JPH03240282A - Laser device - Google Patents

Abstract

PURPOSE:To safely, easily and accurately detect a variation in an optical property due to fog of a transmitting window material, adherence of dust by introducing a laser light from a reference laser to the material, and detecting a reflected light, transmitted light or a scattered light through the material. CONSTITUTION:A laser light from a reference laser 1 impinges obliquely to a transmitting window material 5a (5b) through a prism mirror 2, a mirror 3a (3b), a half mirror 13a (13b), and a reflected light from the material 5a (5b) is detected by a photodetector 8a (8b) through an interference filter 12a (12b). In this case, if the material 5a (5b) has fog or dust, the intensity of the detected light becomes small. Accordingly, an output signal ratio from a monitoring photodetector 14a (14b) is obtained by a discriminator 9. Then, it is compared with a threshold output ratio previously determined here, its result is displayed on a display unit 10 to know a variation in an optical property. Here, when the position of the photodetector 8a (8b) is deviated, a scattered light, etc., can be detected.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a laser device, and in particular, in a gas laser or the like, a transmission window material is provided in a part of a laser gas container in which a gas medium is enclosed, and a laser beam is transmitted through the transmission window material. The present invention relates to a laser device provided with means for measuring optical properties due to changes over time, such as cloudiness, of the transmission window material when emitting light.

(Conventional technology) Conventionally, gas lasers have been made by sealing a gas medium in a glass tube such as quartz, placing reflectors facing each other at both ends of the quartz tube, and applying a high voltage from the outside to the inside of the quartz tube. This causes stimulated emission, which emits highly monochromatic coherent light. At this time, in order to confine the gas medium within the glass tube such as quartz, a transmission window material is provided in a part of the optical path of the glass tube such as quartz.

Generally, this transparent window material changes over time as laser oscillation is performed, for example, clouding occurs, the optical properties change, and the light energy output from the laser changes.

Conventional methods for confirming changes in the optical properties of the transparent window material at this time include directly observing the transparent window material with the naked eye, detecting a decrease in laser output, and checking the cross section of the emitted laser beam. Methods such as measuring the light intensity distribution are used.

(Problems to be Solved by the Invention) The conventional method of directly observing with the naked eye as a method of confirming changes in the optical properties of a transparent window material has the risk of directly viewing a powerful laser beam, and the observation of a transparent window material There was a problem in that the resonator had to be removed when doing so, resulting in poor workability.

Further, there is a problem in that it is difficult to distinguish the method of detecting a decrease in laser output or the method of measuring the light intensity distribution of a cross section of a laser beam from other factors.

By using a reference laser, appropriately constructed irradiation means, and photodetector, the present invention eliminates the risk of exposure to laser light, and eliminates the need for special work, allowing for easy and high-precision prevention of fogging of the transparent window material, etc. The object of the present invention is to provide a laser device that can measure changes in optical properties.

(Means for Solving the Problems) The laser device of the present invention is configured to emit a laser beam through a transparent window material provided in a laser gas container containing a gaseous medium. , a reference light is irradiated from a reference light source by an irradiation means, the reference light is detected by a photodetector through the transparent window material, and an output signal from the photodetector is used to detect the optical characteristics of the transparent window material. It is characterized by measuring properties.

In particular, the present invention is characterized in that the photodetector detects scattered light, reflected light, or transmitted light from the transparent window material.

(Embodiment) FIG. 1 is a schematic diagram of a main part of a first embodiment of the present invention. In the figure, reference numeral 4 denotes a laser gas container, which is made of, for example, a quartz tube, and is filled with a gas medium corresponding to the wavelength of the emitted laser beam.

5a. 5b is a transparent window material made of quartz, and is attached to the light exit surface of the laser gas container @4. Reference numerals 6 and 7 each designate a resonator mirror, which constitutes one element of the laser resonator.

Each of the above elements 4, 5, 6.7 is the same as a conventionally known laser, and constitutes one element of the main laser 101 in this embodiment. The main laser 101 of this embodiment consists of an rF excimer laser.

11 is the wavelength λ=248.
It is a 4 am laser beam. A reference laser (probe laser) 1 emits a laser beam having a wavelength different from the oscillation wavelength of the main laser 101. Here the reference laser is He-
It consists of a No laser (λ=632.8 nm). 2 is a prism mirror, 3a and 3b are mirrors, and 13a and 13b are half mirrors.

In the figure, a laser beam from a reference laser 1 is divided into two directions by a prism mirror 2, and transmitted through a mirror 3a (3b) and a half mirror 13m (13b) to a transparent window material 5a (5b).
) at a predetermined angle from an oblique direction. 12al,
12bl.

Reference numerals 12a2 and 12b2 each indicate an interference filter, which has a spectral characteristic that allows light of the oscillation wavelength of the reference laser 1 to pass therethrough. 8a and 8b are photodetectors.

In the figure, the intensity of the reflected light from the transparent window material 5a (5b) among the laser beams from the reference laser 1 that entered the transparent window material 5a (5b) is detected by the photodetector 8a ( 8b).

14a and 14b are photodetectors for monitoring. The photodetector 14a (14b) is a half mirror 13a (13b)
A part of the laser beam of the reference laser 1 that has been reflected and split is detected via an interference filter 12a2 (12b2), and the optical output of the reference laser 1 is detected. 9 is a discrimination circuit, 10
is an indicator.

The determination circuit 9 determines whether the output signal from the photodetector 8a (8b) is greater than or equal to a predetermined value using a photodetection amount 14a for monitoring.
The determination is made with reference to the output signal from (14b). The display 10 displays the determination result by the determination circuit 9.

In this embodiment, similarly to a conventional gas laser, a resonator mirror 6.7 sandwiching a laser gas container 4 and a transmission window material 5a (5b) is used.
When the laser medium in the laser gas container 4 is excited by discharge or the like between the two, dielectric emission occurs, laser oscillation occurs, and a monochromatic coherent laser beam 11 passes through the resonator mirror 7 and is emitted. At this time, the transmission window material 5a (5b) changes over time, for example, becomes cloudy, and dust and the like adhere to it, causing its optical properties to change. Also, there may be scratches due to handling.

Therefore, in this embodiment, the laser beam is transmitted from the reference laser 1 to the prism, the mirror 2, the mirror 3m (3b), and the half mirror 13.
The light is made to enter the transmission window material 5a (5b) from an oblique direction via a (13b). The reflected light from the transparent window material 5a (5b) is detected by a photodetector 8a (8b) via an interference filter 12g (12b). At this time, if the optical properties of the transparent window material 5a (5b) change due to the reasons described above, the light intensity detected by the photodetector 8a (8b) decreases.

In this embodiment, the output signal E from the photodetector 8a (8b)
. Light detection 1314a for ut and monitor.

Output signal E1° from 14b. The ratio of E. ut/Eea.

1 is determined by a discriminating circuit 9, and it is determined whether or not it is lower than a predetermined threshold output ratio. That is, the transparent window material 5a
It is determined whether there is cloudiness or the like in (5b) and the optical properties have changed. This result is then displayed on the display 10.

In this embodiment, instead of using the photodetector 8a (8b) to detect the reflected light from the transparent window material 5a (5b), the positions of the photodetectors 8a and 8b are changed to the specularly reflected light position as shown in FIG. Scattered light generated from the transparent window material 5a (5b) is detected by shifting the light from the transmitting window material 5a (5b), and the amount of scattered light at this time is detected by referring to the output signals from the monitoring photodetectors 14a and 14b. However, the object of the present invention can be achieved in the same way.

In addition, in this embodiment, the main laser 10 is used as the reference laser 1.
The object of the present invention can be similarly achieved by using a laser that emits light of the same wavelength as the oscillation wavelength from 1. It is also possible to use other light sources than the He-Ne laser.

2 to 4 are schematic diagrams of main parts of second to fourth embodiments of the present invention, respectively.

In each of these embodiments, the same elements as those shown in FIG. 1 are given the same reference numerals.

Next, each of these embodiments will be described, focusing mainly on the configurations that are different from the first embodiment shown in FIG.

In the second embodiment shown in FIG. 2, a part of the laser gas container 4 is provided with light passing windows 21a and 21b. The light passing window 2
1a and 21b, a photodetector 8a (
8b).

Then, using the output signal from the photodetector 8a (8b) and the output signal from the monitoring photodetector 14a (14b), the optical properties of the transparent window materials 5a, 5b are determined in the same manner as in the first embodiment. Changes are detected and the detection results are displayed on the display 10.

In the third embodiment shown in FIG. 3, a reflection section 31 made of an AR coating film is provided in a part of the light transmission section of the laser gas container 4. Then, the laser beam from the reference laser 1 is made obliquely incident on one of the transparent window materials 5a through the half mirror 13a, and the laser beam that has passed through the transparent window material 5a is reflected into the reflection section 31.
After being reflected by the laser beam, the laser beam is incident on the other transparent window material 5b, and the laser beam that has passed through the transparent window material 5b is detected by the photodetector 8.

Then, using the output signal from the photodetector 8 and the output signal from the monitoring photodetector 14, a change in the optical properties of the transparent window materials 5a and 5b is detected in the same manner as in the first embodiment,
The detection results are displayed on the display 10.

In this embodiment, one laser beam is made incident on two transmitting window materials using the reflecting section 31, thereby simplifying the entire apparatus.

In the fourth embodiment shown in FIG. 4, 41 is a rotatable mirror that can be inserted and removed, 42 is a storage part that stores the rotary mirror 41, and 43 is a light detection means that can be inserted and removed, and an interference filter 12 and a photodetector are shown. It has 8.

In this embodiment, only when detecting a change in the optical properties of the transmission window materials 5a and 5b, the rotating mirror 41 and the light detection means 43 are connected to the optical path between the main laser resonator mirrors 6 and 7 as shown in the figure. It is placed inside. Then, the laser beam from the reference laser 1 is reflected by the rotating mirror 41 via the half mirror 13, and is sequentially transmitted through the two transmission window materials 5a and 5b via the laser gas container 4. The transmitted light at this time is detected by the photodetector 8a via the interference filter 1281. As a result, in the same manner as in the first embodiment, the transparent member 5a
, 5b is detected.

FIG. 6 is a block diagram of an exposure apparatus equipped with the laser apparatus of the present invention. A indicates an exposure apparatus main body having an exposure optical system. Reference numeral 100 denotes the rF excimer laser device shown in FIGS. 1 to 5, and is fixed on an XYθ stage 102 placed on a laser surface plate 3 on a vibration-proof cushion 104. B is a transmission system that transmits the laser beam 120 from the laser device 100 to the optical system of the exposure apparatus main body A, and is composed of a plurality of optical components including the illustrated mirror 105. 106 is an illumination optical system, 109 is a reticle on which a circuit pattern for semiconductor manufacturing is drawn, 190 is a reticle holder, 110 is a projection lens system for projecting the circuit pattern of the reticle 109, 111 is a lens support, and 112 is a wafer. , 113 is a chuck that suctions and fixes the wafer 112;
114 is an XY stage, 115 is a stepper constant plate, 11
6 is an anti-vibration cushion. Laser light 120 emitted from laser device 100 passes through transmission system B and enters illumination optical system 106 of exposure apparatus main body A. And illumination optical system 1
After the beam diameter is expanded in step 06, the beam passes through a reticle 109 and a projection lens system 110, and reaches the wafer 112.

The exposure optical system consisting of the illumination optical system 106 and the projection lens system 110 is all integrated and fixed by the lens support stand 111 fixed to the stepper fixed plate 115, so each optical system in the exposure apparatus main body A The relative positions of are virtually unchanged. A circuit pattern is drawn on the reticle 109 as described above, and by illuminating it with a laser beam, it is reduced to a size 115 and transferred onto the wafer 112 via the projection lens system 110.

The wafer 112 is vacuum-adsorbed onto a wafer chuck 113, and the wafer chuck 113 is attached to a stepper fixed plate 115.
It is fixed on a movable XY stage 114 provided above. The wafer 112 can be transported by the XY stage 114 in two directions, X and Y, which are orthogonal to each other.
The reduced pattern can be transferred to any location on the wafer 112.

Usually, several dozen shots of reduced patterns are transferred onto the wafer 112, so the operation of moving the XY stage 114 in the X or Y direction, irradiating laser light, and performing transfer is repeated.

Further, 117 is an illuminance meter consisting of a photodetector fixed on the XY stage 114, and by driving the XY stage 114, it is positioned on the image plane of the projection lens system 110. Measure illuminance.

The illuminance measured by this illuminance meter 117 is regarded as the illuminance on the surface of the wafer 112, and is used as control data for controlling the exposure amount during exposure.

In the exposure apparatus shown in FIG. 6, the deterioration of the transparent window material of the laser apparatus 100 can be accurately monitored at any time.
0 can be replaced at an appropriate time when the performance of the exposure apparatus will not deteriorate excessively due to deterioration of the transmission window.

(Effects of the Invention) According to the present invention, by making the laser beam from the reference laser enter the transparent window material with the above-described configuration and detecting the reflected light, transmitted light, or scattered light through the transparent window material, Therefore, it is possible to achieve a laser device that can safely, easily, and highly accurately detect changes in optical properties due to clouding of a transmission window material, adhesion of dust, etc.

[Brief explanation of drawings]

1 to 4 are schematic diagrams of the main parts of the first to fourth embodiments of the present invention, respectively, FIG. 5 is a schematic diagram of the main parts of one embodiment when a part of FIG. The figure is a schematic diagram of an embodiment in which the laser device of the present invention is applied to an exposure device for semiconductor manufacturing. In the figure, 51 is a reference laser (probe laser), 2 is a prism mirror, 3a and 3b are mirrors, 4 is a laser gas container,
5a, 5b are transparent window materials, 6, 7 are resonator mirrors, 8, 8
a, 8b, 14a. 14b is a photodetector, 9 is a discrimination circuit, 10 is a display, 11
is laser light, f2al, 12bl. 12a2, 12b2.12 are interference filters 13a, 1
3b is a half mirror.

Claims (4)

[Claims] (1) A reference light source is used to irradiate a reference light from a reference light source to a transparent window material of a laser that emits a laser beam through a transparent window material provided in a laser gas container that confines a gaseous medium. A laser device characterized in that the reference light is detected by a photodetector through a transparent window material, and the optical properties of the transparent window material are measured using an output signal from the photodetector. (2) The laser device according to claim 1, wherein the photodetector detects scattered light, reflected light, or transmitted light from the transmission window material. (3) The laser device according to claim 1, wherein the reference light source comprises a reference laser that emits laser light as reference light. (4) The laser device according to claim 3, wherein the wavelength of the laser light emitted from the laser and the wavelength of the laser light emitted from the reference laser are different.