Line Narrowing Module for Exposure Light Sources
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Solution Overview
Problem
Conventional photolithography exposure apparatuses face challenges in producing exposure light with precise narrow bandwidth due to chromatic aberration and inefficiencies in line narrowing processes, leading to degraded precision and wasted optical energy.
Innovation Solution
A light source with a line narrowing module that includes a diffraction grating, elliptical mirror, and laser beam dispersion and extraction unit, which selectively outputs a laser beam with a predetermined narrow bandwidth while returning most other light back to the laser oscillator, enhancing optical efficiency and precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional line narrowing module disperses laser beam and returns only one line to the laser oscillator, then the bandwidth of exposure light is narrowed, but most optical energy is wasted
Solution Approach 1:
The patent applies the principle of discarding and recovering by separating the narrow bandwidth exposure light (which is output for use) from the remaining laser lines (which are returned to the laser oscillator for recovery and reuse). This resolves the contradiction by ensuring that only the necessary bandwidth is discarded while the rest of the optical energy is recovered and reused, thereby narrowing bandwidth precision without wasting optical energy.
2Object-affected harmful factors
If excimer lasers emit monochromatic laser light with narrow bandwidth, then chromatic aberration is prevented, but the laser beam contains multiple lines that degrade bandwidth precision
Solution Approach 1:
The patent applies the principle of taking out (extraction) by extracting only the specific laser line with the desired narrow bandwidth from the multi-line laser beam generated by the excimer laser. This is achieved through dispersion and selective extraction mechanisms that separate the useful monochromatic light from other lines, thereby preventing chromatic aberration while maintaining high bandwidth precision.
3Measurement precision
If conventional line narrowing returns one extracted line to laser oscillator, then bandwidth is narrowed, but the extracted light commingles with other lines degrading precision
Solution Approach 1:
The patent applies the principle of taking out (extraction) by extracting the narrow bandwidth light from the laser oscillator and directing it through a separate optical path that does not return to the laser oscillator. This prevents commingling with other laser lines, thereby maintaining both bandwidth precision and output precision/reliability.
4Adaptability or versatility
If oscillating laser emits deep ultraviolet light with large bandwidth, then light source is versatile, but chromatic aberration occurs in the image
Solution Approach 1:
The patent applies the principle of intermediary (mediator) by introducing a line narrowing module as an intermediary component between the oscillating laser and the exposure system. This module disperses the broad bandwidth laser light and selectively extracts only the desired narrow bandwidth portion, thereby acting as a mediator that preserves the versatility of using oscillating lasers while eliminating the harmful chromatic aberration effect.
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 achieves a consistent and precise output of exposure light with a narrow bandwidth, improving optical energy efficiency and preventing chromatic aberration, thereby enabling the production of fine patterns on semiconductor substrates with higher precision.
Implementation Method 1
the laser beam passes through a slit 31, is dispersed by a prism beam expander 32, and then is reflected by a total reflection mirror 34 onto a diffraction grating 36. The laser beam is diffracted by the diffraction grating 36 to thereby separate the light which entered the module 30 into different bands or lines.
Implementation Method 2
an elliptical mirror 220 having a high-reflective coating formed over an inner surface thereof. The diffraction grating 230 is disposed at a second focus of the elliptical mirror 220 and the front window 112 of the laser oscillator 110 is disposed at a first focus of the elliptical mirror 220.
Data Source
AI summary
A line narrowing module includes an elliptical mirror, a diffraction grating disposed at a first focus of the mirror for separating an incident beam into different lines, and a laser beam dispersion and extraction unit. The laser beam dispersion and extraction unit disperses incident laser over the diffraction grating and selectively extract from the resulting lines a laser beam having a desired narrowed bandwidth. A light source that employs the line narrowing module also includes a laser oscillator for generating the beam, and a light returning unit that returns one fraction of the beam extracted from the laser oscillator back to the laser oscillator. Another fraction of the beam is extracted from the laser oscillator through a front window of the laser oscillator, and undergoes line narrowing in the module. The laser beam having the narrowed bandwidth is immediately output as the exposure light from the module.