JPH0781819B2 - High precision interferometer - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positioning / dimension measuring method, which is a problem in the field of precision production such as in the electronics industry and machinery industry, and in the calibration technology such as weighing and surveying.

[0002]

2. Description of the Related Art Recently, many kinds of light wave interferometers have been developed to measure the length accurately, and the resolution of the measurement has reached 1 nanometer, but the length is several tens of millimeters or more. In the above, the measurement accuracy of these length measuring instruments was limited to about several ppm due to the influence of atmospheric fluctuations . For this, 2-color method as saying, as a light source of the optical interference measuring meter, by measuring using a two-color laser wavelength emits a pulsed laser beam of two different colors, the optical length-measuring by optical interference It has been proposed to correct the atmosphere for the values in real time.

Now, considering the interference between the light having the wavelength λ1 and the light having the wavelength λ2 , the light for one element divided into a large number is divided.
The geometrical measurement value D can be calculated by D = D ₁ −A × (D ₁ −D ₂ ) ... (1) . Where D ₁ and D ₂ are waves
Length lambda _1, lambda ₂ of the optical measurements by the light, as it were a raw data <br/>, The coefficient A is in the above formula (1), A = {( n 1 -1) / (n 1 - n ₂ )} is a constant given by (2) . Where n ₁ and n ₂
Is the refractive index of the atmosphere in the optical path of light of wavelengths λ ₁ and λ _2.
ing. The optical measurement value D described above Jozure the division necessity prime number
For example, it is possible to calculate the geometrical measurement value of the measured object. However, in the above-mentioned conventional “two-color method” , the above-mentioned formula is used.
Since the coefficient A in (1) is a value of several tens to several hundreds ,
As can be seen from the above equation (1) , even if the raw data D ₁ , D
_Even if the accuracy of ₂ is good , the value of (D ₁ -D ₂ ) is several tens of times
Or the value multiplied by several hundred is subtracted, so the final measurement
The problem that the accuracy of the value of the long value D decreases and the resolution deteriorates accordingly, and the advantage of the "two-color method" cannot be fully utilized.
was there.

[0004]

SUMMARY OF THE INVENTION In order to solve the deterioration of the measurement resolution due to the value of the coefficient A in the interferometer using the two-color method, the present invention is to solve the problem of the interference fringe count value and the length of the interference fringe related to the correction of the atmosphere. Simultaneously with the interference fringe count value related to
The purpose is to measure the length without reducing the resolution by performing the calculation processing separately .

[0005]

In order to solve the above problems, it is important from the above discussion that the coefficient A in the two-color method is small, and at the same time it is necessary to improve the resolution of interference fringe measurement. Is. The present invention does not directly solve these problems but realizes high resolution and high precision measurement by another method , and the influence of the atmosphere becomes uniform in a spatial region of 1 mm or less. , That is, the number of lights
the influence of the atmosphere in the case of advance a distance of about μm is constant and everyone
It is what makes use of. That is, as shown in FIG. 1, the interference fringes of two colors are separately counted at the same time as in the conventional method, but these count values are separated into two paths, and in one path, the interference fringe meter related to the length is measured. Measurement from numerical values
Although constant is raw data is input in a conventional manner as a personal computer, in the other path, the large
The interference fringe count value, which is related to the correction for the refractive index of air, is
It is measured for each one of the divided elements.
A predetermined number N of the raw data obtained ( for example, N = 100 to 1000).
0) are pieces product min, mean values averaged by the number N is calculated,
It is input to a personal computer and the geometric length is calculated. Resolution of the averaged data, so-called
That the "averaging effect" of √N amount of resolution is defined by the division of the interference fringes 1 (e.g., N = 100 to 100
In the case of 00, it becomes 1/10 to 1/100) . At this time,
Data no information as many μm the change in the spatial refractive index between doing an average, but if the limit of resolution due to quantization errors √N (N = 100~10000 10
.About.100) times better, and the reduction in resolution due to the coefficient A can be eliminated. As a result, high-precision measurement on the order of nanometers is realized.

[0006]

[Function] At present, the light wave interferometer is used in many fields of science and industry, and it can be used for high precision of parts in the advanced electronic and mechanical industries, and also in a place where measurement environment is not stable or long. The demands for use in the optical path are increasing. In this case, the problem is correction of atmospheric fluctuation and its refractive index. In the present invention, the accuracy of lightwave interferometry in the atmosphere can be easily increased by automatically correcting the refractive index of the atmosphere in real time, so that even researchers and engineers who are not familiar with optical measurement can understand it. It can be used effectively.

[0007]

FIG. 2 shows a two-color interferometer with an interference fringe coefficient method which is an embodiment of the present invention . Gauge interferometer shown in FIG. Is a polarization gauge interferometer which has become the same optical path with respect to two wavelengths, the polarization method utilizing lambda / 8 plate, so as to obtain the phase by 90 ° for 2 wavelengths different signals There is . In the figure
The interferometric length meter shown is a laser light emitting means as a light source.
It is equipped with a two-wavelength laser 13, and has 1.06 μm YAG laser light (wavelength: λ ₁ ) and its second harmonic laser light (wave
Length: λ ₂₎ is Ru is used. Here, 1.6 μm YAG
The laser light corresponds to the first laser light, and its second harmonic
The light corresponds to the second laser light. After the polarization state of these laser lights is adjusted by the λ / 2 plate 1 , the first
It goes to the beam splitter 2 which is an optical path separating means . The light that has passed through the beam splitter 2 and traveled along the first optical path is reflected by the probe mirror 5, which is a movable mirror, in the direction opposite to the traveling direction . When measuring the length, set the probe mirror 5
On the first optical path at a speed of, for example, 10 mm / sec.
To move. On the other hand, the light reflected by the beam splitter 2 and traveling in the second optical path passes through the λ / 8 plate 3 and is reflected by the fixed mirror.
It faces a certain reference mirror 4, where it is reflected in the direction opposite to the direction of travel . Reflected light reflected by the probe mirror 5 and the reference mirror 4
The reflected light reflected by the beam interferes with the beam splitter 2. The interference light of these two wavelengths of light is transmitted by the second optical path separating means.
A certain dichroic mirror 6 causes the second interference with the light of the fundamental wave which is the first interference light.
It is separated into light of the second harmonic which is light . Interfering light of fundamental wave
Enters the polarization beam splitter 7 and the phase is only 90 °
The light is separated into two different lights, and these signals are detected by the photoelectric device 9
And 10, photoelectrically detected. Where the polarized beamsp
The litter 7 and the photoelectric devices 9 and 10 constitute a first detecting means.
is doing. In addition, the interference light of the second harmonic is
Two lights that enter the liter 8 and have a phase difference of 90 °
These signals are separated, and these signals are transmitted by the photoelectric elements 11 and 12.
Is detected. Here, the polarization beam splitter 8 and the light
The electric elements 11 and 12 form second detecting means. The number of interference fringes of the fundamental wave contained in these signals and the second harmonic
The number of interference fringes after being counted reversible counters electrical signal processing system 14 (not shown), are input to the personal computer 15, the geometrical length of Chobutsu measuring the is calculated. Here, the interference fringe of the fundamental wave becomes the first interference fringe
The second harmonic interference fringe corresponds to the second interference fringe.
It Here, the electrical signal processing system 14 and the personal
The calculation method in the computer 15 is shown in FIG.
Will be described with reference to. Figure 1 is calculated from the interference fringes of the fundamental wave.
Shows the first measurement value D _1ij for the issued number divided elements
And for the multiple split elements calculated from the interference fringes.
2 shows the length _measurement value D _2ij . In Figure 1, one vertical
The line shows the length measurement value data for each divided element.
A river (not shown) in the electrical signal processing system 14 of this embodiment
The sibble counter is used for the first interference fringe and the second interference fringe.
From the fringes, the number of interference fringes was separately counted simultaneously as before, and each
First measurement value D _1ij for split element and each split element
The second length _measurement value D _2ij is calculated. However, in this embodiment,
Separate the processing of these measurement values for each divided element into two paths.
ing. On one path, the
The first measured value D1ij for the personal computer 15 is
Entered in. But in the other path, each
The first measured value D _1ij for the dividing element and each dividing element
A predetermined number N (N = _{100 to 1} ) for the second measured value D _2ij
0000) pieces of data are integrated to obtain Σ _i D _1ij and Σ _i D
_2ij and the first average length measurement value D _1N
(= Σ _i D _1ij / N) and the second average measurement value D _2N (= Σ _i D
_2ij / N) and these are personal computers
15 and the length measurement value D _ij for each divided element is obtained by the following equation D _ij = D _1ij −A × (D _1N −D _2N ) ... (3) . This
If the optical measurement value D _ij of is multiplied by the number of division elements,
The geometric length of the object is calculated. In the above, electrical
The signal processing system 14 and the personal computer 15 are operators.
The steps are made up.

[0008]

As described above, according to the present invention,
The atmospheric correction value in the measurement value for each division element must be divided.
A predetermined number N of measurement data for each prime (for example, N = 100 to 1)
0000) and use the value averaged over the number N
Therefore, compared to the conventional two-color method Michelson interferometer
It is possible to improve the resolution of the total length measurement by about 10 to 100 times.
The measurement can be performed without being affected by the refractive index of the atmosphere.
Wear. The measurement technology of the present invention is a new length measurement technology that has never existed before, and can improve the quality of parts and products in the electronic-related production industries such as semiconductor devices and various precision industry-related fields such as machinery. Highly valuable as a length calibration technique.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the basic principle of the present invention.

FIG. 2 is an optical configuration diagram showing an embodiment of the present invention.

[Explanation of symbols]

1 λ / 2 plate 2 Beam splitter 3 λ / 8 plate 4 Reference mirror 5 Probe mirror 6 Two-color mirror 7 Polarization beam splitter for fundamental wave 8 Polarization beam splitter for second harmonic wave 9,10 Photoelectric element for fundamental wave 11, 12 Second harmonic optoelectronic device 13 Two-wavelength laser 14 Electrical signal processing system 15 Personal computer

Claims (1)

[Claims] 1. A first laser beam having a _first wavelength (λ ₁ )
And the second laser light having the second wavelength (λ ₂ ) and the same light flux
Light emitting means for emitting as a laser light of (13)
And separating the laser light of the same light flux into a first optical path and a second optical path.
A first optical path separating means (2) which is fixed to the first optical path and has traveled along the first optical path.
A fixed mirror (4) for reflecting the laser light in the opposite direction, and a movable mirror provided in the second optical path in the second optical path.
When measuring the geometrical length of the DUT,
It has been moved in the direction of the two optical paths and has traveled along the second optical path.
A movable mirror (5) that reflects laser light in the opposite direction, the first reflected light from the fixed mirror (4) and the movable mirror (5).
The second reflected light from the first optical path separating means (2).
The interference light formed by the interference between the first interference light and the second interference light.
A second optical path separating means (6) for separating the light into light, and a first detecting means for detecting a first interference fringe from the first interference light.
Outputting means (7, 9, 10) and a second detector for detecting a second interference fringe from the second interference light.
The output means (8, 11, 12) and the number of the detected first interference fringes are counted and divided into a large number.
First measured value D of the measured object for each divided element
_1ij is calculated, and the detected second interference fringe
The number of the
The second measured value D _2ij of the measured _object is calculated, and the first measured _value is calculated.
A predetermined number N of D _1ij are integrated and averaged by the predetermined number N.
The first average length measurement value D _1N is calculated, and the second length measurement is performed.
The value D _2ij is integrated by the predetermined number N and averaged by the predetermined number N.
The calculated second average measured value D _2N is calculated and
When the correction coefficient to be set is A,
The length measurement value D _ij of the length-measurable _object for the division element is calculated by the following equation D _ij = D _1ij −A × (D _1N −D _2N ) , and the length measurement value D _ij indicates the number of the division elements.
Calculate the geometric length of the measured object by multiplying
A high-precision interferometer , which is provided with a computing means (14, 15) .