JP2010019798A - Surface inspection method and surface inspection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the contrast of an interference fringe image and a surface image. <P>SOLUTION: A surface inspection device 1 includes: a light source 17 for emitting an illumination light for irradiating the test surface 10A of a lens to be inspected 10; a reference lens 37, having a reference surface 11A reflecting a part of the illumination light disposed on a main optical path 5; an imaging element for obtaining images acquired by the reflected light of the reference surface emitted from the light source 17 and reflected by the reference surface 11A and the reflected light of the surface to be inspected, which is transmitted through the reference surface 11A and reflected by the test surface 10A of the lens to be inspected 10, having an optical path difference of not more than the coherence length with respect to the reflected light of the reference surface; and an image processing part 43 for processing the image obtained by the imaging element, wherein the image processing part 43 includes a memory part 42 for storing a first light intensity distribution, consisting of only the reflected light of the reference surface and a calculation part 44 for subtracting the first light intensity distribution stored in the memory part 42, from a second light intensity distribution obtained from the reflected light of the reference surface and the reflected light from the test surface. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a surface inspection method and a surface inspection apparatus. In particular, the present invention relates to a surface inspection method and a surface inspection apparatus for inspecting surface accuracy and surface defects of a lens surface having a small curvature radius and close to a hemisphere.

Conventionally, as a means for observing the surface shape of an optical component or the like, a surface inspection apparatus using a Fizeau interferometer having a path matching mechanism is known (see Patent Document 1).
According to the interferometer for measuring a transparent thin plate described in Patent Document 1, of the light output from the light source, the reflected light reflected by the reference surface of the reference body and the transparent thin plate transmitted through the reference surface The surface shape of the test surface is measured based on an interference fringe image formed on the CCD element by interfering with reflected light reflected by the test surface.

Japanese Patent Laid-Open No. 9-21606

  However, in the transparent thin plate measurement interferometer described in Patent Document 1, a reference body is present on the optical path of the light irradiated on the surface to be measured. Since the light from the light source is divided into two light beams, four reflected lights are generated from the reference body and the test surface in the interferometer optical path. Among these, since only two light beams are used for creating interference fringes, the remaining two light beams become noise light (flare). As described above, the interferometer for measuring a transparent thin plate described in Patent Document 1 has a disadvantage in that flare is generated by the reflected light on the reference surface of the light irradiated on the test surface, and the contrast of the interference fringe image is lowered.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a surface inspection apparatus capable of improving the contrast of an interference fringe image and a surface image.

In order to solve the above problems, the present invention employs the following means.
The present invention relates to interference fringe measurement comprising a low-coherent light source, a Fizeau interference optical system having a path matching mechanism constituted by two optical paths, an imaging device, and an image processing device that processes and displays an image from the imaging device. A surface inspection method for measuring surface accuracy of a lens to be inspected and inspecting a surface defect by using an apparatus, wherein the lens to be tested is not set in the interference fringe measuring device, and the Fizeau interference optical system is referred to A first step of acquiring and storing a reflection image from the reference surface of the lens, and setting the lens to be tested in the Fizeau interference optical system, and matching the interference distance by the path matching mechanism to generate interference fringes The second step of creating and acquiring and storing the interference fringe image, and after erasing the interference fringe by slightly different the interference distance of the two optical paths from the state of the second step by the path matching mechanism, A third step of focusing the surface of the imaging device on the surface of the test lens to acquire and store a surface image of the lens to be tested, and the reflection from each of the light amount distribution of the interference fringe image and the light amount distribution of the surface image There is provided a surface inspection method comprising a fourth step of subtracting a light amount distribution of an image to create a new interference fringe image and a surface image of the lens to be tested, and switching and displaying each.

  In addition, the present invention provides a light source that emits illumination light that irradiates the surface of a subject, and is disposed on an optical path between the light source and the subject, has the same optical axis as the subject, A reference member having a reference surface that partially reflects, reference surface reflected light emitted from the light source and reflected by the reference surface, and reflected by the surface of the subject through the reference surface and reflected by the reference An image pickup device that acquires an image obtained by test surface reflection light having an optical path difference equal to or less than a coherence distance with respect to the surface reflection light, and an image processing unit that processes the image acquired by the image pickup device The image processing unit stores a first light amount distribution consisting only of the reference surface reflected light, and a second light amount distribution obtained from the reference surface reflected light and the test surface reflected light, Subtracting the first light quantity distribution stored in the storage unit To provide a surface inspection apparatus and a calculation unit.

  The above invention includes a beam splitter that divides the illumination light into two, and an optical path length adjustment mechanism that adjusts the optical path length of one illumination light and the other illumination light divided by the beam splitter, The optical path difference between the surface reflected light and the test surface reflected light may have a first state in which the optical path difference is the same as the coherence distance of the light source and a second state in which the optical path difference is greater than the coherence distance of the light source. .

  Further, in the above invention, further comprising a focusing mechanism, and when in the second state, focusing is performed so that an image of the subject is formed on the imaging element by the focusing mechanism, The calculation unit may subtract the first light amount distribution from the second light amount distribution obtained in the focused state.

  Further, in the above invention, a focusing mechanism is further provided, and the optical path length adjustment mechanism includes a blocking member capable of blocking one of the one illumination light or the other illumination light, and the inspection by the blocking member When the light or the reference light is blocked, the focusing mechanism performs focusing so that an image of the subject is formed on the imaging element, and the calculation unit is obtained in the focused state. Alternatively, the first light amount distribution may be subtracted from the second light amount distribution.

  According to the present invention, it is possible to improve the contrast of the interference fringe image and the surface image.

Hereinafter, a surface inspection apparatus 1 according to an embodiment of the present invention will be described with reference to the drawings.
The surface inspection apparatus 1 according to the present embodiment is, for example, a white path match Fizeau interferometer as shown in FIG. 1, and is a lens, a lens mold type or the like (hereinafter simply referred to as “test lens”) 10. In particular, the surface accuracy and surface appearance of a spherical surface having a small radius of curvature and close to a hemispherical lens are inspected.

  The surface inspection apparatus 1 includes a light source unit 3, a path match optical system unit 18, a light source relay unit 7, an interference optical unit 2, a stage 6, an imaging unit 12, and an image processing unit 15.

  The light source unit 3 includes a low coherent light source 17, a collimator lens 14, and a polarizer 16. Examples of the low coherent light source 17 include an SLD (super laser diode) which is a kind of white light source. The collimator lens 14 converts the light emitted from the low coherent light source 17 into a parallel light flux. Further, the polarizer 16 is disposed so as to emit light that becomes P-polarized light with respect to the polarization beam splitter 13.

  A path match optical system unit 18 is disposed on the light emitting side of the light source unit 3. The path match optical system unit 18 includes a first mirror unit 20, a second mirror unit 21, and a moving mechanism (optical path length adjusting mechanism, not shown).

  The first mirror unit 20 includes a half mirror (beam splitter) HM1 and a half mirror HM2. The half mirror HM1 is fixed in an optical path (optical axis) through which the parallel light beam from the light source unit 3 travels, and divides the parallel light beam into two light beams traveling in a straight traveling direction and a direction orthogonal thereto. Yes. Further, the half mirror HM2 combines the two light beams divided by the half mirror HM1.

The second mirror unit 21 includes two mirrors M1 and M2. The mirror M1 is disposed at a position facing the half mirror HM1, and the mirror M2 is disposed at a position facing the half mirror HM2. With such a configuration, it is possible to bypass the light beam divided and deflected by the half mirror HM1 and return it to the half mirror HM2.
The moving mechanism moves the second mirror unit 21 in the direction indicated by the arrow c in FIG. 1 with respect to the first mirror unit 20.

  In this path match optical system unit 18, an optical path that travels straight through the half mirror HM1 is referred to as a basic optical path, and an optical path that is deflected by the half mirror HM1 and detoured by the second mirror unit 21 is referred to as an adjustment optical path. The difference (2d) between the two optical path lengths is referred to as the adjustment distance.

  A light source relay unit 7 is disposed on the light emission side of the path match optical system unit 18. The light source relay unit 7 includes a condenser lens 22 and a pinhole 23. The condensing lens 22 condenses the collimated light flux that has passed through the basic optical path and the adjustment optical path in the path match optical system unit 18 and is superimposed again. The pinhole 23 is arranged at the condensing point so as to adjust the light flux.

  The interference optical unit 2 is disposed on the light emission side of the light source relay unit 7. The interference optical unit 2 includes a polarization beam splitter 13, a λ / 4 plate 8, a collimator lens 9, and a reference lens system 11. As described above, the light from the low-coherent light source 17 is converted to P-polarized light by the polarizer 16. The polarization beam splitter 13 has a characteristic of transmitting P-polarized light and reflecting S-polarized light. Therefore, the light emitted from the light source relay unit 7 passes through the polarization beam splitter 13, becomes circularly polarized by the λ / 4 plate 8, and enters the collimator lens 9.

  The collimator lens 9 converts a light beam that has passed through the pinhole 23 of the light source relay unit 7 into a parallel light beam having a flat wavefront. This parallel light beam is incident on the reference lens system 11. The light emitted from the reference lens system 11 is incident on the surface “(hereinafter referred to as“ test spherical surface (test surface) ”” 10 </ b> A of the test lens (subject) 10.

  The reference lens system 11 includes a plurality of lenses 33, 35, and 37 arranged in the optical axis direction, and the final surface facing the test spherical surface 10A is the reference surface 11A. It is a lens (reference lens (reference member) 37) having an aperture angle of about 0.6 (about 120 °). That is, at the same time as the 120 ° convergent reference light is applied to the lens 10 to be examined, the reference surface 11A emits reflected light (hereinafter referred to as “reference surface reflected light”) with a reflectivity of about 4%. To send back to the side. This is a so-called interference fringe reference light.

  With this configuration, the test lens 10 is placed on the stage 6 movable in the XY (plane perpendicular to the paper surface and the optical axis) direction and the Z (optical axis) direction, and is centered with respect to the optical axis and the collection of the reference surface 11A. The work of matching the center of curvature of the test lens 10 with the light spot is performed, and the light beam from the reference lens system 11 to be irradiated is reflected by the reflectivity of the test lens 10 (hereinafter referred to as “test spherical reflection light”). .) Is sent back to the reference lens system 11. This is so-called interference fringe inspection light.

  The two reflected lights pass through the reference lens system 11 and the collimator lens 9 and enter the λ / 4 plate 8. The two reflected lights (circularly polarized light) are first converted into linearly polarized light (S-polarized light) orthogonal to the incident time by the λ / 4 plate 8, enter the polarizing beam splitter 13, and are deflected at right angles by the reflecting surface 13 a. Thus, the imaging unit 12 is reached.

  The imaging unit 12 receives an imaging optical system 47 that collects the reference surface reflected light and the test surface reflected light guided by the polarizing beam splitter 13, and the test surface reflected light collected by the imaging optical system 47. And an imaging device (imaging unit) 41 having an imaging element (not shown) for acquiring an image. Information from the imaging unit 12 is input to the image processing unit 15. The image processing unit 15 includes an image processing device 43 that processes an image acquired by the image sensor, and a monitor 45 that displays an image or the like processed by the image processing device 43.

The imaging optical system 47 moves the lens 47b constituting the imaging optical system 47 in the optical axis direction so as to focus on the interference fringes and the lens 10 to be examined. Reference numeral 47a is a pinhole.
As the imaging device 41, for example, a CCD camera can be used.

  The image processing device 43 stores the image of the reference surface 11A and the image of the test spherical surface 10A acquired by the image sensor, the light amount distribution of the reference surface reflected light, and the light amount distribution of the test surface reflected light, An arithmetic unit 44 that performs arithmetic processing based on the light amount distribution of the reference surface reflected light and the light amount distribution of the test surface reflected light is provided.

A surface inspection method according to the present embodiment using the surface inspection apparatus 1 according to the present embodiment configured as described above will be described below.
The surface inspection method according to the present embodiment includes a first step of acquiring and storing a reflection image from the reference surface 11A of the reference lens system 11 in a state where the lens 10 to be tested is not set on the stage 6, and the test A second process of setting the lens 10 on the stage 6, creating interference fringes by matching the interference distance by the path match optical system unit 18, acquiring and storing the interference fringe image, and the path match optical system from the second state After the interference fringes are erased by slightly different the interference distance between the two optical paths in the unit 18, the image sensor is focused on the subject spherical surface 10A, and a surface image of the subject lens 10 is acquired and stored. A new interference fringe image and a surface image of the lens to be tested 10 are created by subtracting the light amount distribution of the reflected image from each of the process and the light amount distribution of the interference fringe image and the light amount distribution of the surface image. The fourth work to display It is equipped with a door.

First, a method for acquiring a reference surface reflected light amount distribution image of the sum of two light beams passing through the basic optical path and the adjustment optical path from the reference surface 11A in the first step will be described.
When the imaging optical system 47 is switched to an unillustrated focusing optical system (a glass slide with an index instead of the pinhole 47a, a sliding glass observation optical system instead of the imaging optical system 47), the reflected light from the reference surface 11A is reflected on the sliding glass. Therefore, the optical axis of the reference lens system 11 can be matched with the optical axis of the surface inspection apparatus 1 by matching the spot with the index of the ground glass.

  In this state, the focusing optical system is switched to the imaging optical system 47, and a reference surface reflection light amount distribution image (FIG. 5) of the sum of two light beams passing through the basic optical path and the adjustment optical path is acquired and stored. In addition, when taking separately the reference surface reflection light quantity distribution images of the two light beams passing through the basic optical path and the adjustment optical path, as shown in FIG. 2, a shutter (shielding plate) is provided for each of the two optical paths of the path match optical system unit 18. ) 31 is possible.

  Here, the two lights that have passed through the adjustment optical path and the basic optical path are reflected by the reference surface 11A and the test spherical surface 10A, respectively, to produce four reflected lights, which contribute to making interference fringes and a surface defect image. The reflected light is two of them, and the other two are flare on the image due to noise light, and the reason why the image quality is lowered will be described with reference to FIG.

  Interference by the low coherent light source 12 occurs only in a state where the distance from the low coherent light source 12 to the reference surface 11A and the distance from the low coherent light source 12 to the reference spherical surface 10A and reaching the reference surface 11A coincide. In FIG. 2, the reflected lights L1 to L4 are written so as to be reflected obliquely so as to be easily understood. The reflected lights L1 and L2 are the reflected light from the reference surface 11A of the illumination light that has passed through the basic optical path and the test spherical surface 10A, and the reflected lights L3 and L4 are the reference surface 11A of the illumination light that has passed through the adjustment optical path and the target light. This is the reflected light from the detected spherical surface 10A.

  The optical path lengths of the reflected lights L2 and L4 that have passed through the reference surface 11A and reflected by the test spherical surface 10A are twice (2L) the distance L between the reference surface 11A and the test spherical surface 10A; When searching for a combination of reflected light having the same optical path length by looking at the difference between the optical path lengths of the basic optical path and the adjusting optical path in the path match optical system 18 being 2d, the reference surface reflected light L3 passing through the adjusting optical path and the basic It can be seen that the test surface reflected light L2 passing through the optical path matches when L = d.

  Since interference fringes are created in this state, the second step is to capture the interference fringe image (FIG. 3) (light quantity distribution) and store it in the storage unit 42. Reflected lights L1 and L4 that are not involved in interference on the image become noise light and appear as flare on the image. However, the amount of image light is L1 + L2 + L3 + L4.

The amount of flare at this time is approximately equal to the amount of light that generates interference fringes and the amount of flare when the light amounts of the adjustment optical path and the basic optical path are substantially the same as the reflectance of the reference surface 11A and the subject spherical surface 10A. It can be said that there is a huge flare compared with a general camera.
The coherence distance of illumination light from the low-coherent light source 12 having a wavelength of about 700 nm is about 50 μm, and the optical path length difference between the two optical paths of the path match optical system unit 18 matches this range in order to create interference fringes. In this range, the interference fringes are adjusted to have the best contrast.

  It is assumed that the light amounts of the adjustment optical path and the basic optical path and the reflectances of the reference surface 11A and the test spherical surface 10A are substantially the same. Even in an actual interferometer, as the interference of light related to the two interferences is equal, a fringe with good contrast is formed. The light amounts of the adjustment optical path and the basic optical path are adjusted to be substantially equal, and the reference surface 11A and the test spherical surface 10A often have a reflectance of about 4% while being a polished glass surface.

  Assuming the basic optical path as an example, assuming that the basic optical path light quantity is 100, the reference surface 11A reflects 4% first, so the light quantity of the reflected light L1 related to the interference from the reference surface 11A is 4, and the light quantity directed to the test spherical surface 10A. When the reflectance at the test spherical surface 10A is 4%, the amount of the reflected light L2 returning to the reference surface 11A again is 96 × 4% = 3.84, and the reflected light L2 is 4% at the reference surface 11A. The amount of light involved in interference passing through the reference lens system 11 while being forced to reduce the amount of light by reflection is 3.84 × 96% = 3.69. That is, the amount of reflected light from the reference surface 11A and the test spherical surface 10A is substantially equal (L1 = L2). Since this approximation is for flare removal, precise measurement is not necessary and may be used sufficiently.

On the other hand, the same result is obtained for the adjustment optical path, and the reflected light amounts from the reference surface 11A and the test spherical surface 10A are substantially equal (L3 = L4). As a result, L1 = L2 = L3 = L4.
Therefore, an image may be acquired and stored as the sum of the light amounts of the reflected lights L1 and L4 as noise light is the same as the sum of the reference surface reflected lights L1 and L3 of the basic optical path and the adjustment optical path. Specifically, the first step is to take the reference surface reflected light distribution image (FIG. 5) of the basic optical path and the adjustment optical path by removing the test spherical surface 10A from the state at the time of interference fringe observation.

  Of course, the four reflected light amounts can also be measured individually. That is, after inserting a shutter into the optical path on one side of the path match optical system unit 18, the reference surface reflected light amount is measured without setting the test lens 10, and the test lens 10 is set and the reference surface reflected light is set. The sum of the light amounts of L1, L3 and test surface reflected light L2, L4 is measured. Thereafter, by subtracting the reference surface reflected light amount from the sum, the light amounts of the test surface reflected lights L2 and L4 can be measured. It is effective when used when the reflectance of the subject spherical surface 10A is different.

Next, a method for creating interference fringes in the second step will be described.
After acquiring the reference surface reflected light amount distribution image, the test spherical surface 10A is placed on the stage 6, and the imaging optical system 47 of the imaging device 41 is switched to the focusing optical system. The reflected light from the apex of the test spherical surface 10A forms a spot on the frosted glass, so that the apex image spot is moved to and matched with the target of the frosted glass so that the apex of the test sphere 10A matches the optical axis of the surface inspection apparatus 1. be able to.

  If the subject spherical surface 10A is a convex spherical surface, it is moved to the reference surface 11A side, and if it is a concave spherical surface, it is moved away from the reference surface 11A. The arrangement of the test spherical surface 10A at this time is as shown in FIG. 1, and the distance between the reference surface 11A and the test spherical surface 10A is L. Therefore, the optical path difference is 2L in consideration of reflection. The interference fringes can be observed when the second mirror unit 21 is moved by the moving device of the path match optical system unit 18 with the optical path difference equal to the distance 2L, and the optical path difference between the basic optical path and the adjustment optical path becomes 2L. Become.

  The optical path difference between the basic optical path and the adjustment optical path is 1 to 2d. That is, interference fringes can be created when L = d. In this state, the ground glass observation optical system of the image pickup apparatus 41 is switched to the original image pickup optical system 47, and the interference fringe image (FIG. 5) is obtained in a state where the fringe distortion is eliminated around the image by adjusting the interference fringes linearly. ) Is captured and stored.

  At this time, shielding plates are alternately inserted into the basic optical path and the adjustment optical path, and the total reflected light amount distribution image from the individual reference surface 11A and the test spherical surface 10A passing through each optical path is acquired and acquired individually as described above. By subtracting the reference surface reflected light amount distribution image of each of the two light beams passing through the basic optical path and the adjustment light path, a light amount distribution image only from the subject spherical surface 10A of each of the two light beams passing through the basic light path and the adjustment light path can be obtained. Can do. Therefore, four reflected light quantity distributions may be stored and used. That is, the test spherical reflected light L4 of the light passing through the adjustment optical path in FIG. 2 can be accurately measured, and by using this value, the contrast of the interference fringe image can be improved when the test surface reflectance is different. .

  At this time, the subject spherical surface 10A may be removed from the surface inspection apparatus 1, and a light quantity distribution image of the reference surface reflected light that is the sum of the two light beams passing through the basic optical path and the adjustment optical path may be acquired, stored, and used. Good.

  Thereafter, when the light amount distribution image of only the reference surface reflected light is subtracted from the interference fringe image already stored in the storage unit 42 in the image processing device 43 and displayed on the monitor 45, the flare-free contrast as shown in FIG. A good interference fringe is created. When inspecting the same spherical surface 10A to be inspected, it is not necessary to take a reference surface reflected light amount distribution image each time if a stored light amount distribution image is used.

Next, a method for acquiring a surface defect image in the third step will be described.
If the adjustment optical path distance is shifted by about 0.2 mm in the state in which the above interference fringes are created, the difference between the two optical path distances deviates from the coherent range, so that the interference fringes disappear. In this state, when the focus of the fringe imaging optical system is adjusted to the test spherical surface 10A, a surface defect image of the test spherical surface 10A is captured and stored. This is a surface image of the test spherical surface 10A in which the two light beams are reflected by the test spherical surface 10A, and the reflected light amount distribution image in which the two light beams are reflected by the reference surface 11A is overlapped as a flare.

  Here, the reason why the surface defect image of the test spherical surface is obtained is shown in FIG. In FIG. 10, the light source unit 17 and the path match optical system unit 18 are not shown. If the test spherical surface 10A is scratched when the illumination light from the light source unit 17 is irradiated to the test spherical surface 10A through the reference lens system 11, scattered light or diffracted light is generated by the scratch, and the reference lens system 11 side Head for.

  Then, a pupil is formed at the focal position (aperture position) of the collimator lens 9 and at the same time, a scratch image is formed at a position D corresponding to the distance from the reference lens system 11 position of the subject spherical surface 10A. By moving the focusing lens along the optical axis, a secondary image of this scratch is created on the imaging surface of the imaging device 41.

  At this time, the size of the field of view on the imaging surface of the imaging device 41 depends on the spherical angle of the test spherical surface 10A with respect to the test spherical surface 10A irradiation angle (120 ° in FIG. 10) of the reference lens system 11, and It doesn't matter big or small. For example, if the angle of the subject spherical surface 10A is 80 °, the image on the imaging surface is 80% of the maximum diameter regardless of whether the radius of curvature of the subject spherical surface 10A is 2 mm or 10 mm.

  Therefore, from the magnification of the image, the smaller the radius of curvature of the subject spherical surface 10A, the higher the magnification. In actual observation, a scratch of 5 μm on the subject spherical surface 10A having a curvature radius of 2 mm can be observed. If the angle exceeds 120 °, the portion exceeding 120 ° cannot be observed.

  The reason why the surface observation method according to the present embodiment is suitable for the inspection of the test spherical surface 10A having a small curvature radius is based on such circumstances. However, in lens design and manufacture, a lens close to a hemisphere often has a radius of curvature of 5 mm or less, and it is difficult to detect a surface defect with a lens with a small radius of curvature and has many applications.

  Even in this case, the light contributing to the surface defect detection image is the reflected light L2 and L4 from the test spherical surface 10A of the basic optical path of the path match optical system unit 18 and the adjustment optical path. The reflected lights L1 and L3 from the reference surface 11A of the remaining basic optical path and adjustment optical path become flare and greatly reduce the contrast of the surface defect detection image. The amount of light contributing to the flare at this time is almost equal to the amount of light contributing to the surface defect detection image as in the case of the interference fringe image, and a large flare is generated.

Next, acquisition of interference fringe images and surface defect images with good contrast in the fourth step will be described.
In the fourth step, the light amount distribution of the image stored in the first step is subtracted from the light amount distribution of the interference fringe image stored in the second step and the surface defect image stored in the third step. It is a process of displaying.

  FIG. 6 is a graph showing the cross-sectional light amount distribution of FIG. 5 and symbol b is a graph showing the cross-sectional light amount distribution of FIG. 3 in order to make the process of subtracting the light amount distribution between images easy to understand. The result of the subtraction is shown in FIG. According to this, it can be seen that flare is lost and an image with good contrast is obtained.

  Similarly, in FIG. 7, reference symbol a is a graph showing the cross-sectional light amount distribution of FIG. 5, reference character c is a graph showing the cross-sectional light amount distribution of FIG. 4, and FIG. 9 shows the result of subtracting these. Similarly, it can be seen that a flare is lost and an image with good contrast is obtained.

Thus, according to the surface inspection apparatus 1 and the surface inspection method according to the present embodiment, the distance from the low coherent light source 17 of the light that has passed through the adjustment light path to the reference surface 11A and the low light that has passed through the basic optical path. When the distance from the coherent light source 17 to the test spherical surface 10 </ b> A matches, an interference fringe can be created, and an interference fringe image is acquired by the imaging device 41 including the imaging optical system 47. By observing the interference pattern of the interference fringe image, the shape of the subject spherical surface 10A, that is, the surface accuracy of the spherical surface can be measured.
Further, when the distance of the light passing through the adjustment optical path to the reference surface 11A does not match the distance of the light passing through the basic optical path to the test spherical surface 10A, the surface defect image in the imaging device 41 including the imaging optical system 47. Is acquired. From this surface defect image, the presence / absence and size of the surface of the subject spherical surface 10A can be inspected.

  Further, according to the surface inspection apparatus 1 according to the present embodiment, the measurement radius is low, the measurement accuracy is high, the vibration is strong, and the curvature radius of the inspectable test spherical surface is limited using an interference optical system that does not require extreme accuracy. There is an advantage that the inspection area of the subject spherical surface 10A can be enlarged.

  In the present embodiment, the path match optical system unit 18 is not limited to the one shown in FIG. 1, and various path match optical systems such as those described in US Pat. No. 4,872,755 can be used. It may be adopted.

It is a schematic block diagram which shows the surface inspection apparatus which concerns on one Embodiment of this invention. It is a figure which shows four reflected light which arises on the reference surface or inspection surface of a reference light and inspection light in the surface inspection apparatus of FIG. It is a figure which shows the interference fringe image before reducing noise. It is a figure which shows the surface image of the to-be-tested surface before reducing noise. It is a figure which shows the reflected image of the reference surface of a reference lens. It is a figure which shows the light quantity distribution of the reflective surface of FIG. 2, and the light quantity distribution of the interference fringe image of FIG. It is a figure which shows the light quantity distribution of the reflective surface of FIG. 2, and the light quantity distribution of the surface image of FIG. It is a figure which shows the interference fringe image after reducing the noise of FIG. It is a figure which shows the surface image after reducing the noise of FIG. It is a figure which shows a mode that illumination light is irradiated to the to-be-tested spherical surface in the surface inspection apparatus of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Surface inspection apparatus 3 Light source part 10 Test lens (test object)
10A Test surface (surface)
11 Reference lens system 11A Reference surface 12 Imaging unit 15 Image processing unit 17 Low coherent light source 18 Path match optical system unit HM1 Half mirror (beam splitter)
31 Shutter (shielding plate)
37 Reference lens (reference member)
42 Storage Unit 43 Image Processing Device (Image Processing Unit)
44 Calculation unit

Claims (5)

Using an interference fringe measuring device comprising a low-coherent light source, a Fizeau interference optical system having a path matching mechanism composed of two optical paths, an imaging device, and an image processing device that processes and displays an image from the imaging device , A surface inspection method for measuring surface accuracy of a lens to be examined and inspecting surface defects,
A first step of acquiring and storing a reflected image from a reference surface of a reference lens of the Fizeau interference optical system in a state in which the test lens is not set in the interference fringe measuring apparatus;
A second step of setting the test lens in the Fizeau interference optical system, creating interference fringes by matching interference distances with the path matching mechanism, and acquiring and storing interference fringe images;
After eliminating the interference fringes by slightly different the interference distances of the two optical paths from the state of the second step by the path matching mechanism, the surface of the lens to be examined is brought into focus with the surface of the lens to be examined. A third step of acquiring and storing an image;
Subtract the light amount distribution of the reflected image from each of the light amount distribution of the interference fringe image and the light amount distribution of the surface image to create a new interference fringe image and a surface image of the test lens, and switch between them. A surface inspection method comprising: a fourth step of displaying. A light source that emits illumination light to irradiate the surface of the subject;
A reference member disposed on an optical path between the light source and the subject, having a reference surface that has the same optical axis as the subject and reflects a part of illumination light;
A reference surface reflected light emitted from the light source and reflected by the reference surface, and an optical path difference that is transmitted through the reference surface and reflected by the surface of the subject and is less than a coherence distance with respect to the reference surface reflected light. An image sensor for acquiring an image obtained by the test surface reflected light having
An image processing unit that processes the image acquired by the imaging device,
The image processing unit stores the first light amount distribution including only the reference surface reflected light, and the second light amount distribution obtained from the reference surface reflected light and the test surface reflected light. A surface inspection apparatus comprising: a calculation unit that subtracts the first light quantity distribution stored in the unit. A beam splitter that divides the illumination light into two, and an optical path length adjustment mechanism that adjusts the optical path length of one illumination light and the other illumination light divided by the beam splitter,
2. A first state in which an optical path difference between the reference surface reflected light and the test surface reflected light is the same as a coherent distance of the light source, and a second state in which the optical path difference is larger than the coherent distance of the light source. 2. The surface inspection apparatus according to 2. Further equipped with a focusing mechanism,
When in the second state, the focusing mechanism performs focusing so that an image of the subject is formed on the imaging element,
The surface inspection apparatus according to claim 3, wherein the calculation unit subtracts the first light amount distribution from the second light amount distribution obtained in the focused state. Further equipped with a focusing mechanism,
The optical path length adjusting mechanism includes a blocking member capable of blocking one of the one illumination light or the other illumination light,
When the inspection light or the reference light is blocked by the blocking member, focusing is performed so that an image of the subject is formed on the imaging element by the focusing mechanism,
The surface inspection apparatus according to claim 3, wherein the calculation unit subtracts the first light amount distribution from the second light amount distribution obtained in the focused state.

Images