JPH01158302A - Optical measuring apparatus having autofocusing mechanism - Google Patents

Abstract

PURPOSE:To obtain an optical measuring apparatus, which can be focused, without utilizing the edge part of an object to be measured itself, by superimposing the image of a knife edge as a pattern filter on a part of lighting light through a projection lighting system. CONSTITUTION:A pattern filter 26 has an edge part. A knife edge image 26A of the knife edge 26 is formed on an object surface to be measured 8 through a projecting lens 14. The knife edge 26 is arranged in this way. A sensor 42 is arranged in the vicinity of an image forming plane IP. When a reconstituted image of the knife 26B of the image 26A through the lens 14 crosses a part in front of the plane IP, a focal point signal (a), which is varied with the variation of occulting light, is outputted. A vibrator 28 vibrates the filter 26 and outputs synchronizing signals d1 and d2 in correspondence with the vibrations. A control circuit operates the vibrator 28 and operates a Z-axis driving device 16 at the same time so that the changing amount of a focal point signal (c) becomes the maximum value. It is judged that the object to be measured is focused at a position, where the changing amount of the signal (c) becomes the maximum value. Thus the focusing can be achieved without using the edge part of the object to be measured itself.

Description

[Detailed description of the invention]

[Industrial Application Field 1] The present invention relates to an optical measuring machine with an autofocus mechanism,
In particular, the present invention relates to improvements in optical measuring instruments equipped with an autofocus mechanism suitable for use in projectors, measuring microscopes, and the like. 2. Description of the Related Art Various autofocus mechanisms have been proposed for optical measuring instruments such as projectors and measuring microscopes 11 in order to reduce the burden on workers and speed up measurement work. The applicant also disclosed in Japanese Patent Application Laid-open No. 60-84522 that the object to be measured is conversely focused on the projection lens system due to the rounding of the output signal of an edge detection device including a four-divided light receiving element for detecting edges in projection image production. We have proposed an autofocus mechanism that detects whether or not the Specifically, this autofocus mechanism relatively images the image of the edge portion of the object to be measured and the sensor section of the edge detection device, and generates an S-curve curve that is an output edge detection signal. , which takes advantage of the fact that the amplitude is maximum when in focus and is small when out of focus.The S-curve curve is measured by moving the stage on which the object to be measured is placed up and down while observing the S-curve curve. The stage is fixed at the point where the rate of change is greatest.

[Problems to be solved by the invention]

However, the autofocus Q 4M proposed in JP-A No. 60-84522 has the following problems because it uses the image of the edge of the object itself to focus. Ta. (2) It takes time to move the image of the edge of the object to be measured to the front of the sensor of the edge detection device. ■It is necessary to mechanically vibrate either the stage on which the object to be measured or the sensor is placed, and it takes a long time to focus. (2) When the sensor is vibrated, the structure becomes complicated, and on the other hand, when the stage is vibrated, an excessive load is placed on the drive motor of the stage, especially when the object to be measured is heavy.

[Purpose of the invention]

The present invention has been made in order to solve the above-mentioned conventional problems, and it is an object of the present invention to provide an optical measuring instrument with an autofocus mechanism that can perform focusing without using the edge portion of the object to be measured. purpose.

[Means to solve the problem]

The present invention provides a stage for placing an object to be measured, an illumination system for illuminating the object to be measured, an imaging optical system for forming an image of the object to be measured on an imaging plane, and the above-mentioned object. An optical measuring machine that includes a stand and a drive device that relatively displaces an imaging optical system along the optical axis of the imaging optical system, which has an edge portion, and whose image is measured through the imaging optical system. A pattern filter disposed so as to be formed on the target surface, and a re-formed image of the edge portion of the pattern filter disposed near the imaging plane by the imaging optical system, is formed on the front surface of the pattern filter. a sensor that outputs a focus signal that changes according to changes in brightness when crossing the pattern filter, an exciter that vibrates the pattern filter and outputs a synchronization signal in response to the vibration, and an exciter that operates the exciter. and a υ control circuit for operating the driving device so that the amount of signal change in the focus signal is maximized while the measurement target is focused at a position where the signal change m in the focus signal is maximized. By determining that there is, the above objective has been achieved.

[Effect]

In the present invention, instead of using the conventional edge portion of the object to be measured for focusing, a vibrating edge pattern image is projected onto the surface of the object to be measured and used for focusing. That is, a vibrating edge pattern image is formed on the measurement target surface of the measurement target placed on the stage, further images of the pattern image are received by the sensor, and signal change measures of the sensor output signal are performed. It is determined that the object to be measured is in focus at the maximum position. Therefore, there is no need to move the image of the edge portion of the object to be measured to the front of the edge sensor. Furthermore, there is no need to mechanically vibrate the edge sensor or the stage. Therefore, the mechanism is also IP pure, and no excessive burden is placed on the drive motor or the like.

【Example】

Embodiments of the present invention will be described in detail below with reference to the drawings. The first embodiment of the present invention, as shown in FIG. The present invention is applied to an epi-illumination reflective projection inspection machine that includes a Z-axis drive device 16 that relatively moves an imaging optical system including a projection lens 14 along the optical axis X of the projection lens 14. It was applied. The document table 10 is connected to the Z-axis drive circuit 1 of the two-axis drive device 16.
It is arranged to be displaced in the vertical direction (Z direction) by a Z-axis motor 16B which is rotationally driven by the output of the motor 6A. The document table 10 is also driven by an X-axis motor 18 that is rotationally driven by the output of an X-axis drive circuit (not shown) and a Y-axis motor 20 that is rotationally driven by the output of a Y-axis drive circuit (not shown). X direction and Y direction perpendicular to Z direction, respectively
The position in the X-axis direction and the Y-axis direction are detected by an X-axis detector 19 and a Y-axis detector 21, respectively. The measurement target surface 8 of the measurement target placed on the object table 10 is irradiated with illumination light via a half mirror 24 from the epi-illumination system 12 including, for example, a lamp and a condenser lens. . A part of the illumination light from this epi-illumination system 12 includes an image 26 of a knife 26 as a pattern filter according to the present invention.
A is superimposed. That is, a knife 26 is provided for irradiating pattern light with a contrast of light and dark for use in autofocus, and the exciter 2
The image was taken by 8. This exciter 28 is composed of, for example, a piezoelectric element or a tuning fork camera, and is synchronized by an optical switch or the like built in the exciter 28 at the top dead center B and bottom dead center A of the vibration of the knife 26. Signals d1 (corresponding to bottom dead center A) and d2 (corresponding to top dead center B) are generated (see FIG. 2). The knife 26 is, for example, a laser diode (L
Illuminated with D>30, auxiliary lens 32, mirror 3
4 and a half mirror 35 inserted into the optical path of the epi-illumination system 14, the light beam is superimposed on the optical system of the epi-illumination system 12. Therefore, @26A of the naifetsuji 26
is also reflected by the half mirror 24, and is imaged by the projection lens 14 onto the measurement target surface 8 on the measurement target. However, this knife image 26A is in focus when the surface to be measured 8 is on the focal plane FP, but becomes an out-of-focus image when the surface to be measured 8 is vertically displaced. The image of the object to be measured and the knife image 26A on the object surface 8 are formed by the imaging lens 14 and the half mirror 2.
4 onto the image plane IP on the screen 36. Therefore, when the measurement target surface 8 is displaced vertically from the focal plane FP, the re-formation 11126B of the knife image formed on the imaging plane IP on the screen 36 also becomes a defocused image. A sensor 42 is fixed on the screen 36 by, for example, a transparent fixing plate 40 at a position where the re-formed image 26B of the knife is formed, for example, at the center position. As shown in detail in FIG. 2, this sensor 42 includes, for example, a light-receiving cable 42A divided into two parts on a response circle. 42B and a preamplifier 44A144 that processes its output.
B, the detection signal a of the preamplifier 44A, 44B output,
b, and a differential amplifier 46 which obtains a focus signal C as a differential amplification value. An edge signal generation circuit 48 for generating an edge signal (pulse) m from the detection signal a of the sensor 42 and the focus signal C output from the differential amplifier 46 based on the brightness and darkness contrast of the reflected image corresponding to the unevenness of the object to be measured. For example, as disclosed in Japanese Patent Application Laid-Open No. 61-128105 by the applicant, an edge signal m is generated when the focus signal C crosses zero within a certain area by moving the stage 10 in the X-Y direction. Has a function. The specific configuration is disclosed in Japanese Patent Application Laid-Open No. 61-1281.
05, detailed explanation will be omitted. The control circuit 50 includes a focus detection circuit 52 according to the present invention for detecting the focus from the focus signal C output from the sensor 42.
, a two-axis speed setting circuit 54 for giving the Z-axis speed setting to the Z-axis drive circuit 16A, and a central processing unit (C
PU) 56 and a system bus 58. The focus detection circuit 52, as shown in detail in FIG.
Peak hold circuit 52A consisting of a diode, a capacitor, a switch, and a high input resistance operational amplifier
, an analog-to-digital (A/D) converter 52B for converting the peak hold signal g output from the peak hold circuit 52A into a digital signal, and the A/D converter 52B.
Two latch circuits 52G and 52D that sequentially latch outputs
, a comparison circuit 52E that compares adjacent peak values H and I of the outputs of the latch circuits 52G and 52D, and the comparison circuit 5.
a pulse generating circuit 52F that generates a pulse as a focusing signal at the falling edge of the output signal j of 2E, and the vibrator 28.
OR gate 5 for inputting synchronization signals d, d2 from
2G, and a delay circuit 52H that delays the synchronization signal e, which is the output of the OR gate 52G, to produce the synchronization signal f. In this 'focus detection circuit 52, the A/D conversion value of the peak hold signal Q is latched at the timing of the synchronization signal e inputted from the OR gate 52G, and becomes a peak value H. On the other hand, the peak value I latched by the latch circuit 52D at the same time becomes a value that exceeds the peak value H by one cycle of the synchronizing signal e, and the comparison circuit 52E updates the peak value H by one period of the synchronizing signal e. The optical signals H and I are latched by adjacent pulses of the synchronization signal e of the hold signal 0, and the magnitudes of the optical signals H and I are compared.
When the output signal j is rIJ and H≧1, the output signal j is set to “0”. Also, at the falling edge of this signal j, a focusing signal k is sent from the pulse generation circuit 52F.
is output as a pulse. As shown in FIG. 1, a proximity switch 60 is disposed near the document table 10, and the proximity switch 60 detects when the document table 10 has descended and reached the bottom dead center. A signal n that turns on is output and input to the CPLJ 56 via the system bus 58. The vibration exciter 28 and the CPU 56 are connected to an excitation signal a output from the CPU 56 for causing vibration, and that the knife 26 is at the bottom dead center, output from the vibration exciter 28. They are connected by a synchronization signal d1 that notifies them of the A speed signal 0 is output from the CPU 56 to the Z-axis speed setting circuit 54 to send the stage 10 in the Z-axis direction at high or low speed or to stop the stage 10 via the Z-axis drive circuit 16A. has been done. In FIG. 1, 62 is a keyboard, 64 is a display device, 6
6 is a printer. Hereinafter, the operation of the first embodiment will be explained with reference to FIGS. 3 and 4. FIG. 3 shows the detection signals a and b of the sensor 42, the focus signal C, and the edge signal when the knife 26 swings from the bottom dead center A to the top dead center B in FIG. 2 and returns to the bottom dead center A. This shows an example of the relationship between m. Since it is expressed by the focus signals ct and ta-b, it becomes an S-curve curve as shown in the third factor, and when the measurement target surface 8 is in the focus plane FP, it becomes C3 and its signal 9 changes fuAP (
However, as the stage 10 moves up and down from the in-focus plane and the measurement target surface 8 deviates from the in-focus plane, c
2. cl and its signal change PAP decrease. Therefore, the point where the focus signal C reaches a state like 03 can be determined to be the in-focus position. FIG. 4 shows examples of signal waveforms of various parts when focusing. First, the stage 10 is lowered to the bottom dead center position where the signal n is generated from the proximity switch 60. Next, the speed signal 0 is set as a positive value, and the stage 10 is raised at high speed. Then,
Timing of release signal @t (delayed signal of synchronization signal e) (
F etc. in FIG. 4), the peak hold signal 9 is released. When the focus signal C exceeds the peak Cat, the peak value H<1
Therefore, H≧I (Fig. 4 El), and the first focusing signal k
is output. At this time, since the object is moved a little too far above the in-focus position due to high-speed feeding, the speed signal 0 is changed to lower the stage 10 at a low speed. And focus signal C
When it passes the beak C32 and the focus signal k is obtained again (E2 in FIG. 4), it is determined that the focus is in focus, the speed signal 0 is set to zero, and the excitation signal is also set to zero. On the other hand, edge detection is performed by moving the stage 10 in the X-Y direction and detecting the contrast of brightness and darkness of the reflected image of the object to be measured.
8105, detailed description thereof will be omitted. In this embodiment, the control circuit 50 includes a peak hold circuit 52A that sequentially holds the peak hold (ilg) of the focus signal C at the timing of the synchronization signal f;
a comparison circuit 52E that compares the magnitudes of the peak values H and I of the held adjacent focus signals 0, and the comparison circuit 52
Since it is equipped with a focus detection circuit 52 that excites the focus signal k at the timing when the output of E is inverted, it is relatively l\\? With the Iqi circuit configuration, the in-focus position can be detected reliably. Note that the configuration of the focus detection circuit is not limited to this, and may be any other configuration as long as it can detect that the signal change ff1AP of the focus signal C has reached a maximum. In addition, in this embodiment, since the knife 26 is used as the pattern filter, the h of the pattern filter is
9?1 formation is extremely simple. Note that the structure of the pattern filter is not limited to this, but may be similar to the second embodiment shown in FIG. In this second embodiment, when the glass disk 70 is rotated by a pulse motor 74 serving as an exciter, the edge portion vibrates in the irradiation area 30A of the laser diode LD. It can be used as the vibrating edge pattern of the invention. In FIG. Drive circuit, 78A178
B is a light emitting diode (LE) for illuminating the synchronization mark 8o formed on the peripheral edge of the glass disk 70.
D), 82A. 82B is the LED 7 that has passed through the glass disk 70;
The synchronization signals d1 and d are received by receiving the lights of 8A and 78B, respectively.
2, 84A and 84B are preamplifiers, and 86A and 86B are inverters. In this second embodiment, a vibrating pattern can be generated simply by rotating the glass disk 70, so the rotational balance is good and there is no possibility that the optical system or the like will be adversely affected by reciprocating vibration. Furthermore, in the first embodiment, the knife 26 as the pattern filter is illuminated by the epi-illumination system 12 for illuminating the object to be measured, so the configuration of the illumination system is simple. Note that the configuration for illuminating the pattern filter is not limited to this, and it is also possible to illuminate with an illumination system provided separately from the epi-illumination system 12. In this case, it is possible to select a wavelength that matches the light-receiving sensitivity of the sensor, making it possible to improve detection accuracy. The configuration of the illumination system for illuminating the object to be measured is not limited to the epi-illumination system 12 of the embodiment described above, and the present invention can also be applied to a transmission type projection inspection machine or the like. In the case of a transmission type, the pattern filter may be projected from below so that the image of the pattern filter is formed on the surface to be measured excluding the object to be measured. Further, in the first embodiment, the sensor 42 includes two light receiving elements 42A and 42B divided on the same circle,
The differential amplifier 46 calculates the difference between the outputs of the two light receiving elements 42A and 42B.
Since the output of the focus signal C is used as the focus signal C, the sensor configuration is simple, and since it can also be used as an edge sensor, the overall configuration is simple. Note that the type of sensor is not limited to this, and for example, the applicant has disclosed
It is also possible to use an edge sensor that includes a four-divided light receiving element as disclosed in 2003, or to provide a separate sensor for edge detection from that for autofocus. Alternatively, only the sensor may be provided inside the projector. When using different sensors for edge detection, two light-receiving probes 90A190B are provided adjacently as the autofocus sensor according to the present invention, as in the third embodiment shown in FIG. A differential amplifier 46 similar to the first embodiment that calculates the difference between the outputs of the two light receiving elements 90A and 90B.
The output of the differential amplifier 46 can be used as the focus signal C. In the figure, 44A and 44B represent the first
This is a preamplifier similar to that of the embodiment. The focus signal waveform in this third embodiment is as shown in FIG. 7, and since the amplitude AP of the focus signal is maximum, the focus position (C3) is determined in the same manner as in the first embodiment. It is possible to detect. In this third embodiment, the configuration of the sensor is simple, and the autofocus mechanism can be configured at low cost.

【Effect of the invention】

As explained above, according to the present invention, focusing can be performed without using the edge portion of the object to be measured itself. Therefore, there is no need to move the image of the edge portion of the object to be measured to the front of the sensor, and the time required for focusing can be shortened. In addition, there is no need to mechanically vibrate the sensor or the stage, which not only allows quick focusing, but also simplifies the mechanism and prevents excessive burden on the drive motor of the stage. It has the excellent effect of not having

[Brief explanation of the drawing]

FIG. 1 shows autofocus according to the present invention! FIG. 2 is a partial block diagram showing the sensor and control circuit of the first embodiment in detail. 3 is a diagram showing an example of the focus signal of the first embodiment, and FIG. 4 is a diagram showing an example of the signal waveform of each part. The diagram, FIG. 5, does not show the structure of the vibrator and pattern filter used in the second embodiment of the present invention, and the perspective view, including a partial block diagram, and FIG. FIG. 7 is a plan view including a partial block diagram showing the configuration of the sensor used in the third embodiment, and is a diagram showing an example of the focus signal of the third embodiment. 8... Measurement target surface, FP... Focusing plane, 10... Stage, 12... Epi-illumination system, 14... Projection lens, 16... Two-axis drive device, 26. ...Naifetsuji (pattern filter), 26A
... Naifetsu image, 26B... Naifetsuji re-formed image, 28... Exciter, 30... Laser diode (LD), 36... Screen, IP... Image forming surface, 42 ...sensor, 42A, 42B...light receiving element, 46...differential amplifier, C...focus signal, 50...presence control circuit, 52...focus detection circuit, 52A...peak Hold circuit, 52G, 52D...Latch circuit, 52E...Comparison circuit, 52F...Pulse generation circuit, 56...Central processing unit (CPU), B...Excitation signal, 9... Peak hold signal, k... Focus signal, H, I... Peak value, 70... Glass disk, 72... Edge pattern, 74... Pulse motor, 90A, 90B... Light receiving element .

Claims (6)

[Claims] (1) A stage for placing the object to be measured, an illumination system for illuminating the object to be measured, an imaging optical system for forming an image of the object to be measured on an imaging plane, and the stage for the object to be measured. and a drive device that relatively displaces the imaging optical system along the optical axis of the imaging optical system, the optical measuring device having an edge portion, the image of which passes through the imaging optical system to the measurement target. a pattern filter disposed so as to be formed on a surface; and a pattern filter disposed near the imaging plane, in which an image of an edge portion of the pattern filter is re-formed by the imaging optical system, and the front surface thereof is A sensor that outputs a focus signal that changes depending on the change in brightness when crossing the pattern filter, an exciter that vibrates the pattern filter and outputs a synchronization signal in response to this vibration, and an exciter that operates the exciter. and a control circuit that operates the drive device so that the amount of signal change in the focus signal is maximum, and the measurement target is focused at a position where the amount of signal change in the focus signal is maximum. An optical measuring device with an autofocus mechanism that performs judgment. (2) The control circuit includes a peak hold circuit that sequentially holds the peak value of the focus signal at the timing of the synchronization signal, and a comparison circuit that compares the peak values of the held adjacent focus signals. 2. The optical measuring instrument with an autofocus mechanism according to claim 1, further comprising a focus detection circuit that excites a focus signal at the timing when the output of the comparison circuit is inverted. (3) The optical measuring instrument with an autofocus mechanism according to claim 1 or 2, wherein the pattern filter is illuminated by the illumination system. (4) The optical measuring instrument with an autofocus mechanism according to claim 1 or 2, wherein the pattern filter is illuminated by an illumination system provided separately from the illumination system. (5) The sensor includes two light-receiving elements divided concentrically and a differential amplifier that calculates the difference between the outputs of the two light-receiving elements, and the sensor includes: An optical measuring instrument with an autofocus mechanism according to any one of claims 1 to 4, wherein the output is the focus signal. (6) The sensor includes two light-receiving elements arranged adjacent to each other and a differential amplifier that calculates the difference between the outputs of the two light-receiving elements, and the output of the differential amplifier is An optical measuring instrument with an autofocus mechanism according to any one of claims 1 to 4, wherein the focus signal is the focus signal.