JPH02254306A - Optical measuring apparatus - Google Patents

Abstract

PURPOSE:To make it possible to make servo-gain approximately constant with respect to a board range of reflectivities by providing a gain switching means by which the servo-gain can be changed in response to the reflectivity of a surface to be measured. CONSTITUTION:An operating part 80 is an operating part for switching servo- gain in response to the reflectivity of a surface to be measured. The operating part 80 is provided with the following parts: a reflectivity switch (a) for changing the reflectivities of semiconductor laser light and Zeeman laser light at the surface to be measured in three ranges; a linking switch (d) for selecting the linked operation and the independent operation in switching the reflectivities of both laser light beams; and a reflected-light-amount monitoring meter which displays the amount of the reflected light of each laser light. In this constitution, since the servo-gain can be switched in response to the reflectivity of the surface to be measured, the servo-gain can be made constant with respect to the reflectivities in a broad range, and the range of the surfaces to be measured which can be measured highly accurately can be expanded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is an optical measuring device that measures the shape of a surface to be measured in a non-contact manner by performing servo control based on the amount of laser light reflected from the surface to be measured. It is related to.

Conventional technology In optical disk devices, etc., the technique of applying focus servo to the objective lens based on the reflected light of the laser beam on the disk surface is well known, but the present applicant has previously filed a patent application filed in 1973.
Japanese Patent Application No. 9-239751, Japanese Patent Application No. 60-39178, Japanese Patent Application No. 62-76927, etc. propose techniques that allow the servo system to operate normally even if there are variations in the reflectance of the disk surface. There is.

By the way, in Japanese Patent Applications No. 59-228114 and No. 60-148715, the present applicant measures the aspherical shape of an aspherical lens or mirror by directly irradiating the surface to be measured with a laser beam. A separate optical measurement device is proposed.

This involves separating two wavelengths of laser light into measurement light and Tosa, irradiating the measurement light onto the surface to be measured and irradiating the reference light onto a reference mirror, and then guiding each reflected light to the same photodetector.
This method uses interferometric measurement based on the optical heterogain method, which detects the movement of the surface to be measured from the Doppler shift it of the frequency that occurs in the reflected light of the measurement light due to the movement of the surface to be measured. By applying focus servo or f-circle servo according to the error signal and light amount signal, ultra-high precision measurement of ±0.1 to 0.01 μm can be achieved.

Problems to be Solved by the Invention In optical measurement devices, unlike the variation in reflectance on the surface of an optical disk, the reflectance varies over a wide range from 0% to 100% depending on the surface to be measured.

Therefore, even if the above-mentioned conventional technique is applied as is, it is difficult to expand the range of reflectance that can be measured by an optical measuring device.

When laser beams with different wavelengths are used as in the optical measuring device described above, special conditions of use must be met in that the reflectance of the same surface to be measured may differ depending on the wavelength.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical measuring device that can make the servo gain substantially constant over a wide range of reflectance.

Means for Solving the Problems The optical measurement device according to claim 1 is an optical measurement device that performs servo control based on reflected light of a laser beam irradiated onto a surface to be measured. The optical measuring device according to claim 2, further comprising gain switching means capable of switching the servo gain, is characterized in that the servo gain is switched according to the reflectance of the laser beam used for focus servo on the surface to be measured. and gain switching means capable of switching the servo gain according to the reflectance of the laser beam used for the tilt servo on the surface to be measured, and select interlocking or independent operation of the amount switching means. It is characterized by having a selection means for.

In each of the configurations described above, it is preferable to provide a monitoring means capable of monitoring the amount of laser light reflected from the surface to be measured.

According to the invention described in claim 1, since the servo gain can be switched according to the reflectance of the surface to be measured, the servo gain can be made substantially constant over a wide range of reflectance, and the measurement can be performed easily. The range of possible surfaces to be measured can be expanded.

According to the invention as claimed in claim 2, since each servo gain can be switched in conjunction or independently for each laser beam used, the reflectance due to the wavelength of the laser beam on the same surface to be measured can be changed. Even for differences, the respective servo gains can be made substantially constant. As a result, the focus servo and tilt servo can be operated normally according to their respective reflectances, making it possible to achieve ultra-high precision measurement in optical measurement devices that use laser beams of different wavelengths. can.

By providing a monitor capable of monitoring the amount of laser light reflected from the surface to be measured, it is possible to switch the gain while checking the reflectance of the surface to be measured during measurement.

Embodiment An optical measuring device according to an embodiment of the present invention will be explained with reference to FIGS. 1 to 14.

This device measures the X-Y-Z coordinate position based on the optical heterogain method, and uses semiconductor laser light (λ-780
The measurement H
E-Ne Zeeman laser light (λ-633 nm) F is focused perpendicularly onto the surface to be measured 2, and the shape of the surface to be measured 2 is measured while applying tilt correction servo based on the reflected light.

In the overall configuration of the device shown in Fig. 3, 3 is a lower stone surface plate serving as the base of the main body, and 4 is connected to this lower stone surface plate 3 through an X table 5 and a Y table 6 in the X-Y direction. a movable upper stone surface plate; 7 is a Z moving part provided on the front surface of the upper stone surface plate 4 and supported movably in the Z direction; 8 is an L-shaped holding base for holding the object to be measured 1; 9; is this holding table 8
An air spindle 10 that rotates around an axis P in the direction (see FIG. 11) is a swivel base that supports the air spindle 9 so that it can move up and down and can rotate around an axis Q in the Z direction.

As shown in FIG. 1, the Z moving section 7 includes a linear motor 10
Upper right foot I! by spring 11 through ! It is suspended from 14. Inside the Z moving section 7, as shown in FIG. 4, a semiconductor laser 12 that emits semiconductor laser light G is installed. The semiconductor laser beam G emitted from the semiconductor laser 12 passes through the lens 13 , the polarizing prism 14 , and the λ/4 wavelength plate 15 , is totally reflected downward by the guichroic mirror 16 , and is reflected by the open low cup of the objective lens 17 . The light enters and is focused on the surface to be measured 2 of the object to be measured 1 . The condensing position of the semiconductor laser beam G is approximately the same as the irradiation position of the measurement light Fz used for measuring the Z coordinate of the Zeeman laser beam F. If the surface to be measured 2 is tilted, a part of the reflected light of the semiconductor laser beam G is reflected outside the aperture of the objective lens 17, but the rest is reflected into the aperture of the objective lens 17. . The reflected light returning to the objective lens 17 is reflected by the guichroic mirror 1
6 and polarizing prism 14, condensed by lens 18, and divided into two by half mirror 19.

Each of the divided reflected lights passes through each pinhole 20 installed before and after the focus, and is irradiated onto each photodetector 21. If the focusing position of the objective lens 17 is on the surface to be measured 2, as shown in FIG. When the distance (in two directions) changes, the irradiation position on each photodetector 21 shifts and the amount of light decreases, as shown in FIG. A focus error signal is generated in a focus error signal generating section 22 shown in FIG. When the switch SW is in the position indicated by the phantom line in FIG. 1, the drive circuit 23 controls the linear motor 10 so that the focus error signal becomes zero, and the Z
The moving unit 7 is moved in the Z direction. In this way, the measurement light Fz of the semiconductor laser light G and the Zeeman laser light F, which will be described next.

Focus servo is applied so that the light convergence position is always on the surface to be measured 2.

A part of the laser light F emitted from the He-Ne Zeeman frequency stabilized laser 24 that oscillates at two frequencies f5 and f2 passes through the first half mirror 25 and is separated by the second half mirror 26. It is used to measure the x-y coordinates of the measurement position. On the other hand, the laser beam Fz reflected by the first half mirror 25 is used to measure the Z coordinate of the measurement position. This laser beam Fz is polarized by a polarizing prism 27, and is converted into a measuring beam F.
z, and reference light Fz. The difference between the frequency f of the measurement light Fz and the frequency f2 of the reference light Fz is several hundred K1.
1z, and are linearly polarized light that is perpendicular to each other. Furthermore, X-
The laser beams Fx and Fy used for Y coordinate measurement are also converted into measuring beams Fx+ by the respective corner cubes 44 in the middle of each optical path.
, FV+ and reference beams r''xg and Fyz.

As shown in FIG. 7, the measurement light Fz used for the Z coordinate measurement consists of a special polarizing prism 28 that completely transmits P polarized waves and partially transmits S polarized waves, a Faraday element 29, and a λ/2 plate 3.
0, becomes S-polarized wave, and is totally reflected by the polarizing prism 31. Then, the measurement light Fz that passes through the λ/4 plate 32 and the condensing lens 33, is focused on the mirror 34, and is reflected becomes P polarized light by the λ/4 plate 32, and is completely transmitted through the polarizing prism 31. The light then enters the objective lens 17 and is focused perpendicularly to the surface to be measured 2 . The reflected light from the surface to be measured 2 returns along the same optical path as the above-mentioned incident light, but it becomes S-polarized and is partially reflected by the special polarizing prism 2 days, then totally reflected by the polarizing prism 27, and the Z-axis destination is detected. Reaches vessel 3.5. Measured surface 2
When measuring the shape of
f, +Δ. Note that when the optical path of the reflected light is about to deviate depending on the inclination of the surface to be measured 2, the 4-split photodetector 36 detects the reflected light that is partially reflected by the special polarizing prism 28.
The condenser lens 33 is moved in XY direction by the condenser lens moving means 37.
By moving in the direction to change the position of incidence of the incident light on the objective lens 17, tilt correction servo is applied so that the reflected light always returns along the same optical path.

On the other hand, the reference light Fzz is totally reflected by the polarizing prism 27 and then condensed onto the Z-axis mirror 39 by the lens 38, and the frequency of the zero reflected light that is reflected and reaches the Z-axis tip detector 35 is , due to errors such as movement straightness of Y table 5.6, r! It becomes ten δ. Therefore, the Z-axis tip detector 35
Then, (f1+Δ)−(f2+δ) is detected as a beat signal, and the two-coordinate detection device 37 accurately obtains the Z coordinate of the measurement position on the surface to be measured 2.

Note that the X and Y coordinates of the measurement position on the surface to be measured 2 are determined by the Z moving unit 7.
F focused on the X and Y axis mirrors 38 and 39 installed at
The reflected light of
．． Based on the frequency difference between Fyi and the reflected light, it is detected by the X and Y narrow photodetectors 42 and 43.

As shown in FIG. 8, the holding stand 8 that holds the object to be measured 1 includes a Z-axis slide plate 45, an X-axis slide plate 46, and a substrate 47.
Z-x via a slide guide device basically constructed from
It is attached to the air spindle 9 so as to be movable in the direction. These Z-axis slide plate 45, X-axis slide plate 46, and substrate 47 are made of magnetic material. In the Z-axis slide plate 45, an X-direction concave groove 48 formed on the back side fits into an X-direction convex portion 49 formed on the front side of the X-axis slide plate 46 in a surface contact state. An X-direction concave groove 50 formed on the back side of the X-axis slide plate 46 fits into an X-direction convex portion 51 formed on the front side of the substrate 47 in surface contact. The surfaces of these concave groove portions 4850 and convex portions 49.51 are polished smooth.

A holding member 52 fixed to the upper surface of the X-axis slide plate 46 rotatably holds the Z-axis line screw 53. The threaded end of the two-axis feed screw 53 is threaded into a female threaded portion 54 threaded onto the top of the Z-axis slide plate 45. One of the frame members 55 attached to both sides of the X-axis slide plate 46 rotatably holds an X-axis feed screw 56. A threaded portion of the X-axis feed screw 56 is screwed into a female threaded portion 57 bored in one side of the board 47. At approximately the center of this board 47,
A female screw portion 59 that screws into the screw portion of a fixing screw 58 that fixes the slides of the two-axis slide plate 45 and the X-axis slide plate 46.
is drilled. An elongated hole 50 extending in the X direction is formed approximately at the center of the temporary X-axis slide 46, through which the shaft of a fixing screw 58 is inserted.

A large diameter rectangular hole 61 is provided approximately at the center of the Z-axis slide plate 45, through which the shaft portion is inserted. X-axis slide plate 46
Four circular holes 62 are opened in the hole 62, and each circular hole 62 has a cylindrical magnet 6 with a cylindrical collar 63 made of a non-magnetic material surrounding it.
4 is fitted.

Both end surfaces of the magnet 64 are slightly sunken below the surface of the X-axis slide plate 46. In this embodiment, the attraction force of the magnet 64 to the magnetic material causes the X-axis slide plate 46 and Z-axis slide plate 4
5 and the substrate 47 is further improved. The material of the magnet 64 is preferably samarium cobalt, but other materials may be used.

In such a slide guide device, when moving the object to be measured 1 on the holding table 8 in the X direction, as shown in FIG. Slide finely. When moving in the X direction, as shown in FIG. 10, the X-axis slide plate 46 is finely slid by rotating the X-feeding screw 56. When fixing, tighten the fixing screw 58. According to the slide guide device of this embodiment, there is virtually no looseness that occurs during polar coordinate measurement of the surface to be measured 2, and it is possible to measure the surface to be measured 2 with ultra-high precision. This will greatly contribute to its realization.

As shown in FIG. 3, the swivel base 10 includes a support plate 65 on which the air spindle 9 is installed and fixed, and this support plate 65.
It is provided with four support columns 66 that guide and support the robot so as to be movable up and down, and a swing base 67 on which these support columns 66 are erected.

The pivot base 67 is pivotably supported by a pivot pin 68. On the rotating base 67, there is a feed screw 69 that screws into a female threaded portion bored in the support plate 65, and
A motor 70 for rotating the motor 9 is provided.

The feed screw 69 is rotated via a gear 71 fixed to its lower part and a worm 72 that meshes with the gear 71.

According to the swivel table 10 configured in this way, when measuring the shape of the surface to be measured 2 while holding the object 1 on the holding table 8, the measurement position shown by the solid line in FIGS. 11 and 12 is A holding stand 8 is installed at. When measuring the shape of a larger object to be measured, the motor 70 is driven to lower the air spindle 9 to a position where its upper end is lower than the lower end of the upper stone surface plate 2, as shown in FIG. Next, in this state, move the swivel base 1O to the pivot pin 68 in the direction shown by the arrow in FIG.
Rotate around the center. Thereby, the holding table 8 can be moved from the measurement position below the Z moving part 7 to the retracted position, and the space below the Z moving part 7 can be expanded.

When performing polar coordinate measurement, the air spindle 9 is moved up and down by the motor 70 so that the approximate center of curvature of the surface to be measured 2 coincides with the rotation axis P of the air spindle 9.

Next, the focus servo system will be explained in detail using FIGS. 1 and 2.

In FIG. 3, 73 is a position detector that detects the amount of displacement of the Z moving unit 7 from the equilibrium position in the Z direction, 74 is a position signal generation circuit that generates a position signal based on the output from the position detector 73, and 75 is a Z of the Z moving unit 7 based on the position signal
Position display means for displaying the position in the direction, 76 is 0.3Hz
A frequency oscillator 77 is a volume for moving the second moving part 7 in the Z direction, and a frequency oscillator 78 amplifies the position signal based on the operation setting voltage of the volume 77 to eliminate the influence of the restoring force of the spring 11 and sends it to the drive circuit 23. differential amplifier to send the signal, 7
9 is a gain control circuit, and 80 is an operation unit for switching the servo gain according to the reflectance of the surface 2 to be measured. As shown in FIG. 2, this operation section includes a reflectance changeover switch for switching the reflectance of the semiconductor laser beam G and the Zeeman laser beam F on the surface to be measured 2 into three ranges, and a An interlocking switch for selecting between interlocking and independent operation of G and F reflectance switching, and each laser beam G
, , F is equipped with a reflected light amount monitor meter that displays the amount of reflected light.

As a result, each servo gain can be switched according to the reflectance of the surface to be measured 2, so the servo gain can be kept approximately constant over a wide range of reflectance, allowing high-precision measurement to be performed. The range of surface 2 can be expanded. Furthermore, since it is possible to deal with differences in reflectance caused by the wavelengths of the laser beams G and F on the same surface to be measured 2, the focus servo and tilt servo can be operated normally according to their respective reflectances. can. Furthermore, gain switching can be performed while checking the reflectance of the surface to be measured 2 during measurement using the respective laser beams G and F. In this embodiment, the range of reflectance that can be handled is 3 to 100%, but it may be 0 to 100%.

In order to measure the shape of the surface to be measured 2 using the non-curved lens as the object to be measured 1 in the optical measurement apparatus configured as described above, the object to be measured 1 is first held on the holding table 8 . At this time, the air spindle 9 is raised and lowered or the slide guide device is finely slid in the X-Z direction so that the rotation axis P of the air spindle 9 passes through the center of curvature of the surface 2 to be measured. The moving unit 7 is moved in the Z direction, and the objective lens 17 is moved to a position 1 to 2II above the focus position with respect to the tip of the surface to be measured 2, as shown in FIG.
Set the initial position to the position IIl. At this time, it is preferable to install a scale 81 as shown in the figure on the front side of the upper stone surface plate 4.

When the switch Sw is turned on, the Z moving section 7 descends until a focus error signal is output, that is, until the objective lens 17 reaches the focus pull-in range. When a focus error signal is detected, switch Swt is switched to apply focus servo. Thereby, the objective lens 17 can be pulled into the focus position.

Next, the measurement origin S (
(not shown) will be explained with reference to FIG.

The current focusing position of the laser beam G on the surface to be measured 2 is defined as the initial origin (Xa, Za)S, and the amount of deviation of this initial origin S0 from the center of the surface to be measured 2 at the same -Y coordinate position is calculated. First thing to look for
In order to obtain the target origin S1, the X-Z coordinates of two positions are measured in a certain range near the initial origin S6 at the same -Y coordinate position. The respective XZ coordinates are (X,, Zd,), (X t
, Z dz).

Let Zd be the amount of deviation of the measurement surface (solid line in Figure 1) obtained by measurement from the calculation sphere (imaginary line in Figure 1), then it can be set as X'' + Y'' + (Z + R - Zd)'' = R2.

However, R is the radius of curvature near the initial origin S0.

On the other hand, the calculation sphere is R-, /"-principal two r-=■]-the measurement surface is R--XIXa)"-Za, so Zd becomes ---+a-Za.

Here, if X(R), Zd #R-X”÷2R-R+ (XIXa)”+2R
=Za"'((XIXa)"-X")+2R=Za#X
a -X+R+Xa"+2R-Zawhere, Xa"+
Since 2R=Za, Zd=Xa−X+R.

Therefore, Xa = R + X - Zd "R. (Zdl zaz) " (XI Xz) In the above manner, the first target origin S can be obtained. Thereafter, in the same manner, the Y-Z coordinates of two positions at the same -X coordinate position near the first target origin S1 are measured,
The amount of deviation of the first target origin S1 from the center of the surface to be measured 2 is determined to obtain a second target origin St (not shown).

This second target origin Sz coincides with the center of the surface to be measured 2, so this target origin S2 is
By measuring the shape of the surface to be measured 2 using the measurement origin S in the coordinates, it is possible to measure a symmetrical range in the X-Y direction. Based on this, it is also possible to determine the measurement position when performing polar coordinate measurement.

The present invention can be configured in various ways other than those shown in the above embodiments. For example, the type of laser light to be used, its wavelength, and the switching range of reflectance are not limited to those shown in the above embodiments, and can be appropriately designed as necessary.

Effects of the Invention According to the invention described in claim 1, the servo gain can be made substantially constant over a wide range of reflectance, and the range of the surface to be measured that can be measured can be expanded.

According to the second aspect of the invention, the respective servo gains can be kept approximately constant even when the reflectance differs due to the wavelength of laser light on the same surface to be measured. It is possible to realize ultra-high precision measurement in an optical measurement device using light.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a focus servo system in an optical measurement device according to an embodiment of the present invention, Fig. 2 is a front view of a reflectance switching operation section in the same device, and Fig. 3 is a schematic diagram showing the overall configuration of the device. A perspective view, Fig. 4 is an optical path diagram, Fig. 5 is an optical path diagram when the objective lens is in the focus position, Fig. 6 is an optical path diagram when the objective lens is out of the focus position, and Fig. 7 is the same device. Optical path diagram of the tilt servo system in
The figure is an exploded perspective view of a slide guide device that guides and supports the holding frame of the object to be measured in the same device so as to be movable in the X-Z direction relative to the air spindle, and FIG. 9 is a vertical side view thereof.
Fig. 10 is a cross-sectional plan view thereof, Fig. 11 is a front view of the swivel table in the same device, Fig. 12 is a plan view thereof, Fig. 13 is an explanatory diagram of the position setting of the objective lens in the same device, and Fig. 14 is a FIG. 2 is a schematic explanatory diagram for determining a target origin from an initial origin in the Y direction on a surface to be measured in the same apparatus. 79...gain control circuit, 80...
...Operation unit, FSG...Laser light. Name of agent: Patent attorney Shigetaka Awano (1 person)
Figure 2

Claims (3)

[Claims] (1) An optical measurement device that performs servo control based on the reflected laser beam that irradiates the surface to be measured, and is equipped with a gain switching means that can switch the servo gain according to the reflectance of the surface to be measured. An optical measurement device featuring: (2) A gain switching means that can switch the servo gain according to the reflectance of the laser beam used for focus servo on the measured surface, and a gain switching means that can change the servo gain according to the reflectance of the laser beam used for tilt servo on the measured surface. What is claimed is: 1. An optical measuring device comprising: gain switching means capable of switching gain; and selection means for selecting interlocking or independent operation of both switching means. (3) The optical measuring device according to claim 1 or 2, further comprising a monitor means capable of monitoring the amount of laser light reflected from the surface to be measured.