Optical: systems and elements – Lens – With field curvature shaping
Reexamination Certificate
2001-10-01
2004-01-27
Spector, David N. (Department: 2873)
Optical: systems and elements
Lens
With field curvature shaping
C359S619000, C359S627000, C355S067000, C353S052000
Reexamination Certificate
active
06683728
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
REFERENCE TO A MICROFICHE APPENDIX
Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an illumination system, in particular for a microlithographic projection exposure apparatus, having a rod integrator, having an entry surface, and an exit surface; an objective for imaging an object field, the objective being arranged after the rod integrator in the direction of light propagation.
2. Technical Field
An exposure system of this kind is known from U.S. Pat. No. 6,285,443.
The illumination system is constructed along an optical axis and comprises a rod integrator, followed in the direction of light propagation by an objective that images an object field onto an image field.
In the illumination system of U.S. Pat. No. 6,285,443, the entry surface of the rod integrator is illuminated by a light incoupling optics. The rod integrator, of inside reflection type integrator, for example a glass rod or a hollow lightguide, mixes and homogenizes the incident ray bundle by multiple internal reflection, so that a nearly homogeneous intensity distribution is produced at the exit surface of the rod integrator. A masking device is situated in the neighborhood of the exit surface of the rod integrator, and is imaged by a following objective, a so-called REMA (Reticle Masking) objective, onto a structure-carrying mask, the so-called reticle, whereby the illuminated region on the reticle is sharply bounded. A further illumination system with a glass rod and a following REMA objective is known from U.S. Pat. No. 5,675,401.
German Patent Documents DE 199 12 464 A1 likewise describes an illumination system with a rod integrator. The exit surface of the rod integrator is imaged on the reticle by means of an objective.
The documents cited above do not, however, contain any teaching regarding a specific embodiment of the objective, which is respectively arranged after the rod integrator.
Embodiments of REMA objectives are shown in U.S. Pat. No. 5,982,558 and German Patent Document DE 196 53 983 A1 (U.S. patent application Ser. No. 09/125,624). These documents also show projection exposure apparatuses with a glass rod as a rod integrator and a following REMA objective.
BRIEF SUMMARY OF THE INVENTION
The invention has as its object to provide an improved illumination system with a rod integrator and a following objective, in particular the energy load on the lenses within the objective being reduced in the system.
This object is attained with an illumination system. The illumination system has a rod integrator having an entry surface and an exit surface and an objective for imaging an object field onto an image field, the objective being arranged after the rod integrator in a direction of light propagation. A lens-free interspace is situated in the objective. A plane optically conjugate to a plane of the entry surface is situated within the lens-free interspace. The lens-free interspace has an axial length along the optical axis of at least 30 mm. Within the interspace, first rays have first ray heights with respect to the optical axis. The first rays are not reflected at the side surfaces of the rod integrator. Second rays have second ray heights with respect to the optical axis, and are reflected at the side surfaces of the rod integrator. The first ray heights have lower absolute values than the second ray heights. All of the first rays and all of the second rays start from a central field within the entry surface of the rod integrator. The central field has a field width and a field height. The ratio of the field width to the width of the entry surface is at most 0.7, and the ratio of the field height to the height of the entry surface is at most 0.7.
The energy load on the lenses of the objective is reduced by providing the objective with a lens-free interspace, the position and the axial size of the lens-free interspace primarily depending on the dimensions of the rod integrator. The rod integrator has an entry surface and an exit surface, with a width and a height and four side surfaces with a length along the optical axis. The entry surface is not limited to a rectangular cross section. It can also have a polygonal external shape, where the cross section of the entry surface can be inscribed in a respective rectangle having a width and a height. In this case, the rod integrator has more than four side surfaces. The rod integrator can be constructed from plural rod integrators that follow one another in direct succession. It is also possible to install a deflecting mirror or a deflecting prism between the individual rod integrators. The length of the rod integrator is then given by the sum of the individual lengths of the combined rod integrators.
As a development of the invention, there is within the objective a plane that is conjugate to the plane of the entry surface. Images of the entry surface arise in this plane. The number of images depends on the number of reflections of the rays within the rod integrator. This plane conjugate to the plane of the entry surface is situated within the lens-free interspace, which preferably has an axial size of at least 30 mm, and in particular at least 50 mm. As a development of the invention, the plane conjugate to the plane of the entry surface is advantageously situated nearly in the middle of the lens-free interspace.
As a further development of the invention, the position and size of the lens-free interspace is determined as follows. Rays within the illumination system are considered that start from the entry surface of the rod integrator and are conducted through the illumination system. Rays that pass through the rod integrator without reflection at the side surfaces, and rays that are reflected one or plural times at the side surfaces, are differentiated here. There is a region within the objective in which the rays that are not reflected have a smaller ray height than the rays that are reflected one or more times. This region defines the lens-free interspace. The ray heights here indicate the distance of the rays to the optical axis. For the determination of the lens-free interspace, not all the rays that are possible in principle are considered, but only those rays that start from a central field in the entry surface of the rod integrator. The field width of the central field then amounts to at most 70% of the width of the entry surface, in particular, at most 50% of the width of the entry surface. The field height of the central field is at most 70% of the height of the entry surface, in particular, at most 50% of the height of the entry surface. The smaller the central field from which the rays for the determination of the lens-free interspace start, the more extended is the lens-free interspace. The central field thus does not limit the illuminated region on the entry surface, but gives the place of origin of the rays, which are taken into consideration for determination of the lens-free interspace.
The interspace is lens-free when, within the interspace, there is no surface vertex of a lens on the optical axis. The lens-free interspace has a gas filling with air, an inert gas, or a mixture of inert gases, or can be evacuated.
As a further development of the invention, local intensity peaks that arise within the objective in an illumination system with a rod integrator and the following objective do not lead to any materials damage. The local intensity peaks occur within the lens-free interspace when the light is coupled into the rod integrator in as loss-free a manner as possible. For this purpose, the optical components arranged before the rod integrator produce a constriction of the ray bundle, a so-called secondary light source, near the entry surface of the rod integrator. The lateral extent of the real secondary light source is, preferably, smaller than the cross section of the entry surface. A grid of virtual secondary light sources is produced in the plane of the real secondary light source by the multiple reflecti
Köhler Jess
Sohmer Alexander
Carl-Zeiss-Stiftung
Spector David N.
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