JP2014167414A - Object surface inspection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an object surface inspection device using an interferometer that improves visibility even when a low reflectance object is placed on a test surface, and can generates sufficient interference fringes.SOLUTION: A polarization interferometer causes interference between reference light having light from a predetermined light source reflected on a reference surface and test light having light from the predetermined light source reflected on an inspecting object. The polarization interferometer has: a half-wave plate that controls a polarization branch intensity ratio of first linear polarized light of the light from the predetermined light source and second linear polarized light orthogonal to the first linear polarized light; and polarization separation means for separating the first linear polarized light and the second linear polarized light, which pass through the half-wave plate, by a predetermined angle, and transmitting the separated first linear polarized light and second linear polarized light to the reference surface and the inspecting object.

Description

  The present invention relates to an object surface inspection apparatus.

  A conventional object surface inspection apparatus uses interference fringes, has a reference surface that transmits and reflects laser light emitted from a laser, and the laser light transmitted through the reference surface is a test surface (test object). Surface). Then, interference fringes are formed by the test light in which the reflected light is transmitted again through the reference surface and the reference light that is reflected light on the reference surface. Further, the flatness of the test surface is detected based on the shape of the interference fringes (see, for example, Patent Document 1).

JP 2006-90829 A

  However, in the above-described conventional example, when an ultra-low reflectance object is installed on the test surface, the reference light that is reflected light from the reference surface is relatively high in intensity, but the test light is an ultra-low reflectance object. Since the light is reflected at, the intensity is extremely low. Therefore, since there is too much difference between the intensity of the reference light and the intensity of the test light, visibility (contrast) is extremely low, and sufficient interference fringes cannot be obtained. The ultra-low reflectance is generally said to be a reflectance of about 0.3% or less.

  That is, in an ultra-low reflectivity object surface inspection apparatus using an interferometer, the visibility is E, the reflectivity at the reference surface is A, and the reflectivity of the ultra-low reflectivity object surface (test surface) is B. Then, visibility E = {B / (A + B)} × 100.

  For example, when the reflectance A is 4% and the reflectance B is 0.2%, the visibility E = {B / (A + B)} × 100 = {0.2 / (4 + 0.2)} × 100 = (0.2 / 4.2) × 100≈4.76 (%). On the other hand, if the reflectance B is the same as the reflectance A, the visibility E = {B / (A + B)} × 100 = {4 / (4 + 4)} × 100 = (4/8) × 100≈50 (%) It is.

  That is, if the reflectance B of the test surface is high, the visibility E is 50%, and sufficient interference fringes can be obtained. However, if the reflectance B of the test surface is extremely low, the visibility E is low and sufficient. Interference fringes cannot be obtained.

  That is, in the above-described conventional example, in an object surface inspection apparatus using an interferometer, when an ultra-low reflectance object is installed on the test surface, the intensity of the test light reflected on the test surface is the reflected light reflected on the reference surface. Since it is extremely lower than the intensity of a certain reference light, there is a problem that visibility is extremely low and sufficient interference fringes cannot be obtained.

  The present invention provides an object surface inspection apparatus that can improve visibility and obtain sufficient interference fringes even when an object with low reflectance is installed on a test surface in an object surface inspection apparatus using an interferometer. For the purpose.

  The object surface inspection apparatus of the present invention is a polarization interferometer that causes interference between reference light reflected from a reference surface by light from a predetermined light source and test light reflected from a test object by light from the predetermined light source. A half-wave plate for controlling a polarization branching intensity ratio between the first linearly polarized light and the second linearly polarized light orthogonal to the first linearly polarized light out of the light from the predetermined light source; The first linearly polarized light and the second linearly polarized light that have passed through the wave plate are separated at a predetermined angle, and the separated first linearly polarized light and second linearly polarized light are separated from the reference plane and the object to be inspected. And a polarization separation means for sending to the light source.

  According to the present invention, in an object surface inspection apparatus using an interferometer, when an object with low reflectance is installed on the test surface, the intensity of the reference light reflected by the reference surface and the intensity of the test light reflected by the test surface Therefore, it is possible to improve visibility and obtain sufficient interference fringes.

It is a figure which shows the ultra-low-reflectance object surface inspection apparatus 100 which is Example 1 of this invention. 2 is an explanatory diagram of a half-wave plate 2. FIG. It is a figure which shows the relationship between the rotation angle in the case of rotating the half-wave plate 2, and ratio of polarization splitting intensity. 6 is a chart showing a relationship between a rotation angle of a half-wave plate 2 and a polarization branching ratio. It is a figure explaining operation | movement of the Wollaston prism. It is a figure which shows the ultra-low-reflectance object surface inspection apparatus 100, and is a figure which abbreviate | omits and shows the path | route of the light reflected by the to-be-tested object 6, and abbreviate | omitted the path | route of the light reflected by the reference plane 5. FIG. It is a figure which shows the ultra-low-reflectance object surface inspection apparatus 200 which is Example 2 of this invention.

  The modes for carrying out the invention are the following examples.

  FIG. 1 is a diagram showing an ultra-low reflectivity object surface inspection apparatus 100 that is Embodiment 1 of the present invention.

  The ultra-low reflectivity object surface inspection apparatus 100 includes a laser 1, a half-wave plate 2, a Wollaston prism 3, a beam splitter 4, a reference plane 5, a test object 6, a beam splitter 41, A monitor camera 42, a pinhole 7, a polarizing plate 8, a CCD 9, and interference fringe analysis means 10 are included.

  Laser 1 is an example of a light source. The half-wave plate 2 controls the polarization branching intensity ratio between the horizontal linearly polarized light s and the vertical linearly polarized light p in the light from the laser 1.

  The Wollaston prism 3 separates the horizontal linearly polarized light s that has passed through the half-wave plate 2 and the vertical linearly polarized light p at a predetermined angle.

  The beam splitter 4 reflects and transmits the horizontal linearly polarized light s and the vertical linearly polarized light p that have passed through the Wollaston prism 3.

  The reference plane 5 reflects and transmits the light reflected by the beam splitter 4.

  The test object 6 is installed so as to reflect the light that has passed through the reference plane 5 and the reflected light passes through the reference plane 5. In the embodiment, the test object 6 is an extremely low reflectivity object, and its reflectivity is extremely low, and the reflectivity is 0.3% or less.

  The pinhole 7 allows only the horizontal linearly polarized light s of the light reflected by the reference plane 5 to pass, and allows only the vertical linearly polarized light p of the light reflected by the test object 6 to pass.

  The beam splitter 41 is provided between the beam splitter 4 and the pinhole 7. The monitor camera 42 is installed so as to receive the light reflected by the beam splitter 41. The monitor camera 42 is installed so that the center of the screen of the monitor camera 42 is equivalent to the position of the pinhole 7.

  The polarizing plate 8 is an element that changes the horizontal linearly polarized light and the vertical linearly polarized light in the 45-degree direction, and thereby two lights in the same direction can be generated, thereby causing interference.

  The CCD 9 is an example of an image sensor that receives light that has passed through the pinhole 7.

  The interference fringe analyzing means 10 is a reference light that is a reflected light reflected by the reference surface 5 and a test light that is a light that is transmitted through the reference surface 5, reflected by the test object 6, and then transmitted through the reference surface 5 again. The interference fringe with the spatial carrier obtained by is analyzed.

  FIG. 2 is an explanatory diagram of the half-wave plate 2.

  When the half-wave plate 2 is rotated with respect to the direction of the optical axis of the crystal, the ratio of the intensity of the horizontal linearly polarized light s emitted from the laser 1 to the intensity of the vertical linearly polarized light p is expressed as follows: Change.

  FIG. 3 is a diagram showing the relationship between the rotation angle θ and the ratio of the polarization splitting intensity when the half-wave plate 2 is rotated.

  The ratio of the polarization splitting intensity is the ratio between the intensity of the vertical linearly polarized light p and the intensity of the horizontal linearly polarized light s. In FIG. 3, the solid line indicates the intensity of the horizontal linearly polarized light s, and the broken line indicates the intensity of the vertical linearly polarized light p. When light having an intensity of vertical linearly polarized light p: intensity of horizontal linearly polarized light s = 1: 1 is incident on the half-wave plate 2, if the rotation angle of the half-wave plate 2 is 0 degree, the light is vertical. If the intensity of the linearly polarized light p: the intensity of the horizontal linearly polarized light s = 1: 0 and the rotation angle of the half-wave plate 2 is 22.5 degrees, the intensity of the vertically linearly polarized light p: the intensity of the horizontal linearly polarized light s. = 0.5: 0.5 = 1: 1, and if the rotation angle of the half-wave plate 2 is 45 degrees, the intensity of the vertical linearly polarized light p: the intensity of the horizontal linearly polarized light s = 0: 1. If the rotation angle of the half-wave plate 2 is 67.5 degrees, the intensity of the vertical linearly polarized light p: the intensity of the horizontal linearly polarized light s = 0.5: 0.5 = 1: 1.

  FIG. 4 is a chart showing the relationship between the rotation angle of the half-wave plate 2 and the polarization branching ratio.

  If the rotation angle of the half-wave plate 2 is set to 3 degrees close to 0 degrees, the intensity of the vertical linearly polarized light p: the intensity of the horizontal linearly polarized light s = 1: 0.01 = 100: 1. That is, if only the vertical linearly polarized light p is used as the test light reflected by the object 6 and only the horizontal linearly polarized light s is used as the reference light reflected by the reference plane 5, the reference light that causes interference fringes, With respect to the test light, the intensity of the reference light: the intensity of the test light = 1: 100 can be changed. That is, the intensity of the test light can be 100 times the intensity of the reference light. This can solve the problem that the intensity of the test light is too low when an ultra-low reflectance object surface is used as the reflecting surface.

  FIG. 5 is a diagram for explaining the operation of the Wollaston prism 3.

  The Wollaston prism 3 is a prism in which two identical crystals 31 and 32 having birefringence are joined to each other, and antireflection film coats 33 and 34 are provided on the incident surface and the output surface, respectively, in order to improve transmittance. The whole is covered with a metal frame 35.

  When random polarized light is incident on the incident side of the Wollaston prism 3, the light is separated into horizontal linearly polarized light s and vertical linearly polarized light p at a predetermined separation angle and emitted. That is, random polarized light can be reliably separated into horizontal linearly polarized light s and vertical linearly polarized light p.

  Next, the operation of the ultra-low reflectance object surface inspection apparatus 100 will be described.

  First, the optical path of the reference light will be described. In FIG. 1, the path of the reference light reflected by the reference plane 5 is shown, and the path of the light toward the test object 6 and the reflected test light is omitted.

  The laser 1 emits random polarized light, and this random polarized light is incident on the half-wave plate 2. The ratio of the intensity of the horizontal linearly polarized light s and the intensity of the vertical linearly polarized light p varies depending on the rotation angle of the half-wave plate 2. In Example 1, the rotation angle of the half-wave plate 2 is set to 3 degrees. Therefore, as shown in FIG. 3, the intensity of the horizontal linearly polarized light s is 1, and the intensity of the vertical linearly polarized light p is 100. is there. That is, the intensity of the vertical linearly polarized light p is 100 times the intensity of the horizontal linearly polarized light s.

  When the horizontal linearly polarized light s and the vertical linearly polarized light p, the intensity ratio of which has been changed by the half-wave plate 2, are incident on the Wollaston prism 3, the Wollaston prism 3 receives the incident linearly polarized light (randomly polarized light). ), The horizontal linearly polarized light s and the vertical linearly polarized light p are separated and emitted at a predetermined separation angle. The separated horizontal linearly polarized light s and vertical linearly polarized light p are reflected by the beam splitter 4 and travel toward the reference plane 5. Half of the polarized light toward the reference plane 5 is reflected by the reference plane 5 and the other half is transmitted through the reference plane 5.

  The reference light (horizontal linearly polarized light s, vertical linearly polarized light p) reflected by the reference plane 5 passes through the beam splitter 4 and travels toward the pinhole 7. Here, the pinhole 7 allows only one of the reference light (horizontal linearly polarized light s and vertical linearly polarized light p) to pass therethrough. In the first embodiment, only the horizontal linearly polarized light s passes through the pinhole 7, and the vertical linearly polarized light p hits a portion other than the pinhole 7 and does not pass through the pinhole 7. That is, since the Wollaston prism 3 has a predetermined separation angle between the direction of the horizontal linearly polarized light s and the direction of the vertical linearly polarized light p, the pinhole 7 has one of the horizontal linearly polarized light s and the vertical linearly polarized light p. The position of the pinhole 7 and its diameter are set so as to pass only through the pin.

  Note that whether the horizontal linearly polarized light s or the vertical linearly polarized light p is allowed to pass through the pinhole 7 may be adjusted by the position of the pinhole 7.

  The horizontal linearly polarized light s of the reference light that has passed through the pinhole 7 passes through the polarizing plate 8 and reaches the CCD 9. A light signal received by the CCD 9 is sent to the interference fringe analyzing means 10.

  FIG. 6 is a diagram showing the ultra-low reflectance object surface inspection apparatus 100, in which the path of the test light reflected by the test object 6 is described, and the path of the reference light reflected by the reference plane 5 is omitted. It is.

  The horizontal linearly polarized light s and the vertical linearly polarized light p transmitted through the reference plane 5 are reflected by the test object 6, pass through the beam splitter 4, and travel toward the pinhole 7. Here, the pinhole 7 allows only the vertical linearly polarized light p of the test light (horizontal linearly polarized light s, vertical linearly polarized light p) reflected by the test object 6 to pass therethrough. The horizontal linearly polarized light s hits a portion other than the pinhole 7 and does not pass through the pinhole 7. That is, since the Wollaston prism 3 has a predetermined separation angle between the direction of the horizontal linearly polarized light s and the direction of the vertical linearly polarized light p, only the vertical linearly polarized light p of the test light is pinholed in the pinhole 7. 7 can be passed. The vertical linearly polarized light p is adjusted so as to pass through the pinhole 7 by adjusting the direction of the test object 6 with respect to the optical axis.

  In order to set the direction of the test object 6 so that only the vertical linearly polarized light p of the test light (horizontal linearly polarized light s, vertical linearly polarized light p) reflected by the test object 6 passes through the pinhole 7, Do as follows.

  First, the monitor camera 42 receives the light reflected by the beam splitter 41 provided between the beam splitter 4 and the pinhole 7. In this case, the monitor camera 42 is installed so that the center of the screen of the monitor camera 42 is a position equivalent to the position of the pinhole 7. Among the two light spots by the two test lights (horizontal linearly polarized light s and vertical linearly polarized light p), the upper light spot (light spot formed by the light beam indicated by the broken line) in FIG. The inclination of the test object 6 is adjusted so that it is displayed at the center of the screen. As a result, only the vertical linearly polarized light p of the test light reflected by the test object 6 passes through the pinhole 7. Then, the vertical linearly polarized light p of the test light passing through the pinhole 7 passes through the polarizing plate 8 and reaches the CCD 9. A light signal received by the CCD 9 is sent to the interference fringe analyzing means 10.

  Since the CCD 9 receives the horizontal linearly polarized light s of the reference light reflected by the reference plane 5 and the vertical linearly polarized light p of the test light reflected by the test object 6, these two kinds of received light Causes interference fringes. The polarizing plate 8 changes the horizontal linearly polarized light s and the vertical linearly polarized light p in the 45-degree direction, respectively. As a result, two lights in the same direction can be generated, which causes interference.

  According to the above embodiment, in the ultra-low reflectivity object surface inspection apparatus using an interferometer, when the ultra-low reflectivity object 6 is installed on the test surface, the intensity of the reference light reflected by the reference surface 5 and the reference surface By adjusting the angle of the half-wave plate 2, the intensity of the test light transmitted through 5 and reflected by the test object 6 can be made substantially the same. Moreover, the horizontal linearly polarized light s and the vertical linearly polarized light p are separated by a predetermined angle by the Wollaston prism 3, and the separated polarized light is selected by the pinhole 7, that is, the horizontal linearly polarized light s of the reference light is selected. The vertical linearly polarized light p of the test light can be selected. That is, the vertical linearly polarized light p of the test light has 100 times the intensity of the reference light, and interference fringes are formed by the test light having the intensity of 100 times and the reference light having the intensity of 1 time. Is done. Therefore, visibility (contrast) is improved and sufficient interference fringes can be obtained.

  In the above embodiment, the pinhole 7 allows only the horizontal linearly polarized light s of the reference light to pass and allows only the vertical linearly polarized light p of the test light to pass. The hole 7 may pass only the vertical linearly polarized light p of the reference light and pass only the horizontal linearly polarized light s of the test light.

  FIG. 7 is a diagram showing an ultra-low reflectance object surface inspection apparatus 200 that is Embodiment 2 of the present invention.

  The ultra-low reflectivity object surface inspection apparatus 200 is provided with a PBS (polarization beam splitter) 3 ′ instead of the Wollaston prism 3 in the ultra-low reflectivity object surface inspection apparatus 100, and instead of the reference plane 5. Is provided with a reference surface 5 ′, a test object 6 ′ is provided instead of the test object 6, QWPs (Quarter Wave Plates) 31 ′ and 32 ′ are provided, beam splitters 4 and 41, a monitor This is a device in which the camera 42, the pinhole 7, and the polarizing plate 8 are omitted. The reference surface 5 'directs the reference light transmitted through the PBS 3' to the PBS 3 '. The test object 6 'has a spherical reflecting surface. The PBS 3 'separates incident light into two lights having a 90 degree angle to each other.

  In the ultra-low reflectance object surface inspection apparatus 200, when the angle of the half-wave plate 2 is set to about 3 degrees, the intensity of the laser beam emitted from the laser 1 is the intensity of vertical linearly polarized light p: horizontal linearly polarized light s. Intensity = 1: 0.01 = 100: 1, and the intensity of the vertical linearly polarized light p is 100 times the intensity of the horizontal linearly polarized light s. Then, the linearly linearly polarized light p having an intensity of 100 times reflects the PBS 3 ′ and reflects by the test object 6 ′, and the reflected test light passes through the PBS 3 ′ and passes through the lens 81 to the CCD 9. Head. On the other hand, the horizontal linearly polarized light s having an intensity of 1 is transmitted through the PBS 3 ′ and reflected by the reference surface 5 ′. The reflected reference light is reflected by the PBS 3 ′ and travels toward the CCD 9 through the lens 81.

  That is, in the ultra-low reflectivity object surface inspection apparatus 200, the intensity of the reference light reflected by the reference surface 5 ′ and the intensity of the test light reflected by the test object 6 ′ having the ultra-low reflectivity are substantially the same. Therefore, visibility (contrast) can be improved and sufficient interference fringes can be obtained.

  In the ultra-low reflectivity object surface inspection apparatus 200, PBS 3 'is provided instead of the Wollaston prism 3 in the ultra-low reflectivity object surface inspection apparatus 100, but other light separating means are provided instead of these. You may do it. Further, in the ultra-low reflectance object surface inspection apparatus 200, a reference curved surface is provided instead of the reference plane 5 in the ultra-low reflectance object surface inspection apparatus 100. That is, the reference surface may be a flat surface or a curved surface.

  Further, for example, when the ultra-low reflectivity object surface inspection apparatus 100 shown in FIG. 1 is tilted 45 degrees clockwise, the horizontal linear polarization and the vertical linear polarization described in the first embodiment are merely tilted linear polarization. In this case, it cannot be expressed as horizontal linear polarization or vertical linear polarization. In this case, if the first linearly polarized light and the second linearly polarized light (linearly polarized light orthogonal to the first linearly polarized light) are expressed, they can be distinguished from each other. That is, in the above embodiment, the horizontal linear polarization is an example of the first linear polarization, and the vertical linear polarization is an example of the second linear polarization orthogonal to the first linear polarization. The same applies to the ultra-low reflectance object surface inspection apparatus 200 shown in FIG.

  The above embodiment is an apparatus for inspecting an object surface with an ultra-low reflectivity, but it is also effective for an apparatus for inspecting an object surface having a reflectivity greater than the ultra-low reflectivity. That is, even if the above embodiment is applied to an apparatus for inspecting an object surface having a reflectance higher than an ultra-low reflectance (reflectance of 0.3% or less), visibility can be improved. For example, when inspecting an object surface with a reflectance of 0.5 to 0% by attaching a multi-coat to the reflection surface, or when inspecting an object surface with a reflectance of 0.5% or more, The above embodiment can be applied.

100: Ultra low reflectance object surface inspection device,
1 ... Laser,
2 ... 1/2 wavelength plate,
3 ... Wollaston prism
4 ... Beam splitter,
5 ... Reference plane,
6 ... Test object,
7 ... pinhole,
8 ... Polarizing plate,
9 ... CCD,
10: Interference fringe analysis means,
200: Ultra low reflectance object surface inspection device,
3 '... PBS,
5 '... reference plane,
6 '... Test object.

Claims (6)

In a polarization interferometer that causes interference between reference light reflected from a reference surface by light from a predetermined light source and test light reflected from a test object by light from the predetermined light source,
A half-wave plate for controlling a polarization branching intensity ratio between the first linearly polarized light of the light from the predetermined light source and the second linearly polarized light orthogonal to the first linearly polarized light;
The first linearly polarized light and the second linearly polarized light that have passed through the half-wave plate are separated at a predetermined angle, and the separated first linearly polarized light and second linearly polarized light are separated from the reference plane, Polarized light separating means to be sent to the test object;
An object surface inspection apparatus characterized by comprising: In claim 1,
The object plane inspection apparatus, wherein the polarization separation means is a Wollaston prism or PBS. In claim 1,
The object surface inspection apparatus, wherein the reference surface is a flat surface or a curved surface. In claim 1,
A beam splitter that reflects the first linearly polarized light and the second linearly polarized light that have passed through the polarization separating means;
Of the first linearly polarized light and the second linearly polarized light, which is test light that reflects light that has passed through the reference surface and is reflected by a test object that is installed so that the reflected light passes through the reference surface. A pinhole that passes only one of the first linearly polarized light and the second linearly polarized light that is the reference light reflected by the reference surface;
An image sensor for receiving light passing through the pinhole;
Interference fringe analyzing means for analyzing an interference fringe having a spatial carrier obtained by the reference light passing through the pinhole and the test light passing through the pinhole;
An object surface inspection apparatus characterized by comprising: In claim 1,
The reference surface is provided at a position that reflects the light that has passed through the polarization separating means;
An imaging device that receives the test light reflected by the polarization separation means, reflected by the object to be examined, passed through the polarization separation means, and reference light reflected by the reference surface and reflected by the beam splitter;
Interference fringe analyzing means for analyzing an interference fringe having a spatial carrier obtained by the test light and the reference light;
An object surface inspection apparatus characterized by comprising: In claim 1,
An object surface inspection apparatus, wherein a reflectance of the test object is 0.3% or less.

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