Cell-Cell Subtraction Perpendicular to Stage Motion for Semiconductor Inspection

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Solution Overview

Problem

Semiconductor wafer inspection tools face challenges in detecting defects due to positional distortion and noise from beam deflection and stage motion, leading to increased systematic errors and false-positive defect detections, especially when using conventional methods that subtract images shifted by cell widths in the stage movement direction.

Innovation Solution

The method involves moving the substrate in a continuous motion perpendicular to the scan direction and generating difference images by subtracting pixel values from cells displaced in the scan-line direction, reducing positional distortion and allowing for a lower defect detection threshold without false positives, using apparatus with electron or optical beams and image processors to process data efficiently.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If images are subtracted using cells displaced by one or multiple cell widths in the stage movement direction, then defect detection can be performed on repeating patterns, but positional distortion and noise from beam deflection and stage motion increase leading to false-positive defect detections

Engineering Contradiction:

Improvedefect detection accuracyVSAvoidimage alignment precision

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

Instead of subtracting images of cells displaced in the stage movement direction (conventional approach), the patent inverts the approach by subtracting images of cells displaced in the scan-line direction (perpendicular to stage motion). This inversion eliminates the accumulation of systematic errors from stage motion and beam deflection that occur in the conventional method, thereby resolving the contradiction between defect detection capability and measurement precision.

Inventive Principle:

Principle #13The other way round (Inversion)

2Productivity

If conventional image subtraction methods are used with cells displaced in stage movement direction, then defect detection is enabled, but systematic errors increase leading to higher false-positive rates

Engineering Contradiction:

Improveinspection throughputVSAvoidfalse-positive rate

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent applies the inversion principle by changing the displacement direction from stage movement direction to scan-line direction. This allows the system to maintain high inspection throughput while dramatically reducing false-positive rates, as the new method eliminates the systematic errors that accumulate when subtracting images taken at different times during continuous stage motion.

Inventive Principle:

Principle #13The other way round (Inversion)

3Measurement precision

If cells displaced in scan-line direction are used for subtraction, then distortion noise and image aliasing are reduced, but the method differs from conventional approaches requiring new processing algorithms

Engineering Contradiction:

Improveimage alignment precisionVSAvoidimage processing complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

While the inversion approach does require modified processing algorithms to select and subtract cells displaced in the scan-line direction rather than stage movement direction, this complexity is justified by the significant improvement in measurement precision. The new approach eliminates systematic errors from stage motion and beam deflection, providing much cleaner difference images for defect detection.

Inventive Principle:

Principle #13The other way round (Inversion)

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

This approach significantly reduces distortion noise and image aliasing, enabling more sensitive detection of physical defects and weakest voltage-contrast defects, with faster acquisition times and reduced false positives, allowing for high-throughput inspection.

Implementation Method 1

control the beam to scan it across the surface of the substrate and collect corresponding image data

Methodology Applied

Scientific EffectElectron beam interaction: Electron Beam

Data Source

PatentUS8106355B1Automated inspection using cell-cell subtraction perpendicular to stage motion direction

Publication Date: 2012.01.31 KLA CORP

AI summary

One embodiment relates to an apparatus for automated inspection of a semiconductor substrate. Processor-executable code is configured to control the stage electronics to move the substrate using a continuous motion in a substrate-translation direction and is configured to control the beam to scan it across the surface of the substrate and collect corresponding image data, scan lines of the scan being along a scan-line direction perpendicular to the substrate-translation direction. Processor-executable code is also configured to select from the image data two cells of the repeating pattern on the surface of the substrate, the two cells being displaced from each other by one or multiple cell heights in the scan-line direction. Finally, processor-executable code is configured to generate a difference image by subtracting image data from said two cells on a pixel-by-pixel basis. Other embodiments, aspects and features are also disclosed.