CHROMATICALLY CORRECTED OBJECTIVE AND PROJECTION EXPOSURE APPARATUS INCLUDING THE SAME
An objective having a plurality of optical elements arranged to image a pattern from an object field in an object surface of the objective to an image field in an image surface region of the objective at an image-side numerical aperture NA>0.8 with electromagnetic radiation from a wavelength band around a wavelength λ, includes a number N of dioptric optical elements, each dioptric optical element i made from a transparent material having a normalized optical dispersion Δn i =n i (λ 0 )− n i (λ 0 +1 pm) for a wavelength variation of 1 pm from a wavelength λ 0 . The objective satisfies the relation ∑ i = 1 N Δ n i ( s i - d i ) λ 0 NA 4 ≤ A for any ray of an axial ray bundle originating from a field point on an optical axis in the object field, where s i is a geometrical path length of a ray in an ith dioptric optical element having axial thickness d i and the sum extends on all dioptric optical elements of the objective. Where A=0.2 or below, spherochromatism is sufficiently corrected
1 . An objective comprising:
a plurality of optical elements arranged to image a pattern from an object field in an object surface of the objective to an image field in an image surface region of the objective at an image-side numerical aperture NA>0.8 with electromagnetic radiation from a wavelength band around a wavelength λ, the optical elements including a number N of dioptric optical elements, each dioptric optical element i made from a transparent material having a normalized optical dispersion
Δn i =n i (λ 0 )− n i (λ 0 +1 pm)
for a wavelength variation of 1 pm from a wavelength λ 0 , wherein the objective satisfies the relation
∑
i
=
1
N
Δ
n
i
(
s
i
-
d
i
)
λ
0
NA
4
≤
A
for any ray of an axial ray bundle originating from a field point on an optical axis in the object field;
where s i is a geometrical path length of a ray in an ith dioptric optical element having axial thickness d i and the sum extends on all dioptric optical elements of the objective, and where
A=0.2.
2 . The objective according to claim 1 , where A=0.1.
3 . The objective according to claim 1 , wherein dioptric optical elements in an image-side end portion of the objective adjacent to the image surface have a substantially aplanatic construction.
4 . The objective according to claim 1 , wherein the optical elements form:
a first objective part configured to image the pattern from the object surface into a first intermediate image, and having a first pupil surface;
a second objective part configured to image the first intermediate image into a second intermediate image, and having a second pupil surface optically conjugate to the first pupil surface,
a third objective part configured to image the second intermediate image into the image surface, and having a third pupil surface optically conjugate to the first and second pupil surface.
5 . The objective according to claim 4 , wherein a maximum value of pupil distortion, PD MAX =Max(D P ) within the third objective part is less than 20%, where a normalized pupil distortion D P =V/NA 3 and V is the pupil distortion at a maximum value of image-side NA for which the objective is sufficiently corrected, where V at a given position is given by a difference between an actual ray height RH and a paraxial ray height PRH, normalized by the paraxial ray height PRH according to V=(RH−PRH)/PRH.
6 . The objective according to claim 5 , wherein PD MAX <15%.
7 . The objective according to claim 4 , wherein the second objective part includes a concave mirror having a reflective mirror surface positioned at or close to the second pupil surface, and a lens group with negative refracting power immediately in front of the concave mirror and coaxial with the concave mirror and passed twice by radiation.
8 . The objective according to claim 4 , wherein an aperture stop defining an effective image side numerical aperture NA of the objective is arranged at the first pupil surface or at the second pupil surface.
9 . The objective according to claim 1 , wherein the objective includes a concave mirror arranged at or optically close to a pupil surface of the objective and a negative group comprising at least one negative lens arranged in front of the concave mirror on a reflecting side thereof in a double pass region such that radiation passes at least twice in opposite directions through the negative group.
10 . The objective according to claim 1 , wherein the objective is configured as an immersion objective with image-side numerical aperture NA≧1 when used in conjunction with an immersion liquid in an image-side working space between an exit surface of the objective and the image surface during operation.
11 . The objective according to claim 1 , wherein the objective has an immersion lens group having a convex object-side entry surface bounding at a gas or vacuum and an image-side exit surface in contact with an immersion liquid in operation, wherein the immersion lens group is at least partly made of a high-index material with refractive index n≧1.6 at the wavelength λ.
12 . The objective according to claim 11 , wherein the immersion lens group is a monolithic plano-convex lens made of the high-index material.
13 . The objective according to claim 12 , wherein the high-index material is chosen from the group consisting of aluminum oxide (Al 2 O 3 ), beryllium oxide (BeO), magnesium aluminum oxide (MgAlO 4 , spinell), yttrium aluminium oxide (Y 3 Al 5 O 12 ), yttrium oxide (Y 2 O 3 ), lanthanum fluoride (LaF 3 ), lutetium aluminium garnet (LuAG), magnesium oxide (MgO), calcium oxide (CaO), lithium barium fluoride (LiBaF 3 ).
14 . The objective according to claim 1 , wherein NA/n I >0.8, where NA is the image-side numerical aperture and n I is the refractive index of the image space.
15 . The objective according to claim 1 , wherein the objective has an image-side numerical aperture NA≧1.35.
16 . The objective according to claim 1 , wherein a maximum angle of incidence on an optical surface of an imaging objective part imaging a last intermediate image onto the image surface fulfills the condition sin(i MAX )<E*NA/n I , wherein NA is the image-side numerical aperture, n I is the refractive index in an image space, and E=0.95.
17 . The objective according to claim 1 , wherein the objective is a projection objective for microlithography.
18 . An objective comprising:
a plurality of optical elements arranged to image a pattern from an object field in an object surface of the objective to an image field in an image surface region of the objective at an image-side numerical aperture NA>0.8 with electromagnetic radiation from a wavelength band around a wavelength λ,
the optical elements including optical elements forming a focussing lens group imaging a field surface closest to the image surface onto the image surface,
wherein a maximum value of pupil distortion, PD MAX =Max(D P ) within the focusing lens group is less than 20%, where a normalized pupil distortion D P =V/NA 3 and V is the pupil distortion at a maximum value of image-side NA for which the objective is sufficiently corrected, where V at a given position is given by a difference between an actual ray height RH and a paraxial ray height PRH, normalized by the paraxial ray height PRH according to V=(RH−PRH)/PRH.
19 . The objective according to claim 18 , wherein PD MAX <15%.
20 . The objective according to claim 18 , wherein the optical elements include a number N of dioptric optical elements, each dioptric optical element i made from a transparent material having a normalized optical dispersion
Δn i =n i (λ 0 )− n i (λ 0 +1 pm)
for a wavelength variation of 1 pm from a wavelength λ 0 , wherein the objective satisfies the relation
∑
i
=
1
N
Δ
n
i
(
s
i
-
d
i
)
λ
0
NA
4
≤
A
for any ray of an axial ray bundle originating from a field point on an optical axis in the object field;
where s i is a geometrical path length of a ray in an ith dioptric optical element having axial thickness d i and the sum extends on all dioptric optical elements of the objective, and where
A=0.2.
21 . The objective according to claim 20 , wherein A=0.1.
22 . The objective according to claim 18 , wherein dioptric optical elements in an image-side end portion of the objective adjacent to the image surface have a substantially aplanatic construction.
23 . The objective according to claim 18 , wherein the optical elements form:
a first objective part configured to image the pattern from the object surface into a first intermediate image, and having a first pupil surface;
a second objective part configured to image the first intermediate image into a second intermediate image, and having a second pupil surface optically conjugate to the first pupil surface,
a third objective part configured to image the second intermediate image into the image surface, and having a third pupil surface optically conjugate to the first and second pupil surface.
24 . The objective according to claim 23 , wherein the second objective part includes a concave mirror having a reflective mirror surface positioned at or close to the second pupil surface, and a lens group with negative refracting power immediately in front of the concave mirror and coaxial with the concave mirror and passed twice by radiation.
25 . The objective according to claim 23 , wherein an aperture stop defining an effective image side numerical aperture NA of the objective is arranged at the first pupil surface or at the second pupil surface.
26 . The objective according to claim 18 , wherein the objective includes a concave mirror arranged at or optically close to a pupil surface of the objective and a negative group comprising at least one negative lens arranged in front of the concave mirror on a reflecting side thereof in a double pass region such that radiation passes at least twice in opposite directions through the negative group.
27 . The objective according to claim 18 , wherein the objective is configured as an immersion objective with image-side numerical aperture NA≧1 when used in conjunction with an immersion liquid in an image-side working space between an exit surface of the objective and the image surface during operation.
28 . The objective according to claim 18 , wherein the objective has an immersion lens group having a convex object-side entry surface bounding at a gas or vacuum and an image-side exit surface in contact with an immersion liquid in operation, wherein the immersion lens group is at least partly made of a high-index material with refractive index n≧1.6 at the wavelength λ.
29 . The objective according to claim 28 , wherein the immersion lens group is a monolithic plano-convex lens made of the high-index material.
30 . The objective according to claim 29 , wherein the high-index material is chosen from the group consisting of aluminum oxide (Al 2 O 3 ), beryllium oxide (BeO), magnesium aluminum oxide (MgAlO 4 , spinell), yttrium aluminium oxide (Y 3 Al 5 O 12 ), yttrium oxide (Y 2 O 3 ), lanthanum fluoride (LaF 3 ), lutetium aluminium garnet (LuAG), magnesium oxide (MgO), calcium oxide (CaO), lithium barium fluoride (LiBaF 3 ).
31 . The objective according to claim 18 , wherein NA/n I >0.8, where NA is the image-side numerical aperture and n I is the refractive index of the image space.
32 . The objective according to claim 18 , wherein the objective has an image-side numerical aperture NA≧1.35.
33 . The objective according to claim 18 , wherein a maximum angle of incidence on an optical surface of the focussing lens group fulfills the condition sin(i MAX )<E*NA/n I , wherein NA is the image-side numerical aperture, n I is the refractive index in an image space, and E=0.95.
34 . The objective according to claim 18 , wherein the objective is a projection objective for microlithography.
35 . A projection exposure apparatus configured to expose a radiation-sensitive substrate arranged in a region of an image surface of a projection objective with at least one image of a pattern of a mask that is arranged in a region of an object surface of the projection objective, comprising:
a radiation source emitting ultraviolet radiation from a wavelength band around a wavelength λ;
an illumination system receiving the radiation from the radiation source and shaping illumination radiation directed onto the pattern of the mask; and
a projection objective according to claim 1 .
36 . The projection exposure apparatus according to claim 35 , wherein λ<260 nm and wherein the Full Width at Half Maximum FWHM of the radiation source is greater than 0.5 pm.
37 . The projection exposure apparatus according to claim 36 , wherein the radiation source is a laser emitting at about λ=193 nm.
38 . The projection exposure apparatus according to claim 37 , wherein FWHM≧1 pm.
39 . A projection exposure apparatus configured to expose a radiation-sensitive substrate arranged in a region of an image surface of a projection objective with at least one image of a pattern of a mask that is arranged in a region of an object surface of the projection objective, comprising: a radiation source emitting ultraviolet radiation from a wavelength band around a wavelength λ;
an illumination system receiving the radiation from the radiation source and shaping illumination radiation directed onto the pattern of the mask; and
a projection objective according to claim 18 .
40 . The projection exposure apparatus according to claim 39 , wherein λ<260 nm and wherein the Full Width at Half Maximum FWHM of the radiation source is greater than 0.5 pm.
41 . The projection exposure apparatus according to claim 40 , wherein the radiation source is a laser emitting at about λ=193 nm.
42 . The projection exposure apparatus according to claim 41 , wherein FWHM≧1 pm.