JPH11305136A - Laser microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of interference stripes in the image of a sample by making non-parallel at least two planes of optical path dividing elements arranged in the optical path of a microscope. SOLUTION: A laser beam from a laser light source 1 introduced into a main body 2 of microscope is passed through an aperture stop 3, relay lens system 4, visual field stop 5, correction glass 6 and half mirror 7 and perpendicularly reflected by a full reflection mirror 8. The reflected laser beam is passed through an objective lens 9 and a prescribed area on the sample is simultaneously irradiated with it. The reflected light from the sample is returned to the objective lens 9 again, perpendicularly reflected by the full reflection mirror 8, perpendicularly reflected by the half mirror 7 and separated from the optical path of an optical illumination system. Afterwards, the light is converged and an image is formed by an image forming lens 10. In this case, the half mirror 7 is wedge-shaped. Namely, since a plane 7a on the incidence side of illuminating light and a plane 7b on the emission side are made non-parallel, the interference of laser beams is not generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microscope that uses a high-intensity laser as an illumination light source, and more particularly to a high-resolution laser microscope that is effective for inspecting semiconductors that have been miniaturized in recent years.

[0002]

2. Description of the Related Art As a conventional light source for a microscope, a tungsten lamp and a halogen lamp are generally known. Tungsten lamps and halogen lamps are usually used as light sources for lighting systems called Koehler lighting.
The structure is such that the sample can be illuminated as a whole without unevenness (hereinafter, the above-mentioned illumination is referred to as collective illumination).

When inspecting an opaque sample such as a semiconductor using the above-described illumination system, an illumination system called a reflection illumination or an epi-illumination is formed, and the illumination system is divided into an illumination optical path and an observation optical path. An optical member such as a half mirror or a half prism is inserted between the image and the image so that illumination light impinges on the sample. There is also a type that uses a laser as a light source, such as a confocal microscope. However, such a microscope using a laser as a light source partially shares an illumination optical system and an observation optical system, and illuminates a sample. Is an optical system that is completely different from the above-described collective illumination, since only one point is illuminated instead of collective illumination, and an image is formed by scanning it.

[0004]

As described above, a tungsten lamp or a halogen lamp is used as a conventional light source for a microscope when collectively illuminating, as in the case of Koehler illumination as described above. However, when a higher-luminance illuminating light is required or when a single wavelength having a very narrow half-value width is required as the illuminating light, the tungsten lamp or the halogen lamp is insufficient in brightness and is insufficient.

Therefore, a laser can be considered as a light source for illumination of a microscope which collectively illuminates. However, since the laser has coherence, interference fringes are likely to occur. It is very difficult to prevent. In order to prevent interference fringes, it is conceivable to apply a high-performance anti-reflection coat on the surfaces of optical members that interfere with each other, but deposit an anti-reflection coat with low reflectance until the interference fringes are completely eliminated. It becomes very difficult and expensive.

In particular, when illuminating all at once with a reflection illumination system, it is necessary to use a half mirror or a half prism for branching the illumination optical path and the observation optical path. However, interference fringes may actually occur in these optical members. Many. Therefore, even when illumination light having a high brightness and a narrow half width is required, the use of a laser as a light source in batch illumination has not existed until now.

If an optical system such as a confocal microscope is constructed and a laser beam is used as a light source, the demand for high-brightness and narrow half-width illumination light can be answered. However, the system itself must be large. Become
And it becomes very expensive. The present invention has been made in view of such a conventional problem. Even when a high-intensity laser with a very narrow half-value width is illuminated as a light source for a microscope by a reflection illumination, the interference with the image of the sample is prevented. It is an object of the present invention to obtain an inexpensive microscope system that does not generate fringes.

[0008]

According to a first aspect of the present invention, there is provided a laser microscope, comprising: a light source for emitting laser light; and an illumination optical system for irradiating a predetermined area on a sample with the laser light from the light source. A microscope, an observation system that obtains reflected light from the sample and forms an image of the sample, and an optical path splitting element that separates the reflected light from the sample from the optical path of the illumination optical system and guides the reflected light to the observation system. At least two planes of the optical path splitting element disposed therein are configured to have a non-parallel relationship.

At least two planes of the optical path splitting element arranged in the microscope optical path have a non-parallel relationship. Examples of the optical path splitting element include a wedge-shaped half mirror and a half prism. With this configuration, even if the sample is illuminated collectively using a laser having strong coherence, no interference occurs in the optical path splitting element, so that no interference fringes occur in the sample image obtained by the observation optical system.

According to a second aspect of the present invention, in the laser microscope according to the first aspect, a correction member for correcting the inclination of the optical axis generated by the optical path splitting element is disposed in at least one of the optical path of the illumination optical system or the observation system. It is characterized by having been done. If the light path splitting element is, for example, a wedge-shaped half mirror, the light passes through the light path splitting element, causing the optical axis of each light before and after passing to be inclined. It is not practical to arrange an optical member constituting an observation system or an illumination optical system in accordance with the inclination, because it requires labor and cost in manufacturing. With the configuration described above, since light passes through the optical path splitting element and the correction member, the inclination of the optical axis of each light before and after passing can be corrected. Accordingly, it is not necessary to arrange the optical members constituting the observation system or the illumination optical system in accordance with the inclination, and the manufacturing cost can be reduced.

According to a third aspect of the present invention, in the laser microscope according to the first or second aspect, the correction member is disposed in the illumination optical system and has a plurality of regions having different transmittances. Are selectively insertable into the illumination optical path. With this configuration, it is possible to suppress the occurrence of interference fringes in the sample image, change the amount of illumination light, and effectively use the space in the optical path of the illumination optical system.

[0012]

FIG. 1 is a diagram showing a schematic configuration of a laser microscope according to a first embodiment of the present invention. Less than,
The first embodiment will be described with reference to FIG. Laser light from the laser light source 1 is introduced into the microscope main body 2 via, for example, an optical fiber. The laser light introduced into the microscope main body passes through the aperture stop 3, the relay lens system 4, the field stop 5, the correction glass 6, and the half mirror 7, and is reflected at right angles by the total reflection mirror 8. The laser light reflected by the total reflection mirror 8 passes through the objective lens 9 and is collectively applied to a predetermined region on the sample. An illumination optical system is configured by the aperture stop 3, the relay lens system 4, the field stop 5, the correction glass 6, the half mirror 7, the total reflection mirror 8, and the objective lens 9.

The reflected light from the sample returns to the objective lens 9, is reflected at right angles by the total reflection mirror 8, is reflected at right angles by the half mirror 7, and is separated from the optical path of the illumination optical system. Thereafter, the light is condensed by the imaging lens 10 and a sample image is formed on an imaging surface of a CCD camera as an observation system. The sample image captured by the CCD camera 11 is displayed on a display device (not shown).

In the present embodiment, the half mirror 7 has a wedge shape. That is, the plane 7a on the incident side of the illumination light and the plane 7b on the exit side have a non-parallel relationship. With such a shape, interference of laser light does not occur inside the half mirror 7, and therefore, no interference fringes occur in the sample image captured by the CCD camera 11.

Since the half mirror 7 has a wedge shape, the optical axis of the illumination optical system is inclined before and after the half mirror 7. The correction glass 6 is a wedge-shaped glass having an angle that corrects the inclination. That is, the plane 6a on the incident side of the illumination light and the plane 6 on the exit side
b has a non-parallel relationship. The optical axis of the illumination optical path on the side entering the correction glass 6 and the optical axis of the illumination optical path on the side exiting from the half mirror 7 are made parallel by the correction glass 6, and an optical element constituting an illumination optical system like a normal microscope. The members can be arranged on a straight line.

Next, a second embodiment of the present invention will be described. FIG. 2 is a diagram showing a schematic configuration of a laser microscope according to a second embodiment of the present invention. Members having the same functions as those of the first embodiment are denoted by the same reference numerals. This embodiment is different from the first embodiment in that the CCD camera 11 is arranged on the optical axis of the objective lens 9.

The laser light from the laser light source 1 is reflected at right angles by the half mirror 7 via the aperture stop 3, the relay lens system 4, and the field stop 5. The laser light reflected by the half mirror 7 is collectively applied to a predetermined region on the sample via the objective lens 9. The reflected light from the sample is again guided to the half mirror 7 via the objective lens 9 and passes through the half mirror 7. Thereafter, the light is condensed by the imaging lens 10 via the correction glass 6, and the sample image is
A sample image is formed on one imaging surface.

The half mirror 7 in the present embodiment also has a wedge shape as in the first embodiment. That is, the plane on the incident side of the light from the sample and the plane on the exit side have a non-parallel relationship. With such a shape,
No interference of laser light occurs inside the half mirror 7, and therefore, no interference fringes occur in the sample image captured by the CCD camera 11.

Since the half mirror 7 has a wedge shape, the optical axis of the illumination optical system is inclined before and after the half mirror 7. The correction glass 6 is a wedge-shaped glass having an angle that corrects the inclination. The correction glass 6 allows light from the sample to pass through the half mirror 7.
The optical axes of the observation optical path on the side incident on the lens and the observation optical path on the side exiting from the correction glass become parallel, and the optical members arranged in the observation optical path like a normal microscope can be arranged on a straight line. it can.

In the first and second embodiments described above,
Although a wedge-shaped half mirror is used as the optical path splitting element, a wedge-shaped half prism may be used. Further, an ND filter for adjusting the amount of light passing through the optical path may be arranged in the illumination optical path or the observation optical path. At this time, it is desirable that the ND filter is arranged such that the filter surface is not perpendicular to the optical axis of the optical path but has a certain inclination. This is because there is a possibility that interference fringes may occur in the sample image even with the ND filter.

In the first and second embodiments, the correction glass 6 may be used also as an ND filter. Specifically, this is achieved by depositing a thin film having a predetermined transmittance on the correction glass 6. At this time, it is better that the thin film deposited on the correction glass 6 is deposited on a surface inclined with respect to the optical axis of the microscope optical path (for example, the surface 6a in FIG. 1) among the two surfaces arranged in the microscope optical path. desirable.

Further, a plurality of correction glasses 6 having different transmittances may be arranged side by side on a slide switching member or the like, and may be selectively arranged in the illumination light path. In the above-described embodiment, the CCD camera is used as the observation system. However, the present invention is not limited to this, and may be an observation lens barrel including a two-dimensional sensor or an eyepiece. Although the present invention has been described with respect to a laser microscope, the present invention can also be applied to an optical device having a microscope function, for example, an apparatus that acquires an enlarged image of a sample and performs dimension measurement, defect inspection, and the like by image processing or the like.

[0023]

As described above, according to the present invention, even when a high-intensity laser having a very narrow half-value width is collectively illuminated by reflection illumination as a light source of a microscope, interference with the image of the sample can be achieved with a simple configuration. An inexpensive microscope system free from stripes can be obtained. Further, according to the present invention, since the light passes through the optical path splitting element and the correction member, the inclination of the optical axis of each light before and after the light can be corrected. Accordingly, it is not necessary to arrange the optical members constituting the observation system or the illumination optical system in accordance with the inclination, and the manufacturing cost can be reduced.

According to the third aspect of the present invention,
The occurrence of interference fringes in the sample image can be suppressed, the amount of illumination light can be changed, and the space in the optical path of the illumination optical system can be used effectively.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a first embodiment of the present invention.

FIG. 2 is a diagram showing a schematic configuration of a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Laser light source 2 ... Microscope main body 3 ... Aperture stop 4 ... Relay lens system 5 ... Field stop 6 ... Correction glass 7 ... Half mirror 8 ... Total reflection mirror 9 Objective lens 10 Image forming lens 11 CCD camera

Claims (3)

[Claims] 1. A light source that emits laser light, an illumination optical system that collectively irradiates a predetermined area on a sample with the laser light from the light source, and an observation that obtains reflected light from the sample and forms an image of the sample. A light path splitting element that separates the reflected light from the sample from the light path of the illumination optical system and guides the reflected light from the sample to the observation system, wherein at least two planes disposed in the microscope light path of the light path splitting element are provided. And a non-parallel relationship. 2. The apparatus according to claim 1, wherein a correction member for correcting an inclination of an optical axis caused by the optical path splitting element is arranged in at least one of the optical paths of the illumination optical system or the observation system. Laser microscope. 3. The correction member is disposed in an illumination optical system and has a plurality of regions having different transmittances from each other, and each of the regions can be selectively inserted into an illumination optical path. The laser microscope according to claim 1, wherein: