Pulse Splitting Optical Path for High-Speed Semiconductor Defect Inspection

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Solution Overview

Problem

Current defect inspection methods for semiconductor wafers using pulsed laser light sources are limited by low sampling rates and potential damage from high-intensity illumination, which hinders the detection of defects at higher frequencies and varying defect sizes and shapes.

Innovation Solution

A defect inspection method that splits a single pulse of a pulsed laser beam into multiple pulses to maintain a constant peak value, allowing for higher sampling rates without damaging the sample, and uses a configuration to detect scattered light from multiple viewing fields simultaneously under uniform illumination conditions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the intensity of the laser light is increased to enhance sensitivity of scattered light detection, then the detection sensitivity is improved, but sample damage occurs due to instantaneously raised temperature and average raised temperature

Engineering Contradiction:

Improvedetection sensitivityVSAvoidsample damage

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The single pulse of pulsed laser beam is divided into multiple sub-pulses by the pulse splitting optical path. This segmentation allows the total energy to be distributed across multiple lower-intensity pulses, reducing the peak temperature rise and average temperature rise that cause sample damage, while maintaining sufficient scattered light intensity for detection.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention changes the temporal distribution parameter of the laser illumination by splitting a single pulse into multiple sub-pulses with different time intervals. This parameter change allows the peak intensity to be reduced while maintaining the total energy, thereby reducing thermal damage to the sample while preserving detection sensitivity.

Inventive Principle:

Principle #35Parameter changes

2Power

If a pulsed laser light source with several kHz oscillation frequency is used, then high power and short wavelength are achieved, but the sampling rate is limited to triple digits or more slower than the required several MHz sampling frequency

Engineering Contradiction:

Improvelaser powerVSAvoidsampling rate

Core Design Contradiction:

PowerVSProductivity

Solution Approach 1:

By splitting a single high-power pulse into multiple sub-pulses, the system creates multiple sampling opportunities from one laser oscillation cycle. This allows the sampling rate to exceed the pulse oscillation frequency, achieving several MHz sampling rate from a several kHz laser source.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention uses periodic pulse splitting within each laser pulse duration to create multiple periodic sampling instances. The scattered light from each sub-pulse is detected separately, enabling high-rate periodic sampling that exceeds the original pulse repetition frequency.

Inventive Principle:

Principle #19Periodic action

3Productivity

If the pulse oscillation frequency is increased to achieve higher sampling rate, then the sampling rate is improved, but the peak value of the pulse increases causing sample damage

Engineering Contradiction:

Improvesampling rateVSAvoidsample damage

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The single pulse is segmented into multiple sub-pulses, allowing the sampling rate to be effectively increased without increasing the peak value of individual pulses. Each sub-pulse maintains a safe peak intensity level while the multiple sub-pulses provide high sampling rate capability.

Inventive Principle:

Principle #1Segmentation

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-speed defect inspection at sampling rates exceeding the pulse oscillation frequency, while minimizing sample damage and enhancing sensitivity to varied defect distributions.

Implementation Method 1

splitting a single pulse of a pulsed laser beam emitted from a laser light source into a plurality of pulses to form a pulse-split pulsed laser beam

Methodology Applied

Scientific EffectPulse splitting:

Implementation Method 2

detecting a scattered light generated from the sample by the irradiating of the pulse-split pulsed laser beam

Methodology Applied

Scientific EffectScattered light detection: Scattering

Implementation Method 3

focusing and detecting a scattered light generated from the sample

Methodology Applied

Scientific EffectFocusing: Focusing

Implementation Method 4

a laser light source that emits a pulsed laser

Methodology Applied

Scientific EffectPulsed laser emission: Laser

Data Source

PatentUS8958062B2Defect inspection method and device using same

Publication Date: 2015.02.17 HITACHI HIGH TECH CORP

AI summary

In order to enable inspections to be conducted at a sampling rate higher than the pulse oscillation frequency of a pulsed laser beam emitted from a laser light source, without damaging samples, a defect inspection method is disclosed, wherein: a single pulse of a pulsed laser beam emitted from the laser light source is split into a plurality of pulses; a sample is irradiated with this pulse-split pulsed laser beam; scattered light produced by the sample due to the irradiation is focused and detected; and defects on the sample are detected by using information obtained by focusing and detecting the scattered light from the sample. Said defect inspection method is configured such that the splitting a single pulse of the pulsed laser beam into a plurality of pulses is controlled in such a manner that the peak values of the split pulses are substantially uniform.