Pulse Stretcher Optical Paths Wafer Inspection

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Solution Overview

Problem

Existing wafer inspection tools face challenges with high-powered lasers due to the damage caused by short pulse DUV illumination, which results in marginal illumination capabilities and laser-induced damage to optical components.

Innovation Solution

A pulse stretcher is designed using a plurality of substantially parallel slab-like optical paths of different lengths and reflecting surfaces to spread out optical pulses over time, reducing peak intensity and extending pulse duration, thereby mitigating damage and improving illumination capabilities.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If short pulse lasers are used to generate high intensity pulses, then illumination intensity is improved, but optical components suffer from laser-induced damage

Engineering Contradiction:

Improveillumination intensityVSAvoidlaser-induced damage

Core Design Contradiction:

Illumination intensityVSObject-affected harmful factors

Solution Approach 1:

The single high-intensity pulse is segmented into multiple lower-intensity pulses using a pulse train generator. The pulse train divides the total energy into N separate pulses, each with reduced peak intensity, thereby maintaining illumination effectiveness while preventing laser-induced damage to optical components.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention employs periodic pulse trains instead of single isolated pulses. By generating a sequence of pulses with appropriate timing and duty cycle, the system maintains average power requirements for illumination while reducing peak power to safe levels that prevent optical component damage.

Inventive Principle:

Principle #19Periodic action

2Power

If high-powered lasers are used for illumination, then illumination capabilities are improved, but damage to optical components occurs

Engineering Contradiction:

ImprovepowerVSAvoiddamage to optical components

Core Design Contradiction:

PowerVSObject-affected harmful factors

Solution Approach 1:

The high power output is segmented into multiple lower-power pulses within a pulse train. The total energy delivery is maintained for effective illumination, but the peak power of individual pulses is reduced to levels that prevent damage to optical components through non-linear optical effects.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention changes the temporal parameters of the laser output by controlling pulse width, repetition rate, and duty cycle. By adjusting these parameters, the system delivers sufficient average power for illumination while keeping peak power below the damage threshold for optical components.

Inventive Principle:

Principle #35Parameter changes

3Object-affected harmful factors

If arc lamps are used for illumination, then damage to optical components is reduced, but illumination capabilities are marginal

Engineering Contradiction:

Improvedamage to optical componentsVSAvoidillumination capabilities

Core Design Contradiction:

Object-affected harmful factorsVSIllumination intensity

Solution Approach 1:

The invention introduces a pulse train generator as an intermediary between the arc lamp and the optical system. This intermediary modulates the arc lamp output into controlled pulse trains, enabling the system to achieve high illumination intensity with reduced peak power, thereby maintaining both effective illumination and optical component safety.

Inventive Principle:

Principle #24Intermediary (Mediator)

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

The pulse stretcher effectively reduces peak intensity and extends pulse duration, minimizing damage to optical components and enhancing the illumination capabilities of wafer inspection tools, allowing for safer and more effective use of high-intensity light sources.

Implementation Method 1

a plurality of substantially parallel slab-like optical paths of different lengths... spreads out optical pulses over time, reducing the peak intensity of the pulses and extending the pulse duration

Methodology Applied

Scientific EffectOptical path length difference:

Implementation Method 2

a plurality of reflecting surfaces located at a second end of each optical path... each optical beam is reflected from a corresponding one of the plurality of reflecting surfaces such that the optical beam does not intersect any of the other optical beams

Methodology Applied

Scientific EffectReflection: Reflection

Data Source

PatentUS7804866B1Pulse stretcher

Publication Date: 2010.09.28 KLA TENCOR TECHNOLOGY CORP

AI summary

A pulse stretcher includes a plurality of substantially parallel slab-like optical paths of different optical path lengths and a plurality of reflecting surfaces, which are totally internally reflecting surface formed, located at an end of the corresponding optical path. Due to the different path lengths, the pulse stretcher can spread out an input pulse into a stretched pulse having a longer pulse duration and proportionally lower intensity than the initial pulse.