JPH10300587A - Apparatus and method for measurement of wavelength - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an apparatus and a method in which not only the change amount of a wavelength but also the absolute wavelength of light to be detected can be detected with high accuracy, by a method wherein data based on a plurality of peak positions of the interference of the light to be detected is used and reference light whose wavelength is known is used. SOLUTION: Light to be detected is incident on a diffusion plate 3 from a light source 1, and it is diffused so as to enter an etalon 4 at various incident angles. Then, the light to be detected is transmitted through a condensing lens 5. Interference fringes are formed on a focal plane. The distribution of its quantity of light is detected by a line sensor 6. A processing device 7 computes a plurality of peak positions of the interference fringes. The relationship between the peak positions and their degree is fitted by a quadratic function. On the basis of the change amount of the extreme value of the quadratic function, the change amount of the wavelength of the light to be detected is found. Then, by using a mirror 8, the light to be detected is changed over to reference light from a reference light source 9, and the reference light is incident. Then, in the same manner as in the case of the light to be detected, the peak positions of the interference fringes are computed, and the extreme value of a quadratic function is found. Then, on the basis of the extreme value and on the basis of the extreme value regarding the light to be detected, the absolute wavelength of the light to be detected can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength measuring device for detecting a wavelength variation and an absolute wavelength of a laser beam.

[0002]

2. Description of the Related Art In recent years, in the manufacture of semiconductors and semiconductor chip mounting substrates, circuit patterns have become increasingly finer, and semiconductor device manufacturing apparatuses for printing these patterns have been required to have higher resolution. ing. In order to expose a fine circuit pattern, a semiconductor exposure apparatus that uses an excimer laser that emits a shorter wavelength and higher output ultraviolet light as a light source instead of an ultra-high pressure mercury lamp that has been used as a conventional ultraviolet light. Also, a wavefront aberration measuring device for an exposure projection lens used in the semiconductor exposure device has been developed. However, since the excimer laser has an unstable oscillation wavelength, it is necessary to accurately measure the wavelength variation or the absolute wavelength of the light source in order to accurately measure the wavefront aberration. Conventionally, as a method of measuring the wavelength of light using this type of excimer laser as a light source, a method of generating interference fringes using a Fabry-Perot interferometer and analyzing the interference fringes is known.

[0003]

However, in the conventional wavelength measurement, only one of a plurality of concentric interference fringes generated by a Fabry-Perot interferometer is used to reduce the wavelength variation. As a result, wavelength measurement with high measurement accuracy could not be performed. In addition, the interference fringes by the Fabry-Perot interferometer are obtained as a plurality of concentric interference fringes, but when the amount of wavelength variation is obtained from only the information of one interference fringe, the reading error of the interference fringes is directly measured accuracy. Had the disadvantage of affecting
Therefore, an object of the present invention is to provide a wavelength measuring apparatus and a wavelength measuring method capable of measuring a wavelength fluctuation amount and an absolute wavelength of a light source having an unstable oscillation wavelength such as an excimer laser with high accuracy.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to a method of diffusing test light from a light source with a diffuser plate, causing the light to enter an etalon, and collecting the test light transmitted through the etalon. In a wavelength measuring device that measures the wavelength variation of the test light by focusing the test light on the focal plane with a condenser lens and detecting the interference fringes generated on the focal plane with a line sensor, A wavelength measuring apparatus having a processing device for fitting a relationship between a peak position and an order of an interference fringe by a quadratic function and obtaining a wavelength fluctuation amount of the test light based on a fluctuation amount of an extreme value of the quadratic function. It is.

According to the present invention, the test light from the light source is diffused by a diffusion plate and made incident on an etalon, the test light transmitted through the etalon is made incident on a condenser lens, and the test light is focused by the condenser lens. In a wavelength measurement device that measures the absolute wavelength of the test light by detecting the interference fringes generated on the focal plane by a line sensor by focusing the light on the surface, in the optical path between the light source and the diffusion plate,
An optical path switching means for switching the test light to the reference light from the reference light source is disposed, and the relationship between the peak position and the order of the interference fringes when the test light is made incident on the diffuser is fitted by a quadratic function to perform the quadratic function. The relationship between the peak position and the order of the interference fringes when the reference light is made incident on the diffusion plate is fitted by a quadratic function to obtain the extremum of the function, and the extremum of the quadratic function is obtained. A wavelength measuring device comprising a processing device for obtaining an absolute wavelength of test light based on a value and an extreme value of a reference light.

According to the present invention, the test light from the light source is diffused by a diffusion plate and made incident on an etalon, the test light transmitted through the etalon is made incident on a condenser lens, and the test light is focused by the condenser lens. The light is condensed on a plane, the interference fringes generated on the focal plane are detected by a line sensor, the relationship between the peak position and the order of the interference fringes is fitted by a quadratic function, and the test is performed based on the variation of the extreme value of the quadratic function This is a wavelength measurement method for obtaining the wavelength variation of light.

According to the present invention, the test light from the light source is diffused by a diffusion plate and made incident on an etalon, the test light transmitted through the etalon is made incident on a condenser lens, and the test light is focused by the condenser lens. Focusing the light on a surface, detecting interference fringes generated on the focal plane with a line sensor, fitting the relationship between the peak position and the order of the interference fringes by a quadratic function to obtain an extreme value of the quadratic function, Substituting the reference light source and fitting the relationship between the peak position and the order of the interference fringes of the reference light from the reference light source by a quadratic function to obtain an extremum of the quadratic function; Obtaining the absolute wavelength of the test light based on the extreme value of

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a description will be given of a wavelength measuring apparatus for measuring a wavelength variation of a test light according to an embodiment of the present invention. FIG. 1 shows an arrangement diagram of the wavelength measuring apparatus according to the present embodiment. A Fabry-Perot interferometer is used as an interference optical system used in the wavelength measuring apparatus according to the present embodiment. The test light emitted from the light source 1 passes through the variable ND filter 2 for adjusting the light amount, and then enters the diffusion plate 3 and is diffused.
The etalon 4 enters the etalon 4 at various incident angles. The test light transmitted through the etalon 4 transmits through the condenser lens 5 and forms interference fringes on the focal plane. The light amount distribution of the interference fringes is detected by the line sensor 6 arranged on the focal plane, and the peak position of the interference fringes is calculated by the processing device 7. The line sensor 6 is disposed so as to intersect the optical axis z of the interferometer on the focal plane.

Here, a method of obtaining the wavelength variation of the test light will be described. A schematic diagram of the Fabry-Perot interferometer is shown in FIG. In FIG. 2, the test light is an etalon 4 in which mirror surfaces 4a and 4b having high reflectivity are opposed at an interval d.
To be incident at the incident angle theta _m. The test light that has passed through the etalon 4 passes through the condenser lens 5 and forms interference fringes on the focal plane of the condenser lens 5. At this time, the basic formula of the interference fringe by the Fabry-Perot interferometer is It is. Here, λ is the wavelength of the test light, n is the refractive index of an environment (generally, air) in which two etalon plates are arranged, and m is an integer representing the order of interference fringes.

Further, the condenser lens 5 has an angle θ._mIncident on
Of the focused light beam (the center O of the interference fringes on the focal plane
Distance from the optical axis z) x (M) is the focusing light
If the focal length of lens 5 is f,It is.

Considering the incident angle θ _m within a relatively small range, The following two approximations hold. Substituting equations (3) and (4) into equations (1) and (2), and substituting equation (2) into equation (1), Is obtained.

Based on the equation (5), the peak position x of the interference fringes
FIG. 3 shows the relationship between (m) and the order m. Equation (5) is the interference fringe
Peak position x (M) and a quadratic function with the order m as a variable
Yes, peak position x of interference fringes (M) and the order m, (5)
By fitting according to the equation, the equation (5)
The extreme value is obtained. First, the peak position x of the interference fringe is determined. (M)
It is necessary to make the order m of the interference fringes correspond. Interference fringe
The peak position x of the innermost fringe that occurs (M)
Is the maximum order m defined by the equation (1)._maxCorresponds to
, But this maximum order m_maxIs determined as follows.

Now, the extreme value of the equation (5) is represented by m _extThenSince approximate values of n, d, and λ are known,
From equation (6), the extreme value m _extNot accurate but approximate
Can be determined. Note that the order m is an integer.
, Whereas the extreme value m _extIs generally a real number. This extreme value m
_extApproximate value of m _ext'And the approximate value m _extNot exceed ′
The maximum integer is [m _ext'] And α is m _ext′ Decimal part
Then m _ext'= [M _ext'] + Α (0 ≦ α <1) (9)_maxIs m_max= [M _ext].

In general, m_max= [M _ext'] =
[M _ext], But the approximate value of the extreme value m
_ext'Is the true extremum m _extBecause there is an error between
Considering this error, the maximum order m when α is close to 0
_maxIs [m _ext'] Or [m _ext'] -1
And the maximum degree m when α is close to 1_maxIs [m
_ext'] Or [m _ext'] +1. sand
That is, for example, m _ext'= 10000.01
Is the maximum order m_maxIs 9999 or 10000
Is one of the following values. On the other hand, m _ext'= 10000.
If 99, the maximum order m_maxIs 10,000,
Alternatively, the value becomes one of 10001. in this case
And the maximum order m_maxIs [m _ext'] Or
[M _ext'] -1 or [m _ext'] Or
[M _ext'] +1
Approximate value of extreme value m as follows _ext′ And the peak of the interference fringes
Position x (M) may be compared.

First, x in equation (5) (M) = 0 (hara
Point). The interference fringes due to etalon 4
On the focal plane where the in-sensor 6 is located, m concentric circles
Formed. Therefore, for example, for k-th order interference fringes,
Therefore, a point x symmetrical with respect to the center of the interference fringe (K), x ′
(K) is measured. This pair of points x (K), x ′
(K) midpoint (x (K) + x '(K)) / 2
Thus, the coordinates of the center O of the interference fringes can be obtained.
The center O of this interference fringe is defined as the origin x in the equation (5).
(M) = 0. And when α is close to 0
The origin x (M) = 0 peak position of interference fringes near 0
x If (m) is detected, m_max= [M _ext']
If not detected, m_max= [M _ext'] -1
Refuse. On the other hand, when α is close to 1 and the origin x
(M) = 0 near the interference fringe peak position x (M)
If issued, m_max= [M _ext'] +1 and detected
If not, m_max= [M _ext'].

The maximum order m thus obtained_maxIs the interference
The peak position x of the interference fringe occurring at the innermost position among the fringes
(M_max), The coordinates (m_max, X
(M_max)), And outward from the center of the fringes,
In order, (m_max-1, x (M_max-1)), (m_max−
2, x (M_max-2)), some coordinates of ‥‥‥
The fitting is performed according to the equation (5), and the extreme value m is obtained. _extAsk for
Can be

In the expression (6), the extreme value m _ext
Differentiating with respect to wavelength λ, Where λ ² / 2nd on the right side of equation (8) is etalon 4
FSR (Free Spectrum Range)
Equation (8) is It can be expressed as. From the above, the wavelength variation Δλ of the test light can be obtained from the product of the variation Δm _ext of the extreme value in Expression (5) and the FSR of the etalon. The barometric pressure or temperature is measured with a barometer or a thermometer, and the FSR of the etalon 4 is corrected from the refractive index n of the air corrected based on the results, so that the wavelength variation Δλ of the test light can be further accurately determined. Can be requested.

Next, a wavelength measuring apparatus for measuring the absolute wavelength of the test light according to another embodiment of the present invention will be described.
In the wavelength measuring apparatus according to the present embodiment, before or after measuring the test light, the wavelength measuring apparatus shown in FIG. 1 performs the same process as the test light using the reference light whose wavelength is known. By doing so, the extreme value of equation (5) is associated with the wavelength, and the absolute wavelength of the test light is determined.

In the wavelength measuring apparatus according to the present embodiment, a mirror 8 as an optical path switching means is inserted into an optical path between the light source 1 and the diffusion plate 3 in FIG. Switching to the reference light, the reference light is made incident on the Fabry-Perot interferometer. In the wavelength measuring apparatus according to the present embodiment, a mirror 8 is arranged between the light source 1 and the variable ND filter 2 in order to adjust not only the amount of the test light but also the amount of the reference light.

In the wavelength measuring apparatus according to the present embodiment, the test light
The known wavelength λ^* Reference light with
Is incident on the etalon 4 and the line sensor 6 detects interference fringes.
Detect light intensity distribution. From the light intensity distribution of this interference fringe,
The peak position x of the interference fringe by the device 7^*Calculate (m)
And the peak position x of this interference fringe^*(M)
As in the case described above, the order m is made to correspond to the
The extremum m for the reference light^* _extAsk for
You. Extreme value m^* _extIs, from equation (5),Therefore, by comparing equation (10) with equation (6),
Thus, the following equation is obtained.In equation (11), the wavelength λ of the reference light^* Is known
The absolute wavelength λ of the test light Can be calculated.

It should be noted that x _m = 0 in equation (5) (origin)
Is obtained by calculating the coordinates of the center O of the interference fringes by calculating the midpoint (x _k + x _k ') / 2 of the points x _k and x _k ′ symmetrical with respect to the center of the interference fringes as described above. It is defined that the origin x _m = 0 in the equation (5). As a result, even if the line sensor 5 receives external vibration and the entire interference fringe shifts in the diameter direction of the interference fringe, the relative positional relationship between the peak position of the interference fringe and the origin does not change. It is not affected by the vibrations, and it is possible to measure the wavelength fluctuation amount and the absolute wavelength with high accuracy.

[0022]

As described above, according to the present invention, the Fabry-Perot interferometer is used to accurately detect the test light based on the data on the plurality of peak positions of the formed concentric interference fringes. It has become possible to measure the wavelength variation. Also,
By using the reference light whose wavelength is known, it has become possible to obtain not only the amount of change in the wavelength but also the absolute wavelength of the test light.

[Brief description of the drawings]

FIG. 1 is a layout diagram of a wavelength measuring device according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of a Fabry-Perot interferometer

FIG. 3 is a diagram showing a relationship between a peak position of an interference fringe and an order.

[Explanation of symbols]

1: Light source 2: Variable N
D filter 3 ... Diffusion plate 4 ... Etalon 4a, 4b ... Mirror surface 5 ... Condenser lens 6 ... Line sensor 7 ... Processing device 8 ... Mirror 9 ... Reference light source z ... Optical axis

Claims (4)

[Claims] 1. A test light from a light source is diffused by a diffusion plate and made incident on an etalon, and the test light transmitted through the etalon is made incident on a condenser lens. In a wavelength measuring apparatus that measures the wavelength variation of the test light by converging light on a focal plane and detecting an interference fringe generated on the focal plane with a line sensor, a relationship between a peak position of the interference fringe and an order Is fitted with a quadratic function, and a processing device for obtaining the wavelength fluctuation amount of the test light based on the fluctuation amount of the extreme value of the quadratic function is provided. 2. A test light from a light source is diffused by a diffusion plate and made incident on an etalon, and the test light transmitted through the etalon is made incident on a condenser lens. By condensing on a focal plane and detecting an interference fringe generated on the focal plane with a line sensor, in a wavelength measuring device for measuring the absolute wavelength of the test light, in a light path between the light source and the diffusion plate, An optical path switching means for switching the test light to a reference light from a reference light source is disposed, and a relationship between a peak position and an order of the interference fringes when the test light is incident on the diffusion plate is fitted by a quadratic function. Then, the relationship between the peak position and the order of the interference fringes when the reference light is incident on the diffusion plate is fitted by a quadratic function to obtain the extremum of the quadratic function. To determine the Wavelength measuring apparatus characterized by having a processing device for determining the absolute wavelength of the test light on the basis of said extreme value for extreme and the reference light. 3. The test light from a light source is diffused by a diffusion plate and made incident on an etalon, and the test light transmitted through the etalon is made incident on a condenser lens. The light is focused on the focal plane, interference fringes generated on the focal plane are detected by a line sensor, and the relationship between the peak position and the order of the interference fringes is determined by two.
A wavelength measurement method in which fitting is performed using a quadratic function, and the wavelength fluctuation amount of the test light is obtained based on the fluctuation amount of the extreme value of the quadratic function. 4. A test light from a light source is diffused by a diffusion plate and made incident on an etalon, and the test light transmitted through the etalon is made incident on a condenser lens. The light is focused on the focal plane, interference fringes generated on the focal plane are detected by a line sensor, and the relationship between the peak position and the order of the interference fringes is determined by two.
Fitting an extremum of the quadratic function by a quadratic function, replacing the light source with a reference light source, and fitting a relationship between a peak position and an order of interference fringes of reference light from the reference light source by a quadratic function. Obtaining an extremum of the quadratic function by using the extremum of the test light and the extremum of the reference light.