SEM Working Distance Measurement Using Laser Interferometry

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Solution Overview

Problem

Existing SEM instruments struggle to accurately measure the working distance between a charged particle column and non-conductive samples, such as dielectric materials, using capacitive sensors, which affects imaging precision.

Innovation Solution

Employing a laser beam and mirrors to direct electromagnetic radiation to a close proximity on the sample, utilizing interferometry techniques to determine the working distance, enabling precise measurement on both conductive and non-conductive samples.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If capacitive sensors are used to measure working distance, then measurement is feasible for conductive samples, but measurement fails for non-conductive (dielectric) samples

Engineering Contradiction:

Improvesample type compatibilityVSAvoidworking distance measurement accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent replaces the capacitive sensor (electrical measurement system) with an optical measurement system using a laser beam and detector. This substitution allows working distance measurement for both conductive and non-conductive samples by using light reflection instead of electrical capacitance, thereby resolving the limitation with dielectric samples while maintaining measurement precision

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The optical measurement system is designed to universally measure working distance for all sample types (conductive, non-conductive, dielectric) by using a laser beam that can reflect off any sample surface. This universal approach eliminates the need for different measurement methods for different sample types, achieving both versatility and precision

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Measurement precision

If the laser beam is directed to a position close to the region being imaged, then measurement accuracy improves, but the risk of interfering with the charged particle beam increases

Engineering Contradiction:

Improveworking distance measurement accuracyVSAvoidcharged particle beam interference

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent positions the laser beam and detector in a different spatial dimension (above and below the sample along the vertical axis) rather than in the horizontal plane where the charged particle beam travels. This dimensional separation allows the laser to measure working distance at a position very close to the imaged region without interfering with the charged particle beam path, achieving both high measurement precision and avoiding harmful interference

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

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 accurate and real-time adjustment of the working distance, maintaining imaging precision across different regions of the sample, even with warpage, for both conductive and non-conductive samples.

Implementation Method 1

where interferometry techniques can be used to determine the working distance between the sample and charged particle column

Methodology Applied

Scientific EffectInterferometry: Interference

Implementation Method 2

Some embodiments employ a laser and multiple mirrors to direct a laser beam generated by the laser to a position on the sample

Methodology Applied

Scientific EffectLaser: Laser

Implementation Method 3

one or more mirrors disposed within the vacuum chamber and positioned to direct the electromagnetic radiation generated by the optical distance measurement system to a measured location on the sample

Methodology Applied

Scientific EffectReflection: Reflection

Data Source

PatentUS12518945B2Using laser beam for SEM base tools, working distance measurement and control working distance SEM to target

Publication Date: 2026.01.06 APPL MATERIALS ISRAEL LTD

AI summary

A system for processing a sample comprising: a vacuum chamber having a window formed along one of its walls; a sample support configured to hold a sample within the vacuum chamber during a sample processing operation and move the substrate within the vacuum chamber along the X, Y and Z axes; a charged particle beam column configured to direct a charged particle beam into the vacuum chamber and focus the beam to collide with a region of interest on the sample; an optical distance measurement device configured to generate and direct electromagnetic radiation into the vacuum chamber through the window, detect photons from the electromagnetic radiation reflected off the sample, and determine a working distance between the sample and charged particle column based on the generated electromagnetic radiation and the detected photons; and one or more mirrors disposed within the vacuum chamber and positioned to direct the electromagnetic radiation generated by the optical distance measurement system to a measured location on the sample that is in close proximity to the region of interest, the one or more mirrors comprising at least one mirror positioned directly under a portion of the charged particle column.