JP2002286410A - Interferometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an interferometer that an oblique-incidence interferometer for measuring the surface shape of a test object is formed integral with a transmittant interferometer for measuring the transmitting wave surface of the sample, it is designed so that transmittant interferometer is inclined by a specified quantity to the oblique-incidence interferometer, and it is suitable for a case where a parallel flat is used as a light transmission body by using a low coherence light source for oblique-incidence measurement. SOLUTION: In the oblique-incidence interferometer, a multi-mode laser light is split by a light flux splitting means 3, a reference light 21 is reflected on a reference surface 17a, a measuring light 22 is reflected on a surface 1a to be tested, and then both lights 21 and 22 are synthesized by a light flux synthesizing means 4. An interference fringe image generating from the synthesized light is used to measure the shape of the surface 1a to be tested. In a transmittant interferometer, a single-mode laser light enters a reference plate 2, and a reference light reflecting on the reference surface 2a and a measuring light reciprocating between the reference surface 2a and a reference reflecting surface 37a are synthesized on this surface. An interference fringe image generating from the synthesized light is used to measure the transmitting surface of a test object 1. The surface 1a is arranged nearly parallel to the reference surface 17a and is arranged inclined by a specified quantity to the reference surface 2a and reference reflecting surface 37a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interferometer apparatus for performing measurement using interference fringes generated by optical interference between reference light and measurement light, and more particularly, to a test surface having relatively large irregularities. The present invention relates to an interferometer apparatus in which a grazing incidence interferometer for measuring the surface shape of a transparent object and a transmission interferometer for measuring the thickness unevenness and refractive index distribution of a transparent object are integrated.

[0002]

2. Description of the Related Art Conventionally, an oblique incidence interferometer for measuring an uneven shape of a surface of a parallel flat glass as an object, for example, as an interference fringe measurement which is thin and has a certain degree of parallelism but a large deflection. And transmission wavefront measurement by a transmission interferometer for measuring thickness unevenness and the like.

The oblique incidence interferometer allows measurement light to be obliquely incident on the surface to be measured, thereby lowering the measurement sensitivity, thereby enabling the measurement of the surface shape of the surface to be measured having relatively large irregularities. Various types of such oblique incidence interferometers are known, and the one shown in FIG. 3 is an example disclosed in Japanese Patent Publication No. 6-17787.

In this oblique incidence interferometer apparatus, as shown in FIG. 3, half mirrors 53 and 54 and a mirror 58 are respectively arranged substantially perpendicular to a surface 56a to be inspected, and a mirror 5 is provided.
Reference numeral 7 denotes a device disposed orthogonally to the optical path of the reflected light (reference light) 61 of the projection light 60 by the half mirror 53. In this device, the projection light 60 from the light source 50 converted into a parallel light beam by the collimator lens 55
As a result, the light passes through the half mirror 53 and is
Is split into a measurement light 62 obliquely incident on the mirror and a reference light 61 reflected by the half mirror 53 toward the mirror 57. Then, the measuring beam 62 is reflected by the mirror 58 after being reflected by the surface 56a to be measured, and goes to the half mirror 54. On the other hand, a part of the reference beam 61 reflected by the mirror 57 functioning as a reference plate is half The light passes through the mirror 53 and goes to the half mirror 54. The half mirror 54 combines the measurement light 62 reflected by the mirror 58 and the reference light 61 reflected by the mirror 57 and transmitted through the half mirror 53 on the half mirror surface.

In this device, even when the light source 50 is a low coherence light source having a short coherence distance, the light is emitted from the collimator lens 55, divided by the half mirror 53, and thereafter passed through the mirror 57 to the half mirror 54. Reference light 6
1 is set to be equal to the optical path length of the measuring light 62 which is emitted from the collimator lens 55 and is divided by the half mirror 53 and thereafter reaches the half mirror 54 via the test surface 56a and the mirror 58. As a result, the reference light 61 and the measurement light 62 synthesized by the half mirror 54 interfere with each other. As shown in the figure, a compensating plate 52 for compensating for the influence of dispersion due to the presence of the half mirror may be inserted in the optical path of the measurement light 62 from the half mirror 53 via the test surface 56a to the half mirror 54. desirable. By projecting the interference fringes formed by the light interference on the screen 51, the observer measures the shape of the test surface 56a.

Various types of transmission interferometers are known, and FIG. 4 shows a schematic configuration of a Fizeau interferometer as an example. That is,
The laser light output from the light source 70 composed of a laser light source passes through the objective lens 71 and the pinhole plate 72 to be a divergent light beam, and enters the half prism 79. A part of the light is reflected in the right angle direction by the half prism 79, is converted into a parallel light flux by the collimator lens 75, and is incident on the reference plate 76. A part of the laser light incident on the reference plate 76 is transmitted in the direction of the subject 73, but the remaining part is
Is reflected by the reference surface 76a, which is the surface on the subject side, and is used as reference light.

The laser beam transmitted through the reference plate 76 in the direction of the subject 73 is transmitted through the flat subject 73, and the reference reflection surface 77.
The light is reflected by a, passes through the subject 73 again, is returned to the reference surface 76a as object light, and passes through the reference surface 76a. Both the reference surface 76a and the reference reflection surface 77a have high-precision planarity and are parallel to each other. The front and back surfaces of the subject 73 are the reference surface 76a and the reference reflection surface 7a.
7a is arranged substantially in parallel.

In this manner, on the reference surface 76a, optical interference occurs due to the wavefront of the reference light reflected by the surface and the wavefront of the object light returned to the surface. The return light of the laser light is applied to the half prism 79 via the collimator lens 75. In the half prism 79, a part of the return light is transmitted and emitted toward the observation optical system, and an interference fringe image is projected on an interference fringe projection surface (not shown). The interference fringe image obtained by the light interference is generated in accordance with the thickness unevenness of the subject 73 and the stress distortion inside the subject 73 depending on the material of the subject 73. 73 can be performed.

[0009]

However, these grazing incidence interferometers and transmission interferometers are generally large and expensive, and require a separate device for surface profile measurement and transmitted wavefront measurement. In order to save space and reduce cost, there is a demand for a device that can perform both measurements with one device. It is preferable that these two measurements can be easily switched, and it is desirable that the device be capable of simultaneously performing these two measurements once the subject is adjusted to a predetermined position.

The present invention has been made in view of such circumstances, and is an apparatus capable of measuring the surface shape and transmitted wavefront of an object, and an interferometer apparatus capable of simultaneously performing these two measurements. The purpose is to provide.

[0011]

The interferometer device of the present invention comprises:
Oblique incidence measurement light that is emitted from the oblique incidence measurement light source and becomes parallel light by the oblique incidence measurement collimator lens, and that is a part of this parallel light and is obliquely incident on the test surface of the subject,
The oblique-incidence measurement reference light composed of a part of the parallel light and reflected by the reference surface is combined and interfered with each other, and the generated interference fringes are formed by the oblique-incidence measurement interference fringe observation means. The grazing incidence interferometer and the coherent outgoing light from the transmission-type measurement light source are made into parallel light by the transmission-type measurement collimator lens, and the object is inserted between the reference plate and the reference reflection plate. Reciprocating, the transmission-type measurement light transmitted through the subject and reflected on the reflection surface of the reference reflection plate and returned to the reference surface of the reference plate, and the transmission-type measurement reference light reflected from the reference surface And a transmission type interferometer configured to form the generated interference fringes on a transmission type interference fringe observation unit, wherein the interferometer device comprises: And the axis of the transmission type measurement light beam are not parallel to each other. It is characterized in that configured.

In the oblique incidence interferometer, the oblique incidence measurement light and the oblique incidence measurement reference light are split into the two beams by a beam splitting unit including a half mirror, and the two beams are split by a beam combining unit including a half mirror. May be combined.

In the oblique incidence interferometer, a low coherence light source having a short coherence distance is used as the oblique incidence measurement light source, and the oblique incidence measurement reference light and the oblique incidence measurement light are used. After the light is emitted from the collimator lens, the optical path length difference between the light beam splitting means and the light beam synthesizing means being combined by the light beam combining means is different from the oblique incidence measurement reference light and the oblique incidence measurement light. It is preferable that the distance is set within a range that causes interference.

Means for arranging the reflection surface of the reference reflection plate at the position of the test surface in a state where the test object is not disposed, and recording the reference interference fringe information on the reflection surface obtained at this time as correction information Recording means, and the reference interference fringe information recorded in the recording means is subtracted from the interference fringe information of the subject obtained in a state where the subject and the reference reflector are arranged at the regular measurement positions. It is more preferable to have an operation means for performing the operation.

In this specification, the “axis of the light beam” is
It means the central axis of the light beam.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings of an interferometer apparatus according to a first embodiment described later as a representative. FIG. 1 is a schematic diagram illustrating a configuration of the interferometer apparatus according to the first embodiment. This apparatus is an interferometer apparatus in which a grazing incidence interferometer for measuring the surface shape of a subject and a transmission interferometer for measuring a transmitted wavefront of the subject are integrated. Will be described in order.

First, a configuration for measuring the surface shape of a subject in this embodiment will be described. The divergent ray bundle emitted from the oblique incidence measurement light source unit 10 having the coherent light source is converted into a parallel ray bundle by the collimator lens 15 and is incident on the light beam splitting unit 3 to be converted into the reference light 21 and the measurement light 22. Divided. For example, as shown in FIG. 1, on a half mirror surface formed on the surface of the light beam splitting means 3 on which the parallel light beam enters, a part of the parallel light beam is reflected by this surface to become the measurement light 22. The remaining parallel light beam passes through this surface and becomes reference light 21.

The parallel light beam split as the reference light 21 is applied to the reference surface 17a of the reference plate 17. The reference surface 17a is a surface with extremely high planar accuracy, and reflects the irradiated reference light 21 toward the light beam combining means 4.
On the other hand, the parallel light beam split as the measurement light 22 is obliquely incident on the uneven surface 1a of the test object 1 and is reflected by the test surface 1a so that the measurement light 2 carrying the test surface information.
It is set to 2. Note that the subject 1 has a reference surface 17
It is arranged so as to be substantially parallel to a. A part of the measurement light 22 reflected by the test surface 1 a is reflected toward the light beam combining means 4 and is combined with the reference light 21 in the light beam combining means 4. For example, as shown in FIG. 1, on a half mirror surface formed on the surface of the light beam combining means 4 on the reference plate side, the reference light 21 is reflected on this surface and the measurement light 22 is transmitted through this surface. Light is synthesized. Both lights are CC
It is configured such that a part thereof overlaps on the D light receiving surface.

Since the oblique incidence interferometer uses a coherent light source, the combined light causes optical interference. The synthesized light carrying the interference fringe information is converged by the imaging lens 16 and reaches the CCD light receiving surface of the oblique incidence measurement imaging unit.
The image is superimposed on the image of the test surface 1a formed on the CD light receiving surface by the imaging lens 16. The interference fringe image formed on the light receiving surface of the CCD is converted into a video signal and displayed on a monitor (not shown), whereby the surface 1a of the subject 1
Is to be measured.

Next, a configuration for measuring the transmitted wavefront of the subject in this embodiment will be described. The divergent light beam emitted from the transmission type measurement head 33 having the coherent light source is converted into a parallel light beam by the collimator lens 35, the direction is changed by the mirror 32, and is incident on the reference plate 2. A part of the parallel light beam incident on the reference plate 2 is transmitted in the direction of the subject to be used as a transmission type measurement light, and the remaining portion is a reference surface 2 which is a surface of the reference plate 2 on the subject side.
The light is reflected by a and becomes the transmission-type reference light for measurement.

The transmission type measurement light transmitted through the reference plate 2 in the direction of the subject passes through the flat subject 1, is reflected by the reference reflecting surface 37 a of the reference reflecting plate 37, passes through the subject 1 again, and passes through the reference 1. The light is returned to the reference surface 2a of the plate 2 and passes through the reference surface 2a. The reference surface 2a of the reference plate 2 and the reference reflection surface 37a of the reference reflection plate 37 both have high-precision planarity and are parallel to each other. Also, as will be described later, the subject 1
Are arranged such that the test surface 1a is inclined by a predetermined amount with respect to the reference surface 2a.

Here, since this transmission interferometer uses a coherent light source, the wavefront of the transmission-type reference light reflected by the reference surface 2a and the wavefront of the reference plate 2 and the reference reflection plate 37 are separated. Optical interference occurs due to the wavefront of the transmission-type measurement light that has been reciprocated between, ie, transmitted through the subject 1 and reflected on the reference reflection surface 37a and returned to the reference surface 2a of the reference plate 2. These return lights are collimated by a collimator lens 35 functioning as an imaging lens.
Thus, interference fringes due to these return lights are imaged on the CCD light receiving surface provided in the transmission type measurement head 33. The interference wave pattern formed on the light receiving surface of the CCD is converted into a video signal and projected on a monitor (not shown), so that the transmitted wavefront of the subject 1 is measured. The interference fringe image obtained in this manner is, when the subject 1 is thin and has a certain degree of parallelism but has a large deflection, for example, in the case of a parallel plane glass, it mainly occurs in accordance with the thickness unevenness. It is. By measuring this data, the transmitted wavefront of the subject 1 can be measured.

As described above, the interferometer device of the present embodiment is configured such that the surface shape of the subject 1 (the
a) and the transmitted wavefront of the subject 1 can be measured. Further, the interferometer device is set such that the normal line of the surface 1a to be measured and the axis of the transmission type measurement light beam are not parallel to each other. In other words, the transmission interferometer is arranged such that the axis of the transmission measurement light beam is inclined by a predetermined amount with respect to the normal line of the surface 1a to be measured, whereby the surface 1a to be measured is reflected by the reference surface 2a and the reference reflection. That is, it is inclined by a predetermined amount with respect to the surface 37a.

Here, in the transmitted wavefront measurement, the test surface 1a
Will be described with respect to the reference surface 2a and the reference reflection surface 37a. In the transmitted wavefront measurement, as described above, the reference surface 2a and the reference reflection surface 37a are parallel to each other, and the wavefront of the transmission-type reference light reflected by the reference surface 2a, the reference surface 2a, and the subject 1 And the interference fringe image generated by the wavefront of the transmission type measurement light reflected by the reference reflecting surface 37a and returned to the reference surface 2a. Therefore, if the test surface 1a is arranged in parallel with these surfaces, the light reflected on the test surface 1a may also return to the CCD light receiving surface, and when the test object 1 is a parallel flat glass, The measurement of the thickness unevenness of the subject 1 causes noise. Further, when the test object 1 is a plane-parallel glass, if the test surface 1a is arranged in parallel with these surfaces, the surface of the test object 1 opposite to the test surface 1a (hereinafter, this surface is referred to as The reflected light on the back side may return to the CCD light receiving surface and become noise.

Therefore, by measuring the transmitted wavefront, the object 1
When measuring the thickness unevenness of the specimen 1a or the specimen 1
To the extent that the reflected light from the back of the
It is preferable that the test surface 1a is arranged to be inclined with respect to the reference surface 2a and the reference reflection surface 37a.

According to the present embodiment, the normal line of the surface 1a to be measured and the axis of the transmission type measurement light beam are set so as to be non-parallel to each other. When performing the measurement, there is no need to move the position of the subject 1 or tilt the test surface 1a, and the two measurements can be easily switched. Further, when performing both measurements, it is not necessary to retreat a member disposed at a position blocking each optical path or insert a necessary member. Therefore, once the subject 1 is adjusted to a predetermined position, the surface shape measurement is performed. And the transmitted wavefront measurement can be performed simultaneously.

In the interferometer apparatus according to the present embodiment, when the oblique incidence measurement light source is a coherent light source as described above, the oblique incidence interferometer is located at the position where each member for the oblique incidence interferometer is disposed. There are not so many restrictions and the degree of freedom in design is high. However, in the interferometer device of the present embodiment, it is more preferable to use a low coherence light source having a short coherence distance as the light source for oblique incidence measurement. However, in this case, due to such light source characteristics, the oblique incidence measurement reference light 21 and the oblique incidence measurement light 22
After both lights are emitted from the collimator lens 15,
The difference in the optical path lengths from the splitting by the light beam splitting means 3 until the light beam combining means 4 combines them is set so that the oblique incidence measurement reference light 21 and the oblique incidence measurement light 22 interfere with each other. Must be configured. That is, it is more preferable that the optical path lengths of the two lights be substantially equal to each other.

The oblique incidence interferometer shown in FIG. 1 has a configuration in which the optical path lengths of both lights from the collimator lens 15 to the light beam splitting means 3 are equal. In such a case, it suffices that the optical path lengths of the two light beams after the division by the light beam dividing means 3 until the light beams are combined by the light beam combining means 4 become substantially equal to each other.

Such a configuration using a low-coherence light source having a short coherence distance can be used, for example, when the subject 1 is a thin parallel flat glass, and transmits through the subject surface 1a in oblique incidence measurement. Even the light reflected on the back surface of the surface 1a is the reference light 21.
This has the effect of preventing the interference fringe image on the test surface 1a from becoming noise. That is, when a low coherence light source having a short coherence distance is used, an interference fringe image occurs only when the optical path lengths are substantially equal. The optical path length is different from that of the measurement light 22 reflected by the test surface 1a, and it is difficult for the measurement light 22 to interfere with each other. Thus, the shape of the test surface can be measured without interference fringe noise from the back surface. In the present embodiment, even if a low coherence light source having a short coherence distance is used, the degree of freedom in designing the grazing incidence interferometer is high, so that the optical path length between the grazing incidence measurement reference light 21 and the grazing incidence measurement light 22 is reduced. The configuration is easy to make equal.

As such a low coherence light source, it is preferable to use, for example, a light emitting diode or a laser having a single transverse mode and a multimode longitudinal mode. However, other examples of the low coherence light source include, for example, natural light and a fluorescent lamp, and this does not prevent the use of these light sources.

Further, in the interferometer of the present embodiment,
By configuring the measurement light 22 obliquely incident on the test surface 1a to be an S-polarized light beam with respect to the test surface 1a,
The amount of light reflected on the test surface 1a is increased, and accordingly, the amount of light reaching the back surface of the subject 1 is suppressed. As a result, interference fringe noise from the back surface of the subject 1 is further reduced, and an interference fringe image with good contrast is obtained. And the measurement accuracy can be improved.

As described above, this embodiment uses a low coherence light source having a short coherence distance,
Is emitted from the collimator lens 15 and thereafter the light beam splitting means 3
It is desirable that the optical path lengths of the reference light 21 and the measurement light 22 be substantially equal to each other until the light is synthesized by the light beam synthesizing means 4 through the division in. Is less likely to cause interference.
However, even if the reflected light from the rear surface does not cause interference fringe noise on the CCD light receiving surface, it will enter the CCD light receiving surface together with the combined light of the reference light 21 and the measurement light 22. May deteriorate the contrast.

In the oblique incidence interferometer having a large incident angle on the surface 1a to be inspected as in this embodiment, the S-polarized light is easily reflected and the transmittance on the surface 1a is low. Therefore,
When the S-polarized light beam enters the surface 1a, the surface 1a
And a small amount of light that is transmitted to the rear surface and reflected from the rear surface and transmitted through the test surface 1a toward the CCD light receiving surface.
As a result, the influence of the reflected light from the back surface on the interference fringe image is reduced.

As described above, as a method for converting the measurement light 22 obliquely incident on the surface 1a to be detected into an S-polarized light beam with respect to the surface 1a, for example, a straight line having a single transverse mode and a multimode longitudinal mode is used. A light source such as a polarized laser may be used to emit a light beam having a predetermined polarization direction from the light source unit 10, or a circularly polarized laser or a light emitting diode having a single transverse mode and a multimode longitudinal mode may be used. It is possible to use a polarizing plate that transmits only a predetermined polarization component in the optical path from the light source unit 10 to the surface to be measured 1a.

Further, the interferometer apparatus of the present embodiment operates with the reference reflection surface 3 of the reference reflection plate 37 in a state where the subject 1 is not disposed.
Means for arranging the reference 7a at the position of the test surface, recording means for recording the reference interference fringe information on the reference reflection surface 37a obtained at this time as correction information, and It is preferable to include a calculating means for subtracting the reference interference fringe information recorded in the recording means from the interference fringe information on the subject 1 and the test surface 1a obtained in the state of being arranged at the position.

By providing these means, the systematic error of the oblique incidence interferometer or transmission interferometer of the present embodiment is measured in advance and recorded as correction information, and the object 1 is actually arranged and measured. The interference fringe information can be corrected based on this correction information. For example, the systematic error means that the light beam is divided into the light beam splitting unit 3 and the light beam combining unit 4.
There is an error that occurs when light is transmitted, and an error that occurs when light is reflected by a mirror or the like. Since the reference interference fringe information generated due to such an error is also superimposed on the interference fringe information actually measured by arranging the subject 1, this reference interference fringe information is measured and recorded in advance. Subject 1 actually
By disposing the reference interference fringe information from the interference fringe information obtained by arranging the reference interference fringe at a regular measurement position, a highly accurate measurement value can be obtained.

According to the present embodiment, there is no need to use a dedicated member to measure such a systematic error in advance, and the reference reflection surface 3 is set in a state where the subject 1 is not arranged.
The reference reflection surface 37 is provided by means for arranging the reference reflection surface
Since a can be arranged at the position of the surface to be inspected, such an error can be measured with a simple configuration. Further, by using a computer as the recording means and the arithmetic means, quick and accurate processing becomes possible.

Further, in the interferometer of the present embodiment,
When measuring interference fringes, a fringe scanning method (phase shift method) using a computer or the like may be performed to perform phase analysis processing. For example, in the transmission type measurement, the reference plate 2 and the reference reflection plate 37 are moved by a very small amount in the optical axis direction of the transmission type measurement using a piezo actuator, so that the optical path length difference between the reference light and the measurement light is changed to change the phase. Scanning can be performed. In oblique incidence measurement, phase scanning can be performed by moving the reference plate 17 by a small amount in a direction orthogonal to the reference surface 17a.

Further, it is possible to control the position and the inclination using a piezo actuator. For example, interference fringes measured by a grazing incidence interferometer and a transmission interferometer are imaged on a CCD light receiving surface of an imaging camera, and input to a computer equipped with a CPU and an image processing memory via an image input board. The input / output interference fringe image data is subjected to various arithmetic processing to determine the amount of excess or deficiency displacement of the piezo actuator. It is instructed to transmit a drive signal, whereby the reference plate 17, the reference plate 2, or the reference reflection plate 37 held by the piezo actuator can be configured to move by a predetermined minute amount.

[0040]

Embodiments of the present invention will be described below.
In each embodiment, the same members are denoted by the same reference numerals. <Embodiment 1> FIG. 1 shows an interferometer apparatus according to this embodiment.
As described above, this interferometer apparatus is an apparatus in which the oblique incidence interferometer and the transmission interferometer are integrated, and the normal line of the test surface 1a and the axis of the transmission measurement light beam are not parallel to each other. Is set to Therefore, once the subject 1 is adjusted to a predetermined position, the surface shape measurement and the transmitted wavefront measurement can be easily switched and performed, and both measurements can be performed simultaneously.

The oblique incidence measurement light source unit 10 of this embodiment includes a laser light source having a single horizontal mode and a multimode vertical mode, and the transmission type measurement head 33 includes a single mode laser light source. In the oblique incidence interferometer of the present embodiment, the oblique incidence measurement reference light 21 and the oblique incidence measurement light 22 are emitted from the collimator lens 15 and split by the light beam splitting means 3 and thereafter synthesized by the light beam synthesizing means 4. The oblique incidence measurement reference light 21 and the oblique incidence measurement light 22 are configured such that the optical path lengths thereof are substantially equal to each other until the oblique incidence measurement light source 10 has a short coherence distance. Even if the light source is a coherent light source, the reference light 21 and the measurement light 22 may cause interference.

In this embodiment, as shown, the light beam splitting means 3 is a half mirror having a half mirror surface on the light source side, and the light beam combining means 4 is a half mirror having a half mirror surface on the reference plate 17 side. It has been.
Further, as the oblique incidence interferometer, the half mirror of the light beam splitting means 3, the surface to be inspected 1a, the half mirror of the light beam synthesizing means 4 and the reference plate 17 are disposed so as to be substantially parallel to each other. Oblique incidence measurement light can be incident at a relatively large angle of incidence.

Since the present embodiment has such a configuration, as shown, the light beam splitting means 3, the subject 1, the light beam synthesizing means 4, and the reference plate 17 are arranged in a so-called rhombic pantograph shape. I have. Therefore, by making each member movable in accordance with the expansion and contraction of the distance between the reference plate 17 and the test surface 1a related to the pantograph, the incidence of the oblique incidence measurement light 22 obliquely incident on the test surface 1a is achieved. By changing the angle, it is possible to change the sensitivity of the oblique incidence measurement on the test surface 1a. By moving each member without breaking the pantograph relationship, even when the sensitivity of oblique incidence measurement is changed, the relative relationship between the members is stabilized, and the alignment adjustment becomes easy.

As described above, in this embodiment as well, the measuring light 22 obliquely incident on the surface 1a to be measured is configured to be an S-polarized light beam with respect to the surface 1a, The error can be measured and recorded as correction information, and the interference fringe information actually measured with the subject 1 arranged can be corrected based on this correction information. Further, the reference plate 2 and the reference reflection plate 37 are moved by a very small amount in the optical axis direction of the transmission type measurement by using a piezo actuator, and the reference plate 17 is moved to the reference surface 1.
The phase scanning may be performed by moving by a small amount in a direction orthogonal to 7a.

<Embodiment 2> FIG. 2 shows an interferometer apparatus according to this embodiment. As described above, this interferometer apparatus is an apparatus in which the oblique incidence interferometer and the transmission interferometer are integrated, and the normal line of the test surface 1a and the axis of the transmission measurement light beam are not parallel to each other. Is set to Therefore, once the subject 1 is adjusted to a predetermined position, the surface shape measurement and the transmitted wavefront measurement can be easily switched and performed, and both measurements can be performed simultaneously. As described above, the test surface 1a is arranged so as to be inclined by a predetermined amount with respect to the reference surface 2a and the reference reflection surface 37a having high precision flatness. The angle between the axis of the pattern measuring light beam and the axis is small and not so large as is clearly shown in the figure.

Hereinafter, points of the interferometer apparatus according to the present embodiment that are different from those of the first embodiment will be described, and description of the same points as those of the first embodiment will be omitted. First, a configuration of the interferometer apparatus according to the present embodiment for measuring the surface shape of the subject will be described.

The divergent light beam emitted from the oblique incidence measurement light source unit 10 having a laser light source having a single transverse mode and a multimode longitudinal mode has its direction changed by the half prism 19 and is collimated by the collimator lens 15. The light beam is made into a light beam, and thereafter enters the light beam splitting / combining means 5. This beam splitting / combining means 5 is composed of a single plate-shaped member.
As will be described later, the collimated light is split into a reference light 21a and a measuring light 22a (22aC and 22aCC are collectively referred to as 22a), and the reference light 21b and the measuring light 22b.
(A light flux related to the generation of interference fringes among 22bC or 22bCC is referred to as 22b). Here, the reference light 21b is a light beam returned by the reference light 21a being reflected by the reference surface 17a, and the measurement light 22b is transmitted by the measurement light 22a via the surface to be measured 1a and the plane reflection mirror 18 to the light source unit 10. This is a light beam that has been sent backward with an optical axis substantially coincident with the optical axis from the light source.

The parallel light beam incident on the light beam splitting / combining means 5 is converted into a light beam splitting / combining surface 5a on which a half mirror surface is formed.
And a part of the transmitted light is used as the reference light 21a and the reflected light is used as the measurement light 22a. That is, of the measurement light 22a reflected by the light beam splitting / combining means 5, the light beam 22a reflected by the clockwise splitting portion 6 of the light beam splitting / combining surface 5a
C is reflected by the plane reflection mirror 18, is obliquely incident on the test surface 1a of the test object 1, is reflected and becomes the measurement light 22bC carrying information on the test surface 1a, and turns the light beam splitting / combining surface 5 clockwise.
It returns to the counterclockwise division part 7 of a. On the other hand, of the measurement light 22a reflected by the light beam splitting / combining means 5, the light beam 22aC reflected by the counterclockwise splitting portion 7 of the light beam splitting / combining surface 5a
C indicates the light path of the light beams 22bC and 22aC as the light beam 2
The light beam is fed back as 2aCC and 22bCC, and returns counterclockwise to the clockwise division portion 6 of the light beam division / combination surface 5a.

The light beam 21a transmitted through the counterclockwise division portion 7 of the parallel light beam transmitted through the light beam splitting / combining surface 5a is transmitted via the compensating plate 12 to the reference surface 17 of the reference plate 17.
a. The reference surface 17a is a reflection surface with high planar accuracy, and irradiates the irradiated reference light 21a with the reference light 2
1b, the light beam splitting / combining surface 5 of the light beam splitting / combining means 5
The light is reflected toward the counterclockwise division part 7 of FIG. As for the light beam transmitted through the clockwise division portion 6, the compensating plate 12 and the reference plate 16 are not arranged on the optical path as shown in the figure, and the light beam
Since it does not return to the clockwise division 6 in FIG. 7A and does not contribute to the generation of interference fringes, the description is omitted.

As a result, on the light beam splitting / combining surface 5a of the light beam splitting / combining means 5, the counterclockwise splitting portion 7
, The reference light 21b and the measuring light 22bC are combined. Note that the measurement light 22bCC that has returned to the clockwise division portion 6 is not combined with the reference light because the reference light flux does not return, and is not involved in the generation of interference fringes. .

The plane reflecting mirror 18 is arranged before the position where the measurement light 22aC is obliquely incident on the surface 1a to be measured, and has a high flatness for totally reflecting the measurement light 22aC. By the action of the plane reflection mirror 18, the measuring light 22aC is obliquely incident on the surface 1a to be measured,
The light 2bC is guided to the counterclockwise division portion 7 of the light beam division / combination means 5 and the reference light 21b and the measurement light 22bC are combined on the half mirror surface formed at this portion.

In this case, the oblique incidence interferometer uses the reference beam 21
a and 21b (hereinafter, reference light involved in the generation of interference fringes in this embodiment is referred to as reference light 21) and measurement light 22aC,
22bC (hereinafter, measurement light involved in the generation of interference fringes in this embodiment is referred to as measurement light 22), and after both light beams are emitted from the collimator lens 15, the light beam splitting / combining means 5 The optical path length difference until the light beam is combined at 5 is set within a range where the reference light beam 21 and the measurement light beam 22 interfere with each other. Further, since the oblique incidence interferometer uses a low coherence light source having a short coherence distance as a light source, the optical path length difference between the reference light 21 and the measurement light 22 is very small, and the optical path lengths of both lights are substantially equal. It can be said.

That is, assuming a virtual plane orthogonal to the optical axis in the light beam immediately after exiting the collimator lens 15, the optical path length of the measuring light 22 is calculated from this virtual surface by the light beam splitting / combining surface of the light beam splitting / combining means 5. The light is reflected by the clockwise dividing portion 6 of FIG. 5a, is reflected by the plane reflecting mirror 18, obliquely enters the test surface 1a of the subject 1, is reflected and is counterclockwise rotated by the light beam dividing and combining surface 5a of the light beam dividing and combining means 5. This is until returning to the division site 7. On the other hand, the optical path length of the reference light 21 is given by
The light passes through the counterclockwise dividing portion 7 of the light beam dividing / combining surface 5 a of the light beam dividing / combining means 5, passes through the compensating plate 12 and passes through the reference plate 17.
Is reflected by the reference surface 17a of the light beam, passes through the compensator 12 again, and returns to the counterclockwise division portion 7 of the light beam splitting / combining surface 5a of the light beam splitting / synthesizing means 5, so that these optical path lengths are substantially equal. This combined light causes optical interference.

The synthesized light carrying the interference fringe information reaches the CCD light receiving surface 11 through the half prism 19 by the collimator lens 15 and the imaging lens (not shown), and reaches the CCD light receiving surface by the collimator lens 15 and the imaging lens (not shown). 11 is superimposed on the image of the test surface 1 a formed on the image 11. By converting the interference fringe image formed on the CCD light receiving surface 11 into a video signal and projecting the video signal on a monitor (not shown), the shape of the test surface 1a of the test object 1 is measured. ing.

It is preferable that the light beam splitting / combining means 5 has a half mirror surface on the entire surface of the light beam splitting / combining surface 5a in order to reduce costs and facilitate optical adjustment of members. It is also possible to use a half mirror surface only for a range sufficient to transmit a light beam that can cover the inspection surface 1a with a margin as the measurement light 22aC. Further, two half mirrors may be provided on a metal disk provided with an opening for passing a light beam at a predetermined position and a seat for fixing an optical member such that the surfaces thereof are substantially flush with each other. good.

It is more desirable that the clockwise division portion 6 be formed with a total reflection surface instead of a half mirror surface. That is, the reflected light from the total reflection surface is used as the measurement light 22aC and is irradiated on the surface 1a to be measured.
It is desirable that the bC be combined with the reference light 21bCC at the counterclockwise division part 7 where the half mirror surface is formed. By forming the total reflection surface, the light use efficiency is improved and the reference light 2
1b and the measuring light 22bC are combined in a well-balanced
An interference fringe image with good contrast can be obtained on the CD light receiving surface 11. As a means for adjusting the light amounts of the reference light 21 and the measurement light 22 in this way, a filter for adjusting the light amount may be arranged in one or both optical paths. As an example, the light amount adjusting filters 14a and 14b are shown by dotted lines.

As described above, also in this oblique incidence interferometer, the measuring beam 22aC obliquely incident on the surface 1a to be measured is used.
However, it is preferable that the light beam is S-polarized light with respect to the test surface 1a. In this embodiment, the polarizing plate 13 is indicated by a dotted line as a method thereof.

The oblique incidence interferometer has a reference beam 21
A compensating plate 12 of the same material and the same thickness as the light beam splitting / combining means 5 is arranged in the optical path of the reference beam 21. The reference light 21 and the measuring light 22 from the clockwise split portion 6 to the counterclockwise split portion 7 are both emitted twice. Each is configured to transmit through this material. As a result, the color fringing of the interference fringe image is reduced, the deterioration of contrast can be prevented, and the measurement accuracy is improved. However, such a compensating plate 12 is not essential in the grazing incidence interferometer of the apparatus of the present invention, and is not necessarily arranged only in the optical path of the reference light 21.

As shown, the present embodiment is configured such that the reference plate 17 is moved by a small amount along the axis of the light beam of the reference light 21 by the piezo actuator 41 in order to perform phase scanning for oblique incidence measurement. ing.

Next, the configuration of the interferometer device according to the present embodiment for measuring the transmitted wavefront of the subject will be described. The divergent light beam emitted from the transmission type light source unit 30 having the single mode laser light source is changed in direction by the half prism 39, converted into a parallel light beam by the collimator lens 35, and enters the reference plate 2. A part of the parallel light beam incident on the reference plate 2 is transmitted in the direction of the subject to be used as the transmission type measurement light, and the remaining portion is used as the reference plate 2.
Is reflected by the reference surface 2a, which is the surface on the subject side, and is used as the reference light for transmission measurement.

Thereafter, also in the transmission interferometer of the present embodiment, similarly to the first embodiment, the wavefront of the transmission-type reference light reflected by the reference surface 2a and the reference reflection surface transmitted by the subject 1 are transmitted. 3
Optical interference occurs due to the wavefront of the transmission-type measurement light reflected by 7a and returned to the reference surface 2a of the reference plate 2. These return lights are converged by the collimator lens 35 functioning as an imaging lens and are irradiated on the half prism 39. In the half prism 39, a part of the return light is transmitted, and interference fringes due to the return light are imaged on the CCD light receiving surface 31. The interference fringe image formed on the CCD light receiving surface 31 is converted into a video signal and projected on a monitor (not shown), so that the transmitted wavefront of the subject 1 is measured.

As shown in the figure, the present embodiment is configured so that the reference plate 2 is moved by a small amount along the optical axis of the transmission type measurement by the piezo actuator 40 in order to perform the phase scanning of the transmission type measurement. I have.

In any of the interferometers of this embodiment, a systematic error is measured in advance and recorded as correction information, and interference fringe information actually measured with the subject 1 placed is based on this correction information. It is possible to make a configuration so that the correction can be performed.

Incidentally, the interferometer device according to the present invention is not limited to the above-described embodiment, and various modifications can be made. For example, the members used as the light beam dividing means and the light beam combining means can be appropriately selected. As an example, in an interferometer device having a configuration substantially the same as that of the first embodiment, a diffraction grating may be provided instead of a half mirror as a light beam dividing unit and a light beam combining unit. When a diffraction grating is used, it is desirable that the + 1st-order diffraction light and the -1st-order diffraction light by the diffraction grating of the light beam splitting means 3 be used as reference light and measurement light, and that a light source and an imaging unit for oblique incidence measurement be appropriately arranged.

Further, in the embodiment of the present invention, each member can be appropriately arranged according to a desired incident angle of the measuring light to the surface to be measured. Further, it is possible to insert a mirror for changing the optical path in any optical path.

[0066]

As described above, according to the interferometer apparatus of the present invention, the normal line of the surface to be inspected and the axis of the transmission type measurement light beam are set so as to be non-parallel to each other. It is possible to obtain an interferometer device that can perform the surface shape measurement and the transmitted wavefront measurement of the sample, and can simultaneously perform these two measurements.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an interferometer apparatus according to a first embodiment.

FIG. 2 is a schematic configuration diagram of an interferometer apparatus according to a second embodiment.

FIG. 3 is a schematic configuration diagram of a conventional grazing incidence interferometer apparatus.

FIG. 4 is a schematic configuration diagram of a conventional transmission interferometer apparatus.

[Explanation of symbols]

1, 73 subject 1a, 56a test surface 2, 76 reference plate 2a, 76a reference surface 3 light beam splitting device 4 light beam synthesizing device 5 light beam splitting / combining device 5a light beam splitting / combining surface 6 clockwise splitting portion 7 counterclockwise splitting portion 10, 50 Light source for oblique incidence measurement 11 CCD light receiving surface for oblique incidence measurement 12, 52 Compensator 13 Polarizer 14a, 14b Light amount adjustment filter 15, 35, 55, 75 Collimator lens 16 Imaging lens 17 Reference plate 17a Reference surface 18 Plane reflection mirror 19, 39, 79 Half prism 21, 21a, 21b, 61 Reference light 22, 22a, 22b, 62 Measurement light 22aC, 22bC Measurement light 22aCC, 22bCC via clockwise division part Counterclockwise division part Measurement light passing through 30, 70 Light source for transmission type measurement 31 CCD light receiving surface for transmission type measurement 32, 7,58 mirror 33 transmissive measuring head 37 reference reflection plate 37a, 77a reference reflecting surface 40 and 41 piezoelectric actuator 51 screen 53, 54 a half mirror 60 projection light 71 objective lens 72 Pin hole plate

Continued on the front page F-term (reference) 2F064 AA09 FF03 GG12 GG22 GG32 GG59 GG70 HH03 2F065 AA54 FF51 GG07 HH12 JJ03 JJ08 JJ26 LL12 LL30 LL46 LL57 2G059 AA02 AA05 BB08 EE01 GG01 JJ01 GG02 MM01 MM10 PP04

Claims (4)

[Claims] 1. An oblique-incidence measuring light source is converted into parallel light by a grazing-incidence measuring collimator lens, and a part of the parallel light is obliquely incident on a surface to be inspected of a subject. The measurement light and the oblique incidence measurement reference light composed of a part of the parallel light and reflected by the reference surface are combined and caused to interfere with each other, and the generated interference fringes are formed by the oblique incidence measurement interference fringe observation means. The oblique incidence interferometer configured as described above, the collimated outgoing light from the transmission type measurement light source is made into parallel light by the transmission type collimator lens, and the reference object and the reference reflection plate into which the subject is inserted. And a transmission-type measurement light transmitted through the subject, reflected on the reflection surface of the reference reflection plate, and returned to the reference surface of the reference plate, and a transmission-type measurement light reflected from the reference surface. The reference interference light is combined with each other to cause interference with each other, and the generated interference fringes are transmitted through. A transmission interferometer configured to be formed in a pattern measurement interference fringe observation unit, wherein the normal line of the surface to be measured and the axis of the transmission measurement beam are mutually An interferometer device configured to be non-parallel. 2. The oblique incidence interferometer, wherein the oblique incidence measurement light and the oblique incidence measurement reference light are split into the two beams by a beam splitting unit including a half mirror, and are split by a beam combining unit including a half mirror. 2. The interferometer device according to claim 1, wherein the two light beams are combined. 3. The oblique incidence interferometer, wherein a low coherence light source having a short coherence distance is used as the oblique incidence measurement light source, and the oblique incidence measurement reference light and the oblique incidence measurement light are
After the two light beams are emitted from the collimator lens, the optical path length difference until the light beam splitting device is combined by the light beam combining device through the splitting unit is the oblique incidence measurement reference light and the oblique incidence measurement light. 3. The interferometer apparatus according to claim 1, wherein the interferometers are set within a range where interference occurs with each other. 4. A means for arranging the reflection surface of the reference reflection plate at a position of a test surface in a state where the test object is not disposed;
Recording means for recording the reference interference fringe information on the reflection surface obtained at this time as correction information, and the subject and the reference reflector obtained at a state where the reference reflector is disposed at a regular measurement position. The interferometer apparatus according to any one of claims 1 to 3, further comprising a calculating unit for subtracting the reference interference fringe information recorded in the recording unit from the interference fringe information.