WO2017212683A1 - Laser-driving light source device - Google Patents

Abstract

[Problem] To attempt to provide a laser-driving light source device provided with a laser source, and a plasma container on which laser light from the laser source is condensed and made to be incident to generate plasma, wherein excitation light emitted from the plasma container is inhibited from returning to the laser source once again, and the laser source is prevented from being damaged by being heated by the returning excitation light. [Solution] The present invention is characterized in that a filter which blocks the excitation light from the plasma container is disposed between the laser source and a laser light condensing position inside the plasma container.

Description

Laser drive light source device

The present invention relates to a laser-driven light source device, and more particularly to a laser-driven light source device used as a light source for a semiconductor, a liquid crystal substrate or a color filter, or a light source for a projector.

Conventionally, for example, as a light source mounted on a semiconductor exposure apparatus or the like, a discharge lamp that emits ultraviolet rays has been widely used. The discharge lamp has a pair of electrodes arranged opposite to each other in a bulb in which mercury and a rare gas are sealed, energizes between the electrodes to generate plasma, and maintains discharge by electric energy supplied through the electrodes. ing. Further, the light emitted from the discharge lamp is required to have higher brightness and higher output in order to shorten the processing time and cope with large area exposure. However, in order to form and maintain such plasma, there is a problem that the electrode itself becomes very high temperature, and the material constituting the electrode evaporates and scatters, causing blackening of the inner surface of the bulb.

Various countermeasures have been studied for such problems. For example, in the laser-driven light source device disclosed in Japanese Translation of PCT International Publication No. 2009-532829 (Patent Document 1), laser light is condensed from the outside into a gas sealed in a chamber (quartz bulb) and excited by the laser light. By generating a high-temperature plasma of the sealed gas, stable emission intensity with a spectral distribution according to the component composition of the sealed gas can be obtained, and furthermore, the emission center position is determined by the focal position of the laser beam from the outside. It is expected as a light source that can always be maintained stably.

9 and 10 show a schematic structure of the prior art. 9, the laser drive light source device 30 includes a laser source 31 and a chamber (plasma container) 32, and the chamber 32 is provided with a concave reflecting mirror 33 such as a paraboloid so as to surround it. Laser light A from the laser source 31 is condensed by the condensing optical system 34, and is collected and incident on the chamber 32 through the incident window 35 provided in the rear opening of the concave reflecting mirror 33. Thereby, the plasma P is generated in the chamber 32, the encapsulated light emitting element such as mercury or xenon is excited, and the excitation light EL having a wavelength corresponding to the light emitting element is emitted.

FIG. 10 discloses another embodiment. The chamber 32 is provided with a pair of electrodes 32a and 32b as an ignition source, and a preliminary discharge is performed between the pair of electrodes 32a and 32b. The plasma P is generated by irradiating the laser beam A.

In such a laser-driven light source device 30, as the excitation light EL generated in the chamber (plasma container) 32 by the laser light A, light in a wide wavelength range including the used wavelength is generated.
By the way, although the excitation light EL generated in the plasma container 32 is irradiated to the object, a part of the excitation light EL also returns to the laser source 31 side. The light returning to the laser source 31 is incident on the laser source 31, which heats the laser source 31 and eventually damages the laser source 31.

Special table 2009-532829

In view of the above-described problems of the prior art, the present invention provides a laser-driven light source device including a laser source and a plasma container that generates a plasma by condensing and entering a laser beam from the laser source. It is an object of the present invention to provide a laser-driven light source device that prevents the emitted excitation light from returning to the laser source again and prevents the laser source from being damaged.

In order to solve the above-described problems, in the laser drive light source device according to the present invention, a filter that blocks excitation light from the plasma container is disposed between the laser source and a laser beam condensing position in the plasma container. It is characterized by being.
The filter may be a long pass filter.
The filter may be a band pass filter that is configured by a combination of a long pass filter and a short pass filter and transmits only the laser beam.
Further, the plasma container has a tube shape, and a concave reflecting mirror surrounding the plasma container is provided. The plasma container includes a concave reflecting mirror, an incident window provided in a rear opening of the concave reflecting mirror, and an emission window provided in a front opening of the concave reflecting mirror, and the concave reflecting mirror and the A sealed space is formed by the entrance window and the exit window. Further, the filter is provided in the incident window.

In the present invention, a filter that blocks the excitation light is disposed between the laser source and the laser beam condensing position of the plasma container, so that the light is emitted from the plasma container and returns to the laser source side. Since the excitation light is blocked, the light does not enter the laser source and does not enter, and the laser source is not damaged.

Explanatory drawing of 1st Example of this invention Example of transmission spectrum showing characteristics of filter used in the present invention Explanatory drawing of 2nd Example of this invention Explanatory drawing of 3rd Example of this invention Explanatory drawing of 4th Example of this invention Explanatory drawing of 5th Example of this invention. Explanatory drawing of 6th Example of this invention. Explanatory drawing of 7th Example of this invention Illustration of prior art Illustration of other prior art

FIG. 1 shows a laser-driven light source device 1 according to a first embodiment of the present invention. The laser-driven light source device 1 includes a plasma container 2, a laser source 3, and a condensing means 4. The condensing means 4 is composed of, for example, a condensing lens, and is provided on the optical path from the laser source 3 to the plasma container 2.
Although various forms can be adopted for the plasma vessel 2, in this embodiment, it has a tube shape. Here, the tube shape means an arc tube shape such as a substantially spherical shape or a substantially elliptic rotating body shape in the lamp technology.
The laser beam A oscillated from the laser source 3 is condensed by the condensing means 4 and enters the plasma container 2 and is condensed inside the plasma container 2.

The inside of the plasma vessel 2 is filled with a luminescent element, but various luminescent elements are used depending on the application. For example, mercury is used as a light emitting element as a light source for exposure. For example, as a light source for a projector, xenon gas is used as a light emitting element.

The plasma container 2 receives the laser light A from the laser source 3 and emits the excitation light EL from the light emitting element. Therefore, the plasma container 2 transmits the laser light A from the laser source 3 and excites the light emission gas. It is composed of a member that transmits light EL. Specifically, for example, in the case of an exposure light source, when the wavelength of the laser light A from the laser source 3 is 1064 nm, the light emitting element is mercury, and the wavelength 365 nm of the excitation light EL is used, The plasma container 2 is made of, for example, quartz glass that transmits a wavelength of 1064 nm and transmits a wavelength of 365 nm.

The laser source 3 includes a medium to be excited, a light source that injects energy into the medium, a resonator that resonates the excitation light when the medium is excited by the light source, and the like. The light A is incident on the plasma container 2 while being condensed by the condensing means 4 and is condensed at the condensing position inside.
In addition, the condensing position of the laser beam A is not limited to the center point of the plasma container 2, and may be an arbitrary position inside the plasma container 2. However, it can be expected that the thermal influence of the plasma on the wall surface of the plasma container 2 is not locally biased and uniform because the condensing position is at the center position of the plasma container 2.

A filter 5 is disposed on the optical path from the laser source 3 to the plasma container 2. In this embodiment, the filter 5 is disposed between the laser source 3 and the condensing means 4.
The filter 5 is a filter that transmits laser light from the laser source 3 and blocks excitation light from the plasma container 2.
As such a filter 5, it is possible to use a filter in which an optical glass which is a low fluorescent glass (for example, BK7) is used as a substrate and a dielectric multilayer film and a metal vapor deposition film are formed on the substrate.
As such a filter 5, a long pass filter that cuts a shorter wavelength side than desired excitation light from the plasma container 2 can be used. Further, it is possible to use a band-pass filter that is configured by a combination of a long-pass filter and a short-pass filter and transmits only laser light.
In the first embodiment of FIG. 1, the filter 5 is disposed between the laser source 3 and the condensing unit 4, but may be disposed between the condensing unit 4 and the plasma container 2. .

FIG. 2 shows an example of a transmission spectrum showing the characteristics of the filter 5 used in the laser-driven light source device 1 of the present invention. (A) and (B) are examples of a long-pass filter, and (C) Is an example of a bandpass filter.
In FIG. 2A, the long pass filter is an infrared transmission filter and cuts light having a wavelength of 800 nm or less.
FIG. 2B shows an example in which the long pass filter is sapphire coated with ZnO ₂ and cuts vacuum ultraviolet light having a wavelength of 200 nm or less.
FIG. 2C shows a band-pass filter that is a combination of a long-pass filter and a short-pass filter. In this example, an Nd: YAG laser is used as the laser beam.
A band-pass filter having a half-width of 20 nm centered on the wavelength λ = 1064 nm, which is the center wavelength of the Nd: YAG laser, transmits only the laser light, includes the excitation light from the plasma vessel 2, and transmits other light do not do.

In the second embodiment shown in FIG. 3, a band-pass filter configured by combining the above-described long-pass filter and short-pass filter is used as the filter 5. The filter 5 is disposed between the condensing means 4 and the plasma container 2, and the filter 5 is a bandpass filter including a long pass filter 51 and a short pass filter 52, as shown in FIG. In addition, only the laser beam is transmitted and other light is blocked.
The band-pass filter 5 blocks light by reflecting or absorbing light (excitation light) from the plasma container 2 and restricts return light to the laser source 3.

In the third embodiment shown in FIG. 4, a concave reflecting mirror 6 is arranged around the plasma container 2.
The concave reflecting mirror 6 can be a parabolic mirror or an elliptical mirror. In this example, a parabolic mirror is shown, and the condensing position of the laser beam A coincides with the focal position of the concave reflecting mirror 6. Arranged. Also, in this example, an incident window 7 is provided in the rear opening of the concave reflecting mirror 6.
The laser light A from the laser source 3 is incident on the plasma container 2 through the incident window 7 of the concave reflecting mirror 6 while being condensed by the condensing means 4. The excitation light EL generated by the plasma P generated in the plasma container 2 exits the plasma container 2, is reflected by the concave reflecting mirror 6 to the front opening side, and is emitted to the outside as parallel light.

In addition, a part of the excitation light EL emitted from the plasma container 2 is returned to the laser source 3 side. However, the excitation light is blocked by the filter 5 and does not return to the laser source 3. This is the same as the second embodiment.

FIG. 5 shows another fourth embodiment in which the plasma container 2 of each of the above embodiments has a tube shape, whereas in this embodiment, the shape mainly composed of the concave reflecting mirror 6 is shown. It is. That is, an entrance window 7 is provided at the rear opening of the concave reflecting mirror 6, and an exit window 8 is provided at the front opening. The concave reflector 6, the entrance window 7, and the exit window 8 are hermetically sealed. A space is formed to form the plasma container 2. A light emitting element is enclosed in the plasma container 2.
Also in this embodiment, the laser beam A from the laser source 3 enters the plasma container 2 through the incident window 7 while being collected, and is collected at the focal point of the concave reflecting mirror 6.
The excitation light EL generated by the plasma P generated in the plasma container 2 is reflected by the concave reflecting mirror 6 and emitted as parallel light to the outside from the emission window 8.
Also in this embodiment, the excitation light from the plasma container 2 is blocked by the filter 5 and does not return to the laser source 3.

Of course, also in the second to fourth embodiments shown in FIGS. 3 to 5, the filter 5 may be disposed between the laser source 3 and the condensing means 4.

In another fifth embodiment shown in FIG. 6, the filter 5 is formed in the incident window 7 of the plasma container 2. That is, the filter 5 is formed by forming a dielectric multilayer film and a metal vapor deposition film on the surface of the incident window 7 as a base material.
As a result, of the excitation light EL generated by the plasma P in the plasma container 2, the light that attempts to return to the laser source 3 through the incident window 7 is blocked by the filter 5 and prevented from returning to the laser source 3.

In the sixth embodiment shown in FIG. 7, the structure of the plasma vessel 2 having a structure other than the tube shape is different from the embodiment shown in FIG.
The plasma container 2 has a cylindrical main body 10, and a concave reflecting surface 11 is formed on the inner surface thereof. The concave reflecting surface 11 is appropriately selected such as an elliptical shape or a parabolic shape.
The main body 10 is formed with a rear opening 10a and a front opening 10b. An entrance window 12 is provided corresponding to the rear opening 10a, and an exit window 13 is provided corresponding to the front opening 10b.
The incident window 12 corresponding to the rear opening 10 a of the main body 10 is attached to a metal window frame member 14, and the window frame member 14 is attached to the main body 10 by a metal cylinder 15. A sealed space is formed by the main body 10, the entrance window 12, and the exit window 13 to form the plasma container 2, and a light emitting element is enclosed in the sealed space.

Also in the case of the sixth embodiment, the laser beam A from the laser source 3 enters the plasma container 2 through the incident window 12 while being collected, and is collected at the focal point of the concave reflecting mirror surface 11.
The excitation light EL generated by the generated plasma P is reflected by the concave reflecting surface 11 and is emitted from the front emission window 13 to the outside as parallel light.
Also in this embodiment, the excitation light EL returning from the plasma container 2 to the laser source 3 through the incident window 12 is blocked by the filter 5 and is not returned to the laser source 3.

In the seventh embodiment shown in FIG. 8, the filter 5 is formed in the incident window 7 of the plasma container 2, as in the fifth embodiment shown in FIG. 6.
In the fifth embodiment of FIG. 6 and the seventh embodiment of FIG. 8, the filter 5 is formed on the front surface (outer surface) side of the incident windows 7 and 12 in the laser beam traveling direction. You may form in the back surface (inner surface) side.

In the sixth embodiment shown in FIG. 7 and the seventh embodiment shown in FIG. 8, the main body 10 constituting the plasma vessel 2 can employ a ceramic material or a metal material such as aluminum, and can also be incident. The window 12 is transmissive to laser light, and the exit window 13 is transmissive to excitation light, both of which can employ a crystal material such as quartz or sapphire.
When the main body 10 is made of a ceramic material, the outer peripheral surface at the rear end is metallized, and the metal cylinder 15 is joined thereto by brazing, and the metal window frame member 14 is welded to the metal cylinder 15. What is necessary is just to join.
Moreover, when the main-body part 10 is metal, the metal cylinder 15 may be weld-joined and the metal window frame member 14 may be weld-joined to this.

Thus, according to the sixth embodiment of FIG. 7 and the seventh embodiment of FIG. 8, ceramics and metals other than quartz glass can be used as the plasma container constituent material, and high output UV from the plasma can be used. Even when irradiated with light or VUV light, ultraviolet distortion is not generated in the plasma container, and a laser-driven light source device with higher output and longer life can be realized.

Further, according to the fifth embodiment of FIG. 6 and the seventh embodiment of FIG. 8 in which the filter 5 is formed in the incident windows 7 and 12 of the plasma container 2, the laser source 3 passes from the plasma container 2 through the incident windows 7 and 12. Excitation light EL that attempts to return to the side is blocked by the filter 5 formed in the incident windows 7 and 12 and is not emitted from the plasma container 2.
Therefore, when the laser-driven light source device 1 of the present invention is used as a light source device in which xenon gas is sealed in the plasma container 2 and emits VUV light having a wavelength of 200 nm or less as excitation light, VUV light is emitted from the plasma container 2. There is no emission to the laser source 3 side, and no ozone prevention measures are required.
That is, when VUV light is emitted from the plasma container 2 to the laser source 3 side, it is absorbed by oxygen in the atmosphere and ozone is generated. According to the fifth and seventh embodiments, the VUV light is emitted from the plasma container. Since it is not radiated | emitted from 2 outside, the countermeasure becomes unnecessary.
In addition, it goes without saying that ozone countermeasures using VUV light emitted from the emission windows 8 and 13 are naturally necessary if the measures against the VUV light are used. For example, an inert gas such as nitrogen gas is filled in the light path on the emission side to prevent ozone from being generated by VUV light and to take measures to prevent attenuation of VUV light.

In the laser-driven light source device that emits VUV light as described above, for example, sapphire coated with ZrO ₂ or TiO ₂ is used for the laser light incident windows 7 and 12, thereby, FIG. As shown in B), ultraviolet light in the region of VUV light having a wavelength of 200 nm or less is blocked.
Further, as the entrance windows 7 and 12 for blocking VUV light, glass materials such as Ti-doped quartz glass, borosilicate glass, and aluminosilicate glass can be used in addition to the sapphire. When these glass materials are used as an entrance window, the entrance window itself has a filter function for blocking VUV light.

As described above, according to the laser-driven light source device of the present invention, the filter that blocks the excitation light from the plasma container is disposed between the laser source and the laser beam condensing position in the plasma container. As a result, the excitation light that returns from the plasma container to the laser source is blocked so that it does not return to the laser source, so that the laser source is prevented from being damaged by the return light.
In addition, in the case of using VUV light as excitation light, the VUV light is not emitted from the plasma container toward the laser source by providing a filter function to the incident window of the plasma container. No need for ozone countermeasures.
In the description of each embodiment, a so-called electrodeless type plasma electrode without an electrode has been described. However, the present invention can also be applied to an electrode having an electrode as an ignition source as in the conventional example shown in FIG. Needless to say.

DESCRIPTION OF SYMBOLS 1 Laser drive light source device 2 Plasma container 3 Laser source 4 Condensing means 5 Filter 51 Long pass filter 52 Short pass filter 6 Concave reflection mirror 7 Incident window 8 Emission window 10 Main body 11 Concave reflection surface 12 Incident window 13 Emission window 14 Window frame member 15 Metal cylinder A Laser light EL Excitation light P Plasma

Claims (6)

1. A laser-driven light source device comprising: a laser source; and a plasma container that generates plasma by condensing and entering a laser beam from the laser source. The laser source and a laser beam condensing position in the plasma container A laser-driven light source device characterized in that a filter for blocking excitation light from the plasma container is disposed therebetween.
2. The laser-driven light source device according to claim 1, wherein the filter is a long pass filter.
3. The laser-driven light source device according to claim 1, wherein the filter is a band-pass filter configured by a combination of a long-pass filter and a short-pass filter and transmitting only the laser beam.
4. The laser-driven light source device according to any one of claims 1 to 3, wherein the plasma container has a tube shape and is provided with a concave reflecting mirror surrounding the plasma container.
5. The plasma container includes a concave reflecting mirror, an incident window provided in a rear opening of the concave reflecting mirror, and an exit window provided in a front opening of the concave reflecting mirror, and the concave reflecting mirror and the incident window The laser-driven light source device according to any one of claims 1 to 3, wherein a sealed space is formed by the emission window.
6. The laser-driven light source device according to claim 5, wherein the filter is provided in the incident window.

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