Optical: systems and elements – Having significant infrared or ultraviolet property – Including continuously variable magnification or focal length
Reexamination Certificate
2002-10-29
2004-10-05
Robinson, Mark A. (Department: 2872)
Optical: systems and elements
Having significant infrared or ultraviolet property
Including continuously variable magnification or focal length
C359S351000, C359S355000, C359S365000, C359S380000
Reexamination Certificate
active
06801357
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to an ultra-broadband ultraviolet (UV) catadioptric imaging microscope system, and more specifically to an imaging system that comprises a UV catadioptric objective lens group and a wide-range zooming tube lens group.
2. Description of the Related Art
Catadioptric imaging systems for the deep ultraviolet spectral region (about 0.19 to 0.30 micron wavelength) are known. U.S. Pat. No. 5,031,976 to Shafer and U.S. Pat. No. 5,488,229 to Elliott and Shafer disclose two such systems. These systems employ the Schupmann achromatic lens principle and the Offner-type field lens. Axial color and primary lateral color are corrected, but not higher order lateral color. This is the limiting aberration in these systems when a broad spectral range is covered.
The above-noted '976 Shafer patent discloses an optical system based on the Schupmann achromatic lens principle which produces an achromatic virtual image. A reflective relay then creates an achromatic real image from this virtual image. The system, reproduced here as
FIG. 1
, includes an aberration corrector group of lenses
101
for correcting image aberrations and chromatic variation of image aberrations, a focusing lens
103
for receiving light from the group
101
and producing an intermediate image at plane
105
, a field lens
107
of the same material as the other lenses placed at the intermediate image plane
105
, a thick lens
109
with a plane mirror back coating
111
whose power and position are selected to correct the primary longitudinal color of the system in conjunction with the focusing lens
103
, and a spherical mirror
113
located between the intermediate image plane and the thick lens
109
for producing a final image
115
. Most of the focusing power of the system is due to the spherical mirror
113
which has a small central hole near the intermediate image plane
105
to allow light form the intermediate image plane
105
to pass through to the thick lens
109
. The mirror coating
111
on the back of the thick lens
109
also has a small central hole
119
to allow light focused by the spherical mirror
113
to pass through to the final image
115
. While primary longitudinal (axial) color is corrected by the thick lens
109
, the Offner-type field lens
107
placed at the intermediate image
105
has a positive power to correct secondary longitudinal color. Placing the field lens slightly to one side of the intermediate image
105
corrects tertiary longitudinal color. Placing the field lens slightly to one side of the intermediate image
105
corrects tertiary longitudinal color. Thus, axial chromatic aberrations are completely corrected over a broad spectral range. The system also incidentally corrects for narrow band lateral color, but fails to provide complete corrections of residual (secondary and higher order) lateral color over a broad UV spectrum. The above-noted '229 patent to Elliott and Shafer provides a modified version of the optical system of the '976 patent, which has been optimized for use in 0.193 micron wavelength high power excimer laser applications such as ablation of a surface
121
′ as seen in FIG.
2
. This prior art system has an aberration corrector group
101
′, focusing lens
103
′, intermediate focus
105
′, field lens
107
′, thick lens
109
′, mirror surfaces
111
′ and
113
′ with small central opening
117
′ and
119
′ therein and a final focus
115
′ as in the prior '976 patent, but repositions the field lens
107
′ so that the intermediate image or focus
105
′ lies outside of the field lens
107
′ to avoid thermal damage from the high power densities produced by focusing the excimer laser light. Further, both mirror surfaces
111
′ and
113
′ are formed on lens elements
108
′ and
109
′. The combination of all light passing through both lens elements
108
′ and
109
′ provides the same primary longitudinal color correction of the single thick lens
109
in
FIG. 1
, but with a reduction in total glass thickness. Since even fused silica begins to have absorption problems at the very short 0.193 micron wavelength, the thickness reductions is advantageous at this wavelength for high power levels. Though the excimer laser source used for this optical system has a relatively narrow spectral line width, the dispersion of silica near the 0.193 micron wavelength is great enough that some color correction is still needed. Both prior art systems have a numerical aperture of about 0.6.
Longitudinal chromatic aberration (axial color) is an axial shift in the focus position with wavelength. The prior art system seen in
FIG. 1
completely corrects for primary, secondary and tertiary axial color over a broad wavelength band in the near and deep ultraviolet (0.2 micron to 0.4 micron region). Lateral color is a change in magnification or image size with wavelength, and is not related to axial color. The prior art system of
FIG. 1
completely corrects for primary lateral color, but not for residual lateral color. This is the limiting aberration in the system when a broad spectral range is covered.
U.S. patent application Ser. No. 08/681,528, filed Jul. 22, 1996, now U.S. Pat. No. 5,717,518, is for a catadioptric UV imaging system with performance improved over the systems of the above-describe patents. This system employs an achromatized field lens group to correct for secondary and higher order lateral color, which permits designing a high NA, large field, ultra-broadband UV imaging system.
Zooming systems in the visible wavelengths are well-known. They either do not require very high levels of correction of higher-order color effects over a broad spectral region, or do require correction, but accomplish this by using three or more glass types. In the deep UV, there are very few materials that can be used for chromatic aberration correction, making the design of high performance, broadband optics difficult. It is even more difficult to correct for chromatic aberrations for ultra-broadband optics with wide-range zoom.
There remains, therefore, a need for an ultra-broadband UV microscope imaging system with wide-range zoom capability.
SUMMARY OF THE INVENTION
The present invention has an object to provide a catadioptric imaging system which corrects for image aberrations, chromatic variation of image aberrations, longitudinal (axial) color and lateral color, including residual (secondary and higher order) lateral color correction over an ultra-broad spectral range in the near and deep UV spectral band (0.2 to 0.4 micron).
Another object is to provide an UV imaging system, useful as a microscope or as micro-lithography optics, with a large numerical aperture of 0.9 and with a field of view of at least one millimeter. The system is preferably telecentric.
The invention is a high performance, high numerical aperture, ultra-broad spectral region catadioptric optical system with zooming capability, comprising an all-refractive zooming tube lens section with one collimated conjugate, constructed so that during zooming its higher-order chromatic aberrations (particularly higher-order lateral color) do not change; and a non-zooming high numerical aperture catadioptric objective section which compensates for the uncorrected (but stationary during zoom) higher-order chromatic aberration residuals of the zooming tube lens section.
These and other objects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description and accompanying drawings.
REFERENCES:
patent: 4971428 (1990-11-01), Moskovich
patent: 5031976 (1991-07-01), Shafer
patent: 5488229 (1996-01-01), Elliott et al.
Chuang Yung-Ho
Shafer David R.
Tsai Bin-Ming B.
Fineman Lee
KLA - Tencor Corporation
Robinson Mark A.
Smyrski & Livesay, LLP
LandOfFree
Ultra-broadband UV microscope imaging system with wide range... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Ultra-broadband UV microscope imaging system with wide range..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ultra-broadband UV microscope imaging system with wide range... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3297423