JPH06188505A - Laser output controller - Google Patents

Abstract

PURPOSE:To allow long term stabilized output control of excimer laser by transmitting the light, which transmitted through a diffuser, through a lens and controlling the output of a laser based on an output from a light intensity detector located substantially at the focal point of the lens. CONSTITUTION:A part of laser light is sampled through a beam splitter 6 and introduced to an output detecting section 10 where the laser light is diffused through a diffuser 11, transmits through a condenser lens 12, and impinges on the light receiving part 15b of a light intensity detector 15 located at the focal point of the condenser lens 12. At the focal point of the lens 12, lights transmitted through the diffuser 11 are superposed and made uniform. Consequently, intensity of light to be detected does not fluctuate even upon variation of the profile of sampled output laser light. The light intensity detector 1 delivers a detection signal to an output controller 20 which controls a power supply 30 for laser to sustain a constant laser output. This constitution allows long term stabilization of laser output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser output control device, and more particularly to a laser light output control device for an excimer laser which is an ultraviolet laser light.

[0002]

2. Description of the Related Art Conventionally, as a device for controlling the output of a laser beam of an excimer laser, Japanese Patent Laid-Open No. 2-229258 has been disclosed.
No. 2, Japanese Unexamined Patent Publication (Kokai) No. 2-93331, and Questec Catalog are known. For example, a conventional publicly known example described in the Questec Catalog, which is one of them, has a structure shown in FIG. In this example, the output light (L) from the laser chamber 51 is sampled by the beam splitter 53, diffused by the beam diffuser 55, and collected by the collecting cone 57 to collect the light intensity detector 59.
The pulse energy is detected by.

[0003]

However, in the case of the ultraviolet laser, since the photon energy is large, the surface state of the collecting cone portion is changed by the irradiation of the laser beam, and the reflectance is changed with the lapse of time. . Therefore, the amount of light reaching the light intensity detector changes, and when the laser output is controlled based on this light intensity detector, the actual laser output value and the laser output value that is feedback-controlled inside the laser are different, It has been difficult to perform highly accurate output control for a long period of time.

Furthermore, in the case of very short wavelengths (248 nm, 193 nm) such as KrF and ArF excimer lasers, there is no metal that totally reflects at various angles.
Therefore, when the beam shape of the output laser light changes, the number of reflections at the collecting cone changes, so that even if the same light intensity is output, the light intensity reaching the light intensity detector is different.

The present invention has been made in view of the above problems, and in particular,
Even if the beam profile of the output laser light changes, the output of the laser can be detected with high accuracy and output control can be performed.
An object of the present invention is to provide a laser output control device capable of controlling the laser output of an excimer laser that is stable for a long period of time.

[0006]

To this end, the first aspect of the present invention is provided.
In the invention, means for guiding the light sampled from the output laser light to the diffusion plate, means for transmitting the light transmitted through the diffusion plate to the lens and disposing the light receiving portion of the light intensity detector at the substantially focal position of the lens, and the light intensity Means for controlling the laser output based on the detection value of the detector is provided.

Further, in the second invention, means for guiding the light sampled from the output laser light to the first diffusing plate, and the light transmitted through the diffusing plate are passed through the lens to form a second focal point on the lens.
And a means for detecting the light transmitted through the second diffuser plate with a light intensity detector, and a means for controlling the laser output based on the detection value of the light intensity detector.

[0008]

According to the above construction, when the light transmitted through the diffusion plate is condensed by the lens, the light is superposed at the focal point of the lens and the light receiving section of the light intensity detector is placed at this position where the light is made uniform. By arranging them, the pulse energy of the laser can be detected with high accuracy. Further, the pulse energy of the laser can be detected with high accuracy by disposing the second diffusion plate at this position and detecting the transmitted light with the light intensity detector. As a result, even if the beam profile of the output laser light changes, the laser output (pulse energy) can be detected with high accuracy, and accurate output control can be performed. Further, since it is detected optically, it does not change over time in the long term.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a laser output control device according to the present invention will be described in detail below with reference to the drawings. 1 is a schematic view showing a first embodiment of a laser output control apparatus according to the present invention, and FIG. 2 is a partially enlarged view of the second embodiment. In FIG. 1, windows 2 and 3 for outputting laser light oscillated by a laser medium (not shown) and excitation means of the laser medium are provided in the laser chamber 1, and a front side (left side in the figure) of the laser chamber 1 has a front side. A mirror 4 and a rear mirror 5 on the rear side are provided to intensify the output laser light. Further, a beam splitter 6 is disposed on the front side (left side in the drawing) of the front mirror 4,
Part of the laser light is sampled by the beam splitter 6, and the sampled light is detected by the output detector 10.
The detected value is fed back to the output control device 20 such as a controller.

An electrode (not shown) is arranged in the laser chamber 1, and power is supplied from a power source 30 to this electrode. Further, the power amount from the power supply 30 is controlled by the output control device 20 so that the laser output maintains a constant value according to the value detected by the output detection unit 10. The output detection unit 10 includes a diffusion plate 11, a condenser lens 12, and a light intensity detector 15. The light intensity detector 15 is composed of a window 15a and a light receiving portion 15b. The light receiving portion 15b is arranged at the focal position of the condenser lens 12 and is protected by the window 15a.

In the above-mentioned structure, as an example of the diffusion plate 11, frosted glass of quartz or the like through which laser light is transmitted may be used. Further, examples of the light intensity detector 15 include a photodiode, a photomultiplier, and a pyroelectric element. At this time, the distance between the diffusion plate 11 and the condenser lens 12 is indefinite.

The operation of the above structure will be described.
A rare gas such as Kr or Ar, a halogen gas such as fluorine, or a buffer gas such as He or Ne gas is enclosed in the laser chamber 1.
F, ArF, and other excimers are generated, and rare gas is generated again.
When it returns to the state of fluorine gas, it emits ultraviolet light. The ultraviolet light is used for the front mirror 4 and the rear mirror 5.
Then, the front mirror 4 outputs the ultraviolet laser light. Then, a part of the output laser light is sampled by the beam splitter 6, and the sampled light is guided to the output detector 10. Output detector 1
The light incident on 0 is first scattered by the diffusion plate 11 of the output detector 10 and then transmitted through the condenser lens 12.

Then, the light is incident on the light receiving portion 15b of the light intensity detector 15 placed at the focal position of the condenser lens 12.
At this time, at the focal position of the lens, the light transmitted through the diffusion plate 11 is superposed and made uniform. By receiving this homogenized light, the detected light intensity does not change even if the profile of the sampled output laser light changes.
The detection signal detected by the light intensity detector 15 is sent to the output control device 20. The output control device 20 calculates the laser output, controls the laser power supply 30 based on the output value and the command value, and performs feedback control so that the laser output maintains a constant value.

FIG. 2 is an enlarged view of the output detector of the second embodiment. A part of the laser light is sampled by the beam splitter 6, and the sampled light is detected by the output detector 40. The detected value is fed back to the output control device 20 such as a controller. The output detector 40 is the diffusion plate 1
1, a condenser lens 12, a diffusion plate 41, and a light intensity detector 15. The light intensity detector 15 is provided with a window 15a and a light receiving portion 15b. Further, the diffusion plate 11, the condenser lens 12, the diffusion plate 41, and the light intensity detector 15 are arranged in the housing 43.

The operation of the above structure will be described.
The sample light (M) of the output laser is applied to the diffusion plate 11, and the transmission surface of the diffusion plate 11 becomes a planar secondary light source. The light emitted from the secondary light source passes through the condenser lens 12, and the light is superposed and made uniform at the position of the focal plane of this lens. (This lighting method is called Koehler lighting.)

The homogenized light is scattered again by the diffusion plate 41, and the scattered light is detected by the light intensity detector 15. In this way, by disposing the diffuser plate 41 and detecting the scattered light by the light intensity detector 15, the positioning accuracy of the light intensity detector 15 is loosened. As a result, the detection can be performed with higher accuracy than in the first embodiment.

Further, the output detector 40 is surrounded by a housing 43,
The inner surface is made of a material that absorbs ultraviolet light, does not generate outgas, and does not deteriorate, or is coated. As an example of this, Pyrex, BK7
Etc. If the scattered light is weak, the housing 40 of the detection unit
The inner surface of white mite, black mite, black chrome, black nickel,
You may coat copper oxide black etc.

[0018]

As described above, according to the present invention, the light transmitted through the diffusion plate is condensed by the lens, and the light is made uniform by superimposing the light at the focal point of the lens. The pulse energy of the laser can be detected with high accuracy by receiving the light with the light receiving section. Further, the pulse energy of the laser can be detected with high accuracy by disposing the second diffusion plate at the position of the light receiving portion of the light intensity detector and detecting the transmitted light by the light intensity detector. As described above, even if the beam profile of the output laser light changes, the output of the laser can be detected with high accuracy, output control can be performed, and there is an excellent effect that it does not change over time in the long term.

[Brief description of drawings]

FIG. 1 is a schematic view showing a first embodiment of a laser output control device according to the present invention.

FIG. 2 is a partially enlarged view of a second embodiment of a laser output control device according to the present invention.

FIG. 3 is a schematic view showing a first embodiment of a conventional laser output control device.

[Explanation of symbols]

 1 Laser Chamber 2, 3 Window 4 Front Mirror 5 Rear Mirror 6 Beam Splitter 10 and 40 Output Detector 11 Diffuser 12 Condenser Lens 15 Light Intensity Detector 16 Light Receiver 20 Output Control Device 30 Power Supply

Claims (2)

[Claims] 1. A means for guiding light sampled from output laser light to a diffusion plate, and a means for transmitting light transmitted through the diffusion plate to a lens and disposing a light receiving portion of a light intensity detector at a substantially focal position of the lens. An output control device for a laser, comprising means for controlling the output of the laser based on a detection value of a light intensity detector. 2. A means for guiding light sampled from the output laser light to a first diffuser plate, and a second diffuser plate for allowing light passing through the diffuser plate to pass through a lens, and a second diffuser plate being disposed on a substantially focal plane of the lens. Two
2. A laser output control device comprising: means for detecting light transmitted through the diffuser plate by a light intensity detector; and means for controlling laser output based on a detection value of the light intensity detector.