EUV Optical System Polarization Control via Geometric Rotation

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Solution Overview

Problem

Microlithographic projection exposure apparatuses face challenges in flexibly varying polarization distributions without the use of birefringent or optically active elements, which limits the optimization of imaging contrast and intensity distributions in the pupil plane.

Innovation Solution

An optical system comprising a mirror arrangement with independently adjustable mirror elements and a polarization-influencing optical arrangement that uses geometric polarization rotation through multiple reflections, not all in a common plane, to achieve flexible setting of polarization distributions, minimizing light losses and avoiding the need for birefringent elements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If birefringent or optically active elements are used to set polarization distributions, then polarization control capability is improved, but device complexity and light losses increase

Engineering Contradiction:

Improvepolarization distribution controlVSAvoidoptical system complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The invention extracts and eliminates birefringent and optically active elements from the optical system, replacing them with a mirror arrangement that uses geometric polarization rotation through multiple reflections. This removes the problematic elements while maintaining polarization control capability.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention replaces optical elements (birefringent crystals, polarizers) with a mechanical mirror arrangement that achieves polarization control through geometric reflections. The mirror elements are positioned and oriented to create the desired polarization distributions without requiring birefringent materials.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Manufacturing precision

If birefringent elements are used to optimize imaging contrast, then imaging quality is improved, but light losses increase

Engineering Contradiction:

Improveimaging contrastVSAvoidlight losses

Core Design Contradiction:

Manufacturing precisionVSLoss of energy

Solution Approach 1:

The invention converts the potential harm of light losses by using reflective mirror elements instead of transmissive birefringent elements. The mirror arrangement achieves the desired polarization effects while minimizing absorption losses that occur with birefringent materials.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Measurement precision

If multiple optical elements are used to control polarization and intensity, then control precision is improved, but device complexity increases

Engineering Contradiction:

Improvepolarization setting precisionVSAvoidnumber of optical elements

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The mirror arrangement serves multiple functions simultaneously: it controls polarization distributions through geometric reflections, adjusts intensity distributions through the mirror element configurations, and defines angular distributions of reflected light. This multi-functionality reduces the need for separate optical elements.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The invention employs adjustable mirror elements that can be dynamically positioned and oriented to achieve different polarization and intensity distributions. This dynamic adjustability allows precise control without requiring fixed, complex optical assemblies.

Inventive Principle:

Principle #15Dynamics

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

Enables flexible and efficient setting of polarization distributions, optimizing imaging contrast and intensity distributions without the use of birefringent elements, while maintaining low light losses, even at extreme wavelengths like EUV.

Implementation Method 1

a polarization-influencing optical arrangement which is arranged downstream of the mirror arrangement in the light propagation direction; wherein the polarization-influencing optical arrangement reflects a light beam incident on the arrangement in at least two reflections, which do not occur in a common plane, for at least one angular distribution of the light reflected by the mirror arrangement

Methodology Applied

Scientific EffectGeometric polarization rotation: Reflection

Data Source

PatentUS9488918B2Optical system for a microlithographic projection exposure apparatus and microlithographic exposure method

Publication Date: 2016.11.08 CARL ZEISS SMT GMBH

AI summary

The invention relates to an optical system for a microlithographic projection exposure apparatus, and to a microlithographic exposure method. An optical system for a microlithographic projection exposure apparatus comprises at least one mirror arrangement having a plurality of mirror elements, wherein these mirror elements can be adjusted independently of one another for changing an angular distribution of the light reflected by the mirror arrangement, and a polarization-influencing optical arrangement which is arranged downstream of the mirror arrangement in the light propagation direction, wherein the polarization-influencing optical arrangement reflects a light beam incident on the arrangement in at least two reflections, which do not occur in a common plane, for at least one angular distribution of the light reflected by the mirror arrangement.