JP3525512B2 - Method for measuring surface characteristics of plane mirror and method for moving table - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the surface characteristics (straightness) of a plane mirror used in a stage device of an exposure apparatus for VLSI, a mask moving stage of a mask inspection apparatus, or the like, which requires high positioning accuracy. Degree) measuring method.

[0002]

2. Description of the Related Art Conventionally, a laser interferometer has been used as a measuring sensor for positioning control in a stage device which performs positioning with high accuracy. The reason for this is that the wavelength of the laser beam whose frequency is stable is used as the standard for length measurement, and therefore the reproducibility is excellent and the absolute accuracy is high over a long measurement range. A stage apparatus equipped with this laser interferometer is often used in an exposure apparatus for manufacturing a semiconductor device, which requires submicron positioning accuracy, an electron beam apparatus, and the like.

FIG. 6 is a perspective view showing a schematic structure of a stage device equipped with a conventional laser interferometer. Here, the laser interferometer is not shown, but the laser beam for length measurement emitted from the laser interferometer is shown by a dotted line. The Y stage 51 and the Y motor 53 together with the base 5
It is movable in the Y direction by rotating the feed screw 54, which is placed on the No. 0 and screwed with a nut (not shown) fixed therein, by the Y motor 53. The X stage 52 on which the workpiece 59 (for example, a wafer) is placed is X
It is provided on the Y stage together with the motor 55, and the X
The feed screw 56 is rotated by the motor 55 to move in the X direction. Plane mirrors (moving mirrors) 57 and 58 that reflect the measurement beams Bx and By from the X and Y laser interferometers are fixed to the ends of the X stage 52 so as to be orthogonal to each other.

By driving the X and Y motors based on the position information from the X and Y laser interferometers, the workpiece can be moved to a predetermined position. However, the moving mirrors 57 and 58 still have processing errors during manufacturing, and when they are attached to the X stage 52, they are deformed. In order to realize an exposure apparatus for manufacturing an LSI having a line width of 0.25 μm level, the straightness error of the moving mirrors 57, 58 needs to be ± 10 nm or less. The straightness error is a deviation from an actual moving mirror with respect to an ideal plane. However, it is difficult to reduce the straightness error even if the moving mirror material, processing method, and mounting method are devised.

On the other hand, there is an idea of positively measuring and correcting the straightness error of the movable mirror. As an example of this kind, Japanese Utility Model Laid-Open No. 59-98446 can be mentioned. this is,
Installed a 2-axis laser interferometer, which is parallel to both X and Y,
The aim is to measure and correct the straightness error of the moving mirror.

[0006]

Recently, as the line width of semiconductor elements has become finer, there has been a demand for a stage device capable of accurately positioning with respect to the fine line width. However, this correction method described above has a limit in accuracy because it cannot detect a fine cycle deformation or deviation within the interval between the biaxial lasers. Further, since the two-axis laser interferometer is installed in the stage device, the structure of the device itself becomes complicated and the device becomes large in size.

In view of the above-mentioned problems, it is an object of the present invention to provide a method for measuring the straightness error of a movable mirror mounted on a stage with higher accuracy than a biaxial laser interferometer. .

[0008]

Means for Solving the Problems The present inventor has diligently studied means for solving such problems. In the exposure apparatus as described above, the entire apparatus including the stage is usually installed in an environmental chamber in which the temperature can be adjusted with high accuracy.
Experiments have shown that in this kind of environment, the temporal change of the mirror surface of the movable mirror once installed on the table is very small. Therefore, it is not always necessary to periodically correct the straightness error (surface characteristic) of the movable mirror.

Therefore, the present invention provides a surface characteristic measuring method for a plane mirror of a stage apparatus in order to solve the above-mentioned problems. The method for measuring the surface characteristics of the plane mirror of the stage device includes the following first to seventh steps. First step: a predetermined base, a first plane mirror placed on the base and extending in a first direction, and a second plane mirror extending in a second direction substantially perpendicular to the first direction. A table on which and are installed and a drive mechanism for driving the table in the horizontal direction are prepared. Second step: An interferometer for mirror surface inspection (for example, Fizeau interferometer) is fixed to a base so that surface characteristics of a part of the first plane mirror can be measured. Third step: A part of surface characteristics of the first plane mirror is measured by an interferometer for mirror surface inspection. Fourth step: The table is moved by the drive mechanism along the first plane mirror by a distance smaller than the measurement width of the interferometer for mirror surface inspection. Fifth step: The third step and the fourth step are repeated to measure the surface characteristics of the entire surface of the first plane mirror. Sixth step: Calculation is performed based on the measurement value of the interferometer for mirror surface inspection, and the surface characteristic of the entire first plane mirror is obtained. Seventh step: storing the surface characteristics of the entire surface of the first plane mirror.

[0010]

When the stage device is assembled or adjusted, the mirror surface interferometer is fixed to the base to measure the straightness error of the moving mirror. The interferometer for mirror surface inspection measures part of the mirror surface of the movable mirror, moves the table within a range smaller than the measurement width of the interferometer for mirror surface inspection, and again measures part of the mirror surface. This is performed over the entire mirror surface of the movable mirror. After measuring the entire surface, connect the measurement values of the interferometer for mirror surface inspection, overlap the parts,
Get the straightness error of the entire mirror surface. This error is stored and used for correction when the stage moves to the target position.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic diagram showing the outline of a laser interferometer according to an embodiment of the present invention. Moving mirrors 3 and 4 are mounted on a table 1 fixed to a base (not shown).
A workpiece 2 (for example, a wafer) is placed on the table 1. The X and Y drive mechanisms 21 and 22 can move in the X and Y directions along the movable mirrors 3 and 4.
The movable mirrors 3 and 4 are irradiated with a laser beam emitted from a laser light source, and the reflected light is received to detect the position of the table 1 with high accuracy (for example, a resolution of 0.01 μm) (this position). A device that performs detection is called a laser interferometer. The laser interferometers 12 and 13 are also fixed to the base.

The electric signal processing system 14 calculates the position of the table 1 from the detection signal, and outputs the position to the control system 15. On the other hand, the surface characteristics of the movable mirrors 3 and 4 are stored in the memory 16 in association with the table position information. Control system 15
Calculates the moving distance from the moving target position, the position information from the electric signal processing system 14, and the surface characteristics of the moving mirrors 3 and 4 corresponding to the moving target position stored in the memory 16. The memory 16 retains the contents of the memory even if the power source of the device is turned off, unless the battery retains data and the memory is rewritten. The moving distance is output to the D / A converters 17 and 18 and converted into an analog signal. The analog signal is amplified by the power amplifiers 19 and 20 and applied to the X and Y drive mechanisms 21 and 22 to drive the table 1. This allows the table 1 to move to the target position.

Next, the outline of the laser interferometer will be described with reference to FIG. The laser light source 5 is a well-known Zeeman two-frequency stabilized HeNe laser, and emits linearly polarized laser lights which are orthogonal to each other and have different frequencies by a Zeeman split frequency (hereinafter referred to as a difference frequency for simplification). This light is then split by the non-deflecting laser beam splitter 6 into two directions of XY, and each is guided to the interferometers of the XY axes. Hereinafter, since the configurations are the same, only the X side will be described. First, the laser light is incident on the deflecting beam splitter 7a, and the optical path is divided into the P-deflecting component and the S-deflecting component. The P deflection component goes straight and is reflected by the reference fixed mirror 10a. On the way
Since there is the quarter-wave plate 9a, when it returns to the deflection beam splitter 7a, it is reflected because the deflection direction is rotated by 90 °, and the light enters the detector 11a. The S polarization component is reflected by the polarization beam splitter and then reflected by the movable mirror 4. Since there is a quarter-wave plate 8a on the way, when returning to the deflection beam splitter 7a, the deflection direction is rotated by 90 °, so the light travels straight and the light is detected by the detector 11a.
Incident on. The detector 11a has 4
It has a built-in polarizer tilted at 5 °, and the photoelectric sensor installed behind the polarizer receives the interference light of both polarization components.
Convert to electrical signal. Therefore, when the stage is stationary, a signal modulated by the difference frequency of the laser light source 5 is detected. When the stage moves, the frequency of the light beam reflected from the movable mirror 4 changes, so that the modulation frequency changes. By inputting this signal together with the reference difference frequency signal output from the laser light source into the electric signal processing system (frequency counter) and performing heterodyne phase detection, the position of the stage can be detected with high resolution.

Next, an interferometer for mirror surface inspection for detecting the surface characteristics of the movable mirrors 3 and 4 will be described. The interferometer 20 for mirror surface inspection described here is composed of a so-called Fizeau interferometer. The laser light emitted from the laser light source 21 passes through the beam shaping optical system 22 and is converted into a parallel beam having an appropriate size. Next, the light is condensed by the lens 23, but the rear focal point of the lens 23 and the front focal point of the Fizeau lens 26 coincide with each other. Therefore, the light passing through the Fizeau lens 26 becomes a parallel light flux, passes through the reference surface 27, and then is vertically incident on the movable mirror 4, which is the surface to be inspected, by the 45 ° bending mirror 28.

Usually, the reference surface 27 uses a single glass reflecting surface of about 4%, while the reflecting surface of the movable mirror 4 is usually a vapor-deposited surface of aluminum or the like and has a reflectance of about 80%. have. For this reason, if left as it is, the light fluxes of the measurement light flux reflected by the movable mirror and the reference light flux reflected by the reference surface are extremely different from each other, resulting in poor contrast. Therefore, in order to reduce the contrast of the measurement light flux, the reflectance of about 4% is required.
A bending mirror 28 is interposed.

The light reflected from the movable mirror 4 travels in the opposite direction on the optical path and is reflected by the half mirror 24.
Along with the reference light reflected from the reference surface 27, the detector 29
And the interference fringes of both are detected. The detector 29 is
It is composed of a television camera (for example, a two-dimensional CCD camera). For example, when the TV camera has 200 pixels in the measurement direction and the measurement width of the movable mirror 4 is 60 mm, the surface characteristic of the movable mirror 4 can be measured with a resolution of 0.3 mm. This resolution is a value sufficiently smaller than the beam diameter (6 mm) of the laser interferometer. The detector 29 measures the surface characteristic of the movable mirror 4 by this interference fringe. The mirror surface interferometer 20 is
The above-mentioned structure is integrally formed and can be easily fixed to the base.

The surface characteristics of the reference surface 27 and the 45-degree folding mirror 28 are measured with high accuracy by using a reference surface whose surface characteristics are measured in advance, and the measured values are automatically corrected. It is supposed to be done. further,
In FIG. 3, the measurement range of the interferometer 20 for mirror surface inspection is shown so as to correspond to only a part of the movable mirror 4. In this case, the table 1 may be sent in the Y direction and the surface characteristics of the adjacent movable mirrors 4 may be sequentially measured. At this time, measurement is performed so that adjacent measurement ranges partially overlap. The surface characteristics of the entire movable mirror 4 can be measured by adjusting the offset component, the tilt component, and the like included in the measurement value so that the shapes of the overlapping portions match each other.

By thus reducing the measurement range, it is possible to reduce the size of the interferometer 20 for mirror surface inspection to the extent that it can be easily moved and installed. An embodiment of the present invention will be described with reference to the flowchart of FIG. Here, the measurement of the surface characteristics of the movable mirror 4 will be described. This measurement is performed when the stage device is assembled.

Step 101: The interferometer 20 for mirror surface inspection is fixed to the base so that the surface characteristics of the movable mirror 4 can be measured. Here, the mounting position is set at a position where the entire surface of the movable mirror 4 can be measured by moving the table 1. Then, the table 1 is moved in the direction along the movable mirror 4 so that the movable mirror 4 can be sequentially measured from one corner. Also,
It is connected via an A / D converter (not shown) so that the measured value can be input to the control system 15. Further, in order to detect the amount of movement of the table 1 in the direction along the movable mirror 4, a position detection device (laser interference length measuring device, encoder, etc.) is installed. The table 1 is connected via an A / D converter so that the detection value of the position detection device can be input to the control system 15 when the table 1 is moved.

Step 102: The surface characteristic of the movable mirror 4 is measured with the measurement width of the interferometer 20 for mirror surface inspection. At this time, the laser interferometer measuring the Y direction of the table 1 detects the position in the Y direction, and the position is stored in the control system 15. Step 103: move the table in the Y direction. This moving distance is smaller than the measurement width of the interferometer 20 for mirror surface inspection.

Step 104: Steps 102 and 103 are repeated until the entire surface of the movable mirror 4 is measured.
FIG. 5 shows that the width of the movable mirror 4 is measured by the measurement width 112 of the interferometer 20 for mirror surface inspection, and the entire surface of the movable mirror 4 is measured by performing the measurement five times. There is. Step 105: Calculate the surface characteristics of one moving mirror 4 based on the measurement results of the plurality of portions of the moving mirror 4 measured in step 103. This means that even if the table 1 is moved along the movable mirror 4, at the nanometer level, the table 1 tilts in the XY plane or slightly moves in the XY plane in a direction perpendicular to the moving direction. Therefore, it is necessary to correct inclinations and offsets of a plurality of measurement results, and combine the measurement results to obtain one surface characteristic measurement value.

This calculation method includes (1) position information of the position detecting device in the direction along the movable mirror 4 and the interferometer 20 for mirror surface inspection.
The respective measurement results of the overlapping portions of the adjacent measurement results are calculated from the measurement width of. In FIG. 5, the overlapping portion 121 of the first measurement and the second measurement corresponds to this. Overlapping part 1
The same applies to 22 to 124. (2) The measurement results of the first measurement and the second measurement in the overlapping portion 121 are calculated by the least squares method, and the overlapping portion 1 of the first measurement is calculated.
The inclination and offset of the overlapping portion 121 of the second measurement with respect to 21 are obtained. (3) The entire measurement result of the second measurement is set so that the measurement result of the second measurement overlapping portion 121 becomes equal to the measurement result of the first measurement overlapping portion 121.
(2) ”is corrected by the inclination and offset obtained in this way. By this, the measurement result of the first measurement can be combined. (4) Similarly, the measurement results of the second measurement to the fifth measurement are combined. ) Corresponding the combined measurement results so as to have a one-to-one relationship with the position of the laser interferometer in the Y direction The surface characteristic of the entire surface of the movable mirror 4 is calculated by the above calculation.

Step 106: Table 1 in memory 16
The surface characteristics of the movable mirror 4 are stored in association with the position of. Step 107: The interferometer 20 for mirror surface inspection is removed, and the measurement of the surface characteristics of the movable mirror 4 is completed. Although not shown in FIG. 4, steps 102-
It is possible to obtain the surface characteristics of the moving mirror with higher accuracy by repeating the step 105 several times to perform the whole surface measurement a plurality of times and averaging the measurement results.

The surface characteristics of the movable mirror 3 can be obtained by the same scanning. When the laser interferometer in the Y direction has a function of determining the rotation amount of the table 1 by irradiating the movable mirror 3 with two light beams, the inclination can be corrected by the following method. (1) The tilt is detected by detecting the difference between the rotation amount of the table 1 at the first measurement position and the rotation amount of the table 1 at the second measurement position. (2) The measurement result of the second measurement is corrected from this inclination and is combined with the measurement result of the first measurement. The measurement results are similarly combined after the third measurement. In this case, the inclination of the measurement result can be corrected without calculating the inclination of the measurement result of the overlapping portion. Since the offset measurement can be performed by slightly overlapping the measurement results, it is possible to reduce the number of measurement times of the mirror surface interferometer for measuring the entire surface of the movable mirror 4.

Further, it is possible to measure the surface characteristics of the movable mirrors 3 and 4 as well as the surface characteristics of the surrounding area to which the light beam of the laser interferometer is irradiated. When a leveling mechanism that tilts the table 1 itself on which the movable mirrors 3 and 4 are mounted is attached, the position where the movable mirrors 3 and 4 are irradiated with the light beam changes. It is possible to drive the table 1 based on the surface characteristics of the position corresponding to the changed irradiation position.

The present invention is not limited to the above-mentioned embodiments, and it goes without saying that various configurations can be adopted without departing from the gist of the present invention.

[0027]

The present invention uses a miniaturized interferometer for mirror surface inspection to measure the surface characteristics of one plane mirror in multiple times and connect them to measure the surface characteristics of the plane mirror.
Therefore, it is possible to perform more accurate measurement than the measurement of the surface characteristics using the biaxial laser interferometer.

[Brief description of drawings]

FIG. 1 is a block diagram of a control system of a stage device according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a laser interferometer.

FIG. 3 is a schematic configuration diagram of an interferometer for mirror surface inspection according to the present invention.

FIG. 4 is a flow chart for explaining the operation of the embodiment.

FIG. 5 is a diagram showing the relationship between the measurement width of the interferometer for mirror surface inspection with respect to the movable mirror and the overlap of the measurement areas when a plurality of measurements are performed in the example.

FIG. 6 is a perspective view showing a schematic configuration of a stage device equipped with a conventional laser interferometer.

[Explanation of symbols]

1 table 3, 4 moving mirror 5 Laser light source 14 Electric signal processing system 15 Control system 16 memory 20 Interferometer for mirror surface inspection

Claims (9)

(57) [Claims] 1. A first step of preparing a plane mirror and an interferometer for mirror surface inspection for irradiating the plane mirror with a coherent light beam to simultaneously measure surface characteristics of a predetermined width narrower than the width of the plane mirror. A second step of measuring the surface characteristic of the flat mirror with the predetermined width by the mirror surface interferometer; and the flat mirror in a direction perpendicular to the light beam by a distance smaller than the predetermined width. A method for measuring surface characteristics of a plane mirror, comprising a third step of moving, and repeating the second step and the third step. 2. A table provided with a predetermined base, a first plane mirror placed on the base and extending in a first direction, and a table placed on the base. The first step of preparing a stage device including a drive mechanism that is driven in the horizontal direction, and an interferometer for mirror surface inspection that simultaneously measures surface characteristics of a predetermined width narrower than the width of the first plane mirror. A second step of fixing the surface characteristic of the first surface mirror to the base so that it can be measured, and a third step of measuring the surface characteristic of the predetermined width in the horizontal direction of the first plane mirror by the mirror surface interferometer. A fourth step of moving the table along the first plane mirror by a distance smaller than the predetermined width by the drive mechanism, and the third step and the fourth step are repeated to obtain a surface of the first plane mirror. Measure characteristics 5 Step a, the sixth step and the surface characteristic measuring method of a flat mirror having a storing surface characteristics of the first flat mirror whole surface. 3. The surface characteristic measuring method according to claim 2 is used.
The entire surface of the first plane mirror and the first plane perpendicular to the first direction.
A second plane mirror extending in two directions and arranged on the table
The surface characteristics of the entire surface of the table are stored, and the two stage interferometers are used to irradiate the first plane mirror and the second plane mirror with coherent light beams to measure the position of the table from a predetermined reference position. and, wherein the stored first plane mirror and the surface characteristics of the second plane mirror, based on a detection value of the two stage interferometer, table <br/>, characterized by moving the table How to move. Wherein said planar mirror is a movable mirror provided on the two-dimensional movable table in a predetermined plane, when the measurement of the surface characteristics of the mirror surface inspection interferometer, the said table by a position detecting device The surface characteristic measuring method according to claim 1, wherein a position in a plane is measured. Wherein said mirror surface inspection interferometer, surface characteristic measuring method according to claim 1, 2 or 4, characterized in that it comprises a Fizeau interferometer. Wherein said surface characteristics, surface characteristics measuring method according to claim 1 or 4, characterized in that it comprises a two-dimensional plane properties of the region where the light beam is irradiated to the plane mirror. 7. An interferometer for specular inspection is a two-dimensional CCD.
The surface characteristic measuring method according to claim 6, wherein the surface characteristic of the plane mirror is measured by a camera. From 8. Measurement of the overlapping portions in a predetermined width when the plane mirror has moved distance less than said predetermined width results in the direction perpendicular to the slope and the plane mirror of the plane mirror caused by the movement 8. The surface property measuring method according to claim 1, wherein the measurement results of the overlapping portions are combined by correcting the offset of the plane mirror. 9. The surface characteristic measurement according to claim 1, wherein the surface characteristics of the entire surface of the plane mirror are measured a plurality of times to average the measurement results. Method.