Angle-Selective Filter for Projection Exposure Numerical Aperture Control

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Solution Overview

Problem

Microlithographic projection exposure systems face challenges in setting desired image-side numerical aperture values without limitations from conventional mechanical aperture stops and in maintaining imaging quality across various illumination settings and pattern types, especially due to non-uniform heating of optical components.

Innovation Solution

An angle-selective filter arrangement is positioned at or near the field surface of the projection objective, optically downstream of the pattern, to control the image-side numerical aperture by blocking unwanted radiation based on angle of incidence, reducing sensitivity to heating effects and allowing for faithful imaging of diverse mask structures.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a mechanical aperture stop is used to control the effective numerical aperture, then the numerical aperture can be set for specific applications, but the installation space is constrained and optical surfaces cannot be positioned at the pupil surface

Engineering Contradiction:

Improveeffective numerical aperture settingVSAvoidinstallation space constraint

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent replaces the mechanical aperture stop with an angle-selective filter arrangement that uses optical filtering based on the angle of incidence of radiation. This substitution eliminates the need for mechanical components at the pupil surface, allowing optical surfaces to be positioned without space constraints while maintaining control over the effective numerical aperture through angular selective filtering.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The angle-selective filter arrangement acts as an intermediary between the radiation source and the projection objective. By filtering radiation based on its angle of incidence, it controls the effective numerical aperture without requiring direct mechanical intervention at the pupil surface, thus resolving the space constraint issue.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Manufacturing precision

If the effective numerical aperture is reduced to increase depth of focus for isolated features, then imaging quality of isolated features improves, but resolution of densely packed line patterns deteriorates

Engineering Contradiction:

Improvedepth of focusVSAvoidresolution

Core Design Contradiction:

Manufacturing precisionVSMeasurement precision

Solution Approach 1:

The patent employs a variable angle-selective filter arrangement that can dynamically adjust the cut-off angle of incidence. This dynamic adjustment allows the effective numerical aperture to be changed during operation, enabling optimization of the balance between depth of focus and resolution for different pattern types without requiring physical reconfiguration of the system.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the parameter of angle of incidence cut-off in the filter arrangement to control the effective numerical aperture. By varying this parameter, the system can adapt to different imaging requirements - using higher NA for line patterns and lower NA for isolated features - thereby resolving the contradiction between resolution and depth of focus.

Inventive Principle:

Principle #35Parameter changes

3Adaptability or versatility

If mechanical aperture stops are used to control numerical aperture, then aperture control is achieved, but pupil filter elements and manipulation devices cannot be positioned close to the pupil surface

Engineering Contradiction:

Improveaperture controlVSAvoidpositioning of optical elements

Core Design Contradiction:

Adaptability or versatilityVSEase of operation

Solution Approach 1:

The patent substitutes the mechanical aperture stop with an angle-selective filter that operates through optical filtering rather than mechanical blocking. This eliminates the mechanical component that would otherwise occupy space at the pupil surface, allowing pupil filter elements and manipulation devices to be positioned close to the pupil surface for optimal performance.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 enables flexible setting of image-side numerical aperture values without mechanical aperture stops, stabilizes imaging under different illumination conditions, and reduces sensitivity to optical component heating, ensuring high-quality imaging of various pattern types.

Implementation Method 1

Methodology Applied

Scientific EffectAngle-selective filtering: Filter (optical)

Data Source

PatentUS9146475B2Projection exposure system and projection exposure method

Publication Date: 2015.09.29 CARL ZEISS SMT GMBH

AI summary

A projection exposure system includes an illumination system configured to illuminate a mask with radiation. The projection exposure system also includes a projection objective configured to project an image of a pattern of the mask onto a radiation-sensitive substrate. The projection exposure system further includes an angle-selective filter arrangement arranged at or close to a field surface of the projection objective in a projection beam path optically downstream of the object surface. The angle-selective filter arrangement is effective to filter radiation incident on the filter arrangement according to an angle-selective filter function.