JPS63277922A - Length measuring instrument - Google Patents

Abstract

PURPOSE:To increase a stroke and to obtain high accuracy by performing length measurement with a large stroke by a 1st length measuring means which generates a pulse signal at intervals of specific unit length and performing interpolation between pulse signals with an electric level signal from a 2nd length measuring means. CONSTITUTION:A Y stage YS is mounted on a state base DS and an X stage XS is mounted on the Y stage YS. A laser interference length measuring instrument LI as a large-stroke length measuring instrument measures the movement quantities and positions of the X and Y stages XS and YS. A length measuring instrument which generates the electric level signal corresponding to a displacement quantity within a range of one measurement length pitch by the laser interference length measuring instrument LI in a space DS on the X stage XS. This length measuring instrument and laser interference length measuring instrument LI measure the movement and positions of the X and Y stages XS and YS.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a length measuring device with high precision and a large stroke.

[Prior Art] Conventionally, laser interferometers and grating interferometers have been used for high-precision length measurement.

However, while these interferometers are capable of measuring relatively large strokes of, for example, 100 mm or more, they basically measure a predetermined pitch determined by the optical arrangement, such as the wavelength of the measurement light or the order and polarization state of the diffracted light. Since the length is measured as a length, the resolution is low, and the accuracy is low when measuring minute distances of, for example, submicrons or less.

Therefore, for example, in a grating interferometer, it has been proposed to further electrically divide signals determined by the optical arrangement, such as the order of diffracted light and the polarization state, to increase the resolution.

[Problems to be Solved by the Invention] However, electrical division tends to cause errors due to fluctuations in the amount of light, fluctuations in diffraction efficiency, etc.

An object of the present invention is to provide a length measuring device with a larger stroke and higher accuracy.

[Means for Solving the Problems] In order to achieve the above object, the present invention uses a first length measurement device that outputs pulse signals at intervals corresponding to a fixed length, such as a laser interferometer or a grating interferometer. The present invention is characterized in that the minute distance between the pulses of the means is calculated and interpolated from a voltage level signal generated in response to a minute distance displacement from a second length measuring means such as an autofocus means.

[Operations and Effects] For example, the scanned surface position detection means (hereinafter referred to as AF length measurement means) used in autofocus (hereinafter referred to as AF) of optical pickup devices used in digital audio discs, video discs, etc. , has high precision and high resolution, but its length measurement stroke is extremely small. Moreover, if the stroke of such an AF length measuring means is attempted to be increased, the accuracy will decrease.

In the present invention, the length of a large stroke is measured by a first length measuring means that generates a pulse signal every predetermined unit length, such as an interferometric length measuring needle, and between the pulse signals at constant intervals, an automatic focusing means or the like is used. Interpolation is performed using an electrical level signal corresponding to the minute distance displacement generated from the second length measuring means. Therefore, for length measurement of large strokes, the accuracy of the first length measurement means is further improved by further dividing the unit length, and even for minute distances, the second length measurement means has high accuracy and accuracy. Length measurement can be performed with resolution.

[Example] The present invention will be explained in detail below.

FIG. 1 shows an overview of a length measuring device according to an embodiment of the present invention. This processing apparatus processes or measures a workpiece or a measured object using an optical probe.

In the same figure, DS is a stage base, the Y stage base is on this base DS, and the X stage X is on Y stage YS.
It is equipped with S. The base DS has a y direction guide YG%
The Y stage YS is provided with an X direction guide XG,
, Y are each stage xs, ys of X, Y (not shown), respectively.
Driven by Y motor, kite XG, X along YG.

8 shifts in the y direction.

LI is a laser interference length measuring device as a large stroke length measuring device that measures the movement amount and position of each stage xs, ys of 180＠This is a corner chiave prism for inverting the light and returning it to the length measuring device LI through an optical path parallel to the original. A portion DV indicated by a dotted line on the X stage XS is a space for arranging a small stroke stage, a high-resolution length measuring device, an optical probe, and the like. Length measuring device L! and stage base'
The DS is fixed on a surface plate (not shown).

Fig. 2 shows a partially enlarged view of the optical probe arrangement space DV in Fig. 1. In the figure, DFS is a base for a small stroke stage, and an X-direction guide YFG for the small stroke stage is provided. , is fixed on the X stage XS. A small stroke X stage YFS is mounted on this base DFS so as to be movable along a guide YFG.
On the stage YFS, a small stroke
P is fixed.

The position of this optical probe LP is determined by the length measuring device MY for y-coordinate detection, which consists of a y-direction standard SY attached to the base DFS and a y-direction length measuring head I (Y) attached to the Y stage YFS.
, and the X-direction standard S attached to the Y stage YFS.
x and X-direction measuring head H attached to X stage XFS
Based on the length measurement @MX for X coordinate detection consisting of
It is detected as relative position coordinates with respect to FS (ie, X stage XS). On the other hand, the coordinates of the small stroke stage base DFS with respect to the surface plate are measured as the positions of the X and Y stages by the laser interferometer LI.

That is, in FIG. 2, the large stroke stage
Laser interference length measuring device L is used to move S and YS! Stages XFS and YFS17 in the workpiece area with small strokes
) The movement is measured by the length measuring devices MX and MY"l'. In this way, the length measuring means has a composite configuration for the movement of a specific area, and the length measurement of the small stroke movement is measured by the length measurement of the stage movement of the large stroke. A length measuring device (laser interferometric length measuring device) is installed separately to perform high-precision (high-resolution) length measurement, and by not relying on the error of the length measuring device for large stroke travel, it is possible to We were able to achieve stroke and highly accurate length measurement.

Here, the length measuring device with a small stroke movement does not need to have a small stroke, but it needs to be more accurate (higher resolution) than the length measuring device with a large stroke movement, at least in the specific area mentioned above. .

FIG. 3 shows an example in which a high-precision, high-resolution length measuring device according to another embodiment of the present invention is set on a single-axis stage. This length measuring device is used in a grating interference length measuring device and an autofocus device. By combining it with a focus detection means and interpolating between the pulse signals at constant intervals determined by the optical arrangement of the grating interferometric length measurement device with the focus length measurement output of the focus detection means,
While maintaining the high accuracy of the grating interferometric length measurement device, the resolution is increased,
This is an attempt to achieve even higher precision and resolution. This length measuring instrument itself is a more concrete representation of the overall configuration of the above embodiment, and at the same time is a length measuring instrument for small stroke movement (as shown in Fig. 2), which is a part of the above embodiment. Long MX
, MY) can also be suitably used.

In Fig. 3, SR is a moving stage, GS is a diffraction grating as a reference standard, MH is a measuring head for measuring the amount of movement of the moving stage SR with respect to the diffraction grating GS, RG is a guide, SS is a feed screw, and MT is the motor. Guides RG, RG, and diffraction grating O3 are fixed on a surface plate sp parallel to the moving direction of moving stage SR shown by arrow A, and moving stage SR is rotated by guide RG by the action of a feed screw SS rotated by motor MT. along the arrow A.

FIG. 4 is an explanatory diagram of the configuration of the length measuring head MH.

In the figure, SP is a surface plate, on which a movable stage SR is movably mounted and a diffraction grating GS is fixed in parallel to the moving direction A of the movable stage SR. Further, a plane mirror PM having a mirror surface perpendicular to the movement direction A is fixed to the 8-stage stage SR, and a fine movement stage (AF stage) AFS is mounted thereon. The fine movement stage AFS is connected to the movement stage SR via a fine drive mechanism PD such as a piezo drive mechanism, and the fine movement stage AFS is connected to the movement stage SR with respect to the movement stage SR (in the direction of arrow A). ) can be moved by a minute amount in the direction of arrow B, which is the same direction. Further, a length measurement optical system consisting of a grating interference length measurement system and an autofocus (hereinafter referred to as AP) length measurement system is installed on the fine movement stage AFS.

This length measurement optical system includes a light source LD such as a semiconductor laser, a collimator lens CL, a beam splitter HMI, and HM2.
, phase difference plate FPI, FP2, prism mirror or corner cube prism CCI, CC2, polarizing beam splitter BS, photodetector PDI, PO2, objective lens LN, optical position detector (position sensor) PS, etc., and light source LD and The collimator lens CL is shared by the grating interference length measurement system and the AF length measurement system, and other optical components are omitted.

In FIG. 4, the light beam emitted from the light source LD and collimated by the collimator lens CL is transmitted to the beam splitter H.
The MI splits the beam into two beams, one of which is passed through the objective lens L.
N and the other enters the diffraction grating GS via the beam splitter I (M2).

The light incident on the diffraction grating GS is diffracted by the diffraction grating GS, and the phase δ of the diffraction grating GS is added to the diffraction wavefront. If the initial phase of the incident light is 0, the phase light of the diffraction wave is exp(
i (ω is 10 mδ)).

Here, m is the diffraction order; for example, the +1st order light and the 11th order light are exp(i(ωt+δ)) and exp(i(ωt+δ)) and exp(i(ωt+δ)), respectively.
t-δ)). The light ray Lll, which is the +1st order light, and the light ray L12, which is the 11st order light, are connected to the phase difference plates FPI and F, respectively.
Corner cube prism CCI, C via P2
A reflected ray L11. which is incident on C2 and reflected here in a direction parallel to and opposite to the incident direction. L12 is a phase difference plate FP1. The light is made into clockwise and counterclockwise circularly polarized light by passing through FP2 twice, and is diffracted again at point P2, which is distant from point P1 of diffraction grating GS in the moving direction of moving stage SR (in the direction of arrow A). Furthermore, it enters the polarizing beam splitter BS via the beam splitter HM2. Light ray L having clockwise and counterclockwise circular polarization characteristics incident on this polarizing beam splitter BS 11. L 1
2 transmits and reflects the polarizing beam splitter BS. The transmitted lights LRI and LR2 and the reflected lights LSI and LS2 become linearly polarized lights, interfere with each other, and enter the photodetectors PDI and PO2.

Since the photodetectors PDI and PO2 detect orthogonal components of two circularly polarized lights as interference light intensity, the photodetectors PDI when the length measurement head Ml ((AP stage AFS) moves with respect to the diffraction grating GS).

The outputs R and S of PO2 have a phase difference of 90° as shown in FIGS. 5(a) and 5(b). These two signals R and S are each binarized by a circuit (not shown) as shown in (e) and (d) based on a constant level, and at the timing of the rise and fall of the two signals, as shown in (e), By generating four pulses per period and counting the number of pulses, the amount of relative movement between the length measuring head MH and the diffraction grating GS can be measured. In this case, the period of intensity change of the interference light for one pitch movement of the diffraction grating GS is 4 periods,
The number of pulses is 16. Further, during pulse counting, the direction of the relative movement is detected, and it is determined whether to add or subtract the counted value depending on the detection result. The direction of movement is
Signal (C) at the generation timing of each pulse in FIG. 5(8).

It can be determined based on the level (d). For example, if the level of the signal (d) at the falling timing of the signal (C) is "H" when moving in the forward direction, it becomes "L" when moving in the reverse direction.

Furthermore, the signals R9S shown in FIGS. 5(a) and 5(b) are added and subtracted to create signals R+S and R-3 having a phase difference of 45 degrees with respect to the signals R and S, and these are also described above. If the signal is similarly binarized and pulses are generated at the rising and falling timings, 32 pulses can be generated for one pitch movement of the diffraction grating GS. However, in this case, in order to reliably process these signals, it is necessary to take into account fluctuations in the amount of light and diffraction efficiency.

FIG. 6 is an explanatory diagram of the principle of the grating interferometric length measuring device.

In the figure, coherent light incident on the diffraction grating GS is diffracted as ±1st-order light. The phase of this diffracted light is the grating G
When the diffraction grating GS moves one pitch in the X direction, the phase of the +1st-order diffracted light Lll advances by one wavelength, and the -1st-order diffracted light L12 delays by one wavelength, as shown in FIG. These diffracted lights L11. L1
2 is returned by Cornakieve CPI, CF2,
When diffracted again by the grating GS, the previous +1st-order diffracted light Ll
l advances one wavelength further, -! The next diffracted light L12 is delayed by one wavelength. Therefore, the interference light that is the final combination of Lll and L12 has a brightness of 4 when the diffraction grating GS is worked one pitch.
change times. Therefore, one pitch of the diffraction grating is 1.6 μm.
Then, the brightness changes every 0.4 μm, which is 1/4 of 1.6 μm. By photoelectrically converting this change in brightness and darkness and counting the brightness, pulses at intervals of 0.4 μm can be obtained. In the above-mentioned interferometric measurement system shown in FIG. 4, in order to further increase the resolution, electrical processing is performed to generate 16 or 32 diffraction gratings per pitch, that is, 0. Pulses are generated every 1 μm or 0.05 μm.

Next, a method for detecting the direction of the grating interferometric length measuring device will be explained.

In order to detect the length measurement direction, it is necessary to extract two signals with a 90° phase difference.

As shown in Figure 6, linearly polarized coherent light is
4 plate QWI, QW2 45 to its first axis
It can be made into circularly polarized light by making it incident on the beam and transmitting it.

When the +1st-order diffracted light and the 11th-order diffracted light are combined into counterclockwise and clockwise circularly polarized light, respectively, the gold wave light becomes linearly polarized light.

The polarization direction of the linearly polarized light is determined by the phase difference φ between the ±1st-order lights.

Now, the left-handed circularly polarized light due to the +1st-order light is y+ = a exp (t (ω - φ/2)) Xs =
a exp (i (ωt-π/2-φ/2)) - the left-handed circularly polarized light due to the first-order light is expressed as y + W a exp (i (ωt, +φ/2)
)x−xa exp(i (ωt−yr/ 2+φ/
2)) When these are combined, the plane wave is y
! y◆+y− Tomi a(exp(iφ/2) +exp(−iφ/2)) XWX and +X− =a(axp(iφ/2) −exp(−Lφ/2)), which is shown in As shown in , the polarization direction θ is φ/2
It can be seen that the light is linearly polarized.

Here, a represents the amplitude of the light wave, and ω represents the angular frequency of the light wave.

Therefore, by moving the grating GS by X in FIG. 6, the phase difference φ of the ±1st-order light becomes as follows, where p is the pitch of the grating GS. Therefore, the polarization direction θ of the combination of the ±1st-order lights becomes 4 π θmaro□X.

As shown in FIG. 6, this combined linearly polarized light is split by a beam splitter HM3 and sent to a polarizing plate PPI.

After passing through PP2, it enters detector PDI and PO2. 2
By setting a difference of 45@ between the transmission axes of the two polarizing plates PPI and PP2, for example, when detecting the peak of the light amount when the detector PDI after passing through the first polarizer PPI is θ=O, the second Detector PD2 after passing through polarizer PP2 of
The amount of light reaches its peak at . This becomes a signal with a 90° phase difference compared to the signal of the detector PDI by the first polarizer. This makes it possible to determine the length measurement direction.

Explain how to do this.

The accuracy (resolution) of the length measuring device shown in FIG. 3 is, for example, 0.01 μm to 0.002 μm, as described later. In order to make the most of the high accuracy of this AF length measurement system, it is necessary to generate pulse signals with high repeatability in the interferometric length measurement system. This repeatability requires a repeatability of 0.002 μm or less, which is resolved by AF.

As mentioned above, in the method of increasing the number of pulses per grating pitch by electrical processing, factors that deteriorate accuracy include fluctuations in light amount and diffraction efficiency.For example, (a) in Fig. 5, Signals R, S as shown in (b)
If there are fluctuations in the DC level or amplitude, the slice position "!R+VSS" will change and the repeat accuracy will deteriorate.

Therefore, we propose here to use 0° and 180° signals.

By detecting the difference between the 0° and 180° signals, DC level fluctuations and amplitude fluctuations can be removed because they are common to the two signals o" and taoo. 8th
The figure shows this situation.

When using signals of 0", 18G", the pulse signal is 172
Emitted for each wavelength. In this case, a pulse signal will be output every 0.2 μm, but it may be used as is.

FIG. 9 shows an example of a configuration for implementing this method. That is, the polarizing plates PPI and P whose azimuth angles are O' and 45°
In addition to P2, a 90° polarizing plate PP3 may be provided in the separately sold market. In the figure, )1M3°HM4 is an eight-view mirror, and PDl, PO2, and PO2 are detectors (photodetectors).

Returning to FIG. 4, the light emitted from the light source LD, collimated by the collimator lens CL, and transmitted through the beam splitter HMI is input to the objective lens LN of the AF length measurement system.

FIG. 10 is an explanatory diagram of the operation of the AF length measurement system.

In the figure, light from the light source LD is transmitted through the objective lens LN.
The beam is incident at a position eccentric from the main optical axis. When the target of the objective lens LN (the mirror surface of the plane mirror PM fixed to the movable stage SR in FIG. 4) is at the focusing position (A), the light from the light source LD passes through the optical path of the solid line in FIG. After that, an image of the light spot projected onto the mirror surface is formed at the center (A) on the sensor PS, which is placed at a conjugate (imaging) position of the focal position (A) with respect to the objective lens LN.

Also, the target PM is the deocus of the objective lens LN (
When the camera is in the out-of-focus) positions (b) and (c), it travels through the optical paths indicated by the two-dot chain line and dashed line in Figure 1O, respectively, to the position (b) and the position away from the center (a) on the sensor PS. Form a defocused image on (c).

FIG. 11 shows the upper two planes corresponding to the above-mentioned plane mirror PM positions.
The difference between the sensor signal amount of the A zone and the sensor signal amount of the B zone on the upper 2923 plane, which indicates the spot state and light intensity distribution on the 923 plane, has a so-called 5-shaped curve characteristic. FIG. 12 shows a differential signal ΔI (=IA-Ia) between the sensor signal amount IA and 1 obtained by a differential amplifier (not shown).
shows the relationship with the defocus amount (target position).

The AF length measurement system shown in FIG. 4 utilizes a region in this S-shaped characteristic curve in which the relationship between the defocus amount and the differential signal Δl is linear.

Next, the flowchart in Fig. 13 and Fig. 14 and 1.
The operation of the length measuring device shown in FIGS. 3 and 4 will be explained with reference to the output waveform diagram shown in FIG.

The length measuring device shown in FIG. 3 is constructed so that its entire operation is controlled by a central processing unit (not shown).

First, when starting an operation such as when turning on the power, the moving stage S
Initial setting is performed by moving R to the origin 8 times and resetting the counter when the moving stage SR reaches the origin.
Thereafter, it waits for input of an 8th shift stage drive command.

When a stage drive command is input in the standby state,
First, AF operation is performed. In other words, based on the output of the AF length measurement system, the piezo minute drive mechanism (piezoelectric actuator) FD
AF stage AFS is driven to focus objective lens LN on plane mirror PM. When in focus, AF
Stage AFS is locked to moving stage SR at that position, and moving stage SR is driven by motor MT.

In this length measuring instrument, when the moving stage SR moves, the electric circuit (not shown) of the grating interferometric length measuring system is activated as described above.
The period p of the diffraction grating GS fixed with respect to the surface plate SP from
A pulse signal is generated every 1/16 of the time (see Figs. 5 and 14). The counter integrates the number of pulses.

When a stop command is input during the movement of the 8th shift stage SR, the central processing unit stops the moving stage SR and calculates the cumulative number of pulses by the counter.

After that, the AF stage AFS is unlocked, and the piezoelectric actuator FD is driven to move the AF stage AFS on which the AF system and grating interference optical system are mounted, and the pulse signal of the grating interference length measurement system obtained above is The position of the moving stage is detected. In other words, as shown in FIG. 14, the positions where the moving stage SR is stationary are defined as five points,
If the number of pulse counts at that time is N, the position of the five points is set to the count number N and the next N+1 by the autofocus means.
Determine with high precision which position between.

First, the pulse accumulation number N of the counter when the moving stage SR stops is memorized, and the piezoelectric actuator FD moves the AF stage AFS, that is, the length measuring optical system MH by a minute amount (slightly more than the pulse interval ΔX). Then, defocus is added to the AF measurement system that targets the plane mirror PM fixedly attached to the moving stage SR, and the differential output signal ΔI (AF
Sensor PS difference signal! e-ta) changes. At this time,
If the feed amount of the piezo drive amount is set within the range where the relationship between the defocus amount and the difference signal is linear, the relationship between the difference signal and the defocus amount is known in advance, so when the difference signal is given, The amount of defocus can be uniquely determined. Therefore, if the piezo drive moves a small amount to the position corresponding to the Nth pulse, a difference signal at the position corresponding to the Nth pulse will be obtained, and if this is the defocus amount and δ is the Nth pulse generation position. The amount obtained by adding δ to N·ΔX becomes the length measurement position of the point S where the moving stage SR stopped.

Here, ΔX is the period of the pulse train of the grating interferometry system.

Note that until the moving stage SR comes to rest, the fine movement stage AFS on which the optical system is mounted remains at rest at the position (focusing position) where the AF flaw signal O is generated.

In this length measuring device, for example, if the grating pitch of the diffraction grating GS is 1.6 μm, the period of the pulse signal of the grating interference length measurement system is 0.1 μm. Therefore, the piezo drive amount is ~0
．． The above method is possible if it is shaken by about 2 μm,
Length measurement can be achieved with AF accuracy by maintaining the high stroke of the grating interferometric length measurement device, and positioning of the stage etc. can be achieved with high precision.

For example, the accuracy of AF length measurement is
100 (NA40.9), AF sensor PS
If you use CCD or physical sun sensor etc. as 0601
Accuracy on the order of μm to 0.002 μm is achieved. In this case, the area where the AF scratch signal is linear is about 1 μm.

In addition, in the length measuring device shown in Fig. 3, the AF optical system does not necessarily require that the plane mirror PM position and the AF sensor PS position have an imaging (conjugate) relationship; Sensor differential signal and light spot position signal (
A system in which the amount of defocus in the direction of movement) is linear or has near-linear characteristics is fine. If it is not linear, store the relationship between the amount of movement (defocus) and the signal in read-only memory (ROM). It is preferable to obtain the minute movement amount by reading out the movement amount according to the signal.

In this way, the length measuring device shown in Fig. 3 combines a long-stroke length-measuring means with an optical system whose signal output is close to linear with respect to the amount of movement. ) By filling in the gaps, the accuracy of long-stroke length measuring means is further improved.

This makes it possible to eliminate fluctuations in light intensity and diffraction efficiency that occur when signals determined by the optical arrangement, such as the order of diffracted light and the polarization state, are further electrically divided to increase resolution in the case of conventional grating interferometers. The problem of easy occurrence of errors is solved.

Note that it is also possible to modify the length measuring device shown in FIG. 3 in the following points.

For example, in the above, when detecting the defocus amount δ, the AF stage AFS is minutely driven to the position corresponding to the Nth pulse and the N+1th pulse, and the difference signal at both positions is detected to detect the defocus amount. By calculating δ, it is possible to obtain an accurate defocus amount δ even when the pulse interval or the AF sensor output fluctuates.

Further, the long stroke length measuring means is not limited to the grating interferometric length measuring device, but may be other methods such as a laser interferometric length measuring device.

Further, the optical system mounted on the fine movement stage may include only the objective lens of the AF system and a grating interference length measuring device system.
It is not necessary that all of the F system be placed on the fine movement stage.

Further, although FIG. 3 shows movement in one axis, a composite structure may be similarly used for length measurement in two or more axes.

In addition, although the AF system in Fig. 4 shows the TTL-AF method,
It may be an AF system used for optical pickup of DAD (digital audio desk) or video desk, or an AF system used for autofocus of a camera.

In addition, as mentioned above, the AF system does not need to be in a so-called imaging relationship; it is sufficient that the sensor signal output is close to linear in the direction of movement, and the AF system is a system in which the light spot moves linearly on the sensor surface. In this case, the points on the plane mirror surface shown in FIG. 4 and the sensor surface do not necessarily have to be conjugate.

FIG. 16 is an example in which the length measuring apparatus according to the embodiment of the present invention is assembled as a length measuring device unit.

This length measuring unit has a light source LD on the stage movable part ST.
, collimator lens CL, polarizing beam splitter) IM
I, λ/4 plate QW, condenser lens GLI.

AP means PS consisting of an optical position detection sensor such as GL2 and CCD is arranged, and the movement of the stage movable part ST is detected by a pulse train using a linear grating GS fixed to the stage movable part ST and a reading head MH arranged on the stage fixed part SS. Detected as a signal.

The stage movable portion ST is actively moved by an actuator AT. The length measurement reference surface O8 of the object to be measured MO is a mirror surface with high surface accuracy.

The main point of this method is that each time the focus detection circuit FF in the detection processing circuit ED receives a pulse signal from the pulse train length measuring device electrical system PC, it updates and stores the AP output value at that point. be.

FIG. 17 shows the operation flow. Further, FIG. 18 shows an example of pulse intervals and AF voltage values.

When it is confirmed that the object to be inspected MO has stopped, the actuator AT of the length measurement unit is driven and tries to autofocus on the reference plane O5 to be inspected. This movement is caused by the movement attached to the stage movable part ST. The scale GS and reading head MH detect the change in the amount of interference light, and the pulse train length measuring device electrical system PC counts this change in the amount of light as a pulse signal and measures the length.The resolution in this case is the pulse interval ΔX
(Figure 18).

During that time, each time the central processing system CPU receives a pulse signal, the current focusing voltage vAF is updated and stored.
When the autofocus system indicates a focus signal, that is, Var"OV, the actuator AT stops.

Therefore, the central processing system CPU uses the count number j that had been counted up to that point and the focus voltage Vj that was last stored by the focus detection system FF to set the length measuring device 11x to x=j・Δx+Vj ・
Calculate ξ. Here, ΔX is a moving distance corresponding to the pulse interval, and is, for example, a pitch of 0.4 μm. It is also assumed that ξ has been calibrated in advance using the AF sensitivity.

FIG. 19 shows an example in which this length measuring unit is used for two axes, and is used for highly accurate positioning of an AA (auto alignment) head of a semiconductor exposure apparatus.

FIG. 20 shows an example in which a laser interferometric length measuring system is used in place of the diffraction grating interferometric measuring system of the length measuring instrument shown in FIG.

In FIG. 20, parts common or corresponding to those in FIG. 3 are given the same reference numerals. In FIG. 20, a laser head LZ, an interference unit IU, and a corner cube prism CP constitute a laser interferometric measurement system. The interference unit IU is fixed to the surface plate sP, and the corner cube prism CP is fixed to the fine movement stage AFS.

FIG. 21 shows the length measuring optical system on the fine movement stage AFS of FIG. 20. In FIG. 4, the beam splitter HM2. Retardation plate FPI, FP2, corner cube prism CCI
, CC2, a stand R fixed on a fine movement stage AFS with a corner cube prism CP for removing the polarizing beam splitter BS and the photodetectors P, Dl, PD2 and instead reflecting the laser beam toward the laser interference unit.
It is set on T. The AF length measuring optical system has the same configuration as shown in FIG.

This length measuring device also follows the same procedure as the one in Figure 3 (1)
(see Figure 3) and action, the length is measured. That is,
A pulse signal is output from the laser interference system each time coarse movement stage SR and fine movement stage AFS are moved and fine movement stage AFS or an object to be measured such as an optical probe (not shown) fixed thereto moves by a predetermined unit length ΔX. The distance between these pulses is interpolated using the analog length measurement output of the AF length measurement system. As a result, while maintaining the accuracy of the laser interferometric measuring system when measuring lengths over large strokes, it is possible to achieve higher resolution (higher precision) length measurement by interpolating between the pulses of this laser interferometric measuring system. be able to.

FIG. 22 shows yet another embodiment of the invention.

In the figure, SM is a reference member provided with a diffraction grating corresponding to the diffraction grating GS in FIG. 4, and is fixed to one of two objects that are movable relative to each other. Optical components other than the reference member SM shown in the figure constitute a length measuring head optical system MH, and are fixed and arranged as one body on the other of the two objects. As shown in FIG. 23, the reference member SM is provided with a diffraction grating GS for grating interference length measurement, and furthermore, blazed gratings BGI, BG2 and AF length measurement standards for AF length measurement are provided in parallel with this grating GS. A plane FT serving as a reflective surface is provided. The two blazed gratings BGI and BG2 are shifted from each other by half of the grating pitch p in the direction of relative movement between the reference member SM and the measuring head optical system MH (in the direction of arrow A).

In FIG. 22, light source LDI, half mirror HM2
．． Phase plate FPI and FP2, mirror CPI and CF2, polarizing beam splitter BS and photodetector PDI and PD2
constitutes an interferometric length measurement optical system. The interferometric length measuring optical system and the grating interferometric length measuring grating GS on the reference member SM correspond to the optical system and sensor that generate the pulse train described in FIG. 4 and the like.

Light source LD2, collimator lens CL, half mirror HM
II, HM12, objective lenses LNI, LN2, and optical position detectors Psi, PS2 constitute two sets of AF length measurement optical systems. Each AF length measuring optical system is constructed optically equivalent to that described in FIG. 4 and the like. In addition, these AP length measurement optical systems each have a blazed grating BG1 . ．． BG2
It is arranged so that the focus is near the surface of the object.

Furthermore, the light source LD3 such as a semiconductor laser and the light spot position detection sensor PS3 are for detecting the relative inclination between the detection surface of the length measuring head optical system MH and the reference member SM. The light spot position detection sensor PS3 receives the reflected light from the area FS to obtain a parallelism detection signal between the reference member SM and the measuring head optical system MH. ing.

FIG. 25 shows the pulse train signal output from the grating interferometric measurement system in FIG. 22 and the blazed grating BGI on the reference member SM.
, the cross-sectional shape of BO2 (therefore the output of the AF length measurement system)
Indicates the relationship between The pitch of the blazed gratings BGI and BO2 is P11%, and the height difference is H. The pitch Pa is an even multiple of the period ΔX of the pulse train of the grating interferometric measurement system, for example 1
It's 0x.

During length measurement with this device, the pulse train of the grating interference length measurement system has a cumulative number of...-N-1,N as shown in the figure.

N+1. Blazed lattice BG1 counting... Each AF length measurement system that measures the BG2 surface position is, for example, the AF on the grating BO2 side just before the step of the grating BGI.
Switch to the length measurement system, and then switch to the AF length measurement system on the grid BGI side immediately before the step of the grid BG2. In other words, when the relative movement of the reference member with respect to the length measuring head MH is in the negative direction of the x-axis, as shown in FIG. 25, the reference member S M h< Switch from the BO2 side to the BGI side at the timing of the pulse, and switch from the BGI side to the BGI side at the timing of the N+4th pulse.
When the relative movement direction of the reference member SM, which switches to the O2 side, is the positive direction of the X-axis, the reference member SM, which switches in the opposite direction, moves relative to the measuring head optical system MH. Which way it is moving is determined by the lattice BGI and BO2
This can be determined based on the AF length measurement signal corresponding to each.

Therefore, the switching direction may be determined based on this discrimination information.

The output signal (AP signal) of the AF length measurement system that is focused near the surface of the blazed grating changes as the defocus amount of the AF length measurement optical system changes as the reference member SM moves relatively. Therefore, the movement of the reference member SM in the X-axis direction can be extracted as information on the height direction of the blazed grating surface. ), it is necessary to make the height H of the blazed grating smaller than the height at which AF flaw signal nearness is guaranteed.
Differential output signal ΔI (11th and 12th
If the focus is set so that (see the figure) becomes 0, that is, the focus is set, a signal of the height δ will be obtained at the position of the point shown in Fig. 25, and the signal of the height δ will be obtained in the The length is δ・H
/ PB. Therefore, if the pulse train corresponding to the 0 point is the Nth point, the position of the point is N・ΔX+δ・H/
It is found as p a.

In addition, as shown in Fig. 26, each time a pulse signal is generated from the interferometric measurement system, the AF detection voltage vAr at that time is memorized, and the difference voltage from this voltage vAF is used until the next pulse signal is generated. Interpolation may also be performed based on this.

Note that when the light for AF length measurement is incident on the blazed grating, it is preferable to set the plane where the incident light and the reflected light extend to be nearly perpendicular to the direction of relative movement with respect to the reference member SM.

The blazed lattice can be manufactured by known methods such as a wet etching method that utilizes the relationship between the crystal direction of Si and the etching speed, a mechanical processing method using a so-called ruling engine, or a manufacturing method using so-grain etching and dry etching. can.

The pitch p of the grating for grating interference length measurement is 1.6 μm, the pulse train period of the grating interference length measurement system is 0.4 μm, and the AF length measurement system is equipped with an objective lens LNI of X 100 (NA ~ 0.9).
, LN2 as a blazed grating with pitch P a
When using an f 3μms height difference H41μm and a tilt angle θ-18° with respect to the plane FS, the linear range of the AF scratch signal was a little less than 1μm, and the maximum differential output value (!^-
Ia)-1□ is approximately 2 volts, noise (N) is 5 mV
Met. Differential output value ΔI (
The AF accuracy required as S) was 0.0025 μm. Further, the length measurement accuracy of the relative movement amount between the reference grating SM and the length measurement head optical system MH was 0.007 μm.

In this embodiment, the large stroke length measuring device is not limited to the grating interferometric length measuring device, but may be any other type of length measuring device that can obtain a pulse signal for length measurement, such as a laser interferometric length measuring device. Good too.

In addition, in Fig. 22, each AF length measurement system is the TTL-AP of the embodiment.
The system is not limited to the optical pickup system used in DAD (digital audio desk) or video desk,
It is also possible to use a system that is used for autofocus in cameras.

Furthermore, either the reference member SM or the measuring head optical system MH may move, or both may move.

Furthermore, in the above embodiment, two rows of blazed gratings are used, but as shown in FIG.
, PR2 may be attached. In this case, it is preferable that the two probes aim at points substantially shifted by half a pitch on the blazed grating.

In the length measuring device shown in Fig. 22, the length measuring device that outputs pulse signals at intervals corresponding to a fixed length, such as a grating interferometric length measuring device or a laser interferometric length measuring device, uses a blazed lattice pattern to generate pulses. High precision (high resolution) that focuses on the surface shape of the component
Interpolation is performed using the measured length value of the short-stroke AF length measuring means, so while maintaining the high accuracy of the pulse generation position of the length measuring device that generates the pulse, it is possible to further resolve the pulses to achieve high accuracy and high resolution. It is possible to measure the length of

Furthermore, since the AF length measuring means has an extremely small stroke of, for example, about 1 μm, in the embodiment shown in FIG. 3, the stage on which the length measuring head is mounted has a two-stage structure consisting of a moving stage SR and a fine movement stage AFS. Here, we use a blazed lattice-like member consisting of a repeated array of slopes with minute height differences to convert the displacement of a small stroke in the direction of movement of the object to be measured into displacement in the direction transverse to this direction of movement, and then measure it. Therefore, if the height difference of the blazed grid member is set to be within the stroke of the AFs length means, the length of the small stroke displacement of the large stroke movement can be measured without moving the AF means. Can be done.

Furthermore, two rows of blazed lattice-like members can be arranged with their step positions shifted in the moving direction, or a point shifted by about half a pitch on one row of blazed lattice-like members can be used as the target for AF length measurement. By switching the target member or position of AF length measurement before and after and not using the AF length measurement signal at a portion where the surface shape of the blazed grid member is uncertain, higher accuracy can be achieved.

FIG. 28 shows a diffraction grating interferometric length measuring device constructed without using corner cubes. In the figure, a relatively moving diffraction grating GS is fixed to one of two relatively moving objects, and the length measuring head The part MW is fixed to the other of the two objects.

Laser light emitted from a light source LD, for example, a semiconductor laser, of the length measuring head MW is turned into a plane wave by a collimator lens CL, and is divided into two beams by a half mirror HM2O. 2
Two luminous fluxes LOI and LO2 are each λ/4 plate QWI
, QW2, it is diffracted by the fixed gratings FI and GF2, and the ±N-order diffracted lights LNI and LN2 enter the relative moving grating S, where they receive reflected diffraction again and return to the same direction and merge. do.

This light is converted into an electric signal by half mirrors HM21 to HM23 using a combination of polarizing plates PPI to PP4 and sensors (photodetectors) PDI to PD4 and extracted.

Here, the λ self-plate Q placed in the light beams LO1 and LO2
WI and QW2 are set so that their first axes are +45° and -45° with respect to the linearly polarized laser beam, respectively, and the polarizing plates PPl to PP4 are set so that their polarization directions are 0° and 45°1, respectively. ．． ', 9o', .

Set the angle so that it is 135°.

Then, the amount of light incident on the sensors PDI to PD4 changes as shown in FIG. 29 as the relative movement grating GS moves, and this is obtained as a light amount detection output. In other words, outputs whose phases are shifted by 90'' are obtained from each of the sensors PDI to PD4.

Fig. 30 shows the state of the diffracted light beam when the output wavelength of the light source LD changes in the length measuring device of Fig. 28. In Fig. 30, the optical path of the light beam in the best adjusted state is shown as a solid line, The optical path at that time is shown by a dotted line and a dashed-dotted line. When there is a wavelength fluctuation, the outputs of the sensors PDI to PD4 are as shown in FIG. 31, and a so-called bias amount unrelated to the amount of movement of the relative movement grating GS is superimposed on this output. The reason for this is that, as shown in Figure 30, the area of light flux where no interference fringes occur will increase other than the shaded interference area, and the size of the area where no interference fringes will occur will change depending on the amount of wavelength fluctuation. . Therefore, fluctuations as shown in the output signal waveform of the photodetector PCI-PD4 in FIG. 31 occur. However, when processing is performed based on four detection signals whose phases have changed every 90'', division into the signal period can be performed with high accuracy even if a wavelength change occurs. Only two sensors are used, and the phase is 0° and 90°.
By electrically processing only the seed signal, the sensor can be
If you try to obtain a pulse with the same pitch as when using
When there is wavelength variation, the electrical division accuracy of the obtained signal deteriorates. This is the same as described above using FIGS. 5-8.

In addition, with the configuration shown in Figure 6, the light entering the grating GS at 21 points changes in the diffraction direction (angle) as the wavelength of the light source LD changes.
changes. Corresponding to this characteristic, corner cubes (prisms) cci and CC2 are arranged. A corner cube is a prism formed by processing the angle between its many faces to 90'' so that the light is reflected and returned in the same direction as the direction of the incident light. However, this corner cube requires high precision in machining, which results in high costs.

In the apparatus shown in Fig. 28, in addition to the moving grating GS, there are also diffraction gratings (fixed gratings FI, GF) on the length measuring head MH side.
2), the ±N-order light from the fixed grating is re-diffracted by the moving grating, and the diffracted light passes through the same optical path and reaches the sensor. Therefore, as described above, even without a corner cube, it is possible to obtain interference light whose brightness changes according to the movement of the moving grating when the wavelength changes. In other words, this grating interferometric length measuring device does not require a corner cube and has good stability against wavelength fluctuations, so it is possible to reduce the cost of the device. Further, as shown below, it becomes easy to implement the IC.

For example, a grating interferometer with the configuration shown in Figure 6 uses a light source LD.
, polarizing mirror BS, corner cube CCI, CC2
, polarizing plates PPI, PP2, detector PD1. P02 etc. were combined separately to form a three-dimensional structure. Therefore, there is a problem in that errors are mixed into the interference signal due to mechanical fluctuations between optical members, temperature changes, and air fluctuations, resulting in deterioration of length measurement accuracy. In addition, since the light source and detection system were installed separately, they occupied a large space, making it impossible to make them smaller. Furthermore, due to the spatial distance from the detection system to the processing circuit, noise is likely to enter, resulting in problems such as poor measurement accuracy.

FIG. 32 shows a grating diffraction length measuring device in which the above-mentioned drawbacks are solved by converting the main parts into ICs. Here, an example is shown in which a portion corresponding to the optical system of the length measuring head MH of the length measuring device shown in Fig. 28 and a signal processing electrical system that generates pulses depending on the brightness of interference light are formed on a GaAs substrate. shows.

A dielectric waveguide WG layer is formed on the GaAs substrate SB, and light waves propagate along a preset optical path.

The light source LD can be formed on the GaAs substrate SB by, for example, MBE (molecular beam epitaxy). The lens and beam splitter section LS formed in the waveguide WG convert the diverging light from the light source LD into parallel light and then split it into two directions. The grating coupler GCI, CC2 emits the light wave propagated in the thin film waveguide WG into space at a certain angle.

The reference diffraction grating GS is the moving grating GS of the length measuring device shown in FIG.
It is equivalent to grating Kabra GCI
, and diffract the light waves from CC2 in the same direction. The photodetector PD detects the interference light intensity of the diffracted light from the reference diffraction grating GS.

Next, the operation will be explained.

The light wave from the light source LD propagates in the waveguide WG, and is propagated in the waveguide WG as parallel lights LO1 and LO2 in two different directions by the lens and beam splitter section LS. Each light L 01. L02 is reflected in the waveguide WG by mirrors MRI and MR2 so as to be parallel to the longitudinal direction of the reference grating GS, and is reflected by the grating coupler GC.
I, enter GC2. Grating Cabra GCI,
The GC2 emits the light waves that have propagated in the waveguide WG from the substrate surface to the outside through the waveguide surface at a certain set angle.

This angle is related to the pitch of the reference grating GS and the wavelength of the light, and when using a reference grating with a pitch p = 1.6 μm,
If the wavelength is λ = 0.83μm, the output angle is 58.8''
”.

The two light waves from the grating coupler GCI and GC2 are vertically diffracted by the standard diffraction grating S, and the photodetector P
Enter D. The photodetector 1lPD photoelectrically converts the interference intensity of the two diffracted lights.

Next, the principle of operation as a length measuring device will be explained.

The light waves emitted into space by the gratings GCI and GC2 are diffracted on the reference grating GS, and the intensity distribution of the diffracted light at that time is expressed by the following equation.

Here, is the diffraction order diffracted at .

Now m! +1, new-1, pml, 6μm,
■ becomes 1 for each 0.1 μm pitch movement of the reference grating GS.
It can be seen that the signal is a periodic sine wave signal. The detector PD is
By counting the period of this sine wave signal, the amount of movement of the reference grating GS can be measured.

This grating interferometric length measuring device integrates the light source, optical components, and detection system processing circuit on the same board, making it more compact and
Low noise and high accuracy are possible.

Next, a means for detecting the reference path and the moving direction of the child GS will be described.

To detect the direction of movement, it is necessary to obtain two signals with a phase difference of 1/4 period.

As a specific method, for example, as shown in FIG. 33, two grating line arrays GLI and GL2 are formed by shifting the phase by a base (for example, 178 pitches for mwt and nw-t).
Further, two photodetectors PDI and PD2 are formed on the substrate SB corresponding to each grid line array.

Each grid line row GL1. The diffracted light from each GL2 is sent to separate spatially separated sensor poi.

Receive at PD2. The signal thus obtained can be obtained as a signal whose phase is shifted by 174 cycles, as shown in FIG.

FIG. 35 is an example in which a grating interferometric length measuring device is converted into an optical heterodyne.

In this case, a frequency shifter FS, for example, □SA
W (Surfaca A caustic W
ave) device, it is possible to obtain a light wave whose frequency is shifted by Δf, which is the oscillation frequency of the oscillator OSC, with respect to the frequency fo of the output light from the light source LD. These light waves of frequencies f0 and fo+Δf are incident on a reference path 100S having one row of grating lines through grating couplers GCI and GC2, respectively, and the light diffracted by the reference grating GS is received by a photodetector PD.

The signal directly obtained by the photodetector PD is as follows, and by detecting the phase difference with the output signal of the oscillator OSC by the phase detection circuit PSD, the B movement amount and the 8 movement direction of the reference grating GS are detected in the same way as in the previous embodiment. can do.

The feature of this device is that there is no need to use a special grid for determining direction (see, for example, FIG. 33), and furthermore, time averaging can be performed in a short time, so the amount of movement can be detected with high accuracy.

Note that in the length measuring device ICs shown in FIGS. 32 and 35, a GaAs substrate is used as the substrate SB, but this may also be on a Si substrate. In that case, the light source LD would be externally attached. .

In this way, by integrating the optical system other than the reference grating and the signal processing electrical system on a single substrate in a grating interferometric length measuring instrument, it is possible to achieve a compact, lightweight, and highly accurate device that does not require assembly or adjustment and is resistant to external disturbances. length measurement becomes possible.

In a typical grating interferometric measurement device, a system is constructed by arranging mirrors, corner cubes, etc. In particular, mirrors and the like are used in the optical system that enters the grating, making assembly and adjustment difficult and making it compact.

FIG. 36 shows an example in which the optical system until the light enters the grating is simplified by making the light incident on a relatively moving grating using a birefringent prism such as a Wallaston prism.

In the figure, light emitted from a light source LD such as a semiconductor laser is converted into a plane wave by a collimator lens CL, and is vertically incident on a Wallaston prism WP. A Wallaston prism is made by bonding two birefringent materials, such as calcite, into a prism shape, which separates the light into two mutually perpendicularly polarized components so that light from both components can be extracted. This situation is shown in FIG. The light entering the Wallaston prism WP is, for example, both P and S polarized light LOP.

It may be linearly polarized light having a polarization direction of, for example, 45 degrees with respect to LO5, or it may be circularly polarized light by inserting a λ/4 plate between collimator lens CL and Wallaston prism WP.

In Fig. 37, the P-polarized light and the S-polarized light of the light exiting the Wallaston prism WP are at the same angle of incidence with respect to the grating GS, and the components in the relative movement direction of the grating GS (direction of arrow A) are in opposite directions. The state is as follows. This light is λ
When passed through a /4 plate QW, the P-polarized light and the S-polarized light become circularly polarized light with opposite rotation directions. These circularly polarized lights spatially interfere with each other. This interfered light is split by a beam splitter BS and guided to two photodetectors PDI and PO2, which have polarizing plates PPI and PP2 in front, as shown in Figure 5. A signal output as shown in FIG. 3 is obtained, and the signal of the grating interferometer is obtained by performing the electrical processing as described above for the apparatus shown in FIG. The polarizing plates PPI and PP2 have their polarization axes shifted by 45° from each other.

In the apparatus shown in FIG. 36, other birefringent prisms such as a Rochon prism or a Glan-Thompson prism may be used. However, in the case of these prisms, the relationship between the alignment of the incident light and the prism is not like that of the Wallaston prism, where the incidence is perpendicular to the end face.

Fig. 38 shows the length measurement standard grating GS by folding the optical path using a corner cube and making the diffracted light go back and forth twice.
An example of a grating interferometer that increases the resolution of the system by increasing the number of light divisions to 8 is shown below.

For example, in a length measuring instrument with the configuration shown in Fig. 4, the sensor PDI
, the amount of light at PO2 is shown in FIG. 5(a).

As shown by the signal R%S in (b), it changes at a period of 174 times the pitch of the reference grating GS. In the above-mentioned grating interferometric length measuring device, the light amount detection signal R% of the sensors PDI and PD2 is
The resolution is improved by electrically dividing the period of S to increase the number of pulse signals per pitch of the grating GS.

However, when dividing by electrical processing, the pulse interval may vary due to fluctuations in signal amplitude or DC level, resulting in deterioration of accuracy.

On the other hand, here, the number of diffractions at the length measurement standard grating GS is increased and the standard grating GS! By configuring the optical system so that the light intensity of the sensor changes many times, such as 8 times, during the pitch movement, the light intensity of the sensor can be changed at a fine cycle of 178 times, which is the pitch of the reference grating. , the number of divisions into the grating is increased by optical arrangement.

In FIG. 38, the light emitted from the light source LD such as a semiconductor laser of the grating interferometric length measurement optical system is transmitted through the collimator lens C.
It is made into a plane wave light beam LO at L, and is incident on a point P1 on the length measurement reference grating GS, which is movable relative to the optical system. This incident light is diffracted by the reference grating GS. Diffracted light L of ±Nth order, respectively 11. L 12 is corner cube CCI.

CC2, where it is reflected in a direction parallel to and opposite to the original optical path, and returns to point P2. on the length measurement standard grating GS. It reaches point P3 and is diffracted again by the grating GS. Light L diffracted again
21. L22 changes its polarization state by passing through the phase difference plates FPI and FP2, and is then reflected by the corner cubes CC3 and CC4 to points P4 and P on the grating GS.
Return to 5. Light L31. which is diffracted again by the grating GS. L
32 is reflected once again by the corner cubes CCI and CC2 and returns to the same point P6 on the grating GS, where it undergoes the fourth diffraction. Lights L41 and L42 that have undergone four degrees of diffraction interfere with each other. This interference light is reflected by mirror M
R, the beam splitter HM splits the beam into two beams, passes through polarizing plates PPI and PP2, and sends them to sensors PDI and PD.
2.

The retardation plates FPI and FP2 are, for example, λ/4 plates, and each uses a laser beam L21. The first axis is set to +45'' and -45' for the linearly polarized light of L22.The polarizers PPI and PP2 are set to 0, respectively.
It is sufficient to set the angle of the polarizing plate so that the angle becomes 6.45''. Then, the two sensors PDI and PD2 obtain signals whose phases are shifted by 90 degrees and whose intensity fluctuates.
For example, if the length measurement reference grating has a pitch of 2.4 μm and all the diffraction orders are ±1, the sensors PDI and PD2 obtain signals with a period of 0.3 μm, which is 178 of the pitch of the grating. If this is further divided, for example, by the electrical division method described above for the length measuring instruments of FIGS. 4 and 6, it is possible to obtain 32 pulses per pitch, which is twice the number described above, with a period of 0.075 μm.

In the length measuring device having the configuration shown in FIGS. 4 and 6, the signal intensity at the sensor has a period of 0.8 μm for a grating pitch of 2.4 μm. Therefore, compared to the length measuring instruments shown in FIGS. 4 and 6, this embodiment can obtain twice the resolution due to the optical arrangement.

[Brief explanation of drawings]

Fig. 1 is an overview of a length measuring device according to an embodiment of the present invention, Fig. 2 is a partially enlarged view of the arrangement space for optical probes, etc. in Fig. 1, and Fig. 3 is a length measuring device set on a 1-axis stage. A schematic configuration diagram of a length measuring device according to an embodiment of the present invention; FIG. 4 is an explanatory diagram of the configuration of the length measuring head in FIG. 3; FIG. 5 is an output waveform diagram of the photodetector in FIG. 4; Fig. 6 is an explanatory diagram of the operation of the grating interferometric length measurement system in Fig. 4, Fig. 7 is an explanatory diagram of the rotation of the polarization direction of the detection light in the configuration of Fig. 6, and Fig. 8 is a diagram illustrating the rotation of the polarization direction of the detection light in the configuration of Fig. 6. iA6 A signal waveform diagram of phases o0 and 180° in the configuration shown in FIG. ,
The working theory of the AF length measurement system tuyere in FIG. 4; FIG. 11 is a diagram showing the spot state and light amount distribution on the position sensor surface with respect to the plane mirror position in FIG. 1θ; FIG. A characteristic diagram showing the relationship between the differential signal ΔI (=IA-Is) created from the output of the position sensor and the position (defocus amount) of the plane mirror, FIG. 13 is the length measuring device shown in FIG. Flowchart showing the operation of FIG. 14 is an output signal characteristic diagram of the grating interference length measurement system in the length measurement device shown in FIG. Signal characteristic diagram, Figure 16 is a configuration diagram showing an embodiment assembled as a length measuring unit, Figure 17 is a flowchart showing the operation of the length measuring unit in Figure 16, Figure 18 is the diagram shown in Figure 16. 19 is a characteristic diagram showing the relationship between the grating interferometric length measurement pulse signal and the AF length measurement output voltage in the length measurement unit of FIG. 19. FIG. 19 is a schematic configuration diagram when the length measurement unit of FIG. FIG. 20 is a schematic configuration diagram showing an embodiment using a laser interferometric length measurement system as the interferometric length measurement system. FIG. 21 is a diagram showing details of the length measurement optical system on the fine movement stage in FIG. 20. 23 is a perspective view of the reference member on which the blazed grating is formed. FIG. 24 is a diagram showing the blazed grating and AF length measurement in FIG. 22. FIG. 25 is an explanatory diagram showing the positional relationship with the long system, and FIG. 26 is a characteristic diagram showing the relationship between the output pulse train signal of the grating interferometric length measurement system and the output of the AF length measurement system in FIG. An explanatory diagram showing the relationship between the reference member position and the AF length measurement signal switching state in a modification of the embodiment shown in FIG. 20, and FIG. 27 shows a blazed grating and an AF length measurement system in another modification of the embodiment shown in FIG. FIG. 28 is a configuration diagram of a diffraction grating interferometer according to an embodiment of the present invention configured without using a corner cube. FIG. 29 is an explanatory diagram showing the positional relationship between the 30 is an explanatory diagram showing the state of the diffracted light flux when the output wavelength of the light source fluctuates in the length measuring device shown in FIG. 28. FIG. 31 shows the fluctuation of the light source wavelength in FIG. 28. Fig. 32 is a configuration diagram of a grating diffraction length measuring device according to an embodiment of the present invention in which the main parts are integrated into ICs, and Fig. 33 is a diagram of the length measuring device of Fig. 32. 34 is an output waveform diagram of each photodetector in the length measuring device shown in FIG. 33. FIG. 35 is a further modified example of the length measuring device shown in FIG. 32. FIG. 36 is a block diagram of a grating interferometric length measuring device according to an embodiment of the present invention using a Wollaston prism, and FIG. 37 shows the action of the Wollaston prism in FIG. 36. Explanatory diagram,
FIG. 38 is a configuration diagram of a grating interferometric length measuring device according to an embodiment of the present invention in which the resolution of the system is increased by making the diffracted light go back and forth to the length measuring reference grating twice. DS: Stage base XS: X stage YS: Y stage L! : Laser interference length measurement device CP: Corner cube prism Dv = placement space for optical probes, etc. DFS: Base for small stroke stage XFS: Small stroke X stage YFS Small stroke small stroke destage: Optical probe SX: x direction standard HX : x-direction measuring head MX: x-coordinate detection length measuring device SY: y-direction standard HY: y-direction measuring head MY: /coordinate detection length measuring device SR: Moving stage GS: Diffraction grating (standard, 8 MH: Measuring head SP: Surface plate PM: Plane mirror AFS: Fine movement stage (AF stage) FD: Fine drive mechanism LD: Light source CL: Collimator lens HM: Beam splitter (or half mirror) CC: Corner cube Prism (or prism mirror) BS: Polarizing beam splitter PD: Photodetector (detector, optical sensor) LN: Objective lens PS: Optical position detector (sensor) ST: Stage movable part QW: λ/4 plate GL: Light condensing Lens SS: Stage fixing part AT: Actuator MO: Test object O3: Length measurement reference plane ED: Signal processing electrical system PC: Pulse train length measuring device electrical system FFz Focus detection system CPU: Central control calculation system Lz: Laser head! U: Interference unit SM: Reference member BG: Blazed grating FT: Plane serving as a reflective surface FP: Retardation plate GF: Fixed grating PP: Polarizing plate SB: GaAs substrate WG: Dielectric waveguide layer LS: Lens and heam splitter section GC Nigelating coupler FS: Frequency shifter OSC: Oscillator PSD: Phase detection circuit MR: Mirror WP: Wallaston prism AP near aperture Patent applicant Canon Co., Ltd. agent Patent attorney Tetsuya Ito Patent attorney Tatsuo Ito No. 3 Figure 5 Figure 6 Figure 15 k. Figure 18 Figure 24 Front 26 rl! I 27th rl! j Figure 37 PD2 Figure 38

Claims (9)

[Claims] (1) a first length measuring means that outputs a pulse signal every time the relative positions of two relatively moving objects displace by a predetermined pitch;
A second circuit that generates an electrical level signal according to the amount of displacement between objects.
A length measuring device comprising a length measuring means and a calculation means for detecting the amount of displacement of the relative position based on the pulse signal and the electrical level signal with a resolution smaller than one pitch of the predetermined pitch. . (2) The first length measuring means is configured by disposing an interferometric length measuring head equipped with a light source and a photodetector on one of the two objects and a diffraction grating on the other, and using the diffraction grating as a standard and measuring the length. 2. The length measuring device according to claim 1, which is a grating interferometric length measuring device that outputs a pulse signal according to a change in the intensity of light obtained by interfering diffracted lights of different orders formed by a diffraction grating. (3) The length measuring device according to claim 1, wherein the first length measuring means is a laser interference length measuring device. (4) one of the two objects is a second stage with a smaller stroke than the first stage mounted on the first stage;
The second length measuring means outputs an electrical level signal according to the amount of relative displacement of the second stage with respect to the first stage, and the calculating means outputs an electric level signal from the first length measuring means when the first stage moves. calculate the relative displacement amount in units of the predetermined pitch by accumulating the pulse signals generated, and drive the second stage by a distance such that at least one pulse signal is output from the first length measuring means in the vicinity of the measured position. and detects the output of the second length measuring means at the pulse signal generation position and the measured position, and calculates the distance between the pulse signal generation position and the measured position based on these outputs. A length measuring device according to claim 2 or 3. (5) The second length measuring means includes an objective lens fixed to the second stage and capable of focusing on a plane perpendicular to the relative movement direction of the first stage, The length measuring device according to claim 4, which is an autofocus detection means that outputs an electric signal according to a focus state. (6) a light source in which the autofocus detection means enters a light beam at a position eccentric from the main optical axis of the objective lens;
6. The length measuring device according to claim 5, further comprising a light position detecting means for detecting the incident position of the light beam reflected by the vertical surface and incident through the objective lens. (7) The second length measuring means includes a surface arranged on one of the two objects along the relative movement direction and inclined with respect to the relative movement direction, and a surface that is fixed to the other object and arranged in the relative movement direction. 4. The length measuring device according to claim 2, further comprising means for measuring the distance from the side surface of the slope to the inclined surface. (8) The length measuring device according to claim 7, wherein the second length measuring means is an autofocus detection means that outputs an electric signal near the inclined surface according to a focus state on the inclined surface. (9) a light source in which the autofocus detection means enters a light beam at a position eccentric from the main optical axis of the objective lens;
9. The length measuring device according to claim 8, further comprising a light position detecting means for detecting an incident position of a light beam reflected by the vertical surface and incident through the objective lens.