JPH1138298A - Method for adjusting optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to easily carry out the alignment of spot light sources with respect to lens groups. SOLUTION: This optical system is constituted to collimate light emitted from the many spot light sources of a pinhole array, etc., to parallel light rays by a first lens group 5a of first and second lens groups 5a, 5b constituting a telecentric optical system with respect to the spot light sources and to focus the parallel light rays to a focal plane by means of the second lens group 5b. In such a case, a transparent parallel flat plate 10 is inserted between the first and second lens groups described above. This parallel flat plate 10 is oscillated and the image formed on the focal plane as a result of this oscillation is observed. The positions of the spot light sources are adjusted so that the movement of the image by the oscillation of the parallel flat plate 10 is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for adjusting an optical system in an optical system such as a confocal optical device by observing whether or not light between a plurality of lens groups is parallel. It is.

[0002]

FIG. 1 shows a confocal optical device which is an example of an optical system to which the present invention is applied. Light emitted from a light source 1 is transformed into a parallel light by a condenser lens 2 and is converted into a two-dimensional light. Light emitting pinhole array 3
The light is emitted as a two-dimensional array of point light sources.
In FIG. 1, only two optical paths are shown as an example.

After passing through the beam splitter 4, the emitted light is condensed on an object 6 to be measured by first and second lens groups 5a and 5b. Then, the reflected light passes through the first and second lens groups 5a and 5b in the opposite direction, is reflected by the beam splitter 4, and is projected on the light receiving pinhole array 7 conjugate with the light projecting pinhole array 3. Is done. Behind the light receiving pinhole array 7, a detector array 8 is arranged to detect the intensity of light passing through the light receiving pinhole array 7.

At this time, when the light projected on the measured object 6 is focused on the surface thereof, the amount of light passing through the light receiving pinhole array 7 becomes maximum, so that it is close to the measured object 6. If the second lens 5b is moved in the Z direction (optical axis direction), the surface shape of the measured object 6 in the range where light is projected can be measured, and this can be scanned in the XY directions (front-back, left-right directions). A wider range can be measured.

The first and second lens groups form a telecentric optical system, the details of which are shown in FIG.

Assuming that the focal points of the first and second lens groups 5a and 5b are f ₁ and f ₂ , the distance from the light projecting pinhole array 2 to the principal point of the first lens group 5a is f ₁ , The two lens groups 5a and 5b are installed in parallel with each other at a distance of f ₁ + f ₂ from the principal point of the first lens group 5a to the principal point of the second lens group 5b. The state where the distance between the two lens groups 5a and 5b is accurate and the degree of parallelism is maintained,
This optical system is referred to as being aligned.

At this time, the light emitted from the light projecting pinhole array 3 becomes parallel light between the first and second lens groups 5a and 5b, and the light emitted from the light projecting pinhole array 3 becomes the object 6 to be measured. At a scale of f ₂ / f ₁ . That is, measurement can be performed at the pitch of the light spot projected on the measured object 6.

As shown in FIG. 2, if the second lens group 5b is moved in the Z direction, the focal position moves in the Z direction without moving in the XY directions as indicated by the dotted line, and The height of the measurement object 6 can be measured.

In such a confocal optical system, alignment between the pinhole arrays 3 and 7 and the lens groups 5a and 5b is an important problem that is deeply related to inspection accuracy.

That is, as shown in FIG. 3, even if the light projecting pinhole array 3 is parallel to the first lens group 5a, the separation distance is f ₁ ′ (≠ f ₁ ). First
If deviated from the focus f ₁ of the lens unit 5a, since the measure f ₂ / f ₁ is no longer accurate, light spot that is projected on the measurement object 6, to know what kind of pitch And this significantly reduces the accuracy of the measurement.

At this time, as shown in FIG. 3, since the light between the two lens groups 5a and 5b is not parallel,
When the second lens group 5b is moved in the Z direction for inspection, there is a problem that the focal length shifts in the XY directions, and the same location cannot be measured, resulting in a measurement error. Further, as shown in FIG. 4, when the light projecting pinhole array 3 is not parallel to the lens groups 5a and 5b, the focal plane does not become horizontal, and a measurement error also occurs.

[0012]

As described above, in order to perform accurate measurement in this type of optical system, the distance between the first lens group 5a and the light projecting pinhole array 3 and the degree of parallelism must be accurate. Must be suitable for For this purpose, all of the light beams emitted from the light projecting pinhole array 3 are first
When passing between the second lens groups 5a and 5b, they must be parallel. As an apparatus for measuring the parallelism of this single light, there is an apparatus called a shear plate manufactured by Kino Melles Griot. This utilizes interference fringes of light, and it is possible to accurately observe whether light passing through the plate is parallel light.

However, the first and second lens groups 5
This shared plate cannot be used between a and 5b because a plurality of lights pass at the same time. For this reason, the first lens group 5a and the light emitting pinhole array 3
It was very difficult to accurately adjust the alignment between the two.

[0014]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and the method of adjusting the optical system uses a method in which light is emitted from a number of point light sources such as a pinhole array. The light from the point light source is converted into parallel light by a first lens group of first and second lens groups constituting a telecentric optical system with respect to this point light source, and the light is focused by a second lens group. In an optical system focused on a plane, a transparent parallel plate is inserted between the first and second lens groups, and the parallel plate is swung to observe an image formed on the focal plane. Then, the position of the point light source is adjusted so that the image does not move due to the swing of the parallel plate.

In the above-mentioned optical system adjusting method, the parallel flat plate can be accurately and stably rocked by a motor at a speed and an angle, and the point light source member can be finely moved by an alignment adjusting mechanism, so that the focus can be adjusted. An image formed on the surface is subjected to image processing, and the alignment adjustment mechanism is operated based on a signal resulting from the image processing.

According to the above optical system adjusting method, the alignment of the point light source with respect to the first and second lens groups constituting the telecentric optical system is performed by inserting a parallel plate between the two lens groups and swinging the same. The alignment of the point light source with respect to this lens group can be easily performed. Then, the alignment of the point light source can be automatically performed based on the image on the focal plane of the optical system.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. This embodiment is an embodiment applied to a confocal optical device as in the above-described conventional case, and the same members as those in the conventional case are denoted by the same reference numerals and described.

Between the first and second lens groups 5a and 5b, there is interposed a transparent parallel flat plate 10 whose upper and lower surfaces are finished to be exactly parallel. The first and second lens groups 4
It is assumed that a and 4b are aligned. As shown in FIG. 6, the parallel plate 10 can be accurately and stably oscillated at a speed and an angle by a motor 11 about an axis orthogonal to the optical axis of the confocal optical device. ing. Then, CC which is an example of a means for photographing the respective focal images at a plurality of focal positions of the second lens group 5b
The D cameras 12a, 12b,...

The projection pinhole array 3 can be aligned with the optical axis of the confocal optical device by an alignment adjusting mechanism 13. As an example, the alignment adjusting mechanism 13 uses a micrometer 13a as shown in FIG. The second lens group 5b includes a lens moving device 14 for moving the second lens group 5b in the optical axis direction.

The operation of the above configuration will be described with reference to FIGS. As shown in FIG. 8, the first lens group 5a and the second lens group 5a
If the light between the lens groups 5b is parallel, the incident position on the second lens group 5b is shifted even if the parallel plate 10 is swung in the direction of the arrow, but the focal position by the second lens group 5b There is no deviation.

On the other hand, as shown in FIG. 9, if the light between the two lens groups 5a and 5b is not parallel,
The focal position of the second lens group 5b moves in the X and Y directions according to the swing of. This movement of the focus is performed by the CCD camera 12a,
It can be known by taking a picture at 12b,.

As shown in FIG. 9, when the focal point moves in accordance with the swing of the parallel plate 10, the light emitting pinhole array 3
FIG. 3 shows the alignment of both lens groups 5a and 5b.
As shown in FIG. 4, the light emitting pinhole array 3 is shifted by the alignment adjusting mechanism 13.
The posture is adjusted and alignment is performed until the focus position does not move. Although the images of all the CCD cameras 12a, 12b,... Do not shift even though the parallel plate 10 swings, the alignment between the light projecting pinhole array 2 and the first lens group 5a is perfectly matched. Is where you are.

At this time, when the light projecting pinhole array 3 is moved in the optical axis direction, the focal position is shifted in the optical axis direction,
When the D cameras 12a, 12b,... Are observed, the focus becomes out of focus and the observation becomes difficult. Therefore, observation is facilitated by moving the second lens group 5a in the optical axis direction by the lens moving device 14.

In the embodiment described above, the alignment adjusting means 13 and the lens moving device 14, which are moving means of the light projecting pinhole array 3 and the second lens group 5b, are manually operated independently of each other. However, each of them may be operated electrically using a micromotor. In this case, as shown in FIG. 10, images from the CCD cameras 12a, 12b,.
, And the signal is sent to the micromotor driver 17 to finely move the light projection pinhole array 3 and the second lens group 5b, and the resulting image is subjected to signal processing again. This makes it possible to automate the alignment.

In each of the embodiments described above, a confocal optical device using a telecentric optical system has been described. Some of these confocal optical devices use a hologram as shown in FIGS. The present invention can also be applied to a confocal optical system using this hologram.

FIG. 11 shows a confocal optical system of this type.
The light becomes parallel light via 1a and 21b and enters the hologram 22 as reference light. The hologram 22 reproduces light equivalent to a point light source emitted from each pinhole position of the pinhole array 23 by diffracting the reference light.

The reproduced light is projected onto the object 6 by the second lens group 24b, scattered by the object 6, and
The light is reflected, transmitted through the second lens group 24b and the hologram 22, and passed through the first lens group 24a.
Focus on 3. FIG. 11 represents light at one pinhole position as a representative. 25 is a detector array.

FIGS. 12, 13 and 14 show the relationship between the focal point of the projected light by the second lens group 24b and the positional relationship between the surface of the measured object 6 in the optical axis direction (Z direction). Shows how an image is formed in the vicinity of the pinhole array 23. According to this, as shown in FIG. 12, the reflected light passes through the pinhole 23a of the pinhole array 23 only when the focal point and the surface of the measured object 6 coincide (focus), but at other times That is, when the focal point is reflected on the object 6 to be measured as shown in FIG. 13 (back focus), or when it is before reflection as shown in FIG. The light is blocked by the pinhole array 23 and hardly passes therethrough, so that a so-called light receiving stop function is performed.

By utilizing this characteristic, the pinhole array 23 is moved while moving the measured object 6 in the optical axis direction (Z direction).
By measuring the amount of reflected light passing through a with the two-dimensional detector array 25 as shown in FIG. 11, the position where the maximum amount of light is obtained is the surface of the object, that is, The position of the surface of the measurement object 6 can be measured. This is called peak processing.

On the other hand, the hologram 22 is manufactured in a process shown in FIG. That is, the light source 20 ′ is a coherent light source such as a laser,
The light is divided by the wavefront 7 and becomes light sources for the reference light and the object light of the hologram 22, respectively. When the light from the light source 20 ′ exhibits linear polarization characteristics, the polarization direction of the linear polarization is rotated by rotation of the first half-wave plate 28 a, and a polarization beam splitter is adopted as the beam splitter 27.
The intensity ratio of the division is set to a desired value.

The reference light and the object light split by the beam splitter 27 are divided into first, second and third and fourth magnifying lenses 2.
The light is enlarged by 9a, 29b, 29c, and 29d and is incident on the hologram 22 and the pinhole array 23, respectively. The light transmitted through the pinhole array 23 is diffracted by each pinhole and becomes light equivalent to a point light source.
Is converted into parallel light by the lens group 24a, and is incident on the hologram 22 as object light. By adjusting the second and third half-wave plates 28b and 28c, the polarization directions of the reference light and the object light are set to desired directions (generally the same direction), and the hologram exposure is performed. Preparation is completed.

In the confocal optical system using such a hologram, the distance and the parallelism between the first lens group 24a and the pinhole array 23 must be exactly the same as in the case of the telecentric optical system. Must.
Therefore, as shown in FIG. 16, the transparent parallel flat plate 10 is inserted between the first and second lens groups 24a and 24b in a state where only the object light is irradiated, and is swung as described above. An image focused through the second lens group 24b is converted to a CCD image.
Observing with the camera 12a and adjusting the pinhole array 23 and the second lens group 24b so that the image does not move,
The pinhole array 23 and the first lens group 24a are aligned.

[Brief description of the drawings]

FIG. 1 is a configuration explanatory diagram showing a confocal optical device using a telecentric optical system.

FIG. 2 is an explanatory diagram of an operation of a telecentric optical system.

FIG. 3 shows that a pinhole array is parallel to a lens group,
FIG. 4 is an optical path diagram when the distance is shifted.

FIG. 4 is an optical path diagram when a pinhole array is inclined with respect to a lens group.

FIG. 5 is a configuration explanatory view showing an embodiment of the present invention.

FIG. 6 is a perspective view showing a configuration for swinging a parallel flat plate.

FIG. 7 shows an embodiment illustrating an example of an alignment adjustment mechanism of a pinhole array.

FIG. 8 is an optical path diagram when light is parallel.

FIG. 9 is an optical path diagram when light is not parallel.

FIG. 10 is an explanatory diagram of a configuration of an apparatus when the method of the present invention is automated.

FIG. 11 is a schematic diagram illustrating the configuration of a confocal optical system using a hologram.

FIG. 12 is an explanatory diagram illustrating an image forming state of a reflected light near a pinhole.

FIG. 13 is an explanatory diagram showing an image forming state of a reflected light near a pinhole.

FIG. 14 is an explanatory diagram showing an image forming state of a reflected light near a pinhole.

FIG. 15 is an explanatory diagram of a configuration when exposing a hologram.

FIG. 16 is an optical path diagram showing an embodiment applied to a confocal optical system using a hologram.

[Explanation of symbols]

 1, 20, 20 'light source 2 condenser lens 3, 7, 23 pinhole array 4, 27 beam splitter 5a, 5b, 24a, 24b lens group 6 measured object 8, 25 detector array 10 ... Parallel plate 11 ... Motors 12a, 12b, ... CCD camera 13 ... Alignment adjustment mechanism 14 ... Lens moving device 15 ... Image processing device 16 ... cpu

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI G02B 21/00 G02B 21/00

Claims (3)

[Claims] 1. The light emitted from a number of point light sources such as a pinhole array is transmitted to said point light source by a first lens group of first and second lens groups constituting a telecentric optical system. In an optical system in which light from a point light source is converted into parallel light and a focal plane is focused by a second lens group, a transparent parallel flat plate is inserted between the first and second lens groups. An optical system characterized by oscillating the parallel plate, observing an image formed on the focal plane as a result, and adjusting the position of the point light source so that the image does not move due to the swing of the parallel plate. System adjustment method. 2. The optical system adjusting method according to claim 1, wherein the parallel plate is swung accurately and stably at a speed and an angle by a motor. 3. The method according to claim 1, wherein the point light source member is finely movable by an alignment adjustment mechanism, an image formed on a focal plane is image-processed, and the alignment adjustment mechanism is operated based on a signal resulting from the image processing. The method for adjusting an optical system according to claim 1, wherein: