Laser Pulse Superposition to Overcome Amplifier Saturation

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Solution Overview

Problem

Existing methods for generating laser pulses for EUV lithography face limitations in power and yield due to amplifier saturation, where short pulses quickly deplete energy levels, leaving little power for the later part of the pulse, while long pulses allow refilling but result in reduced amplification.

Innovation Solution

Generating first and second laser pulses with different beam properties, amplifying them with a time offset, separating and delaying the first pulses, and superimposing them to form high-energy, short-duration pulses, allowing for maximum amplification by refilling energy levels during the second pulse's amplification.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Duration of action of moving object

If short laser pulses are used to amplify in the amplifier, then the pulse duration is reduced, but the amplifier saturation occurs quickly and power is depleted before the pulse is complete

Engineering Contradiction:

Improvepulse durationVSAvoidpower availability

Core Design Contradiction:

Duration of action of moving objectVSPower

Solution Approach 1:

The laser pulse is segmented into multiple sub-pulses (first laser pulse, second laser pulse, third laser pulse) that are amplified separately and then superimposed. This allows each sub-pulse to be optimized for short duration while the combined effect achieves high peak power without premature amplifier depletion

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The first laser pulse is amplified preliminarily to prepare the amplifier medium, then the second laser pulse is amplified after a time offset that allows partial refilling of energy levels. This preliminary action sequence ensures sufficient power is available when the pulses are superimposed

Inventive Principle:

Principle #10Preliminary action

2Power

If long laser pulses are used to allow energy level refilling, then power is maintained, but the pulse duration increases and amplification is reduced

Engineering Contradiction:

Improvepower maintenanceVSAvoidpulse duration

Core Design Contradiction:

PowerVSDuration of action of moving object

Solution Approach 1:

Multiple laser pulses are introduced into the amplifier at periodic intervals with specific time offsets. The first, second, and third pulses are spaced to allow energy level refilling between them, maintaining power while keeping individual pulse durations short

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

Multiple amplified laser pulses are superimposed to merge their energy and achieve high peak power. The superposition of the first, second, and third pulses combines their individual energies while maintaining short overall pulse duration

Inventive Principle:

Principle #5Merging (Combining)

3Power

If a single laser pulse is amplified, then the system is simple, but the power and energy are limited

Engineering Contradiction:

Improvepower outputVSAvoidsystem complexity

Core Design Contradiction:

PowerVSDevice complexity

Solution Approach 1:

The amplifier is designed to handle multiple laser pulses sequentially with different time offsets, making it multi-functional. The same amplifier medium serves to amplify each pulse while allowing refilling between pulses, eliminating the need for separate amplifiers for each pulse

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 method achieves superimposed laser pulses with up to twice the power and energy of individual pulses, optimizing power distribution and yield by ensuring continuous energy availability during amplification.

Implementation Method 1

the energy level which was emptied by stimulated emission can be refilled by adjacent energy levels

Methodology Applied

Scientific EffectStimulated emission:

Implementation Method 2

separating the first laser pulses from the second laser pulses using an optical beam splitter based on at least one beam property

Methodology Applied

Scientific EffectOptical beam splitting:

Implementation Method 3

A time duration for each respective first laser pulse to pass through a retardation section of the retardation unit corresponds to the time offset in relation to the respective second laser pulse

Methodology Applied

Scientific EffectOptical retardation:

Data Source

PatentUS20240255767A1Method and device for generating laser pulses

Publication Date: 2024.08.01 TRUMPF LASER SYSTEMS FOR SEMICONDUCTOR MANUFACTURING GMBH

AI summary

A method for generating laser pulses includes generating first laser pulses and second laser pulses using at least one laser source, and amplifying the first laser pulses and second laser pulses using an optical amplifier. Each respective second laser pulse passes through the optical amplifier offset in time in relation to a respective first laser pulse by a time offset. The method further includes separating the first laser pulses from the second laser pulses using an optical beam splitter based on at least one beam property, and passing the first laser pulses through a retardation unit. A time duration for each respective first laser pulse to pass through a retardation section of the retardation unit corresponds to the time offset. The method further includes superimposing the first laser pulses with the second laser pulses using a superposition unit to form superimposed laser pulses.