Pulse Stretcher for Lithography Speckle Reduction
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Solution Overview
Problem
Lithographic apparatuses face challenges in reducing speckle-induced local critical dimension variations and overlay issues due to radiation-induced optical damage and coherence effects, particularly in deep ultraviolet lithography, which affect the uniformity and yield of semiconductor manufacturing processes.
Innovation Solution
A pulse stretcher apparatus that splits an input radiation beam into two beams, recombines them with an optical delay, and uses phase-modulating optical elements to reduce coherence between the beams, specifically employing phase plates or diffusers with varying thickness and random phase regions to minimize speckle by altering the wavefront phase and reducing constructive interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pulse stretching is used to reduce radiation-induced optical damage, then the lifetime of optical components is improved, but the complexity of the optical system increases
Solution Approach 1:
The optical beam is divided into multiple sub-beams using beam splitters, with each sub-beam traveling through a separate optical path. This segmentation allows the total optical power to be distributed across multiple lower-intensity paths, reducing radiation damage to individual optical components while maintaining the overall system functionality.
Solution Approach 2:
An optical delay line is introduced as an intermediary element between the beam splitter and the recombination point. This delay line creates a time delay between the reference beam and the delayed beam, enabling pulse stretching without requiring complex modulation systems. The intermediary element simplifies the overall system architecture.
2Manufacturing precision
If pulse stretching is used to reduce speckle effects, then critical dimension uniformity is improved, but the device complexity increases
Solution Approach 1:
The pulse stretcher creates multiple periodic sub-pulses within the extended pulse duration. These periodic sub-pulses have reduced peak intensity and their interference patterns average out speckle effects over time. The periodic structure is achieved through simple beam splitting and time-delayed recombination, avoiding complex modulation schemes.
Solution Approach 2:
The invention transforms the problem from a spatial domain issue (speckle patterns) to a temporal domain solution. By introducing time delays between beam paths and recombining them, the system stretches the pulse in the time dimension, which naturally averages out spatial interference patterns and reduces speckle effects.
3Duration of action of moving object
If beam splitting and recombination is used to stretch pulses, then pulse length is increased, but optical losses increase
Solution Approach 1:
Multiple beam paths are merged back together at the recombination point to form a single output beam. The optical energies from the reference beam and delayed beam are combined constructively, recovering most of the power that was initially split. This merging process minimizes overall energy losses compared to alternative pulse stretching methods.
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 solution effectively reduces speckle in the outgoing radiation beam, leading to improved critical dimension uniformity and overlay, thereby enhancing the yield and quality of substrates in lithography processes by averaging out intensity variations and reducing coherence-related issues.
Implementation Method 1
a beam splitter configured to split an input radiation beam into a first beam and a second beam
Implementation Method 2
at least a portion of the first beam is recombined with the second beam into a modified beam after an optical delay of the first beam caused by the optical arrangement
Implementation Method 3
at least one optical element in an optical path of the first beam, the at least one optical element configured such that the phase of different parts of a wavefront of the first beam is varied to reduce coherence between the first beam and the second beam
Implementation Method 4
Speckle is the optical interference between radiation beams due to temporal and spatial coherence
Data Source
AI summary
An apparatus (10) for increasing a pulse length of a pulsed radiation beam, the apparatus comprising: a beam splitter (16) configured to split an input radiation beam (18) into a first beam (24) and a second beam (22); an optical arrangement (12, 14), wherein the beam splitter and the optical arrangement are configured such that at least a portion of the first beam is recombined with the second beam into a modified beam after an optical delay of the first beam caused by the optical arrangement; and at least one optical element (30) in an optical path of the first beam, the at least one optical element configured such that the phase of different parts of a wavefront of the first beam is varied to reduce coherence between the first beam and the second beam.