Method of inspecting phase shift masks employing phase-error enhancing
First Claim
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1. A method for inspecting a phase-shifting mask for photolithography, comprising the steps of:
- (a) obtaining a phase shifting mask inspection microscope having a phase contrast objective, and further having an adjustable phase shifter capable of phase shifting the zeroth order light by θ
;
(b) adjusting said adjustable phase shifter to phase shift the zeroth order light by θ
to enhance the detection of a phase error in the phase-shifting mask, wherein θ
is a predetermined value according to;
space="preserve" listing-type="equation">θ
=2φ
-(1±
2m)π
where φ
is the phase shift of a mask element being inspected, m is an integer, and π
is the mathematical constant pi; and
(c) subsequently using the microscope to inspect the phase-shifting mask.
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Abstract
A phase-contrast microscope with a quarter-wave plate in a pupil plane with a thickness of λθ/2π is provided for the inspection of a phase-shifting mask. The angle θ and the wavelength λ are adjustable to optimize the phase detection sensitivity. A similar θ and λ optimization scheme is applied to an interference microscope assembly wherein an inspection beam is split into two beams by a beam splitter to be reflected by mirrors and then recombined at a second beam splitter. A mirror in one of the beams can be moved to change θ to its optimum value at a given λ which can be changed by light source selection or by filter change.
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Citations
2 Claims
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1. A method for inspecting a phase-shifting mask for photolithography, comprising the steps of:
-
(a) obtaining a phase shifting mask inspection microscope having a phase contrast objective, and further having an adjustable phase shifter capable of phase shifting the zeroth order light by θ
;(b) adjusting said adjustable phase shifter to phase shift the zeroth order light by θ
to enhance the detection of a phase error in the phase-shifting mask, wherein θ
is a predetermined value according to;
space="preserve" listing-type="equation">θ
=2φ
-(1±
2m)πwhere φ
is the phase shift of a mask element being inspected, m is an integer, and π
is the mathematical constant pi; and(c) subsequently using the microscope to inspect the phase-shifting mask.
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2. A method for inspecting a phase-shifting mask for photolithography, comprising the steps of:
-
(a) obtaining a phase shifting mask inspection microscope having an interference objective, and further having an adjustable phase shifter capable of phase shifting the reference light by θ
;(b) adjusting said adjustable phase shifter to phase shift the reference light by θ
to enhance the detection of a phase error in the phase-shifting mask, wherein θ
is predetermined value according to;
space="preserve" listing-type="equation">θ
=2φ
-(1±
2m)πwhere φ
is the phase shift of a mask element being inspected, m is an integer, and π
is the mathematical constant pi; and(c) subsequently using the microscope to inspect the phase-shifting mask.
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Specification
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Current AssigneeInternational Business Machines Corporation
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Original AssigneeInternational Business Machines Corporation
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InventorsLin, Burn J.
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Primary Examiner(s)Turner, Samuel A.
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Assistant Examiner(s)KIM, ROBERT H
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Application NumberUS07/968,745Time in Patent Office1,033 DaysField of Search356/345, 356/351, 356/354, 359/370, 359/371, 359/386US Class Current356/520CPC Class CodesG02B 21/14 affording illumination for ...G02B 27/52 Phase contrast optics in mi...
