Illumination Optical System with Phase Modulation Against Retardation
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Solution Overview
Problem
Conventional exposure apparatuses face challenges in maintaining a required polarization state of light due to retardation effects from subsequent optical systems, leading to reduced contrast in pattern imaging on photosensitive substrates.
Innovation Solution
Incorporating a phase modulating member after a polarization converting member to convert obliquely polarized light into elliptically polarized light, adjusting the polarization state to counteract retardation effects from subsequent optical systems, ensuring a desired polarization state is maintained.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a polarization converting member is used to create a circumferentially polarized state on the illumination pupil, then the illumination condition suitable for faithful transfer of microscopic pattern is improved, but the light is unlikely to be focused in the required circumferentially polarized state on the photosensitive substrate due to retardation effects
Solution Approach 1:
The patent applies preliminary action by converting obliquely polarized light into elliptically polarized light in advance using a phase modulating member positioned just behind the polarization converting member. This preliminary conversion compensates for the retardation effects that will occur later in the optical path, ensuring the light maintains the required circumferentially polarized state when focused on the photosensitive substrate.
Solution Approach 2:
The patent applies preliminary anti-action by using the phase modulating member to create elliptically polarized light that counteracts the harmful retardation effects of subsequent optical systems. The phase modulation is specifically designed to offset the polarization distortion that would otherwise occur, thereby maintaining the desired polarization state throughout the optical path.
2Manufacturing precision
If the beam is set in a linearly polarized state with circumferential polarization direction, then pattern contrast is improved, but subsequent optical systems cause retardation that reduces the polarization state quality
Solution Approach 1:
The patent converts the harmful effect of retardation into a benefit by using the phase modulating member to deliberately introduce phase changes that compensate for the expected retardation. The obliquely polarized light is transformed into elliptically polarized light with specific phase characteristics that, after passing through the subsequent optical system, result in the desired circumferentially polarized state with high pattern contrast.
3Reliability
If a phase modulating member is added to convert polarization state, then the desired polarization state is maintained, but device complexity increases
Solution Approach 1:
The patent applies local quality by positioning the phase modulating member at a specific location just behind the polarization converting member where it can most effectively influence the polarization state. Rather than modifying the entire optical system, the phase modulation is applied locally at the critical point where polarization conversion occurs, minimizing overall system complexity while achieving the desired effect.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The illumination optical system achieves improved pattern contrast on photosensitive substrates by reducing the impact of retardation, enabling high-quality device manufacturing.
Implementation Method 1
a phase modulating member transmits light from a pupil intensity distribution so as to convert obliquely polarized light into required elliptically polarized light
Implementation Method 2
a polarization converting member having an optical rotatory power, to create a desired circumferentially polarized state on the illumination pupil
Data Source
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AI summary
One of embodiments relates to an illumination optical system which can illuminate an illumination target surface with light in a required polarization state, while reducing influence of retardation caused by a subsequent optical system behind a polarization converting member. According to an embodiment, the illumination optical system (1-12) for illuminating an illumination target surface (M) with light from a light source (LS) is provided with a polarization converting member (5A) which converts a polarization state of incident light so as to form a pupil intensity distribution in a predetermined polarization state on an illumination pupil of the illumination optical system; and a phase modulating member (5B) which is arranged in the optical path on the illumination target surface side with respect to the polarization converting member and which transmits light from the pupil intensity distribution so as to convert linearly polarized light thereof polarized in a first direction, into required elliptically polarized light and maintain a polarization state of linearly polarized light polarized in a second direction (X-direction or Y-direction) obliquely intersecting with the first direction, in order to reduce influence of retardation caused by a subsequent optical system between the polarization converting member and the illumination target surface.