JPH08261734A - Shape measuring apparatus - Google Patents

Abstract

PURPOSE: To realize a novel shape measuring apparatus which accurately can measure a surface shape at a high speed. CONSTITUTION: Parallel luminous fluxes radiated from a light source 1 are incident to a lens 2 having a small aperture via luminous flux displacing means 11 and incident to a positive lens 5 having a large aperture via a half mirror 4. An afocal system is formed of the lens 2 and the lens 5 to emit the fluxes emitted from the lens 5 to a surface 61 to be measured, and the reflected fluxes are condensed to a position sensor 7 via the lens 5. The fluxes are displaced in an optical axis perpendicular direction by the means 11, the surface 61 is scanned by the flux emitted to the surface 61, the inclined distribution is obtained by the output of the sensor 7, and numerically integrated to obtain the shape of the surface 61.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shape measuring apparatus, and more particularly to a shape measuring apparatus which measures the inclination distribution of a surface to be measured and obtains the shape of the surface to be measured by integrating the obtained inclination distribution. . The present invention can be suitably used for measuring the flatness of silicon wafers and the like.

[0002]

2. Description of the Related Art As a method for measuring a surface shape with relatively few undulations, a method is known in which the inclination angle of a surface to be measured is measured and the surface shape is obtained by integrating the inclination angle.

As a shape measuring apparatus utilizing such a measuring method, one disclosed in Japanese Patent Application Laid-Open No. 1-233307 is known.

This shape measuring device uses two light beams,
The inclination angles of two points close to each other on the surface to be measured are each measured, but there is a problem that the calculation is complicated and time consuming because the calculation includes Fourier transform and the like.

Further, since the above-mentioned shape measuring device scans the surface to be measured in the direction orthogonal to the two parallel light beams, the moving means for scanning tends to be large, and the scanning is performed by mechanical displacement. There is also a problem that scanning takes time.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide a novel shape measuring apparatus capable of measuring a surface shape with high accuracy and high speed (claim 1). ~ 6).

[0007]

The shape measuring apparatus of the present invention is a "shape measuring apparatus which measures the inclination distribution of a surface to be measured and obtains the shape of the surface to be measured by integrating the obtained inclination distribution". A light source, a light flux displacement means, a lens having a small aperture, a positive lens having a large aperture, a half mirror,
It has a position sensor and a calculation means (Claim 1).

The "light source" is a light source that emits a parallel luminous flux, and a laser light source such as an LD or a combination of an LD or LED and a collimating lens can be preferably used. Of course, a white light source may be used as long as it emits a parallel light flux.

The "light flux displacing means" is means for displacing the parallel light flux from the light source in the direction orthogonal to the optical axis.

The "lens having a small diameter" is a lens into which the parallel light flux that has passed through the light flux displacement means is incident, and has a small diameter. The lens having a small aperture may be a positive lens or a negative lens.

The "positive lens having a large aperture" is arranged so as to face the measurement area of the measurement stage, and constitutes an afocal system together with the lens having a small aperture.

The "half mirror" is arranged between a lens having a small aperture and a positive lens having a large aperture, and between the positive lens having a large aperture and its object-side focal point.

The "position sensor" is provided on the object-side focal plane of a positive lens having a large aperture, which is a reflection conjugate plane of a half mirror, and receives the light reflected from the surface to be measured.

The "calculation means" is means for performing a predetermined calculation on the output of the position sensor.

In the shape measuring device according to claim 1,
A "deflection angle detecting means" can be provided between the light beam displacement means and the lens having a small diameter (claim 2).

The deflection angle detecting means has a half mirror, a positive lens, and a position sensor. "Half mirror" is
It is arranged between the light beam displacement means and the lens having a small diameter to separate a part of the light beam.

The "positive lens" is a lens for condensing the parallel light flux separated by the half mirror.

The "position sensor" is provided on the image side focal plane of the positive lens and detects the position of the focused spot by the positive lens.

The "position sensor" of the invention described in claims 1 and 2 is a sensor for detecting the incident position of the light spot in one direction, and is a commercially available position sensor from the past, or a CCD sensor or the like. Can be used.

The above "flux displacing means" can have various configurations.

For example, the luminous flux displacing means has "two positive lenses whose optical axis and focal point match each other, and displacing means which displaces these two positive lenses integrally in the direction orthogonal to the optical axis". (Claim 3).

Alternatively, the luminous flux displacing means can be configured so as to have "a reflecting optical element and a displacing means for displacing the reflecting optical element in a predetermined direction" (claim 4). in this case,
As the reflective optical element, a penta prism, a prism, a corner cube, or a plane mirror can be used (claim 5).

Further, according to a sixth aspect of the present invention, the light beam displacement means includes a "first positive lens, a galvano mirror in which the rotation axis of the mirror surface is aligned with the focal position of the first positive lens," And a second positive lens which is arranged such that the optical axis intersects with the optical axis of the first positive lens so as to match the focal point with the focal position and which makes the light flux reflected by the galvanomirror parallel light flux ”. be able to.

[0024]

When the x axis is taken in a predetermined direction in relation to the surface to be measured and the shape of the surface to be measured in the x direction is y = f (x), dy / dx = f '(x) = tan { θ (x)}.

Therefore, if tan {θ (x)} is known,
The shape: f (x) can be obtained by the integral: ∫tan {θ (x)} dx.

In particular, when the surface to be measured has few undulations (close to a flat surface), θ (x) << 1, and in this case ta
n {θ (x)} = θ (x), and the above integration is ∫θ (x) dx.

In this specification, the "inclination distribution" of the surface to be measured generally means tan {θ (x)}, and particularly θ
For a surface to be measured for which (x) << 1 holds, θ (x) is meant.

In the present invention, the parallel light flux emitted from the light source is applied to the surface to be measured through the "afocal system composed of a lens having a small diameter and a positive lens having a large diameter".

The illuminating light beam is a parallel light beam, and when reflected on the surface to be measured, it enters a positive lens having a large aperture and becomes a condensed light beam, which passes through the half mirror or is reflected by the half mirror. The light is focused as a spot on the position sensor and the position is detected.

The "reflection angle of the reflected light beam" can be known from the condensing position of the spot on the position sensor, and the "tilt angle: θ" of the surface to be measured can be known from this.

By displacing the light beam in one direction by the light beam displacement means, the surface to be measured can be scanned in the x direction, and the inclination distribution: θ (x) at each scanning position: x is known. (x) or ta known from θ (x)
The shape of the surface to be measured can be known by numerically integrating n {θ (x)}.

[0032]

EXAMPLES Specific examples will be described below.

In FIG. 1, reference numeral 1 is a light source, reference numeral 11 is a light beam displacement means, reference numeral 2 is a lens having a small aperture, reference numeral 4 is a half mirror, reference numeral 5 is a positive lens having a large aperture, and reference numeral 6 is shown.
Is an object to be inspected, reference numeral 7 is a position sensor, reference numeral 14 is a control / arithmetic device, and reference numeral 15 is a display.

The device under test 6 is fixed on the measuring stage 13. The surface 61 of the test object 6 is a surface to be measured, and has a shape of y = f (x) where the horizontal direction of the figure is the coordinate: x.

The parallel light flux emitted from the light source 1 passes through the light flux displacement means 11 and enters the lens 2 having a small aperture. The lens 2 is a "convex lens" in this embodiment, and converts the incident light flux into a condensed light flux.

After the light flux converted into the condensed light flux is condensed,
It is incident on the half mirror 4 while diverging, and the measurement component is reflected and enters the positive lens 5 having a large aperture.

The positive lens 5 is provided so as to face a measurement area (area corresponding to the surface 61 to be measured) on the measurement stage 13, while the object side (light source 1 side) focal point P of the lens 2 is small. Of the afocal system (reference numeral 1 in the figure indicates
2)) ".

On the optical path from the lens 2 to the positive lens 5, the half mirror 4 has a focus P on the object side of the positive lens 5.
Position (= image-side focal position of the lens 2) of the positive lens 5
It is deployed to be located on the side.

The position sensor 7 is arranged at the position of the conjugate plane of reflection by the half mirror 4 on the object side focal plane of the positive lens 5. Therefore, the point Q shown in the figure is the mirror image position of the focus P by the half mirror 4.

The light beam from the light source 1 is a parallel light beam, and since the lens 2 and the positive lens 5 form an afocal system 12, the light beam emitted from the positive lens 5 to the surface 61 to be measured is a parallel light beam.

The afocal system 12 has a "function of enlarging the diameter of the light beam". If the magnification of the function of enlarging the diameter of the light beam is m and the diameter of the light beam emitted from the light source 1 is d, the measured object is measured. The diameter of the parallel light flux with which the surface is irradiated is md.

This light beam diameter: md is set so that "the measured surface is sufficiently small with respect to the degree of undulation", that is, the light reflected by the measured surface becomes a substantially parallel light beam. d is appropriately determined according to the magnification: m.

In this way, the light beam reflected from the surface 61 to be measured enters the positive lens 5, becomes a condensed light beam, and the component that has passed through the half mirror 4 is condensed on the light receiving surface of the position sensor 7. The "position" is detected.

As shown in FIG. 1, when the “angle formed by the incident light flux and the reflected light flux” on the surface-to-be-measured 61 is 2θ, the inclination of the light-beam irradiation portion of the surface-to-be-measured 61 is the angle: θ.

Since the incident light flux is parallel to the optical axis of the positive lens 5, the reflected light flux passes through the positive lens 5 and then its chief ray forms an angle: 2θ with the optical axis.

When the angle between the incident light beam and the reflected light beam on the surface to be measured 61 is 0, assuming that the reflected light beam is focused at the point Q in FIG. 1, the incident light beam and the reflected light beam form an angle: 2θ. At this time, the distance D between the focal position Q ′ and the point Q is given by D = F · tan (2θ) using the focal length F of the positive lens 5.

“F” is a known focal length of the positive lens 5, and “D” is detected by the position sensor 7. Also, t
because it is an (2θ) = 2tanθ / { 1-tan 2 θ}, equation: (D / F) = 2tanθ / a {1-tan ² θ} by solving concerning the tan .theta, gradient: knowing tan .theta You can Especially when 2θ << 1,
tan (2θ) = 2θ, and the inclination: θ is D / 2F.

Hereinafter, for the sake of concreteness of explanation, “2θ <<
1 ”.

When the light beam displacing means 11 displaces the light beam from the light source 1 in the direction orthogonal to the optical axis within a range of ± h, the aforesaid magnifying power of the afocal diameter: m is applied to the surface 61 to be measured. The irradiation position of the light flux is displaced within a range of ± mh with the optical axis of the positive lens 5 as the center.

Therefore, the surface to be scanned 61 is moved from -x ₀ (= -mh) to + x in a predetermined direction (x direction, left-right direction in FIG. 1).
It is possible to scan up to ₀ (= mh), and the inclination distribution: θ (x) at each scanning position: x can be known from D (x) / F.

The control / calculation device 14 includes the light flux displacement means 11
The output D (x _i ) of the position sensor 7 is sampled at appropriate intervals according to the variable x _i corresponding to the amount of light beam displacement, and the result is calculated by D:
(x) / F is performed to obtain a slope distribution: θ (x), and then “integration: ∫θ (x) dx” is executed by numerical integration, and the result is displayed on the display 15.

In this way, the shape of the measured surface 61 can be known.

The control / calculation device 14 and the display 15 constitute "calculation means" in this embodiment. The control / arithmetic unit 14 is a computer and an I / O port unit that transmits the control signal to the drive unit of the light flux displacement unit 11.
It is composed of an I / O port unit or the like which receives an input signal from the position sensor 7.

FIG. 2 schematically shows only a main part of a modified embodiment of the invention described in claim 1. In order to avoid complication, the parts which are considered not to be confused with each other are denoted by the same reference numerals as those in FIG. 1, and the description thereof is omitted. The calculation means is the same as that of the embodiment shown in FIG.

In this embodiment, the lens 20 having a small aperture which constitutes the afocal system together with the positive lens 5 is a concave lens, and its object-side focal point p coincides with the object-side focal point of the positive lens 5. Further, the position sensor 7 has its light-receiving surface aligned with the reflection conjugate surface of the half mirror 7 of the object-side focal plane of the positive lens 5, and the conjugate image of the reflection of the half mirror 4 at the focal point p is located at the point q. To do.

Similar to the embodiment of FIG. 1, the shape measurement is performed by displacing the parallel light flux from the light source 1 by the light flux displacing means 11 in the direction orthogonal to the optical axis, and the inclination distribution: θ from the condensing position of the reflected light flux by the position sensor 7. This is done by detecting (x) and integrating it.

FIG. 3 schematically shows only an essential part of an embodiment in which the invention described in claim 2 is applied to the embodiment shown in FIG.

This embodiment is characterized in that the deflection angle detecting means 8 is provided between the light beam displacing means 11 and the lens 2 of the afocal system 12 having a small diameter.

The deflection angle detecting means 8 is arranged between the light flux displacing means 11 and the lens 2 having a small diameter, and has a half mirror 4a for separating a part of the light flux, and a parallel light flux separated by the half mirror 4a. The positive lens 9 that emits light and the position sensor 7b provided on the image-side focal plane of the positive lens 9 constitute the main part.

When there is no deviation in the optical system, the light beam separated by the half mirror 4a is always focused on the same position of the position sensor 7b regardless of the amount of light beam displacement by the light beam displacement means 11.

When a change occurs in the direction of the parallel light flux emitted from the light source 1 due to a lapse of time, the focus position on the position sensor 7b changes. Therefore, from this variation, the light flux from the light source 1 changes. Direction error can be detected, and the inclination distribution: θ (x) obtained from the output of the position sensor 7 can be corrected.

Further, even when the direction of the parallel light beam emitted from the light beam displacement means 11 changes with time, the error in the light beam direction can be detected in the same manner, and the inclination distribution: θ (x) can be corrected.

The "flux displacing means" indicated by reference numeral 11 in each of the embodiments shown in FIGS. 1 to 3 can have various configurations. Hereinafter, five specific examples of the light beam displacement means will be described.

The example of the light flux displacement means shown in FIG. 4 is a "displacement mechanism" in which the holder 100 holding a pair of lenses 140 is composed of a step motor 110 and a screw rod 112.
Is configured to be displaced in the direction (vertical direction in the drawing) orthogonal to the light beam optical axis (claim 3).

In this example, the pair of lenses 140 are convex lenses having the same focal length, share the optical axis, and match their focal positions. In the light flux displacement means having such a configuration, when the holding body 100 is displaced by the distance: s, the light flux can be translated in that direction by s ′ = 2s.

In the example shown in FIG. 5, the luminous flux displacement means uses the holder 100 holding the pentaprism 80 as a displacement mechanism composed of a step motor 110 and a screw rod 112.
It is configured so as to be displaced in the optical axis direction of the incident light flux (vertical direction in the figure) (claims 4 and 5).

In the luminous flux displacing means having such a structure, when the holder 100 is displaced by the distance: s, the luminous flux can be translated in that direction by s.

In the example of FIG. 6, the luminous flux displacing means causes the holder 100, which holds the corner cube 150, to move in a direction perpendicular to the optical axis of the incident luminous flux by a displacement mechanism composed of a step motor 110 and a screw rod 112 ( The light flux reflected by the corner cube 150 is reflected by the mirror 113 fixed to the device space (claims 4 and 5).

In the luminous flux displacing means having such a configuration, when the holder 100 is displaced by the distance: s, the luminous flux can be largely translated (distance: s') in that direction. A prism may be used instead of the corner cube 150.

The luminous flux displacement means shown in FIGS.
The configuration is such that a motion error of the holder 100 is optically compensated.

In the example of FIG. 7, the light beam displacement means is the plane mirror 1.
The holding body 100 holding 60 is used as a step motor 110.
And a screw rod 112 for displacing the incident light beam in a direction (right and left direction in the drawing) orthogonal to the optical axis (claims 4 and 5). The moving direction of the holder 100 may be parallel to the incident light beam from the light source 1.

In the example shown in FIG. 8, the luminous flux displacement means has a first positive lens 200a whose optical axis is aligned with the optical axis of the parallel luminous flux from the light source 1, and a mirror surface at the focal position of the first positive lens 200a. The Galvano mirror 300 whose rotation axis is aligned with the second
And the positive lens 200b of (6).

The second positive lens 200b has its focal point aligned with the focal position of the first positive lens 200a, and its optical axis intersects with the optical axis of the first positive lens 200a (in this example, it is orthogonal). The galvano mirror 300 is arranged so as to collimate the luminous flux reflected by the galvano mirror 300.

By deflecting the Galvano mirror 300, the parallel light flux emitted from the second positive lens 200b can be translated in a direction orthogonal to the optical axis of the second positive lens 200b.

In the luminous flux displacement means shown in FIGS. 7 and 8, the displacement of the luminous flux depends on the movement error of the holder 100 and the galvano mirror 30.
It is affected by the positional error between the reflection point of 0 and the focal positions of the positive lenses 200a and 200b. Therefore, such a light beam displacement means is preferably used together with the "deflection angle measurement means" in the shape measuring apparatus according to the second aspect described with reference to FIG.

[0076]

As described above, according to the present invention, a novel shape measuring device can be provided.

In the shape measuring apparatus of the present invention, the parallel luminous flux irradiating the surface to be measured is displaced by the luminous flux displacing means, and the luminous flux displacement is enlarged by the afocal system to scan the surface to be scanned. High-speed scanning is possible without increasing the size of the moving mechanism.

Further, since the slope distribution can be detected with high accuracy by autocollimation and the calculation can be performed only once, the calculation is simple, the calculation time can be shortened, and high-speed measurement is possible.

[Brief description of drawings]

FIG. 1 is a diagram for explaining one embodiment of the invention according to claim 1;

FIG. 2 is a diagram for explaining a modified embodiment of the invention according to claim 1;

FIG. 3 is a diagram for explaining one embodiment of the invention according to claim 2;

FIG. 4 is a diagram for explaining a characteristic part of one embodiment of the invention according to claim 3;

FIG. 5 is a diagram for explaining a characteristic part of one embodiment of the invention described in claims 4 and 5;

FIG. 6 is a diagram for explaining a characteristic part of another embodiment of the invention described in claims 4 and 5;

FIG. 7 is a diagram for explaining a characteristic portion of another embodiment of the invention described in claims 4 and 5;

FIG. 8 is a diagram for explaining a characteristic part of one embodiment of the invention according to claim 6;

[Explanation of symbols]

 1 light source 2 lens with small aperture 4 half mirror 5 positive lens with large aperture 7 position sensor 11 luminous flux displacement means 12 afocal system

Claims (6)

[Claims] 1. A shape measuring device for measuring a tilt distribution of a surface to be measured and integrating the obtained tilt distribution to obtain the shape of the surface to be measured, comprising: a light source for emitting a parallel light beam; and a parallel light beam from the light source. Light beam displacing means for displacing the light beam in a direction orthogonal to the optical axis, a lens having a small diameter through which the parallel light flux that has passed through the light beam displacing means is incident, and a lens arranged so as to face the measurement area of the measurement stage and having the small diameter A positive lens having a large aperture forming an afocal system together with a lens, and a half mirror provided between the lens having a small aperture and the positive lens having a large aperture, and between the positive lens and its object-side focal point. And a position sensor disposed on the object-side focal plane of the positive lens having a large aperture, which is a reflection conjugate plane by the half mirror, and receives the reflected light from the measured surface, and this position A shape measuring device, comprising: a calculation unit that performs a predetermined calculation on the output of the sensor. 2. The shape measuring device according to claim 1, wherein a half mirror is provided between the light flux displacing means and the lens having a small aperture to separate a part of the light flux, and a parallel mirror separated by the half mirror. A shape measuring device comprising: a positive lens for condensing a light beam; and a deflection angle detecting means including a position sensor provided on an image-side focal plane of the positive lens. 3. The shape measuring device according to claim 1 or 2, wherein the light flux displacing means includes two positive lenses whose optical axis and focal point match each other, and these two positive lenses in the direction orthogonal to the optical axis. A shape measuring device, comprising: a displacement unit that displaces integrally. 4. The shape measuring device according to claim 1, wherein the luminous flux displacing means includes a reflective optical element and a displacing means for displacing the reflective optical element in a predetermined direction. 5. The shape measuring apparatus according to claim 4, wherein the reflective optical element is a pentaprism, a prism, a corner cube, or a plane mirror. 6. The shape measuring device according to claim 1 or 2, wherein the luminous flux displacement means comprises a first positive lens and a galvano mirror in which a rotation axis of a mirror surface is aligned with a focal position of the first positive lens. And a second positive lens which is provided so as to match the focal point with the optical axis and intersects the optical axis of the first positive lens, and which collimates the light flux reflected by the galvano mirror. Shape measuring device.