Overlay Reference Wavelength Selection for Wafer Alignment Accuracy

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Solution Overview

Problem

Existing overlay measurement processes in semiconductor manufacturing face challenges due to variations in photolithography and overlay measurement processes, leading to inconsistent overlay measurement values across different locations on a wafer, which affect the accuracy of alignment between upper and lower patterns.

Innovation Solution

A method to determine an overlay reference wavelength by filtering first measurement wavelengths based on first setup values proportional to target sigma values and selecting second measurement wavelengths based on inverse proportional stack sensitivity values, ensuring accurate reflection of measurement distribution and alignment between overlay keys.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of stationary object

If overlay measurement is performed at multiple locations on a wafer, then comprehensive coverage of the wafer surface is achieved, but measurement values vary due to process variations

Engineering Contradiction:

Improvewafer surface coverageVSAvoidoverlay measurement consistency

Core Design Contradiction:

Area of stationary objectVSMeasurement precision

Solution Approach 1:

The patent changes the parameter of measurement wavelength to optimize overlay measurement. By selecting a reference wavelength from multiple candidate wavelengths based on stack sensitivity analysis, the measurement system adapts to different wafer conditions and pattern structures, thereby improving measurement consistency across the wafer surface while maintaining comprehensive coverage

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent performs preliminary analysis of stack sensitivity at multiple wavelengths before conducting the actual overlay measurement. This preliminary action involves calculating sensitivity values for different wavelengths and selecting the optimal reference wavelength in advance, which prevents measurement variations caused by poor wavelength selection and ensures consistent results across different wafer locations

Inventive Principle:

Principle #10Preliminary action

2Ease of operation

If a fixed reference wavelength is used for overlay measurement, then the measurement process is simple, but it cannot account for variations in measurement distribution across the wafer

Engineering Contradiction:

Improvemeasurement process simplicityVSAvoidalignment prediction accuracy

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The patent introduces dynamic selection of the reference wavelength based on stack sensitivity analysis. Instead of using a fixed wavelength, the system dynamically determines the optimal reference wavelength by evaluating sensitivity values at multiple wavelengths and selecting the one that best reflects the measurement distribution. This dynamic approach maintains operational simplicity while significantly improving alignment prediction accuracy

Inventive Principle:

Principle #15Dynamics

3Measurement precision

If multiple wavelengths are evaluated to determine the optimal reference wavelength, then measurement accuracy is improved, but the process complexity increases

Engineering Contradiction:

Improveoverlay measurement accuracyVSAvoidwavelength selection process

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent replaces complex physical trial-and-error wavelength selection with a computational approach. By using stack sensitivity calculations and mathematical analysis to determine the optimal reference wavelength, the system eliminates the need for iterative physical measurements at different wavelengths. This substitution of computational methods for physical experimentation reduces process complexity while maintaining high measurement accuracy

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS12572084B2Methods of determining overlayer reference wavelength

Publication Date: 2026.03.10 SAMSUNG ELECTRONICS CO LTD

AI summary

A method of determining an overlay reference wavelength, the method comprising: forming a pattern structure including a wafer and overlay keys on the wafer; obtaining first setup values of the pattern structure for first measurement wavelengths, respectively; selecting second measurement wavelengths among the first measurement wavelengths by filtering the first measurement wavelengths based on the first setup values; obtaining second setup values of the pattern structure for the second measurement wavelengths, respectively; and selecting a reference wavelength among the second measurement wavelengths based on the second setup values, wherein each of the first setup values is proportional to a deviation value of target sigma values of the overlay keys at a respective first measurement wavelength, and wherein each of the second setup values is inversely proportional to a deviation value of stack sensitivity values of the overlay keys at a respective second measurement wavelength.