Illumination System Polarization Compensation for Microlithography

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Solution Overview

Problem

Microlithographic projection exposure systems face issues with unwanted changes in polarization distribution due to stress birefringence from optical components, leading to defects in imaging lattice structures.

Innovation Solution

An illumination system with a first and second polarization-influencing optical element, where the second element causes a 90° rotation of the polarization direction, compensating for interference effects by interchanging the phase differences of light components, ensuring a consistent polarization distribution across the reticle field.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If conventional optical components are used in the illumination system, then the system structure is simple, but unwanted polarization changes occur due to stress birefringence and dielectric layer effects

Engineering Contradiction:

Improveillumination system structureVSAvoidpolarization distribution consistency

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

A polarization-influencing optical element is introduced as an intermediary component between the light source and the reticle. This element actively compensates for unwanted polarization changes by introducing equal and opposite polarization effects, thereby maintaining consistent polarization distribution across the reticle field while accounting for stress birefringence and dielectric layer influences from conventional optical components

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If polarization-influencing optical elements are added to compensate for polarization changes, then polarization distribution consistency is improved, but device complexity increases

Engineering Contradiction:

Improvepolarization distribution consistencyVSAvoidillumination system structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The polarization-influencing optical element is designed to introduce specific polarization parameter changes (phase shifts and rotation angles) that precisely counterbalance the unwanted polarization effects from conventional components. By carefully controlling these parameter changes, the system achieves consistent polarization distribution while minimizing the complexity increase from adding only one specialized element

Inventive Principle:

Principle #35Parameter changes

3Reliability

If the second polarization-influencing optical element rotates polarization direction through 90°, then interference effects are compensated, but manufacturing precision requirements increase

Engineering Contradiction:

Improveinterference compensation effectivenessVSAvoidpolarization rotation accuracy

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The 90° polarization rotation introduced by the second polarization-influencing optical element converts harmful interference effects into beneficial compensation effects. The element is specifically designed to rotate the polarization direction by exactly 90°, which transforms the phase differences between light components in a way that cancels out interference influences from optical components, thereby improving imaging quality

Inventive Principle:

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

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 solution maintains consistent imaging contrast and defect-free imaging by compensating for interference influences from optical components, achieving a desired polarization distribution across the entire reticle field.

Implementation Method 1

unwanted changes in the state of polarization from a desired polarization distribution in the reticle field. These unwanted changes can result from, for example, stress birefringence induced by holder components in the material of the optical components

Methodology Applied

Scientific EffectStress birefringence: Birefringence

Implementation Method 2

the second polarization-influencing optical element causing an effective rotation of the preferred polarization direction through 90° over its optically effective surface

Methodology Applied

Scientific EffectPolarization rotation: Polarisation

Data Source

PatentUS8035803B2Subsystem of an illumination system of a microlithographic projection exposure apparatus

Publication Date: 2011.10.11 CARL ZEISS SMT GMBH

AI summary

In general, in one aspect, the disclosure features an illumination system for a microlithographic projection exposure apparatus configured so that during operation the illumination system illuminates a reticle plane of the microlithographic projection exposure apparatus with light of a desired polarization distribution. The illumination system includes a first polarization-influencing optical element and a second polarization-influencing optical element. During operation the first polarization-influencing optical element converts a first polarization distribution produced by a light source unit into a second polarization distribution which is different from the first polarization distribution. The second polarization-influencing optical element converts the second polarization distribution into a third polarization distribution corresponding to the desired polarization distribution, the second polarization-influencing optical element causing an effective rotation of the preferred polarization direction through 90° over its optically effective surface.