Device and method for wavefront measurement of an optical imaging system by means of phase-shifting interferometry
View Patent ↗Device and method for wavefront measurement of an optical imaging system by means of phase-shifting interferometry, having a mask structure ( 6 a ) to be arranged on the object side, and/or a grating structure ( 7 a ) to be arranged on the image side. The object-side mask structure includes one or more one-dimensional mask structure patterns, and the image-side grating structure includes one or more two-dimensional grating structure patterns. Alternatively, conversely, the mask structure includes one or more two-dimensional patterns, and the grating structure includes one or more one-dimensional patterns. Additionally or alternatively, a pupil position offset caused by a lateral relative movement of the mask structure and detector element can be taken into account by back calculating the interferogram, respectively recorded by the detector element, using an associated phase-shift characteristic, or by a computational correction of wavefront derivatives, obtained from the recorded interferograms, in the direction of lateral movement. The method and/or the device can by used, for example, for determining aberration in the case of high-resolution projection objectives of microlithography exposure machines using shearing or point interferometry.
1. A method for wavefront measurement of an optical imaging system by means of a phase-shifting interferometry technique, the method comprising:
at least one of:
moving a phase-shifting structure and a detector element laterally relative to the optical imaging system to be measured, and
moving an object-side mask structure laterally relative to the detector element,
wherein a pupil image offset occurring owing to the relative lateral movement is taken into account by back calculating interferograms, wherein the interferograms are respectively recorded by the detector element, using a phase-shifting characteristic associated with the lateral movement, or
wherein the pupil image offset is taken into account by a computational correction of wavefront derivatives, obtained from the recorded interferograms, in the direction of lateral movement.
2. The method according to claim 1 , wherein the computational correction of wavefront derivatives in the direction of lateral movement is performed using the relationship:
I
(
2
)
(
n
)
=
cos
(
S
x
(
1
)
-
∂
S
x
(
1
)
∂
x
Δ
x
(
n
-
1
)
N
+
2
π
(
n
-
1
)
N
)
,
which specifies the intensity values I (2) of individual detector element pixels as a function of the nth lateral phase shift with S x (1) as errored wavefront derivative in the phase-shifting direction, from which an error-corrected wavefront derivative (S x (2) ) is then calculated, wherein N denotes a total number of phase steps.
3. The method according to claim 1 , carried out with aid of a device comprising:
a mask structure which is arranged on an object side, and
a grating structure which is arranged on an image side,
wherein the mask structure which is arranged on the object side comprises one or more mask structure patterns with a periodicity in exactly one direction, and the grating structure to be arranged on the image side comprises one or more grating structure patterns with a periodicity in exactly two non-parallel directions, or
wherein the mask structure comprises one or more mask structure patterns with a periodicity in exactly two non-parallel directions, and the grating structure comprises one or more grating structure patterns with a periodicity in exactly one direction.
4. The method according to claim 2 , carried out with aid of a device comprising:
a mask structure which is arranged on an object side, and
a grating structure which is arranged on an image side,
wherein the mask structure which is arranged on the object side comprises one or more mask structure patterns with a periodicity in exactly one direction, and the grating structure to be arranged on the image side comprises one or more grating structure patterns with a periodicity in exactly two non-parallel directions, or
wherein the mask structure comprises one or more mask structure patterns with a periodicity in exactly two non-parallel directions, and the grating structure comprises one or more grating structure patterns with a periodicity in exactly one direction.