Lithographic Projection Lens Wavefront Aberration Correction

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Solution Overview

Problem

Conventional methods for reducing wave front aberration in lithographic projection systems are inadequate in addressing higher-order aberration errors, leading to pattern errors and reduced throughput due to residual thermal deformations caused by radiation absorption.

Innovation Solution

A method that involves obtaining information on the spatial distribution of radiant intensity in the projection system's pupil, selecting a threshold intensity, and applying adjustments only to areas with local intensity above this threshold to minimize wave front aberration, using a limited set of grid points for least square fitting to reduce higher-order aberrations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If conventional lens manipulators are used to reduce wave aberration, then lower order aberrations can be corrected, but higher order aberration errors remain uncorrected

Engineering Contradiction:

Improvewave aberration correctionVSAvoidaberration correction capability

Core Design Contradiction:

Manufacturing precisionVSAdaptability or versatility

Solution Approach 1:

The patent segments the wave aberration correction problem into different spatial zones within the pupil. By dividing the pupil into multiple zones and applying zone-specific adjustments to optical elements, the system can address both lower and higher order aberrations that were previously uncorrectable with conventional uniform correction methods.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent applies local quality by making the correction approach spatially varying rather than uniform. Different regions of the pupil receive different adjustment treatments based on their specific aberration characteristics, allowing higher order aberrations in certain zones to be corrected while maintaining correction of lower order aberrations in other zones.

Inventive Principle:

Principle #3Local quality

2Productivity

If radiation power is increased to enhance throughput, then more wafers can be exposed per unit time, but thermal deformations and wave aberration errors increase

Engineering Contradiction:

ImprovethroughputVSAvoidpattern accuracy

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The patent applies preliminary anti-action by measuring and compensating for wave aberrations before they significantly degrade pattern accuracy. The system continuously monitors aberrations and applies corrective adjustments in advance, preventing the accumulation of thermal deformation effects even during high-power operation that maximizes throughput.

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

The patent implements a feedback mechanism where wave aberrations are measured during exposure and the measured data is used to calculate and apply real-time adjustments to optical elements. This closed-loop control allows the system to maintain pattern accuracy despite high radiation power by continuously counteracting thermal deformations as they occur.

Inventive Principle:

Principle #23Feedback

3Manufacturing precision

If lens element adjustments are applied to correct wave aberration, then optical performance improves, but device complexity increases

Engineering Contradiction:

Improveoptical wave accuracyVSAvoidlens manipulator system

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent applies partial action by focusing adjustments on specific optical elements and pupil zones that have the greatest impact on correcting higher order aberrations. Rather than adjusting all lens elements uniformly, the system selectively applies corrections where they are most needed, reducing the overall complexity while maintaining correction effectiveness.

Inventive Principle:

Principle #16Partial or excessive action

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 effectively reduces thermally induced residual wave front errors by a factor of two, improving pattern accuracy and throughput in high-power lithographic processes.

Implementation Method 1

The beam of radiation propagating through the projection lens causes a local, generally non-uniform heating of optical elements

Methodology Applied

Scientific EffectAbsorption (EM radiation): Absorption (EM radiation)

Implementation Method 2

Such a heating may cause thermal deformations of the projection lens elements and hence, an optical wave aberration error

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS7580113B2Method of reducing a wave front aberration, and computer program product

Publication Date: 2009.08.25 ASML NETHERLANDS BV

AI summary

A method of reducing a wave front aberration is provided for a lithographic process whereby the reducing is based on the selected pattern to be printed and the selected illumination mode used for exposure. Wave front aberrations of a projection system of a lithographic apparatus are measured and reduced by calculating adjustments of optical elements of the projection system and applying the calculated adjustments to the projection system. The calculation of adjustments is based on information on a spatial distribution of radiant intensity in a pupil of the projection system as present during exposing the radiation sensitive layer, and is limited to aberrations in projection lens pupil areas of relative high radiant flux.