JP2963995B1 - All-in-focus reflective optical microscope - Google Patents

Abstract

Abstract: PROBLEM TO BE SOLVED: To provide an all-in-one reflection optical microscope in which an ultra-thin film sample on a substrate is focused on the entire surface when observing the sample using a reflection microscope. SOLUTION: P-polarized illumination light 2 is made incident on a substrate 3 on which a thin film sample 4 is placed at a Brewster angle θ ₁ , and reflected light 5 is put not at the center but at the end of an imaging lens 6. By using a non-axial optical system, the inclination angle between the axis perpendicular to the image plane 8 and the optical axis 9 of the microscope is reduced, and the photoelectric surface 7 of the CCD camera is arranged so as to match the image plane 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection-type optical microscope apparatus for observing the structure of an ultra-thin film or a material surface, and more particularly, to a method for removing optical noise. The present invention relates to a white illumination reflection type microscope and an angular dispersion compensator for the same.

[0002]

2. Description of the Related Art Conventionally, in order to observe an ultra-thin sample on a substrate, P-polarized light (polarized light in the plane of incidence) is applied to the ultra-thin sample on the substrate by a Brewster on the substrate. Brewster's angle microscope (BA), which is incident at an angle and observes reflected light with the naked eye or a CCD camera using an imaging optical system.
M) has been used.

At Brewster's angle, the reflection of P-polarized light from the substrate disappears (actually, the reflectance is only about one millionth). Therefore, only reflection from a sample having a refractive index different from that of the substrate is selected. Is observed. Even for a thin film having a thickness of nanometers or less, it is possible to observe the thin film structure with high contrast by strictly setting the Brewster angle. It is widely used for observing single-layer films (Langmuir films) of organic molecules on the water surface, Langmuir-Blodgett films, and various ultrathin films.

[0004] As a more generalized microscope of BAM,
Ellipsometry microscopes have been developed. It is a technology that has historically preceded BAM and allows quantitative measurement of film thickness and refractive index by making use of the principle of ellipsometry, but has not been widely used due to the complicated structure of the device.

In the conventional BAM and ellipsometry microscopes, as shown in FIG. 4, an object to be observed on a substrate (hereinafter, referred to as a “substrate” in this specification) such as glass or water. Laser 3 for sample 34
The P-polarized parallel illumination light 32 from 1 is incident obliquely at a Brewster angle θ, and a normal microscope equipped with an imaging lens 33 that forms an image of a symmetric reflected light 35 of the illumination light 32 is used. Observe. This Brewster angle θ
Is 53 degrees for water and 57 degrees for glass.

For this reason, the image plane 36 of the thin film sample 34 is formed not at right angles to the optical axis 35 but at an angle. Except for the vicinity of the intersection with the optical axis, focusing cannot be performed entirely. Therefore, the quality of the BAM image is
There is a problem that distortion is formed, which is significantly inferior to that of a normal optical microscope, and that the resolution is non-uniform in an image.

In addition, in order to perform illumination at the Brewster angle θ, incident light must be sufficiently collimated parallel light. Therefore, in the conventional BAM, laser light is used for illumination without exception. However, since laser light has extremely high brightness and coherence, scattering from optical components and dust often mixes into the field of view and generates noise such as interference fringes that cannot be completely removed.

[0008] Even if this noise is completely removed, a false image is generated in principle by interference at a non-focus state, and thus the visibility of the image is deteriorated.

Another problem is that spectral information such as light absorption characteristics and wavelength dispersion of a sample cannot be obtained because a monochromatic laser beam is used.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to solve such a conventional problem. When observing an image of an ultra-thin film on a substrate with a reflection microscope, the present invention aims to solve the problem. An object of the present invention is to provide an all-in-one reflection optical microscope so that the entire surface is in focus.

[0011]

Further, in the above-mentioned all-in-one reflection optical microscope,
To provide an all-in-one reflection optical microscope using white illumination that applies white light to enable focusing on the entire surface and has a synergistic function of removing interference fringes and other scattered light. It is.

[0013]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems by causing P-polarized illumination light to enter a substrate on which a sample is placed at a Brewster angle, and reflecting the reflected light. An all-in-one-reflection optical microscope characterized in that the tilt angle between the axis perpendicular to the image plane and the optical axis of the microscope is reduced by using a non-axial optical system by inserting it into the end of the imaging lens instead of the center. provide.

The photoelectric surface of the CCD camera may be arranged so as to match the image plane.

By making the illumination of the microscope inverted, the Brewster angle may be reduced by inputting the illumination light from the side of the substrate having a higher refractive index than air, so that the microscope is focused.

A laser beam may be used as the illumination light.

The illumination light may be configured to remove interference fringes and other optical noises by using collimated white light. In this case, a configuration may be employed in which white light is allowed to pass through the dispersing prism to correct chromatic dispersion.

[0018]

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described based on embodiments with reference to the drawings. FIG. 1 shows a first embodiment of an all-in-one reflection optical microscope according to the present invention. FIG.
In, the total focal reflection optical microscope, illumination light 2 is parallel light P deflected from the laser light source 1, at Brewster angle theta ₁ from the air to the substrate 3, are incident on the thin film sample 4 on the substrate 3, The reflected light 5 is transmitted through an imaging lens 6 having a large numerical aperture (NA) to a photoelectric surface 7 (FIG. 1) of a CCD camera.
Is indicated by a dotted line. ) To form an image plane 8 (indicated by a solid line in the figure).

When the reflected light 5 is imaged, the reflected light 5
Is arranged so that the imaging lens 6 passes through the end of the imaging lens 6 instead of the center thereof.
Are not perpendicular to the optical axis 9 of the imaging lens 6 but are tilted and shifted so as to coincide with the image plane 8.

The operation of the all-in-one reflection optical microscope according to the first embodiment will be described. The thin film sample 4 on the substrate 3 is irradiated with illumination light 2 from the laser 1 at a Brewster angle θ ₁ . Then, the P-polarized light applied to the surface of the substrate 3 is erased, and only the reflected light from the thin film sample 4 forms an image on the optical axis 9 of the imaging lens 6 and on the photoelectric surface 7 of the CCD camera. An image plane 8 is formed.

In this case, since the reflected light 5 passes not through the center of the imaging lens 6 but through the end, the displacement between the axis perpendicular to the image plane at the center of the image plane 8 and the optical axis of the imaging lens 6 is determined by the conventional technique. And the image plane is formed on the photocathode 7 of the CCD camera, so that distortion components are reduced and a good image is formed.

FIG. 2 shows a second embodiment of the all-in-one reflection optical microscope according to the present invention. The second embodiment is an inverted microscope in which the P-polarized illumination light 1 from the laser 10 is used.
1 is incident from the substrate 13 side on which the thin film sample 12 is placed at a Brewster angle θ ₂ from the substrate 13 to the air, and the reflected light 14 from the thin film sample 12 is transmitted through an imaging lens 15 to C
An image is formed on the photocathode 16 of the CD camera.

In this arrangement, the image plane (shown by a solid line in FIG. 2) 17 and the CC placed perpendicular to the reflected light 14
The difference δ between the tilt angle of the D-camera photoelectric surface (indicated by a dotted line in FIG. 2) 16 does not become so large, and the distortion becomes small.

FIG. 3 shows a third embodiment of the present invention, and is a white illumination reflection type microscope. In the third embodiment illustrated in FIG. 3, a white light source 18 is provided instead of a laser, and white light is used as the illumination light 20. P from white light source 18
The optical fiber 19 is used to prevent the polarized white light from diffusing.
Through the optical fiber 19, the collimating lens 21 converts the illumination light 20 into substantially parallel light.

Then, in order to correct the wavelength dispersion of the illumination light 20, the light passes through a dispersion prism 22 or a grating.
The combination lenses 23 and 24 irradiate the thin film sample 26 on the substrate 25 with the P-polarized illumination light 20 at a Brewster angle from air to the substrate 25 corresponding to each wavelength. The reflected light 27 from the thin film sample 26 is converted into an imaging lens 28
To image the image plane 30 on the photoelectric surface 29 of the CCD camera.

In the third embodiment, since white light is used as the illumination light 20 and substantially collimated by the collimating lens 21, interference fringes which are a problem when using laser light can be removed. By correcting the wavelength dispersion by the prism 22 or the grating, the light of all the wavelengths included in the white light can be converted into the substrate 2 at the respective Brewster angles.
5 can be incident.

Although not shown in FIG. 3, the reflected light 2
By using the non-axial optical system through the end rather than the center of the imaging lens in the same manner as in the first embodiment, in addition to the effects of the third embodiment, in addition to the inclination between the axis perpendicular to the image plane and the optical axis of the microscope, It is possible to realize an all-in-one reflection optical microscope using white illumination, which has a synergistic function and an effect of reducing the angle and enabling focusing on the entire surface.

[0029]

Since the present invention is configured as described above, it has the following effects.

By forming the light obliquely reflected from the sample not through the center of the imaging lens but through the end,
The reflection angle of the imaging system can be made smaller than the Brewster angle.

Furthermore, by shifting the photoelectric surface of the CCD camera from the optical axis normal to the actual image plane direction, it is possible to focus almost on the entire surface.

Further, since the refractive index of the substrate is usually higher than that of air, the Brewster angle becomes smaller if the illumination light is passed in the reverse direction from the substrate to the air side. Distortion can be reduced.

Further, by using the collimated white light for illumination, interference fringes appearing in the case of laser light can be removed.

Further, since white light in which light of various wavelengths is collected is used, reflection spectrum information of the sample can be obtained.

Here, the wavelength dispersion, which is a problem in the case of white light, is corrected by a dispersion prism or a grating, so that light of all wavelengths can be made incident at respective Brewster angles.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention, and is a diagram of a full-field focal Brewster angle microscope using a non-axis optical system and a tilted CCD.

FIG. 2 is a view showing a second embodiment of the present invention, and is a view of an inverted Brewster angle microscope.

FIG. 3 is a diagram showing a third embodiment of the present invention, and is a diagram of an achromatic Brewster angle microscope using angular dispersion-compensated white illumination.

FIG. 4 is a view showing a conventional Brewster angle microscope.

[Explanation of symbols]

 1, 10 Laser 2, 11, 20 Illumination light 3, 13, 25 Substrate 4, 12, 26 Thin film sample 5, 14, 27 Reflected light 6, 15, 28 Imaging lens 7, 16, 29 Observation surface (CCD photoelectric surface 8, 17, 30 Image plane 9 Optical axis 18 White light source 19 Optical fiber 21 Collimating lens 22 Dispersion prism 23, 24 Lens 25

Continuation of the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) G02B 19/00-21/00 G02B 21/06-21/36

Claims (6)

(57) [Claims] 1. An off-axis optical system in which P-polarized illumination light is made incident on a substrate on which a sample is placed at a Brewster angle, and the reflected light is introduced into the end of the imaging lens instead of the center. Wherein the tilt angle between the axis perpendicular to the image plane and the optical axis of the microscope is reduced. 2. The all-focus reflective optical microscope according to claim 1, wherein a photoelectric surface of the CCD camera is arranged so as to match the image plane. 3. An all-in-focus system characterized in that the microscope illumination is inverted so that the Brewster angle is reduced by focusing illumination light from the side of the substrate having a higher refractive index than air, thereby achieving focusing. Reflective optical microscope. 4. The all-in-one reflection optical microscope according to claim 1, wherein a laser beam is used as the illumination light. 5. The all-focal reflection type according to claim 1, wherein a collimated white light is used as said illumination light to remove interference fringes and other optical noises. Light microscope. 6. The all-in-focus reflective optical microscope according to claim 5, wherein the white light is passed through a dispersion prism to correct chromatic dispersion.