JP3536952B2 - Lens curvature measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring the state of curvature of a lens, and more particularly, to an inspection apparatus using an optical sensor for measuring the state of curvature of an objective lens or an imaging lens from the center to the periphery. The present invention relates to a lens bending state measuring device capable of detecting a uniform and symmetrical surface with a changing state of the lens surface bending along a predetermined spherical surface as a light receiving axis of an optical sensor.

[0002]

2. Description of the Related Art An inspection apparatus using various optical sensors has an objective lens system and an imaging lens system. A one-dimensional or two-dimensional optical sensor is used to receive reflected light or scattered light from the inspection object via these lenses. In order to improve inspection accuracy with this type of device, it is of course to align the optical axis of the lens system with the light receiving center of the optical sensor, but in order to further suppress shading of the image, one-dimensional or two-dimensional It is necessary to align the axis with an axis having a uniform and symmetric curved surface along a predetermined spherical surface as viewed from the center as much as possible.
Therefore, it is necessary for the lens system to have a uniform and symmetrical change in distortion from the center to the periphery as much as possible in a plan view. FIG. 4 is an explanatory view of this type of conventional optical system inspection method. Reference numeral 1 denotes a stripe pattern plate which receives light from the white light source 2 and reflects the light to the lens 3 to be inspected. Reference numeral 4 denotes a magnifying lens system provided in alignment with the optical axis L of the lens 3 to be inspected. 5 is a screen,
It is translucent, and the projected fringes of the fringe pattern plate 1 projected from the back side can be observed. Magnifying lens system 4
Is a lens system provided for the measurement and has high accuracy with almost no distortion. Therefore, the state of the lens is inspected by observing and measuring the state of the stripe, and the mounting axis is determined.

[0003]

However, in such a method, the stripe pattern is visually measured by a person, which is troublesome, and the width and length of the stripe pattern enlarged by the magnifying lens system are increased. For some reasons, the measurement accuracy is limited because each measurement point is not specified. The accuracy of an optical inspection apparatus such as a foreign substance inspection apparatus for inspecting a recent wafer or the like cannot be fully supported. SUMMARY OF THE INVENTION An object of the present invention is to solve such a problem of the prior art, in which a plane which is uniform and symmetrical along a predetermined spherical surface and which serves as a light receiving axis of an optical sensor is efficiently used. It is an object of the present invention to provide a lens bending state measuring device capable of detecting a target with high accuracy.

[0004]

In order to achieve the above object, a lens bending state measuring apparatus according to the present invention comprises: a light projecting optical system for forming a point light source image at a focal position of a lens to be inspected; And a measuring optical system that is coupled to the lens to be inspected and receives light of the light source image from the lens to form an image on the light receiving surface of the light receiving device, and relatively moves the light receiving device along the optical axis of the measuring optical system A first moving means for moving the measuring optical system and the lens under test linearly in a direction perpendicular to the optical axis, and a light receiving means for driving the first and second moving means. The measurement optical system is moved two-dimensionally relative to the detector, and the light reception level obtained from the light receiver is obtained together with the coordinates of each two-dimensional measurement point, and a level equivalent to the light reception level of each two-dimensional measurement point is used as a map. And an arithmetic processing unit for outputting That.

[0005]

As described above, a point light source is telecentrically received by a lens to be inspected, and the received light is imaged as a point light source image on a light receiving surface of a light receiver by a measuring optical system. Moving along the optical axis, and further moving the light receiving surface in one axis direction perpendicular to the optical axis, and collecting the light receiving level at each measurement point in two dimensions, and forming a contour line having the same light receiving level. By performing mapping output, the bending state of the lens can be observed. In other words, if the curvature is uniform and symmetric, the figure formed by the same level of the received light level will be uniform and symmetric, but if the curvature is asymmetric, the figure formed by the same level will be It will be according to. Therefore, it is possible to specify the direction of a lens having a uniform and symmetrical curvature along a predetermined spherical surface by using a figure formed by equal levels. In general, in a mechanically polished lens, there are portions where the curvature is uniform and symmetrical along a predetermined spherical surface with high accuracy according to the characteristics, and portions where the curvature is not so. Since a unit incorporating a plurality of such lenses has a directionality specific to the unit, either attach the lens in consideration of the directionality or set the axis of the optical sensor so that the curve as much as possible follows a predetermined spherical surface. It can be mounted along a uniform and symmetric axis.

[0006]

FIG. 1 is a block diagram of an embodiment of a lens bending state measuring apparatus according to the present invention. FIG. 2 is a flowchart of the measurement processing, and FIG. 3 is a measurement result. In FIG. 1, reference numeral 20 denotes a lens bending state measuring device,
It comprises a light projecting system 21, a measuring lens system 22, an imaging system 23, a data processing device 24, and an XYZ drive device 25. In addition, L is an optical axis, which is arranged so as to coincide with the Z axis of the illustrated XYZ coordinate system. The light projecting system 21
It comprises a laser light emitting diode (LD) 211, a condenser lens 212 for condensing this light, and a pinhole plate 213, and forms a point light source at a focal position F1 of the optical axis L (Z axis).

Reference numeral 16 denotes an objective lens provided as a lens to be inspected, which is usually a telecentric lens unit on which an attachment reference position or a mark indicating the X axis or the Y axis is mechanically engraved. The lens to be inspected 16 is arranged so that the focal point is located at the focal point F1. The measurement lens system 22 is a lens 2 of the imaging system.
21 and a mount 222 for integrally connecting the lens and the test lens 16 with their optical axes aligned. The mount 222 is fixed to the XYZ driving device 25, whereby the measuring lens system 22 moves in the XYZ directions together with the lens 16 to be inspected. The imaging lens 221 is
This is a high-precision lens system which forms a point light source on the focal point F2, has a small spherical distortion, and is formed uniformly and symmetrically along a predetermined spherical surface. Therefore, it is assumed that this does not affect the measurement of the spherical state. Imaging system 2
3 has a CCD camera 231 and its Z drive device 232. The CCD camera 231 is moved by the Z driving device 232 on the Z axis (optical axis L), and the position is adjusted so that the CCD image forming surface (light receiver) is located at the focal position F2 of the measurement lens system 22.

The data processing unit 24 includes an MPU (microprocessor) 241 and a memory 242, an A / D conversion circuit (A / D) 243 for converting an analog value into a digital value in 8-bit 256 gradations, a buffer memory 244, a CRT. A display (CRT) 245, a printer 246, and the like are connected to each other.
It is connected to U241 and controlled by MPU241.
In the figure, an interface for coupling the bus 247, the XYZ drive device 25, and the Z drive device 232 is omitted. The XYZ drive device 25 and the Z drive device 232 are devices each including a drive control circuit that drives a moving mechanism in accordance with a signal from the MPU 241 and a moving mechanism. Here, the memory 242 controls the XYZ driving device 25 and the Z driving device 232 to perform YZ scanning.
The Z-scanning program 248 and the XYZ drive 25
Focusing program 249 for controlling focusing and Z driving device 232 for focusing, measurement data detecting program 2
50, and a map output program 251 are provided.

The YZ scanning program 248 drives the XYZ driving device 25 to move the mount 222 in the Y direction,
Further, the Z drive device 231 is driven to drive the CCD camera 231.
Is moved back and forth in the Z direction, and the lens 16 to be inspected is scanned YZ with light from the light projecting system 21. The focusing program 249 drives the XYZ driving device 25 in the Z direction to adjust the focal position of the lens 16 to be inspected to the focal point F1 and moves the lens 16 in the XY directions so that the center of the measuring lens system 22 is the optical axis L as Z. In accordance with the axis, Z drive 2
32, the maximum level of the received light is detected, and the imaging plane of the CCD camera 231 is made to coincide with the focal point F2, which is set as the scanning origin "0" in the Z direction. When a spot (point light source image) is formed on the image plane of the CCD camera 231, the measurement data detection program 250 reads the A / D conversion data from the buffer memory 244, extracts the measurement data, and extracts the peak data. The value is stored in the memory 242 together with the YZ coordinates of the measurement point. The map output program 251 is
The maximum light receiving level is detected from the data of each measurement point, and the position is set as the center. The maximum light receiving level is set to 100%, and the percentage (%) of each measurement data is calculated corresponding to each YZ scanning position. CRT display 245 generates map data that connects every other measurement data with contour lines.
Or output to the printer 246.

Next, the measurement process will be described with reference to FIG. First, measurement processing is started by a measurement key input interrupt, and data such as the width of YZ to be scanned is input by initial value setting (step 101). And MPU2
41 executes the focusing program 249 to focus the lens 16 to be inspected on the focal point F1, further aligns the center of the lens of the measuring lens system 22 with the optical axis L,
A focusing process is performed to make the image plane of the CCD camera 231 coincide with the focal point F2 (step 102). Next, M
The PU 241 executes the YZ scanning program 248 to move the measurement lens system 22 to the starting point of the scanning point in the YZ direction (for example, Y
Assuming that the focal point F2 in the Z direction is “0” at the left corner of the scanning range (Y = −18 mm, see FIG. 3), the position close to the 300 μm measuring lens system 22 (Z = −300 μm, see FIG. 3)
(Step 103). At this time, a point light source image on the light projecting side is formed on the image forming plane of the CCD camera 231 and the video signal is added to the A / D 243. The light receiving level data at the start point (first measurement point) is 256 floors. Tonal,
The data is stored in the buffer memory 244 as a digital value, and the data at the measurement point is collected (step 104).

Next, the MPU 241 executes the measurement data detection program 250, and obtains a peak value as the measurement data for the point light source from among the data stored in the buffer memory 244 at a predetermined level or higher. Is stored in a predetermined area of the memory 242 together with the YZ coordinates of the measurement point (step 105). Then, it is determined whether or not scanning in the Y direction has been completed (step 106). If the result of this determination is that scanning has not been completed, the next Y
The measurement lens system 22 is moved to the measurement point in the direction (Step 107), and the flow returns to Step 104 to repeat the same measurement. When the scanning in the Y direction is completed in this way, it is determined whether the scanning in the Z direction is completed (step 108). When the scanning is not completed, the scanning is performed by one measurement point in the Z direction (step 108). 109), returning to step 104, scanning in the Y direction is performed again, and it is determined whether or not the scanning is completed (step 106).

When the YZ scanning is performed in this manner, and the scanning in the Z direction is terminated in the determination of step 108, the MPU 241 executes the map output program 251 to execute the maximum light receiving from the data stored in the memory 242. The level is detected (step 110), and the maximum light receiving level is set to 100% with the position of the YZ coordinate as the center.
(Step 111), map data connecting measurement data every 10% by contour lines is generated (step 112), displayed on the CRT display 245, and output to the printer 246 (step 113).

FIG. 3 shows the map output in this manner. By obtaining the center position O and the mounting rotation angle θ according to this map, it is possible to obtain the center position and the optimum mounting angle of the objective lens, which is the lens 16 to be inspected. In the data of FIG. 3, there is a maximum level at the position of "0" of the Y coordinate, and this point is the center position O, so that there is no shift in the center position in the Y direction. Also, in a lens system having a uniform and symmetrical curvature, the contour distribution pattern is a uniform elliptical contour line that is symmetrical with respect to the Z axis and is symmetrical with respect to the Y axis. The above-mentioned θ can be determined by determining the axis Yo as an axis suitable for light reception close to the axis based on this. The above is the measurement of the center position in the Y direction and the mounting angle.
The same data can be collected by rotating the degree measurement lens system 22 and setting the Y axis as the X axis.

When the lens system is actually mounted on the measuring optical system, by rotating the lens system by θ with respect to the mounting reference position or by displacing the center position in accordance with the data thus obtained, the shading is reduced. An image can be obtained. In this case, the axis on the optical sensor side may be rotated by θ to match the axis Yo. In particular, when the measurement is performed in the Y direction and the X direction, the rotation angle θ
It is good to take the average value of each of them, and to attach them by shifting the attachment position in the XY directions.

Further, based on such received light data on the curved surface of the lens, the obtained measurement data can be corrected for the attached lens system based on the received light data of the curvature measurement. If the measurement lens system 22 has a similar curvature, the map may be output after correcting the curvature. As a method of performing these corrections, a correction data table is provided in the memory of the inspection apparatus, and from the measurement results of the XY coordinates or the X and Y coordinates and each light receiving level, the contour lines of which the measurement results are uniform and symmetrical are obtained. It is sufficient to calculate a ratio corresponding to the% of the position, and correct the measured value by multiplying the reciprocal of the ratio. In addition,
In the embodiment, the objective lens is a lens to be inspected.
The measurement object of the present invention can be similarly applied to an imaging lens, and may be a combination unit of an objective lens and a coupling lens. The same applies to other lens systems. Further, in the embodiment, CC
The D camera is moved in the Z direction along the optical axis,
It goes without saying that the CCD camera side may be fixed and moved in the Z direction including the measuring lens system, the lens to be inspected, the light projecting optical system, and the like. The light receiving device on the detection side is not limited to a CCD camera.

[0016]

As described above, according to the present invention, a point light source is telecentrically received by a lens to be inspected, and the received light is imaged as a point light source image on a light receiving surface of a light receiver by a measuring optical system. Then, the light receiving surface is relatively moved along the optical axis, and further, the light receiving surface is moved in one axis direction orthogonal to the optical axis, and the light receiving level at each measurement point is sampled in two dimensions. By outputting the contour lines having the same light receiving level as a map, the curved state of the lens can be observed. As a result, without measuring by visual observation, the state of the lens is examined, and the curved state from the center to the periphery is uniform and symmetric along the predetermined spherical surface, and the surface is the light receiving axis of the optical sensor. Can be detected efficiently and with high accuracy.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of a lens bending state measuring apparatus according to the present invention.

FIG. 2 is a flowchart of the measurement process.

FIG. 3 is a graph showing the measurement results.

FIG. 4 is an explanatory view of a conventional lens bending state measuring device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Stripe pattern board, 2 ... White light source, 3, 16 ... Inspection lens, 4 ... Magnification lens system, 5 ... Screen, 20 ... Lens curvature state measuring device, 21 ... Projection system, 22 ... Measurement lens system, 23 imaging system, 24 data processing device, 25 X
YZ drive device, 211 ... laser light emitting diode, 212
... Condenser lens, 213 ... Pinhole plate, 221 ... Lens, 222 ... Mount, 241 ... Microprocessor (MPU), 242 ... Memory, 243 ... A / D conversion circuit (A / D), 244 ... Buffer memory, 245 … CRT
Display, 246: Printer, 247: Bus, 24
8 YZ scanning program, 249 focusing program, 250 measurement data detection program, 251 map output program.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-137995 (JP, A) JP-A-5-45248 (JP, A) JP-A-55-44949 (JP, A) JP-A-54-44949 87547 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01B 11/00-11/30 G01M 11/00-11/08

Claims (2)

(57) [Claims] 1. A light projecting optical system for forming a point light source image at a focal position of a lens to be inspected, a light receiving device, and a light receiving device coupled to the lens to be inspected and receiving light receiving the light source image from the lens. A measuring optical system that forms an image on the light receiving surface of the first optical system, and a first optical system that relatively moves the light receiver along the optical axis of the measuring optical system.
Moving means, and the measuring optical system and the lens to be inspected are linearly moved integrally in a direction orthogonal to the optical axis.
Moving means, driving the first and second moving means to two-dimensionally move the measurement optical system relative to the light receiver, and reducing the light reception level obtained from the light receiver to the two-dimensional An arithmetic processing unit which obtains the coordinates of each measurement point together with the light reception level of each of the two-dimensional measurement points and outputs the same level as a map. 2. The point light source image is formed by a pinhole; the lens to be inspected is a telecentric lens system; the light receiving device is a CCD optical sensor;
The moving means moves the CCD optical sensor with respect to the measuring optical system. The arithmetic processing unit has a microprocessor and a memory, and converts a detection signal of the optical sensor into an A / D signal. Receiving the converted light to obtain the light receiving level of each of the measuring points, wherein the map displays the light receiving level at each of the measuring points by a contour line as a percentage of the maximum light receiving level. A lens bending state measuring apparatus according to the above.