JPH06186086A - Wavelength detecting device - Google Patents

Abstract

PURPOSE:To reduce the time for calculation so as to enable high-speed control by detecting change in the fine wavelength of light for detection from the radius of one interference fringe detected, and detecting change in the coarse wavelength of the light for detection from the center position of the interference fringe. CONSTITUTION:A front mirror is provided at the front of an excimer laser chamber 21 and a narrowing unit 30 is provided at the back of the chamber to narrow laser beams for output. A beam splitter for detecting laser beam wavelengths is disposed on the side of the laser beams outputted. A driver 50 driven by a command from a wavelength controller 40 for controlling wavelengths is connected to the wavelength selecting element 31 of the unit 30 to vary the wavelengths of the laser beams for output. The controller 40 is connected to the driver 50 and to a wavelength detector 10 connected to the beam splitter 23. Also, the controller 40 calculates the wavelength of a sample beam and outputs a signal to the driver 50 to drive the wavelength selecting element 31 so as to vary the wavelengths of the laser beams for output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength detecting device,
In particular, the present invention relates to a wavelength detection device for stabilizing the wavelength of a narrow band excimer laser device used as a light source of a semiconductor exposure device.

[0002]

2. Description of the Related Art Conventionally, as a wavelength detector of a narrow band excimer laser, laser output light is sampled again by a beam splitter 101 as shown in FIG. 8, and the sampled light (L) is scattered by a diffuser 103. Through the coarse etalons 105a and 105b and the condenser lens 107,
The interference fringes (A) generated by the coarse etalons 105a and 105b are detected by the line sensor 109, and a large wavelength interval is detected from the interference fringes (A). Similarly, the total reflection mirror 111 reflects the sample light, and the diffusion plate 1
Fine etalon 115a, 11 after scattering at 13
The line sensor 109 detects the interference fringes (A) generated by the fine etalons 115a and 115b through the 5b and the condenser lens 117, and detects the fine wavelength interval from the interference fringes (B).

Here, the fine etalon 115 on one side has a larger interval between the mirrors than the fine etalon 105 on the other side, and the free spectral range [FSR = λ 2 /
(2nd)] is reduced. For this reason,
This is because the finesse (F) of the etalon is determined by the surface accuracy and the parallelism of the etalon, so that an etalon having a finesse of a predetermined value or more cannot be manufactured. Therefore, in order to increase the wavelength detection accuracy, the resolution of the etalon (R = FS
R / F) needs to be improved, and the free spectral range is reduced. However, although the fine etalon 115 with a small free spectral range can detect the detailed movement of the wavelength, when the wavelength of the light to be detected changes by a multiple of the free spectral range, the interference fringes are exactly the same, so a large change in wavelength is caused. It could not be detected. Therefore, a large movement of the wavelength of the detected light is detected by the other coarse etalon 105 having a large free spectral range, and the wavelength of the detected light is calculated.

[0004]

However, when two interference fringes generated by two monitor etalons are detected by two line sensors, the following problems occur. (1) It takes a very long time to calculate the wavelength by analyzing the data of the two interference fringes from the two line sensors, and it is not possible to support the high speed control. (2) It is large because it requires two etalons, their optical system, and a line sensor. (3) The cost of the wavelength detection device is high. There is a problem.

The present invention has been made in view of the above-mentioned problems, and relates to a wavelength detection device, and a wavelength detection device of a narrow band excimer laser device capable of shortening the time required for detection of interference fringes and calculation of wavelength and supporting high-speed control. Intended for improvement.

[0006]

To this end, the first aspect of the present invention is provided.
In the invention, means for allowing the light to be detected to enter and transmit the diffuser plate,
Means for making the scattered light incident on and transmitted through the etalon, means for making the light passing through the etalon transmit or reflect at the angle dispersion element, means for making the light transmitted or reflected at the angle dispersion element incident on the condenser lens and transmitting It is provided with means for detecting interference fringes generated on the focal plane of the lens and means for calculating the wavelength of the output laser light based on the interference fringes.

According to a second aspect of the invention, in a narrow band laser provided with a wavelength selection element, a means for sampling a part of the output laser light, a means for allowing the sample light to enter and transmit the diffuser plate, and a scattered light for entering and transmitting the etalon. Means, means for transmitting or reflecting the light transmitted through the etalon to or from the angle dispersive element, means for allowing the light transmitted or reflected by the angle dispersive element to enter the condenser lens, and generated on the focal plane of the condenser lens. Means for detecting the interference fringes, means for calculating the wavelength of the output laser light based on the interference fringes, means for calculating the deviation between the wavelength of the output laser light and the set wavelength, and controlling the selected wavelength of the wavelength selection element are provided. I have it.

In the third invention mainly based on the first invention or the second invention, a prism or a transmission type or reflection type grating is used as the angle dispersion element.

In the fourth invention, which is mainly based on the first invention, the second invention or the third invention, the output laser light is calculated based on the radius and center position of the interference fringes as means for calculating the wavelength of the output laser light. A means for calculating the wavelength is provided.

[0010]

According to the above structure, the means for allowing the light to be detected to enter the diffuser plate and the diffused light to be incident on the etalon, and the light transmitted through the etalon to be transmitted or reflected by the angle dispersive element. The transmitted or reflected light is made incident and transmitted to the condenser lens, the interference fringes generated on the focal plane of the condenser lens are detected, and the wavelength of the output laser light is calculated based on the interference fringe.

The principle of this invention is shown in FIG. The detected light passes through the diffuser plate 1 and is scattered. The scattered light enters the etalons 2a and 2b, transmits the light having an angle corresponding to the wavelength of the light to be detected, and enters the angle dispersion element 3. The light is transmitted by the angle dispersion element 3 through the angle dispersion element 3 having a wavelength corresponding to the detected light. Then, these lights pass through the condenser lens 4, and interference fringes are generated on the focal plane of the condenser lens 4. This interference fringe is detected by the line sensor 5.

Next, FIG. 9 shows the principle of a Fabry-Perot interferometer (monitor etalon), which will be described in order to facilitate understanding of the present invention. In the following, in the formula,
When representing the Nth power of X (X ^N ), it is expressed as X ^N. Figure 9
As shown in (a), when the light L is incident on the etalon 2 having the mirror spacing d with an incident angle θ and is transmitted through the etalon 2 and the condenser lens 4, on the detection surface separated from the condenser lens 4 by the focal length f. The interference fringes (C) of the light L are formed at. The basic formula of the etalon is

## EQU1 ## 2nd.cos θ = mλ. Here, in the basic equation (1) of the etalon, the angle θ =
When m is 0 and the wavelength is λ when 0,

[Equation 2] 2nd = mO · λ.

Here, the formula (2) -the formula (1) is performed, and the half-angle formula [cos θ = 1-2 sin ^ 2 (θ / 2)] is added to this.
And apply

## EQU00003 ## 2sin ^ 2 (.theta. / 2) = (. Lambda./2nd)(mO-m) is obtained. If the angle θ is a relatively small angle, si
It can be approximated as n (θ / 2) = θ / 2, and by substituting this into equation (3) and rearranging,

## EQU4 ## θ ^ 2 = (λ / nd) (mO-m).

Here, if the distance from the center of the interference fringe (C) is r, as shown in FIG. 9B, the focal length of the condenser lens 4 is f,

## EQU00005 ## r = f.theta. = F (.lamda. / Nd) ^ 1 / 2.times. (MO-m) ^ 1/2, and c = f ^ 2.lamda ./ (nd), and both sides of the equation (5) are 2 When you get on

## EQU6 ## r ^ 2 = c (mO-m). (See FIG. 9 (b))

Here, considering the p-th and p + 1-th peaks, from (6),

## EQU7 ## c = c (mp + 1-mp) = rp ^ 2-rp + 1 ^ 2. Further, when the integer m in the formula (2) is differentiated by the wavelength λ,

[Expression 8] Δλ = (λ ^ 2 / 2nd) · Δm = FSR · Δm. However, FSR = (λ ^ 2 / 2nd) is the free spectrum range of the etalon 6.

Substituting equation (6) into equation (8),

## EQU9 ## Δλ = FSR · r ^ 2 / c. Here, when the wavelength when m = mO is λo,
The required wavelength λ is (9),

It is obtained as λ = λo-FSR · r ^ 2 / c.

Equation (10) shows that the wavelength λ is proportional to the radius r ^ 2 of the interference fringe (C).
Therefore, if the square of the radius of the interference fringes can be correctly obtained, the wavelength of the detected light can be accurately obtained.

Next, the present invention will be described. FIG. 2 shows the waveform of the interference fringes measured by the line sensor 5,
The horizontal axis shows the position of the interference fringes, and the vertical axis shows the light intensity. When the peak positions of the interference fringes are X1 and X2, respectively, the radius r of the interference fringes is

## EQU11 ## r = (X2-X1) / 2.

Further, as shown in the principle of the above Fabry-Perot interferometer (monitor etalon), the wavelength λf calculated from the radius r of the interference fringes generated by the etalon is expressed as follows.

[Mathematical formula-see original document] Therefore, it is possible to calculate a fine change in the wavelength of the detected light from the radius r of the interference fringes according to the equation (12). On the other hand, the center position S of the interference fringes also changes depending on the wavelength due to the angle dispersive element. The center position S of the interference fringe is

## EQU13 ## S = (X2 + X1) / 2.

Assuming that the angular dispersion of the angular dispersion element is α, the wavelength λc obtained by this is expressed as follows.

## EQU14 ## λc = λco + (So−S) f / α where λco is the wavelength when S = So Then, the rough wavelength change of the detected light is detected from the center position S of the interference fringes by the equation (14). can do. The wavelengths of the detected light are calculated by comparing and comparing λf and λc. (Figure 7)

[0021]

Embodiments of the wavelength detecting device according to the present invention will be described below in detail with reference to the drawings. FIG. 3 is a block diagram showing a first embodiment of the wavelength detector according to the present invention. The same parts as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

In FIG. 3, as compared with FIG. 1, a prism 11 is used as an angle dispersion element between the etalon 2 and the condenser lens 4.
It is an example in the case of arranging. The light to be detected passes through the diffusion plate 1 and is scattered. This scattered light is the etalon 2a,
The light having an angle corresponding to the wavelength of the light to be detected is incident on the prism 2 b and is incident on the prism 7. Those lights are refracted by the prism 7 and pass through the prism 7 at an angle of the wavelength corresponding to the detected light. Then, these lights pass through the condenser lens 4 and generate interference fringes (C) on the focal plane. The wavelength of the detected light is calculated based on this interference fringe (C).

FIG. 4 shows a second wavelength detecting device according to the present invention.
It is a block diagram which shows an Example. The same parts as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. FIG. 4 shows an embodiment in which a transmissive grading 8 is arranged between the etalon 2 and the condenser lens 4. Since the transmission type grading 8 has a different diffraction angle depending on the wavelength, it serves as an angle dispersion element for the wavelength.

FIG. 5 shows an example of controlling the wavelength of a narrow band laser using the wavelength detector of the present invention. In FIG. 5, a laser chamber 21 has a window for outputting laser light oscillated by a laser medium (not shown) and a pumping means for this laser medium, and a front mirror on the front side (upper side in the figure) of the laser chamber 21. A narrow band unit 30 is provided on the rear side, and narrows the band of the laser light to be output and outputs it. A beam splitter 23 that detects the wavelength of the laser light is provided on the side of the laser light that is output.

The band narrowing unit 30 is composed of a wavelength selection element 31 such as an etalon or a grating (not shown). Wavelength selection element 31 of band narrowing unit 30
Is connected to a driver 50 that is driven by a command from a wavelength controller 40 that controls the wavelength, and changes the wavelength of laser light to be output. The wavelength controller 40 is connected to the driver 50 and the wavelength detection device 10 connected to the beam splitter 23. The wavelength controller 40 calculates the wavelength of the sample light and outputs to the driver 50 a signal that drives the wavelength selection element 31 and changes the wavelength of the laser light to be output. In addition, the wavelength controller 40 is input with a signal of a wavelength sampled and detected from the wavelength detector 10.

The wavelength detector 10 is an embodiment in which a transmission type grading 8 is arranged as an angle dispersion element as in the second embodiment, and a beam splitter 11 is provided between the etalon 2 and the condenser lens 4. It is arranged. The sample light transmitted through the beam splitter 11 passes through the beam splitter 11, the beam splitter 11, and the condenser lens 4 again to generate interference fringes (C) in the line sensor 5 on the focal plane.

In the above, the operation will be described below. The wavelength selection element 31 narrows the band and outputs the laser light of the excimer laser. Then, this output laser light is sampled by the beam splitter 23, and the diffusion plate 1
Is transmitted through and is scattered. The scattered light is etalon 2
After passing through a and 2b, and also through the beam splitter 11, it is incident on the reflective grading 8 and is diffracted at an angle substantially the same as the incident angle. Again, the light that has entered the beam splitter 11 and is reflected this time is made incident on and transmitted through the condenser lens 4, and the line sensor 5 detects interference fringes on the focal plane of the condenser lens 4. Then, the wavelength controller 40 calculates the wavelength of the sample light based on the interference fringes, controls the driver 50 of the wavelength selection element 31 in the narrow band unit 30 so as to have the set wavelength, and makes the selected wavelength. ing.

FIG. 6 shows an example of a flowchart performed by the wavelength controller. First, it is confirmed whether or not the laser oscillates, and it is confirmed that the laser oscillates (step 10).
1). Next, the line sensor 5 detects the interference fringe (C) (step 102). Then, the radius r of the interference fringe is calculated by the equation (11) r = (X2-X1) / 2, and the center position S of the interference fringe is calculated by the equation (13) S = (X2 + X1) / 2 (step 103). The wavelength λc is calculated from the center position S of the interference fringe by the formula (14) λc = λco + (So−S) f / α (step 104).

Next, the wavelength λf is calculated from the radius r of the interference fringe by the formula (12) λf = λo-FSR · r ^ 2 / c (step 105). Then, a subroutine for calculating the oscillation wavelength λ from the wavelength λc and the wavelength λf is entered and λ is calculated (step 106). Next, the difference Δλ from the set wavelength λt is calculated from the equation Δλ = λt−λ (step 107). Then, the selected wavelength of the wavelength selection element in the band narrowing unit is shifted by Δλ (step 108). Then return to the starting point and repeat this work.

FIG. 7 shows an example of a subroutine for calculating the oscillation wavelength λ from λc and λf. First, it is determined whether or not the absolute value of the difference between λc and λf is smaller than one half of the free spectral range (FSR) of the etalon used (step 201). If yes, step 20
In step 203, the process returns to step 107 and returns to step 107. On the other hand, NO in step 201
In the case of, the magnitude of λc and λf is judged (step 20).
4).

Here, when λc is smaller than λf, the routine proceeds to step 205, where λf = λf + FSR is set, and the routine proceeds to step 201 and returns to the start. On the other hand, when λc is larger than λf, the procedure goes to step 206, where λf = λf−
As FSR, go to step 201 and return to the start. The above calculation is repeated to calculate the oscillation wavelength λ.

[0032]

As described above, according to the present invention, a small change in the wavelength of the detected light is detected by the radius of one detected interference fringe, and the detected light is rough depending on the center position of the interference fringe. Since the wavelength of the light to be detected is calculated by detecting the change in wavelength, the time required for detecting the interference fringes and calculating the wavelength is shortened, and high-speed control can be supported. Furthermore, it is compact and inexpensive. Therefore, the narrow band excimer laser device equipped with the wavelength control device of the present invention is optimal as a light source for a reduction projection exposure device.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of a wavelength detection device according to the present invention.

FIG. 2 is a diagram showing a waveform of an interference fringe measured by a line sensor 5, a horizontal axis shows a position of the interference fringe, and a vertical axis shows a light intensity.

FIG. 3 is a configuration diagram of a first embodiment of a wavelength detection device according to the present invention.

FIG. 4 is a configuration diagram of a second embodiment of a wavelength detection device according to the present invention.

FIG. 5 is a configuration diagram of a wavelength-controlled embodiment of a narrow band laser using the wavelength detection device of the present invention.

FIG. 6 is a flowchart of control of the wavelength controller of the present invention.

FIG. 7 is a flowchart of a control subroutine of the present invention.

FIG. 8 is a configuration diagram of a conventional wavelength detection device.

FIG. 9 is a diagram showing the principle of a Fabry-Perot interferometer (monitor etalon).

[Explanation of symbols]

 1 Diffuser 2 Etalon 3 Angular Dispersion Element 4 Condenser Lens 5 Line Sensor 7 Prism 8 Grading 10 Wavelength Detector 30 Narrowing Bandwidth Unit 40 Wavelength Controller 50 Driver

Claims (4)

[Claims] 1. A means for allowing incident light to be incident on and transmitted through a diffusion plate, a means for allowing scattered light to be incident on and transmitted to an etalon, a means for transmitting or reflecting light transmitted through the etalon to or from an angle dispersive element, and an angle dispersive element. A means for making the transmitted or reflected light incident and transmitted to the condenser lens, a means for detecting the interference fringes generated on the focal plane of the condenser lens, and a means for calculating the wavelength of the output laser light based on the interference fringes are provided. A wavelength detection device characterized by the above. 2. In a narrow band laser having a wavelength selection element, means for sampling a part of the output laser light, means for allowing the sample light to enter and pass through the diffusion plate, and means for allowing the scattered light to enter and pass through the etalon. Means for transmitting or reflecting the light transmitted through the etalon to or from the angle dispersive element, means for making the light transmitted or reflected by the angle dispersive element incident on the condenser lens, and detecting the interference fringes generated on the focal plane of the condenser lens Means for calculating the wavelength of the output laser light based on the interference fringes, and means for calculating the deviation between the wavelength of the output laser light and the set wavelength to control the selected wavelength of the wavelength selection element. Characteristic wavelength detection device. 3. The wavelength detecting device according to claim 1, wherein a prism or a transmission type or reflection type grating is used as the angle dispersion element. 4. A means for calculating the wavelength of the output laser light, comprising means for calculating the wavelength of the output laser light based on the radius and center position of the interference fringes.
Alternatively, the wavelength detection device according to claim 3.