JPH11211439A - Surface form measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the surface form of an object without performing Z- scanning by arranging a confocal image pickup system so that the object-side focal plane is tilted to the moving direction of the object. SOLUTION: A confocal image pickup system A is arranged while tilting in the X-direction (moving direction) to XY plane which is the placing base plane of an X-table 1. The X-table 1 is step-moved and rested every step movement to input a confocal image to an image processing device 5 by the confocal image pickup system A. Namely, the field of view of the confocal image pickup system A is divided equally to N pieces to provide a confocal image every 1/N field-of-view movement, and the surface form of an object 4 is calculated from a plurality of resulting confocal images by the image processing device 5. Since the object-side focal plane 2 of the confocal image pickup system A is tilted, the focal positions in the same position of the object 4 on N-pieces of confocal images are shifted, respectively, and this corresponds to Z-scanning in N-stages.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a surface shape measuring device for measuring a surface shape of an object.

[0002]

2. Description of the Related Art An optical system for obtaining an image by a confocal optical system is called a confocal imaging system, and an image obtained by the confocal imaging system is called a confocal image.

A confocal optical system has a characteristic called optical sectioning or depth discrimination. That is, when the object or the confocal imaging system is moved in the direction of the optical axis (hereinafter, referred to as Z axis) (hereinafter, referred to as Z scan), the object side focus surface of the confocal optical system coincides with the object surface (hereinafter, in-focus). ), The image becomes brighter.

The surface shape of an object can be measured using these characteristics. In other words, a confocal image is obtained every time a minute distance is moved when performing the Z scan, and the Z position of the confocal image that gives the maximum brightness among many confocal images having different Z positions is set for each pixel. Thus, the Z position of the object surface for each point of the image, that is, the object surface shape is obtained.

[0005]

In many cases, the size of an object does not fit within one field of view of a confocal imaging system. Therefore, the position of the field of view of the confocal optical system with respect to the object is actually XY
It is necessary to move using a table. That is, considering a moving mechanism for Z scanning, control of XYZ three axes,
You need to move. The number of moving axes should be as small as possible in consideration of the equipment cost and handling.

Further, in such a conventional technique, XY
Since it is necessary to perform Z-scan while moving and stopping the XY table, the cycle of XY movement, stop, and Z-scan must be repeated. Considering the high speed and easy handling of the apparatus, it is better to be able to measure without stopping in the XY movement as much as possible.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a surface shape measuring apparatus capable of measuring a surface shape without performing a Z scan and stopping as much as possible in the XY movement.

[0008]

In order to achieve the object, at least one-axis moving mechanism and a confocal point arranged such that an object-side focus surface of the moving mechanism is inclined with respect to a moving direction of a certain axis. A plurality of confocal images obtained by dividing the field of view of the imaging system and the confocal imaging system into N parts in the moving direction and obtaining a confocal image by the confocal imaging system each time the 1 / N field of view moves And an image processing device that calculates the surface shape of the object from the image data.

In this manner, the same part of the object is shown in the N consecutive confocal images shifted by 1 / N field of view, and the object-side focus surface of the confocal imaging system is inclined. Therefore, the images of the same part of the object appearing in the N confocal images are out of focus, which means that the N-stage Z scan has been performed. What is necessary is just to search for an image which gives the maximum brightness from the image whose focus position is shifted by N steps, similarly to the surface shape measurement by the conventional confocal optical system. Since the inclination of the object-side focus surface of the confocal imaging system can be accurately measured in advance, the Z position of the object surface can be determined according to the order of the N-stage image that gives the maximum luminance. It is possible to obtain the exact value.

Further, the confocal imaging system is an all-pixel simultaneous exposure type confocal imaging system, and the movement of the confocal imaging system in the direction in which the object-side focus surface is inclined moves without stopping within the measurement range. However, if exposure for imaging is performed using a shutter or strobe or both in synchronization with a signal from the timing sensor for each 1 / N field of view, a very wide field of view can be measured at high speed. become.

The confocal imaging system is an all-pixel simultaneous-exposure confocal imaging system, and the object-side focus surface of the confocal imaging system is tilted with respect to the optical axis of the objective lens. In this case, since the optical axis of the optical system does not tilt with respect to the object, better illumination can be performed.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a first example of an embodiment of the present invention. A confocal imaging system A is installed so as to be tilted in the X direction with respect to an XY plane, which is a mounting table plane of an X table 1 which is a uniaxial movement table. That is, the object-side focus surface 2 of the confocal imaging system A is parallel to the Y axis in the Y direction, and is inclined with respect to the X axis in the X direction.
Here, the confocal imaging system A may be a laser scanning confocal microscope or a Nippow disk scanning confocal microscope, or an all-pixel simultaneous exposure confocal imaging system described in detail later. May be. Here, for simplicity of description, the object 4 is moved in the Y direction in the field of view 3 of the confocal imaging system A.
, And has a size several times larger than the field of view 3 in the X direction. The X table 1 performs step movement, stops at each step movement, and inputs a confocal image to the image processing device 5 by the confocal imaging system A. Assuming that the size of the visual field 3 in the X direction is a and the inclination of the object-side focus surface 2 is θ, the step movement amount is represented by (a / N) cos θ, and the visual field 3 has N areas as shown in FIG. Is divided into X table 1 moves to the right with respect to field of view 3 (a / N)
cos θ, the N regions are divided into regions 1, 2,. . . , Area N, the image of the same part of the object 4 is sequentially moved from the area 1, 2, 3,. . . , N. At this time, since the object-side focus surface 2 of the confocal imaging system A is tilted with respect to the X axis, the object-side focus moves by (a / N) sin θ every time the part of the object 4 moves from the area 1. The distance from the surface 2 will change. That is, the Z scan is achieved. At this time, the scan range of Z is almost a (N−1 / N) sin.
In θ, the focus position differs by N steps by N movements.
An N-size image set is obtained. This 1 /
For each pixel of an N-size image, an image providing the maximum luminance value (that is, at the time of focusing) is searched from among focus positions different in N stages, and the Z position can be obtained from the X position in the image. . Once the image set is obtained, a similar (i.e., 1 / N size) image set of a part next to the current part is obtained for each movement, so that all the objects can be obtained. It is only necessary to keep moving until an image set of the part is obtained.

The case where N = 4 will be described more specifically with reference to FIGS. Confocal image 4 obtained continuously
From the sheets I1, I2, I3 and I4, the portions where the same part of the object (the tip part of the object in FIG. 3) is shown are pulled out (region I1 to region 1, region I2 to region 2, I
3 to region 3, I4 to region 4). This is one image set, and corresponding pixels of each image are compared in this image set to find an image that gives the maximum luminance value. For example, the pixel (x, y) in I1, the pixel (x + a / 4, y) of I2, and the pixel (x + a / 2, y) of I3
And the luminance of the pixel (x + 3a / 4, y) of I4. As shown in FIG. 4, if the position of x = 0 in the field of view is defined as z = 0, the position of z is given by z = x · sin θ according to the value of x. The surface position of the object at that point is (x + a / 2) si
nθ. By performing the same calculation for all the pixels, surface shape data of this image set portion can be obtained.

When the image is moved again to obtain the image of I5, the regions 1 and 2 of the images of I2, I3, I4 and I5 are obtained.
Since an image set of a new part is obtained from the region 2, the region 3, and the region 4, the surface shape data of the object can be obtained by the same calculation. Move until an image set of all parts of the object is obtained to obtain all data.

When the pitch (a / N) sin θ of the focus positions of each image in the image set is a sufficiently small value, as described above, the point at which the maximum luminance is obtained from the different points of the corresponding N focus positions is determined. It is sufficient to find it and multiply the X coordinate value by sinθ. However, if the pitch is small, there is a problem that a very large number of images must be processed or a sufficient Z scan range cannot be obtained. .

On the other hand, if the pitch is increased, x · si
Since the pitch corresponds to the measurement resolution in the calculation of nθ, the measurement resolution is reduced. Therefore, it is considered that the pitch is widened by using the interpolation calculation and the measurement resolution is not reduced.

The output characteristic of the confocal optical system with respect to the movement of an object in the direction of the optical axis has a mountain-shaped characteristic called an optical sectioning characteristic as shown in FIG. The peak position of this curve indicates the focus position, and it is necessary to find this position. When the pitch is small, the curve is sampled almost continuously, so that the curve can be obtained from the position of the sampling point of the maximum value. Now, when sampling is performed at a coarse pitch as shown by a dotted line in FIG. 5, the position of each sampling point is x _i · sin
given by _{θ (x i + 1 = x} i + a / N), the peak position when the front and rear of the sampled values, respectively and f _i-1, f i _{+ 1} of the f _i the maximum value in the sampling points as f _i is By fitting to a Gaussian function, z = x _i · sin θ + (lo
g (f _{i + 1} ) -log (f _i-1 )) · (a / N) · sin
θ / (2 · (2 · log (f _i ) −log (f _{i + 1} ) ₋₁ )
og (fi _-1 ))).
Of course, the fitting function is not necessarily a Gaussian function, and a quadratic curve (parabolic) function, an approximate function of a Gaussian function, or the like can be used. In addition to the fitting calculation, for example, a center-of-gravity calculation or a mountain-shaped template may be prepared, and it may be obtained from the cross-correlation with the template. In addition, it is not always necessary to calculate three points, and five points or seven points may be used. By using such an interpolation operation, the number of N can be reduced, the number of images required for the operation can be reduced, and the resolution can be maintained.

Next, a second example of the embodiment of the present invention will be described. Here, an all-pixel simultaneous exposure type confocal imaging system is used as the confocal imaging system. The all-pixel simultaneous-exposure confocal imaging system does not perform XY scanning such as a Nippow disk scanning type or a laser scanning type, and two-dimensionally arranges pinholes with respect to an objective lens (or an optical effect having an equivalent effect). System), and is a confocal imaging system that simultaneously exposes the entire image by using a system, and has a feature that high-speed imaging using a shutter or a strobe is possible. This all-pixel simultaneous exposure type confocal imaging system is disclosed, for example, in Japanese Patent Application No.
94682. This will be described in detail below.

An all-pixel simultaneous exposure confocal imaging system described in Japanese Patent Application No. 8-94682 will be described with reference to FIG. Light source 601
The emitted illumination light passes through the pinhole 602 and is emitted as collimated light by the collimator lens 603. The optical path branching optical element 604 is a polarization beam splitter, and passes illumination light as linearly polarized light. The illumination light that has passed through the optical path branching optical element 604 is
And is collected at the focal point of each microlens. A pinhole array 606 is provided at the focal position of the microlens array 605, and each pinhole is present at the position of the focal point of the illumination light collected by each microlens. The illumination light by the pinhole array 606 is
In other words, it is a point light source array. The illumination light having passed through the pinhole is incident on the objective lens 607, becomes a circularly polarized light by the quarter-wave plate 609 provided inside the objective lens 607, and projects the image of the pinhole onto the object 4. The objective lens 607 is a double-sided telecentric lens having a telecentric stop 608 and lenses 607a and 607b inside, so that a change in magnification does not occur even if the object 4 or the optical system is moved in the optical axis direction. The reflected light from the object 4 enters the objective lens 607 again, becomes linearly polarized light orthogonal to the illumination light by the 波長 wavelength plate 609, is collected, and reaches the pinhole array 606 again. The reflected light that has passed through the pinholes of the pinhole array 606 is emitted by the microlens array 605 as a parallel light flux. Since the reflected light is linearly polarized light orthogonal to the illumination light, the reflected light is deflected by the optical path branching optical element 604, which is a polarization beam splitter, to form an imaging lens 610.
Incident on. The reflected light that has entered the imaging lens 610 reaches the two-dimensional detector 611. In the imaging lens 610, the surface of the microlens array 605 and the surface of the two-dimensional detector 611 are conjugate. As a result, a confocal image is obtained on the two-dimensional detector 611, photoelectrically converted by the two-dimensional detector 611, and output as an electric signal.

As described above, when an optical system having such a structure is used, a confocal image can be obtained by simultaneous exposure of all pixels. Therefore, the electronic shutter function of the two-dimensional detector 611, strobe lighting, or a combination thereof can be used. Thus, the moving object can be obtained as a still image.

The second embodiment is basically the same as the first embodiment, but differs from the first embodiment in that the X-table can be moved stepwise by using the all-pixel simultaneous exposure type confocal imaging system described above. It would be possible to increase the speed by using continuous movement instead.

This will be described with reference to FIG. Here, the confocal imaging system A is an all-pixel simultaneous exposure type confocal imaging system. A linear encoder 6 is attached to the X table 1 and outputs a pulse indicating a moving amount to the timing sensor 7.
The timing sensor 7 can grasp the movement amount by counting the pulses. Step moving amount (a / N) c as in the first embodiment
Instead of stopping the X table 1 every osθ, in this example, the X table 1 moves continuously, and the timing sensor 7 issues an imaging timing signal to the confocal imaging system A every step movement amount. Has become. Upon receiving the timing signal, the confocal imaging system A immediately performs short-time exposure by the electronic shutter function, and transmits the image signal to the image processing device 5. At this time, the moving speed of the X table 1 is set to be sufficiently low with respect to the exposure time by the electronic shutter of the confocal imaging system A. More specifically, for example, the moving distance of the X table 1 during the exposure time depends on the confocal imaging system A.
Is set to be 1/10 or less of the horizontal resolution (the field of view equivalent to one pixel). By doing so, the confocal image can be acquired at a high speed by continuously moving the X table 1 with almost no reduction in accuracy.

If the amount of light is insufficient due to the short exposure time, the illumination is not strobed illumination but strobe illumination. In this case, the timing signal is also sent to the strobe lighting device side, and light is emitted in conjunction with the electronic shutter of the confocal imaging system. In this way, an image with a sufficient light amount can be obtained with little influence of disturbance light.

Next, a third embodiment of the present invention will be described. In this example, instead of tilting the object-side focus surface by tilting the confocal imaging system, the confocal imaging system itself is not tilted, and the pinhole array unit of the confocal imaging system is tilted to shift the object-side focus surface. Try to tilt. FIG. 8 shows this state. The confocal imaging system B is an all-pixel simultaneous-exposure confocal imaging system, which is described in the second example, except that the integrated part of the microlens array 605 and the pinhole array 606 is inclined. The X table 1 is the same as in the first example, but may be a continuous movement as in the second example.

By tilting the pin-pole array 606 of the all-pixel simultaneous-exposure confocal imaging system to tilt the object-side focusing surface 2, the optical axis itself does not tilt. For example, even when the object 4 is a plane mirror, the illumination light and the reflected light pass through the same optical path, and the illumination efficiency is improved.

[0026]

According to the present invention, the surface shape can be measured at high speed without stopping the XY movement without performing the Z scan.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first example of an embodiment of the present invention.

FIG. 2 is a diagram illustrating a field of view of a confocal imaging system according to the present invention.

FIG. 3 is a diagram for explaining an image processing method of the present invention.

FIG. 4 is a diagram showing the relationship between the position of the visual field and the position of the Z coordinate of the confocal imaging system of the present invention.

FIG. 5 is a diagram illustrating optical sectioning characteristics of a confocal optical system.

FIG. 6 is a diagram for explaining an all-pixel simultaneous exposure confocal imaging system.

FIG. 7 is a diagram showing a second example of the embodiment of the present invention.

FIG. 8 is a diagram showing a third example of the embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 X table 2 Object-side focus surface 3 Field of view 4 Object 5 Image processing device 6 Linear encoder 7 Timing sensor A, B Confocal imaging system

Claims (3)

[Claims] 1. A confocal imaging system, comprising: a moving mechanism having at least one axis; a confocal imaging system arranged such that a focus surface on an object side of the moving mechanism is inclined with respect to a moving direction of a certain axis; The field of view is divided into N equal parts in the moving direction, and a confocal image is obtained by the confocal imaging system every time the 1 / N field of view moves,
A surface shape measurement device comprising: an image processing device that calculates a surface shape of an object from a plurality of obtained confocal images. 2. The confocal imaging system is an all-pixel simultaneous-exposure confocal imaging system. Movement of the confocal imaging system in a direction in which the object-side focus surface is inclined does not stop within the measurement range. 2. The exposure apparatus according to claim 1, wherein the exposure is performed by using a shutter and / or a strobe in synchronization with a signal from a timing sensor for each 1 / N field of view.
The surface shape measuring device according to the above. 3. The confocal imaging system is an all-pixel simultaneous-exposure confocal imaging system, and the object-side focusing surface of the confocal imaging system is tilted with respect to the optical axis of the objective lens. The surface shape measuring device according to claim 1, wherein the surface shape is measured.