Metrology Target with Orthogonal Polarization Interference

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Solution Overview

Problem

Current metrology techniques in lithographic processes face challenges in achieving high throughput, flexibility, and accuracy, particularly when measuring small target structures using dark-field image-based techniques, and struggle with robustness to process variations and structural asymmetry.

Innovation Solution

A method and apparatus that utilize two coherent, orthogonally polarized radiation beams to illuminate periodic structures on a metrology target, with the diffracted radiation being combined to interfere and detected, allowing for the determination of parameters such as overlay and structural asymmetry, while optimizing the intensity ratio and phase difference between the beams to enhance measurement performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional single-beam metrology techniques are used, then the measurement process is simple, but measurement accuracy and robustness to process variations are insufficient

Engineering Contradiction:

Improvemeasurement accuracyVSAvoidmetrology system complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The metrology target is divided into multiple periodic structures with different orientations (first periodic structures and second periodic structures). Each structure type is illuminated by a corresponding radiation beam with specific polarization, allowing independent optimization of measurement parameters for each structure while maintaining overall system coherence.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces a polarization dimension to the measurement system by using radiation beams with different polarizations (first polarization and second polarization, which are different from each other). This adds a new degree of freedom that enables enhanced measurement capability without increasing spatial complexity.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Productivity

If dark-field image-based techniques are used for small target structures, then throughput is improved, but accuracy and robustness to structural asymmetry deteriorate

Engineering Contradiction:

ImprovethroughputVSAvoidmeasurement accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The patent changes the polarization parameter of the incident radiation beams to optimize the interaction with different periodic structures. By adjusting polarization states, the system maintains high throughput from dark-field imaging while improving accuracy through enhanced contrast and reduced sensitivity to structural asymmetries.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If multiple periodic structures with different orientations are measured, then measurement robustness to process variations is improved, but the complexity of combining and analyzing data increases

Engineering Contradiction:

Improverobustness to process variationsVSAvoiddata processing complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent employs periodic structures with different orientations (asymmetric arrangements) to measure various parameters. The first periodic structures and second periodic structures are oriented differently, allowing the system to detect and compensate for process variations by comparing measurements from these asymmetric structures.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

Multiple periodic structures serve as copies of each other with different orientations. These replicated structures provide redundant measurement information that can be combined to improve robustness, while the systematic variation in orientation allows for separation of measurement signals through polarization filtering.

Inventive Principle:

Principle #26Copying

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 improves measurement accuracy, precision, and robustness to process variations, enabling better detection of small target structures and larger application range with optimized metrology target designs.

Implementation Method 1

illuminating at least a first periodic structure of a metrology target with a first radiation beam having a first polarization; illuminating at least a second periodic structure of the metrology target with a second radiation beam having a second different polarization; combining radiation diffracted from the first periodic structure with radiation diffracted from the second periodic structure to cause interference

Methodology Applied

Scientific EffectDiffraction: Diffraction

Implementation Method 2

combining radiation diffracted from the first periodic structure with radiation diffracted from the second periodic structure to cause interference; detecting the combined radiation using a detector

Methodology Applied

Scientific EffectInterference: Interference

Implementation Method 3

Methodology Applied

Scientific EffectPolarization: Polarisation

Data Source

PatentUS10379445B2Metrology method, target and substrate

Publication Date: 2019.08.13 ASML NETHERLANDS BV

AI summary

A method, involving illuminating at least a first periodic structure of a metrology target with a first radiation beam having a first polarization, illuminating at least a second periodic structure of the metrology target with a second radiation beam having a second different polarization, combining radiation diffracted from the first periodic structure with radiation diffracted from the second periodic structure to cause interference, detecting the combined radiation using a detector, and determining a parameter of interest from the detected combined radiation.