JPH10284790A - Housing device for narrow-band chemico-optical element with - Google Patents

Abstract

PROBLEM TO BE SOLVED: To completely isolate a housing inside form the outer circumstance by providing an air curtain forming means which forms the air curtain of predetermined gas near a laser-passing hole. SOLUTION: A laser chamber 1 is provided with a laser output mirror 2 and a region module 3 with a narrow band. The module 3 with narrow band is constituted of a beam spreading optical system 4, a mirror 5, a grating 6 and a housing 7. Inert gas in an inert gas bottle 10 is filled in the housing 7. A gas piping 12 is provided with a bypass piping 14, by extending and the bypass piping 14 is extended to the near of a laser passing hole 8 in the housing 7 via a diaphragm 13. The inert gas, of which supplying pressure is increased after passing through the diaphragm 13, is ejected near the laser passing hole 8 in the housing 7 and an air curtain 14 of the inert gas is formed near the laser-passing hole 8. By this means, the inside of the housing is compactly isolated from the outside atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to a narrow band gas laser such as a narrow band excimer laser, and accommodates an optical unit including a narrow band optical element in a predetermined housing to isolate the optical unit from an external atmosphere. The present invention relates to an improvement in a housing device for a band-narrowing optical element, wherein the vicinity of a laser passage hole formed in a wall surface of the housing is more reliably isolated from an external atmosphere.

[0002]

2. Description of the Related Art An excimer laser has been attracting attention as a light source of a reduction projection exposure apparatus for manufacturing a semiconductor. In this case, the emitted excimer laser light is required to have a narrow band of 3 pm or less, and Large output power is required.

As a promising technique for narrowing the band of an excimer laser for a reduction projection exposure apparatus, there is a technique using an etalon, a prism, or a grating (diffraction grating) as a wavelength selection element.

Here, in the conventional excimer laser, the optical element such as the above-mentioned narrow band optical element is housed in a predetermined housing in order to isolate the optical element from an external atmosphere. The inert gas is filled, and its configuration is shown in FIG.

FIG. 4 shows a technique disclosed in Japanese Patent Application Laid-Open No. 6-5952. In this conventional technique, an airtight container 21 is disposed adjacent to a laser chamber 20 and the airtight container 21 is provided in the airtight container 21. A prism 22 and a grating 23 for narrowing the band are accommodated. The airtight container 21 has a valve 25 for filling N2 or He gas 24 and a vacuum pump 2 for evacuating the container 21.
6 and a valve 27 are connected, and a desiccant 28 is disposed in the airtight container 21.

That is, according to the prior art shown in FIG.
The band-narrowing optical element is accommodated in an airtight container 21 filled with a purge gas such as an inert gas, and (1) dust is prevented from adhering to the band-narrowing element. (2) The band-narrowing element is cooled. (3) An effect of preventing deterioration of the reflection film on the surface of the band-narrowing element is obtained.

[0007]

However, in an excimer laser using a halogen gas (fluorine, chlorine, etc.) as a laser gas, it is only necessary to house the narrow band element in an airtight container filled with an inert gas as described above. ,
It turned out that it was not possible to completely prevent the halogen gas from entering the airtight container.

That is, in a gas laser device such as an excimer laser, a blower (fan) is built in the laser chamber to circulate the laser gas sealed in the laser chamber. In order to rotate this fan, a motor is required. However, since the motor is corroded by a laser gas (eg, a halogen gas), the motor 30 is installed outside the laser chamber 20 as shown in FIG. Accordingly, the motor and a fan (not shown) in the laser chamber 20 are connected by a rotating shaft, and bearings 31 for supporting the rotating shaft are provided on both side surfaces of the laser chamber.

Here, grease used for the bearing portion 31 is:
If evaporants or fine particles of lubricant such as oil enter the laser chamber, they become impurities and hinder laser oscillation, causing problems such as shortening the life of the laser gas. It is necessary to make sure it is shut off. For this reason, a shaft seal made of a magnetic fluid or the like is used for the bearing.

On the other hand, in such an excimer laser, dust (dust and the like) in the laser chamber generated by laser oscillation has a bad influence on the movement of the bearing portion. Is supplied to the bearing portion to periodically perform a purge process for protecting the bearing portion. At this time, an inert gas is supplied to the bearing via the magnetic fluid seal. In FIG. 5, 32 is an N2 gas cylinder, 33 is a valve, and 34 is an N2 gas cylinder.
A gas supply pipe, 35 is an N2 gas exhaust pipe, 36 is a narrow band box in which a narrow band optical element is built, and 37 is a laser beam passage hole.

However, in the excimer laser as shown in FIG. 5, when purging with an inert gas is performed, an ultra-trace amount of halogen gas remaining in the magnetic fluid seal portion from an exhaust pipe opening for purging is removed. It was discovered that the gas was released into the atmosphere together with the exhausted inert gas, and that the released gas extremely entered the narrow band box 36 via the laser beam passage hole 37 of the narrow band box 36.

Here, optical elements such as prisms, gratings, etalons, and mirrors built in the band narrowing box 36 are made of optical glass, and the glass base material and the coating material on the surface thereof are made of halogen gas. Therefore, even if the halogen gas enters the narrow-band narrowing box 36 very slightly, in the long term such as half a year or one year, the optical power within the narrow-band narrow box 36 is consequently increased. There is a risk of damaging the element, which causes a reduction in band narrowing performance.

As described above, gas lasers such as excimer lasers are not always completely sealed, and there is a possibility that a very small amount of halogen gas flows out during the above-mentioned purging or gas exchange. As a result, there is a danger that the halogen gas enters the narrow-band box.

Therefore, when an attempt is made to increase the gas pressure of the gas filling the airtight container (narrowing box), the relative refractive index of the internal optical element is changed due to this, and the laser oscillation efficiency is reduced.

It is also conceivable to completely cover the laser passage window 37 formed in the hermetic container with glass or the like. However, in this method, reflection and scattering on the glass surface adversely affect laser oscillation, and the laser oscillation efficiency is reduced. It cannot be adopted because it falls.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is intended to completely isolate a housing accommodating a narrow band optical element from an external atmosphere without lowering laser oscillation efficiency by a simple configuration. It is an object of the present invention to provide a narrowed band optical device housing device.

[0017]

According to the present invention, an optical unit including at least a band-narrowing optical element is provided in a housing, and a laser passage hole through which laser light passes is formed on a wall surface of the housing. In the housing device for a narrow band optical element described above, an air curtain forming means for forming an air curtain of a predetermined gas near the laser beam passage hole is provided.

That is, according to the present invention, an air curtain made of an inert gas or the like is formed in the vicinity of the laser light passage hole formed on the wall surface of the narrow band optical element housing device so as to pass through the laser light passage hole. This prevents the entry of halogen gas or the like into the housing.

Therefore, according to the present invention, the inside of the housing accommodating the band-narrowing optical element can be completely isolated from the external atmosphere without lowering the laser oscillation efficiency.

[0020]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 shows an embodiment of the present invention.
A laser output mirror 2 which is a partially transmitting mirror is provided on one side of a laser chamber 1 of the excimer laser device, and a band narrowing module 3 is provided on the other side. In this case, the band narrowing module 3 includes a beam expanding optical system 4 including a plurality of prisms, a mirror 5, a grating 6, and a housing 7 for isolating these optical elements from an external atmosphere. Have been. Further, a laser light passage hole (slit) 8 through which the laser light passes is formed on the wall surface of the housing 7. That is, in this case, a resonator is constituted by the grating 6 and the laser output mirror 2.

The inside of the housing 7 of the band narrowing module 3 is filled with an inert gas such as N 2 through a purge gas supply port 9, whereby the optical element in the housing 7 is deteriorated by impurities in the external atmosphere. Alternatively, the performance is prevented from being reduced. That is, the inert gas in the inert gas cylinder 10 is supplied to the housing 7 through the valve 11, the gas pipe 12, and the purge gas supply port 9.
Is filled in.

On the other hand, the gas pipe 12 has a bypass pipe 1
The bypass pipe 14 extends through the throttle 13 to the vicinity of the laser beam passage hole 8 in the housing 7.

Therefore, the inert gas whose supply pressure has been increased after passing through the restrictor 13 is ejected in the vicinity of the laser light passage hole 8 in the housing 7, and is injected near the laser light passage hole 8. The air curtain 14 is formed by the active gas.

In this case, however, the flow rate of the inert gas ejected near the laser beam passage hole 8 is such that impurities such as halogen gas do not enter from outside the housing and the beam profile and spectrum of the laser beam are not affected. It is set to the value of.

FIG. 2 shows an outlet portion 15 of the gas pipe near the laser beam passage hole 8. In this case, the shape of the gas outlet portion is tapered so that the width of the gas outlet portion corresponds to the width of the slit 8. ing. However, in this case, the width of the tapered outlet portion is set to be larger than the width of the slit 8.
As a result, no gap is formed in the formed air curtain.

Next, FIG. 3) shows various modifications near the laser light passage hole. In FIG. 3 (a), an inert gas flow from the inside of the housing to the outside of the housing via the laser light passage hole 8 is shown. The laser light passage hole 8 is inclined with respect to the housing wall surface so that the laser light can easily flow.

In FIG. 3B, the direction of the gas outlet portion 15 is also inclined corresponding to the inclination of the laser passage hole 8, so that the flow from the inside of the housing to the outside of the housing becomes stronger. This makes it difficult for impurities to enter the housing.

In FIG. 3C, the direction of the laser passage hole 8 is not inclined, but only the direction of the gas outlet portion 15 is inclined.

As described above, in this embodiment, an inert gas air curtain is formed in the vicinity of the laser light passage hole 8 of the band narrowing module 3 so that the halogen gas is passed through the laser light passage hole 8. As a result, it is possible to completely prevent the inside of the housing, in which the narrow band optical element is housed, from the external atmosphere, and to achieve stable laser oscillation efficiency over a long period of time. Can be obtained.

In the above-described embodiment, the N2 gas cylinder 32 for purging the bearing shown in FIG. 5 may be used as a source of the inert gas to the band narrowing module. In this case, a bypass may be formed from the gas pipe 34 before reaching the bearing 31 in FIG.

Further, as the band-narrowing element housed in the housing 7, any other band-narrowing element such as an etalon may be adopted.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a perspective view showing the vicinity of a gas outlet.

FIG. 3 is a diagram showing various modifications.

FIG. 4 is a diagram showing a conventional technique.

FIG. 5 is a diagram for explaining a problem according to the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Laser chamber 2 ... Output mirror 3 ... Narrow band module 4 ... Beam expansion optical system 5 ... Mirror 6 ... Grating 7 ... Housing 8 ... Laser light passage hole 13 ... Aperture 14 ... Air curtain

Claims (7)

[Claims] An optical unit including an optical unit including at least a band-narrowing optical element is provided in a housing, and a laser passage hole through which laser light passes is formed in a wall surface of the housing. An air curtain forming device for forming an air curtain of a predetermined gas in the vicinity of the laser beam passage hole. 2. An air curtain forming means for introducing a predetermined gas into the housing and ejecting a predetermined gas near the laser beam passage hole, and supplying the gas to the gas introduction pipe. 2. A housing device for a band-narrowing optical element according to claim 1, further comprising gas supply means. 3. The housing device for an optical element having a narrow band according to claim 2, wherein the gas outlet of the gas introduction pipe has a tapered shape. 4. The housing device for an optical element having a narrow band according to claim 3, wherein a width of a tip of said tapered gas outlet portion is set to be larger than a width of said laser passage hole. 5. The housing device for a narrow-band optical element according to claim 2, wherein an output portion of said gas introduction pipe is installed in a direction such that a gas flows from the inside of the housing to the outside. 6. The laser light passage hole is formed so that the axis of the laser light passage hole is inclined at a predetermined angle with respect to the housing wall surface, and the laser light passage hole extends from the inside of the housing to the outside along the inclination direction of the laser light passage hole. 3. The housing device for a narrow-band optical element according to claim 2, wherein the output portion of the gas introduction tube is installed in a direction such that the gas flows through the housing. 7. The housing device for a narrow-band optical element according to claim 1, wherein said predetermined gas is an inert gas.