JPS5979104A - Optical device - Google Patents

Abstract

PURPOSE:To improve the measurement precision by detecting deviations of the position and the distribution of a reflected light due to the inclination of an object face to be irradiated and moving an object lens in the direction vertical to the optical axis in accordance with an error signal obtained from this detection output. CONSTITUTION:The light emitted from a Zeeman laser 9 having oscillation frequencies f1 and f2 is divided into lights of frequencies f2 and f1, which are polarized in two directions of polarization, by a lambda/4 plate 10. A beat frequency f1-f2 is detected by a photodetector 12. The light of f2 reaches a photodetector 15 by a polarizing prism 13. The light of f1 is reflected on the surface of an object 16 to be measured and is reflected totally by the polarizing prism 13 and reaches the photodetector 15. A beat frequency f1+DELTAf-f2 between frequencies f2 and f1+DELTAf is attained on the photodetector 15, and DELTAf is obtained on a basis of the difference between this beat frequency and the beat frequency f1-f2 obtained on the photodetector 12 and is integrated to obtain a displacement Z. The movement of an objective lens 20 in the Z-axis direction is measured by measuring the displacement of the object to be measured. Thus, the measurement precision is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an apparatus for measuring a surface shape using a Matsuhatsu Ender interferometer type laser interferometric length measuring device or a laser interferometric length measuring device using an optical heterodyne method. This is an optical device used in devices that detect information 1/9 or defects recorded on a surface, and focuses laser light onto the irradiated surface using an objective lens, and detects the surface of the irradiated surface from the reflected light. Optical technology that detects some information on the irradiated surface, such as surface irregularities, reflectance, defects, etc., or measures surface shape, surface deviation, etc. from the wavefront shift of reflected light or Doppler shift of frequency. It is related to the device.

Structure of the conventional example and its problems In the conventional optical device of this type, as shown in Fig. 1, the irradiated object l]1i (3) is located at the focal position of the objective lens (2). , when the repulsed light passes through the objective lens (2) again, it returns in the same direction as the incident light. Therefore, when an image is formed using the reflected light and the entire lens, even if there is a slight inclination on the irradiated surface (3), the image will be formed at the same point. Therefore, this image forming point will be a fixed point. , information was detected by placing a photodetector at or near this imaging point.However, in the actual festival,
Even in such a conventional device, the tolerance for the inclination of the irradiated surface (3) is extremely strict. Because the first
As shown in the figure, when the irradiated surface (3) is tilted by θ, the reflected light is tilted by 2θ1, so if the incident light is parallel light, the center position lif of the reflected light after passing through the objective lens (2) is F ,5in2
It changes by θ. Note that F is the focal length of the objective lens (2). Since this phenomenon has a negative effect on the optical system, the tolerance of the tilt of the irradiated surface in conventional devices is extremely strict.

- For example, within 0.005° for a laser interferometer;
For photonics, it is within 0.2°. On optical discs,
The system is designed to be within this accuracy, but with interferometric length measuring instruments, a method such as attaching a JIX corner cube to the object to be measured and measuring the movement of the object by the movement of the corner cube is usually used. There is.

Part of the Invention J The present invention solves the above-mentioned conventional drawbacks. Even if the incident surface is tilted to the object 1, as long as the tilt is within the aperture angle of the objective lens, the reflected light is the same as the incident light. Follow the route, therefore? & The purpose is to obtain an optical device with very high tolerance to the tilt of the irradiation surface.

Structure of the Invention In order to achieve the above object, an optical device of the present invention is provided.
A light emitting means comprising a synchrotron radiation source and an optical system that converts the light emitted from the synchrotron radiation source into synchrotron radiation having a fixed spot size and a spread angle υ; An objective lens condenses light onto the object surface, and receives a portion of the reflected light from the irradiated object surface. & A first photodetector that detects a shift in the position and distribution of the reflected light caused by the inclination of the irradiated object surface; and a driving means for moving the light emitting means in a direction perpendicular to the optical axis, and the light reflected from the surface of the object to be irradiated takes substantially the same optical path as the incident light.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will now be described based on the drawings.

First, I will explain the principle of the ``muko'' in Noshihon with Figures 2 and 3. When the irradiated surface (4) is tilted by 02, the reflected light is tilted by 2θ2, and the center of the reflected light after passing through the objective lens (5). The position !tM changes by (';2s'u+2θ2.F2 is the focal length #t of the objective lens (5).However, if the objective lens (5) or the center of the incident light is
If it is translated by Inθ2, the reflected light returns along the same optical path as the incident light. In other words, as shown in FIG. 2, if there is a positional shift in the reflected light, a portion of the reflected light is received by the photodetector (6), which is divided into four parts, and an error signal generated in accordance with the positional shift is detected. The objective lens (5) is moved in a direction perpendicular to the optical axis, and servo is applied so that the position of the reflected light is constant, as shown in FIG. The shape of the photodetector and the direction of the error signal are highly conceivable. For example, even if the reflected light is not separated by a beam splitter (7), a four-part photodetector (8) with a hole (8a) the size of the incident light as shown in Figure 4 can be used.
Using , we can obtain the error signal.

You can also use a commercially available optical position detector, which changes the voltage generated at both terminals depending on the light receiving position.

If the irradiated surface (4) deviates from the focal position, the optical path of the reflected light will no longer be constant, which is not good. For example, the reflected light is reflected by the lens and the inner column lens, an error signal is extracted from the astigmatism that occurs, and the objective lens (5) or the object to be irradiated is moved in the direction of the optical axis. Apply focus servo. The method of calculating the total number of focus errors from astigmatism is the most common method, but various other methods such as the Naifezi method are also known, and they can also be used in the optical device according to the present invention. It is.

The driving mechanism that does not move the objective lens (5) or the object to be irradiated by the above-mentioned error signal can be a method of moving a feed screw with a motor, a method of using a linear motor, or the like.

When the optical device according to the present invention is applied to a laser interferometric length measuring device, it is possible to directly and precisely measure the thickness of a curved surface with an inclination of 0J. The tilt of the irradiated surface (4) is limited by the aperture angle of the objective lens (5), so even if ENA
(Numerical aperture) When using the -0.6 objective lens (5), the aperture angle is 36° from the optical axis, so ±, 300
Sufficient measurement up to the irradiated surface (4) with a certain degree of inclination "J'
(+'r<. However, in such usage, the diameter of the luminous flux of the incident light that enters the objective lens (5) must be made sufficiently smaller than the entrance pupil diameter of the objective lens (5).

For example, in order for an objective lens (5) with an NA of 06 to be able to measure the irradiated surface (4) with an inclination of ±30° without vignetting, the diameter of the incident light beam must be It needs to be 1/6 or less of the entrance pupil diameter of the lens (5).

However, when the incident light is diverging light or converging light, moving the objective lens (5) in the optical axis direction shifts the focal position, causing errors. Therefore, in this case, it is better that the incident light be parallel light.

When the objective lens (5) is moved according to the inclination of the irradiated surface (4), the position of the focal point moves by the amount of movement of the objective lens (5). This strictly holds true if the incident light is parallel light. In curved surface thickness measuring devices and defect inspection devices using the laser interferometric length measuring device mentioned above, the position of the measurement point is
-Need to know by Y coordinate.

In this case, the position of the measurement point is the mobile phase of the object to be measured: (X,
“.

Movement amount of objective lens (5) (X2.Y,, )
added (X.

-1-X2. Y, 10Y2). Objective lens (5)
If the incident light is moved without moving, the return point position will not move.

Although the measurement accuracy of the laser interferometric length measuring device is extremely high at 0.01 .mu.m, the effect is very large when it is combined with the optical device according to the present invention. For example, it has been considered extremely difficult to precisely measure the shape of an aspherical lens surface in the prior art. The thickness Z of the aspherical lens surface is determined by the function type with respect to the X-Y coordinates, and the shape thereof is determined. By using the optical device according to the present invention, any X of the lens can be
-Y I! Since the value of thickness Z with respect to the P target position can be measured with the accuracy of a laser interferometer, the deviation of the actual measurement dimension from the value derived by the given function can be eliminated and measured manually within 14 minutes. It becomes a possible system.

FIG. 5 shows a surface shape measuring device in which the optical device according to the present invention is applied to a laser interferometric length measuring device using the optical heterodyne method. , the light emitted from the f2 Zeeman laser (9) is split into two polarization directions by a λ/4 plate (10). , the light is polarized in a direction parallel to the plane of the paper and is divided into light fl.

Then, some of the light is separated by the beam splitter Uυ,
The heat frequency (f, -f2) is detected by the photodetector θ. The light beam f2 that has passed through the beam splitter (+1) is retracted upward by the polarizing prism a3 and is reflected by the fixed mirror (1) (-) and reaches the photodetector aυ.

On the other hand, the light fl is reflected by the surface of the object to be measured OQ, but when the object to be measured Ut9 moves 4 times, the moving speed Z1
divided by the dam zero force, the above position servo and]A
- Photodetector O→ to generate the error signal of the customer servo
(Achieves above Ic. The polarizing prism has the property of completely transmitting the P polarized wave, partially reflecting the S polarized wave, and transmitting the remaining light. , it is totally reflected by the polarization prinium (c) and reaches the photodetector (to).The beat frequency f1+Δf-f2 of f2, f, and +Δf is obtained on the photodetector Q9, and the photodetector @1 Δf is determined from the difference between the beat frequencies f and -f2 obtained in , and displacement Z is determined by integrating this.The measurement accuracy of Z determined in this way is approximately 0.1 to 0.01μ7/Z. It is possible to measure the movement of the objective lens (e) in the Z direction to measure the displacement of the plane of incidence on jKJ, but in this case, the measurement accuracy is the number μ2
It is 21. Note that c2]) is a beam splitter, (4
) (c) is λ/4 t&, (goods) ~ (a) are lenses, (
C) is a cylindrical lens, (C) is a measured value display section, I is a measured object measurement position display section, (to) is an objective lens drive device, 4
31+1l-1: An apparatus for moving one object to be measured.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, even if the irradiated surface is tilted, as long as the inclination is within the aperture angle of the objective lens, the reflected light will follow the same path as the incident light. It is possible to obtain an optical device with a very large tolerance for adjusting the inclination of the surface, and its industrial value is extremely large.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the optical path in the optical system of a conventional device;
3 and 3 are explanatory diagrams of an embodiment of the present invention, FIG. 4 is an explanatory diagram of a photodetector used in an optical device IT (in an embodiment of the present invention), and FIG. It is a schematic diagram of an optical device in one embodiment of the present invention. (S) UV SOUIW (R)...Photodetector, (9)
... Zeeman laser, 0()(2)...λ/4 plate,
Circumference)...beam splitter, UQ force...polarizing prism, circle...fixed mirror, αQ...object to be measured, (4)
...Objective lens, (C) - (A)...Lens, (A)...Cylindrical lens, (C)--Measurement value display section, wire...
...Measurement object measurement position display section, CyJ...Objective lens drive device, color 11...Measurement object drive device agent Yoshihiro MorimotoFigure 1Figure 2Figure 3

Claims (1)

[Scope of Claims] 1. A light emitting means comprising a radiation light source and an optical system that converts the light emitted from the radiation light source into radiation having a fixed 7-pot size and a polygonal spread, and this light emitting means. an objective lens for condensing the emitted light from the irradiated object onto the surface of the irradiated object; and a first photodetector for detecting deviations in the optical distribution and distribution; an optical device having a driving means for moving in a vertical direction, and configured such that light reflected from the surface of the irradiated object follows substantially the same optical path as the incident light. 2. Receives part of the reflected light from the surface of the irradiated object. a second photodetector for detecting a change in the optical path of the reflected light caused by a deviation from a condensing position of the emitted light by the objective lens on the surface of the irradiated object; and a combination of the objective lens and the second photodetector. a light-transmissive, reflective, or light-blocking optical means located between, for converting the optical path of the reflected light into a form capable of obtaining a suitable focus error signal on the second photodetector; 2. The optical system according to claim 1, wherein the objective lens or the object to be irradiated is moved in the optical axis direction by a focus error signal, and the condensing position is always positioned on the surface of the object to be irradiated. Device. 3. The optical device according to claim 1 or 2, wherein the beam diameter of the emitted light just before it enters the objective lens is smaller than the entrance pupil of the objective lens. 4. The optical device according to any one of items 1 to 3, wherein the emitted light is lattice line light. 5. Special if equipped with a means to measure the total amount of movement of the objective lens in the direction perpendicular to the optical axis of the synchrotron radiation! f. The optical device according to any one of claims 1 to 4. 6. A means for adding the measured value of the amount of movement of the objective lens in the direction perpendicular to the optical axis of the synchrotron radiation to the measured value of the amount of movement of the irradiated object in the direction perpendicular to the light axis. An optical device according to any one of claims 1 to 5. 7. The reflected light from the surface of the object to be irradiated with the synchrotron radiation, and the second synchrotron radiation that is partially separated before the synchrotron radiation reaches the objective lens, or the third synchrotron radiation that is different from the synchrotron radiation. , the same light-receiving surface′! 1: Interference fringes on the light-receiving surface or the OiJ light analysis detector due to the interference between the reflected light and the second or third emitted light described in 11. The optical device+ffi according to any one of claims 1 to 6, further comprising a detection means for detecting information such as a reversal of the surface of the irradiated object from a change or a change in the beat frequency.