JPH063578A - Focus detecting device - Google Patents

Abstract

PURPOSE:To provide a focus detecting device capable of focusing control with high accuracy without being influenced by the surface shape of a testee body. CONSTITUTION:Reflected light reflected from the surface 41 of the testee body 39 illuminated with a laser beam emitted from a laser diode 23 is condensed on a bisected photodetector 49, and focusing is performed based on a light quantity received by the photodetector 49 in this focus detecting device, which is provided with a limit edge 45 for shielding only the reflected light harmful to focus detection out of the reflected light reflected from the surface 41 of the testee body 39.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus detecting device for focusing on a subject in a microscope or an optical measuring machine.

[0002]

2. Description of the Related Art A device of this type has been disclosed in Japanese Patent Laid-Open No.
A focus detection device disclosed in Japanese Patent Publication No. 42725/1992 (hereinafter, referred to as a conventional example) is known. FIG. 3 schematically shows the configuration of a conventional focus detection device.

As shown in FIG. 3, a laser beam emitted from a laser diode (LD) 1 is regulated by a collimator lens 3 into a parallel light beam, and then half of it is covered by a shield plate 5 arranged in the optical path. Is blocked. The remaining half of the luminous flux is imaged by the condenser lens 7 (intermediate imaging position P), and then is irradiated on the polarization beam splitter 9. The laser beam reflected by the polarization beam splitter 9 is a quarter wavelength plate 11 and an imaging lens 13.
And is focused on the surface 19 of the subject 17 via the objective lens 15.

The reflected light reflected from the surface 19 of the subject 17 is again subjected to the objective lens 15, the imaging lens 13 and 1/4.
The polarized beam splitter 9 is irradiated through the wave plate 11. At this time, the polarization direction of the reflected light applied to the polarization beam splitter 9 is shifted by 90 ° with respect to the initial polarization direction by the quarter-wave plate 11. Therefore, the reflected light passes through the polarization beam splitter 9 and forms an image on the two-divided light receiving element 21 (indicated by the image forming position S).

The two-divided light receiving element 21 is provided with two photoelectric conversion units A and B, and each of these photoelectric conversion units A and B has a function of outputting a voltage signal corresponding to the amount of received light. There is. FIG. 4A shows change characteristics of the voltage signals A and B output from the photoelectric conversion units A and B with the position of the subject 17 as the horizontal axis in the state shown in FIG. The voltage signals having such characteristics are input to the corresponding detection mechanisms (not shown), a predetermined calculation is performed, and the focus detection signal is output. FIG. 4B shows the signal characteristic obtained as a result of the calculation on the voltage signals A and B, and the focus detection signal is obtained from the signal characteristic.

Specifically, the dotted line C is (AB) / (A +
The signal characteristic obtained from the calculation result of B) is shown, and the solid line D shows the signal characteristic obtained from the calculation result of (AB). A focus detection signal is obtained based on the zero-cross signal of these two signal characteristics C and D, and the focus position is calculated from this focus detection signal.

[0007]

However, as shown in FIG. 5, in the conventional apparatus, the focusing spot diameter for focusing on the surface 19 (see FIG. 3) of the subject 17 during focusing is as follows. The diffraction limit is narrowed down and it becomes extremely small. Therefore, when the laser beam is focused on the surface 19 of the subject 17 having a fine structure such as roughness or IC pattern,
Due to the irregular reflection due to the roughness of the surface 19 of the subject 17, the diffraction due to the IC pattern, the inclination of the subject 17, etc., reflected light (reflected light indicated by arrow Q in the figure) that follows an optical path that should not originally pass may be generated. is there. It should be noted that FIG. 5 shows a simplified configuration of the apparatus shown in FIG. 3 for convenience of explanation.

As shown in FIG. 6A, when such reflected light is generated, the voltage signals A and B output from the photoelectric conversion units A and B of the two-divided light receiving element 21 are disturbed. This means that the voltage signal output when the surface 19 of the subject 17 is a mirror surface (electrical signal indicated by a dotted line in FIG. 6A).
It is clear when compared with.

Further, the disturbance of the voltage signals A and B (see FIG. 6A).
6) also causes a disturbance as shown in FIG. 6B in the focus detection signal, resulting in pseudo focusing as shown by reference signs c and d.

The present invention has been made to eliminate such an adverse effect, and an object thereof is to provide a focus detection apparatus capable of performing focus detection with high accuracy without being influenced by the surface shape of the subject. Especially.

[0011]

In order to achieve such an object, the focus detection apparatus of the present invention divides the reflected light reflected from the surface of the subject illuminated by the illumination light emitted from the light source into divided light beams. A focus detection system that focuses on an element and performs focus detection based on the amount of light received by this split light receiving element, and focus detection of the reflected light that is provided in this focus detection system and reflected from the surface of the subject. And a limiting edge that shields only reflected light harmful to.

[0012]

The illumination light emitted from the light source is focused on the surface of the subject through the focus detection system, and the reflected light reflected from the surface is removed by the limiting edge only the reflected light harmful to the focus detection. And is focused on the divided light receiving element.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A focus detecting device according to an embodiment of the present invention will be described below with reference to FIG. FIG. 1 schematically shows the configuration of the focus detection apparatus of this embodiment.

As shown in FIG. 1, the laser beam emitted from the laser diode (LD) 23 is regulated by the first collimator lens 25 into a parallel light beam,
A half of the light flux is blocked by the shield plate 27 arranged in the optical path. The other half of the light flux is imaged by the first condenser lens 29 (shown by the intermediate image formation position F),
The polarized beam splitter 31 is irradiated. The laser beam reflected by the polarization beam splitter 31 is 1
The light is focused on the surface 41 of the subject 39 via the / 4 wavelength plate 33, the imaging lens 35, and the objective lens 37.

The reflected light reflected from the surface 41 of the subject 39 is again subjected to the objective lens 37, the imaging lens 35, and the 1/4.
The polarized beam splitter 31 is irradiated via the wave plate 33. At this time, the polarization direction of the reflected light applied to the polarization beam splitter 31 is shifted by 90 ° with respect to the initial polarization direction by the quarter-wave plate 33. Therefore, the reflected light passes through the polarization beam splitter 31.

In the focus detection apparatus of this embodiment, the polarization beam splitter 3 is sandwiched between the positions where the reflected light transmitted through the polarization beam splitter 31 forms an image (that is, the intermediate image formation position G).
A second collimator lens 43 is arranged so as to face 1. Therefore, the reflected light that has passed through the polarization beam splitter 31 is regulated into a parallel light flux via the second collimator lens 43 after being subjected to intermediate image formation (indicated by reference character G).

Regarding the reflected light which is regulated into a parallel light flux by the second collimator lens 43, the half of the light flux on the side where there is no reflected light is blocked by the limiting edge 45. The other half of the luminous flux is imaged on the two-divided light receiving element 49 via the second condenser lens 47 (imaging position R).

The two-divided light receiving element 49 is provided with two photoelectric conversion units J and K, and each of these photoelectric conversion units J and K has a function of outputting a voltage signal corresponding to the amount of received light. There is.

The voltage signals output from these photoelectric conversion units J and K are output to the corresponding arithmetic units and subjected to predetermined arithmetic operations. Then, focus detection is performed based on the calculated data.

As described above, the focus detection apparatus of this embodiment is
Since the limiting edge 45 is arranged in the optical path between the second collimator lens 43 and the second condensing lens 47 so as to block half the luminous flux of the reflected light guided through the optical path. , Diffuse reflection due to the roughness of the surface 41 of the subject 39,
Due to the diffraction by the fine pattern, the inclination of the object 17, etc.,
It is possible to shield reflected light that follows an optical path that should not originally pass, that is, noise light harmful to focus detection (indicated by arrow N in the figure). As a result, highly accurate focus detection with a high S / N ratio can be performed without being affected by the surface shape of the subject 39.

The present invention is not limited to the configuration of the above-described embodiment, but can be variously modified within the scope of the claims. For example, as shown in FIG. 2, the laser beam emitted from the laser diode (LD) 23 is
It is also possible to directly irradiate the modified beam splitter 31 via the first condenser lens 29. However, in the optical path between the second collimator lens 43 and the second condensing lens 47, the limiting edge 4 is arranged so as to block half the luminous flux of the reflected light guided through the optical path.
Since 5 is arranged, noise light N
Even if (see FIG. 1) is mixed, the noise light N
The reason is that the light can be surely shielded by the limiting edge 45. Further, in the above-described embodiment, the two-divided light receiving element 4 is used.
9 is applied, for example, a position sensor (P
It is also possible to apply SD).

[0022]

In the focus detecting device of the present invention, since the limiting edge is arranged in the optical path of the focus detecting system, irregular reflection due to the roughness of the surface of the subject, diffraction due to a fine pattern, inclination of the subject, etc. may occur. It is possible to block reflected light that follows an optical path that should not originally pass, that is, noise light that is harmful to focus detection. As a result, highly accurate focus detection with a high S / N ratio can be performed without being affected by the surface shape of the subject.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a configuration of a focus detection device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a modified example of the device shown in FIG.

FIG. 3 is a diagram schematically showing a configuration of a conventional focus detection device.

4 (a) is a diagram showing a change characteristic of an electric signal output from a two-divided light receiving element applied to the device shown in FIG.
(B) is a figure which shows the signal characteristic obtained as a result of calculation with respect to a voltage signal.

5 is a diagram showing a state in which reflected light that follows an optical path that should not originally pass is generated in the apparatus shown in FIG.

6A is a diagram showing a state in which a voltage signal output from a two-divided light receiving element is disturbed by the reflected light shown in FIG. 5, and FIG. 6B is a focus detection due to a voltage signal disturbance. The figure which shows the state in which the disturbance was caused to the signal.

[Explanation of symbols]

23 ... Laser diode, 39 ... Subject, 41 ... Surface, 45 ... Limiting edge, 49 ... Two-division light receiving element.

Claims (1)

[Claims] 1. The focus detection is performed based on the amount of light received by the divided light receiving element by condensing the reflected light reflected from the surface of the subject illuminated by the illumination light emitted from the light source on the divided light receiving element. A focus detection system, comprising: a focus detection system; and a limiting edge that is provided in the focus detection system and that shields only reflected light harmful to focus detection out of reflected light reflected from the surface of the subject. apparatus.