Methods for reducing polarization aberration in optical systems
AssigneeASML Netherlands B.V.
InventorJames McGuire
Life of this patent
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Abstract
An optical system includes multiple cubic crystalline optical elements and one or more uniaxial birefringent elements in which the crystal lattices of the cubic crystalline optical elements are oriented with respect to each other to reduce the effects of intrinsic birefringence and produce a system with reduced retardance. The net retardance of the system is reduced by the cancellation of retardance contributions from the multiple cubic crystalline optical elements and the uniaxial birefringent element. The optical system may be used in a photolithography tool to pattern substrates such as semiconductor substrates and thereby produce semiconductor devices.
Claims24
A method of reducing the retardance caused by intrinsic birefringence in an optical system comprising a plurality of [111] cubic crystalline optical elements with respective [111] crystal axes aligned along an optical axis, said method comprising:
- clocking at least one said [111] cubic crystalline optical element to provide a more circularly symmetric retardance pattern over a pupil centered about said optical axis at least for on-axis field points;
- and
- introducing one or more uniaxial birefringent elements comprising media having a single birefringence axis into said optical system, said one or more uniaxial birefringent elements having a substantially circularly symmetric retardance pattern associated therewith that is distributed over said pupil centered about said optical axis at least for on-axis field points,
- wherein said retardance pattern corresponding to said plurality of [111] cubic crystal optical elements and said retardance pattern corresponding to said one or more uniaxial birefringent elements are opposite such that retardance introduced into an optical beam transmitted through said plurality of [111] cubic crystalline elements is substantially offset by retardance introduced into said optical beam upon transmitting said beam through said one or more uniaxial birefringent optical elements.
An optical method comprising:
- propagating a beam of light having first and second orthogonal polarization components through first optics comprising a plurality of optical elements disposed along an optical axis, said first optics having radial and tangential eigenpolarization states that form a circularly symmetric pattern around said optical axis, said radial and tangential eigenpolarization states being phased delayed with respect to each other so as to introduce phase delay between said first and second orthogonal polarization components in said beam of light;
- and
- substantially reducing said phase delay between said first and second orthogonal polarization components in said beam of light by propagating said light through second optics disposed along said optical axis, said second optics having radial and tangential eigenpolarization states that form a circularly symmetric pattern around said optical axis, said radial and tangential eigenpolarization states in said second optics being phased delayed with respect to each other opposite said phase delay between said radial and tangential eigenpolarization states of said first optics.
Dependencies are inferred from the claim text.