Projection exposure system having a reflective reticle

Abstract

A projection exposure system for microlithography includes an illuminating system (2), a reflective reticle (5) and reduction objectives (71, 72). In the reduction objective (71, 72), a first beam splitter cube (3) is provided which superposes the illuminating beam path (100) and the imaging beam path (200). In order to obtain an almost telecentric entry at the reticle, optical elements (71) are provided between beam splitter cube (3) and the reflective reticle (5). Advantageously, the reduction objective is a catadioptric objective having a beam splitter cube (3) whose fourth unused side can be used for coupling in light. The illuminating beam path (100) can also be coupled in with a non-parallel beam splitter plate. The illuminating beam path is refractively corrected in passthrough to compensate for aberrations via the special configuration of the rear side of the beam splitter plate. Advantageously, a beam splitter plate of this kind is used within a reduction objective in lieu of a deflecting mirror and only refractive components are introduced between the beam splitter plate and the reflective reticle.

Description

FIELD OF THE INVENTION[0001]The invention relates to a projection exposure system having a reticle which operates in reflection.BACKGROUND OF THE INVENTION[0002]Projection exposure systems having a reflective reticle have been used in the past, inter alia, together with 1:1 Dyson objectives. These projection exposure systems are described in the following publications:[0003]a) Owen et al, “⅛μm optical lithography” J. Vac. Sci. B 10 (1992), pages 3032 to 3036, especially Parts B and C;[0004]b) Pease et al, “Lithography for 0.25 μm and below . . . ” IEEE Symp. VLSI Technology (1992), pages 116 and 117;[0005]c) Jeong et al, “Optical projection system . . . ” J. Vac. Sci. B 11 (1993), pages 2675 to 2679; and,[0006]d) U.S. Pat. No. 4,964,705.[0007]The incoupling of the illumination takes place via a partially transmitting mirror as shown, for example, in U.S. Pat. No. 4,964,705 (FIGS. 3A and 3B). Beam splitter cubes or beam splitter plates are not provided in these designs.[0008]Reflecti...

AI Technical Summary

Benefits of technology

[0019]According to a feature of the invention, a beam splitter cube functions to superpose the illuminating and imaging beam paths. In this way, numerous objective design concepts for reflective reticles can be adapted as will be shown in the following examples. Erroneous entries by the beam splitter plate are avoided by utilizing a beam splitter cube in lieu of a planar parallel beam splitter plate. The beam splitter plate is operated in passthrough and mounted at 45°.

[0020]According to another feature of the invention, optical elements are provided between the beam splitter cube and the reticle. With these optic elements, it is possible to reduce the angle of incidence of the main beams of the reduction objective on the reticle in such a manner that the incident angle has values between −15 mrad and +15 mrad.

[0022]According to another feature of the invention, a polarization beam splitter cube is used in order to reduce transmission losses at the beam splitter cube and so that no scattering light is deflected onto the wafer. For an optimal operation, the illuminating light should be linearly polarized to more than 95%. The polarization direction is dependent upon whether the illuminating beam path is intended to be reflected or not at the beam splitter layer. In the case of a reflection, the illuminating light has to be polarized parallel to the beam splitter surface and, in the case of the transmission, the illuminating light has to be polarized perpendicularly to the beam splitter surface.

[0024]The coupling in of the illuminating beam path with a beam splitter cube is especially advantageous when the beam splitter cube is already a part of the reduction objective. Then, the fourth unused face of the beam splitter cube can be used to couple in the illuminating beam path.

[0030]The beam splitter plate is configured to have a wedge shape in accordance with another embodiment of the invention for correcting the astigmatism of the lowest order. The use of a beam splitter plate is especially advantageous when it is used in lieu of a deflecting mirror provided in the design of the reduction objective.

[0031]The superposition of the illuminating optics and the projection optics make possible the use of reflective reticles especially at operating wavelengths in the range from 100 to 200 nm. In this way, the difficulties are avoided which occur in the manufacture of transmission reticles because of machining of the materials transparent at these wavelengths.

Problems solved by technology

The inclined incidence of the illuminating light on the reflective reticle has the disadvantage that the raised mask struts lead to vignetting.

The production of transmission reticles (that is, masks operated in transmission for microlithography) is difficult for deep ultraviolet wavelengths, especially 157 nm, inter alia, because of suitable transmitting carrier materials.

However, reticles made of CaF2 or MgF2 are difficult to process and are therefore very expensive.

In conventional reduction objectives, the use of reflective reticles is not easily possible.

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