JP2006293197A - Exposure light source using semiconductor laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain high-accuracy parallel light to irradiate a substrate through a photomask. <P>SOLUTION: The exposure light source U comprises a semiconductor laser 1 and an optical system 7, wherein the optical system 7 includes a first lens group 3, an optical polygonal column 4 and a second lens group 5. Light 2 emitted from the semiconductor laser 1 is converged by the first lens group 3 onto the entrance face of the optical polygonal column 4. The light whose luminance is homogenized by the optical polygonal column 4 is converted into parallel light 6 by the second lens group 5 to irradiate the substrate 11 through a photomask 8. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  In the present invention, a pattern drawn on a photomask is formed by irradiating the substrate with light through a photomask by placing a photomask facing the photosensitive film (photoresist) formed on the surface of the substrate. The present invention relates to an exposure light source for use in an exposure process to be transferred onto a photosensitive film on a substrate surface.

In recent years, circuit patterns of printed circuit boards and the like have been improved in definition, and an exposure process for faithfully transferring a high-definition pattern drawn on a photomask to the substrate is desired.
The exposure method includes so-called “contact exposure” in which light is applied to the substrate through the photomask while the photomask is in close contact with the photosensitive film formed on the surface of the substrate, and the photomask and the substrate are lightly contacted. There are so-called “contact exposure” in which exposure is performed in a state in which the exposure is performed, and so-called “gap exposure (non-contact exposure)” in which exposure is performed with a gap provided between the photomask and the substrate. Compared to contact exposure and contact exposure, gap exposure does not cause the photomask and the substrate to contact each other, so there is no generation of scratches due to contact between the photomask and the substrate, and the adhesion of dust is drastically reduced. Further, the gap exposure does not require time for bringing the photomask and the substrate into close contact with each other, and thus the processing speed is increased. Furthermore, since there is no misalignment due to vacuum suction when the photomask and the substrate are brought into close contact with each other, the alignment accuracy between the photomask and the substrate is also improved. As described above, the gap exposure can be said to be an excellent exposure method compared to the contact exposure and the contact exposure.

  However, when high-definition pattern transfer is performed by gap exposure, the light irradiated to the photomask and the substrate is high-precision parallel light with a small collimation half angle and declination angle over the entire irradiation area. And a uniform illuminance distribution must be obtained.

  In order to obtain such highly accurate irradiation light, the size of the illuminant is extremely small due to geometric optics, and the light emitted from the illuminant is converted into parallel light with uniform light quality including illuminance. It is necessary that the accuracy of the optical system for conversion is high. In addition, it is optically desirable that the wavelength of the irradiated light be a single wavelength equal to the photosensitive wavelength of the photosensitive film (photoresist) formed on the surface of the substrate.

  However, the arc length of a lamp conventionally used as a light emitter is about 5 to 10 mm in a high-power lamp for performing exposure by irradiating the entire surface of a large substrate (approximately 500 mm square or more) at once. large.

In addition, since the light emitted from the lamp is emitted at a wide angle, the light emitted from the lamp is first condensed by a concave mirror, and then the illuminance is made uniform and converted into parallel light by a lens, a reflecting mirror, or the like. However, since the optical system is complicated and large, it is difficult to increase the accuracy of the optical system from the viewpoint of price. Thus, when a lamp is used as a light emitter as in the past, the light emitter is large. Since the accuracy of the optical system cannot be high, the light quality of the irradiated light is limited to a collimation half angle of 1.0 °, a declination angle of 1.0 °, and an illuminance distribution of about 10%. there were.

  When a conventional lamp with poor light quality is used as a light source for exposure, the contact exposure described above has no practical problem except for extremely thin patterns, but in gap exposure, it is drawn on a photomask. It was difficult to faithfully transfer the pattern onto the photosensitive film on the substrate surface.

  In the present invention, light irradiated onto a substrate through a photomask is made to be parallel light with higher accuracy than conventional light, and thereby, a gap exposure which is an excellent exposure method can be more practically used. The problem is to do.

  Therefore, the present invention solves the above problems by using a semiconductor laser as a light emitter instead of a conventional lamp and combining it with a simple and highly accurate optical system to achieve irradiation with high-precision parallel light. It is something to try.

  Since the size of the light emitting part of the semiconductor laser is very small, about 0.1 mm or less, it is easy to convert it into highly accurate parallel light, and the radiation angle of the light emitted from the light emitting part is narrow, so a simple optical system You can achieve your purpose.

Therefore, according to the present invention,
A photomask is placed opposite to the photosensitive film formed on the surface of the substrate, and light is applied to the substrate through the photomask, so that the pattern drawn on the photomask is formed on the photosensitive film on the substrate surface. An exposure light source used in an exposure process for transferring, comprising a semiconductor laser and an optical system, and using these to convert light emitted from the semiconductor laser into parallel light and irradiate the photomask and the substrate An exposure light source made is provided.

  The optical system includes a first lens group, an optical polygonal column, and a second lens group, which are arranged in order from the semiconductor laser toward the substrate, and emits light emitted from the semiconductor laser. The light may be condensed on the incident surface of the optical polygonal column by the first lens group, emitted with the illuminance uniformized by the optical polygonal column, and converted into parallel light by the second lens group.

The collimation half angle and the declination angle of the parallel light applied to the photomask and the substrate can both be within 0.5 degrees.
According to the present invention, a scanning exposure light source comprising a plurality of the above-described exposure light sources arranged to irradiate the substrate with light while moving relative to the substrate to be exposed. Is also provided.

The exposure may be performed in a state where a photomask is arranged close to the photosensitive film formed on the surface of the substrate with an arbitrary interval.
Alternatively, the exposure may be performed in a state where a photomask is placed in contact with the photosensitive film formed on the surface of the substrate.

Reference will now be made in detail to the preferred embodiments of the present invention with reference to the accompanying drawings and graphs.
First, the relationship between light quality and transfer accuracy in gap exposure will be described with reference to FIG. FIG. 1A is a principle diagram showing the relationship between light quality and transfer accuracy in gap exposure, and shows a photomask 8 and a substrate 11 facing each other with a gap D therebetween. FIG. 1B is a graph showing the illuminance distribution on the substrate 11.

On the surface 8 of the photomask facing the substrate 11 side, non-translucent portions 9 are drawn on both sides of the translucent portion T having the pattern width L.
The parallel light 12 emitted from the light source is applied to the photosensitive film (photoresist) 10 formed on the substrate 11 through the light transmitting portion T having the pattern width L of the photomask 8, thereby having the pattern width L. The drawn line is transferred onto the photosensitive film 10.

  As described above, the parallel light 12 has an inclination angle represented by the declination angle θ and the collimation half angle θ2. The declination angle θ is a square angle of the parallel light 12 with respect to the photomask 8 and is represented by 90 ° −θ1. On the other hand, the collimation half angle θ2 is an angle related to the size of the light source viewed from the photomask 8 side, and may be regarded as an inclination angle with a line indicating the parallel light beam 12 as a center line.

The accuracy of transferring the transmission part T having the pattern width L to the photosensitive film 10 on the substrate 11 is mainly influenced by the collimation half angle θ2.
As shown in the drawing, theoretically, the light irradiated to the photosensitive film 10 at the collimation half angle θ2 has zero illuminance at the position C1, 50% at C2, and 100% at the position C3. This illuminance distribution is shown in a graph as shown in FIG. 1B, and a region G between C1 and C3 is called a gray zone. In this gray zone G, since the illuminance is non-uniform, unstable transfer is performed, which causes a decrease in transfer accuracy. Accordingly, in order to reduce the value of the gray zone G and improve the transfer accuracy, it is desired to reduce the collimation half angle θ2.

  This will be described based on specific numerical values. The gap D between the photomask 8 and the substrate 11 is set to 0.3 mm in consideration of the flatness of the photomask 8 and the substrate 11. In addition, since the pattern width L is generally 50 to 75 μm, the pattern width L is set to 50 μm (0.05 mm). Under this condition, when the collimation half angle θ2 is 1.0 ° which is the limit value of the conventional lamp light source, the width of the gray zone G is 10.5 μm. In the gray zone G, an area with an illuminance of 70% or less does not contribute to pattern transfer, but the remaining 30% of an illuminance with an illuminance of 70% or more is an unstable area that affects the transfer accuracy. The width is 3.1 μm. Generally, the allowable transfer accuracy is ± 2 to 5%, but the value of 3.1 μm is ± 6% for the pattern width of 50 μm, which exceeds the allowable transfer accuracy. Further, since errors such as the gap D, declination angle, and illuminance distribution are also affected, it can be said that gap exposure is difficult under the above conditions.

  Next, the case of a semiconductor laser used for the exposure light source according to the present invention will be considered. When a semiconductor laser is used, the collimation half angle θ2 can be 0.5 ° or less. When the collimation half angle θ2 is set to 0.5 °, the transfer accuracy is about twice that when the collimation half angle θ2 is 1.0 °. Therefore, it can be said that the gap exposure under the above conditions is sufficiently possible. As described above, when the collimation half angle θ2 is 0.5 ° or less, gap exposure can be performed with an acceptable transfer accuracy for a pattern width of 50 μm or more which is generally employed.

  Furthermore, according to the present invention, since the collimation half angle θ2 can be set to 0.5 ° or less, it is also possible to realize gap exposure of a high-definition pattern having a pattern width of 50 μm or less.

However, since the output of the semiconductor laser is much smaller than that of the lamp, it is impossible to perform exposure by irradiating the entire surface of the large substrate at once.
Therefore, in the present invention, a combination of a semiconductor laser and an optical system is used as an “exposure light source using a semiconductor laser” to obtain a necessary illuminance by irradiating a small area on the substrate with light emitted from the semiconductor laser. Like that. In order to perform exposure by irradiating the entire surface of a large substrate, a plurality of exposure light sources using semiconductor lasers are arranged, and light is irradiated onto the substrate while moving relative to the substrate to be exposed. A light source for scanning exposure is configured.

  The arrangement of a plurality of exposure light sources using semiconductor lasers must be such that the substrate is uniformly irradiated during scanning exposure. That is, when the substrate is irradiated with light while the scanning exposure light source is moved relative to the substrate, the irradiation by the light source of each unit is performed so that the exposure amount along the direction orthogonal to the relative movement direction is made uniform. The shape of the region and the degree of overlap between adjacent irradiation regions are set.

  When scanning exposure is performed with a part of the adjacent irradiation areas overlapping, if the declination angle of the parallel light described above is large, the light of the adjacent irradiation areas crosses and the light quality deteriorates, and the transfer accuracy is reduced. Therefore, it is desirable to make the declination angle as small as possible along with the collimation half angle.

By configuring the scanning exposure light source in this way, it becomes possible to expose a large substrate using a semiconductor laser having a small individual output.
A semiconductor light-emitting element light source has many excellent characteristics as compared with a lamp. That is, since the light emitted from the light emitting source is emitted at a narrow angle, a concave mirror for condensing light is not necessary, and high-precision light irradiation is possible by combining with a small and simple optical system.

  In addition, since the semiconductor laser can be easily turned on and off, the light can be turned on and off without using a shutter necessary for the lamp, so that the structure of the light source can be further downsized. Therefore, it is easy to configure a light source for scanning exposure by arranging a plurality of such small and lightweight light sources, thereby improving reliability and reducing the cost.

In addition, the semiconductor laser has many features such as a very small amount of heat generation, a small cooling load, and a long life, so that it can be easily maintained.
Further, since the light emitted from the semiconductor laser has a single wavelength, there is no difference in the refractive index with respect to the optical system such as a lens, which is suitable for obtaining highly accurate irradiation light.

Even if a scanning exposure light source is configured by using a plurality of small lamp light sources, the light source is complicated and large, and the light quality is inferior to that of a semiconductor laser light source.
FIG. 2 is a schematic side view of an embodiment of an exposure light source U using a semiconductor laser according to the present invention. As illustrated, the exposure light source U includes a semiconductor laser 1 and an optical system 7. The optical system 7 includes a first lens group 3, an optical polygonal column 4, and a second lens group 5 arranged in order from the semiconductor laser 1 toward the substrate 11. The light 2 emitted from the semiconductor laser 1 is condensed on the incident surface of the optical polygonal column 4 by the first lens group 3, and is emitted after the illuminance of the light is made uniform by the optical polygonal column 4. Is converted into parallel light 6 and irradiated onto the photomask 8 and the substrate 11. As a result, the pattern drawn on the photomask 8 is transferred to the photosensitive film 10 on the substrate 11.

As the optical polygonal column 4, a hollow optical polygonal column whose inner surface is a mirror surface may be used.
FIG. 3 is a schematic plan view of a scanning exposure light source S configured by arranging a plurality of exposure light sources U using a semiconductor laser shown in FIG. 2 in order to perform exposure by irradiating the entire surface of a large substrate. FIG. The scanning exposure light source S irradiates the substrate with light while moving relative to the substrate to be exposed.

  FIG. 3 also shows an irradiation region (quadrangle) R of light irradiated to the photomask and the substrate by each exposure light source U and its arrangement. A circle indicated by a dotted line represents the optical system 7 of each exposure light source U. In the arrangement of the irradiation regions R, when light is irradiated toward the substrate while moving the scanning exposure light source S in the scanning direction indicated by the arrow, the exposure amount along the direction orthogonal to the relative movement direction is made uniform. In this way, ½ of the irradiation regions R adjacent to each other is overlapped.

A symbol A in FIG. 3 indicates an effective scanning width capable of maintaining a uniform exposure amount.
The irradiation region R may have a shape other than a quadrangle.

  As described above, the light source for exposure using the semiconductor laser according to the present invention can produce high-precision parallel light, which is difficult with the light source of the conventional lamp, and is thus an excellent exposure method. Exposure was made feasible for high-precision pattern transfer.

The exposure light source using the semiconductor laser according to the present invention is suitable for exposure of glass substrates used for liquid crystal displays and the like in addition to printed circuit boards.
Furthermore, the light source for exposure using the semiconductor laser according to the present invention can also be used in contact exposure.

It is a figure explaining the relationship between the light quality and transfer precision in gap exposure, (a) is a principle figure, (b) is a graph which shows the illumination intensity distribution on a board | substrate. The schematic side view of one Example of the light source for exposure using the semiconductor laser by this invention. FIG. 3 is a schematic plan view of a scanning exposure light source configured by arranging a plurality of exposure light sources using a semiconductor laser shown in FIG. 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor laser, 2 Light from semiconductor laser, 3 1st lens group, 4 Optical polygonal column, 5 2nd lens group, 6 Parallel light, 7 Optical system, 8 Photomask, 9 Non-translucent part, 10 Photosensitive film, 11 Substrate, A Effective scanning width with uniform photosensitivity, D Gap between photomask and substrate, G gray zone, L pattern width, R irradiation area, S scanning exposure light source, T translucent part, U semiconductor Exposure light source using laser, θ declination angle (θ = 90 ° −θ1), θ2 collimation angle.

Claims (6)

A photomask is placed opposite to the photosensitive film formed on the surface of the substrate, and light is applied to the substrate through the photomask, so that the pattern drawn on the photomask is formed on the photosensitive film on the substrate surface. An exposure light source used in an exposure process for transferring, comprising a semiconductor laser and an optical system, and using these to convert light emitted from the semiconductor laser into parallel light and irradiate the photomask and the substrate Light source for exposure made. The optical system includes a first lens group, an optical polygonal column, and a second lens group, which are arranged in order from the semiconductor laser toward the substrate, and emits light emitted from the semiconductor laser. 2. The light is condensed on an incident surface of the optical polygonal column by a lens group, is emitted with the illuminance uniformized by the optical polygonal column, and is converted into parallel light by the second lens group. Light source for exposure. 3. The exposure light source according to claim 1, wherein a collimation half angle and a declination angle of the parallel light applied to the photomask and the substrate are both within 0.5 degrees. 4. A scanning type exposure apparatus comprising a plurality of exposure light sources according to claim 1, wherein the exposure light source is irradiated with light while moving relative to the substrate to be exposed. light source. The exposure light source according to claim 1, wherein a photomask is arranged close to the photosensitive film formed on the surface of the substrate at an arbitrary interval. The exposure light source according to claim 1, wherein a photomask is disposed in contact with the photosensitive film formed on the surface of the substrate.

Images