JPH045514A - Optical fine displacement measuring instrument - Google Patents

Abstract

PURPOSE:To prevent an optical system from not being aligned owing to a collision by detecting the state right before an objective lens collides against a body to be measured with reflected luminous flux from the body to be measured which is emitted originally by a lighting means which shares the objective of a lighting optical system. CONSTITUTION:When the body 4 to be measured is at a distance from the focal length of the objective lens 3, the reflected light from a light source 2 is photodetected by a detector 6. When the body 4 to be measured approaches to the focal length of the objective lens 3, on the other hand, the reflected light deviates from the photodetection surface of the detector 6 gradually and when the body 4 to be measured approaches to a constant distance, the reflected light deviates completely from the photodetection surface of the detector 6. For the purpose, the position of the detector 6 is adjusted to detect the state right before the objective 3 collides against the body to be measured.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an optical minute displacement measuring device for measuring minute displacements, surface roughness, etc. of an object to be measured by optical means.

(Prior Art) Conventionally, as a device for detecting a focus error and measuring minute displacements and surface roughness of an object to be measured, for example, a device using the critical angle method (see Japanese Patent Laid-Open No. 59-90007) , those using the astigmatism method (see Japanese Patent Application Laid-open No. 1705), or those using the Foucault method (light wave technique) contact VOj2B, N [111°1988, P773~
784) etc. are known.

Here, the critical angle method utilizes the fact that the intensity of a light beam incident near a specific critical angle of a prism exhibits a rapid change with respect to a minute change in angle.

FIG. 4 is a block diagram of a conventional optical minute displacement measuring device using the critical angle method. In the drawing, (101) is a laser light source, (102) is a collimating lens, and (103) is a collimating lens.
) is a polarizing beam splitter, (104) is an 18-wave plate,
(105) is the objective Li2, (IN) is the object to be measured, (1
07) is a beam splitter, (108a) (108b)
is a critical angle prism, and (109a) and (109b) are two-split light receiving elements.

Laser light from a laser light source (101) is converted into a parallel beam by a collimating lens (102), and guided as S-polarized light to a 1/4 wavelength plate (104) via a polarizing beam splitter (+03). The laser beam guided by the quarter-wave plate (104) is converted into a circularly polarized beam, and then focused on the surface of the object to be measured (IB) via the objective lens (105). The laser beam reflected by the object to be measured (10B) is P-polarized by the 1/4 wavelength plate (104), then transmitted through the polarizing beam splitter (103), guided to the beam splitter (107), and separated into spectra. . Each of the separated lights is reflected by a critical angle prism (108a) (108b) whose reflecting surface is set at a critical angle, and is incident on a two-split light receiving element (10sa) (tosb), where the amount of light is detected. .

In this way, the object to be measured (+06) is
), the reflected light becomes parallel, the reflectance at the critical angle prism (108a) (108b) is constant for the entire luminous flux, and the two-split light receiving element (109a)
)(+09b) will be the same amount of light.

However, the object to be measured (1011i) is
), the reflected light becomes convergent light, so the critical angle prism (+08a) (108b)
The incident angle of the light flux entering the critical angle prism (108a) is the critical angle prism (108a) on the right side of the figure with respect to its tip axis.
The lower side in the figure becomes smaller than the critical angle, the reflectance decreases, and a difference occurs in the amount of light received by the two-split light receiving elements (109a) (109b). Similarly, when the object to be measured (10B) is located closer than the focal point of the objective lens (105), the reflected light becomes diverging light, which is the opposite of the case described above.
A difference occurs in the amount of light received by the two-split light receiving elements (109a) and (109b). Due to this difference in light intensity, the object to be measured (
10[i) from the focal position of the objective lens (105) can be detected to measure minute displacements and surface roughness of the object to be measured (10[i).

(Problem to be solved) However, in the conventional optical system described above, the detection range is as narrow as several 5 cm, so in order to accommodate the thickness and shape of the object to be measured, the entire optical system must be moved in the focus error detection direction. It is necessary to mount it on a movable stage and make coarse movements. In this case, in order to recognize that the stage has moved and entered the measurable range, for example, the output of the focus error detection optical system shown in FIG. + B + c + D) ■I (A + C) - (B + D) l/(A +
B 1c 1D) will be monitored.

However, the above outputs (2) and (2) may be similar to those in the detection range outside the detection range, and furthermore, the output (2) is unstable because it depends on the reflectance of the object to be measured. Therefore, there is a problem in that the objective lens has a short working distance and is therefore at risk of colliding with the object to be measured.

(Means for Solving the Problems) The present invention provides an optical micro-displacement measuring device that solves the above-mentioned problems.The present invention is characterized by the fact that the objective lens of the illumination optical system is shared, and the object to be measured is irradiated. another lighting means to
The object of the present invention is to include a proximity state detection optical system that detects the state immediately before the objective lens collides with the object to be measured by the light beam reflected from the object by the illumination means.

(Function) FIG. 1 is a basic configuration diagram of the measuring device of the present invention. In the drawing, (1) is a light source A1 (2) that enters the object to be measured (4) through the optical axis of the objective lens (3).
) and another light source B that shares the objective lens (3) and irradiates the object (4), and the light from light source B (2) is incident off the optical axis of the objective lens (3). . (5) is a reflective mirror,
(6) is a detector, and the reflected light from the object to be measured (4) passes through the objective lens (3) again, is reflected by a reflecting mirror (5), and is received by a detector (6).

In the apparatus configured as described above, when the object to be measured (4) is located farther than the focal length of the objective lens (3), the reflected light from the light source B (2) is reflected by the detector (6). Light is received. On the other hand, when the object to be measured (4) approaches the focal length of the objective lens (3) (4 degrees), the reflected light gradually deviates from the light-receiving surface of the detector (6), and when it approaches a certain distance, It will be completely removed from the light receiving surface of the detector (6). Therefore, by adjusting the position of the detector (6), it is possible to detect the state immediately before the objective lens (3) collides with the object to be measured.

(Embodiment) FIG. 2 is a block diagram of an embodiment of the measuring device of the present invention using the critical angle method.

In the drawing, (11) is a light source A of light passing through the optical axis of the objective lens (17), (12) is its collimating lens,
(13) is another light source B that enters the objective lens (17) with a deviation from the optical axis, and (14) is its collimating lens. (15) is a polarizing beam splitter, (16) is 1/
A four-wave plate, (17) an objective lens, (18) an object to be measured, (19) a reflecting mirror, and (20) a detector. Also (2
1) is a beam splitter, (22aH22b) is a critical angle prism, and (23aH23b) is a two-split light receiving element.

FIG. 3 is a block diagram of an embodiment of the measuring device of the present invention using the astigmatism method.

In the drawing, (31) is the light source A of the light passing through the optical axis of the objective lens (37), (32) is its collimating lens,
(33) is another light source B that enters the objective lens (37) with a deviation from the optical axis, and (34) is its collimating lens. (35) is a polarizing beam splitter, (3B) is a wavelength plate, (37) is an objective lens, (38) is an object to be measured,
(3S) is a reflecting mirror, and (40) is a detector. Also (41
) is a beam splitter, (42a) and (42b) are cylindrical lenses, and (43a and 43b) are two-split light receiving elements.

In these embodiments, the optical system of FIG. 1 will be incorporated in the same way, so whatever focus error detection method is used will operate in the same way.

In addition, in this optical system, when the object to be measured is tilted, the distance between the objective lens and the object changes when the reflected light leaves the light-receiving surface of the detector, so take this into consideration when adjusting the allowable range of inclination. It is necessary to make settings with a margin for this.

(Effects of the Invention) As explained above, according to the optical minute displacement measuring device of the present invention, collision can be prevented when the object to be measured approaches the objective lens beyond the measurement range. It is possible to prevent misalignment of the optical system due to Therefore, it is extremely effective when used when the object to be measured is extremely damaged.

[Brief explanation of the drawing]

FIG. 1 is a basic configuration diagram of the measuring device of the present invention. FIG. 2 is a block diagram of an embodiment of the measuring device of the present invention using the critical angle method. FIG. 3 is a block diagram of an embodiment of the measuring device of the present invention using the astigmatism method. FIG. 4 is a block diagram of a conventional optical minute displacement measuring device using the critical angle method. DESCRIPTION OF SYMBOLS 1... Light source A, 2... Light source B13... Objective lens, 4... Measured object, 5... Reflector, 6... Detector. Introduction 2! ! I

Claims (2)

[Claims] (1) In an optical micro-displacement measuring device having an illumination optical system that irradiates a measured object with a light beam from a light source, and a focus error detection optical system that detects a focus error from a reflected light beam from the measured object, the illumination optical system Another illumination means that shares the objective lens of the system and irradiates the object to be measured, and proximity state detection optics that detects the state immediately before the objective lens collides with the object to be measured by the light beam reflected from the object by the illumination means. An optical micro-displacement measuring device characterized by comprising a system. (2) The optical micro-displacement measuring device according to claim (1), wherein the illumination means used for the reflected light flux that enters the proximity state detection optical system is deviated from the optical axis of the objective lens.