Charged Particle Beam Focusing for Non-Planar Surface Imaging

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Solution Overview

Problem

Imaging non-planar surfaces with charged particle beam devices is challenging due to varying distances from the objective lens, leading to measurement errors and reduced accuracy, especially for large-area substrates used in display manufacturing.

Innovation Solution

A method of calibrating the charged particle beam device by determining focal subranges and adjusting the focusing strength of the objective lens based on surface levels, combined with autofocusing processes to maintain accurate imaging across varying distances.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the sample surface is moved into focus by stage movement, then imaging accuracy is improved, but imaging speed deteriorates

Engineering Contradiction:

Improveimaging accuracyVSAvoidimaging speed

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

The patent implements dynamic focusing by adjusting the objective lens focusing strength based on the vertical position of different surface regions rather than moving the stage. The system determines the vertical position of surface regions and automatically adjusts the focusing strength to maintain optimal focus across non-planar surfaces, enabling both high accuracy and fast imaging without mechanical stage movements for focusing.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent replaces the mechanical stage movement mechanism with an optical/electrical focusing adjustment mechanism. Instead of physically moving the stage to bring different surface regions into focus, the system uses electromagnetic lens focusing strength adjustment to achieve the same effect, thereby eliminating the speed-accuracy trade-off associated with mechanical positioning.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If refocusing is performed on non-planar surfaces, then imaging accuracy is improved, but measurement errors are introduced

Engineering Contradiction:

Improveimaging accuracyVSAvoidmeasurement accuracy

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent implements a feedback mechanism where the vertical position of surface regions is determined, and this information is used to adjust the focusing strength of the objective lens. The system continuously monitors surface topography and dynamically adjusts focusing parameters to maintain accurate imaging across varying surface heights, preventing measurement errors that would otherwise be introduced by static focusing settings.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent changes the focusing parameter (focusing strength of the objective lens) based on the vertical position of different surface regions. By dynamically adjusting this parameter according to the actual surface topography, the system maintains optimal focus conditions across non-planar surfaces without introducing measurement errors, thereby resolving the contradiction between imaging accuracy and measurement reliability.

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If charged particle beam is used for imaging, then resolution is improved, but depth of field limitation causes focusing issues on non-planar surfaces

Engineering Contradiction:

ImproveresolutionVSAvoiddepth of field

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent makes the focusing system dynamic by automatically adjusting the objective lens focusing strength based on the determined vertical positions of different surface regions. This dynamic adaptation allows the high-resolution charged particle beam to maintain focus across non-planar surfaces with varying depths, effectively extending the usable depth of field while preserving the inherent high resolution of the charged particle beam imaging capability.

Inventive Principle:

Principle #15Dynamics

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

Enables high-accuracy, fast imaging of non-planar surfaces with predetermined measurement accuracy, enhancing throughput and consistency in metrology and defect inspection.

Implementation Method 1

determining a first focusing strength of an objective lens of the charged particle beam device, the first focusing strength being adapted to focus a charged particle beam on a first surface region of the sample

Methodology Applied

Scientific EffectElectromagnetic focusing: Electromagnet

Data Source

PatentUS12562336B2Method of imaging a sample with a charged particle beam device, method of calibrating a charged particle beam device, and charged particle beam device

Publication Date: 2026.02.24 APPLIED MATERIALS INC

AI summary

A method of imaging a sample with a charged particle beam device, comprising: determining a first focusing strength of an objective lens of the charged particle beam device, the first focusing strength being adapted to focus a charged particle beam on a first surface region of the sample; determining a first focal subrange of a plurality of focal subranges such that the first focusing strength is within the first focal subrange, wherein the plurality of focal subranges is associated with a set of values of a calibration parameter; determining a first value of the calibration parameter, the first value being associated with the first focal subrange; and imaging the first surface region with the first value.