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US 8,027,088 B2Granted
Catadioptric projection objective with tilted deflecting mirrors, projection exposure apparatus, projection exposure method, and mirror
AssigneeCarl Zeiss SMT GmbH
InventorsRalf Mueller, Aksel Goehnermeier, Wolfgang Singer
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Abstract
In general, in one aspect, the invention features a catadioptric projection objective having a plurality of optical elements arranged along an optical axis to image a pattern arranged in an object surface of the projection objective onto an image surface of the projection objective. The optical elements include a concave mirror, a first deflecting mirror tilted relative to the optical axis and a second deflecting mirror. The catadioptric projection objective can image patterns including sub-patterns oriented in various directions such that line width variations due to differences of orientation of sub-patterns are largely avoided.
Claims32
A projection objective having an object surface and an image surface, the projection objective comprising:
- a plurality of optical elements arranged along an optical axis and configured so that during operation the projection objective images a pattern arranged in the object surface onto the image surface, the optical elements comprising:
- a concave mirror;
- a first deflecting mirror tilted relative to the optical axis by a first tilt angle, t1, about a first tilt axis so that during operation the first deflecting mirror deflects light at a wavelength λ from the object surface towards the concave mirror or deflects light at λ from the concave mirror towards the image surface, the first deflecting mirror comprising a first reflective coating with reflectivity Rs1(α1) for s-polarized light at λ and a reflectivity Rp1(α1) for p-polarized light at λ incident on the first deflecting mirror at first angles of incidence α1 for at least a first range of angles of incidence according to (t1−Δα1)≦α1≦(t1+Δα1);
- and
- a second deflecting mirror tilted relative to the optical axis by a second tilt angle, t2, about a second tilt axis, the second deflecting mirror comprising a second reflective coating with a reflectivity Rs2(α2) for s-polarized light at λ and a reflectivity Rp2(α2) for p-polarized light at λ incident on the second deflecting mirror at second angles of incidence α2 for at least a second range of angles of incidence according to (t2−Δα2)≦α2≦(t2+Δα2),
- wherein:
- a first reflectivity sum, RsPE, for s-polarized light at λ of polar edge rays accumulated upon reflection on the first and second deflecting mirrors is substantially equal to a second reflectivity sum, RpE for p-polarized light of equatorial edge rays accumulated upon reflection on the first and second deflecting mirrors;
- Δα1 is an angular difference between a center value of a range of angles of incidence on the first deflecting mirror and an angle selected from the group consisting of a maximum angle of incidence on the first deflecting mirror and a minimum angle of incidence on the first deflecting mirror;
- Δα2 is an angular difference between a center value of a range of angles of incidence on the second deflecting mirror and an angle selected from the group consisting of a maximum angle of incidence on the second deflecting mirror and a minimum angle of incidence on the second deflecting mirror;
- and
- the projection objective is a catadioptric projection objective.
8 more elements
A mirror comprising:
- a mirror substrate;
- a reflective coating supported by the substrate,
- wherein the reflective coating has a reflectivity Rs(α) for s-polarized light at a wavelength λ and a reflectivity Rp(α) for p-polarized light at λ incident on the mirror at angles of incidence α for at least a range of angles of incidence according to (t−Δα)≦α≦(t+Δα) such that the condition:
- (Rs(t−Δα)+Rs(t+Δα))/2=Rp(t)±0.5%
- is fulfilled, wherein:
- t is a tilt angle between 45°±10°, and
- Δα is an angular difference between a center value of a range of angles of incidence on the reflective coating and an angle selected form the group consisting of a maximum angle of incidence on the reflective coating and a minimum angle of incidence on the reflective coating.
4 more elements
An optical imaging system, comprising:
- a plurality of optical elements arranged along an optical axis and configured so that during operation the optical imaging system images a pattern arranged in an object surface of the imaging system onto an image surface of the imaging system, the optical elements comprising:
- a first deflecting mirror tilted relative to the optical axis by a first tilt angle, t1, about a first tilt axis, the first deflecting mirror having a first reflective coating with reflectivity Rs1(α1) for s-polarized light and a reflectivity Rp1(α1) for p-polarized light incident on the first deflecting mirror at first angles of incidence α1 for at least a first range of angles of incidence according to (t1−Δα1)≦α1≦(t1+Δα1);
- and
- a second deflecting mirror tilted relative to the optical axis by a second tilt angle, t2, about a second tilt axis, the second deflecting mirror having a second reflective coating with a reflectivity Rs2(α2) for s-polarized light and a reflectivity Rp2(α2) for p-polarized light incident on the second deflecting mirror at second angles of incidence α2 for at least a second range of angles of incidence according to (t2−Δα2)≦α2≦(t2+Δα2),
- wherein:
- a first reflectivity sum, RsPE, for s-polarized light of polar edge rays accumulated upon reflection on the first and second deflecting mirrors is substantially equal to a second reflectivity sum, RpE for p-polarized light of equatorial edge rays accumulated upon reflection on the first and second deflecting mirrors;
- Δα1 is an angular difference between a center value of a range of angles of incidence on the first deflecting mirror and an angle selected from the group consisting of a maximum angle of incidence on the first deflecting mirror and a minimum angle of incidence on the first deflecting mirror;
- Δα2 is an angular difference between a center value of a range of angles of incidence on the second deflecting mirror and an angle selected from the group consisting of a maximum angle of incidence on the second deflecting mirror and a minimum angle of incidence on the second deflecting mirror.
5 more elements
Dependencies are inferred from the claim text.