Metrology Target Design for Inter-Cell Process Variation Correction

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Solution Overview

Problem

Existing metrology methods face inaccuracies due to inter-cell process variations in overlay scatterometry, which are not effectively addressed, leading to measurement errors and difficulties in identifying and correcting these variations.

Innovation Solution

A metrology method and target design that utilize at least three target cells with different designed misalignments to estimate and reduce measurement inaccuracies by deriving the dependency of inaccuracy on misalignments, incorporating scatterometry overlay targets with opposite designed misalignments to isolate and correct inter-cell process variations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If overlay measurements are performed using conventional SCOL targets with limited target cells, then measurement process is simple, but measurement precision deteriorates due to inter-cell process variations

Engineering Contradiction:

Improveoverlay measurement accuracyVSAvoidtarget design complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The metrology target is divided into multiple target cells (at least three), each with different designed misalignments. This segmentation allows independent measurement of each cell's overlay characteristics, enabling the system to identify and compensate for inter-cell process variations by comparing measurements across cells with different misalignment values.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent varies the designed misalignment parameter across different target cells. By creating cells with different misalignment values (e.g., 0 nm, +10 nm, -10 nm), the measurement system can derive the dependency of measured inaccuracy on designed misalignment and eliminate systematic errors through mathematical correction.

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If conventional overlay measurement methods are used, then measurement process is straightforward, but manufacturing precision deteriorates due to uncorrected inter-cell process variations

Engineering Contradiction:

Improveoverlay alignment accuracyVSAvoidinter-cell process variation detection

Core Design Contradiction:

Manufacturing precisionVSDifficulty of detecting and measuring

Solution Approach 1:

The patent implements a feedback mechanism where overlay measurements from multiple target cells are used to calculate inter-cell process variations. These calculated variations are then fed back to correct the overlay measurements, creating a closed-loop system that continuously improves measurement accuracy by compensating for identified process variations.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent uses target cells with different designed misalignments as intermediaries to detect inter-cell process variations. By measuring overlay at multiple known misalignment points, the system can derive the relationship between misalignment and measurement inaccuracy, using this relationship as an intermediary to correct actual overlay measurements.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If at least three target cells with different designed misalignments are used, then inter-cell process variations can be estimated and corrected, but device complexity increases

Engineering Contradiction:

Improvemeasurement reliabilityVSAvoidmetrology target structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent designs a universal metrology target structure that can simultaneously serve multiple measurement functions. The same target containing multiple cells with different misalignments is used to measure overlay at different points, characterize inter-cell variations, and provide correction data, eliminating the need for separate targets for each measurement objective.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 measurement inaccuracies by identifying and correcting inter-cell process variations, improving the accuracy of overlay measurements and optimizing target designs and algorithms.

Implementation Method 1

Diffraction signals from the SCOL targets are measured at the pupil plane to yield overlay measurements between the layers of in which the periodic structures are produced.

Methodology Applied

Scientific EffectDiffraction: Diffraction

Data Source

PatentUS10415963B2Estimating and eliminating inter-cell process variation inaccuracy

Publication Date: 2019.09.17 KLA CORP

AI summary

Metrology methods and targets are provided, for estimating inter-cell process variation by deriving, from overlay measurements of at least three target cells having different designed misalignments, a dependency of a measured inaccuracy on the designed misalignments (each designed misalignment is between at least two overlapping periodic structures in the respective target cell). Inaccuracies which are related to the designed misalignments are reduced, process variation sources are detected and targets and measurement algorithms are optimized according to the derived dependency.