JP2021026868A - Light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light source device capable of suppressing deterioration and extending a life. A light source device 100 includes a hemispherical or semi-elliptical first curved surface portion 111 that receives laser light, and a hemispherical or semi-elliptical spherical second curved surface portion 113 that faces the first curved surface portion 111. , A closed container 101 having a tubular portion 112 connecting the first curved surface portion 111 and the second curved surface portion 113, an assist gas 103 sealed in the closed container 101, and a first curved surface portion from the outside of the closed container 101. A light source 102 that irradiates the 111 with a laser beam is provided. [Selection diagram] Fig. 1

Description

The present invention relates to a light source device, for example, a light source device applicable to an electrodeless LPP light source.

An LPP (laser-produced plasma) light source is being studied as an inspection machine light source or an EUV (Extreme Ultraviolet) light source which is a semiconductor exposure apparatus. The LPP light source is a light source that emits EUV light from a target material that has been turned into plasma by being irradiated with laser light by condensing and irradiating a liquid or gas target material with laser light.

For example, Patent Document 1 describes a plasma light emitting device in which a gas is sealed in a spherical target bulb, the gas is irradiated with laser light, and plasma light is emitted from the excited gas.

Japanese Unexamined Patent Publication No. 2017-20442

In a high-brightness LPP light source, the illuminant is exposed to high temperatures, and the optical components, the housing supporting them, and the illuminant (bulb) are exposed to a harsh environment. Such a harsh environment affects the equipment maintenance cycle and lifespan.

Therefore, it has been required to extend the life of the light source.

The light source device of one embodiment includes a hemispherical or semi-elliptical first curved surface portion that receives laser light, a hemispherical or semi-elliptical spherical second curved surface portion that faces the first curved surface portion, and the first curved surface portion. A closed container including a tubular portion connecting the first curved surface portion and the second curved surface portion, an assist gas sealed in the closed container, and a laser beam irradiating the first curved surface portion from outside the closed container. It is equipped with a light source to be used.

According to the light source device of one embodiment, by providing the above-mentioned first curved surface portion, second curved surface portion, and tubular portion, the distance that the high-speed gas molecular flow of the assist gas turned into plasma reaches the wall surface of the closed container is long. As a result, the temperature of the gas decreases when it reaches the wall surface, so that the temperature rise of the wall surface of the closed container can be suppressed. Then, the life of the light source device including the closed container can be extended.

The light source device of one embodiment may preferably have a chip portion for closing the closed container after filling the assist gas in the tubular portion.

The light source device of one embodiment may preferably have a chip portion that closes the closed container after filling the assist gas in the second curved surface portion other than the extension of the optical axis of the laser beam.

According to the light source device of one embodiment, since the flow of the plasmaized gas does not hit the chip portion, crystallization and the occurrence of cracks in the chip portion having low strength can be avoided.

The light source device of one embodiment preferably includes a mirror that reflects the laser light from the light source and irradiates the first curved surface portion of the closed container with the laser beam, and the curved surface shape of the first curved surface portion is. The shape may be such that the laser beam is vertically incident.

According to the light source device of one embodiment, such a shape allows the laser light to be focused in a closed container without being refracted by the first curved surface portion 111. As a result, the attenuation (scattering) of the laser beam can be suppressed at the time of focusing.

In the light source device of one embodiment, preferably, the assist gas is Ar, Kr, Xe, He, Ne, N ₂ , Br ₂ , Cl ₂ , I ₂ , H ₂ O, O ₂ , H ₂ , CH _4. , NO, NO ₂ , CH ₃ OH, C ₂ H ₅ OH, CO ₂ , NH ₃ , 1 or more metal halides, Ne / Xe mixture, Ar / Xe mixture, Kr / Xe mixture, Ar / Kr / Xe mixture , ArHg mixture, KrHg mixture, and XeHg mixture may contain at least one of them.

The light source device of the present invention can suppress deterioration and extend the life.

It is sectional drawing of the light source apparatus which concerns on Embodiment 1. FIG. It is a schematic diagram which shows an example of the behavior of the assist gas in a spherical closed container. It is a schematic diagram which shows an example of the behavior of the assist gas in the closed container 101 of Embodiment 1. FIG. It is a graph which shows the relationship between the temperature of glass, the nucleation rate, and the growth rate. It is a graph which shows the relationship between the CW (Continuous wave) power of a laser, and the temperature of a closed container. It is a graph which shows the relationship between the CW power of a laser, and UV (Ultraviolet) power. It is sectional drawing of the light source apparatus which concerns on Embodiment 2. FIG. It is sectional drawing of the closed container of the light source device which concerns on another embodiment. It is sectional drawing of the closed container of the light source device which concerns on another embodiment. It is sectional drawing of the closed container of the light source device which concerns on another embodiment.

Embodiment 1
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of the light source device according to the first embodiment. In FIG. 1, the light source device 100 includes a closed container 101, a light source 102, and an assist gas 103.

The closed container 101 is a closed container in which the assist gas 103 is sealed. The closed container 101 is made of a material that transmits laser light and light emitted by an excited assist gas. For example, the material of the closed container 101 may be a quartz material or a sapphire material. Specifically, it is desirable that the material of the closed container 101 is a glass material. It is desirable that the material of the closed container 101 particularly contains a fused silica glass material. The closed container 101 includes a first curved surface portion 111, a tubular portion 112, a second curved surface portion 113, and a tip portion 114 when distinguished by shape.

The first curved surface portion 111 is a portion that receives laser light from the outside of the closed container 101. It is desirable that the first curved surface portion 111 has a shape that allows laser light to pass through without loss. That is, it is desirable that the first curved surface portion 111 has a shape orthogonal to the laser beam. For example, the first curved surface portion 111 is preferably hemispherical or semi-elliptical.

The tubular portion 112 is a tubular portion that connects the first curved surface portion 111 and the second curved surface portion 113. For example, when the first curved surface portion 111 and the second curved surface portion 113 have a hemispherical shape, it is desirable that the tubular portion 112 has a hollow cylindrical shape or a semi-elliptical spherical shape.

It is desirable that the second curved surface portion 113 has a shape that facilitates convection of the assist gas 103 in the closed container 101. For example, the second curved surface portion 113 may have a hemispherical shape. The second curved surface portion 113 is located so as to face the first curved surface portion 111.

The tip portion 114 closes the opening to be blown when shaping the shape of the closed container 101. After introducing the assist gas 103 into the closed container 101 from the tip portion 114, the opening is closed. Therefore, the tip portion 114 is a portion having a weaker strength than the other portions of the closed container 101.

Therefore, it is desirable that the chip portion 114 is formed at a position where the laser beam is not directly irradiated. For example, the tip portion 114 may be formed on the tubular portion 112 as shown in FIG. Further, the chip portion 114 may be formed on the second curved surface portion 113 other than the optical axis of the laser beam.

The light source 102 is a light source that emits a laser beam that excites the assist gas 103. The wavelength of the laser light emitted by the light source 102 may be any wavelength as long as it excites the assist gas 103. Further, a device that emits a general laser beam can be applied to the light source 102. The light source 102 is installed at a position and a direction in which the laser beam can be applied to the first curved surface portion 111 of the closed container 101. Further, the light source 102 may be provided with optical elements such as a mirror and a lens, if necessary. In FIG. 1, the light source 102 is represented not as an actual shape but as a functional block.

The assist gas 103 is a gas that is turned into plasma by irradiation with laser light. For example, the assist gas _{103, Ar, Kr, Xe, He} , Ne, N 2, Br 2, Cl 2, I 2, H 2 O, O 2, H 2, CH 4, NO, NO 2, CH 3 OH , C ₂ H ₅ OH, CO ₂ , NH ₃ , 1 or more metal halides, Ne / Xe mixture, Ar / Xe mixture, Kr / Xe mixture, Ar / Kr / Xe mixture, ArHg mixture, KrHg mixture, and XeHg It may be a gas containing at least one of the mixtures. Specifically, xenon is preferably used as the assist gas 103. The assist gas 103 may also be referred to as a working gas or an ionized gas. Further, the assist gas 103 may be in a solid state in a state where the temperature is lowered.

With the above configuration, the light source emits light. Next, the behavior of the assist gas in the closed container 101 will be described in comparison with the conventional spherical closed container. FIG. 2 is a schematic diagram showing an example of the behavior of the assist gas in the spherical closed container. Further, FIG. 3 is a schematic diagram showing an example of the behavior of the assist gas in the closed container 101 of the first embodiment.

In FIG. 2, the assist gas in the closed container is turned into plasma by irradiation with laser light. Then, the plasma-generated gas emits a part of the excited energy as light, and the gas, which is a plasma-charged particle, is immediately recombined. Then, the gas becomes a high-speed molecular flow by the rocket action, travels in the optical axis direction of the laser beam (the Z-axis positive direction in FIG. 2), and heads toward the glass wall surface of the closed container. This gas has a low probability (or number of times) of colliding with other gas molecules that move randomly before reaching the wall surface of the closed container. Therefore, the gas reaches the wall surface of the closed container without being deprived of much energy.

The gas that has become this high-speed molecular flow loses a lot of kinetic energy as soon as it reaches the glass wall surface of the closed container, heats the glass, and is reduced to low-temperature gas molecules. In this way, the gas transfers heat to the wall surface of the closed container by converting part of the kinetic energy into heat. The gas then convects along the wall of the vessel.

In this way, the part where the gas reaches in the closed container is the hottest place. However, when comparing the temperatures including the assist gas in the closed container, the locally generated plasma part has the highest temperature. However, it is considered that there is little heating due to radiation from this plasma part to the glass wall surface.

On the other hand, as shown in FIG. 3, the assist gas 103 in the closed container 101 is the same in that it is converted into plasma by laser light and emits light. However, the closed container 101 has a shape longer in the gas moving direction than the spherical closed container. Therefore, the probability (or the number of times) that the gas collides with other gas molecules that move randomly before reaching the wall surface of the closed container by rocket action is higher than that in FIG. As a result, the gas reaches the wall surface of the closed container in a state of being deprived of energy by collision with other gas molecules. Since the energy has already been deprived when the gas reaches the wall surface of the closed container 101, the energy transferred to the wall surface of the closed container is less than that in FIG. The gas then convects along the wall of the vessel.

When the assist gas was actually sealed in the closed containers of the shapes shown in FIGS. 2 and 3 and irradiated with laser light, the glass of the closed container crystallized and became cloudy in less than 1000 hours in the spherical closed container of FIG. Symptoms appeared. And a crack was generated in the crystal part. In the closed container of FIG. 2, it is considered that the gas of high-speed particles has enough energy for the alteration of the glass composition and promotes the crystallization of the glass under high temperature conditions. Moreover, when the plastic deformation region peculiar to glass is exceeded, the glass becomes brittle. As a result, the high-pressure airtight container may burst. In addition, in a spherical airtight container, the gas-sealed tip is located on the crown due to the optical design, so crystallization of glass particularly affects the strength.

On the other hand, in the closed container 101 of FIG. 3, since the distance until the assist gas 103 reaches the wall surface of the closed container 101 is long, the probability (or the number of times) that the assist gas 103 collides with other gas molecules is high, and the assist gas 103 will lose more kinetic energy. As a result, in the closed container 101 of FIG. 3, the temperature of the wall surface is lower than that of the closed container of FIG. 2 (that is, the temperature rise width is small).

Next, the wall surface temperature of the closed container will be described. FIG. 4 is a graph showing the relationship between the temperature of glass and the nucleation rate and growth rate. In FIG. 4, the vertical axis shows the nucleation rate and the growth rate in the glass, and the horizontal axis shows the temperature of the glass. As shown in FIG. 4, when the temperature of the glass becomes higher than the transition temperature, nucleation proceeds. Then, when the temperature of the glass rises further, crystallization progresses in the glass. As a result, the amorphous glass crystallizes. Then, the glass cannot maintain its strength and is damaged. Therefore, it is desirable that the wall surface temperature of the closed container is as low as possible.

FIG. 5 is a graph showing the relationship between the CW (Continuous wave) power of the laser and the temperature of the closed container. In FIG. 5, the vertical axis represents the temperature (° C.) of the closed container, and the horizontal axis represents the CW power (W) of the laser irradiating the closed container.

As shown in FIG. 5, in the conventional spherical closed container, the wall surface temperature of the closed container reaches 650 ° C.-750 ° C. when the CW power is 2500 W. On the other hand, in the closed container 101 of the optical device of the first embodiment, the wall surface temperature is 350 ° C. or lower when the CW power is 2500 W. Further, even if the CW power is raised to 4000 W, the wall surface temperature of the closed container 101 is about 450 ° C. Therefore, in the optical device of the first embodiment, the wall surface temperature of the closed container can be lowered by 250 ° C. or more as compared with the conventional spherical closed container.

FIG. 6 is a graph showing the relationship between the CW power of the laser and the UV (Ultraviolet) power. In FIG. 6, the vertical axis represents the UV power (W) that emits light, and the horizontal axis represents the CW power (W) of the laser that irradiates the closed container.

Referring to FIG. 6 together with FIG. 5, in the case of a spherical closed container, the wall surface temperature of the closed container reaches 650 ° C.-750 ° C. when the CW power is 2500 W. It is difficult to increase the CW power because a further temperature rise leads to damage to the closed container. The UV power at this point is about 240 W, and it is difficult to further increase the UV power emitted.

On the other hand, in the closed container 101 of the optical device of the first embodiment, even if the CW power is raised to 4000 W, the wall surface temperature of the closed container 101 is about 450 ° C., but the UV power reaches 340 W. Therefore, in the optical device of the first embodiment, the wall surface temperature of the closed container 101 is lower than that of the spherical closed container, and the UV power emitted is higher than that of the closed container having a spherical wall temperature. Further, since the wall surface temperature of the closed container 101 is significantly lower than the softening point and crystallization point temperatures of the glass, the life of the closed container 101 can be extended.

As described above, according to the optical device of the first embodiment, by providing the above-mentioned first curved surface portion, second curved surface portion and tubular portion, the high-speed gas molecular flow of the assist gas turned into plasma reaches the wall surface of the closed container. Since the reachable distance becomes longer and the temperature of the gas at the time of reaching the wall surface decreases, it is possible to suppress the temperature rise of the wall surface of the closed container. Then, the life of the light source device including the closed container can be extended. Further, according to the optical device of the first embodiment, it is possible to suppress the temperature rise of the wall surface of the closed container and further increase the UV power that emits light without damaging the closed container.

Further, according to the optical device of the first embodiment, since the flow of the plasmaized gas does not hit the chip portion, crystallization and the occurrence of cracks in the chip portion having low strength can be avoided.

Embodiment 2
In the second embodiment, an example applied to a specific optical device including a lens and a mirror in the optical system will be described. FIG. 7 is a cross-sectional view of the light source device according to the second embodiment.

In FIG. 7, the light source device 700 includes a light source 701, a lens 702, a mirror 703, a half mirror 704, an elliptical mirror 705, a closed container 101, and a lens 706. In FIG. 7, the same configuration as in FIG. 1 is assigned the same number and the description thereof will be omitted.

The light source 701 is a light source that emits a laser beam that excites the assist gas 103 in the closed container 101. The light source 701 emits a laser beam toward the lens 702.

The lens 702 is a lens that refracts the laser light emitted by the light source 701. For example, the lens 702 is a concave lens, and the width of the laser beam may be widened.

The mirror 703 is a mirror that reflects the laser beam transmitted through the lens 702. The laser beam is reflected by the mirror 703 in the direction of the half mirror 704.

The half mirror 704 transmits the laser light reflected by the mirror 703 and advances to the elliptical mirror 705. Further, the half mirror 704 reflects the light emitted from the closed container 101 and advances in the direction of the lens 706.

The elliptical mirror 705 is a mirror that converges the laser light transmitted through the half mirror 704 so that the converged laser light is irradiated to the closed container 101.

The lens 706 refracts the light emitted from the closed container 101 into parallel light. This light is used for inspection machines and the like.

As described above, according to the light source device of the second embodiment, by irradiating the closed container with the focused laser light, it is possible to irradiate the laser light having a large output, and as a result, the output of the light emission can be increased.

Further, it is desirable that the curved surface shape of the first curved surface portion 111 is a shape in which the laser light reflected by the elliptical mirror 705 is vertically incident. For example, it is desirable that the curved surface shape of the first curved surface portion 111 is a hemispherical shape. With such a shape, the laser light can be focused in the closed container 101 without being refracted by the first curved surface portion 111. As a result, the attenuation (scattering) of the laser beam can be suppressed at the time of focusing.

The present invention is not limited to the above embodiment, and can be appropriately modified without departing from the spirit. For example, the cross-sectional shape of the tubular portion in the optical axis direction may be either a straight line or a curved line. FIG. 8 is a cross-sectional view of a closed container of the light source device according to another embodiment. In the closed container 101 of FIG. 8, the opening diameter of the second curved surface portion 113 is larger than the opening diameter of the first curved surface portion 111. The opening of the tubular portion 112 has a size corresponding to the opening of the first curved surface portion 111 and the opening of the second curved surface portion 113, and the tubular portion 112 has a conical shape with the apex portion cut off.

Further, the tubular portion 112 of FIG. 8 may have a curved side surface. FIG. 9 is a cross-sectional view of a closed container of the light source device according to another embodiment. In FIG. 9, the opening diameter of the second curved surface portion 113 is larger than the opening diameter of the first curved surface portion 111, as in FIG. The opening of the tubular portion 112 has a size corresponding to the opening of the first curved surface portion 111 and the opening of the second curved surface portion 113. However, in FIG. 9, the tubular portion 112 has a curved hollow tubular shape.

Further, the tip portion 114 may be provided in addition to the tubular portion 112. Specifically, it may be a region other than the region of the second curved surface portion 113 where the assist gas becomes a high-speed molecular air flow due to the laser light and collides. That is, it may be a region other than the extension of the optical axis of the laser beam in the second curved surface portion 113. FIG. 10 is a cross-sectional view of a closed container of the light source device according to another embodiment. In FIG. 10, the chip portion 114 is provided on the second curved surface portion 113. Specifically, it is preferable that the angle α from the center of the hemispherical shape of the second curved surface portion in the Z-axis direction is larger than 0 degrees and 90 degrees or less.

100,700 Light source device 101 Sealed container 102,701 Light source 103 Assist gas 111 First curved surface part 112 Tube part 113 Second curved surface part 114 Chip part 702,706 Lens 703 Mirror 704 Half mirror 705 Elliptical mirror

Claims (5)

A hemispherical or semi-elliptical first curved surface portion that receives a laser beam, a hemispherical or semi-elliptical spherical second curved surface portion that faces the first curved surface portion, and the first curved surface portion and the second curved surface portion. A closed container with a tubular part that connects the parts, and
The assist gas sealed in the closed container and
A light source device including a light source that irradiates the first curved surface portion with laser light from the outside of the closed container. The light source device according to claim 1, wherein the cylinder portion is provided with a chip portion that closes the closed container after filling the assist gas. The light source device according to claim 1, wherein a chip portion that closes the closed container after filling the assist gas is provided on the second curved surface portion other than the extension of the optical axis of the laser beam. A mirror that reflects the laser light from the light source and irradiates the first curved surface portion of the closed container with the laser light is provided.
The light source device according to any one of claims 1 to 3, wherein the curved surface shape of the first curved surface portion is a shape in which the laser beam is vertically incident. It said assist _{gas, Ar, Kr, Xe, He} , Ne, N 2, Br 2, Cl 2, I 2, H 2 O, O 2, H 2, CH 4, NO, NO 2, CH 3 OH, C ₂ H ₅ OH, CO ₂ , NH ₃ , 1 or more metal halides, Ne / Xe mixture, Ar / Xe mixture, Kr / Xe mixture, Ar / Kr / Xe mixture, ArHg mixture, KrHg mixture, and XeHg mixture The light source device according to any one of claims 1 to 4, which includes at least one.

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