US 7,321,465 B2
Method of optimizing an objective with fluoride crystal lenses, and objective with fluoride crystal lenses
Michael Totzeck, Schwaebisch Gmuend (Germany); Vladimir Kamenov, Essingen (Germany); and Toralf Gruner, Aalen-Hofen (Germany)
Assigned to Carl Zeiss SMT AG, Oberkochen (Germany)
Filed on Mar. 02, 2005, as Appl. No. 11/71,699.
Application 11/071699 is a continuation of application No. PCT/EP2003/009167, filed on Aug. 19, 2003.
Claims priority of application No. 102 41 102 (DE), filed on Sep. 03, 2002; application No. 102 43 080 (DE), filed on Sep. 16, 2002; application No. 102 53 355 (DE), filed on Nov. 14, 2002; and application No. 103 04 116 (DE), filed on Jan. 31, 2003.
Prior Publication US 2005/0180023 A1, Aug. 18, 2005
Int. Cl. G02B 27/28 (2006.01)
U.S. Cl. 359—499  [359/900; 359/352] 19 Claims
OG exemplary drawing
 
11. An objective for a microlithography projection system with lenses of fluoride crystal material with a cubic crystal structure, wherein
each fluoride crystal lens has a lens axis that is oriented approximately parallel to one of the crystallographic (100)-direction, the crystallographic (111)-direction, and the crystallographic (110)-direction,
if the objective includes no polarization-selective optical element (PSE), all of the fluoride crystal lenses that are arranged between an object plane (OB) and an image plane (IM) form a group of fluoride crystal lenses,
if the objective includes a polarization-selective optical element (PSE), all of the fluoride crystal lenses that are arranged between the polarization-selective optical element (PSE) and the image plane (IM) form a group of fluoride crystal lenses,
an optical retardation ORLG of the group of fluoride crystal lenses is smaller than 5% of a working wavelength λ0,
the optical retardation ORLG of a group of fluoride crystal lenses is defined as the sum of birefringence factors BFL of the fluoride crystal lenses of the group,
the birefringence factor BFL of a fluoride crystal lens is defined as BFL=MAL·DIL·SPL,
the material factor MAL indicates the intrinsic birefringence of the lens material for a ray that propagates in the crystallographic (110)-direction,
the orientation factor DIL has a value of −½ for a fluoride crystal lens whose lens axis is oriented in the crystallographic (100)-direction, +⅓ for a fluoride crystal lens whose lens axis is oriented in the crystallographic (111)-direction, and +⅛ for a fluoride crystal lens whose lens axis is oriented in the crystallographic (110)-direction,
the ray factor SPL is defined as
 SPL=OPL·sin2 θL·(7·cos2 θL−1) and depends on a respective aperture angle θL and ray path length OPL of an outer aperture ray in each of the fluoride crystal lenses.