Overlay Correction Using Stack Difference Fit

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Solution Overview

Problem

Existing metrology techniques for overlay measurement in lithographic processes are inaccurate due to structural asymmetry and stack differences between periodic structures, which are not accounted for, leading to incorrect overlay measurements.

Innovation Solution

A method that involves obtaining a fit of data for overlay as a function of stack difference parameters to differentiate measurement recipes, calculate corrected overlay values, or indicate when overlay measurements should be used or modified, using hardware computers to account for structural asymmetry and stack differences.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If dark field scatterometry is used to measure overlay on smaller targets, then measurement capability is improved, but measurement accuracy deteriorates due to structural asymmetry and stack differences

Engineering Contradiction:

Improvemeasurement capabilityVSAvoidoverlay measurement accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent replaces the conventional dark field scatterometry measurement approach with a new method that uses asymmetry parameter analysis. Instead of directly measuring overlay using traditional scatterometry on small targets, the invention introduces a different measurement paradigm that calculates asymmetry parameters from diffraction intensities and uses these to determine overlay, thereby avoiding the accuracy degradation caused by structural asymmetry and stack differences

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the measurement parameter from direct overlay measurement to asymmetry parameter measurement. By measuring asymmetry parameters (which are less sensitive to structural variations) and then deriving overlay information from these parameters, the system maintains measurement capability on small targets while improving accuracy. This parameter transformation allows the measurement to be robust against stack differences and structural asymmetries

Inventive Principle:

Principle #35Parameter changes

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 the accuracy of overlay measurements by correcting for structural asymmetry and stack differences, leading to more reliable process control and design in lithographic processes.

Implementation Method 1

dark field scatterometry in which the zeroth order of diffraction (corresponding to a specular reflection) is blocked, and only higher orders processed

Methodology Applied

Scientific EffectDiffraction: Diffraction

Implementation Method 2

measure one or more properties of the redirected (e.g., scattered) radiation

Methodology Applied

Scientific EffectScattering: Scattering

Data Source

PatentUS10635004B2Correction using stack difference

Publication Date: 2020.04.28 ASML NETHERLANDS BV

AI summary

A method including obtaining a fit of data for overlay of a metrology target for a patterning process as a function of a stack difference parameter of the metrology target; and using, by a hardware computer, a slope of the fit (i) to differentiate a metrology target measurement recipe from another metrology target measurement recipe, or (ii) calculate a corrected value of overlay, or (iii) to indicate that an overlay measurement value obtained using the metrology target should be used, or not be used, to configure or modify an aspect of the patterning process, or (iv) any combination selected from (i)-(iii).