Lithography Focus Metrology via Non-Telecentric Illumination

Solution Overview

Problem

Current focus metrology techniques in lithographic processes, particularly in EUV lithography, face challenges due to the need for sub-resolution features and large pitch grating structures, which are difficult to create and result in weak diffraction efficiency, making it hard to accurately measure focus performance without violating design rules.

Innovation Solution

The method involves printing structures with different non-telecentricities using a reflective patterning device, measuring focus-dependent positional shifts between these structures, and deriving focus performance based on these measurements, allowing for focus monitoring without the need for sub-resolution features.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If sub-resolution features and large pitch grating structures are used for focus metrology, then focus measurement capability is improved, but design rules are violated and manufacturing complexity increases

Engineering Contradiction:

Improvefocus measurement capabilityVSAvoidfeature creation difficulty

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The patent changes the illumination parameters (non-telecentricity angles) to create focus-dependent positional shifts in printed structures. By varying the illumination angle rather than relying on sub-resolution features, the method achieves focus measurement capability while using manufacturable feature sizes that comply with design rules

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the mechanical/physical constraint of using sub-resolution features with an optical approach using non-telecentric illumination. Instead of relying on feature geometry to create focus sensitivity, the method uses illumination geometry to induce measurable positional shifts that depend on focus conditions

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If sub-resolution features are used for focus metrology, then focus measurement is enabled, but diffraction efficiency decreases making measurement difficult

Engineering Contradiction:

Improvefocus measurement accuracyVSAvoiddiffraction efficiency

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent changes the illumination parameters (non-telecentricity angles) to create focus-dependent positional shifts in printed structures. By varying the illumination angle rather than relying on sub-resolution features, the method achieves focus measurement capability while using manufacturable feature sizes that comply with design rules

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the mechanical/physical constraint of using sub-resolution features with an optical approach using non-telecentric illumination. Instead of relying on feature geometry to create focus sensitivity, the method uses illumination geometry to induce measurable positional shifts that depend on focus conditions

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If large pitch grating structures are used for focus metrology, then focus measurement capability is improved, but device complexity and design rule violations increase

Engineering Contradiction:

Improvefocus measurement capabilityVSAvoidstructure design complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent changes the illumination parameters (non-telecentricity angles) to create focus-dependent positional shifts in printed structures. By varying the illumination angle rather than relying on sub-resolution features, the method achieves focus measurement capability while using manufacturable feature sizes that comply with design rules

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the mechanical/physical constraint of using sub-resolution features with an optical approach using non-telecentric illumination. Instead of relying on feature geometry to create focus sensitivity, the method uses illumination geometry to induce measurable positional shifts that depend on focus conditions

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 approach enables accurate and efficient focus monitoring in lithographic processes, improving focus consistency and reducing the complexity of feature design, while adhering to semiconductor manufacturing design rules.

Implementation Method 1

printing one or more printed structures on a substrate using the lithographic apparatus, said one or more printed structures comprising first printed structures and second printed structures, said first printed structures being printed by illumination having a first non-telecentricity and said second printed structures being printed by illumination having a second non-telecentricity

Methodology Applied

Scientific EffectNon-telecentric illumination:

Implementation Method 2

measuring a focus dependent parameter related to a focus-dependent positional shift between said one or more first printed structures and said one or more second printed structures on said substrate

Methodology Applied

Scientific EffectPositional shift measurement:

Data Source

PatentUS11314174B2Methods and patterning devices and apparatuses for measuring focus performance of a lithographic apparatus, device manufacturing method

Publication Date: 2022.04.26 ASML NETHERLANDS BV

AI summary

Disclosed is a method of measuring focus performance of a lithographic apparatus, and corresponding patterning device and lithographic apparatus. The method comprises using the lithographic apparatus to print one or more first printed structures and second printed structures. The first printed structures are printed by illumination having a first non-telecentricity and the second printed structures being printed by illumination having a second non-telecentricity, different to said first non-telecentricity. A focus dependent parameter related to a focus-dependent positional shift between the first printed structures and the second printed structures on said substrate is measured and a measurement of focus performance based at least in part on the focus dependent parameter is derived therefrom.