JPS633206A - Optical thickness measuring instrument - Google Patents

Abstract

PURPOSE:To easily position a specific place on a surface to be inspected on the optical axis of an objective by providing an optical system which irradiates a body to be inspected with light in a direction different from the optical axis of an optical system for thickness measurement and observes the surface to be inspected in a direction symmetrical about the optical axis. CONSTITUTION:The body 5' to be inspected is irradiated with light from a light source 14 through a condenser lens 15 in the direction different from the optical axis of the light source of the optical system 13 to illuminate a position on the object surface to be positioned. Then, light reflected by the surface to be inspected symmetrically about the optical axis of the optical system 13 is guided to a television camera 17 by an image forming lens 16 and projected on a monitor 18, and an observer performs positioning operation according to a positioning index displayed on the monitor 18 previously. Here, an observation surface 17 is arranged slantingly to the optical axis of the lens 16 by an angle beta satisfying a specific expression. Consequently, even if the optical axis of the lens 16 slants by an angle alpha to the surface 5' to be inspected, the image of the object surface is put in focus sharply at a position except on the optical axis of the lens 16, so that the positioning accuracy of the surface to be inspected is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION a. Technical Field The present invention relates to an improvement in an optical thickness measuring device.

b. Prior art and its problems As a method for optically measuring the wall thickness of thin glass, there is an invention for which the present applicant applied for a patent on June 20, 1988. This method uses a sufficiently small light source 1 as shown in Figure 3.
The numerical aperture NA of the light from the transparent or semi-transparent object 5
A condensed light beam is projected by the objective lens 4 having an o, and the convergence point of the condensed light beam or the object to be examined is moved in the optical axis direction of the objective lens, and the condensed light beams are projected on the front and back surfaces of the object. The position of the maximum axial center strength is measured and the wall thickness is determined by calculation. The details of FIG. 3 will be omitted since they will become clear from the embodiment shown in FIG. 1, which will be described later.

Incidentally, there are cases in which it is necessary to measure the wall thickness of a specific location on the surface of the test object, but conventional devices have the following problems. Firstly, as the numerical aperture NA0 of the objective lens increases, the working distance becomes extremely short, making it extremely difficult to align a specific location on the surface to be inspected with the optical axis of the objective lens. It is something that happens. Also, the second
In addition, when alignment is performed with a long working distance, the focus position of the objective lens is no longer in focus, and the focal point becomes blurred and large, making it difficult to achieve one alignment.

Therefore, there is room for improvement in measuring the wall thickness at a specific location on a surface to be inspected using the conventional device.

C1 Purpose Therefore, the purpose of the present invention is to irradiate a test object with light from a direction different from the optical axis of the first optical system for measuring wall thickness,
Furthermore, by arranging an optical system for observing the surface to be measured in a direction symmetrical to the optical axis of the first optical system, it is possible to observe the surface to be measured while maintaining a large distance between the objective lens and the surface to be measured. It is an object of the present invention to provide a device that makes it possible to easily align a specific location on a surface to be inspected with the optical axis of an objective lens (hereinafter referred to as alignment).

d. Structure and operation of the embodiment Hereinafter, one embodiment of the present invention will be described based on FIG.

In the first optical system 13, the light from the linearly polarized laser 1 is expanded by the beam expander 2 and 174
After passing through the wavelength plate 3, it becomes circularly polarized light, and is transmitted to the object 5 having a refractive index n and a wall thickness t by an objective lens 4 having a working distance W1.
It is projected as a condensed light beam with a numerical aperture of NA. The reflected light from the test object 5 becomes light whose polarization direction is perpendicular to that of the laser oscillation light, and is guided to the photoelectric conversion element 7 by the polarizing beam splitter 6. A diaphragm 8 is installed in front of the photoelectric conversion element 7 for selecting the axial center intensity of the reflected light. The analog signal from the photoelectric conversion element 7 is sent to a sample and hold circuit 9. The signal passes through the A/D conversion circuit 10, becomes a digital signal, and is input to the microcomputer 11.

On the other hand, when the test object 5 is moved in the direction of the optical axis of the objective lens 4 by a moving means (not shown), the front and back surfaces of the test object 5 are brought into focus, and A3 No. 1 on the photoelectric conversion element 7 is at its maximum. becomes. The difference X between the focus positions on the front and back surfaces is read by the length measuring scale 12, and the read signal is input to the microcomputer 11. The microcomputer 11 calculates the wall thickness t of the object to be inspected from values such as the refractive index n, the numerical aperture NA, and the difference X between focus positions.

In the optical thickness 8111 determination device described above, when it is necessary to measure the thickness of a specific location on the surface to be inspected, it is necessary to accurately position it. Further, in consideration of workability, this positioning work needs to be performed at a working distance W2 which is sufficiently longer than the working distance W of the objective lens 4, that is, with the object to be examined at the position 5'.

Therefore, light from the second light source 14 in a direction different from the light source optical axis of the first optical system 13 is irradiated onto the test object 5' using the condenser lens 15 to position the test surface of the test object 5'. Illuminate the desired point. The light reflected from the test surface symmetrically with respect to the optical axis of the first optical system has a magnification M (=b/a
) is guided to a television camera 17, which is an observation surface, and displayed on a monitor 18. The observer can easily perform positioning by following a positioning finger (not shown) shown in advance on the monitor 18.

Here, a case where the surface to be inspected is inclined with respect to the optical axis of the imaging lens 16 will be explained using FIG.

The intersection of the light l1illIZ of the imaging lens 16 with the focal length f and the test surface 5' is A, and the intersection of the optical axis Z and the observation surface 17 is A.
', the inclination angle of the test surface 5' with respect to the optical axis Z is α, the inclination angle of the PiA measuring surface 17 with respect to the optical axis Z is β, the intersection of the optical axis Z and the straight line Y inclined by an angle O from the light 4i1ilZ is the O1 straight line The intersection between Y and the surface to be inspected is B, the intersection between straight line Y and the observation surface is B', and the intersections with the optical axis when a line perpendicular to Z is drawn from points B and B' are B and B, respectively. □′, 0A=a, OA
Let'=b, OB,=a', OB,'=b', Therefore, a'b' a b f. This equation can also be written as tanβ/lanα=b/a=M.

As a result, even if the optical axis of the imaging lens 16 is tilted by α with respect to the test surface 5', the a measurement surface 17 can be changed by tanβ/lanα.
If the image forming lens is tilted with respect to the optical axis of the imaging lens by β that satisfies the formula =M, the image of the surface to be measured will be kept in sharp focus even at points other than the optical axis of the imaging lens, and the position of the surface to be measured will be Improves alignment.

e. Effects As explained above, the apparatus of the present invention has the effect that alignment can be easily performed with high accuracy when measuring the wall thickness at a specific position of an object to be inspected.

1st

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing one embodiment of the device used in the present invention, and Fig. 2 shows how a sharp image is formed on the observation surface when the surface to be examined is tilted with respect to the optical axis of the imaging lens. FIG. FIG. 3 is a diagram showing a conventional device. 1: Laser 2: Beam expander 3: 1
/4 wavelength plate 4: Objective lens 5, 5 J, Test object 6: Polarizing beam splitter 7: Photoelectric conversion element 8: Aperture 9: Sample hold circuit 10: A/D conversion circuit 11: Microcomputer 12:
Length measurement scale 13: First optical system for wall thickness measurement 14: Light source 15: Condenser lens 16: Imaging lens 17: Television camera 18: Monitor
19: Observer factor

Claims (1)

[Claims] 1. The light from a sufficiently small light source, which is the first optical system, is projected onto a transparent or semi-transparent object by an objective lens having a numerical aperture NA_0, and the condensed light beam is Move the condensing point or the object to be examined in the optical axis direction of the objective lens, measure the axial central intensity maximum position of the condensed beam on the front and back surfaces of the object, and calculate the position of the center intensity of the object. In an optical thickness measuring device for measuring thickness, a second light source irradiates a test object with light from a direction different from the light source optical axis of the first optical system, and a light source condenses light from the second light source. an imaging lens for forming an image of the surface of the object to be examined in a direction symmetrical to the optical axis of the condenser lens with respect to the optical axis of the first optical system, and the imaging lens An optical thickness measuring device characterized by having an observation surface on an imaging plane. 2 The angle between the optical axis of the imaging lens and the normal to the surface to be measured is α,
When the angle with the normal to the observation surface is β, and the imaging magnification of the imaging lens is M, the object to be inspected, the imaging lens, and the observation surface are arranged so as to satisfy the following relationship: M=tanβ/tanα An optical thickness measuring device according to claim 1, characterized in that: 3. The optical thickness measuring device according to claim 1, wherein the observation surface is a television camera.