Overlay Target Imaging With Sensor Shift Compensation

Solution Overview

Problem

The discrepancy in response times between secondary electron and backscattered electron sensors in charged particle systems leads to time shifts and spatial misalignments in overlay measurements, affecting the accuracy of semiconductor device production.

Innovation Solution

A method and system for compensating for sensor response time differences by determining and applying a compensation shift based on registrations between secondary and backscattered electron images, using opposite scan patterns and pixel grab periods shorter than the backscattered electron sensor's response period.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If images are acquired using a pixel grab period lower than the backscattered electron sensor response period, then measurement speed is improved, but spatial misalignment between secondary electron image and backscattered electron image occurs due to time shift

Engineering Contradiction:

Improvemeasurement speedVSAvoidoverlay measurement accuracy

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The patent performs preliminary actions by acquiring images at high speed first, then subsequently calculates the time shift between secondary electron and backscattered electron images and applies compensation. This allows the system to first capture data quickly and then correct the spatial misalignment through image processing, rather than trying to prevent the misalignment during acquisition.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements a feedback mechanism where the calculated time shift between the two sensor types is used to adjust and compensate the backscattered electron image. The system measures the actual misalignment that occurs during high-speed acquisition and then applies corrective transformation based on this measured feedback, enabling continuous improvement of measurement accuracy.

Inventive Principle:

Principle #23Feedback

2Productivity

If the pixel grab period is reduced to increase acquisition speed, then productivity is improved, but the response time difference between sensors causes spatial shift and measurement precision deteriorates

Engineering Contradiction:

Improveimage acquisition speedVSAvoidoverlay alignment accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The patent introduces an intermediary computational step that acts as a mediator between the two sensors with different response times. By calculating the time shift between secondary electron and backscattered electron images and applying transformation compensation, the system creates a virtual alignment that reconciles the temporal differences between sensors, allowing high-speed acquisition without sacrificing precision.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Loss of time

If high-speed imaging is performed with pixel grab period below sensor response period, then measurement time is reduced, but time shift between sensors increases causing spatial misalignment

Engineering Contradiction:

Improvemeasurement timeVSAvoidoverlay measurement accuracy

Core Design Contradiction:

Loss of timeVSManufacturing precision

Solution Approach 1:

The patent performs preliminary actions by acquiring images at high speed first, then subsequently calculates the time shift between secondary electron and backscattered electron images and applies compensation. This allows the system to first capture data quickly and then correct the spatial misalignment through image processing, rather than trying to prevent the misalignment during acquisition.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements a feedback mechanism where the calculated time shift between the two sensor types is used to adjust and compensate the backscattered electron image. The system measures the actual misalignment that occurs during high-speed acquisition and then applies corrective transformation based on this measured feedback, enabling continuous improvement of measurement accuracy.

Inventive Principle:

Principle #23Feedback

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

Ensures accurate overlay measurements by aligning images despite differing sensor response times, enhancing the precision and quality of semiconductor device fabrication.

Implementation Method 1

a first secondary electron image of an overlay target, the first secondary electron image being indicative of secondary electrons emitted from the overlay target due to a scanning the overlay target with an illuminating electron beam

Methodology Applied

Scientific EffectSecondary electron emission: Electron Impact Desorption

Implementation Method 2

a first backscattered electron image of the overlay target, the first backscattered electron image being indicative of backscattered electrons emitted from the overlay target due to the scanning the overlay target with the illuminating electron beam

Methodology Applied

Scientific EffectBackscattered electron emission: Scattering

Data Source

PatentUS20260009751A1Overlay target measurement and shift compensation in charged particle systems and related methods

Publication Date: 2026.01.08 APPL MATERIALS ISRAEL LTD

AI summary

A method and system that compensate for differences in response times of different types of sensors of a charged particle system. This involves obtaining first and second secondary electron images and backscattered electron images of an overlay target, scanned with an illuminating electron beam in accordance with first and second scan patterns. A secondary electron shift and a backscattered electron shift are determined based on a registration between the first and a rotated second images. A compensation shift is determined based on these shifts. The images are acquired using a pixel grab period lower than a response period of a backscattered electron sensor used to generate the first backscattered electron image.