JPH11289116A - Etalon evaluating method and device as well as laser oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correctly measure the evenness in gap intervals due to positions thereof, by a method wherein optical elements changeable of the irradiating region of irradiating beams are arranged between an excimer laser beam source and an etalon in order to irradiate the etalon with the laser beams from the excimer laser beam source. SOLUTION: A slit 14 having a rotary mechanism 15 is inserted right before an etalon 16 as an objective measured element. Besides, the fluctuation 21 in the gap intervals of the etalon 16 is computed from the signals 19 of a sensor 18 using a computer 20. In order to measure the evenness in the gap intervals due to positions, the slit 14 is turned to record the signals 19 in respective positions for computing the half value widths in the transmission characteristic. In such a constitution, the difference in the gap intervals is reflected in the difference between the minimum and maximum half value widths, thereby enabling the difference in the gap intervals to be measured based on the difference in the half value widths. Accordingly, the evenness in the gap intervals can be evaluated without fail.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an etalon evaluation apparatus and an etalon evaluation method, and more particularly, to an evaluation method of a Fabry-Perot etalon used for narrowing a bandwidth of a laser oscillator, an etalon evaluation apparatus thereof, and an etalon using the etalon. The present invention relates to a laser oscillator having a narrow band.

[0002]

2. Description of the Related Art A Fabry-Perot etalon (hereinafter abbreviated as an etalon) is conventionally used as an element for sweeping a wavelength and analyzing a light spectrum, and is inserted into a laser resonator to select a frequency of laser oscillation. It is used as an element to be used.

In recent years, in order to obtain an excimer laser beam having a high spectral purity used as a light source of a semiconductor exposure apparatus, an etalon has been inserted into a laser resonator as a filter used in an optical region.

The semiconductor exposure apparatus is very important in manufacturing a semiconductor device in which miniaturization is remarkably progressing. As a light source of the semiconductor exposure apparatus, a KrF laser which is an excimer laser has already been put to practical use. I have.

[0005] In a semiconductor exposure apparatus, if the wavelength spectrum of the light source is broad, the resolution decreases due to chromatic aberration of the exposure optical system.

Therefore, in an excimer laser for a semiconductor exposure apparatus, it is necessary to narrow the wavelength spectrum in order to reduce the influence of the chromatic aberration.

In particular, in recent years, semiconductor exposure apparatuses have been miniaturized year by year, and in order to satisfy the demand, a sub-picometer is required for the half-width of the wavelength spectrum of the light source.
That is, the spectral width of this laser was conventionally about 2 to 3 pm at half width, but is now 1 p.
A half width of not more than m has been put to practical use.

As a method for obtaining an excimer laser beam having a high spectral purity by using an etalon as described above, for example, a method described in Japanese Patent Application Laid-Open No. 3-87084 is known.

First, the etalon will be described briefly. FIG. 15 is a side view of the air gap etalon.

In this etalon, two parallel flat plates 153a and 153b having a certain reflectance as shown in FIG. 15 are precisely and parallel to each other at an appropriate gap interval 151, and are caused by light interference. This is a filter in a light region that can selectively transmit only a wavelength determined by the reflectance and the gap interval.

Usually, a plurality of spacers 152 having the same thickness are sandwiched between two parallel flat plates 153a and 153b to realize a gap 151 having good parallelism.

[0012] However, in manufacturing, there are variations in the size of the spacers and variations in the gap interval on the order of nanometers due to the accuracy of assembly. There is a tendency for the gap interval to vary, and two parallel flat plates 153a,
It is general that 153b has a C shape.

The direction in which the variation in the gap interval in the case of FIG. 15 is minimized is perpendicular to the paper surface. Here, the direction from the front to the back of the paper is defined as the direction in which the variation in the gap interval is the smallest, and in FIG.
51 is exaggerated to be wide below.

Next, FIG. 16 is a schematic diagram showing the transmission characteristics of the etalon. The transmission characteristics of the etalon have a free spectral range (Free Spectral Range: FS).
R) indicates a peak for each unique wavelength pitch determined by the etalon gap interval. The sharpness of each peak is mainly determined by the reflectivity, roughness, and parallelism of the parallel plate, and the sharper the higher the reflectivity, the lower the roughness, and the higher the parallelism.

As mentioned above, the narrowing of the laser needs to be uniform throughout the beam.

Now, the laser beams are changed to a, b, and
Let it pass through the beam position of c. At this time, looking at one peak in the transmission characteristics of the etalon, the peak wavelength slightly shifts as shown in FIG. 17 because the etalon gap interval 151 is different at each beam transmission position.

In the case of narrowing the bandwidth to the half-width of the sub-picometer, if the gap interval 151 has a variation of several tens of nanometers, the wavelength shift is on the order of the picometer, and the spread of the half-width due to the variation of the gap interval is ignored. It becomes impossible size.

Therefore, when the etalon is used for an excimer laser for a semiconductor exposure apparatus, the etalon is required to have a parallel gap with high accuracy.

The measurement of the parallelism of the etalon is important in guaranteeing the performance of an excimer laser for a semiconductor exposure apparatus.

FIG. 18 shows a conventional etalon evaluation apparatus. In FIG. 18, a laser beam from an excimer laser light source 181 is expanded to an appropriate beam size by a beam expander 182. This beam is applied to the diffuser 18
3 and scattered in various directions, etalon 1
Irradiate 84.

The light transmitted through the etalon 184 is
An image is formed on the sensor 186 by the lens 185.

The light pattern on the surface of the sensor 186 becomes concentric interference fringes as shown at 19a in FIG.

As shown in FIG. 19A, when the sensor is a vertically long line sensor, a signal 187 from the sensor at this time is as shown in FIG. 19B, for example. When a pattern corresponding to three stripes can be measured in this manner, the FSR of the etalon is known, and thus it becomes an index indicating the half-value width of the transmission characteristic of the etalon.

More precisely, the measured half-value width is obtained by overlapping the spread of the spectrum of the laser beam specified for the measurement. If the spectrum of the laser beam is sufficiently narrow, the measured half-width is measured. Indicates the characteristics of the etalon itself.

[0025]

However, according to the above configuration, it is possible to inspect whether or not the transmission characteristics of the etalon have reached a required level. However, individual characteristics of the etalon, especially, the gap interval can be checked. Variations have not been measured.

That is, in the etalon evaluation method or the etalon evaluation apparatus, it is required to accurately measure the uniformity of the gap interval in the plane of the laser beam. There is a problem that the uniformity according to the location of the interval is not measured.

The present invention relates to a method and an apparatus for evaluating filter characteristics of an etalon used for obtaining such an excimer laser beam having a high spectral purity, and a laser oscillator. It is an object of the present invention to provide a device that accurately measures the characteristics and a laser oscillator that can oscillate a laser beam with higher spectral purity by using an etalon evaluated by the device for narrowing a band.

[0028]

In order to solve this problem, the present invention relates to an optical element provided between an excimer laser light source and an etalon when irradiating the etalon with laser light from an excimer laser light source. Thus, the irradiation area of the irradiation beam can be changed.

This makes it possible to accurately measure the variation of the etalon gap interval depending on the location, that is, the uniformity. In addition, the etalon evaluated by the above configuration is used as a laser oscillator to narrow a band of a laser beam.

[0030]

The present invention according to claim 1 comprises a laser oscillator, a diffusion plate, a condenser lens, and a light receiving sensor, wherein a Fabry-Perot etalon is provided between the diffusion plate and the condenser lens, An etalon evaluation device that measures equitilt interference fringes of a Perot etalon and evaluates characteristics thereof, the device including means for allowing light from the laser oscillator to enter a plurality of regions of the Fabry-Perot etalon. With this configuration, the etalon gap spacing depending on the location, that is, uniformity is accurately measured and evaluated.

More specifically, the present invention according to claim 2 is the device according to claim 1, wherein the means for allowing light from the laser oscillator to enter a plurality of regions of the Fabry-Perot etalon includes: An etalon evaluation apparatus characterized in that it is a slit installed so as to be relatively rotatable with respect to the Fabry-Perot etalon immediately before, whereby a direction in which the gap interval has a large variation can be identified, and the magnitude of the variation can be evaluated.

Alternatively, the present invention described in claim 3 provides
In the apparatus of (1), the means for allowing light from the laser oscillator to be incident on a plurality of regions of the Fabry-Perot etalon is an aperture which is provided to be movable relative to the Fabry-Perot etalon immediately before the Fabry-Perot etalon. This makes it possible to quantitatively evaluate the variation of the gap interval depending on the location.

According to a fourth aspect of the present invention, in the apparatus according to any one of the first to third aspects, an aperture and an optical system are provided between the laser oscillator and the diffusion plate, and a portion where the spectrum of the laser beam oscillated from the laser oscillator is constant is provided. If only one is selected and used for evaluation, more accurate measurement can be performed.

More specifically, as described in claim 5,
In the apparatus according to the fourth aspect, even if the optical system provided between the laser oscillator and the diffusion plate is a beam expander, more accurate measurement can be performed.

Alternatively, as described in claim 6, claim 1
In the devices of (1) to (5), a narrow band excimer laser oscillator may be used as the laser oscillator.

According to a seventh aspect of the present invention, in the device of the third aspect, a line sensor is used as the sensor, and the line sensor is installed in the same direction as the scanning direction of the aperture installed immediately before the Fabry-Perot etalon. The evaluation device is characterized in that the measurement can be performed with higher accuracy.

According to the eighth aspect of the present invention, an evaluation is performed by irradiating a Fabry-Perot etalon with a laser beam diffused therein to measure equi-tilt interference fringes, and to evaluate characteristics of the Fabry-Perot etalon from the equi-tilt interference fringes. An evaluation apparatus having means for calculating a change in the gap interval of the Fabry-Perot etalon from the equi-tilt interference fringes, so that more accurate measurement can be performed.

According to a ninth aspect of the present invention, in the apparatus according to the eighth aspect, the calculating means is configured to irradiate a laser beam to a reference position of the etalon using a slit to obtain an equi-tilt interference fringe.
a and an interference fringe b obtained by irradiating the laser beam to an arbitrary position of the Fabry-Perot etalon using the slit as at least an input signal, and obtaining an etalon from a change in half-value width of the equitilt angle interference fringes a and b. An evaluation device characterized by being a means for calculating a change in the gap interval of
More accurate measurement can be performed.

According to a tenth aspect of the present invention, in the apparatus according to the eighth aspect, the calculating means is configured to irradiate a laser beam to a reference position of the etalon using an aperture, and to obtain an equi-tilt interference fringe a
And an interference fringe b obtained by irradiating the laser beam to an arbitrary position of the Fabry-Perot etalon using the aperture as at least an input signal, and determining a gap interval of the etalon from a moving amount of the equi-tilt interference fringes a and b. This is an evaluation device characterized in that it is a means for calculating a change in, and can perform more accurate measurement.

According to an eleventh aspect of the present invention, in the device of the eighth to tenth aspects, there is provided means for converting an input signal into transmission characteristics based on the wavelength of the etalon, and the signal after conversion into transmission characteristics based on the wavelength. This is an evaluation apparatus characterized by calculating a change in the gap interval of the etalon from the etalon, and can perform more accurate measurement.

According to the twelfth aspect of the present invention,
In the apparatuses 0 and 11, the interference fringes in one direction and the other direction from the center of the concentric circle of the equi-tilt interference fringes are measured, and the average value of the moving amount of each interference fringe is obtained.
This is an evaluation device that corrects a measurement error and calculates a change in a gap interval of an etalon, and can perform more accurate measurement.

According to a thirteenth aspect of the present invention, a laser beam diffused to a Fabry-Perot etalon is irradiated to measure equi-tilt interference fringes, and a change in a gap interval of the Fabry-Perot etalon is calculated from the equi-tilt interference fringes. The evaluation method is characterized in that the measurement can be performed with higher accuracy.

The invention according to claim 14 is the invention according to claim 13
In the evaluation method, the calculation method is such that the laser beam is illuminated to the reference position of the etalon using a slit, and the oblique interference fringes a obtained by irradiating the laser beam using the slit to any position of the Fabry-Perot etalon. Is a method of calculating a change in the gap interval of the etalon from a change in interference fringes b obtained by irradiating the
More accurate measurement can be performed.

The invention according to claim 15 provides the invention according to claim 13
In the evaluation method, the calculation method is such that an equiangular interference fringe a obtained by irradiating a laser beam to a reference position of an etalon using an aperture and the laser beam using the aperture to an arbitrary position of the Fabry-Perot etalon. This is a method of calculating a change in the gap interval of the etalon from the movement amount of the interference fringes b obtained by irradiating the etalon, and can perform more accurate measurement.

The invention of claim 16 provides the invention of claim 13
The evaluation method according to any one of (1) to (15), wherein the input signal is converted into transmission characteristics according to the wavelength of the etalon, and a change in the gap interval of the etalon is calculated from the transmission characteristics according to the wavelength. Measurement can be performed.

The invention according to claim 17 is based on claim 1.
In the devices of Nos. 5 and 16, the interference fringes in one direction and the other direction are measured from the center of the concentric circle of the equi-tilt interference fringes, and the average value of the movement amount of each interference fringe is obtained by measuring
This evaluation method is characterized in that a measurement error is corrected and a change in the etalon gap interval is calculated, so that more accurate measurement can be performed.

The invention according to claim 18 is directed to a laser oscillator in which a Fabry-Perot etalon is provided inside an optical resonator to narrow a band of a laser beam. It is a laser oscillator characterized by narrowing the band of the laser beam oscillating from the laser oscillator by using a region where the change in the gap interval of the etalon is small from the results, and A laser beam with high spectral purity can be obtained.

(Embodiment 1) FIG. 1 is a schematic configuration diagram of an apparatus for evaluating a variation in an etalon gap interval according to a first embodiment of the present invention.

In FIG. 1, 11 is an excimer laser oscillator for measurement, 12 is a beam expander, 13 is a diffuser,
14 is a slit, 15 is a slit rotation mechanism, 16 is an etalon, 17 is a lens, 18 is a sensor, 19 is a signal, 20
Is a calculator, and 21 is a change in the gap interval of the etalon calculated by the calculator 20.

The characteristic configuration of this embodiment is that the slit 14 having the rotation mechanism 15 is inserted immediately before the etalon 16 to be measured, and the calculator 20
The difference is that a change 21 in the gap interval of the etalon is calculated from the signal 19 of FIG. 8 and the other functions are the same as those of the components described in the conventional example.

Here, the positional relationship between the etalon 16 and the slit 14 is shown in FIG. Now, in FIG. 2, when the position of the slit 14 is at the position 2a, interference fringes from the sensor 18 are recorded in the same manner as in the conventional example.

The signal recorded from the sensor 18 at this time is converted into a transmission characteristic by wavelength by the calculator 20, and becomes a signal 3a shown in FIG.

Thereafter, the position of the slit 14 is rotated to the position 2b by the rotation mechanism 15.

Then, the interference fringes from the sensor 18 are recorded,
After being converted into transmission characteristics by wavelength by the calculator 20, the signal becomes like a signal 3b shown in FIG. At this time, the signal 3a and the signal 3b measure the transmission characteristics of the etalon 16 in a horizontally long place in different directions.

In this way, the slit 14 is rotated to record signals at each position. And
The calculator 20 calculates the half-width Δ3a of the transmission characteristic depending on the wavelength,
.DELTA.3b...

The half-value widths obtained in this way are all the same if they are perfectly parallel etalons, but are actually small in a certain direction because they are not parallel to the etalon gap. The value is large in a direction orthogonal to the direction.

Here, assuming that the smallest half width is Δ1 and the largest half width is Δ2, the difference between the half widths at this time reflects the difference in the gap interval at the slit position of each etalon. Assuming that the difference between Δ1 and Δ2 is Δλ, the maximum gap interval difference ΔL on the etalon is approximately represented by the following (Equation 1).

[0058]

(Equation 1)

Here, λ is the wavelength of the excimer laser beam output from the excimer laser oscillator 11, and FSR is the value of the FSR of the etalon 16.

Thus, in this way, the difference in gap spacing in different directions on the etalon can be measured.

As described above, in the present embodiment, the slit is rotated, the signal from the sensor is recorded, and the uniformity of the gap interval in each direction on the etalon is reliably evaluated by the calculator from the received signal. can do.

In this embodiment, the change in the gap interval is obtained by converting the signal from the sensor 19 into the wavelength characteristic of the etalon, but the change in the gap interval is also determined from the difference in the half width of the signal from the sensor 19 itself. You can ask. In that case, the difference between the smallest half width and the largest half width is Δx
In other words, the maximum gap interval difference ΔL on the etalon
Is approximately expressed by the following (Equation 2).

[0063]

(Equation 2)

In this embodiment, for the sake of simplicity, the description has been made on the assumption that the spectrum width of the measuring laser beam is sufficiently narrower than the half width of the transmission characteristic of the etalon. If the spectrum of the light has a spread, the uniformity of the gap interval in each direction on the etalon can be similarly evaluated by appropriately correcting the action of the spread by deconvolution processing or the like.

(Embodiment 2) Hereinafter, a second embodiment of the present invention will be described with reference to the drawings. FIG.
FIG. 3 is a conceptual diagram of an etalon evaluation device according to a second embodiment of the present invention. In FIG. 4, reference numeral 41 denotes a measuring laser oscillator. In this embodiment, an excimer laser oscillator is typically used. 42 is an aperture for controlling a laser beam used for measurement, 43 is a beam expander, 44 is a diffuser, 45
Is an aperture for controlling the irradiation range of the etalon, 46 is a moving mechanism of the aperture 45, 47 is an etalon, 48 is a lens for condensing a laser beam, 49 is a sensor, 50 is a signal extracted from the sensor, 51 is a calculator, 52 is a change in the etalon gap interval calculated by the calculator 51.

Next, the operation will be described. The laser beam emitted from the excimer laser oscillator 41 is transmitted through an aperture 42
Selects only an arbitrary part. In FIG. 4, the laser beam is shown by a dotted line. The laser beam that has passed through the aperture 42 is expanded to an appropriate beam size by the beam expander 43.

This beam irradiates the etalon 47 while being diffused in various directions by the diffusion plate 44. At this time, the aperture 45 controls a portion where the laser beam irradiates the etalon 47. The etalon irradiation range can be selected by moving the aperture by the aperture moving mechanism 46. The laser beam transmitted through the etalon 47 is focused on the sensor 49 by the lens 48.

The light pattern on the sensor 49 is shown in FIG.
As shown in a, the interference pattern is a concentric interference pattern, that is, an equi-tilt interference fringe. In the present embodiment, when the interference pattern for three fringes is measured by using the line sensor, the pattern of the equi-tilt interference fringes can be converted into the transmission characteristic based on the wavelength of the etalon because the FSR of the etalon 47 is known, The wavelength half width can be reduced.

In practice, the half-width obtained in this way includes the spread of the spectrum of the laser beam. However, if the laser spectrum is known, the spread of the spectrum can be removed by deconvolution or the like, and only the characteristics of the etalon can be known. . Also, if you use a laser beam narrowed so that the spread of the spectrum can be ignored,
It goes without saying that the half width of the transmission characteristic of the etalon can be directly obtained from the measurement data.

This embodiment is different from the conventional example in that the aperture 45 and the aperture moving mechanism 46 are provided immediately before the etalon 47.
Is set, and the change of the gap interval of the etalon is calculated from the signal 50 from the sensor using the calculator 51. FIG. 6 shows the positional relationship between the etalon 47 and the aperture 45.

In FIG. 6, the shaded portion is the shield portion of the aperture, and the black portion is the opening portion of the aperture. The hatched portion is the etalon. By moving the aperture, the etalon-irradiated portion can be changed as shown in FIGS. 6A and 6B. When the aperture is at 6a in FIG. 6, interference fringes are measured in the same manner as in the conventional example, and converted into transmission characteristics based on wavelength. Next, the aperture is moved to the position of 6b in FIG. 6 and the same measurement is performed to convert the aperture into a transmission characteristic by wavelength. At this time, the transmission characteristics are as shown in FIG.

In FIG. 7, 7a is the wavelength transmission characteristic when the arrangement of the apertures is 6a in FIG. 6, and 7b is the wavelength transmission characteristic when the arrangement of the apertures is 6b in FIG. Here, when the gap intervals of the etalon are equal regardless of the location, the center positions of the transmission characteristics completely match. However, if there is a difference in the etalon gap interval between 6a and 6b in FIG. 6 due to the surface precision and non-parallelism of the etalon, 7a in FIG.
The center position of 7b is different. Assuming that this difference is Δλ, the difference of the gap interval of 7b of FIG. 7 from 7a of FIG.
Given by

In this manner, the aperture is moved to Δ
λ can be measured, and the etalon gap variation can be calculated from the signal 50 using the calculator 51.
Further, in the present embodiment, the laser beam is used after being expanded to an appropriate size by the aperture 42 and the cut-out beam expander 43. The laser beam output from the excimer laser used in this embodiment may have a different spectral width or wavelength depending on the position of the beam. In such a case, the measurement accuracy is greatly improved by selecting and using only a portion where the spectrum width and the wavelength are constant by the aperture 42.

As described above, by disposing the aperture immediately before the etalon and measuring the transmission characteristic of the etalon every time the aperture is moved, the variation in the gap interval of the etalon can be determined from the movement amount of the center position of the transmission characteristic. It can be evaluated quantitatively.

In this embodiment, an excimer laser oscillator is used as a light source. However, any type of light source can be used as long as it can output light having a band narrow enough to be corrected by deconvolution processing. Further, in this embodiment, the distribution of the equi-tilt interference fringes of the etalon is converted into the wavelength transmission characteristic.
The gap interval of the etalon can also be measured from the displacement Δx of the equi-tilt interference fringes. In this case, the gap interval ΔL of the etalon
Is given by (Equation 2).

In this embodiment, the place where the etalon is irradiated is selected by scanning the aperture. However, the same applies when the aperture is provided with a large number of openings in advance and the measurement is performed while blocking the openings other than the place to be irradiated. It goes without saying that measurements can be made.

(Embodiment 3) Hereinafter, a third embodiment of the present invention will be described with reference to the drawings.
FIG. 8 is a conceptual diagram of an etalon evaluation device according to the third embodiment of the present invention. In FIG. 8, reference numeral 81 denotes a measuring laser oscillator. In this embodiment, an excimer laser oscillator is typically used. Reference numeral 82 denotes an aperture for controlling a laser beam used for measurement; 83, a beam expander; 84, a diffuser;
Reference numeral 5 denotes an aperture for controlling the irradiation range of the etalon, 86 denotes a moving mechanism of the aperture 85, 87 denotes an etalon, 88 denotes a lens for condensing a laser beam, and 89 denotes a sensor. In this embodiment, a line sensor is used. Reference numeral 90 denotes a sensor moving / rotating mechanism, reference numeral 91 denotes a signal extracted from the sensor, reference numeral 92 denotes a calculator, and reference numeral 93 denotes a change in the etalon gap interval calculated from the signal 91 by the calculator 92.

Next, the operation will be described. The laser beam emitted from the excimer laser oscillator 81 is transmitted through an aperture 82
Selects only an arbitrary part. In FIG. 8, the laser beam is indicated by a dotted line. The laser beam that has passed through the aperture 82 is expanded to an appropriate beam size by the beam expander 83. This beam irradiates the etalon 87 while being diffused in various directions by the diffusion plate 84. At this time, the aperture 85 controls a portion where the laser beam irradiates the etalon. Also, the aperture moving mechanism 8
The etalon irradiation range can be selected by moving the aperture according to FIG. The laser beam transmitted through the etalon 87 is focused on the sensor 89 by the lens 88. The light pattern on the sensor 89 is a concentric interference pattern, that is, an equi-tilt interference fringe, as shown at 9a in FIG.

The difference between the present embodiment and the second embodiment is that the sensor 89 is moved as shown in FIG. 9A, and a total of six stripes are measured with three stripes sandwiching the center of the concentric circle.
In addition, the sensor 89, which is a line sensor,
5 is installed in the same direction as the moving direction. Normal sensor 8
9 is set at the focal position of the lens 88,
For example, when there is a manufacturing error, the position where the sensor 89 is installed is slightly shifted from the focal position. Embodiment 3
Is effective in such a case.

FIG. 10 is a diagram showing how the equi-tilt interference fringes change when the etalon cap spacing is evaluated using this evaluation system. In the case of FIG. 10, the sensor is installed at the focal position of the lens without error. The aperture is set to 10a in FIG.
The equi-tilt interference fringes when measured at the position shown in FIG.
10a '.

Next, the equiangular interference fringes when the aperture is set at the position 10b in FIG.
b '. If the etalon cap spacing changes in 10a 'and 10b', the diameter of the equi-tilt interference fringes changes, and the movement amounts 10Δr and 10Δl of the interference fringes at this time are equal to each other. 10Δr and 10Δl are Δx in (Equation 2)
Therefore, the change .DELTA.L of the etalon's cap space can be obtained from Equation 2. Also, when the projection angle interference fringes are converted into transmission characteristics based on the wavelength of the etalon, 10Δr and 10Δl are converted into Δλ in Equation 1, so that the change ΔL in the etalon's gap interval can be obtained from Equation 1.

Therefore, as shown in FIG. 10, when the sensor is installed at the focal position of the lens without error, there is no problem if only one of the three concentric circles of the equiangular interference fringe is measured as in the second embodiment. . Next, consider a case where the installation position of the sensor has an error with respect to the focal position of the lens as shown in FIG. At this time, the apertures are set to 11a and 11b in FIG.
The equidistant-angle interference fringes measured by installing the laser beam at the positions 11a 'and 11b' are as follows. At this time, if there is a difference in the etalon capacities at 11a and 11b, the diameters of the concentric circles of 11a 'and 11b' change.

In the case shown in FIG. 11, in addition to the change in the diameter of the concentric circle, the entire concentric circle of the equi-tilt interference fringes is displaced due to the deviation from the focal position of the sensor installation location. The amount of displacement is substantially 11Δc shown in FIG. 11, and the direction of displacement is the direction of movement of the aperture from 11a to 11b.
The line sensor is installed in the same direction as the moving direction. In such a case, the movement amounts 11Δr and 11Δl of the interference fringes are not equal. Therefore, only by measuring three fringes of the equi-tilt interference fringes as in the second embodiment, it is possible to accurately obtain the difference in the etalon cap spacing. Can not. In the case as shown in FIG. 11, the average value of the movement amounts 11Δr and 11Δl is the movement amount Δx of the interference fringes in Expression 2. If Δx is known, the change in the gap interval of the etalon can be obtained using Equation 2.

Therefore, in the third embodiment, it is possible to measure the interference fringes on both sides of the center of the concentric circle, calculate the average value of the amount of movement of the interference fringes on both sides, and obtain the change in the gap interval of the etalon. I can do it. Also, equi-tilt interference fringes 11a ', 11
By converting b ′ into the transmission characteristic of the etalon depending on the wavelength, the gap interval of the etalon can be obtained. In this case, the wavelength transmission characteristics of the etalon are as shown in FIG.

Here, 12a is the wavelength transmission characteristic of the etalon when the aperture is at the position of 11a in FIG.
2b is the wavelength transmission characteristic of the etalon when the aperture is at the position of 11b. 12Δλr, 12Δλl in FIG.
Are 11Δr and 11Δl converted into wavelengths, and 1
Since the average value of 1Δλr and 11Δλl is Δλ in Equation 1, if 12Δλr and 12Δλl are known, the distribution of the gap interval of the etalon can be measured using (Equation 1).

As described above, when there is an error in the position of the sensor to be installed at the focal position of the lens, the equi-tilt interference fringes are measured for three fringes in total of three fringes across the center of the concentric circle. Then, the variation in the gap interval of the etalon can be quantitatively evaluated from the average value of the movement amount of the center position of the transmission characteristic on both sides of the concentric circle. In this embodiment, an excimer laser oscillator is used as the light source. However, any type of light source can be used as long as it can output light having a band narrow enough to be corrected by deconvolution processing.

In the present embodiment, the equi-tilt interference fringes are measured for a total of six fringes three by three with the center of the concentric circle interposed therebetween, but if more than six fringes are measured, the etalon gap can be more accurately measured. An interval is required.

(Embodiment 4) FIG. 13 is a diagram showing a configuration of an optical resonator of an excimer laser oscillator according to a fourth embodiment of the present invention. In FIG. 13, 131 is a total reflection mirror,
132 is a quarter-wave plate, 133 is a discharge tube, 134 is a polarization separation mirror, 135 is a prism, 136 is an etalon, 138 is a prism, and 139 is a grating.

Next, the operation of the optical resonator will be described with reference to FIG. The light 140 amplified by the laser medium in the discharge tube 133 has its propagation direction separated by the polarization separating mirror 134 depending on the polarization component, and the light of one polarization component is output as the output light 141. The other one of the polarized light components passes through the polarization splitting mirror 134 and becomes the transmitted light 142. Transmitted light 142
Passes through the three prisms 135, 137, 138 and the etalon 136, and enters the grating 139 while the beam size is enlarged. Here, the etalon 136 has wavelength selectivity, so that the light transmitted through the etalon has a narrow wavelength spectrum width.

The spectral width of the transmitted light 142 is narrowed also by the diffraction effect of the grating. The reason for expanding the beam size using the prisms 135, 137, and 138 is to increase the efficiency of narrowing the spectrum of the wavelength due to diffraction of the grating.

Further, since the magnification of one prism is limited to about three times, three prisms are used in this embodiment. The reflected light 143 diffracted by the grating 139 again passes through the polarization splitting mirror 134 and is amplified by the laser medium to become light 144, which is a １ ／ wavelength plate 132.
Enter. The light 144 is reflected by the total reflection mirror 131 to become a reflected light 145. The light 144 passes through the quarter-wave plate 132 twice, becomes equivalent to the light passing through the half-wave plate, and is changed in one direction. Reference numeral 144 denotes reflected light 145 that includes polarization components in both directions.

Next, the reflected light 145 is amplified by the laser medium of the discharge tube 133 and becomes light 140. In the light 140, a polarization component in one direction is output as an output light 141 by a polarization separation mirror 134 and output. The other polarized light component is processed 142 to continue the oscillation.

Next, the features and effects of this embodiment will be described with reference to FIG. FIG. 14 (α) shows etalon 1
FIG. 36 is a view of the light emitting device viewed from the optical axis direction. First, the cross-sectional view of the laser beam transmitted through the etalon is 1 in FIG.
At 4a, it is assumed that the spectrum of the laser beam of the output light 141 at this time is 14a 'in (β) of FIG.

Next, the etalon is evaluated by the evaluation method shown in the first to third embodiments. For example, if the change in the gap interval is the smallest in the region 14b in the etalon 136, the etalon is moved and rotated in the present embodiment. This causes the laser beam to pass through the region 14b. By doing so, the spectrum becomes like 14b 'in (β) of FIG. When comparing 14a 'and 14b', FFWMa> FWHMb, so that a laser beam with higher spectral purity can be obtained by using the region 14b.

As described above, the change in the gap interval of the etalon is evaluated by using the evaluation method as in the first to third embodiments as in the present embodiment, and the region where the change in the gap interval is small is narrowed by the laser beam. By using the band, a laser beam with higher spectral purity can be obtained.

[0096]

As described above, according to the present invention, the advantageous effect that the uniformity of the gap interval of the etalon can be accurately measured can be obtained. Further, by evaluating the etalon according to the present invention and using a region having a good gap interval for narrowing the band of the laser beam, the spectral purity of the laser beam can be further improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of an etalon evaluation device according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a positional relationship between the etalon and a slit.

FIG. 3 is a schematic diagram of a wavelength characteristic of the etalon.

FIG. 4 is a schematic diagram showing a configuration of an etalon evaluation device according to a second embodiment of the present invention.

FIG. 5 is a schematic diagram of an equi-tilt interference pattern and wavelength transmission characteristics of the etalon.

FIG. 6 is a diagram showing a positional relationship between the etalon and an aperture.

FIG. 7 is a view showing a wavelength characteristic of the etalon to be measured.

FIG. 8 is a schematic diagram showing a configuration of an etalon evaluation device according to a third embodiment of the present invention.

FIG. 9 is a schematic diagram of an equi-tilt interference pattern and wavelength transmission characteristics of the etalon.

FIG. 10 is a diagram showing a change in equitilt angle interference fringes when the etalon gap is evaluated using the same evaluation system.

FIG. 11 is a diagram showing a state of a change of equi-tilt interference fringes when evaluating the etalon's cap interval using the present evaluation system when there is a shift in the sensor.

FIG. 12 is a diagram showing a wavelength characteristic of the etalon to be measured.

FIG. 13 is a diagram showing a configuration of an optical resonator according to a fourth embodiment of the present invention.

FIG. 14 is a diagram illustrating the etalon viewed from the optical axis direction and a laser spectrum.

FIG. 15 is a diagram showing a structure of an etalon in a conventional example.

FIG. 16 is a schematic diagram of wavelength characteristics of the etalon.

FIG. 17 is a schematic diagram showing a shift in a wavelength direction of wavelength transmission characteristics due to a change in a gap interval of the etalon.

FIG. 18 is a diagram showing a configuration of the etalon evaluation device.

FIG. 19 is a schematic view of equi-tilt interference fringes and wavelength transmission characteristics of the etalon.

[Explanation of symbols]

 REFERENCE SIGNS LIST 11 excimer laser light source for measurement 12 beam expander 13 diffuser 14 slit 15 slit rotation mechanism 16 etalon 17 lens 18 sensor 19 signal 20 calculator 21 change in etalon gap interval 41 excimer laser oscillator for measurement 42 aperture 43 beam expander 44 Diffusion plate 45 Aperture 46 Aperture moving mechanism 47 Etalon 48 Lens 49 Sensor 50 Signal 51 Calculator 52 Change in etalon gap interval 81 Excimer laser oscillator for measurement 82 Aperture 83 Beam expander 84 Diffusion plate 85 Aperture 86 Aperture moving mechanism 87 Etalon 88 Lens 89 Sensor 90 Sensor moving and rotating mechanism 91 Signal 92 Calculator 93 Change in gap interval of etalon 131 Total reflection mirror 132 Quarter-wave plate 13 3 Discharge Tube 134 Polarization Separating Mirror 135 Prism 136 Etalon 137 Prism 138 Prism 139 Grating 140 Light 141 Output Light 142 Transmitted Light 143 Reflected Light 144 Light 145 Reflected Light 151 Gap Interval 152 Spacer 153a Parallel Plate 153b Parallel Plate Laser Oscillator 182 Beam expander 183 Diffusion plate 184 Etalon 185 Lens 186 Sensor 187 Signal

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Keitaro Takano 3-10-1, Higashi-Mita, Tama-ku, Kawasaki-shi, Kanagawa Prefecture Inside Matsushita Giken Co., Ltd. (72) Inventor Yuji Hashidate 3-chome, Higashi-Mita, Tama-ku, Kawasaki-shi, Kanagawa Matsushita Giken Co., Ltd. (No. 10) Matsushita Giken Co., Ltd.

Claims (18)

[Claims] 1. A laser oscillator, a diffusion plate, a condenser lens, and a light receiving sensor, a Fabry-Perot etalon is provided between the diffusion plate and the condenser lens, and equi-tilt interference fringes of the Fabry-Perot etalon are measured. An apparatus for evaluating characteristics, comprising: means for allowing light from the laser oscillator to enter a plurality of regions of the Fabry-Perot etalon. 2. The apparatus according to claim 1, wherein the means for allowing light from a laser oscillator to be incident on a plurality of regions of the Fabry-Perot etalon is provided so as to be rotatable relative to the Fabry-Perot etalon immediately before the Fabry-Perot etalon. An evaluation device characterized in that it is a slit formed. 3. The apparatus according to claim 1, wherein the means for allowing light from a laser oscillator to be incident on a plurality of regions of the Fabry-Perot etalon is provided immediately before the Fabry-Perot etalon so as to be relatively movable with respect to the Fabry-Perot etalon. An evaluation device, characterized in that the aperture is a compressed aperture. 4. An apparatus according to claim 1, wherein an aperture and an optical system are provided between the laser oscillator and the diffusion plate, and only a portion where the spectrum of the laser beam oscillated from the laser oscillator is constant is selected for evaluation. An evaluation device characterized by being used. 5. The evaluation device according to claim 4, wherein the optical system provided between the laser oscillator and the diffusion plate is a beam expander. 6. An evaluation apparatus according to claim 1, wherein an excimer laser oscillator having a narrow band is used as the laser oscillator. 7. The evaluation apparatus according to claim 3, wherein a line sensor is used as the sensor, and the line sensor is installed in the same direction as the scanning direction of an aperture installed immediately before the Fabry-Perot etalon. . 8. An evaluation apparatus for irradiating a Fabry-Perot etalon with laser light diffused thereto, measuring equi-tilt interference fringes, and evaluating characteristics of the Fabry-Perot etalon from the equi-tilt interference fringes. An evaluation apparatus comprising: means for calculating a change in a gap interval of the Fabry-Perot etalon from a tilt interference fringe. 9. The apparatus according to claim 9, wherein the calculating means is configured to irradiate a laser beam to a reference position of a Fabry-Perot etalon using a slit and to obtain the laser beam using the equi-tilt interference fringe a and the slit. An interference fringe b obtained by irradiating light to an arbitrary position of the Fabry-Perot etalon is used as at least an input signal, and a change in a gap interval of the Fabry-Perot etalon is calculated from a change in a half-value width of the equi-tilt interference fringes a and b. An evaluation device characterized in that the evaluation device is a means for performing evaluation. 10. The apparatus according to claim 8, wherein the calculating means irradiates the laser beam onto the reference position of the Fabry-Perot etalon using an aperture, and obtains an equi-tilt interference fringe a.
And an interference fringe b obtained by irradiating the laser beam to an arbitrary position of the Fabry-Perot etalon using the aperture as at least an input signal, and calculating the Fabry-Perot etalon from the movement amount of the equi-tilt interference fringes a and b. An evaluation device, which is a means for calculating a change in a gap interval. 11. An apparatus according to claim 8, further comprising means for converting an input signal into transmission characteristics according to the wavelength of the Fabry-Perot etalon, and converting the signal converted into transmission characteristics according to the wavelength from the Fabry-Perot etalon. An evaluation device for calculating a change in a gap interval of the evaluation device. 12. The apparatus according to claim 10, wherein the interference fringes in one direction and the other direction are measured from the center of the concentric circle of the equi-tilt interference fringes, and the average of the movement amount of each interference fringe is measured. An evaluation apparatus, wherein a value is taken to correct a measurement error and a change in a gap interval of a Fabry-Perot etalon is calculated. 13. A method of irradiating a Fabry-Perot etalon with a laser beam diffused thereto, measuring equiangular interference fringes, and calculating a change in a gap interval of the Fabry-Perot etalon from the equiangular interference fringes. Evaluation methods. 14. The evaluation method according to claim 13, wherein
The calculation method irradiates the laser beam to an arbitrary position of the Fabry-Perot etalon using the slit and the equi-tilt interference fringes a obtained by irradiating the laser beam to the reference position of the Fabry-Perot etalon using the slit. An evaluation method for calculating a change in the gap interval of the Fabry-Perot etalon from a change in the half-value width of the interference fringes b obtained as described above. 15. The evaluation method according to claim 13, wherein
The calculation method irradiates the laser beam to an arbitrary position of the Fabry-Perot etalon using the aperture by using the equiangular interference fringe a and the aperture obtained by irradiating the laser beam to the reference position of the Fabry-Perot etalon using an aperture. A method of calculating a change in a gap interval of the Fabry-Perot etalon from a movement amount of the interference fringes b obtained by the above method. 16. The evaluation method according to claim 13, wherein the equi-tilt interference fringes are converted into transmission characteristics according to the wavelength of the Fabry-Perot etalon, and a change in the gap interval of the Fabry-Perot etalon is calculated from the transmission characteristics according to the wavelength. An evaluation method characterized by: 17. The evaluation method according to claim 15, wherein the interference fringes in one direction and the other direction from the center of the concentric circle of the equi-tilt interference fringes are measured, and the movement amount of each interference fringe is measured. An evaluation method characterized by correcting an error in measurement by calculating an average value and calculating a change in a gap interval of a Fabry-Perot etalon. 18. A Fabry-Perot etalon is provided inside an optical resonator, and in a laser oscillator for narrowing a band of a laser beam, the Fabry-Perot etalon is evaluated by the evaluation apparatus and the evaluation method according to claim 1 to 17. According to the result, the laser beam oscillated from the laser oscillator is narrowed using a region where the gap interval of the Fabry-Perot etalon changes little.