JPH0429003A - Laser length measuring instrument - Google Patents

Abstract

PURPOSE:To improve positioning accuracy by irradiating two places of an object of measurement in the direction of displacement measurement with laser beams coaxially and taking measurements simultaneously at the two places. CONSTITUTION:A laser beam 22 for measurement is split by a beam splitter in X and Y directions and made incident on 50% beam splitters 39 and 40. The laser beam which is made incident on the beam splitter 39 is split into two directions; and one is made incident on an interferometer 251 and the other is made incident on an interferometer 252 through beam benders 41 and 42 respectively. The laser beam which is made incident on the beam splitter 40, on the other hand, is split into two directions; and one beam is made incident on an interferometer 253 and the other is made incident on an interferometer 252 through beam benders 43 and 44 respectively. Consequently, the interferometers 251 and 252 which face reflecting surfaces 38a and 38b measure X-directional displacement and interferometers 253 and 254 facing reflecting surfaces 38c and 38d measure Y-directional displacement, so that the quantities of displacement of the object of measurement in the X and Y directions can accurately be measured.

Description

[Detailed Description of the Invention] [Summary] The purpose of this invention is to improve the positioning accuracy of a laser length measurement device that uses laser interference by measuring the amount of movement of an object to be measured, such as a stage, with high precision. , in a laser length measuring device that irradiates a laser onto an object to be measured and a reference surface and measures the displacement of the object by utilizing interference between respective reflected lights, the direction of displacement measurement of the object to be measured is The laser beam is coaxially irradiated to two locations, respectively, so that displacement measurements are performed at the two locations simultaneously.

[Industrial Application Field] The present invention relates to a laser length measuring device that utilizes laser interference.

In recent years, with the miniaturization of LSIs, semiconductor manufacturing equipment such as steppers equipped with linear motion stage mechanisms have become smaller than 1/100,000 mm.
This requires extremely high positioning accuracy. For this reason, a laser length measurement method that utilizes laser interference is often used as a means for measuring the position of a movable part of a linear motion stage mechanism. However, with this type of laser oscillator, not only does it take a considerable amount of time for the output to stabilize after the power is turned on, but the temperature of the interferometer, mirror, and retroreflector through which the laser passes and reflects varies depending on the laser. The long value drifts, causing a large error on the order of 0.1 μm in long-term measurements.
Since the position of the reflecting mirror and the actual position to be measured are usually different, errors may occur due to thermal deformation of the object to be measured.

That is, in the laser length measurement method, it is possible to accurately measure length to the order of the minimum resolution in short-time measurements, but it is difficult to obtain stable length measurement values in long-term measurements.

[Conventional technology]

FIG. 4 shows a conventional laser length measuring device that measures the displacement of a stage moving in the linear directions of the X and Y axes.

In this laser length measuring device, a laser beam 2 emitted from a laser oscillator 1 is divided into two by a beam splitter 3, and further divided into two by a beam splitter in the Y-axis direction. Then, the interferometers 41.4g and 43 on each axis cause the reflected light from the stage movable part 5 to interfere with the reference light reflected inside the interferometer, and the receivers 6, . The amount of movement of each axis is measured by converting it into an electric signal in 6□ and 63 and further electrically processing it. In this example, since two laser beams are used in the Y-axis direction, the yawing of the stage movable section 5 can also be measured at the same time. There are various length measurement principles, and for example, one using heterodyne interference will be explained as follows.

In FIG. 5, 11 is an interferometer equipped with a λ/4 plate 12 and retroreflectors 13 and 14, and 15 is a receiver. During the measurement, as shown in FIG. 5, a laser beam (hereinafter referred to as "fl") having two wavelengths with orthogonal polarization planes and slightly different frequencies is used.

f2) is separated into two by the interferometer 11, and one of them, for example fl, is irradiated onto the object to be measured.

If the reflecting mirror 16 attached to the object to be measured is moving, the frequency of the reflected light fl changes by Δf1 due to the Doppler effect, and becomes fl±Δf1. When an interferometer for a plane mirror is used as shown in FIG. 5, the laser beam makes two round trips between the mirror and the mirror, so the frequency of the reflected light ultimately becomes fl±2·Δr1. Then, the reflected light of fl and the other reference f2 are caused to interfere with each other by an interferometer 11 and converted into an electrical signal by a receiver 15, thereby obtaining the displacement amount of the object to be measured.

[Problems to be Solved by the Invention] As described above, the laser length measurement device measures the distance between the interferometer and the reflector (or retroreflector) attached to the object to be measured. When an optical element such as an interferometer is gradually heated by the laser, the optical element is thermally deformed, causing an error in the measured length value. In particular, the drift caused by thermal deformation can reach 0.1 μ-order, which is more than 10 times the length measurement resolution of the laser.

Therefore, with a laser length measuring device, 0.0. Even if a high length measurement accuracy of O1μ- can be achieved, there is a problem in that the length measurement result drifts during length measurement over a long period of time, making it impossible to perform highly accurate measurement.

SUMMARY OF THE INVENTION An object of the present invention is to provide a laser length measuring device that can measure the amount of movement of an object to be measured, such as a stage, with high precision and improve its positioning accuracy.

[Means to solve the problem]

FIG. 1 is an explanatory diagram of the principle of the present invention, and 21 is an object to be measured (
22 is a laser beam.

A laser length measurement device irradiates a laser beam onto an object to be measured and a reference object, and measures the displacement of the object by utilizing the interference between the respective reflected lights. It has a configuration in which two locations in the displacement measurement direction are irradiated with the laser beams arranged coaxially, respectively, so that displacement measurement is performed at the two locations simultaneously.

In this figure, the opposing surface 2 of the object to be measured 21 in the displacement measurement direction is shown.
Reflecting mirrors 23.1a and 21b. ．． 23. Attach the reflecting mirror 23. , 23z is irradiated with the coaxial laser beam 22. In this case, the laser beam 22 is
The beam is divided into two parts by a 0% beam splinter 24, and one beam passes through an interferometer 25° and irradiates a reflecting mirror 231, while the other beam passes through a beam bender 26 and an interferometer 25□ and irradiates a reflecting mirror 23□.

[For production]

In this way, the coaxial laser beam 22 is irradiated to two locations in the moving direction (displacement measurement direction) of the object to be measured 21,
The amount of movement of the object to be measured 21 is measured at the two locations simultaneously. Thereby, even if there is thermal deformation in the optical system through which the laser passes through or is reflected, such as an interferometer or retroreflector, or in the object to be measured 21, errors caused by laser length measurement can be minimized.

This will be explained in detail with reference to the example shown in FIG. That is, the interferometer 25, the reflecting mirror 23. The relative displacement of the reflecting mirror 23□ with respect to the interferometer 25□ (the measured length of the front facing surface 21a) is A, and the relative displacement of the reflecting mirror 23□ with respect to the interferometer 25□ (the measured length of the front facing surface 21a) is
1b) is B, each length measurement value A and B includes drift and error due to thermal deformation of the optical element, but the error value is considered to be the same for both A and B. So,
It is thought that the difference A-B between the measured values is small due to the drift and error in the measured length values.

This will be explained in more detail based on FIG. 2 as follows.

In FIG. 2, the amount of movement of the front part of the object to be measured 21 measured by the laser beam 22 is represented by Xl, the amount of movement of the rear part of the object to be measured by the laser beam 22 is represented by xz, and it is assumed that the actual If the actual amount of movement of a place to be accurately positioned, for example, the center part 26 of the object to be measured, is X3, then When the object to be measured 21 moves, XI and X2 become negative.) Here, Xi and X2 include the drift of the length measurement value due to thermal deformation of the optical element ΔX 101 ΔX zn and the object to be measured 21 Length measurement error ΔX I S + ΔXZ due to thermal deformation of
Contains S. If the amount of movement of the front and rear parts of the object to be measured excluding these errors is Xlr, X2r, then X1=X,
+ΔXID+ΔXl5−(2)X2=X2. +Δχ2.
+ΔXZS- (3) If a laser oscillator with the same output is used and the measurement environment is not significantly different before and after the stage, the thermal deformation of the optical element and the object to be measured will be almost the same before and after the object to be measured. Therefore, ΔX 1
0'-Δx, -(4)ΔX +s'
iΔXZS ... (5) (2), (
3), (4), and (5) into equation (1), X3= (x, r-xz,)/2-(6) As is clear from these equations, one measured object By irradiating the object with a laser beam on the opposing surfaces 21a and 21b coaxially and performing simultaneous length measurements, errors due to laser output, instability of optical elements, and deformation of the object to be measured are eliminated. This makes it possible to accurately measure the amount of movement.

〔Example〕

The invention will now be described in detail with reference to FIGS. 3 and 4.

FIG. 3 is a perspective view showing the structure of the laser length measuring device of this example.
In the figure, 253, 25. is an interferometer for measuring displacement in the Y-axis direction,
31 is a linear motion stage mechanism.

Note that the same reference numerals are used for the same components as in FIG. 1.

The linear motion stage mechanism 31 has a two-tiered structure including a stage X-axis movable section 32 and a stage Y-axis movable section 33. The stage X-axis movable section 32 includes a linear guide 35 guided by a guide bar 34 extending in the X-axis direction.
It is movable in the axial direction. The stage Y-axis movable part 33 is
A linear guide 37 is provided on the stage X-axis rotating section 32 and guided by a guide bar 36 extending in the Y-axis direction, and is movable in the Y-axis direction. This stage Y-axis movable section 33 corresponds to the object to be measured Th21 in FIG.

An orthogonal mirror 38 is mounted on the stage Y-axis rotating section 33 to detect displacement of the stage Y-axis moving section 33 in the X and Y axis directions. This orthogonal mirror 38 has a square shape with sufficient rigidity, and has four reflective surfaces 38 on the circumference.
All of a, 38b, 38c and 38d are finished with high precision to have high surface accuracy.

A laser beam 22 for measurement is divided into X and Y directions by a beam splitter 24, and a 50% beam splitter 3
Enter 9.40. The laser beam entering the beam splinter 39 is split into two directions, and the - side is sent to the interferometer 25. The other beam passes through beam benders 41 and 42 and enters the interferometer 254, respectively. Furthermore, the laser beam entering the beam splitter 40 is also split into two directions, one entering the interferometer 253 and the other entering the interferometer 25□ via beam benders 43 and 44, respectively.

In this way, in this device, the laser beam irradiated from the same laser oscillator is coaxially guided to each interferometer. That is, the displacement in the X-axis direction can be measured by the interferometers 25..25□ facing the reflective surfaces 38a and 38b, and the displacement in the X-axis direction can be measured by the interferometers 253 and 254 facing the reflective surfaces 38c and 38d. Displacement in the X-axis direction is measured.In these displacement measurements in each axis direction, two opposing locations are measured at the same time, so as mentioned above in connection with Fig. 1, fluctuations in laser output and optical element Errors caused by thermal deformation and deformation of the object to be measured can be eliminated, making accurate measurement possible.

Now, the interferometer 25. The length value measured with Xl, interferometer 2
The length value measured with 5□ is X2, the length value measured with interferometer 25° is Yl, - the length value measured with interferometer 254 is Y2
Then, the stage Y-axis movable part 33 which is the object to be measured
The position of the center of is the position in the X-axis direction = (XI-X2)
/2 Position in Y-axis direction = (Yl-Y2)/2. Furthermore, if the obtained position is not divided by 2 as in the above equation, it becomes possible to measure the length of the object to be measured with twice the resolution.

In this example, as mentioned above, a mouth-shaped orthogonal mirror is used to measure the position of the object to be measured, but this mirror shape has sufficient rigidity and is suitable for use during processing and for orthogonal reflections. Even when the forces applied to the mirror differ during the vapor deposition of the surface or the actual installation of the orthogonal mirror, the distortion occurring on the reflective surface can be kept to a small level. Such a mirror structure is the sixth
The present invention can also be applied to a conventional laser length measuring device using a biaxial displacement measuring method as shown in the figure. In FIG. 6, 17. 17 is an interferometer for measuring displacement in the X-axis direction, 18 is a stage movable part (object to be measured) of a linear motion stage mechanism, and 19 is an L-shaped orthogonal mirror. The length measurement in each axial direction is carried out by an interferometer 1 facing the reflecting surfaces 19a and 19b of an L-shaped orthogonal mirror 19 mounted on the stage movable section 18.
7. .

This is performed by laser beam irradiation from 172.

The L-shaped orthogonal mirror 19 used in this conventional device is
If it is applied in the A direction in FIG. 7(a), it will easily deform as shown by the dotted line, but if the mouth-shaped reflecting mirror 38 in FIG. 3 is used instead, as shown in FIG. 7 et al. Even if the same force A is applied, the distortion will be considerably smaller. Therefore, it is possible to manufacture a mirror with higher surface precision, and by mounting this mirror on a linear motion stage mechanism, it becomes possible to position the object to be measured with higher precision.

〔Effect of the invention〕

As described above, according to the present invention, by measuring the position of the object to be measured at two coaxial locations, it is possible to determine from the measured values the instability of the output of the laser itself and the heat of the optical elements making up the beam path. Since the effects of deformation and deformation of the object to be measured can be eliminated, the amount of movement of the object to be measured can be measured with higher accuracy, which greatly contributes to improving the positioning accuracy of the object to be measured. It is.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the principle of the present invention, FIG. 2 is an explanatory diagram of the operation of the laser length measuring device of the present invention, FIG. 3 is a perspective view showing the structure of the laser length measuring device of the embodiment of the present invention, and FIG. The figure is a perspective view showing the structure of a conventional laser length measuring device, Figure 5 is a diagram explaining the length measurement principle of the laser length measuring device, and Figure 6 is a diagram showing the structure of a conventional laser length measuring device using a two-axis displacement measuring method. The perspective views shown in FIGS. 7(a) and 7(b) are comparative illustrations of problems of conventional L-type reflecting mirrors. In the figures, 21 is an object to be measured, and 22 is a laser beam. Figure 4: A perspective view showing the structure of a conventional laser length measurement device.A diagram explaining the length measurement principle of a laser length measurement device.A perspective view showing the structure of a conventional laser length measurement device using the 2@direction displacement measurement method.r M

Claims (1)

[Scope of Claims] A laser that irradiates a laser beam (22) onto an object to be measured (21) and a reference object, and measures the displacement of the object to be measured (21) by utilizing interference between respective reflected lights. In the length measuring device, at two locations in the displacement measurement direction of the object to be measured (21),
irradiating the laser beams (22) on the same axis,
A laser length measuring device characterized in that displacement measurement is performed at two locations simultaneously.