JPH0638533B2 - Wavelength control device for banded excimer laser - Google Patents

Description

The present invention relates to a wavelength control for controlling the oscillation wavelength of a zonal band excimer laser used as a light source of a reduction projection exposure apparatus, a laser light source of a laser beam machine for fine processing, or the like. It relates to the device.

[Conventional technology]

In a reduction projection exposure apparatus that exposes a highly integrated circuit pattern or the like onto a semiconductor wafer, an excimer laser capable of emitting short wavelength light has been attracting attention as a light source for the exposure. At this time, so that it is not necessary to correct the chromatic aberration of the reduction projection lens, the excimer laser light is narrowed into a narrow band by a wavelength selection element such as an etalon, and the narrowed band laser light is used as a light source for exposure. ing.

In addition, excimer lasers are also attracting attention as a laser light source for a laser processing machine for microfabrication that focuses laser light on a minute spot by a navigation lens system for processing. Even in this case, the excimer laser is made into a narrow band by a wavelength selection element such as a diffraction grating, an etalon, or a prism so that light can be condensed to a minute spot without correcting the chromatic aberration of the condenser lens. The narrow band laser light is used as the light source of the laser processing machine for fine processing.

However, the wavelength selection element used for band narrowing causes a material change in the setting conditions due to environmental changes such as temperature change due to laser light irradiation, vibration, and room temperature fluctuations, and the central wavelength of laser oscillation is fluctuate. The change in the oscillation wavelength causes problems such as a defocus of the projected image and a change in the spot diameter of the focused laser beam, multiwavelength oscillation, and a reduction in the laser output.

Therefore, in the narrow band excimer laser applied to the industrial machine as described above, a wavelength control technique for monitoring the oscillation wavelength and correcting the physical change of the setting condition of the narrow band element is required. If a diffraction grating type spectroscope or monitor etalon is simply used as a means for monitoring the oscillation wavelength of the zonal band excimer laser, these spectroscopes will also show the same spectral response to environmental changes such as vibration and room temperature fluctuations. Since the wavelength varies, it is not suitable as a method for monitoring the oscillation wavelength. Therefore, the detection of the laser oscillation wavelength usually used,
The stabilizing method is the following methods (1) to (4).

(1) The laser oscillation wavelength is compared with another reference light having a higher stability than the target wavelength fluctuation allowable range, and fixed at the target wavelength.

(2) The laser oscillation wavelength is fixed to the light absorption line peculiar to atoms and molecules.

(3) The laser wavelength is made to be the light absorption wavelength by observing the fluorescence intensity by injecting the laser light into the cell in which the substance that emits fluorescence by absorbing the light of the target laser oscillation wavelength is enclosed. Fix it.

(4) Fix the laser wavelength to the light absorption wavelength of gas by injecting the laser light into the discharge tube in which the gas that absorbs the light of the target laser oscillation wavelength is sealed and detecting the change of the discharge radio wave. .

Of the above methods (1) to (4), the method (1) is most used because of its simplicity.

However, in the case of a short wavelength ArF laser, there is no light source that serves as an appropriate reference, and the method (2), which is simpler, must be used next.

[Problems to be Solved by the Invention]

The present invention is to solve the problem of the method of solidifying the laser wavelength to the absorption line of the above (2), in order to clarify the problem, first described in comparison with the method of (1) . In the method of (1), a laser beam in a narrow band and a reference light having a wavelength in the vicinity of a target laser oscillation wavelength are incident on the spectroscope, and the wavelength difference between the two lights is a desired laser wavelength. The laser oscillation wavelength is controlled so as to be the difference between the reference light wavelength and the reference light wavelength. Therefore, the target laser oscillation wavelength can be arbitrarily set near the reference light.

On the other hand, in the method of (2), a cell in which a substance that absorbs light of a desired laser oscillation wavelength is sealed is injected with a laser beam having a narrow band, and the difference in the laser intensity before and after the cell is maximum. That is, by controlling the laser wavelength so that the absorption of the laser light by the substance in the cell is maximized, the laser wavelength is fixed to the desired wavelength. But,
This method can be used only when there is a substance having an absorption line at the same wavelength as the desired laser oscillation wavelength, and conversely, it is not possible to set the desired laser wavelength to any wavelength near the absorption line. Can not. This is the problem to be solved by the present invention.

The present invention has been made in view of the above, and it is possible to fix and control the wavelength of a zonal band excimer laser to an arbitrary wavelength within the laser oscillation region, and thus, there has been no conventional reference wavelength light source. High-precision wavelength control is possible even with narrow band ArF excimer lasers, etc.
By using this narrow band excimer laser as the light source of the reduction projection exposure device and the laser light source of the laser processing machine for microfabrication, the optical performance of these devices is improved, and exposure and processing of finer patterns are performed. It is an object of the present invention to provide a wavelength control device for a narrow band excimer laser capable of performing the above.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, the wavelength control device of the zonal band excimer laser according to the present invention has a wavelength selection element arranged inside or outside the excimer laser oscillator to make the laser beam into a strict band, and from this excimer laser oscillator, In the wavelength controller of the zonal band excimer laser that controls the oscillation wavelength of the obtained laser light based on the absorption line of a substance that absorbs light at a specific wavelength in the vicinity of the laser oscillation wavelength range, a cell in which an absorber is enclosed. A light source is disposed behind the cell, and a spectroscope for selectively entering the light from the light source and the laser oscillation light is disposed in the optical path from the cell. An image sensor for detecting the subsequent light component is provided, and a wavelength controller of a laser oscillator is connected to this image sensor.

[Action]

The wavelength component of the light passing through the cell is observed by the spectroscope, and this light and the narrow band laser light from the laser oscillator are alternately incident on the spectroscope, thereby The laser oscillation wavelength can be arbitrarily fixed and controlled in the vicinity of the absorption line of the wavelength component as a reference.

〔Example〕

 An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a basic configuration of an embodiment of the present invention, in which 1 is an excimer laser oscillator of a narrow band excimer laser having a wavelength selection element driver 2 and a wavelength selection element 3.
Reference numeral 4 is a beam splitter arranged in the optical path of the excimer laser oscillator 1, and 5 is a first shutter arranged in the optical path of the light divided by the beam splitter 4.

Reference numeral 6 is a light source for background light, and a second shutter 7 and a cell 8 containing an absorber for absorbing light are interposed in the optical path from the light source 6, and the light in the above two optical paths merges with each other. They are merged at the vessel 9 and are incident on the spectroscope 10. As the absorber in the cell 8, a absorber that absorbs only light having a specific wavelength in the vicinity of the oscillation wavelength of the excimer laser oscillator 1 is used.

The spectroscope 10 is provided with an image sensor 11,
The spectroscope 10 detects a spectral waveform that has been separated into wavelength components, and outputs the detection signal to the wavelength controller 12. The excimer laser oscillator 1 is controlled by the wavelength controller 12.

The operation of the above configuration will be described below.

First, the first shutter 5 is closed, the second shutter 7 is opened, and the light from the background light source 6 is incident on the cell 8. In the cell 8, only the light having a specific wavelength in the vicinity of the oscillation wavelength of the excimer laser oscillator 1 is absorbed by the absorber therein, and then the light is incident on the spectroscope 10. The light incident on the spectroscope 10 is split into wavelength components, and the spectral waveform is as shown in FIG.
Detected by. As a result, the position P ₁ on the image sensor 11 after the absorption line serving as a reference, whose wavelength is already known, is determined.

Next, the second shutter 7 is closed, the first shutter 5 is opened, and the laser light from the excimer laser oscillator 1 is made incident on the spectroscope 10 via the optical combiner 9, and the light of the oscillation wavelength is similarly emitted. The position P ₂ on the image sensor 11 is detected. The wavelength conversion value K · (P ₂ −P ₁ ) of the difference (P ₂ −P ₁ ) between this position and the reference absorption line position is the difference between the absorption line wavelength λ ₁ and the desired laser wavelength λ _2. (Λ ₂ −
If the laser oscillation wavelength is controlled so as to be equal to λ ₁ ), the wavelength of the narrow band excimer laser light can be fixed to a desired wavelength. Note that K is a wavelength conversion coefficient.

This laser oscillation wavelength is controlled by the wavelength controller 12
Is transmitted to the wavelength selection element driver 2, and thereby the wavelength selection element 3 is controlled.

By repeating the above operation, the oscillation wavelength of the zonal band excimer laser can be stabilized by the detection accuracy of the position difference (P ₂ −P ₁ ).

The wavelength selection element 3 of the laser device 1 is an etalon, a diffraction grating, a prism, or the like, and these may be used alone or in combination of two or more depending on the purpose of use of the narrow band excimer laser. It is desirable that the background light source 6 has a uniform wavelength component near the laser oscillation wavelength.
A deuterium lamp is used for the F laser, and a deuterium lamp, a xenon lamp, etc. are used for the KrF and XeC lasers. In the case of ArF laser, oxygen (O ₂ ) or the like is suitable as the substance of the light absorber. In this case, in order to eliminate the influence of oxygen in the air, the optical path surrounded by the chain line in FIG. 1, the resonator part of the laser and the inside of the spectroscope 10 are replaced with nitrogen. As the optical combiner 9, a combined optical fiber or a half mirror is used. As the spectroscope 10, a diffraction grating spectroscope or a monitor etalon is used.
As the image sensor 11, a linear image sensor, C
A CD image sensor or the like is used.

FIG. 3 shows a control flowchart of the wavelength controller when a diffraction grating type spectroscope is used as the spectroscope 10. Each step will be described below.

Step 1 The central position P ₁ of the absorption line on the image sensor 11 of the background light source light including the absorption line after the spectrum is read. Similarly, the center position P ₂ of the oscillation line of the narrow band excimer laser beam after the spectrum is read.

Step 2 The difference ΔP _2-1 between the center positions of the two images is calculated, and the difference Δλ _2-1 between the wavelength of the absorption line and the oscillation wavelength is calculated from this value.

Step 3 The difference Δλ _o between the desired set oscillation wavelength λ _o and the reference center wavelength λ _s of the absorption line and the difference Δλ between this Δλ _o and Δλ _2-1
To calculate.

Step 4 Δλ is the difference between the desired set oscillation wavelength and the current oscillation wavelength, and a signal is sent to the wavelength selection element driver 2 so that the selection wavelength of the wavelength selection element moves by this wavelength difference.

By the above steps, the narrow band excimer laser can be set to a desired set wavelength.

〔The invention's effect〕

According to the present invention, it is possible to fix and control the wavelength of a fox band excimer laser to an arbitrary wavelength within the laser oscillation region, and thus, a fox band ArF excimer laser without a conventional suitable reference wavelength light source. It becomes possible to control the wavelength with high precision even in such cases. By using this narrow band excimer laser as the light source of the reduction projection exposure device and the laser light source of the laser processing machine for fine processing, the optical performance of these devices is improved. Therefore, it becomes possible to expose and process a finer pattern.

[Brief description of drawings]

The drawings show an embodiment of the present invention. FIG. 1 is a diagram for explaining the basic configuration, FIG. 2 is a diagram showing wavelength components of light passing through a cell, and FIG. 3 is a control flowchart of a wavelength controller. 1 is an excimer laser oscillator, 2 is a wavelength selection element driver, 3 is a wavelength selection element, 6 is a light source for background light, 8 is a cell, 10 is a spectroscope, 11 is an image sensor, and 12 is a wavelength controller.

Claims (1)

[Claims] 1. An excimer laser oscillator 1 is provided with a wavelength selection element inside or outside to make a laser beam into a narrow band, and the oscillation wavelength of the laser beam obtained from this excimer laser oscillator 1 is specified in the vicinity of the laser oscillation wavelength range. In a wavelength control device of a zonal band excimer laser that controls the absorption line of a substance having a light absorption at a wavelength of 10 nm as a reference, a light source is arranged behind a cell 8 in which an absorber is enclosed, and an optical path from this cell 8 is arranged. A spectroscope 10 for selectively entering the light from the light source and the laser oscillation light is arranged therein, and the spectroscope 10 is provided with an image sensor 11 for detecting a light component after the splitting of the both lights. A wavelength controller for a zonal band excimer laser, wherein a wavelength controller 12 of a laser oscillator is connected to the image sensor 11.