JP2647924B2 - Height measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] A height measuring device that scans a laser beam with a polygon mirror and measures the height of an object to be measured. A measurement optical system that scans a laser beam with a polygon mirror to irradiate the object to be measured, and outputs a detection signal corresponding to the height of the object to be measured from a photodetector, with the aim of eliminating measurement errors of A height calculating circuit for calculating the height data of the object to be measured by calculating a detection signal of the photodetector, and a synchronization for detecting a rotation cycle of the polygon mirror and scanning synchronization of a plurality of reflection surfaces of the polygon mirror. A detection circuit;
A correction memory for storing in advance a plurality of correction data for correcting a measurement error of the height of each reflecting surface corresponding to an error of a tilt angle of each of the plurality of reflecting surfaces of the polygon mirror, and detecting the rotation synchronization and the scanning synchronization A signal is used to select correction data corresponding to the reflection surface of the polygon mirror currently scanning from the plurality of correction data, and the height data from the height calculation circuit is corrected by the selected correction data and output. And a height error correction circuit.

[Industrial applications]

The present invention relates to a height measuring device, and more particularly, to a height measuring device that scans a laser beam with a polygon mirror and measures the height of an object to be measured.

[Conventional technology]

The present applicant has previously filed Japanese Patent Application No. 63-144846 (June 4, 1988).
(Japanese Patent Application) has proposed a device as shown in FIG. 5 for scanning a laser beam with a polygon mirror and measuring the height of an object to be measured.

In Figure 5, is converted into parallel light L ₃ by a collimator lens with a laser beam from the semiconductor laser is incident on the polygon mirror (rotary polygon mirror) 10. Reflected light L ₄ by the polygon mirror 10 is reflected in a predetermined direction by the parabolic mirror 11. As is well known, the parabolic mirror 11 also has a function of forming an image at its focal length, and the measured object 12 is placed at the focal length of the parabolic mirror 11. Since the DUT 12 is located in a horizontal plane,
First mirror M ₁ between the parabolic mirror 11 so as to incident scanning beam L ₅ vertically from above the object to be measured 12 is provided thereto.

The mirror 13 arranged near the measured object 12 forms an inclination angle β substantially perpendicular to the measured object. Also mirror
13 is arranged in the vicinity of the illumination beam L ₅ to the object to be measured (distance d). As a result, the outward path (irradiation beam)
L ₅₎ and one of the retroreflective system substantially adjacent parallel to and forward is formed. The light reflected by the object to be measured 12 is reflected by the mirror 13 and converges on a double path which is close to and parallel to the outward path, that is, passes through the first mirror M ₁ , the parabolic mirror 11 and the polygon mirror 10. The light is converged on the photodetector 15 by the lens 14. The photodetector 15 is located at the focal length of the converging lens 14. As a result, the reflected light (signal light) from the measured object 12 is re-imaged on the photodetector 15 as a beam spot.

Here, the low portion of the object 12 is indicated by A, and the high portion is indicated by B. Since the mirror 13 forms a predetermined inclination angle β with respect to the measured object 12, the position of the imaging beam spot on the photodetector 15 changes according to the height of the measured object 12. That is, the imaging beam spot from point A forms an image on A ', and the imaging beam spot from point B forms an image on B'. Therefore, by measuring the position of the beam spot of the photodetector 15, the object 12
Height distribution can be detected.

As the light detector 15, for example, a known light spot position detection element PSD (Position Sensitive Detector) is used,
The position and intensity of the light spot are detected from the output signal.

Assuming that the output currents of the two terminals of the photodetector 15 are Ia and Ib, respectively, the light position (corresponding to the height information of the measured object 12) and the intensity (corresponding to the density information of the measured object) are as follows. It is represented by an equation.

Height = Ia−Ib / Ia + Ib (1) Light Intensity = Ia + Ib (2) Note that an f · θ lens may be used instead of the parabolic mirror 11.

[Problems to be solved by the invention]

As shown in FIG. 6, if there is an error in the tilt angle of the polygon mirror 10 [θ], the deviation of the irradiation position of the beam on the workpiece 12 will occur.
d occurs. In this figure, f is used instead of the parabolic mirror 11.
· The θ lens 16 is used, and the deviation Δd of the irradiation position is f ·
Assuming that the focal length of the θ lens is f, △ d = 2 △ θf.

Further, as shown in FIG. 7, a measurement error Δh of the height of the workpiece 12 is caused by the deviation Δd of the irradiation position. Measurement error △ h
Is represented as {h = {d / tan}, where 検 知 is the detection angle. Here, as general values, △ θ = ± 10 seconds, f = 300 mm,
When ψ = 20 ゜, ゜ h = ± 80 μm.

In order to eliminate the above measurement error Δh, the error Δθ of the surface inclination angle of each surface of the polygon mirror 10 may be eliminated.
It is actually very difficult to eliminate the errors of the inclination angles of all the surfaces of the polygon mirror, and the polygon mirror 10 becomes very expensive.

The present invention has been made in view of the above points, and has as its object to provide a height measuring device that eliminates a height measurement error when a polygon mirror having a surface tilt angle error is used.

[Means for solving the problem]

 FIG. 1 shows a principle block diagram of the device of the present invention.

In FIG. 1, a measurement optical system 1 scans a laser beam with a built-in polygon mirror to irradiate the object to be measured, and outputs a detection signal corresponding to the height of the object to be measured from a photodetector.

The height calculation circuit 2 calculates a detection signal output from a photodetector in the measurement optical system 1 to obtain height data of the measured object.

The synchronization detection circuit 3 detects the rotation cycle of the polygon mirror in the measurement optical system 1 and the scanning synchronization of the plurality of reflection surfaces of the polygon mirror.

The correction memory 4 stores in advance a plurality of correction data for correcting a measurement error of the height of each reflecting surface in accordance with an error of a tilt angle of each of the plurality of reflecting surfaces of the polygon mirror.

The height error correction circuit 5 selects the correction data corresponding to the reflection surface of the polygon mirror currently scanning from the plurality of correction data using the detection signals of the rotation synchronization and the scanning synchronization. Is corrected with the selected correction data and output.

The corrected height data output from the height error correction circuit 5 is stored in an image memory 6 and is subjected to image processing by a CPU 8 connected to the image memory 6 and a system bus 7.

[Action]

In the apparatus of the present invention, the error of the inclination angle of each reflecting surface of the polygon mirror of the measurement optical system 1 is left as it is, and the correction data of the measurement error of the height of each reflecting surface caused by the error of the inclination angle is obtained. In advance, the height data output from the arithmetic operation circuit 2 is corrected by the correction data corresponding to the reflection surface at that time.

For this reason, the corrected height data does not include a height measurement error and is accurate, and the polygon mirror can use a conventional polygon mirror, thereby preventing an increase in cost.

〔Example〕

In the apparatus of the present invention, the same optical system as that shown in FIG. The measuring optical system 1 is provided with a synchronization detecting circuit 3 as shown in FIG.

In FIG. 2, the polygon mirror 10 of the measurement optical system 1 has an N prism shape (N = 6 in the figure), and rotates at a constant speed around a rotation shaft 20. Light reflection mark 21 on the upper surface of polygon mirror 10
Is provided at one position, and a reflective photointerrupter 22 is fixed at a position corresponding to the light reflection mark 21.

When the polygon mirror 10 rotates, the reflection type photointerrupter 22 detects the light reflection mark 21 and generates a rotation synchronization signal shown in FIG.

The parallel light L ₃ is reflection surface 10 ₁ to 10 _N of the polygon mirror 10 rotating is irradiated, the reflected light L ₄ are scanned in the range from the angle theta ₁ to theta _2. Photosensor in the above angle theta ₁ direction 24
There are fixed, the photosensor 24 is from terminal 25 to generate a scan synchronizing signal shown in FIG. 3 detects the angle theta ₁ direction of the reflected light during the scanning initiation by people reflecting surface 10 ₁ to 10 _N respectively (B) Output.

The height calculation circuit 2 is the same circuit as the conventional one, and calculates the above-described equations (1) and (2) from the two output currents Ia and Ib output from the photodetector 15 of the measuring optical system 1 to calculate the height. The resulting digitized height data is supplied to a height error correction circuit 5 and light intensity data is supplied to an image memory 6.

FIG. 4 shows a block diagram of the correction memory 4 and the height error correction circuit 5. In the figure, the correction in the memory 4 is the reflection surfaces 10 ₁ to 10 _N correction data of the height of the measurement error when using each is pre-stored for s N number of the reflecting surfaces each of the polygon mirror 10. The above-described correction data is obtained by, for example, measuring a plane having a height of zero as the object to be measured 12 and inverting the sign of the height data obtained by scanning each reflection surface.

The rotation synchronizing signal and the scanning synchronizing signal obtained by the synchronism detecting circuit 3 enter the terminals 30 and 31 of the height error correcting circuit 5 respectively, and are supplied to the counter 32. After being cleared by the pulse of the rotation synchronizing signal, the counter 32 counts the pulse of the scanning synchronizing signal, and sends a count value (1 to N) indicating which reflection surface of the polygon mirror 10 is used for scanning to the data selector 33. Supply.

The data selector 33 determines the reflection surfaces 10 ₁ to 10 _N from the correction memory 4.
Correction data 1 to N corresponding to each are supplied, a single correction data indicated by the count value (1 to N) of the counter 32 is selected, and the extracted correction data is supplied to the addition circuit 34. . Height data is supplied to the addition circuit 34 from a terminal 35, and the addition circuit 34 adds corrected data to the height data to obtain corrected height data, and outputs the corrected height data from a terminal 36. It is supplied to the image memory 6.

The image memory 6 sequentially stores the corrected height data and the light intensity data separately. By moving the object 12 in a direction orthogonal to the scanning direction of the laser beam, corrected height data and light intensity data of the surface of the object 12 are stored in the image memory 6.

The data stored in the image memory 6 is processed by the CPU 8,
The processing result is displayed on a display (not shown),
Alternatively, it is printed out by a printer (not shown).

Thus, the error of the tilt angle of the reflecting surfaces 10 ₁ to 10 _N of the polygon mirror 10 leave its, the correction data of the height of the measurement errors of the reflecting surfaces each caused by the error of the surface inclination angle The height data output from the arithmetic operation circuit 2 is prepared in the correction memory 4 and corrected by the correction data corresponding to the reflection surface at that time.

For this reason, the corrected height data does not include a height measurement error and is accurate, and the polygon mirror can use a conventional one, and there is no increase in cost.

〔The invention's effect〕

As described above, according to the height measuring apparatus of the present invention, it is possible to measure the surface accuracy by removing the height measurement error when using a polygon mirror having a surface tilt angle error,
There is no risk of cost increase, and it is extremely useful in practice.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the principle of the device of the present invention, FIG. 2 is a block diagram of an embodiment of a synchronization detection circuit, FIG. 3 is a waveform diagram of a rotation synchronization signal and a scanning synchronization signal, and FIG. FIG. 5 is a block diagram of a height error correction circuit, FIG. 5 is a configuration diagram of a measurement optical system, and FIGS. 6 and 7 are diagrams for explaining a height measurement error. In the figure, 1 is a measurement optical system, 2 is a height calculation circuit, 4 is a correction memory, 5 is a height error correction circuit, 6 is an image memory, 8 is a CPU, 10 is a polygon mirror, 12 is a measured object, 15 Indicates a photodetector.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Noriyuki Hiraoka 1015 Uedanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Limited (72) Inventor Hiroyuki Tsukahara 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Fujitsu Limited ( 72) Inventor Yoshinori Sudo 1015 Uedanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fujitsu Limited (72) Inventor Mitaka Oshima 1015 Kamikodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fujitsu Limited (72) Inventor Hashinami Shinji Shinagawa 1015 Ueodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Limited (56) References JP-A-62-49202 (JP, A) JP-A-55-154402 (JP, A) Jpn. , U)

Claims (1)

(57) [Claims] A measuring optical system for scanning a laser beam with a polygon mirror (10) to irradiate an object to be measured and outputting a detection signal corresponding to the height of the object to be measured from a photodetector (15). 1)
A height calculation circuit (2) for calculating the height data of the object by calculating a detection signal of the photodetector (15); a rotation cycle of the polygon mirror (10) and the polygon mirror (10 A) a synchronization detection circuit (3) for detecting scanning synchronization of the plurality of reflecting surfaces; and a measurement error of the height of each reflecting surface in accordance with an error of a tilt angle of each of the plurality of reflecting surfaces of the polygon mirror (10). A correction memory (4) preliminarily storing a plurality of correction data for correcting the rotation, and a reflection surface of a polygon mirror (10) which is currently scanning from the plurality of correction data using the rotation period and scan synchronization detection signals. And a height error correction circuit (5) for selecting the correction data corresponding to the height data, correcting the height data from the height calculation circuit (2) with the selected correction data, and outputting the corrected data. Measuring device.