JP2000131618A - Ultraviolet image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a UV image forming device which allows the observation of a very small sample with good resolving power. SOLUTION: This UV image forming device has illumination optical systems 1 to 5 which illuminate the sample with illumination light of a wavelength of an extreme UV area and an objective optical system 7 for forming the image of the sample in accordance with the illumination light. When the wavelength width of the illumination light is defined as Δλ, Δλ<=70 pm is satisfied. When the numerical aperture on the sample side of the objective optical system is defined as NA, 0.7<=NA is preferably satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultraviolet image forming apparatus for obtaining an observation image of a sample at a wavelength in the extreme ultraviolet region.

[0002]

2. Description of the Related Art In an image forming apparatus such as a microscope, the resolution δ is represented by δ = 0.61λ / NA, where λ is the observation wavelength and NA is the numerical aperture on the sample side. Therefore,
In order to improve the resolving power, it is conceivable to shorten the observation wavelength λ and increase the numerical aperture.

[0003]

If the observation wavelength λ is set to a wavelength in the extreme ultraviolet region (λ <300 nm) in order to improve the resolution, the types of glass materials that can transmit light in this wavelength region are limited. It becomes difficult to correct chromatic aberration.
As a result, it is difficult to improve the contrast of the image, and it becomes difficult to observe a fine sample.

[0004] The present invention has been made in view of the above problems, and has as its object to provide an ultraviolet image forming apparatus capable of observing a fine sample with good resolution.

[0005]

In order to solve the above-mentioned problems, the invention according to claim 1 provides an illumination optical system for illuminating a sample with illumination light having a wavelength in an extreme ultraviolet range, and the illumination optical system based on the illumination light. An objective optical system for forming an image of the sample, wherein Δλ ≦ 70 pm (picometer) when the wavelength width of the illumination light is Δλ.

According to a second aspect of the present invention, when the numerical aperture on the sample side of the objective optical system is NA, 0.7 ≦ NA (2) is satisfied.

According to a third aspect of the present invention, the illumination optical system includes a laser light source for supplying the illumination light.

According to a fourth aspect of the present invention, the illumination optical system supplies the illumination light to the sample via the objective optical system.

According to a fifth aspect of the present invention, the objective optical system forms an enlarged image of the sample.

Further, the invention according to claim 6 is characterized by further comprising a photoelectric conversion unit for picking up an image of the sample.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram illustrating a configuration in which an ultraviolet image forming apparatus according to an embodiment of the present invention is applied to a laser microscope. In FIG. 1, a laser light source 1
Is a laser light in an extreme ultraviolet region, for example, a center wavelength λ = 266.
and a laser beam having a wavelength width of △ λ. The laser light is expanded to a predetermined light flux diameter via a beam expander including lenses 2 and 3, passes through an aperture stop AS, and is condensed by a lens 4. Next, the laser light that has passed through the field stop FS passes through the lens 5, is reflected by the half mirror 6, and then enters the objective lens system 7. Reference numeral 7a denotes a body-attached surface of the objective lens system. Then, the laser beam from the objective lens system 7 illuminates the illumination field having a predetermined area on the sample S by epi-illumination. Here, the field stop FS and the sample S are arranged in a conjugate relationship with respect to an optical system in which the lens 5 and the objective lens system 7 are combined. The lenses 4 and 5 are provided so as to form an image of the aperture stop AS in the pupil of the objective lens system 7, and the sample S is subjected to Koehler illumination.

The light reflected by the illumination field on the sample S passes through the objective lens system 7 again, then passes through the half mirror 6, and forms an enlarged image I of the sample via the imaging lens 8.
The CCD 9 captures an image formed by light in the extreme ultraviolet region, and the monitor 1
Display on 0. Further, instead of the CCD 9, a photoelectric converter including an image pickup tube can be used.

In FIG. 1, the lenses 2 to 5, 7, and 8 are shown as a single lens, but the number of these lenses is not limited to one but may be a plurality. More preferably, the lenses 2 to 5, 8 are desirably made of synthetic quartz, and desirably, synthetic quartz is used as the material of the substrate of the half mirror 6.

FIG. 2 is a diagram showing a lens configuration of the objective lens system 7. The objective lens system 7 includes, in order from the sample S side, a negative meniscus lens L1 having a concave surface facing the sample S side and two positive meniscus lenses L2, L having a concave surface facing the sample S side.
3, a biconvex lens L4, two positive meniscus lenses L5 and L6 with the convex surface facing the sample S side, and a biconcave lens L7.
And a positive meniscus lens L8 having a convex surface facing the sample S side. Each of the lens elements L1 to L8 is made of synthetic quartz, and has no joint surface. With this configuration, it is possible to achieve good transmittance in the extreme ultraviolet region, and to obtain a bright sample image.

Table 1 below shows the objective lens system 7 shown in FIG.
Raise the value of the specifications of. In Table 1, fo is a wavelength 266.
The focal length of the objective lens system 7 for the extreme ultraviolet light of nm (not including an imaging lens described later), NA is the numerical aperture on the object side, β is the magnification, and d0 is the distance from the sample S to the lens surface closest to the sample. Each is represented. The numbers at the left end represent the order along the order of incidence of light rays, r is the radius of curvature of the lens surface, d is the distance between the lens surfaces, and n is the wavelength 266.0n.
m represents the refractive index with respect to m.

[0016]

[Table 1] Further, since the objective lens system 7 has an infinity design for forming an image of an object at infinity, it is used in combination with, for example, an imaging lens shown in FIG. Table 2 shows the specifications of the imaging lens. In Table 2, fi is the focal length of the imaging lens, the leftmost number is the order along the order of incidence of light rays, r is the radius of curvature of the lens surface, d is the distance between the lens surfaces, and n is the wavelength 266.0n.
m represents the refractive index with respect to m.

[0017]

[Table 2] FIG. 4 or FIG. 5 is a diagram showing the result of calculating the relationship between the image intensity of the object point on the optical axis and the defocus position. The vertical axis represents the relative intensity normalized so that the maximum value becomes 1, and the horizontal axis represents the defocus position. FIG.
The curve of the relative intensity within the wavelength width (lower wavelength 265.98 nm, upper wavelength 266.02 nm) when the center wavelength λ = 266.0 nm and the wavelength width Δλ = 40 pm is shown. FIG. 5 shows the case where the center wavelength λ = 266.0 nm and the wavelength width Δλ = 200 pm (the lower end wavelength 26
(5.8 nm, top wavelength 266.2 nm).

In FIG. 4 or FIG. 5, the integrated amount from the lower end wavelength to the upper end wavelength indicates the image intensity by the light having the wavelength width. If the relative intensity exceeds 0.8 (80%), it can be considered that there is no aberration.
The value exceeds 0.8 in the entire range of the wavelength width over 40 pm, and it can be seen that there is substantially no aberration within the range of the wavelength width. On the other hand, in FIG. 5 in which the wavelength width is Δλ = 200 pm, the image intensity by the light having the central wavelength exceeds 0.8 at the position where the defocus is zero. However, at this position, an image formed by light having a wavelength longer than the center wavelength (upper wavelength side) or a wavelength shorter than the center wavelength (lower wavelength side) becomes a defocused image, and due to the influence of these defocus images, Since the image intensity at the position is lower than 0.8, it cannot be considered that there is no aberration. 4 and 5 show that when the center wavelength is 266 nm and the sample-side numerical aperture NA is NA = 0.9, the wavelength width of the illumination light should be narrower than 40 pm.

Here, when the numerical aperture on the sample side is reduced under the condition that the resolution is kept within the range of the object of the present invention,
The condition of the wavelength width Δλ can be relaxed by the square of the numerical aperture on the sample side. Therefore, it is desirable that the wavelength width Δλ supplied by the illumination optical system satisfies Δλ ≦ 70 pm (1).

When the numerical aperture is increased to further improve the resolving power, the wavelength width Δλ supplied by the illumination optical system is desirably 40 pm or less.

Furthermore, when the wavelength supplied by the illumination optical system is shortened to improve the resolution, the width of the depth of focus becomes narrow in proportion to the wavelength, and the wavelength of the wavelength causing the same refractive index difference is also reduced. Since the difference is narrowed, the allowable wavelength width is narrowed. Therefore, in such a case, the wavelength width supplied by the illumination optical system is desirably 16 pm or less.

In the present invention, it is desirable that the numerical aperture NA on the sample side of the objective optical system for forming an image of the sample satisfies 0.7 ≦ NA (2).

When the value is below the lower limit of the condition (2), it becomes impossible to achieve a desired resolving power, and it becomes difficult to observe a fine sample as an object of the present invention.

In the present invention, the illumination optical system preferably includes a laser light source. With this configuration, it is possible to illuminate under an illuminance that allows real-time observation of the entire illumination field having a predetermined area,
In addition, there is an advantage that the wavelength width of the illumination light supplied by the illumination optical system can be easily set within the above range.

Note that the objective optical system in the present invention includes a system in which aberration is corrected for at least one wavelength in a wavelength range of visible light (about 400 to 700 nm) for optical adjustment, for example. At this time, the objective optical system is
It is desirable that the aberration be corrected for a wavelength width satisfying the above condition at least in a wavelength region of an extreme ultraviolet region.

As the light source of the present invention, for example, 24
KrF excimer laser light source for supplying 8 nm laser light, ArF excimer laser light source for supplying 193 nm laser light, F ₂ excimer laser light source for supplying 157 nm laser light, for example, harmonic generation for supplying 266 nm or 213 nm laser light A laser light source that supplies laser light having a wavelength in the extreme ultraviolet region, such as a laser light source equipped with a device, can be used.

[0027]

As described above, according to the ultraviolet image forming apparatus of the present invention, a region having a predetermined area on a fine sample can be observed well at a time.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration when an ultraviolet image forming apparatus according to an embodiment of the present invention is applied to a laser microscope.

FIG. 2 is a diagram showing a configuration of an objective lens system.

FIG. 3 is a diagram illustrating a configuration of an imaging lens.

FIG. 4 is a diagram showing a relationship between an image intensity of an objective lens system and a defocus position.

FIG. 5 is another diagram showing the relationship between the image intensity of the objective lens system and the defocus position.

[Explanation of symbols]

 Reference Signs List 1 laser light source 2-5 lens AS aperture stop FS field stop 6 half mirror 7 objective lens system (objective optical system) 7a barrel surface of objective lens system 8 imaging lens S sample I sample image 9 CCD 10 monitor

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H052 AB21 AB24 AC04 AC12 AF14 AF21 2H087 KA09 LA24 NA04 PA08 PA17 PB08 QA03 QA07 QA12 QA21 QA25 QA32 QA42 QA45

Claims (6)

[Claims] An illumination optical system for illuminating a sample with illumination light having a wavelength in an extreme ultraviolet region, and an objective optical system for forming an image of the sample based on the illumination light, wherein the wavelength width of the illumination light is △ λ
Λ <70 pm (1), wherein the ultraviolet image forming apparatus satisfies (1). 2. The ultraviolet image forming apparatus according to claim 1, wherein, when a numerical aperture on the sample side of the objective optical system is NA, 0.7 ≦ NA (2) is satisfied. 3. The ultraviolet image forming apparatus according to claim 1, wherein the illumination optical system includes a laser light source that supplies the illumination light. 4. The ultraviolet image forming apparatus according to claim 1, wherein the illumination optical system supplies the illumination light to the sample via the objective optical system. 5. An ultraviolet image forming apparatus according to claim 1, wherein said objective optical system forms an enlarged image of said sample. 6. The apparatus according to claim 1, further comprising a photoelectric conversion unit for picking up an image of the sample.
6. The ultraviolet image forming apparatus according to 4 or 5.