Multi-Stage Optical Pulse Stretcher for Semiconductor Exposure
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Solution Overview
Problem
Current semiconductor exposure apparatuses face challenges in reducing chromatic aberration due to wide spectrum line widths of KrF and ArF excimer laser beams, leading to decreased resolving power, which is not adequately addressed by existing optical pulse stretcher configurations.
Innovation Solution
A laser apparatus comprising a laser oscillator and multiple optical pulse stretchers (OPS) with specific optical path length relationships, where the optical path lengths of the second and third OPS are integral multiples of the first OPS, optimized to efficiently stretch the pulse width and reduce speckle contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If a conventional optical pulse stretcher configuration is used, then the pulse width can be stretched, but the optical path length becomes excessively long and the system becomes complex
Solution Approach 1:
The optical pulse stretcher is divided into multiple independent stages (first stage with mirrors M1-M4, second stage with mirrors M5-M8, third stage with mirrors M9-M12). Each stage contributes to pulse width stretching through a specific delay path configuration, allowing the total stretching effect to be achieved while keeping individual stage path lengths manageable and the overall system compact.
2Manufacturing precision
If the spectrum line width is narrowed using a line narrowing module, then chromatic aberration is reduced, but the device complexity increases
Solution Approach 1:
The line narrowing function is extracted as a separate module (LNM) with specific optical elements (etalon or grating) that can be independently optimized and adjusted. This allows chromatic aberration to be reduced while keeping the main laser resonator and pulse stretcher configurations relatively simple and modular.
3Duration of action of moving object
If multiple optical pulse stretchers are added to achieve sufficient pulse width stretching, then the pulse width increases, but the optical path length and system complexity increase significantly
Solution Approach 1:
Multiple pulse stretching stages are nested within a compact optical cavity structure. The delay paths of different stages are arranged such that later stages build upon the stretching effect of earlier stages, with each stage contributing a factor of 2 to the total pulse width multiplication. This nested arrangement achieves cumulative stretching effect while minimizing the overall optical path length and system footprint.
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 configuration effectively stretches the pulse width with a relatively short optical path length, reducing speckle contrast and improving coherence, thereby enhancing the resolving power of the semiconductor exposure apparatus.
Implementation Method 1
a first optical pulse stretcher disposed on an optical path of the pulse laser beam, a second optical pulse stretcher disposed on the optical path of the pulse laser beam, and a third optical pulse stretcher disposed on the optical path of the pulse laser beam
Data Source
AI summary
A laser apparatus according to an aspect of the present disclosure includes a laser oscillator configured to emit a pulse laser beam, and a first optical pulse stretcher, a second optical pulse stretcher, and a third optical pulse stretcher that are disposed on an optical path of the pulse laser beam. When L1 represents an optical path length of a delay optical path of the first optical pulse stretcher, L2 represents an optical path length of a delay optical path of the second optical pulse stretcher, L3 represents an optical path length of a delay optical path of the third optical pulse stretcher, and n represents an integer equal to or larger than two, L2 is an integral multiple of L1 by an integer equal to or larger than two and L3 satisfies the following condition: (n−0.75)×L1≤L3≤(n−0.25)×L1.