JPH05172518A - Highly accurate coordinate measuring apparatus - Google Patents

Abstract

PURPOSE:To make the moving part light and to obtain the conditions for excluding the errors in Abbe numbers in measurements of lengths and coordinates. CONSTITUTION:Optical interference is utilized in a length-measuring coordinate measuring apparatus. In this apparatus, a movable holder 2, which can be moved in the direction orthogonal to a reflecting mirror Mx fixed to a base stage 1, is provided. In this holder 2, a position detector 3 and first and second interferometers 20 and 30, which measure the relative moving amounts of the position detectors 3 and the reflecting mirror Mx, are provided. Each interferometer has a measuring optical system and a reference optical system. The optical axes of the measuring optical systems of the first and second interferometers are located at the distances of L and D from the measuring point O of the position detector 3. When the measured moving amount values are d1 and d2 and m=L/D, the moving amount S of the measuring point is computed by S=(d2-md1)/(1-m).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high precision coordinate measuring device utilizing laser interference.

[0002]

2. Description of the Related Art First, FIG. 11 showing the concept of a laser interference coordinate measuring instrument manufactured based on the prior art will be described.
Rectangular reflecting mirrors Mx and My are fixed on the stage 6 movable in the X and Y directions. These reflectors M
x and My are arranged so as to be perpendicular to the measurement arms of the laser interferometer for X-axis measurement (hereinafter referred to as X-axis interferometer) Ix and the laser interferometer for Y-axis measurement (hereinafter referred to as Y-axis interferometer) Iy. There is. When the stage 1 moves in the X direction, the movement amount in the X direction is measured by the X axis interferometer Ix, and when the stage 1 moves in the Y direction, the movement amount in the Y direction is measured by the Y axis interferometer Iy. Reference numeral 3 is a surface position detector such as a position detecting microscope for detecting the position of the drawn figure 5 on the object to be measured 4. The optical axes of the X and Y axis interferometers Ix and Iy and the optical axis of the surface position detector 3 are perpendicular to each other and intersect at one point. With such a configuration, even if the Abbe condition is satisfied and the stage 6 is slightly tilted around the X axis and / or the Y axis, a measurement error (Abbe error) proportional to the tilt angle occurs. Absent. However, in this example, the heavy stage 6 on which the object to be measured 4 is placed must be moved, and therefore, the X-axis interferometer Ix and the Y-axis interferometer Iy are required.
Alternatively, if the base (not shown) to which the surface position detector 3 is fixed does not have sufficient rigidity, the base is bent. As a result, the distance between the interferometer and the reflecting mirror changes and an error occurs. In order to achieve nanometer accuracy, it is necessary to eliminate such errors. For that purpose, the rigidity of the base must be increased, and the entire apparatus becomes large and heavy. Therefore, the key to improving accuracy is to make the moving object as light as possible.

FIG. 12 is a conceptual diagram of three-dimensional measurement.
In addition to the configuration shown in FIG. 1, a Z-axis interferometer Iz in the Z-axis direction and a Z-axis reflecting mirror Mz are added to the lower surface of the stage 6, and the stage 6 is configured to move in three dimensions of X, Y and Z. There is. Further, 5a is a three-dimensional surface. Also in this example, the heavy stage 6 has to be moved, and an error due to the bending of the base is unavoidable. A method of reducing the weight of a moving object is to place interferometers Ix, Iy, and Iz inside the three reflecting mirrors instead of the stage 6 and to move them integrally with the surface position detector 3. In this case, both the interferometer and the surface position detector can be made much lighter than the stage. However, when trying to bring the interferometer close to the surface position detector, the interferometer collides with the object to be measured. Therefore, if the optical axis of the interferometer is shifted upward so as not to make contact, the Abbe condition cannot be satisfied. Such inconvenience is the same in the two-dimensional case.

[0004]

It is so-called that a length measuring system utilizing light wave interference can realize a very high accuracy on the order of nanometers. However, the high accuracy that the interferometer originally has cannot be realized unless the measurement system including the position detection is comprehensively considered. Further, in the conventional coordinate measuring machine, a heavy stage has to be moved in two dimensions, which requires a sturdy base that does not bend, resulting in a large size. Furthermore, a means for measuring a three-dimensional object with high accuracy has not yet been known. It is an object of the present invention to realize high accuracy of an interferometer by reducing the weight of a moving part in length measurement or coordinate measurement.

[0005]

A high precision coordinate measuring apparatus according to the present invention has a reflecting mirror fixed to a base and a movable holder movable in a direction perpendicular to the reflecting mirror. A position detecting device and first and second interferometers for measuring a relative movement amount between the reflecting mirror and the position detecting device are provided.
Furthermore, the first and second interferometers each have a measurement optical system and a reference optical system, and the optical axes of the measurement optical systems of the first and second interferometers are respectively from the measurement points of the position detection device. There are distances L and D (however, D ≠ L), and the moving amount measurement values of the movable holder measured by the first and second interferometers are d1 and d2,
When m = L / D, the moving amount S of the measuring point is calculated by the formula S = (d2-md1) / (1-m).

[0006]

By moving the movable holder provided with the position detecting device instead of the stage, the moving part is made lighter and the measurement error is less likely to occur. In addition, two interferometers are provided at different heights from the measurement point, and the movement distance is calculated based on the interference fringe measurement data obtained from each interferometer using parameters including the position from the measurement point of each interferometer. By the calculation, the Abbe error caused by the tilt of the movable holder is offset and removed.

[0007]

The present invention will be described with reference to the drawings. FIG. 10 is a configuration showing a conceptual diagram of the first embodiment. Flat reflecting mirrors Mx, My, Mz are fixed on the base 1 by appropriate means (not shown). A surface position detector 3, an X-axis interferometer Ix, a Y-axis interferometer Iy, and a Z-axis interferometer Iz are attached to the movable holder 2. The holder 2 is configured to be freely movable in three directions of X, Y and Z by a well-known three-dimensional drive mechanism, and is mounted on the base 1 by a surface position detector 3 attached to the movable holder 2. The surface position of the placed three-dimensional DUT 4 is detected.

An embodiment of a method for removing Abbe's error will be described with reference to FIGS. 1 to 4. 1 is shown in FIG.
It is the figure which extracted and drew only the part which measures the X-axis direction from. In the figure, the X-axis interferometer Ix fixed to the movable holder 2 includes two interferometers 20 and 30 and a subtracter 41 that performs a predetermined calculation based on the number of interference fringes measured by these interferometers. I have it. The interferometers 20 and 30 are fixed to the measuring point O of the position detecting device 3 at intervals of D and L, respectively.

FIG. 2 is an explanatory view of an optical path of a main part of the interferometer 20 shown in FIG. In the figure, all optical components are fixed to a movable holder 2 (not shown here). Reference numeral 21 denotes a polarization prism, and a linearly polarized light component (p component) that oscillates in parallel to the paper surface of the light beam incident on the polarization prism 21 passes through the polarization prism 21 and the quarter-wave plate 23, and the X-axis reflection mirror Mx (here, (Not shown), transmits again through the quarter-wave plate 23, and then is reflected by the polarizing prism 21 to be reflected by another polarizing prism 2
Go to 2. Here, the light is reflected and transmitted through the quarter-wave plate 24, is reflected by the fixed reflecting mirror 8, again passes through the quarter-wave plate 24, and this time passes through the polarization prism 22. Then, after being reflected by the right-angle prism 25, it passes through the polarizing prism 22 and the quarter-wave plate 24 and goes toward the X-axis reflecting mirror Mx. Further, the light flux reflected here passes through the quarter-wave plate 24 again, is reflected by the polarization prism 22 and the polarization prism 21, is reflected by another fixed reflecting mirror 9, and is again polarized by the quarter-wave plate 23. The light is transmitted through the prism 21 and emitted from the interferometer 20.

On the other hand, the linearly polarized light component (s component) which oscillates perpendicularly to the paper surface is reflected by the polarization prism 21, and after being reflected by the 1/4 wavelength plate 26 having a back surface as a reflection mirror, the polarization prism 21, 22 and is reflected by a quarter-wave plate 27 whose rear surface is a reflecting mirror, as with the quarter-wave plate 26.
After that, the light is reflected by the polarization prism 22 and the right-angle prism 25
Is reflected by the polarizing prism 22, again reflected by the 1/4 wavelength plate 27, transmitted through the polarizing prisms 22 and 21,
It is reflected by the / 4 wavelength plate 26 and the polarization prism 21 and emitted from the interferometer. Here, the p component and the s component are ejected together.

FIG. 3 shows the construction of the optical paths of the essential parts of an embodiment of the interferometer 30. However, the difference from that shown in FIG. 2 is that the fixed reflecting mirrors 8 and 9 are removed. In the total 20, the two light beams are directed to the reflecting mirror Mx, but in the case of the interferometer 30, four light beams are directed. Interferometer 2
Light emitted from 0 and 30 is guided to the interference fringe detection system as shown in FIG. In the figure, 11 is a half-wave plate, and the p and s components from each interferometer are the half-wave plate 1 respectively.
After the plane of polarization is rotated by 45 ° around the optical axis by 1, the interference fringes are formed by passing through the polarization prism 7, which is detected by a known photodetector 12. The intensity of the interference fringes is converted into an electric signal by the photodetector 12 and the number of the interference fringes is counted by a known means.

Along with the movement of the movable holder 2, the position detecting device 3
Suppose that the measurement point O of S moves in the X-axis direction by S. After the movement, the movable holder 2 is assumed to be tilted clockwise by α. Number of interference fringes measured by interferometers 20 and 30 Z1
, Z2 is given by the following equation. That is, Z1 = (S-Dα) / (λ / 4) (1) Z2 = (S-Lα) / (λ / 8) (2) Therefore, when the difference Z is calculated by the subtractor 41, Z = Z2 -Z1 = {S- (2L-D) α} / (λ / 4) (3) From this equation, when D = 2L, Z = S / (λ / 4) (4), and the influence of the inclination α is The removed amount S is calculated by the following equation. S = (λ / 4) Z (5) As described above, even if the position detection device 3 rotates about the measurement point O, this value does not change, and thus Abbe's error can be removed. In FIG. 1, 10 is a probe for detecting the position of the measuring point O of the position detecting device 3, which is a photoelectric microscope, a scanning tunneling microscope (STM), an atomic force microscope (AF).
Known devices such as M) can be used.

FIG. 5 shows a second embodiment. This example is shown in Figure 1.
The optical system of the interferometer 20 of the example shown in FIG. 3 is replaced with the interferometer optical system shown in FIG. When counting the number of the interference fringes, the subtractor 41 is entered through a thinning circuit 42 which outputs one counting pulse for the two interference fringes. The other interferometers 31 are the same as the interferometers 30, but one counting pulse for one interference fringe enters the subtractor 41. In this configuration, one fringe counting pulse in each interferometer is λ / 8.
Since it corresponds to the length of, the output of the subtractor 41 is expressed by the equation (3) as before. Therefore, when D = 2L as in the previous embodiment, the Abbe error is removed.

Here, for convenience of explanation, 1 of the interferometer 31 is used.
Although one counting pulse is made to correspond to the interference fringes, it is not possible to measure the fraction of the interference fringes by making a plurality of pulses such as two or four correspond to one interference fringe by a known interference fringe division method. It's easy. Now, as the interference fringe detection system of the interferometer 30, one that detects M counting pulses in one interference fringe is used,
The interference fringe detection system of the interferometer 31 has N (N
If a pulse generating a counting pulse of (> is larger than M) is used, Abbe's error is removed when MD = NL is satisfied, and the interference fringes can be divided into M for finer measurement.

FIG. 6 shows a third embodiment. That is, after counting pulses from the interferometer 30 by the counter 43, the number of pulses is multiplied by M by the multiplier 45, and the interferometer 31 by the counter 44.
After counting the counting pulses from, the number of pulses is multiplied by N by the multiplier 46, and then input to the subtractor 41. Also in this case MD
= NL, the Abbe error is removed. If one counting pulse from the interferometer 30 or the interferometer 31 corresponds to the length of λ / 2K (K is an integer), the movement amount S of the measurement point of the position detecting device 3 is the output of the subtractor 41 as Z. Then, S = λZ / 2K (NM) (6)

FIG. 7 shows the count values Z1 of the counters 43 and 44,
It is a fourth embodiment in which the movement amount S is obtained by the calculator 47 with Z2 as an input. Assuming that the count value measured by the interferometer 30 is Z1, the amount of movement d1 of the movable holder 2 at that portion is
Is d1 = S-Dα = Z1 1 (.lambda. / 2K) (7) Letting Z2 be the count value measured by the interferometer 31,
The amount of movement d2 of the movable holder 2 at that portion is: d2 = S-Lα = Z2 (λ / 2K) (8) The calculator 47 performs the following calculation when m = L / D (9) .. S = (λ / 2K) (Z2-mZ1) / (1-m) (10) or S = (d2-md1) / (1-m) (11) In this way, Abbe's error is not included. Correct movement amount S
Is required. Here, if m = 2/3, D−L = L
/ 2, and the distance (D-L) between the two interferometer optical axes is L /
It can be 2. Even when the number of times the measurement light beams of the two interferometers make a round trip with the reflecting mirror is different, it is extremely easy to derive the equation corresponding to the equation (10) or the equation (11). It goes without saying that it is included in the category.

A fifth embodiment is further shown in FIGS. These are examples in which the light beam emitted by the optical system shown in FIGS. 2 and 3 is returned to the interferometer again by the right-angle prism 48.
The optical system of FIG. 8 is used as the interferometer 20 of the embodiment of FIG. 1, and the optical system of FIG. 9 is used as the interferometer 30. In this example, the measuring light beam of the interferometer 20 makes six round trips with the reflecting mirror Mx. The measuring luminous flux of the interferometer 30 is 8
Make a round trip. Therefore, if 3D = 4L is satisfied, the Abbe error is removed. The optical axis distance between the interferometer 20 and the interferometer 30 is DL, but DL-L / 3. Therefore, if L is the same, the intervals of the interferometer optical system can be reduced, and the interferometer can be compactly assembled.
If the intervals are the same, the measurement points can be set at positions further apart.

As seen in the above embodiment, when two interferometers are used and m = N / M = L / D, (10)
The correct movement amount S that does not include the Abbe error can be obtained by the expression or the expression (11).

In the above embodiment, the interferometer is fixedly mounted on the movable holder and the reflecting mirror is fixed to the base. However, the present invention is not limited to this, and the reflecting mirror is mounted on the movable holder and the interferometer is mounted on the base. If the above is fixed and the above relationship is satisfied, the Abbe error can be removed.

The high-precision coordinate measuring device according to the present invention is capable of highly accurate measurement by eliminating Abbe's error.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment of a high precision coordinate measuring apparatus according to the present invention.

FIG. 2 is an optical path explanatory diagram of the interferometer in FIG.

FIG. 3 is an optical path explanatory diagram of another interferometer in FIG.

FIG. 4 is a schematic diagram of a photodetector omitted in FIG.

FIG. 5 is a configuration diagram of a high precision coordinate measuring device according to a second embodiment of the present invention.

FIG. 6 is a configuration diagram of a main part according to a third embodiment of a high precision coordinate measuring apparatus according to the present invention.

FIG. 7 is a configuration diagram of a main part of a high precision coordinate measuring apparatus according to a fourth embodiment of the present invention.

FIG. 8 is an optical path diagram of the one interferometer according to the fifth embodiment of the present invention.

FIG. 9 is an optical path diagram of another interferometer according to the fifth embodiment of the present invention.

FIG. 10 is a configuration diagram showing the concept of three-dimensional measurement according to the present invention.

FIG. 11 is a configuration diagram showing the concept of conventional two-dimensional measurement.

FIG. 12 is a configuration diagram similarly showing the concept of three-dimensional measurement.

[Explanation of symbols]

 1 base 2 movable holder 3 surface position detector 4 object to be measured 6 stage 7 polarizing prism 8 reflecting mirror 9 reflecting mirror 10 probe 11 1/2 wave plate 12 photodetector 20 interferometer 21 polarizing prism 22 polarizing prism 23 1 / 4 wave plate 24 1/4 wave plate 25 right angle prism 26 1/4 wave plate 27 1/4 wave plate 30 interferometer 41 subtractor 42 thinning circuit 43 counter 44 counter 45 multiplier 46 multiplier 47 calculator 48 Right Angle Prism Mx X Axis Reflector My Y Axis Reflector Mz Z Axis Reflector Ix X Axis Interferometer Iy Y Axis Interferometer Iz Z Axis Interferometer

Claims (6)

[Claims] 1. A base and a reflecting mirror fixed to the base,
A movable holder provided on the base so as to be movable in a direction perpendicular to the reflecting mirror, a position detecting device fixed to the movable holder, the reflecting mirror fixed to the movable holder, and a position detecting device. First and second interferometers for measuring the relative movement amount of the first interferometer, each of the first and second interferometers having a measurement optical system and a reference optical system. The optical axis of the measuring optical system is at a distance L from the measuring point of the position detecting device, and the optical axis of the measuring optical system of the second interferometer is D (however, D ≠ L) from the measuring point. At a distance, the moving amount measurement value of the movable holder measured by the first interferometer is d1, the moving amount measurement value of the movable holder measured by the second interferometer is d2, and m = L / When D, the moving amount S of the measurement point is calculated by the formula S = (d2-md1) / (1-m). High precision coordinate measuring device. 2. A base, a movable holder provided so as to be movable in one direction with respect to the base, a position detection device fixed to the movable holder, and a reflection fixed to the movable holder. A mirror and first and second interferometers fixed to the base and measuring relative movement amounts of the reflecting mirror and the position detecting device,
The first and second interferometers each have a measuring optical system and a reference optical system, and the optical axis of the measuring optical system of the first interferometer is a distance L from the measuring point of the position detecting device. In the second
The optical axis of the measuring optical system of the interferometer is at a distance D (however, D ≠ L) from the measuring point, and the moving amount measurement value of the movable holder measured by the first interferometer is d1, Second
When the measurement value of the moving amount of the movable holder measured by the interferometer is d2 and m = L / D, the moving amount S of the measuring point is calculated by the following equation: S = (d2-md1) / (1-m) A high-precision coordinate measuring device characterized by calculating. 3. A base, and a reflecting mirror fixed to the base,
A movable holder provided on the base so as to be movable in a direction perpendicular to the reflecting mirror, a position detecting device fixed to the movable holder, and the reflecting mirror and position detecting device fixed to the movable holder 2. And a first interferometer for measuring a relative movement amount between the first interferometer and the second interferometer, each of which has a measurement optical system and a reference optical system. The optical axis of the measuring optical system of the meter is at a distance L from the measuring point of the position detecting device, and the optical axis of the measuring optical system of the second interferometer is D from the measuring point (where D ≠ L). The number of times the measuring light beam of the first interferometer travels back and forth between the reflecting mirror and
NL = MD, where N is an integer of 2 or more and M is the number of times that the measuring light flux of the second interferometer travels back and forth with the reflecting mirror. A high-precision coordinate measuring device which satisfies the relationship and further calculates a moving amount of a measuring point from a difference between interference fringes including fractions measured by the two interferometers. 4. A base, a movable holder provided so as to be movable in one direction with respect to the base, a position detection device fixed to the movable holder, and a reflection fixed to the movable holder. A mirror and first and second interferometers fixed to the base and measuring relative movement amounts of the reflecting mirror and the position detecting device,
The first and second interferometers each have a measuring optical system and a reference optical system, and the optical axis of the measuring optical system of the first interferometer is a distance L from the measuring point of the position detecting device. In the second
The optical axis of the measuring optical system of the interferometer is at a distance of D (where D ≠ L) from the measuring point, and the number of times the measuring light beam of the first interferometer travels back and forth between the reflecting mirror and When N times (N is an integer of 2 or more) and M is the number of times the measurement light beam of the second interferometer travels back and forth between the reflecting mirror and M times (M is an integer smaller than N), NL = MD A high-precision coordinate measuring device which satisfies the following relationship and further calculates a moving amount of a measuring point from a difference between interference fringes including fractions measured by the two interferometers. 5. The X-axis and Y-axis reflecting mirrors are fixedly mounted on the X-axis and the Y-axis, respectively, in the reflecting mirror according to claim 1, and the movable holder is X-axis relative to the base. And an X-axis interferometer including the first and second interferometers, which are provided so as to be movable in parallel in the Y-axis direction and face the X-axis and Y-axis reflecting mirrors, respectively, in the movable holder, The high-precision coordinate measuring device according to claim 1, further comprising a Y-axis interferometer. 6. The Z-axis reflecting mirror according to claim 5, wherein the movable holder is provided so as to be movable in parallel to the base in the Z-axis direction, and the movable holder is provided with the Z-axis. 6. A Z-axis interferometer including the first and second interferometers is provided facing the reflecting mirror.
High precision coordinate measuring device.