JP2009168793A - Surface accuracy measurement and surface defect observation apparatus, surface accuracy measurement and surface defect observation method, and surface accuracy and surface defect inspection method - Google Patents

Abstract

Surface accuracy measurement and surface defect observation apparatus capable of performing surface accuracy measurement of a small diameter substantially hemispherical lens and defect observation of a lens surface with high accuracy using an apparatus using a Fizeau interferometer, and A surface accuracy measurement and surface defect observation method is provided.
An apparatus for measuring surface accuracy of a test surface of a test lens and observing a defect on the test surface using a Fizeau interferometer optical system. Upon positioning of the lens 7, first has a first light flux control plate 8 ₁ confirmed configured to be able to position of the lens 7, aperture 8 _{2 a} centered, the shielding portion 8 _{2 b} around a second light flux control plate _82, centered on the shield portion 8 _{3 a,} and a third light flux control plate 8 ₃ having an opening 8 _{3 b} around, desired light flux control of these light flux control plate a light beam control means 8 that detachably on a virtual plane perpendicular to the optical axis Z ₁ of the interferometer optical system including the converging point P ₁ of the reflected light from the reference surface 5a of the plate interferometer optics .
[Selection] Figure 1

Description

  The present invention relates to a surface accuracy measurement and surface defect observation apparatus using a Fizeau interferometer optical system, and a surface accuracy measurement and surface defect observation method, and more particularly to measurement of surface accuracy and surface defects of a micro-diameter substantially hemispherical lens. The present invention relates to a surface accuracy measurement and surface defect observation apparatus, a surface accuracy measurement and surface defect observation method, and a surface accuracy and surface defect inspection method.

High precision surface accuracy is required for a minute hemispherical lens such as a tip of a microscope objective lens.
However, it is conventionally known to use a Fizeau interferometer for measuring the surface accuracy of a test object. A Fizeau interferometer makes light from a light source incident perpendicularly to a reference surface of a reference lens, and irradiates light that has passed through the reference surface of the reference lens vertically to the surface to be examined. The reflected light from the reference surface of the lens is caused to interfere with the reflected light from the test surface of the test object. The surface accuracy can be measured by measuring the interference fringes. As an apparatus using a Fizeau interferometer, for example, there is an apparatus described in Patent Document 1 below.

  Moreover, as an apparatus using a Twiman-Green interferometer, there is an apparatus described in Patent Document 2, for example.

JP 2004-226112 A JP-A-10-122833

  By the way, in the above-mentioned micro-diameter substantially hemispherical lens, in addition to surface accuracy, surface defects such as scratches, grain residue, wiping residue, and edge chipping greatly affect the lens performance. For this reason, it is necessary to detect surface defects with high accuracy as well as to measure surface accuracy.

  However, in a device using a conventional Fizeau interferometer such as the device described in Patent Document 1, when a path-match interferometer using a white light source is used, observation can be performed by switching between interference fringe observation and surface defect observation. In both cases, observation of interference fringes / surface defects is difficult because the contrast is reduced due to the influence of noise reflected light from the reference surface and the test surface. For this reason, defects on the surface of the lens must be observed using observation means different from the apparatus using the Fizeau interferometer, such as a loupe. However, using a plurality of devices in this manner complicates the operation, and even if a loupe is used, defects on the surface of the lens are difficult to observe because they are substantially hemispherical lenses with a small diameter. In many cases, a lens defect due to a defect occurs in a later process.

  In addition, the apparatus described in Patent Document 2 can perform surface accuracy inspection and surface defect inspection with a single apparatus, but can be applied only to a Twiman-Green interferometer. Since the Twiman-Green interferometer is used, the accuracy of the entire optical system is required, and the manufacturing error affects the measurement accuracy of the surface accuracy. In addition, since the optical paths to the lens to be tested and the original device are separate, they are susceptible to vibration. Furthermore, since the beam splitter is inserted immediately before the test lens, the work distance (WD) is reduced, and there are restrictions when inspecting the convex surface, and the aperture angle of the test light (the test light irradiation angle to the test lens) Has a problem that the inspection area of the surface to be measured is reduced.

  The present invention has been made in view of the above-described conventional problems, and uses a device using a Fizeau interferometer to accurately measure the surface accuracy of a minute hemispherical lens and observe defects on the lens surface. An object of the present invention is to provide a surface accuracy measurement and surface defect observation apparatus, a surface accuracy measurement and surface defect observation method, and a surface accuracy and surface defect inspection method.

  In order to achieve the above object, the surface accuracy measurement and surface defect observation apparatus according to the present invention uses a Fizeau interferometer optical system to measure the surface accuracy of a test surface and to observe surface defects in a test lens. And a first light flux control plate configured to be able to confirm the position of the test lens when adjusting the position of the test lens, and has an opening at the center thereof, around the opening. A second light flux controlling plate having a shielding portion, and a third light flux controlling plate having a shielding portion at the center thereof and an opening around the shielding portion. A light beam control means configured to be able to insert and remove the light beam control plate on a virtual plane perpendicular to the optical axis of the interferometer optical system including a condensing point of reflected light from the reference surface of the interferometer optical system; It is characterized by having prepared.

  Further, in the surface accuracy measurement and surface defect observation apparatus of the present invention, as with a commercially available Fizeau interferometer, there is a position adjusting means capable of moving the lens to be measured in a predetermined direction with respect to the optical axis of the interferometer optical system. Is preferred.

  In the surface accuracy measurement and surface defect observation apparatus according to the present invention, an imaging optical system that forms an image of a test surface formed in the vicinity of the condensing point at a predetermined imaging position, and the imaging optical An optical system for observing an image of the first light flux controlling plate disposed on a virtual plane having the same imaging position as the system and including the condensing point and perpendicular to the optical axis of the interferometer optical system; Is preferably detachably inserted into and removed from the optical path of the interferometer optical system, and an imaging device is preferably provided at the imaging position.

  Further, the surface accuracy measurement and surface defect observation method according to the present invention is a method of measuring surface accuracy of a test surface and observing a surface defect in a test lens using a Fizeau interferometer optical system, The first lens is configured to be able to confirm the position of the test lens on a virtual plane perpendicular to the optical axis of the interferometer optical system including a condensing point of reflected light from the reference surface of the interferometer optical system. A first step of adjusting the position of the test lens so that light emitted from the reference surface of the interferometer optical system is perpendicularly incident on the surface of the test lens while setting one light flux control plate; After the first step, the first light flux control plate is replaced with a second light flux control plate having an opening at the center and a shielding portion around the opening, and interference fringe observation is performed. A second step to be performed, and after the second step, the second light flux control plate is shielded at the center. And a third light flux control plate having an opening around the shielding portion, and performing dark field observation, and after the third step, the lens to be tested is decentered. And a fourth step of performing bright field observation.

  In the surface accuracy measurement and surface defect observation method of the present invention, the third light flux control plate can be switched between a plurality of light flux control plates having annular openings having different diameters around the central shielding portion. It is preferable to prepare for.

  Further, the surface accuracy and surface defect inspection method according to the present invention is a surface accuracy and surface defect inspection method for a test lens using a Fizeau interferometer, which includes a reference surface and a test surface. The surface accuracy of the test surface is adjusted by using interference fringes generated by adjusting the position and superimposing the reference light reflected by the reference surface and the measurement light transmitted through the reference surface and reflected by the test surface. The step of inspecting, adjusting the positions of the reference surface and the test surface, removing the reference light reflected by the reference surface, and using the measurement light transmitted through the reference surface and reflected by the test surface And a step of inspecting a surface defect of the test surface.

  According to the present invention, the surface accuracy measurement and the surface capable of performing the surface accuracy measurement of the minute hemispherical lens and the observation of the defect on the lens surface with high accuracy using the apparatus using the Fizeau interferometer. A defect observation apparatus, surface accuracy measurement and surface defect observation method, and surface accuracy and surface defect inspection method are obtained.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is an explanatory view along the optical axis showing the basic configuration of a surface accuracy measurement and surface defect observation apparatus according to an embodiment of the present invention, and FIG. 2 shows the light flux control means of the surface accuracy measurement and surface defect observation apparatus of FIG. FIG. 4 is an explanatory diagram showing a configuration of a light flux control plate provided, where (a) is a plan view of a position adjustment plate that is a first light flux control plate, and (b) is a plan view of an interference fringe observation plate that is a second light flux control plate. (C) is a plan view of a dark field observation plate which is a third light flux control plate. FIG. 3 is an explanatory diagram showing a configuration when the position of the lens to be tested is adjusted in the surface accuracy measurement and surface defect observation apparatus of FIG. FIG. 4 shows an example of the incident state of the reflected light from the test lens on the first light flux control plate at the initial stage of the position adjustment of the test lens using the configuration of FIG. It is explanatory drawing shown as. FIG. 5 shows a configuration for measuring interference fringes caused by interference between reflected light from the test surface of the test lens and reflected light from the reference surface of the reference lens in the surface accuracy measurement and surface defect observation apparatus of FIG. It is explanatory drawing which shows. 6 is an explanatory diagram showing the state of interference fringes obtained as an image in the configuration of FIG. 5. FIG. 5A shows the light flux control plate and the imaging optical system in FIG. 5 after adjusting the position of the test lens in the configuration of FIG. The diagram showing the state of the interference fringes obtained as an image when switching to the interference fringe observation plate and the interference fringe observation optical system shown in FIG. 5B, the lens to be tested in the state of (a) moved in the optical axis direction It is a figure which shows the state of the linear interference fringe obtained as an image when a test lens is slightly decentered after making interference fringes invisible (so-called null state). FIG. 7 is an image obtained by observing the surface of a test lens having a defect using the surface accuracy measurement and surface defect observation apparatus of the present invention, and (a) of the test surface including the defect portion is an interference fringe observation image. (B) is a dark field observation image, (c) is a bright field observation image, (d) is a pseudo bright field observation image obtained by performing image processing on the dark field image shown in (b) and reversing black and white. is there. FIG. 8 is an explanatory diagram showing a state when the night vision observation state is switched to the bright field observation state in the configuration of FIG. FIG. 9 is an explanatory diagram showing the state of the light beam on the dark field observation plate during bright field observation. FIG. 10 is an explanatory diagram showing an example in which a ring-shaped opening is provided around the central shielding portion of the dark field observation plate. In the figure, a ball lens is substituted for the substantially hemispherical lens in order to make the lens curvature center easy to understand.

The surface accuracy measurement and surface defect observation apparatus of the first embodiment is configured using a Fizeau interferometer optical system.
Specifically, the Fizeau interferometer optical system according to the first embodiment includes a laser light source unit 1 (not shown) including a laser light source, a collimating lens, a polarizer, and the like, a light projecting lens 2, a polarizing beam splitter 3a, and a λ / 4 plate 3b, condenser lens 4, and reference lens 5.
In the surface accuracy and appearance inspection of the substantially hemispherical lens, it is necessary to observe a large solid angle of the surface to be measured. Is approximately 0.6 (the observation solid angle is approximately 120 degrees). The inspection solid angle of the hemispherical lens is 180 degrees, and the reference lens 5 is also desired to be 180 degrees, but is limited to about 120 degrees in design. The focal length of the condenser lens 4 with respect to the reference lens 5 is designed to be about 10 times.
An XYZ stage 6 as a position adjusting unit is provided in front of the reference lens 5 (on the left side in the drawing). X-Y-Z stage 6 is a direction along the optical axis Z ₁ relative to the direction perpendicular (X-direction and the Y direction) and the optical axis Z ₁ of the interferometer optics while holding the sample lens 7 (Z-direction) It is configured to be movable.
Behind the polarization beam splitter 3 (on the right side in the drawing), a light beam control means 8 and an imaging optical system 9 are provided.

Light flux control unit 8, with a light flux control plate 8 _{1-8 3} shown in FIG. 2 (a) ~ (c) , is composed of a rotatable turret about an axis of rotation 8 _4. Then, by rotating about an axis of rotation 8 ₄ of the turret, the virtual perpendicular to the interferometer optical axis Z ₁ of the optical system including the converging point P ₁ of the reflected light from the reference surface of the interferometer optics A desired light flux control plate is provided on the plane so that it can be inserted and removed. In the present embodiment, the reference surface of the interferometer optical system is the object side surface 5 a of the reference lens 5. The virtual plane is a plane (not shown) perpendicular to the paper surface in FIG. In the following description, the position of this virtual plane will be referred to as a “condensing position”.

The first light flux control plate _81, upon positioning of the lens 7, a light flux control plate used to check the position of the lens 7. As shown in FIG. 2 (a), the center region and the concentric circular predetermined region have a circular shielding part 8 ₁ a of about φ0.5 mm and an annular shielding part 8 ₁ b of about φ1 mm and φ2 mm, and the back side of the plate Consists of a frost surface that scatters light.
Incidentally, the annular shield unit _{81 b,} upon positioning of the lens 7, the first light flux control plate 8 ₁ a two-dot shape or circular shape on the surface 7a of the lens 7 is incident in a state of being focused This is provided as an index to make the change in the position of the reflected light easier to understand, and may be a cross line. Further, the shape is not limited to a concentric shape.

The second light flux control plate _82, the light flux used to observe the interference fringes generated by the reflected light from the reference surface 5a of the reference lens 5 and reflected light from the test surface of the lens 7 interfere Control board. As shown in FIG. 2 (b), the opening 8 _{2 a} of about φ1mm its center, and is configured to shield portions 8 _{2 b} around the opening 8 _{2 a} respectively have been.

The third light flux control plate 8 ₃ is a light flux control plate used to observe defects in the inspected surface of the lens 7. As shown in FIG. 2 (c), a shielding portion 8 ₃ a having a diameter of about 0.25 mm is provided at the center, and an opening portion 8 ₃ b is provided around the shielding portion 8 ₃ a.

The imaging optical system 9, the interference fringe observation optical system 9 ₁ switchable to each _other, the test lens position adjusting optical system (hereinafter, adjustment optical system) 9 _2, an image pickup device 10b.
Interference fringe observation optical system 9 ₁ is composed of a relay lens 9 _{1 a} and the imaging lens 9 _{1 b.} The relay lens 9 ₁ a is configured to form a secondary image of the test surface on the imaging device 10 b while moving on the optical axis to form a primary image of the test surface of the test lens 7.
Conditioning optics _{9 2} is constituted by the imaging lens _{9 2} a. An imaging lens 9 _{2 a} is configured to image the first image of the light flux control plate ₈₁ inserted into the focusing position on the imaging surface of the imaging device 10b.
An interference fringe observation optical system 9 _1, adjustment optical system 9 _2, either one depending on the application are inserted into the rear optical path than the light flux control unit 8. That is, when performing position adjustment of the lens 7, by inserting the adjustment optical system 9 ₂ behind the light path than the light beam control means 8, when performing observation of measurement and defects of the interference fringes, the interference fringe observation optical system 9 ₁ is inserted into the optical path behind the light beam control means 8.
The imaging device 10b is connected to the image display device 10a.

  In the surface accuracy measurement and surface defect observation apparatus according to the present embodiment, the S-polarized light from the laser light source unit 1 passes through the light projecting lens 2 and enters the polarization beam splitter 3a. To do. The incident polarized light is reflected by the polarization beam splitter 3 a, passes through the λ / 4 plate 3 b and the imaging lens 4, and enters the reference lens 5. A part of the light incident on the reference lens 5 is reflected by the reference surface 5a, and the other light passes through the reference surface 5a and enters the test lens 7. The light reflected by the test lens 7 and the light reflected by the reference surface 5a of the reference lens 5 follow an opposite optical path, and pass through the λ / 4 plate 3b twice so that the polarization direction is 90 °. It is rotated and enters the polarization beam splitter 3a. The incident light passes through the polarization beam splitter 3a and enters the light beam control means 8. The light that has passed through the light beam control means 8 is picked up by the image pickup device 10b via the image pickup optical system 9, and the picked-up image is displayed on the display surface of the image display device 10a.

An operation method of the surface accuracy measurement and surface defect observation apparatus of the present embodiment configured as described above will be described.
(alignment)
Prior to the measurement of the interference fringes, the position of the test lens 7 with respect to the interferometer optical system is adjusted.
In adjusting the position, the lens 7 to be examined is placed on the XYZ stage 6. Further, as shown in FIG. 3, as well as set the first light flux control plate ₈₁ to the condensing position, and sets the adjustment optical system 9 ₂ than the first light flux control plate ₈₁ behind the optical paths.

First, to adjust to the position of the X-Y-direction of the lens 7 (i.e., a direction perpendicular to the optical axis Z ₁ of the interferometer optics) as follows.
From the interferometer optical system, the vertex of the surface 7a of the lens 7 to be tested (substantially at the center of the surface to be tested), that is, the convex surface is the highest point with respect to the interferometer optical axis, and the concave surface is the lowest point. Set visually so that the light is collected in a dot shape. At this stage, no converging point of light from some degree offset by which and the the test surface vertexes reference surface 5a from the optical axis Z ₁ of the vertices of the surface 7a of the lens 7 interferometer optics not match. Reflected light beam from the time the surface 7a of the subject lens 7 is incident on the circular first frost surface of the light flux control plate ₈₁ in a state of being focused on, scattered make bright portion of the circular. Further, light reflected from the reference surface 5a of the reference lens 5, the assembly adjustment have been made to be focused at the focal point P ₁ two-dot-like, circular shielding portion of the first light flux control plate 8 ₁ Light is shielded at 8 ₁ a. The first image of the light flux control plate ₈₁ at this time is imaged through the adjustment optical system 9 _2. Then, as shown in FIG. 4, the display surface of the image display device 10a, an image light reflected from the surface 7a of the lens 7 is displayed on the first light flux control plate ₈₁ in a circular shape Is displayed.

Therefore, the Z-axis of the XYZ stage 6 is adjusted so that the circular bright portion becomes a dot shape. When the light spot is formed, the XY axis is moved to bring the light spot closer to the annular shielding portion 8 ₁ b. This operation is repeated to enter the light spot into the annular shield 8 ₁ b.
At this time, the display surface of the image display device 10a, the first image of the light flux control plate ₈₁ is displayed in a state where the light spot has disappeared (not shown). The reason why the shielding portion 8 ₁ b is ring-shaped with respect to the central circular portion (circular shielding portion 8 ₁ a) is to make it easier to see the movement of the light spot as described above.

Then adjusted as follows in a position capable of measuring the position of the surface accuracy of the Z-direction of the lens 7 (i.e., the direction along the optical axis Z ₁ of the interferometer optics).
The test lens 7 is moved in the Z direction so as to approach the reference lens 5 by the length of the curvature radius via the XYZ stage 6. That is, adjustment is performed so that the light condensing point of the light from the reference surface 5a coincides with the center of curvature of the test surface. Then, on the display surface of the image display device 10a, in the same manner as shown in FIG. 4, the first luminous flux control plate ₈₁ on the light reflected from the surface 7a of the lens 7 is composed of a circular optical portion The image displayed on is displayed.

Therefore, similarly to the position adjustment of the test surface as described above, while the Z-axis adjustment as circular bright portion is point-like, the light spot is first center of the light flux control plate ₈₁ (i.e., circle XY axis is adjusted so that it may approach the shape shielding part 8 ₁ a). Then, incident on the first light flux control plate ₈₁ of the annular shield unit _{81 b} in the state in which the reflected light is focused on the point-like from the test lens 7, is shielded by the annular shield unit _{81 b,} image the first image of the light flux control plate ₈₁ in a state where the light spot on the display surface of the display device 10a has disappeared to be displayed.
In this way, the lens 7 to be tested is set at a position where the light emitted perpendicularly from the reference surface 5a of the reference lens 5 of the interferometer optical system enters the surface 7a substantially perpendicularly.
Thereby, the position adjustment of the test lens 7 is completed. And the surface 7a of the range irradiated with the light beam from the interferometer optical system at this time becomes the inspection range of the test surface.

(Measurement of surface accuracy)
After the position adjustment of the test lens 7 is almost completed, the interference fringes are measured.
When the test lens 7 is set at a position where the light emitted vertically from the reference surface 5a of the reference lens 5 of the interferometer optical system is perpendicularly incident on the surface 7a, the reflected light from the test surface is opposite to the incident light. It follows the path and interferes with the reflected light from the reference surface 5a of the reference lens 5. Then, the interference light is focused at the focal point P _1. However, while the arrangement of Figure 3, would be shielded by the first light flux control plate ₈₁ of the annular shield unit _{81 b.} The adjustment optical system 9 ₂ is configured to image a first image of the light flux control plate ₈₁ via the imaging device 10b, and the image of the interference fringes are imaged at the focal point P ₁ It is not configured to image.
Therefore, in order to image the interference pattern, as shown in FIG. 5, switches the light flux control plate collection point in the second light flux control plate _82, and the test by moving the relay lens 9 _{1 a} The surface is focused on the imaging surface of the imaging device 10a. Further, switching the adjustment optical system 9 ₂ the interference fringe observation optical system 9 _1. At this time, since the position has not been completely adjusted, many interference fringes appear concentrically on the display surface of the image display device 10a as shown in FIG. Therefore, the YYZ stage 6 is finely adjusted so that the entire screen is displayed in the same color (null state) on the display surface of the image display device 10a. When the test lens 7 is slightly decentered from this state, a linear interference fringe as shown in FIG. 6B is generated, and the surface accuracy is measured from the distortion of the fringe.

(Surface defect observation-dark field observation)
Here, when there is a defect such as a scratch on the surface 7a of the lens 7 to be examined, the reflected light from the defect becomes scattered light, passes through a position different from the reference light, and does not interfere with the reference light. For this reason, for example, as shown in FIG. 7A, the image of the defective portion on the surface of the lens 7 to be tested is displayed together with the interference fringes that appear when the light reflected by the surrounding portion interferes with the reference light. Appears on the display surface of the device 10a.
However, the image of the defective portion on the surface of the test lens 7 at this time is hidden by the interference fringes, or the contrast is lowered due to the influence of the reflected light from the reference surface 5a in the bright portion between the interference fringes. .

Therefore, dark field observation is first performed in order to observe the image of the defect portion on the surface with good contrast.
The test lens 7 in a state in which a linear interference fringe appears by the above operation is returned to the position immediately before being decentered via the XYZ stage 6. At this position, since the reflected light from the reference surface 5a and the test surface is in a null state, an image of uniform brightness without interference fringes is displayed on the display surface of the image display device 10a. ing. Also, in this position, it coincides with the optical axis Z ₁ of the center of curvature interferometer optics of the surface 7a of the lens 7. Therefore, the reflected light from the reference surface 5a of the reflected light and the reference lens 5 from the defect-free site on the surface 7a of the lens 7 is focused at the focal point P _1. Further, it reflected light from the defect in the surface 7a of the lens 7 passes through a position shifted a converging point P ₁ becomes scattered and diffracted light.

Therefore, in this state, it switches the light flux control plate to the third light flux control plate 8 _3. Then, light reflected by the reference surface 5a of the zero-order reflected light and the reference lens 5 is reflected at the site without defects on the surface 7a of the lens 7, the third light flux control plate 8 ₃ in the light converging position Are shielded from light by the shielding portion 8 ₃ a. On the other hand, the scattered light and diffracted light reflected by the defect at the surface 7a of the lens 7 passes through the third opening 8 _{3 b} around the shield portion 8 _{3 a} of light flux controlling plate 8 ₃ imaging Images are taken by the apparatus 10b. As a result, as shown in FIG. 7 (b), a dark field image with good contrast due to scattered light and diffracted light from the defect portion on the test surface can be observed, and so-called Schlieren observation can be performed. .

(Surface defect observation-bright field observation)
Further, when the test lens 7 is decentered from this dark field image observation state, as shown in FIG. 8, a bright field image with good contrast due to scattered light and diffracted light from the defect portion on the test surface can be observed. It becomes like this.
That is, when the lens 7 to be tested is decentered with respect to any one of the X and Y axes via the XYZ stage 6, the zero-order reflected light from a portion having no defect on the surface to be tested is collected at the condensing point P. now through was shifted from _first position, without being blocked by the third light flux control plate 8 ₃ of the shielding portion 8 _{3 a,} by the imaging device 10b through the periphery of the opening 8 _{3 b.} Moreover, scattered light and diffracted light reflected by the defect at the surface 7a of the lens 7 is also because a large luminous flux, a part of the light is slightly blocked by the third light flux control plate 8 ₃ of the shielding portion 8 _{3 a} that although, most of the light is picked up by the image pickup device 10b through the opening 8 _{3 b} around the shield portion 8 _{3 a.} In contrast, the reflected light reflected by the reference surface 5a of the reference lens 5 is blocked by the third light flux control plate 8 ₃ of the shielding portion 8 _{3 a.} The light beam passing through the dark field observation plate 8 ₃ at this time, with respect to dark field observation plate 8 _3, for example, turned positional relationship shown in FIG. As a result, as shown in FIG. 7 (c), bright light with good contrast due to zero-order reflected light from the test surface without reflected light from the reference surface 5a, scattered light from the defect portion of the test surface, and diffracted light. A field image can be observed.

Further, by providing a well in an annular shielding portion 8 _{3 c} arranged concentrically as shown in Figure 10 of the shielding portion 8 _{3 a} of the center of the dark-field observation plate 8 _3, predetermined diameter openings 8 _{3 b} By forming the ring in a ring shape, it is possible to prevent the surface to be tested from being decentered excessively and to cut off unnecessary noise light. The diameter of the annular opening 8 ₃ b is preferably about 2 to 5 mm. Then, as can be used by switching depending on the application, have different annular opening 8 _{3 b} diameters in the turret 8, it is advisable equipped with multiple dark field observation plate 8 _3.

Therefore, according to the surface accuracy measurement and surface defect observation apparatus of this embodiment, the surface accuracy of the test lens can be measured with high accuracy using the same apparatus, and the defect of the test lens can be observed with high accuracy. High versatility.
Further, according to the surface accuracy measurement and surface defect observation apparatus of the present embodiment, since the Fizeau interferometer is used, the same reference lens or FNO. Different reference lenses can be used.
In this observation method, the dark field image shown in FIG. 7 (b) is subjected to image processing to produce an image in which black and white are reversed as shown in FIG. 7 (d), and pseudo bright field observation is performed. Good.

  However, if the reference lens is not originally designed for observing the image and the observation solid angle of the test surface is the same and the radius of curvature is different from the use of the interferometer, the image is picked up by the imaging device. It should be noted that the sizes of the images are the same. For example, when the curvature radii are 1 mm and 5 mm, 5 mm is 1/5 and the resolution is lowered. Therefore, although it depends on the detection accuracy actually required in the inspection work, the radius of curvature of the lens to be observed should be about 1/10 of the reference lens.

In the surface accuracy measurement and surface defect observation apparatus according to the present embodiment, the light beam control unit 8 is configured by a turret including the light beam control plates 8 ₁ to 8 ₃ . The configuration is not limited as long as the light flux control plate can be inserted and removed. For example, the light beam control means 8 may be constituted by a slider provided with light beam control plates 8 ₁ to 8 ₃ . Alternatively, the respective light flux control plates in the light flux control means 8 and the observation optical system corresponding to the light flux control plate in the imaging optical system 9 may be combined to form a unit. That is, a unit that combines the first light flux control plate ₈₁ and the adjustment optical system 9 _2, and units in combination the second the light flux control plate ₈₂ and the interference fringe observation optical system 9 _1, third comprising a unit that combines a light flux control plate 8 ₃ and the interference fringe observation optical system 9 _1. Then, by inserting / removing each unit into / from the optical path of the interferometer optical system, a desired light flux control plate may be inserted / removed at the condensing position.

In the Fizeau interferometer manufactured by Olympus, which has the same configuration as that of the present embodiment, Fno. 0.6 Using a reference lens with a focal length of 36 mm and an imaging lens with a focal length of 350 mm as the imaging lens 4, the surface accuracy of a hemispherical lens with a radius of curvature of 1.0 mm to 5.0 mm is measured and surface defects are detected. Observed. FIGS. 7 (a) to 7 (d) show a part of an image of a spherical notched portion (developed diameter of about φ2 mm) obtained by using a hemispherical lens having a curvature radius of 1.0 mm and having an observation field of view of 120 °. 7 (a) is an interference fringe observation image, FIG. 7 (b) is a dark field observation image of a defective portion, FIG. 7 (c) is a bright field observation image of a test surface, and FIG. 7 (d) is FIG. ) Is a pseudo bright field observation image obtained by performing image processing on the dark field image shown in FIG.
As a result of the observation, it was possible to detect a 2 μm-width flaw with the 1R hemispherical lens and a 10 μm-width flaw and a stain remaining after wiping with the 5R hemispherical lens.

Next, the surface accuracy and surface defect inspection method of the present invention will be described using the above-described surface accuracy measurement and surface defect observation apparatus of the present embodiment.
The Fizeau interferometer used in this example uses the surface accuracy measurement and surface defect observation apparatus of the present embodiment described above that has a biaxial tilt adjustment mechanism in the mounting portion of the reference lens 5. By attaching the reference lens 5 to the mounting portion and tilting by the biaxial tilt adjusting mechanism, the reference light can be switched to be incident on the imaging element of the imaging device 10b or not to be incident, that is, to be removed.

The reference lens 5 is attached to the reference lens attachment portion of the Fizeau interferometer body. In addition, the test lens 7 is held on the XYZ stage 6 (three-axis shift stage) of the interferometer body.
Then, by using the first light flux control plate _81, performs a two-axis tilt adjustment and 3-axis shift adjustment of the sample lens 7 of the reference lens 5. After completion of adjustment, the second switching on the light control plate _82, reference light reflected by the reference surface 5a of the reference lens 5, the reference surface 5a passes through the examination region of the test surface of the lens 7 surface The measurement light reflected by 7a is superimposed on the image sensor of the image pickup apparatus 10b inside the interferometer body to generate interference fringes. Then, the optical system of the interferometer body is adjusted so that the surface 7a that is the inspection range of the test surface of the test lens 7 is in focus. Then, by analyzing the interference fringes at this time, the surface accuracy of the test surface of the test lens 7 is inspected. This process is basically the same as the “surface accuracy measurement” described above.

Next, the switch to the second light flux control plate _82, the reference light is adjusted tilt reference lens 5 by the biaxial tilt adjusting mechanism so as not to enter the imaging element of the imaging device 10b. That slightly is tilted from the normal position, the reference light to the eccentric so as not to pass through the second aperture of the light flux control plate _82. At this time, since the measuring light even become misaligned, after the tilt adjustment of the reference lens 5, passing through the aperture reflected light of the second light flux control plate ₈₂ from the surface to be inspected again also shift adjustment of the lens 7 It can be so. Thus, the reference light is removed from the image pickup device of the image pickup apparatus 10b and is not completely incident, and only the measurement light is incident on the image pickup device. In this state, the surface 7a that is the test surface of the test lens 7 is already in focus. Then, the surface defect of the test surface of the test lens 7 is inspected by imaging the measurement light.

  In this way, the reference lens is decentered with respect to the optical axis of the apparatus together with the reference surface. However, since the test surface is decentered relatively on the opposite side, the quality of the image is not greatly deteriorated. Inspection can be realized easily. Moreover, since it is not necessary to insert an optical element between the reference surface and the test surface as in Patent Document 2, the work distance (WD) can be increased.

In this embodiment, the example in which the surface accuracy is first inspected and then the surface defects are inspected is described. However, this may be performed in the reverse order in some cases.
In the above-described embodiment, the case where the first to third light flux control plates are used has been described. However, in the present embodiment, if the biaxial tilt adjustment mechanism is provided in the mounting portion of the reference lens, the reference is made. Since the reference light reflected by the surface can be basically removed by tilting the reference lens, surface accuracy and surface defects can be inspected without any modification of the current Fizeau interferometer.

  INDUSTRIAL APPLICABILITY The present invention is useful in a field in which it is required to accurately inspect for the presence or absence of defects in a small-diameter hemispherical lens such as a front lens of a microscope objective lens.

It is explanatory drawing in alignment with the optical axis which shows the basic composition of the surface accuracy measurement and surface defect observation apparatus concerning one Embodiment of this invention. It is explanatory drawing which shows the structure of the light beam control board with which the surface accuracy measurement and surface defect observation apparatus of FIG. 1 is equipped, (a) is a top view of the position adjustment board which is a 1st light beam control board, (b) Is a plan view of an interference fringe observation plate as a second light flux control plate, and (c) is a plan view of a dark field observation plate as a third light flux control plate. It is explanatory drawing which shows a structure when adjusting the position of the to-be-tested lens in the surface precision measurement and surface defect observation apparatus of FIG. Description showing an example of an incident state of reflected light from the test lens on the first light flux control plate in the initial stage of the position adjustment of the test lens using the configuration of FIG. 3 as an image of the first light flux control plate FIG. 1. Description of the configuration for measuring interference fringes caused by interference between reflected light from the test surface of the test lens and reflected light from the reference surface of the reference lens in the surface accuracy measurement and surface defect observation apparatus of FIG. FIG. 5A is an explanatory diagram showing the state of interference fringes obtained as an image in the configuration of FIG. 5, and FIG. 5A is a diagram illustrating the interference fringes shown in FIG. 5 after adjusting the position of the lens to be tested in the configuration of FIG. The figure showing the state of the interference fringe obtained as an image when switching between the observation plate and the interference fringe observation optical system, (b) is the interference fringe by moving the test lens in the state of (a) in the optical axis direction FIG. 6 is a diagram showing a state of a linear interference fringe obtained as an image when the lens to be examined is decentered after being made invisible (so-called null state). The surface accuracy measurement and surface defect observation apparatus of the present invention is an image obtained by observing the surface of a test lens having a defect, and (a) of the test surface including the defect portion is an interference fringe observation image, (b ) Is a dark field observation image, (c) is a bright field observation image, (d) is a photograph of a pseudo bright field observation image obtained by performing image processing on the dark field image shown in (b) and reversing black and white. . It is explanatory drawing which shows a structure when the night vision observation state is switched to the bright field observation state in the structure of FIG. It is a figure which shows the state of the light beam on the dark field observation board in the bright field observation state in FIG. It is explanatory drawing which shows the structure of the dark field observation board which has a cyclic | annular opening part around the shielding part of a center part as a modification of a 3rd light beam control board.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser light source part 2 Projection lens 3a Polarization beam splitter 3b (lambda) / 4 board 4 Imaging lens 5 Reference lens 5a Reference surface 6 XYZ stage 7 Test lens 7a Surface 8 Light flux control means 8 ₁ 1st light beam Control plate 8 ₁ a Circular shielding portion 8 ₁ b Annular shielding portion 8 ₁ c, 8 ₁ d Frost portion 8 ₂ Second light flux control plate 8 ₂ a Opening portion 8 ₂ b Shielding portion 8 ₃ Third light flux control plate 8 ₃ a Shielding portion 8 ₃ b Aperture 9 Imaging optical system 9 ₁ Optical system for observing interference fringes 9 ₁ a Relay lens 9 ₁ b Imaging lens 9 ₂ Optical system for adjusting lens position to be examined (adjusting optical system)
9 ₂ a Imaging lens 10 a Image display device 10 b Imaging device

Claims (6)

An apparatus for measuring surface accuracy of a test surface of a test lens and observing a defect on the test surface using a Fizeau interferometer optical system,
When adjusting the position of the test lens, a first light flux control plate configured to be able to confirm the position of the test lens, and a second having an opening at the center and a shielding part around the opening. And a third light flux control plate having a shielding portion at the center thereof and an opening around the shielding portion, and the desired light flux control plate among the light flux control plates is interfered with by the interference. And a light beam control means configured to be detachable on a virtual plane perpendicular to the optical axis of the interferometer optical system including a condensing point of reflected light from the reference surface of the meter optical system. Surface accuracy measurement and surface defect observation device.   2. The surface accuracy measurement and surface defect observation apparatus according to claim 1, further comprising a position adjusting unit capable of moving the lens to be measured in a predetermined direction with respect to an optical axis of the interferometer optical system.   An imaging optical system that forms an image of a test surface imaged in the vicinity of the condensing point at a predetermined image forming position; and an image forming position that is the same as the image forming optical system and includes the condensing point. An optical system for observing an image of the first light flux control plate disposed on a virtual plane perpendicular to the optical axis of the interferometer optical system is detachably provided in the optical path of the interferometer optical system, 2. The surface accuracy measurement and surface defect observation device according to claim 1, further comprising an imaging device at the imaging position. Using a Fizeau interferometer optical system, a method for measuring surface accuracy of a test surface in a test lens and observing a surface defect,
The first lens is configured to be able to confirm the position of the test lens on a virtual plane perpendicular to the optical axis of the interferometer optical system including a condensing point of reflected light from the reference surface of the interferometer optical system. A first step of adjusting the position of the test lens so that light emitted from the reference surface of the interferometer optical system is perpendicularly incident on the surface of the test lens while setting one light flux control plate; ,
After the first step, the first light flux control plate is replaced with a second light flux control plate having an opening at the center and a shield around the opening, and interference fringe observation is performed. The second step,
After the second step, the second light flux control plate is replaced with a third light flux control plate having a shielding portion at its center and an opening around the shielding portion, and dark field observation is performed. The third step,
Further, after the third step, there is provided a fourth step of performing bright field observation by decentering the lens to be examined, and a surface accuracy measurement and surface defect observation method.   2. The surface according to claim 1, wherein the third light flux control plate includes a plurality of light flux control plates having annular openings having different diameters around the central shielding portion. Accuracy measurement and surface defect observation method. A method for inspecting surface accuracy and surface defects of a test surface of a test lens using a Fizeau interferometer,
Using the interference fringes generated by adjusting the positions of the reference surface and the test surface and superimposing the reference light reflected by the reference surface and the measurement light transmitted through the reference surface and reflected by the test surface A step of inspecting the surface accuracy of the test surface;
Adjusting the positions of the reference surface and the test surface, removing the reference light reflected by the reference surface, and using the measurement light transmitted through the reference surface and reflected by the test surface Inspecting the surface defects of
A method for inspecting surface accuracy and surface defects, comprising: