Groupwise corrected objective

1. A method of fabricating an objective comprising a plurality of optical elements, the method comprising acts of:

determining groups of optically similar optical elements or surfaces, each group having at least two members;

determining wave front deformations by the optical elements or surfaces;

determining necessary connections for the optical elements or surfaces of at least one of the groups; and

performing corrections for the at least one group at a group member of that group;

wherein the act of determining groups includes:

determining similarity of the optical elements or surfaces; and

grouping the optical elements or surfaces according to the similarity of their optical positions;

wherein similarity of the optical elements or surfaces for determining a group is determined by at least one of pupil closeness and arrangement of the optical elements or surfaces before or behind a pupil; and

wherein pupil closeness is determined by the ratio of subaperture diameter to optical free diameter.

2. The method as set forth in claim 1 , wherein optical elements or surfaces are termed similar when their pupil closeness relative to the maximum value of the values being compared differs by less than 30%.

3. The method as set forth in claim 1 wherein optical elements or surfaces are termed similar when their pupil closeness relative to the maximum value of the values being compared differs by less than 20%.

4. The method as set forth in claim 1 , wherein optical elements or surfaces are termed similar when their pupil closeness relative to the maximum value of the values being compared differs by less than 10%.

5. A method of fabricating an objective comprising a plurality of optical elements, the method comprising acts of:

determining groups of optically similar optical elements or surfaces, each group having at least two members;

determining wave front deformations by the optical elements or surfaces;

determining necessary co-corrections for the optical elements or surfaces of at least one of the groups;

performing corrections for the at least one group at a group member of that group; and

examining a surface of each optical element;

wherein the act of examining the surface includes using an interferometric technique to determine deviations of the surface from a predefined shape.

6. A method of fabricating an objective comprising a plurality of optical elements, the method comprising acts of:

determining groups of optically similar optical elements or surfaces, each group having at least two members;

determining wavefront deformations by the optical elements or surfaces; determining necessary corrections for the optical elements or surfaces of at least one of the groups; and

performing corrections for the at least one group at a group member of that group; and

examining a material of each optical element;

wherein the act of examining the material includes using tomographic techniques to detect localized fluctuations in properties of the material.

7. A method of fabricating an objective comprising a plurality of optical elements, the method comprising acts of:

determining groups of optically similar optical elements or surfaces, each group having at least two members;

determining wavefront deformations by the optical elements or surfaces;

determining necessary corrections for the optical elements or surfaces of at least one of the groups; and

performing corrections for the at least one group at a group member of that group;

wherein the act of determining wavefront deformations includes:

determining the wavefront deformation for a group member that is to be corrected when that group member is in an unfinished condition; and

determining the wavefront deformation for all other group members in the finished condition after coating.

8. A method of fabricating an objective comprising a plurality of optical elements, the method comprising acts of:

determining groups of optically similar optical elements or surfaces, each group having at least two members;

determining wavefront deformations by the optical elements or surfaces;

determining necessary corrections for the optical elements or surfaces of at least one of the groups; and

performing corrections for the at least one group at a group member of that group

wherein the optical elements are provided in sections separated by pupil planes or intermediate image planes; wherein N sections A 1 to A N are provided with N being at least 2; wherein a first corrected optical element is provided in section A j , where j=1 to N; and wherein at least a second corrected optical element is provided in section A k , where k=1 to N in satisfying the condition |k-j| equals an odd number.

9. A method of fabricating an objective comprising a plurality of optical elements, the method comprising acts of:

determining groups of optically similar optical elements or surfaces, each group having at least two members;

determining wavefront deformations by the optical elements or surfaces;

determining necessary corrections for the optical elements or surfaces of at least one of the groups; and

performing corrections for the at least one group at a group member of that group

wherein the optical elements are provided in sections separated by pupil planes or intermediate image planes; wherein N sections A 1 to A N are provided with N being at least 2; and wherein a co-corrected optical element is provided in section A j where j = 1 to N, which corrects or co-corrects at least a similar optical element in section A k where k = 1 to N in satisfying the condition |k-j| equals an even number or zero.

10. An objective comprising:

a plurality of optical elements, grouped together into groups of optically similar elements, each group having at least two members;

wherein at least one group comprises an optical element constructed and arranged to correct a wave front deformation of at least one of a correspondingly corrected optical element and the group members of the at least one group; and

wherein the objective is an EUV projection objective.