JPH0652168B2 - Three-dimensional shape measuring device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a three-dimensional shape measuring apparatus, and more particularly to a three-dimensional shape measuring apparatus capable of performing non-contact high-speed shape measurement.

[Prior art]

Conventionally, various methods have been used for non-contact measurement of a three-dimensional shape, that is, a three-dimensional shape of an object. As such a measuring method, an interference measuring method using coherent light, a method of reading a light section image by slit light, and the like are used. However, while the interferometric method has the advantage that the entire surface of the object to be measured can be simultaneously and accurately measured, it has the drawback that it is difficult to measure when the irregularities on the surface of the object to be measured are considerably large with respect to the wavelength of light. is there. Also,
The method of reading a light-section image has a drawback that it is difficult to measure the uneven shape on the order of the wavelength of light, and therefore high accuracy cannot be expected.

Therefore, a focusing state determination optical system having an internal light source is placed on a moving table, and the moving table is moved so as to focus the optical system on the surface of the object to be measured. A method for measuring the shape has been proposed (Japanese Patent Publication No. 46-40231). According to this, the shape can be measured with considerable accuracy regardless of the degree of unevenness on the surface of the object to be measured.

However, fine irregularities (that is, undulations) on the surface of the measured object
If there is such a difference, it is more accurate to measure the inclination angle at the same time than to express it by measuring only the height difference of the irregularities, that is, the distance. Such accurate information cannot be obtained in the measurement method of.

[Object of the Invention]

The present invention has been made in view of the above-mentioned conventional techniques, and an object of the present invention is to provide a three-dimensional shape measuring apparatus capable of accurately measuring an extremely fine three-dimensional shape with high precision, high stroke, and sport measurement.

In particular, the present invention provides a three-dimensional shape measuring apparatus capable of performing in-focus state determination and tilt angle measurement substantially at the same spot so as to obtain fine data of both at the same specific position. With the goal.

SUMMARY OF THE INVENTION According to the present invention, an object as described above is a focused state in which condensed light is irradiated in the direction of an object to determine the relative positional relationship between the condensed position of the condensed light and the object. The discriminating optical system and the focused state discriminating optical system share an optical path at least in the vicinity of the objective lens, and irradiate in the direction of the object with condensed light condensing at a condensing position substantially the same as that of the focusing state discriminating optical system. A tilt angle measuring optical system for measuring the tilt angle of the object at the light collecting position, and a movable part for moving the light collecting position of the light flux emitted from the focusing state determination optical system and the tilt angle measuring optical system. And a means for measuring the amount of movement of the movable part are provided.

Example of Invention

Hereinafter, specific examples of the measuring apparatus of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing a first embodiment of a three-dimensional shape measuring apparatus of the present invention. In FIG. 1, 2 is an in-focus state determination optical system, and 4 is an inclination angle measurement optical system. The optical systems 2 and 4 are incorporated in a casing 6.

In the focusing state determination optical system 2, 8 is a light source, and 10
Is a collimator lens, 12 is a knife edge, 14 is a polarization beam splitter, 16 is a half mirror, 18 is a 1/4 wavelength plate, 20 is an objective lens, and 22 is a bandpass. A filter, 2
Reference numeral 4 is a lens, and 26 is an optical sensor.

In the tilt angle measuring optical system 4, 28 is a light source, and 30
And 32 are lenses, 34 is a polarization beam splitter, 36 is a bandpass filter, and 38 is an optical sensor. In the optical system 4, the half mirror 16, the quarter-wave plate 18 and the objective lens 20 are shared with the optical system 2.

The casing 6 is an actuator 40 fixed to the outside.
It is connected to the. The casing 6 can be moved along the optical axis X of the objective lens 20 by driving the actuator 40. Actuator 4
As 0, it is preferable to use one having a fluid moving bearing slide mechanism or the like in order to realize highly accurate movement amount control.

The casing 6 is also provided with a length measuring means 42 for measuring the amount of movement. As the length measuring means 42, for example, one using a grating interference length measuring method (Oplus E, 1981)
April issue p84-), in which case 44 in FIG. 1 is a reference grid fixed to the casing 6,
Reference numeral 46 is a grating pitch reading device fixed to the outside.

Reference numeral 50 is an object to be measured whose shape is to be measured.

The focus state determination method of the focus state determination optical system 2 in the present embodiment will be described below. The light emitted from the light source 8 is collimated by the collimator lens 10, and the collimated beam is transmitted through the polarization beam splitter 14. Is reflected by the half mirror 16,
The light passes through the quarter-wave plate 18 and enters the objective lens 20.
It should be noted that the parallel light flux exiting the collimator lens 10 is partially shielded by the knife edge 12, and the objective lens 20 has one of two zones divided by a boundary surface passing through the optical axis X (in the figure, It is incident only on the upper half zone). Thus, the light focused by the objective lens 20 forms a spot on the surface of the DUT 50. The light reflected from the spot passes through the objective lens 20 again,
After passing through the quarter-wave plate 18, it is reflected by the half mirror 16, is reflected by the beam splitter 14, passes through the bandpass filter 22 and the lens 24, and then reaches the sensor 26.

Therefore, at this time, the surface of the DUT 50 and the objective lens 2 are
The distance from 0 causes a difference in the light reaching the sensor 26. That is, as shown in FIG. 2, when the surface of the object to be measured 50 is exactly at the focus position of the objective lens 20 (position a in the figure), the spot on the surface of the object to be measured 50 is just Since the center is located on the optical axis X, the reflected light is centered on the optical axis Y at the sensor 26. When the surface of the DUT 50 is located farther than the focal position of the objective lens 20 (position B in the figure), the spot on the surface of the DUT 50 is displaced from the optical axis X in the figure. Since it comes to be centered in the A zone, the reflected light is centered in the A'zone in the figure which is deviated from the optical axis Y in the sensor 26. On the other hand, DUT 5
When the surface of 0 is located closer to the focal position of the objective lens 20 (position of C in the figure), the spot on the surface of the DUT 50 has a center in the B zone in the figure which is deviated from the optical axis X. Since it is positioned, the reflected light is shifted from the optical axis Y in the sensor 26 by B ′ in the figure.
It will be centered in the zone.

An array sensor such as a CCD (Charge Coupled Device) is used as the sensor 26. FIG. 3 is a plan view of such a sensor 26. This figure shows the sensor 26 in FIG. 2 as viewed from the left. In the figure, the shaded portion indicates the channel stopper portion separating the sensor segments. The sensor 26 of FIG. 3 shows a graph of the spot position and its light amount distribution when the surface position of the DUT 50 is a, b, or c of FIG.

In the sensor 26, if the sum of the outputs of all the sensor segments in the A ′ zone is I _A ′ and the sum of the outputs of all the sensor segments in the B ′ zone is I _B ′, the focus of the optical system 2 on the object 50 to be measured is focused. ΔI = depending on the state
A _A ′ -I _B ′ changes. The relationship is shown in FIG. Fourth
As can be seen from the figure, ΔI changes almost linearly in the vicinity of the case where the focusing is completely performed (the above-mentioned state of a). By utilizing this characteristic, it is possible to determine whether the optical system 2 is in the front defocused state, completely in the focusing state, or in the rear defocused state.

Therefore, automatic focusing can be realized by servo-driving the actuator 40 so that ΔI becomes O based on the output ΔI. By measuring the amount of movement of the casing 6 at this time by the length measuring means 42, the measured object 5
The position of the portion of the surface of 0 that intersects the optical axis X is measured. By performing this position measurement on the entire surface of the object to be measured, a three-dimensional shape can be measured.

Next, the tilt angle measuring method of the tilt angle measuring optical system 4 in the present embodiment will be described below.

The light emitted from the light source 28 passes through the lenses 30 and 32 and then becomes a parallel light flux, which is a polarization beam splitter 34.
Is reflected by the half mirror 16 and 1/4.
It passes through the wave plate 18 and is focused by the objective lens 20. In this optical system 4, the objective lens 20
A light beam incident on the optical axis has a center on the optical axis X and is incident parallel to the optical axis X. Thus the objective lens 2
The light focused by 0 forms a spot having a center on the X axis on the surface of the DUT 50. The light beam reflected from the spot passes through the objective lens 20 again,
After passing through the quarter-wave plate 18, the half mirror 16, the polarization beam splitter 34, and the bandpass filter 36, the light reaches the sensor 38.

At this time, however, a difference occurs in the light reaching the sensor 38 due to the inclination angle of the surface of the DUT 50. That is, as shown in FIG. 5, assuming that the surface of the DUT 50 is inclined at the position on the optical axis X with respect to the plane perpendicular to the optical axis X by an angle α, the reflected light beam from the projected spot is reflected. Enters the objective lens 20 with its center in the direction forming an angle 2α with respect to the optical axis X. Thus, the light beam incident on the objective lens 20 travels in parallel with the optical axis X, and the center of the speed of light is h≈fs from the optical axis X.
They are separated by in2α (here, f represents the focal length of the objective lens 20).

As the sensor 38, a barycentric position detecting sensor of a light beam, a so-called position sensor, or the like is used, and the above α can be obtained by measuring the above h.

As can be seen from the above description, the surface of the object to be measured 50 needs to be at the focal position of the objective lens 20 when measuring the tilt angle, but focusing is always performed by the action of the optical system 2 and the actuator 40. Since this is done, this condition is always met.

In addition, since the focusing state determination optical system 2 and the tilt angle measuring optical system 4 have a part in common, the wavelength band of the light source used in each optical system is different, or the polarization state is different, so that crossing occurs. Make sure there is no talk. Therefore, the bandpass filters 22 and 36, the polarization beam splitters 14 and 34, and the quarter-wave plate 18 are used.

The evaluation of the performance of the three-dimensional shape measuring apparatus of the above embodiment will be attempted below.

First, the accuracy of position measurement is determined by the focus state determination resolution of the optical system 2 and the measurement accuracy of the length measuring means 42. For example,
The objective lens 20 has a focal length f = 2.1 mm and NA = 0.
A lens having a focal length of f ₁ = 6.6 mm is used as the lens 10.
When a lens having a focal length of f ₂ = 85 mm is used as the lens 24 and a CCD sensor array is used as the sensor 26, the linear portion in the graph of FIG. 4 has an inclination of 200 to 1000 mV / μm. Further, the noise of the output of ΔI at this time is 1 to 2 mV or less. As a result, a focus state determination resolution of the optical system 2 of 0.01 to 0.02 μm can be obtained. Also, the length measuring means 4
If 2 using the grating interferometry method is used as 2,
An accuracy of ˜0.01 μm is achieved. The length measuring means 42
Others include those using the optical heterodyne interference method (for example, a laser length measuring machine from Hewlett Packard, Op.
lus E, December 1982, p86-), laser interferometer wave number reading method, etc. can also be used.
Similar precision is achieved by these.

Next, the stroke for position measurement is determined by the stroke of the actuator 40 and the stroke of the length measuring means 42. The grating interferometer length measurement method, the optical heterodyne interference method, the laser interferometer's wave number reading method, etc. are all 1
A high stroke of 00 mm or more can be achieved, and the actuator can also achieve a similar stroke.

Further, the projected spot diameter is determined by the NA of the objective lens 20. For example, if the objective lens 20 having NA = 0.8 is used, the projected spot diameter φ of the optical system 2 is φ = 2.
44Fλ≈2.38 μm (where λ = 0.78 μm), and spot measurement of about 2 μm becomes possible. When it is desired to increase the spot diameter, the effective light beam diameter of the optical system 2 may be reduced to reduce the effective NA of the light beam.

Further, the inclination angle measurement accuracy is determined by the position detection accuracy of the sensor 38. For example, the detection accuracy of the sensor 38 is 0.3
When the focal length f of the objective lens 20 is 3.3 μm, a tilt angle measurement accuracy of about 9 ″ can be realized. Further, the tilt angle measurement range is NA =
If 0.5 to 0.9 is used, it is possible to measure up to about 10 to 30 degrees.

FIG. 6 is a schematic configuration diagram showing a second embodiment of the three-dimensional shape measuring apparatus of the invention. In the apparatus of this embodiment, only the configuration of the tilt angle measuring optical system 4 is different from that of the first embodiment. In the optical system 4 of this embodiment, 60 is a light source, 62 is a collimator lens, and 64 is an aperture,
66 is a half mirror, 67 is a bandpass filter, 68 is a lens, 70 is a mirror,
72 and 74 are lenses, and 76 and 78 are optical sensors. In this optical system, the mirror 70 has an optical axis X.
It is located only in one of the two zones (the lower half zone in the figure) divided by the boundary plane passing through. In addition, the aperture 64 and the mirror 70 form the objective lens 20.
And the lens 68 are arranged in a conjugate manner. That is, the aperture 64 is arranged at the focal position of the objective lens 20.

In the optical system 4 of this embodiment, when the surface of the DUT 50 is not inclined with respect to the plane perpendicular to the optical axis X,
The light reflected by the surface of the DUT 50 reaches the lens 68 at the pupil position of the objective lens 20 without being displaced in parallel with the optical axis X. In this state, the amount of light reflected by the mirror 70 and reaching the sensor 76 via the lens 72 is equal to the amount of light reaching the sensor 78 via the lens 74 without entering the mirror 70. The output of the sensor 78 is made equal. DUT 50
When the surface of the object has an inclination with respect to the surface perpendicular to the optical axis X, the light which hits the surface of the DUT 50 and is reflected causes a parallel shift with respect to the optical axis X at the pupil position of the objective lens 20. It is incident on the lens 68. In this state, the amount of light that is reflected by the mirror 70 and reaches the sensor 76 via the lens 72 and the amount of light that does not enter the mirror 70 and reaches the sensor 78 via the lens 74 are different, and the differential output between the sensors 76 and 78 is obtained. If so, the inclination angle can be obtained from the value.

In the above embodiments, the in-focus state determination optical system 2 is moved so that it is in focus. However, only a part of the optical system 2 is moved. May be. 7 and 8 show a part of such an optical system.

In the optical system 2 shown in FIG. 7, only the objective lens 20 is movable along the optical axis X. A corner cube 80 forming a part of the length measuring means is fixed to the objective lens 20, and a laser beam emitted from the length measuring means main body is reflected by the corner cube 80 and travels to the length measuring means main body. To do.

In the optical system 2 of FIG. 8, only the light source 8 is the lens 10
It is movable along the optical axis of. A corner cube 80 that constitutes a part of the length measuring means is fixed to the light source 8. In this case, the moving amount of the light source 8 is set to the objective lens 2
It is necessary to convert the moving amount of the light flux projected from 0 to the focusing position.

In the embodiment shown in FIGS. 7 and 8, an actuator for moving only the movable portion is provided, but the illustration is omitted.

By thus reducing the size of the movable portion, the actuator can be downsized.

In the above embodiment, the so-called automatic focusing method is called
TTL-A ² F (Through the Taking Lens Active Auto Focu
s) system (Journal of the Television Society, Vol. 35, No. 8, 19)
1981, p637-) was shown, but other methods such as a method used for video pickup or a method used for autofocus of a camera may be used as an automatic focusing method. it can.

〔The invention's effect〕

According to the three-dimensional shape measuring apparatus of the present invention as described above, it is possible to perform three-dimensional shape measurement with a minute spot with high accuracy and high stroke at high speed, and at the same time, the inclination angle of the surface of the measured object at the same specific position. Since the measurement can be performed, accurate information regarding the three-dimensional shape can be obtained in a short time.

[Brief description of drawings]

1 is a block diagram of the device of the present invention, FIGS. 2 and 5 are partial views thereof, FIG. 3 is a plan view of the sensor, and FIG. 4 is a graph of the output of the sensor, FIG. 6 is a block diagram of the device of the present invention, and FIGS. 7 and 8 are partial block diagrams of the device of the present invention. 2: Focus state determination optical system, 4: Inclination angle measurement optical system, 6:
Casing, 8, 28, 60: light source, 20: objective lens, 26, 38, 76, 78: sensor, 40: actuator, 42: length measuring means, 50: object to be measured.

Claims (3)

[Claims] 1. A focused state determination optical system for irradiating a focused light toward a target to determine a relative positional relationship between the focused position of the focused light and the target, and the focused state determination optical system. And irradiating in the direction of the object with condensed light which shares an optical path at least in the vicinity of the objective lens and which is condensed at substantially the same condensing position as the focusing state determination optical system, and determines the inclination angle of the object at the condensing position. A tilt angle measuring optical system to measure, a movable part for moving a focusing position of a light beam emitted from the focusing state determination optical system and the tilt angle measuring optical system, and a moving part for measuring the moving amount of the movable part. And a means are provided. 2. A control means for driving the movable part so that the converging position is matched with the object based on the focus state determined by using the focus state determining optical system. The three-dimensional shape measuring apparatus according to the first item. 3. Two optical systems have light sources of different wavelength bands, and each optical system transmits light of the wavelength band emitted by the light source of the optical system, and transmits light of the wavelength band emitted by the light sources of other optical systems. Having a bandpass filter that does not allow light to pass through
Three-dimensional shape measuring device of item.