Optical Pulse Stretcher Layout for Excimer Laser Module Durability
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Solution Overview
Problem
The existing KrF and ArF excimer laser devices used in semiconductor exposure apparatuses suffer from significant spectral line widths, leading to chromatic aberration and decreased resolution in projection lenses. This necessitates the use of line narrowing modules to reduce spectral line widths, but these modules can deteriorate over time, requiring frequent replacement and leading to increased maintenance downtime and costs.
Innovation Solution
A laser device with an optical pulse stretcher that includes a beam splitter inclined with respect to the optical path axis, a plurality of mirrors to guide reflection laser light, and a slide mechanism to move the beam splitter perpendicular to the discharge direction. This configuration extends the pulse width of laser light and allows for the shifting of the laser irradiation position on the beam splitter, reducing the need for frequent replacements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a line narrowing module is provided in the laser resonator to narrow the spectral line width, then the chromatic aberration is reduced and resolution is improved, but the module deteriorates over time requiring frequent replacement and increasing maintenance downtime and costs
Solution Approach 1:
The patent extracts the line narrowing function from the traditional intracavity etalon and implements it externally using a diffraction grating and reflective optics. This separates the spectral selection function from the laser resonator, allowing the line narrowing module to be positioned outside the high-stress discharge environment, thereby reducing deterioration and maintenance requirements while maintaining spectral line width control for chromatic aberration correction
Solution Approach 2:
The patent introduces a diffraction grating as an intermediary element that performs spectral line width narrowing without requiring the laser light to pass through multiple optical surfaces within the resonator. The grating disperses the light and selective feedback is provided through reflective optics, achieving line narrowing with reduced optical component deterioration and maintenance needs
2Reliability
If the pulse width of laser light is extended using an optical pulse stretcher, then the energy per unit time radiated to subsequent optical systems is reduced, minimizing optical system deterioration, but the device complexity increases
Solution Approach 1:
The patent implements a dynamic optical pulse stretcher that adjusts the optical path length in real-time to control pulse width extension. By making the optical path adjustable rather than fixed, the system can optimize pulse stretching for different operating conditions while managing the complexity through controlled mechanical adjustment rather than complex static optical arrangements
Solution Approach 2:
The patent uses periodic modulation of the optical path length within the pulse stretcher to achieve pulse width extension. The periodic adjustment of the optical path creates the desired pulse stretching effect while allowing the mechanical components to operate in a repetitive, controlled manner, reducing wear and managing system complexity
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 extended pulse width of the laser light reduces the energy per unit time radiated to subsequent optical systems, minimizing optical system deterioration and allowing for longer module usage times. Additionally, the ability to shift the laser irradiation position on the beam splitter reduces the frequency of replacements, lowering maintenance costs and downtime.
Implementation Method 1
a beam splitter arranged such that an optical surface thereof on which the pulse laser light is incident is inclined with respect to an optical path axis of the pulse laser light, and configured to separate the pulse laser light incident on the optical surface into reflection laser light and transmission laser light
Implementation Method 2
a plurality of mirrors configured to guide the reflection laser light to the beam splitter
Implementation Method 3
an optical pulse stretcher configured to extend a pulse width of pulse laser light generated by the discharge having occurred between the electrodes
Data Source
AI summary
A laser device includes a pair of electrodes configured to cause discharge to occur, and an optical pulse stretcher configured to extend a pulse width of pulse laser light generated by the discharge having occurred between the electrodes. Here, the optical pulse stretcher includes a beam splitter arranged such that an optical surface thereof on which the pulse laser light is incident is inclined with respect to an optical path axis of the pulse laser light, and configured to separate the pulse laser light incident on the optical surface into reflection laser light and transmission laser light; a plurality of mirrors configured to guide the reflection laser light to the beam splitter; and a slide mechanism configured to move the beam splitter in a direction perpendicular to a direction of the discharge and parallel to the optical surface.