Microlithography Laser Pulse Timing for Speckle and Throughput Control

Solution Overview

Problem

Existing microlithography projection exposure apparatuses face challenges in achieving high accuracy and throughput due to speckle patterns caused by spatial and temporal coherence of laser light sources, and limitations in increasing pulse energy, repetition rate, and output power due to structural constraints and potential degradation of optical components.

Innovation Solution

An optical system with a laser light source and control unit that varies the time period between successive light pulses to reduce speckle contrast and increase repetition rate, using actuators to manipulate optical components and measure speckle contrast and bandwidth to optimize pulse sequences.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If the pulse energy is increased to increase the output power of the laser light source, then the throughput is improved, but the radiation loading of optical components increases leading to degradation

Engineering Contradiction:

Improveoutput power of laser light sourceVSAvoidoptical component durability

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The patent applies dynamics by making the pulse duration variable rather than fixed. The control unit dynamically adjusts the pulse duration of the laser light source based on process requirements, allowing the system to operate at higher output powers when needed while using shorter, less intense pulses to reduce radiation loading and degradation of optical components during normal operation.

Inventive Principle:

Principle #15Dynamics

2Power

If the repetition rate is increased to increase the output power of the laser light source, then the throughput is improved, but acoustic resonances occur leading to spectral bandwidth rising above acceptable measures

Engineering Contradiction:

Improveoutput power of laser light sourceVSAvoidspectral bandwidth control

Core Design Contradiction:

PowerVSEase of operation

Solution Approach 1:

The patent applies dynamics by making the pulse duration variable rather than fixed. The control unit dynamically adjusts the pulse duration of the laser light source based on process requirements, allowing the system to operate at higher output powers when needed while using shorter, less intense pulses to reduce radiation loading and degradation of optical components during normal operation.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent applies parameter changes by varying the pulse duration as a controllable parameter. The control unit modifies the temporal characteristics of the laser pulses, changing the pulse duration parameter to optimize both the repetition rate and spectral bandwidth, thereby avoiding acoustic resonances while maintaining high throughput.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If optical pulse stretchers are used to stretch pulses to reduce degradation of downstream optical components, then component stress is reduced, but structural space restrictions and decreasing output power with increased reflections are imposed

Engineering Contradiction:

Improveoptical component durabilityVSAvoidoutput power of laser light source

Core Design Contradiction:

ReliabilityVSPower

Solution Approach 1:

The patent applies dynamics by making the pulse duration variable rather than fixed. The control unit dynamically adjusts the pulse duration of the laser light source based on process requirements, allowing the system to operate at higher output powers when needed while using shorter, less intense pulses to reduce radiation loading and degradation of optical components during normal operation.

Inventive Principle:

Principle #15Dynamics

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

Reduces speckle patterns, improves overlay accuracy, and increases throughput by varying the time period between light pulses, while avoiding acoustic resonances and component degradation.

Implementation Method 1

An effect that can occur with regard to the desired accuracy properties to be satisfied inter alia during operation of the laser light sources mentioned above is the occurrence of what are known as speckle patterns, which are attributable to the spatial and temporal coherence of the generated light.

Methodology Applied

Scientific EffectSpeckle pattern: Interference

Data Source

PatentUS12416865B2Optical system, in particular for microlithography, and method for operating an optical system

Publication Date: 2025.09.16 CARL ZEISS SMT GMBH

AI summary

An optical system, in particular for microlithography, comprises a laser light source for generating a multiplicity of light pulses, and a control unit configured to control the laser light source in such a way that, for a light pulse sequence generated by the laser light source, the time period between respectively successive light pulses varies across the light pulse sequence. A method comprises operating the optical system.