Optical: systems and elements – Lens – With field curvature shaping
Reexamination Certificate
2001-10-01
2004-01-20
Schwartz, Jordan M. (Department: 2873)
Optical: systems and elements
Lens
With field curvature shaping
C359S656000
Reexamination Certificate
active
06680803
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a partial objective in an illuminating system of a microlithographic projection exposure apparatus; to a REMA objective that has a partial objective of this kind; and to a microlithographic projection exposure apparatus with a partial objective of this kind.
The partial objective comprises a first and a second lens group that are arranged between a aperture plane and an image plane, an image field to be illuminated being situated in the image plane. The components are arranged centered about an optical axis. Pencils of rays, each with a respective chief ray, enter the partial objective through the aperture plane; the chief rays intersect the optical axis in the region of the aperture plane. The axial distance of the intersection points of the chief rays with the optical axis is here at most 10% of the diameter of the aperture diaphragm. The axial displacement of the intersection points depends on the aberrations of pupil imaging introduced by the portions of the system arranged before the partial objective. Pupil imaging denotes here imaging between pupil planes. The outermost chief ray, which passes through the aperture plane at the maximum angle to the optical axis, strikes the edge of the image field in the image plane. The ray bundle whose chief ray runs along the optical axis defines a central ray bundle. The first lens group then comprises those lenses in which the outermost chief ray has, according to absolute value, smaller ray heights at the lens surfaces than the marginal ray beam of the central ray bundle. The second lens group comprises those lenses in which the outermost chief ray has, according to absolute value, greater ray heights at the lens surfaces than the marginal ray of the central ray bundle. A lens of the second lens group has an aspheric lens surface here.
2. Technical Field
A microlithographic projection exposure device is known from DD 292 727, and has a partial objective of the category concerned between a fly's eye condensor and a structure-carrying mask. A projection objective follows the structure-carrying mask in the beam path, and images the structure-carrying mask, diffraction limited, onto a photosensitive substrate. The first lens group of the partial objective corresponds to the collimator in DD 292 727. The second lens group corresponds to a field lens consisting of only one lens. The field lens has an aspheric correction surface here, in order to affect the angular distribution of the chief rays in the image plane of the partial objective such that the image plane of the projection objective is illuminated nearly telecentrically. The aberrations of pupil imaging between the aperture plane of the partial objective and the aperture plane of the projection objective are reduced by the aspheric correcting surface. The possibilities of correction of pupil imaging with the arrangement of DD 292 727 are limited, since the field lens consists of only a single lens with positive refractive power. Moreover, the embodiment has only an image-side numerical aperture of 0.04 and a maximum field height of 71.75 mm.
So-called REMA objectives have become known from German Patent Document DE 195 48 805 (U.S. Pat. No. 5,982,558) and German Patent Document DE 196 53 983 A1 (U.S. Ser. No. 09/125,621) of the same assignee. REMA objectives are used in microlithographic projection exposure apparatuses directly before the structure-carrying mask (the so-called reticle). REMA objectives image masking devices, so-called REMA (Reticle Masking) blades, with small blur onto the reticle. The REMA blades are usually embodied by adjustable mechanical blades, by means of which the size of the object field of the following REMA objective can be altered. While a REMA objective with purely spherical lenses is shown in the embodiment of U.S. Pat. No. 5,982,558, the use of aspheric lenses for reducing the number of lenses within a REMA objective is proposed in U.S. Ser. No. 09/125,621. The field lens portion of a REMA objective then matches the angular distribution of the chief rays of the REMA objective to the angular distribution of the chief rays of a following projection objective, in order to attain a continuous course of rays between the REMA objective and the projection objective.
European Patent EP 0 811 865 A2 shows a partial objective, which is arranged between a aperture plane and an image plane. Here not the reticle, but a masking device, is arranged in the image plane of the partial objective, and is imaged onto the reticle by a following objective. Therefore, the partial objective has no direct influence on the distribution of the chief ray angle at the interface between the illuminating device and a following projection objective.
Microstructured components with structure sizes below 0.2 &mgr;m can be produced with modem projection objectives. In order to attain these high resolutions, the projection objectives are operated at wavelengths of 248 nm, in particular 193 nm or even 157 nm, and have image-side numerical apertures of greater than 0.65. At the same time, the image field diameter is for the most part greater than 20 mm. The requirements on the optical design for such a projection objective are, therefore, considerable. Besides the field imaging of the reticle onto the photosensitive substrate, the so-called wafer, the pupil imaging is also to be corrected. Thus the forward objective portion, arranged between the object plane and the aperture plane, of a projection objective influences the imaging of the entrance pupil onto the aperture plane, while the rearward objective portion, arranged between aperture plane and image plane, influences the imaging of the aperture plane onto the exit pupil. The aberrations of pupil imaging of the projection objective then become apparent in the distribution of the chief ray angles in the object plane of the projection objective.
BRIEF SUMMARY OF THE INVENTION
The object of the invention is to provide partial objectives of the category concerned, which permit influencing the distribution of the chief ray angles in the image plane of the partial objective over wide ranges. In particular, aberrations of pupil imaging that are introduced by the forward objective portion of a following projection objective are to be compensated.
This object is attained with a partial objective having an optical axis for illumination of an image field, in particular in an illuminating device of a microlithographic projection exposure apparatus. The partial objective is arranged between a aperture plane and an image plane. Pencils of rays, each with a chief ray, start from the aperture plane, and the intersection points of the chief rays with the optical axis are situated apart by at most 10% of the diameter of the aperture plane. The partial objective comprises a first lens group and a second lens group, wherein within the first lens group, an outermost chief ray that passes through the aperture plane at a maximum angle to the optical axis, has according to absolute value smaller ray heights at the lens surfaces than an marginal ray that bounds the pencils of rays whose chief ray runs along the optical axis. Within the second lens group, the outermost chief ray has according to absolute value greater ray heights at the lens surfaces than the marginal rays, and wherein the second lens group has a lens with a first aspheric lens surface, wherein the second lens group has at least a first lens with negative refractive power and at least a second lens with positive refractive power. The maximum field height Y
im
max
within an image field is at least 40 mm, and the image-side numerical aperture is at least 0.15. The chief rays within the image field have field height Y
im
and chief ray angles PF between the surface normals of the image plane (IM) and the respective chief rays. The distribution of the chief ray angles PF over the field heights Y
im
is given by a pupil function PF(Y
im
), which consists of a linear and a non-linear contribution PF(Y
im
)&equals
Epple Alexander
Müller Christa
Schultz Jörg
Sohmer Alexander
Wangler Johannes
Carl-Zeiss SMT AG
Schwartz Jordan M.
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