JPH11325863A - Straightness measurement method using diffraction grating and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a straightness measurement method and the device for improving the signal-to-noise ratio of observation signals, being hardly affected of peripheral disturbance light, and facilitating optical axis adjustment and the assembly of an optical system. SOLUTION: In this measurement method for matching the moving direction of a linear moving mechanism 8 and the normal line of the working surface of a diffraction grating 6 installed on the mechanism, making coherent light emitted from a light source 1 be incident parallelly to the normal line, making +1st order and -1st order diffracted light from the diffraction grating into parallel light in a paralleling optical system 10, then obtaining interference signals by overlapping both of the diffracted light on a photodetector 18 by an interference optical system, and detecting the straightness of the moving mechanism by the phase change of the interference signals, the difference of the number of times of reflection by a mirror or the like until both of the diffracted light after being made into the parallel light reach the photodetector 18 is turned to the odd-number of times. Of the condition is satisfied, regardless of the number of the mirrors inserted in the middle, even when the linear moving mechanism 8 is moved, the optical axes of both of the diffracted light 9a and 9b are shifted in the same direction without separating from each other while keeping a matched state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring straightness of a linear moving mechanism. More specifically, the present invention relates to all devices having a linear moving mechanism, such as a semiconductor manufacturing device, various machine tools, and a measuring instrument.

[0002]

2. Description of the Related Art As a method for measuring the straightness of a linear moving mechanism using a diffraction grating, there is a known example by the present inventors (Japanese Patent Application No. 6-239894). Hereinafter, a conventional technique will be described with reference to FIG.

As shown in FIG. 3, a light source 1 has orthogonal polarization planes, p-polarized light and s-polarized light, and the frequencies of the p-polarized light (frequency f1) and the s-polarized light (frequency f2) are slightly different. The light 29 is emitted and split into two by a beam splitter 3 into a light 29a and a light 29b.
By passing 9a through the polarizer 4 whose polarization axis is appropriately adjusted, the polarization planes of both the p and s polarization components are matched.

As a result, the photodetector 5 generates an interference beat signal (frequency | f1-f2 |), which is used as a reference signal. As shown in FIG. 4, the diffraction grating 6 is set on the table 7 of the linear moving mechanism 8 so that the moving direction of the linear moving mechanism 8 matches the normal direction of the diffraction grating processing surface of the diffraction grating 6. Then, the light 29b is made incident on the diffraction grating 6 such that its optical axis coincides with the normal direction of the diffraction grating processing surface of the diffraction grating 6.

As a result, a + 1st-order diffracted light 9a and a -1st-order diffracted light 9b are generated from the diffraction grating 6.
a, 9 b are parallelized by the biprism 10. Of the + 1st-order diffracted light 9a and the -1st-order diffracted light 9b after being collimated, the -1st-order diffracted light 9b is reflected by the total reflection mirror 11b and then passes through the polarizer 12b so that only the s-polarized light component is emitted. Selected. On the other hand, after the + 1st-order diffracted light 9a is reflected by the total reflection mirror 11a and passes through the polarizer 12a, only the p-polarized light component is selected.

Further, the p-polarized component passes through a half-wave plate 13 so that its polarization axis is adjusted to be in the same direction as the above-mentioned s-polarized component. The light is reflected and reaches the half mirror 15. From the above, the + 1st-order diffracted light 9a and the -1st-order diffracted light 9b that have reached the half mirror 15 are light beams having the same polarization axis, but both optical axes move away from each other as the linear movement mechanism 8 moves. Therefore, the state where the two diffracted lights 9a and 9b overlap each other, that is, the interference state cannot be maintained.

Therefore, a condenser lens 16 is disposed downstream of the half mirror 15 so that the two diffracted lights 9a and 9b always overlap at the focal position of the condenser lens 16 even when the linear moving mechanism 8 moves. Even if the linear movement mechanism 8 moves, both the diffracted light 9
a and 9b can interfere with each other. Here, the optical axis of the two diffracted lights 9a and 9b is the focal position of the condenser lens 16,
Since they overlap at a certain angle, the interference light has a phase distribution on the focal plane.

When this is received by the photodetector 18, the interference signals cancel each other out due to the phase distribution described above, and it becomes impossible to detect the interference signals. Therefore, the photodetector 1
A spatial filter 17 is arranged at the front stage of 8 to spatially limit the phase distribution of the interference light incident on the photodetector 18 so that the interference signal can be measured by the photodetector 18. The two diffracted lights 9 thus obtained by the photodetector 18
Let the interference signals a and 9b be observation signals. The following equation holds between the phase change φ of the observation signal and the reference signal with respect to the grating interval d of the diffraction grating 6 and the in-plane displacement δy.

Φ = 2 × 2π (δy / d) Since the lattice spacing d is a known quantity, the in-plane displacement δy of the diffraction grating, that is, the linear moving mechanism 8 Can be obtained by the above-described apparatus configuration.

[0010]

In the conventional device configuration, as described above, the + 1st-order diffracted light 9a and the -1st-order diffracted light 9b move in the direction away from each other with the movement of the linear moving mechanism 8, so that both Since the optical axes of the diffracted light do not coincide with each other and an observation signal cannot be obtained, the condensing lens 16 causes the two diffracted lights 9a and 9b to interfere at the focal position of the condensing lens 16.

However, the conventional method (Japanese Patent Application No. Hei 6-2398)
No. 94), when the moving amount of the linear moving mechanism 8 is increased, as shown in FIG. 3, the two diffracted lights 9a and 9b
As a result, the spatial phase distribution increases, and the contrast of the observation signal detected by the photodetector 18 decreases. For this reason, the signal-to-noise ratio of the observation signal is deteriorated, and there is a problem that the movement amount of the linear movement mechanism 8 that can measure the straightness is limited.

Further, in the conventional example, since the spatial filter 17 is used in the preceding stage of the photodetector 18, the intensity of the observation signal incident on the photodetector 18 becomes very weak, and is susceptible to ambient disturbance light. There was a problem. For this reason,
A shielding plate for shielding disturbance light must be provided around the photodetector 18, and there is a problem that it is very difficult to adjust the optical axis and assemble the optical system.

[0013]

According to a first aspect of the present invention, there is provided a straightness measuring method for solving the above-mentioned problems, in which a moving direction of a linear moving mechanism coincides with a normal to a processing surface of a diffraction grating. Installing the diffraction grating on the linear movement mechanism, and causing light emitted from a light source that emits coherent light to be incident so as to be parallel to the normal to the diffraction grating, and then diffracting the light. The + 1st order diffracted light and the -1st order diffracted light generated from the grating are collimated by a collimating optical system, and the + 1st order diffracted light and the -1st order diffracted light after being collimated are overlapped on a photodetector by an interference optical system. By acquiring the signal, the amount of displacement (straightness) in the direction orthogonal to the moving direction of the linear moving mechanism is converted into the in-plane displacement of the diffraction grating, and the phase change of the interference signal generated thereby The straightness In the straightness measuring method and apparatus to be output, the difference in the number of times of reflection by a mirror or the like until the + 1st-order diffracted light and the -1st-order diffracted light incident on the collimating optical system reach the photodetector is an odd number. It is characterized by the following.

According to a second aspect of the present invention, there is provided a straightness measuring device for solving the above-mentioned problems, wherein the linear movement mechanism is arranged such that a moving direction of the linear movement mechanism coincides with a normal line of a diffraction grating processing surface. The diffraction grating is installed on a mechanism, and light emitted from a light source that emits light having coherence is incident on the mechanism so as to be parallel to a normal line of the diffraction grating, and then generated from the diffraction grating. The + 1st-order diffracted light and the -1st-order diffracted light are collimated by a collimating optical system, and the + 1st-order diffracted light and the -1st-order diffracted light that have been collimated are superimposed on a photodetector by an interference optical system to obtain an interference signal. By doing so, the displacement amount in the direction orthogonal to the moving direction of the linear moving mechanism,
In a straightness measuring device that converts the diffraction grating into an in-plane direction displacement and detects the straightness based on a phase change of the interference signal generated thereby, the + 1st-order diffracted light and 1 after passing through the parallelizing optical system. An optical system is provided in which the difference in the number of reflections until the next-order diffracted light reaches the photodetector is an odd number.

[Operation] By using the straightness measuring method and apparatus according to the present invention, even if the linear movement mechanism moves, the optical axes of the + 1st-order diffracted light and the 1st-order diffracted light do not separate, and the optical axes always coincide. It moves in the same direction as it is. For this reason,
Observation signals can be easily obtained by simply aligning the optical axes of both diffracted lights with the normal to the photocathode's photocathode without using a condensing lens or spatial filter, which was indispensable in the conventional example. Becomes

Thus, using the method and apparatus configuration according to the present invention produces the following effects.・ Because the optical axes of both diffracted lights are always the same even if the linear movement mechanism moves, in principle, the signal-to-noise ratio of the observed signal can be degraded no matter how much the linear movement mechanism moves. Absent. -Observation signals can be obtained without using a spatial filter, so that the intensity of the observation signals can be improved, and a shield plate or the like installed around the photodetector is unnecessary. -Since no spatial filter is used, adjustment and assembly of the optical system are facilitated.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a straightness measuring apparatus according to the present invention will be described in detail with reference to the embodiments shown in the drawings. FIG. 1 shows a straightness measuring apparatus according to an embodiment of the present invention. In FIG. 1, the same components as those in the conventional example are
The same reference numerals are given and duplicate descriptions are omitted.

More specifically, the method of detecting the reference signal is the same as that of the conventional example, and the method of detecting the observation signal is the same as that of the first-order diffracted light 9a until the + 1st-order diffracted light 9a enters the total reflection mirror 14. Until 9b passes through polarizer 12b, there is no difference from the conventional example.

In this embodiment, the + 1st-order diffracted light 9a incident on the total reflection mirror 14 and reflected there is reflected by the total reflection mirror 32 after passing through the half mirror 31, and returns to the half mirror 31 again. The + 1st-order diffracted light 9a that has returned to the half mirror 31 is reflected here and is
Go to 8. On the other hand, the -1st-order diffracted light 9b that has passed through the polarizer 12b passes through the half mirror 31 as it is, and travels toward the photodetector 18.

At this time, the optical axes of the + 1st-order diffracted light 9a and the -1st-order diffracted light 9b reflected or passed by the half mirror 31 are adjusted to coincide. The number of times of reflection of the + 1st-order diffracted light 9a by the mirror or the like after passing through the biprism 10 and reaching the photodetector 18 is the total reflection mirror 11a.
While the total reflection mirror 14 → the total reflection mirror 32 → the half mirror 31 is four times, the number of times of reflection of the −1st-order diffracted light 9b is only one time by the total reflection mirror 11b, and both the diffracted lights 9a and 9b The difference in the number of reflections is odd.

When the above condition is satisfied, the optical axes of the two diffracted lights 9a and 9b are aligned even if the linear moving mechanism 8 moves, regardless of the number of mirrors inserted in the middle. While maintaining, they shift in the same direction without separating from each other. The two diffracted lights 9a and 9b reflected or passed through the half mirror 31 then pass through the condenser lens 33 and interfere on the photodetector 18 arranged with the photoelectric surface coincident with the focal plane of the condenser lens 33. , An observation signal is obtained.

The purpose of arranging the condenser lens 33 in front of the photodetector 8 is to move the linear movement mechanism 8 so that the optical axes of the two diffracted lights 9a and 9b are kept coincident, but are shifted in the same direction. Therefore, the purpose is to prevent the two diffracted lights 9a and 9b from deviating from the photocathode of the photodetector 18. Therefore, when a photodetector having a large-area photocathode is used, the condenser lens 33 becomes unnecessary. That is, the condenser lens 33 is not an essential component in the present invention.

The intensity of the observation signal obtained as described above is very weak, 0.5 mV in the conventional example, but can be increased to 80 mV, and the signal-to-noise ratio is dramatically increased. At the same time, the adjustment and assembly of the optical system became very easy. Further, in the conventional example, when the linear movement mechanism 8 moves by 30 mm, the intersection angle between the two diffracted lights 9a and 9b by the condenser lens 16 increases, and the phase distribution of the interference light broadens, so that the contrast of the observation signal decreases.

For this reason, in the conventional example, there was a limit to the amount of movement of the linear movement mechanism 8 capable of measuring straightness. However, according to the present invention, such a decrease in the contrast of the observation signal as described above was not recognized. It has been found that straightness can be measured without restricting the amount of movement of the linear movement mechanism 8 in principle. FIG. 2 shows the straightness of the linear moving mechanism 8 evaluated by the arithmetic circuit 19 from the phase difference between the reference signal and the observation signal.

For comparison, a reference mirror is mounted on the linear moving mechanism 8 and a laser length measuring device (AXIOM manufactured by ZYGO) is set in a direction perpendicular to the moving direction of the linear moving mechanism 8.
2/20) also shows the result of measuring the position of the reference mirror. Looking at the results, the straightness evaluated by the present invention was in good agreement with the result evaluated by the laser length measuring device, and the effectiveness of the present invention was confirmed.

[0026]

As described above in detail with reference to the embodiments, the straightness measuring method according to the first aspect of the present invention includes:
The direction of movement of the linear movement mechanism is such that the diffraction grating is installed on the linear movement mechanism so as to coincide with the normal to the processing surface of the diffraction grating, and light emitted from a light source that emits light having coherence, After being incident so as to be parallel to the normal of the diffraction grating, the + 1st-order diffraction light and the -1st-order diffraction light generated from the diffraction grating are collimated by a collimating optical system, and further, the + 1st-order diffracted light is collimated. By superimposing the first-order diffracted light and the minus first-order diffracted light on the photodetector by the interference optical system and obtaining an interference signal, the displacement amount in the direction orthogonal to the moving direction of the linear moving mechanism can be changed within the plane of the diffraction grating. In the straightness measuring method and the straightness measuring method for converting the directional displacement into a directional displacement and detecting the straightness based on a phase change of the interference signal generated thereby, the + 1st-order diffracted light and the -1st-order diffracted light incident on the parallelizing optical system. Since the difference in the number of reflections by a mirror or the like until reaching the photodetector is set to an odd number, the optical axes of both diffracted lights always coincide with each other even if the linear movement mechanism moves. No matter how much the linear movement mechanism moves, the signal-to-noise ratio of the observation signal does not deteriorate.

Further, in the straightness measuring device according to a second aspect of the present invention, the diffraction grating is placed on the linear moving mechanism such that a moving direction of the linear moving mechanism coincides with a normal to a diffraction grating processing surface. Installed, the light emitted from the light source that emits coherent light, and incident so as to be parallel to the normal of the diffraction grating, then + 1st-order diffracted light and -1st-order light generated from the diffraction grating The collimated light is collimated by a collimating optical system, and the collimated + 1st-order diffracted light and -1st-order diffracted light are superimposed on a photodetector by an interference optical system to obtain an interference signal. In the straightness measuring device, which converts a displacement amount in a direction orthogonal to the moving direction into an in-plane displacement of the diffraction grating and detects the straightness by a phase change of the interference signal generated thereby, Chemical light Because an optical system is provided in which the difference in the number of reflections until the + 1st-order diffracted light and the first-order diffracted light reach the photodetector after passing through the system is an odd number, an observation signal can be obtained without using a spatial filter. In addition, the intensity of the observation signal can be improved, and a shield plate or the like installed around the photodetector is not required. Further, since a spatial filter is not used, adjustment and assembly of the optical system become easy.

[Brief description of the drawings]

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

FIG. 2 is a graph showing a result of evaluating the straightness of a linear moving mechanism by a straightness measuring device according to the present invention.

FIG. 3 is a configuration diagram of a straightness measuring device in a conventional example.

FIG. 4 is an explanatory diagram of a table and a diffraction grating of the linear movement mechanism.

[Explanation of symbols]

 Reference Signs List 1 light source 3 half mirror 4 polarizer 5 photodetector 6 diffraction grating 7 table 8 linear movement mechanism 9 first-order diffracted light 10 biprism 11 total reflection mirror 12 polarizer 13 1/2 wavelength plate 14 total reflection mirror 15 half mirror 16 collection Optical lens 17 Spatial filter 18 Photodetector 19 Operation circuit 29 Light 31 Half mirror 32 Total reflection mirror 33 Condensing lens

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takayuki Goto 1-8-1 Koura, Kanazawa-ku, Yokohama-shi, Kanagawa Prefecture Inside the Research Center for Mitsubishi Heavy Industries, Ltd. 8-1 Inside Mitsubishi Heavy Industries, Ltd. Basic Technology Research Laboratory

Claims (2)

[Claims] 1. A diffraction grating is provided on the linear moving mechanism so that a moving direction of the linear moving mechanism coincides with a normal line of a processing surface of the diffraction grating, and the light is emitted from a light source that emits coherent light. The incident light so as to be parallel to the normal line of the diffraction grating, and then +
The first-order diffracted light and the -1st-order diffracted light are collimated by the collimating optical system, and the + 1st-order diffracted light and-
The first-order diffracted light is superimposed on a photodetector by an interference optical system to obtain an interference signal, thereby converting a displacement amount in a direction orthogonal to a moving direction of the linear moving mechanism into an in-plane displacement of the diffraction grating. In the straightness measuring method for detecting the straightness based on a phase change of the interference signal generated thereby, the + 1st-order diffracted light and the -1st-order diffracted light after passing through the parallelizing optical system reach the photodetector. The straightness measuring method is characterized in that the difference in the number of reflections by a mirror or the like is odd. 2. The diffraction grating is installed on the linear movement mechanism so that the direction of movement of the linear movement mechanism coincides with the normal to the processing surface of the diffraction grating, and the light is emitted from a light source that emits coherent light. The incident light so as to be parallel to the normal line of the diffraction grating, and then +
The first-order diffracted light and the -1st-order diffracted light are collimated by the collimating optical system, and the + 1st-order diffracted light and-
The first-order diffracted light is superimposed on a photodetector by an interference optical system to obtain an interference signal, thereby converting a displacement amount in a direction orthogonal to a moving direction of the linear moving mechanism into an in-plane displacement of the diffraction grating. Then, in a straightness measuring device that detects the straightness by a phase change of the interference signal generated thereby, the + 1st-order diffracted light and the first-order diffracted light after passing through the parallelizing optical system reach the photodetector. A straightness measuring device provided with an optical system in which the difference in the number of reflections is odd.