Optical: systems and elements – Lens – Microscope objective
Reexamination Certificate
2002-11-18
2004-11-23
Schwartz, Jordan M. (Department: 2873)
Optical: systems and elements
Lens
Microscope objective
C359S350000
Reexamination Certificate
active
06822805
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to objective lenses, and in particular relates to an objective lens used in a deep ultraviolet-wavelength region around a wavelength of 250 nm for a high-NA (numerical aperture), high-power, and infinity-correction type microscope.
2. Description of the Related Art
As an objective lens employing a deep ultraviolet region around a wavelength of 250 nm, the following four major types classified thereinto are conventionally known.
A first type objective lens is formed of only a plurality of lenses made from the same medium (silica, mostly) as disclosed in Japanese Unexamined Patent Application Publication No. 6-242381 and Japanese Unexamined Patent Application Publication No. 10-104510, and it cannot correct chromatic aberrations in theory.
A second type objective lens is formed of lenses made from different media (silica and calcium fluorite, mostly) cemented together with an adhesive as disclosed in Japanese Unexamined Patent Application Publication No. 5-72482, Japanese Unexamined Patent Application Publication No. 9-243923, and Japanese Unexamined Patent Application Publication No. 11-249025, and it can correct chromatic aberrations.
Also, a third type objective lens, as disclosed in Japanese Unexamined Patent Application Publication No. 11-167067, uses a lens made from silica and a lens made from calcium fluorite so as to correct chromatic aberrations; however it is structured by not cementing both the lenses together with an adhesive.
Further, a fourth type objective lens, as disclosed in Japanese Unexamined Patent Application Publication No. 2001-42224, is structured by cementing a lens made from silica and a lens made from calcium fluorite together with an adhesive so as to correct chromatic aberrations. Furthermore, the second lens group from the image side is designed to be biconcave, in which its curvature on the image side is apparently smaller than that on the object side, enabling active auto-focusing utilizing a near-infrared wavelength to be performed by moving the condensing position of DUV (deep ultra-violet rays) closer to that of NIR (near-infrared rays).
However, these conventional four types of objective lenses have the following problems.
First, the first type of objective lens cannot correct chromatic aberrations in theory, so that it has a problem that when a light source having a wavelength width (a lamp and an excimer laser being not narrowed in band, etc.) is used, the beam condensing function is extremely reduced by chromatic aberrations so that predetermined resolution defined by a wavelength and numerical aperture cannot be obtained.
The second type of objective lens can correct chromatic aberrations so that it does not have such a problem as that of the first type; however, it has another problem that there are few types of adhesives that are able to suitably transmit deep ultra-violet rays and moreover there are only types with a small bonding strength and present difficulties for being used efficiently. In an objective lens using such adhesive, although there is no problem when light rays of a lamp or the like are incident therein, if light rays with high energy such as laser rays enter the lens, the adhesive is degraded the irradiation with the deep ultra-violet rays, so that reduction in the transmission efficiency of the objective lens is a problem.
Furthermore, the third type of objective lens solves the problems of the two types mentioned above. However, Japanese Unexamined Patent Application Publication No. 11-16067 basically relates to an objective lens for laser repair using deep ultra-violet rays, so that there is only a lens with a numerical aperture of about 0.4 disclosed in its embodiment. Thereby, it is impossible to obtain high resolution by reducing the wavelength. That is, the resolution of a microscope is fundamentally defined by a wavelength and a numerical aperture of the objective lens; the center wavelength of visible light employed in an ordinary microscope is about 550 nm and the maximum numerical aperture of a dry-system objective lens is about 0.9. Therefore, if the wavelength used is around 250 nm, the resolution is doubled because the wavelength is halved; however, it is the case that the numerical aperture is identical first-and-foremost. Even if the wavelength used is around 250, when the numerical aperture is about 0.4, the wavelength is about half while the numerical aperture is also half, so that the resolution is counteracted and is no different from a conventional microscope.
Moreover, the fourth type of objective lens is capable of correcting chromatic aberration and of auto-focusing (AF) by moving the image position of a deep ultra-violet region closer to that of an infrared region up to a point; however, in the same way as in the second type of objective lens, an adhesive is degraded by deep ultra-violet rays so as to have a problem of the reduction in the transmission factor of the objective lens.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a high-NA deep ultra-violet objective lens by correcting chromatic aberration without using a cemented lens and by exponentially improving the resolution so as to correspond to miniaturization in connection with the progress toward high integration of semiconductors and high-capacity of optical recording media.
It is another object of the present invention to provide a high-NA deep ultra-violet objective lens capable of focusing in a moment of time by enabling the AF.
In order to achieve the above-mentioned objects, in an objective lens according to the present invention having an NA of at least 0.7 and being constituted by combining a plurality of single lenses as a whole, the objective lens comprises a first lens group having a positive meniscus lens with a convex surface facing an image side and a negative biconcave lens, which are arranged in the sequential order from the image side, so as to have negative refractive power as a whole; a second lens group having at least one couple of a lens pair so as to have positive refractive power as a whole by arranging a positive lens and a negative lens, which are made of a medium different from each other, to have an air gap therebetween; a third lens group having four couples of lens pairs so as to have positive refractive power as a whole by arranging a positive lens and a negative lens, which are made of a medium different from each other, to have an air gap therebetween; a fourth lens group having two couples of lens pairs arranged by a positive lens and a negative lens, which are made of a medium different from each other, to have an air gap therebetween; a fifth lens group having one couple of a lens pair so as to have positive refractive power as a whole by arranging a positive lens and a negative lens including a negative meniscus lens with a concave surface facing an object side, which are made of a medium different from each other, to have an air gap therebetween; and a sixth lens group having at least one positive lens and a positive meniscus lens with a concave surface facing the object side so as to have positive refractive power as a whole, wherein the objective lens satisfies the following conditional expressions (1) and (2):
d/L
<0.025 (1)
0.58
<Rp/Rn
<1.65 (2),
where L(mm) is the overall length of the objective lens; d(mm) is the air gap of the lens pair; Rp is the radius of curvature of each of positive refractive power surfaces opposing each other with the air gap therebetween; and Rn is the radius of curvature of a negative refractive power surface.
In addition, L in the conditional expression (1) is defined as the overall length of the objective lens; alternatively, if the parfocal distance of the objective lens is substantially the same as the overall length of the objective lens, the parfocal distance of the objective lens may be used as L. Also, the overall length of the objective lens is the distance from the first lens surface to the ultimate
Olympus Corporation
Pillsbury & Winthrop LLP
Schwartz Jordan M.
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