Optically Uniaxial Crystal Diffractive Elements for Microlithography

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Solution Overview

Problem

In microlithographic projection exposure apparatuses, diffractive optical elements (DOEs) face issues with polarization state destruction due to material loading, compacting, and birefringence effects, especially when exposed to high-energy laser beams, leading to unwanted changes in the material's density and anisotropies.

Innovation Solution

The use of optically uniaxial crystal materials with beam-deflecting structures oriented substantially parallel or perpendicular to the optical crystal axis, which minimizes compacting and birefringence-induced polarization state destruction by employing diffractive or refractive beam-deflecting elements, such as Computer Generated Holograms (CGHs), and optionally combining with isotropic materials for additional light conductance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If quartz glass DOE is used to generate light conductance, then light conductance is improved, but polarization state is destroyed due to compacting and birefringence under high energy density

Engineering Contradiction:

Improvelight conductanceVSAvoidpolarization state

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent changes the material parameter from isotropic quartz glass to optically uniaxial crystal material, fundamentally altering the optical properties to eliminate compacting-induced birefringence while maintaining light conductance enhancement capabilities

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs composite material structure combining optically uniaxial crystal material with specific beam-deflecting structures, creating a DOE that integrates both light conductance enhancement and polarization state preservation functions

Inventive Principle:

Principle #40Composite materials

2Productivity

If isotropic crystal material DOE is used, then light conductance is improved, but polarization state is destroyed due to crystal structural defects and stress-induced birefringence

Engineering Contradiction:

Improvelight conductanceVSAvoidpolarization state

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent transitions from isotropic crystal material to optically uniaxial crystal material, changing the material's optical parameters to eliminate random birefringence caused by crystal structural defects while preserving light conductance properties

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies local quality by orienting the optical crystal axis in a specific direction (parallel or perpendicular to the beam-deflecting structures) to create localized optical anisotropy that compensates for and eliminates harmful birefringence effects

Inventive Principle:

Principle #3Local quality

3Reliability

If beam-deflecting structures are oriented parallel to optical crystal axis, then polarization state is maintained, but light conductance enhancement is limited

Engineering Contradiction:

Improvepolarization stateVSAvoidlight conductance

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent employs asymmetric orientation of beam-deflecting structures relative to the optical crystal axis, allowing different orientations (parallel or perpendicular) to be used in different regions or configurations, thereby achieving both polarization maintenance and light conductance enhancement through asymmetric design

Inventive Principle:

Principle #4Asymmetry

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

This approach maintains the polarization state integrity even under high irradiation loads, enhancing light conductance without inducing significant birefringence effects, thus ensuring stable and efficient light propagation in microlithographic systems.

Implementation Method 1

the permanent birefringence tensor provided by such a crystal material is considerably greater (typically by at least a factor of 102 to 103) than the birefringence tensor generated e.g. by crystal structural defects

Methodology Applied

Scientific EffectBirefringence: Birefringence

Implementation Method 2

the optical crystal axis of the crystal material is substantially parallel or substantially perpendicular to the first preferred direction

Methodology Applied

Scientific EffectOptical anisotropy: Anisotropy

Implementation Method 3

at least one first light-conductance-increasing element having a plurality of diffractively or refractively beam-deflecting structures

Methodology Applied

Scientific EffectDiffraction: Diffraction

Implementation Method 4

at least one first light-conductance-increasing element having a plurality of diffractively or refractively beam-deflecting structures

Methodology Applied

Scientific EffectRefraction: Refraction

Data Source

PatentUS8068279B2Optical system of an illumination device of a projection exposure apparatus

Publication Date: 2011.11.29 CARL ZEISS SMT GMBH

AI summary

The disclosure relates to an optical system of an illumination device of a microlithographic projection exposure apparatus, including at least one first light-conductance-increasing element having a plurality of diffractively or refractively beam-deflecting structures extending in a common first preferred direction the light-conductance-increasing element having an optically uniaxial crystal material in such a way that the optical crystal axis of the crystal material is substantially parallel or substantially perpendicular to the first preferred direction.