Lithographic objective having a first lens group including only lenses having a positive refractive power
View Patent ↗A projection objective includes a first lens group (G 1 ) of positive refractive power, a second lens group (G 2 ) of negative refractive power and at least one further lens group of positive refractive power in which a diaphragm is mounted. The first lens group (G 1 ) includes exclusively lenses of positive refractive power. The number of lenses of positive refractive power (L 101 to L 103; L 201, L 202 ) of the first lens group (G 1 ) is less than the number of lenses of positive refractive power (L 116 to L 119; L 215 to L 217 ) which are mounted forward of the diaphragm of the further lens group (G 5 ).
1. A projection objective defining an image plane and comprising, in sequence:
an object plane;
a first lens group of positive refractive power adjacent said object plane;
a second lens group of negative refractive power;
a third lens group of positive refractive power including meniscus lenses;
at least one additional lens group having positive refracting power and having a diaphragm mounted therein;
said second lens group including a plurality of negative lenses;
said projection objective defining an image plane;
a distance between each negative lens of said second lens group;
said distance between each negative lens of said second lens group and said image plane being greater than 54 percent of the object plane to image plane distance; and,
a lens of one of said lens groups being an aspheric lens.
2. A projection objective defining an image plane and comprising, in sequence:
an object plane;
a first lens group of positive refractive power adjacent said object plane;
a second lens group of negative refractive power;
a third lens group of positive refractive power consisting of meniscus lenses;
at least one additional lens group having positive refracting power and having a diaphragm mounted therein; and,
said projection objective having a numerical aperture of at least 0.8.
3. A projection objective defining an optical axis and an image plane and comprising:
an object plane;
a plurality of lenses arranged along said optical axis;
a diaphragm interposed between two of said lenses;
a first one of said lenses being an aspheric lens;
a second one of said lenses being arranged between said diaphragm and the image plane; and,
said second lens having a thickness of about at least 6 cm.
4. The projection objective of claim 3 , wherein said thickness of said second lens is measured at said optical axis.
5. The projection objective of claim 4 , wherein said second lens has a varying thickness.
6. The projection objective of claim 4 , wherein said second lens is a plane-parallel plate.
7. A projection objective defining an optical axis and an image plane and comprising:
an object plane;
a plurality of lenses arranged along said optical axis;
a diaphragm interposed between two of said lenses;
a first one of said lenses being an aspheric lens;
a second one of said lenses being arranged between said diaphragm and the image plane;
said second lens having a thickness of about at least 6 cm; and,
said projection objective having a numerical aperture of at least 0.8.
8. A projection objective defining an optical axis and an image plane and comprising:
an object plane;
a plurality of lenses arranged along said optical axis;
a diaphragm interposed between two of said lenses;
a first one of said lenses being an aspheric lens;
a second one of said lenses being arranged between said diaphragm and the image plane;
said second lens having a thickness of about at least 6 cm; and,
a plane-parallel plate.
9. The projection objective of claim 8 , wherein said plane-parallel plate follows said second lens.