Darkfield And Phase Contrast Metrology for Low-Contrast EUV Marks

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Solution Overview

Problem

Conventional inspection tools struggle to detect low-contrast EUV fiducial marks and alignment marks due to degradation concerns with actinic inspection, leading to increased wafer/lot cycle times and mask lifetime issues in semiconductor manufacturing.

Innovation Solution

Implementing darkfield and phase contrast optics in existing brightfield inspection tools to enhance the detection of small phase defects and low-contrast alignment marks using a 193 nm laser, combined with laser interferometry for precise positioning.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If actinic inspection is used to detect defects in EUV blanks, then measurement precision is improved, but mask lifetime is reduced

Engineering Contradiction:

Improvedefect detection precisionVSAvoidmask lifetime

Core Design Contradiction:

Measurement precisionVSDuration of action of stationary object

Solution Approach 1:

The patent changes the inspection wavelength parameter from actinic (13.5 nm EUV) to non-actinic (193 nm deep ultraviolet), allowing defect detection without the harmful effects of actinic radiation on mask lifetime while maintaining measurement capability through adapted optical systems

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If broadband brightfield imaging is used for inspection, then device complexity is reduced, but measurement precision deteriorates for small features

Engineering Contradiction:

Improveinspection system complexityVSAvoidsmall feature detection precision

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent applies different illumination modes (darkfield and phase contrast) to different inspection needs within the same system, using darkfield for particle detection and phase contrast for alignment mark detection, optimizing local inspection quality without requiring multiple separate systems

Inventive Principle:

Principle #3Local quality

3Manufacturing precision

If the number of metrology steps is increased to maintain overlay specifications, then manufacturing precision is improved, but productivity is reduced

Engineering Contradiction:

Improveoverlay precisionVSAvoidwafer/lot cycle time

Core Design Contradiction:

Manufacturing precisionVSProductivity

Solution Approach 1:

The patent combines multiple inspection functions (defect detection, alignment mark detection, and registration metrology) into a single integrated inspection system, eliminating the need for separate metrology steps and reducing overall cycle time while maintaining precision requirements

Inventive Principle:

Principle #5Merging (Combining)

4Duration of action of stationary object

If 193 nm optical inspection tools are used, then mask lifetime is preserved, but measurement precision deteriorates for low-contrast features

Engineering Contradiction:

Improvemask lifetimeVSAvoidlow-contrast feature detection precision

Core Design Contradiction:

Duration of action of stationary objectVSMeasurement precision

Solution Approach 1:

The patent changes the illumination parameters from broadband brightfield to darkfield and phase contrast modes at 193 nm wavelength, enhancing the contrast mechanism to make low-contrast alignment marks and phase defects visible without requiring actinic wavelengths that would damage the mask

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces phase contrast optical components as intermediaries that convert phase shifts in the light wavefront caused by transparent or low-contrast features into intensity variations, making these features detectable by the sensor while using non-damaging 193 nm illumination

Inventive Principle:

Principle #24Intermediary (Mediator)

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

Enhances the capability to detect smaller phase defects and alignment marks on EUV masks, reducing cycle times and mask degradation while maintaining precision in semiconductor manufacturing.

Implementation Method 1

a first optical train configured with phase contrast optical components to focus phase contrast illumination toward one or more features of the semiconductor specimen

Methodology Applied

Scientific EffectPhase contrast:

Implementation Method 2

a second optical train configured with darkfield optical components to focus darkfield illumination toward the one or more features of the semiconductor specimen

Methodology Applied

Scientific EffectDarkfield illumination:

Implementation Method 3

providing position measurements using a laser interferometer

Methodology Applied

Scientific EffectLaser interferometry:

Data Source

PatentUS12567138B2Registration metrology tool using darkfield and phase contrast imaging

Publication Date: 2026.03.03 INTEL CORP

AI summary

The present disclosure is directed to an inspection system for registration metrology and defect detection using darkfield and phase contrast imaging optical systems. The present system includes a transmitted light mode and diffracted light mode to enable imaging of low contrast features on blank EUV masks and semiconductor wafers. In an aspect, this system combines the optics for darkfield and phase contrast imaging, and may also include the optics for brightfield imaging, to provide analyzed data on registration errors and surface defects.