable LED light source that enables uniform
illumination by reducing temperature variations among its LED
elements arranged densely on its substrate and to provide an
photolithography apparatus that involves the use of the LED light
source.
[0019] To achieve the above object, an LED light source according
to the invention comprises: a plurality of LED elements each of
which is formed by connecting an LED chip to electrodes formed on a
ceramic substrate; an LED-mounting substrate on which to mount the
plurality of LED elements, the LED-mounting substrate having
through holes therein; and a heat sink plate for releasing heat
from the LED-mounting substrate, wherein a thermally conductive
resin is present between the LED-mounting substrate and the heat
sink plate and wherein part of the thermally conductive resin
protrudes from the through holes of the LED-mounting substrate and
covers the top surface of the LED-mounting substrate on which the
plurality of LED elements are mounted, so that the part of the
thermally conductive resin is in contact with the plurality of LED
elements.
[0020] Moreover, a method for manufacturing an LED light source
according to the invention comprises the steps of: applying a
thermally conductive resin on a heat sink plate; pressing a bottom
surface of an LED-mounting substrate on a top surface of which a
plurality of LED elements are mounted against the heat sink plate
on which the thermally conductive resin has been applied until the
distance between the heat sink plate and the LED-mounting substrate
becomes a particular value, so that the thermally conductive resin
can spread between the heat sink plate and the LED-mounting
substrate and so that part of the thermally conductive resin can
flow from through holes of the LED-mounting substrate onto the top
surface of the LED-mounting substrate so as to fill spaces between
the plurality of LED elements; and heating the thermally conductive
resin for solidification after the pressing step.
[0021] Further, an LED-based photolithography apparatus according
to the invention comprises: a light source; a photolithography
pattern generation unit for generating photolithography patterns; a
table on which to place a workpiece, the table being movable at
least in one direction; and a control unit for controlling the
light source, the photolithography pattern generation unit, and the
table, wherein the light source comprises: a plurality of LED
elements each of which is formed by connecting an LED chip to
electrodes formed on a ceramic substrate; an LED-mounting substrate
on which to mount the plurality of LED elements, the LED-mounting
substrate having through holes therein; and a heat sink plate for
releasing heat from the LED-mounting substrate, the heat sink plate
being attached by a thermally conductive resin to the LED-mounting
substrate and wherein part of the thermally conductive resin
protrudes from the through holes of the LED-mounting substrate and
covers the top surface of the LED-mounting substrate on which the
plurality of LED elements are mounted, so that the part of the
thermally conductive resin is in contact with the plurality of LED
elements.
[0022] Furthermore, an LED-based photolithography method according
to the invention comprises the steps of: directing light emitted
from a light source to a photolithography pattern generation unit;
and exposing a workpiece on which a photoresist is applied to the
light that has passed through a photolithography pattern generated
by the photolithography pattern generation unit; wherein the light
from the light source is emitted from a plurality of LED elements
of the light source and wherein the plurality of LED elements are
mounted on an LED-mounting substrate with a thermally conductive
resin applied therebetween, and the LED-mounting substrate is
cooled by a water-cooling jacket.
[0023] In accordance with the invention, it is possible to reduce
temperature variations among multiple LED elements mounted on an
LED-mounting substrate because the LED elements are connected to
the LED-mounting substrate by thermally conductive resin. In
addition, because the thermally conductive resin also connects a
heat sink plate to the LED-mounting substrate, the heat of the
LED-mounting substrate can be more efficiently transferred to the
heat sink plate than in conventional technologies.
[0024] Moreover, the temperature variations can be reduced further
when a ceramic or metal substrate higher in thermal conductivity is
used as the LED-mounting substrate instead of using a conventional
resin substrate. This reduces thermal stress on the LED elements
which tend to become high in temperature, thereby enhancing the
reliability of the LED elements.
[0025] Further, the above-described LED light source of the
invention does not require a new manufacturing process and a new
device because it can be manufactured by a conventional
manufacturing process. Thus, manufacturing cost increases can be
prevented.
[0026] Furthermore, application of the LED light source of the
invention to a photolithography apparatus leads to less power
consumption during light exposure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a cross section illustrating the structure of an
LED light source according to Embodiment 1 of the invention;
[0028] FIG. 2A illustrates a process for bonding a heat sink plate
to a substrate according to Embodiment 1, particularly showing when
a given amount of thermally conductive resin is applied to the heat
sink plate;
[0029] FIG. 2B illustrates the bonding process of Embodiment 1,
particularly showing when the substrate is pressed against the heat
sink plate so that the thermally conductive resin can be flattened
by the heat sink plate and the substrate;
[0030] FIG. 2C illustrates the bonding process of Embodiment 1,
particularly showing when the substrate is pressed further downward
so that part of the thermally conductive resin can flow upward from
the through holes of the substrate onto the top surface of the
substrate;
[0031] FIG. 3 is a cross section illustrating the structure of an
LED light source according to Embodiment 2 of the invention;
[0032] FIG. 4 is a cross section of an LED light source according
to Embodiment 3 of the invention, which light source is intended
for use in a photolithography apparatus;
[0033] FIG. 5 is a perspective view of a conventional LED
substrate;
[0034] FIG. 6 is a cross section of a conventional LED light
source;
[0035] FIG. 7 is a cross section of a conventional LED
backlight;
[0036] FIG. 8 is a cross section of another conventional LED light
source;
[0037] FIG. 9 is a cross section of still another conventional LED
light source;
[0038] FIG. 10 is a cross section illustrating heat flows in a
conventional LED light source;
[0039] FIG. 11A illustrates the entire configuration of a
photolithography apparatus according to Embodiment 4 of the
invention; and
[0040] FIG. 11B is a graph showing light exposure conditions for
the photolithography apparatus of Embodiment 4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0041] Embodiments of the present invention will now be described
with reference to the accompanying drawings.
Embodiment 1
[0042] FIG. 1 is a cross section of an LED light source according
to Embodiment 1 of the invention. The LED light source 1 of FIG. 1
includes the following components: a substrate 3; multiple LED
substrates 2a to 2c; and a heat sink plate 4. The LED substrates 2a
to 2c, that is, substrates on which to mount LEDs, are arranged on
the substrate 3 at particular intervals in the form of a single row
or multiple rows. The heat sink plate 4 is attached to the bottom
surface of the substrate 3. The connection among the LED substrates
2a to 2c, the substrates 3, and the heat sink plate 4 is made by
thermally conductive resin 5 (e.g., silicone adhesive).
[0043] Each of the LED substrates 2a to 2c is structurally the same
as the LED substrate 10 of FIG. 5. The LED substrates 2a to 2c each
include a ceramic substrate 201, an LED chip 202, and wires 203.
The ceramic substrate 201 has a square shape with the size of from
2 by 2 mm to 7 by 7 mm and with the thickness of 1.5 to 3 mm. The
LED chip 202, that is, a light-emitting element, has a square shape
with the size of from 0.2 by 0.2 mm to 2 by 2 mm and placed on the
ceramic substrate 201. The wires 203 are used to connect some
electrodes of the LED chip 202 to particular locations of the
conductive wiring patterns on the ceramic substrate 201 (not
illustrated in FIG. 1), which wiring patterns are made of more than
0.3-.mu.m-high Au, Ag, Al, or other highly reflective metal.
[0044] The ceramic substrate 201 is high in thermal conductivity
because it is made of alumina or aluminum nitride. Also, the
ceramic substrate 201 has a concave portion on its top surface. The
LED chip 202 is placed inside the concave portion with its bottom
surface facing the ceramic substrate 201 (the bottom surface is the
surface through which light is not emitted). In this case, the LED
chip 202 is bonded to a particular portion of the conductive wiring
patterns on the concave portion (see FIG. 5). The electrodes on the
light-emitting-surface side of the LED chip 202 are connected by
the wires 203 to particular locations of the conductive wiring
patterns on the concave portion. Note that multiple LED chips 202
with different luminescent colors can also be placed on a single
ceramic substrate 201 in place of a single LED chip 202.
[0045] As illustrated in FIG. 1, multiple ceramic substrates 201
are connected to the top surface of the substrate 3 by solder 32
and electrically conductive paste. This connection is made between
the conductive wiring patterns on the substrate 3 (not illustrated
in FIG. 1) that are used for supply of electric power to LED chips
202 and the conductive wiring patterns located on the bottom
surfaces of the ceramic substrates 201 (not illustrated).
[0046] The substrate 3, which is 0.5 to 5 mm thick, is provided
with multiple through holes 30, each of which is 0.5 to 2 mm in
diameter. The through holes 30 are located near the ceramic
substrates 201 so that the side faces of the ceramic substrates 201
can be sufficiently covered with the thermally conductive resin
5.
[0047] The heat sink plate 4, made of thermally conductive metal
such as aluminum and copper, is glued by the thermally conductive
resin 5 to the substrate 3 located above the heat sink plate 4.
[0048] The thermally conductive resin 5 is a thermoplastic resin or
photo-plastic resin and made by mixing an insulating filler
material, such as alumina, carbon, titanic oxide, and silica, with
silicone resin or with epoxy-based resin. The thermal conductivity
of the thermally conductive resin 5 is from 0.5 to 10 W/mK, its
coefficient of thermal expansion is from 2 to 100 ppm/.degree. C.,
and its viscosity rate is from 10 to 100 Pas. The thermally
conductive resin 5 seals the bottom surfaces or part of the side
surfaces of the ceramic substrates 201a to 201c and the through
holes 30 of the substrate 3. Also, the thermally conductive resin 5
connects the substrate 3 and the heat sink plate 4 together.
[0049] Since the thermally conductive resin 5 is in contact with
the bottom surfaces or part of the side surfaces of the ceramic
substrates 201a to 201c, the thermally conductive resin 5 can
transfer the heat of the ceramic substrate 201b, which tends to be
high, to the ceramic substrates 201a and 201c, which are low in
temperature. This reduces the temperature differences among the
ceramic substrates 201a, 201b, and 201c. Thus, the temperature
variations among the ceramic substrates 201a, 201b, and 201c also
decrease. In fact, the structure of FIG. 1 resulted in a
temperature difference of 3.degree. C. or lower between the ceramic
substrates 201a and 201b when a power of 2 W was applied to each
LED, with the height h of the thermally conductive resin 5 from the
top surface of the substrate 3 being set to about 1 mm. This
temperature difference is lower than the difference obtained with
the conventional structure of FIG. 6, which difference was
7.degree. C.
[0050] When the above-mentioned height h is increased, the
thermally conductive resin 5 can cover larger areas of the ceramic
substrates 201a to 201c, which would result in achieving high
efficiency of thermal transfer in transferring heat from the
ceramic substrates 201a to 201c to the thermally conductive resin
5. As a result, the temperature difference between the ceramic
substrates 201a and 201b can be reduced more.
[0051] Next, a manufacturing process of the LED light source 1 is
described with reference to FIGS. 2A to 2C, which collectively
illustrate a process for bonding the heat sink plate 4 to the
substrate 3.
[0052] As illustrated in FIG. 2A, the LED substrates 2a to 2c are
placed on the substrate 3. The LED substrates 2a to 2c are
self-aligned by reflow soldering. An adjusted amount of thermally
conductive resin 5 is then applied onto the heat sink plate 4 with
the use of a dispenser or the like.
[0053] Then in FIG. 2B, after the substrate 3 is aligned with the
heat sink plate 4, the substrate 3 is pressed against the heat sink
plate 4 from above so as to connect the substrate 3 and the heat
sink 4 by the thermally conductive resin 5. The pressure from above
horizontally flattens the thermally conductive resin 5 located
between the substrate 3 and the heat sink plate 4, with the
conductive resin 5 spreading in the horizontal plane. The pressing
is stopped after the distance between the substrate 3 and the heat
sink plate 4 becomes a particular value.
[0054] Since the substrate 3 has the through holes 30 near the LED
substrates 2a to 2c are placed, adding pressure causes the
thermally conductive resin 5 to flow upward from the through holes
30.
[0055] Referring to FIG. 2C, by continuing to add pressure, the
thermally conductive resin 5 existing between the substrate 3 and
heat sink plate 4 flows through the through holes 30 to underneath
the bottom surfaces or around the side surfaces of the LED
substrates 2a to 2c to fill their associated spaces. This provides
connection of the LED substrates 2a to 2c by the bottom surfaces
and/or the side surfaces with the thermally conductive resin 5. An
amount of thermally conductive resin flows through the through
holes 30 to underneath the bottom surfaces or around the side
surfaces of the LED substrates 2a to 2c shall be determined based
on the following: the height of the thermally conductive resin 5
that flows upward from the through holes 30 is set so as not to
exceed the heights of the LED substrates 2a to 2c.
[0056] Thereafter, the thermally conductive resin 5 is heated at
about 150.degree. C. for an hour for solidification. In
solidifying, the thermally conductive resin 5 hardly changes in
volume. Thus, the thermally conductive resin 5 will neither come
off nor develop cracks. While we assume here that the thermally
conductive resin 5 is a thermoplastic resin, a different
solidification method (light curing or normal temperature leaving)
has to be employed if the thermally conductive resin 5 is made of a
different material such as a photo-plastic resin or the like.
Because the manufacturing method described above is the same as
conventional methods, there is no need to add a different bonding
process and a different device. Thus, manufacturing cost increases
can be prevented.
[0057] Further, since the thermally conductive resin 5 is allowed
to flow upward from the through holes 30, there is no chance of the
thermally conductive resin 5 fouling the light-emitting surfaces of
the LED substrates 2a to 2c. This prevents the light intensity of
their LED chips from dropping.
[0058] In addition, because the thermally conductive resin 5 is
liquid, it can flow into small spaces. Thus, the thermally
conductive resin 5 can be filled in the spaces between the LED
substrates 2a to 2c on the substrate 3 even if the LED substrates
2a to 2c are closely spaced. Even in that case, high thermal
conductivity is maintained because the thermally conductive resin 5
can sufficiently surround the LED substrates 2a to 2c, and the
temperature differences among the LED substrates 2a to 2c can also
be reduced.
Embodiment 2
[0059] FIG. 3 is a cross section of an LED light source according
to Embodiment 2 of the invention. As illustrated, protrusions 307
are formed on the top surface of a heat sink plate 304, and
alignment holes 308 are formed in a substrate 303 so that each of
the protrusions 307 can be inserted into one of the alignment holes
308. By aligning the protrusions 307 with the alignment holes 308,
the position of the heat sink plate 304 relative to the substrate
303 can be determined.
[0060] The height of each of the protrusions 307 is greater than
the thickness of the substrate 303. Thus, the top ends 307a of the
protrusions 307 protrude from the top surface of the substrate 303
on which ceramic substrates 301a and 301b (i.e., LED substrates
300a and 300b) are mounted.
[0061] By applying the same bonding process as illustrated in FIGS.
2A to 2C, thermally conductive resin 305 applied between the heat
sink plate 304 and the substrate 303 flows upward from the through
holes 309 of the substrate 303 and then flows onto the top surface
of the substrate 303 on which the LED substrates 300a and 300b are
mounted, as illustrated in FIG. 3. Thus, the thermally conductive
resin 305 flowed onto the top surface of the substrate 303 contacts
the bottom surfaces and/or the side surfaces of the LED substrates
300a and 300b and also the protrusions 307 of the heat sink plate
304.
[0062] In the above structure, the ceramic substrates 301a and 301b
are connected to the heat sink plate 304 through the thermally
conductive resin 305. Thus, the heat of the LED substrates 300a and
300b is transferred not only through the heat transfer path
mentioned in Embodiment 1, but also from the side surfaces 301a and
301b of the LED substrates 300a and 300b through the protrusions
307 to the heat sink plate 304. Thus, the structure of Embodiment 2
is more effective in releasing the heat of the LED light source. In
addition, the structure of Embodiment 2 is capable of reducing the
temperature difference between the ceramic substrates 301a and 301b
of the LED substrates 300a and 300b and reducing the temperatures
of the ceramic substrates 301a and 301b as well.
Embodiment 3
[0063] FIG. 4 is a cross section of an LED light source according
to Embodiment 3 of the invention, which light source is intended
for use in a photolithography apparatus.
[0064] The LED light source 1A of FIG. 4 differs from its
counterparts of Embodiments 1 and 2 in that a lens substrate 402 is
placed on the ceramic substrates 401 of LED substrates 410. The
lens substrate 402 has windows 411, and a lens 412 is fit in each
of the windows 411 in order to prevent light dispersion. Each of
the lenses 412 is designed to convert radial light rays emitted
from the LED substrates 410 into parallel ones.
[0065] Each of the lenses 412 has a transmittance of 50% or greater
at the wavelength of the light from the LED substrates 410 and is
molded from inorganic glass such as quartz or the like or from
organic resin such as silicone resin, acrylic resin, or epoxy
resin. The lenses 412 can be spherical lenses, aspherical lenses,
or Fresnel lenses.
[0066] The LED light source 1A of FIG. 4 can be fabricated by a
process similar to that of FIGS. 2A to 2C of Embodiment 1. To
fabricate the LED light source 1A of Embodiment 3, the lens
substrate 402 having the lenses 412 is first bonded to a substrate
403 on which the LED substrates 410 were mounted by reflow
soldering. Then, the substrate 403 is aligned with and pressed
against a heat sink plate 404 on which thermally conductive resin
405 was applied. The pressing causes the thermally conductive resin
405, now located between the heat sink plate 404 and the substrate
403, to flow via the through holes 409 of the substrate 403 onto
the top surface of the substrate 403 (the top surface is the
surface on which the LED substrates 410 are mounted). Thus, the
thermally conductive resin 405 is supplied to contact with the
bottom surfaces and/or the side surfaces of the ceramic substrates
401 of the LED substrates 410.
[0067] Thereafter, the assembly of the heat sink plate 404 and the
substrate 403 is heated at about 150.degree. C. for an hour for
solidifying the thermally conductive resin 405. In solidifying, the
thermally conductive resin 405 hardly changes in volume. Thus, the
thermally conductive resin 405 will neither come off from the heat
sink plate 404, the substrate 403, and the LED substrates 410 nor
develop cracks therein. This prevents loss of heat transfer among
the heat sink plate 404, the substrate 403, and the LED substrates
410.
[0068] It should be noted that the above-mentioned process of
bonding the lens substrate 402 to the substrate 403 can instead be
performed after the process of heating the assembly of the heat
sink plate 404 and the substrate 403 for solidifying the thermally
conductive resin 405.
[0069] Since the LED substrates 410 and the heat sink plate 404 are
connected together by the thermally conductive resin 405, the heat
of the LED substrates 410 can be released through the heat transfer
path mentioned in Embodiment 1, which results in good heat release
capabilities of the LED light source 1A. This in turn leads to
small temperature variations among the ceramic substrates 401 of
the LED substrates 410 as well as reduction in the temperatures of
the ceramic substrates 401.
[0070] Note also that the lenses 412 to be fit in the windows 411
of the lens substrate 402 can be collimating lenses. In addition,
as stated above, the presence of the lenses 412 inside the windows
411 as illustrated in FIG. 4 allows conversion of the light rays
emitted from the LED substrates 410, which tend to disperse
radially, into vertical ones with respect to an area to be
illuminated (not illustrated). Thus, illumination light rays with
uniform intensity can be obtained for the illumination area facing
the LED light source.
Embodiment 4
[0071] FIG. 11A illustrates the configuration of a maskless
photolithography apparatus according to Embodiment 4 of the
invention in which LED light sources according to the invention are
used.
[0072] As illustrated in FIG. 11A, the photolithography apparatus
of Embodiment 4 includes the following components: an illumination
system 500; an integrator 503; a collimating mirror 504; a pattern
generation unit 505; a drive unit 5050 for driving the pattern
generation unit 505; a table 5060 on which to place a workpiece 506
or a substrate to be irradiated; and a control unit 510 for
controlling the drive unit 5050, the table 5060, and the
illumination system 500.
[0073] The illumination system 500 that radiates light for
lithography purposes includes multiple light sources 5001, 5002,
and 5003, and these light sources 5001 to 5003 are all attached to
a water-cooling jacket 501 for heat release purposes. The external
wires of the light sources 5001, 5002, and 5003 are connected via
harnesses 5021, 5022, and 5023 to power units 5024, 5025, and 5026,
respectively.
[0074] The arrangements of the light sources 5001 to 5003 including
their tilt angles with respect to the integrator 503 are designed
such that the light emitted from the light sources 5001 to 5003 is
incident on the integrator 503 efficiently. Although not
illustrated in FIG. 11A, the light sources 5001 to 5003 and the
integrator 503 extend in a direction vertical to the page on which
FIG. 11A is shown.
[0075] The light sources 5001 to 5003 of the illumination system
500 are such LED light sources as described in Embodiments 1 to 3.
Such light sources allow uniform illumination of a large area.
Moreover, because the light sources 5001 to 5003 are capable of
emitting light with substantially the same intensity with each
other, they have substantially the same length of life, thereby
extending the life of the illumination system 500.
[0076] In the above photolithography apparatus, the light emitted
from the illumination system 500 passes through the integrator 503.
The collimating mirror 504 then converges the light passed through
the integrator 503, converting it into a linear shaped light ray,
which is extending linearly along the lithography patterns formed
on the pattern generation unit 505 (which is vertical to the page
in FIG. 11A). The linear shaped light ray is projected on the
pattern generation unit 505. The light passes through the
lithography patterns formed on the pattern generation unit 505 is
projected onto the workpiece 506 on which a photosensitive material
(i.e., photoresist) is coated. By that, particular portions of the
photoresist are exposed to the light, thereby transferring the
patterns of the pattern generation unit 505 onto the photoregist
coated on the workpiece 506 (For simplification purposes, FIG. 11A
does not illustrate the optical focusing system of the
photolithography apparatus).
[0077] During the pattern transfer onto the workpiece 506, the
drive unit 5050 drives the pattern generation unit 505, and the
control unit 510 moves the workpiece 506 placed on the table 5060
at a particular speed in a particular direction. The above
photolithography apparatus can be the one disclosed, for example,
in Patent Document 3.
[0078] Since the optical converging system of the photolithography
apparatus of Embodiment 4 does not use a transmissive lens but uses
the collimating mirror 504, it is free from chromatic aberration.
The collimating mirror 504 also allows light exposure of smaller
and shaper patterns when multi-wavelength light is used as the LED
light source.
[0079] FIG. 11B illustrates light exposure conditions for the
illumination system 500 of the above photolithography apparatus.
The photolithography process generally includes the following
steps: workpiece loading; fixation of the workpiece to a particular
position; alignment of the workpiece with a mask; light exposure;
unfastening of the workpiece; and unloading of the workpiece. The
entire photolithography process often lasts 10 to 120 seconds, but
the light exposure step lasts 5 to 60 seconds.
[0080] In a conventional photolithography apparatus that involves
the use of a mercury lamp as its light source, the intensity of
light from the lamp is unstable right after electric power is
supplied to the lamp, which is due to temperature fluctuations of
the lamp. It takes about thirty minutes for the light intensity to
become stable. Accordingly, in using the conventional
photolithography apparatus, its mercury lamp has to be kept turned
on, so that the light intensity can be stabilized for light
exposure. In case of using the LED light sources according to the
invention, however, the light intensity stabilizes in a few
milliseconds after power supply. Therefore, the LED light sources
have only to be turned on during light exposure, which greatly
reduces power consumption by the photolithography apparatus.
* * * * *