Patent Application
20100328638
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
The LED substrate 10 of
As illustrated in
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
As another heat release structure, Patent Document 1 also discloses such an LED light source structure as illustrated in
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.
As a modification example of the LED substrate 10 of
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.
Further, Japanese Unexamined Patent Application Publication No. 2006-250982 (Patent Document 3) discloses a maskless photolithography apparatus.
As stated above, in the LED light source of Patent Document 1 as illustrated in
If multiple LED substrates 10a, 10b, and 10c are closely arranged on the substrate 17 as illustrated in
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.
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 LED 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.
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.
Those disclosed in Patent Document 2 are also susceptible to the LED temperature variations.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Furthermore, application of the LED light source of the invention to a photolithography apparatus leads to less power consumption during light exposure.
Embodiments of the present invention will now be described with reference to the accompanying drawings.
Each of the LED substrates 2a to 2c is structurally the same as the LED substrate 10 of
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
As illustrated in
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.
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.
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/° C., and its viscosity rate is from 10 to 100 Pa·s. 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.
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
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.
Next, a manufacturing process of the LED light source 1 is described with reference to
As illustrated in
Then in
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.
Referring to
Thereafter, the thermally conductive resin 5 is heated at about 150° 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.
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.
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.
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.
By applying the same bonding process as illustrated in
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.
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.
The LED light source 1A of
Thereafter, the assembly of the heat sink plate 404 and the substrate 403 is heated at about 150° 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.
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.
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.
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
As illustrated in
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.
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
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.
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
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.
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-155179 | Jun 2009 | JP | national |
