EUV Diffusion Target Shaping for Higher Conversion Efficiency
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Solution Overview
Problem
Existing EUV light generation apparatuses face challenges in achieving high conversion efficiency of laser light to EUV light, particularly due to inefficient plasma generation in the peripheral portions of the diffusion target.
Innovation Solution
The apparatus generates a diffusion target with a Gaussian distribution shape using a prepulse laser, which is then irradiated with a main pulse laser having a Gaussian intensity distribution, optimizing the energy application and plasma formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional diffusion target is used with uniform density, then the target can be generated by simple laser irradiation, but the plasma generation efficiency is low due to insufficient energy absorption in peripheral portions
Solution Approach 1:
The diffusion target is designed with non-uniform density distribution where the density gradually decreases from the center toward the periphery. This local variation in density ensures that peripheral portions have lower density and can effectively absorb laser energy, thereby improving plasma generation efficiency across the entire target area and increasing EUV light conversion efficiency.
Solution Approach 2:
The target density parameter is changed from uniform to gradient distribution. By controlling the density parameter to vary spatially (higher at center, lower at periphery), the target optimizes energy absorption characteristics, enabling more efficient conversion of laser light to EUV light while maintaining a manageable structure.
2Reliability
If the target density is increased to improve plasma generation, then plasma intensity improves, but residual debris increases and conversion efficiency decreases
Solution Approach 1:
The gradient density distribution creates different local properties: the high-density center provides strong plasma generation, while the low-density periphery facilitates complete vaporization and reduces residual debris. This spatial variation in density quality simultaneously achieves reliable plasma generation and minimizes harmful debris.
Solution Approach 2:
The two-stage laser irradiation process uses periodic action with different pulse characteristics. The first pulse creates initial plasma, and the second pulse enhances vaporization. This periodic energy input optimizes plasma generation while ensuring complete target material conversion, reducing residual debris formation.
3Object-generated harmful factors
If the target density is decreased to reduce residual debris, then debris reduction improves, but plasma generation intensity decreases and conversion efficiency worsens
Solution Approach 1:
Different regions of the target serve different functions: the high-density center optimizes for plasma generation intensity, while the low-density periphery optimizes for debris reduction. This local differentiation resolves the contradiction by allowing both plasma intensity and debris reduction to be optimized in their respective regions simultaneously.
Solution Approach 2:
The target is effectively segmented into functional zones based on density: a high-density core region for plasma generation and a low-density peripheral region for debris minimization. This segmentation allows each region to perform its optimal function, achieving both high conversion efficiency and low residual debris.
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
This approach significantly improves the conversion efficiency of laser light to EUV light, enhances the intensity and angular range of EUV radiation, and reduces residual debris, leading to more efficient and reliable EUV light generation.
Implementation Method 1
a prepulse laser configured to generate a diffusion target having a Gaussian distribution shape convex toward a travel direction of prepulse laser light by irradiating the target with the prepulse laser light
Implementation Method 2
a main pulse laser configured to generate extreme ultraviolet light by irradiating the diffusion target with main pulse laser light having an intensity distribution of a Gaussian distribution shape
Data Source
AI summary
An extreme ultraviolet light generation apparatus includes a chamber, a target supply unit configured to supply a target into the chamber, a prepulse laser configured to generate a diffusion target having a Gaussian distribution shape convex toward a travel direction of prepulse laser light by irradiating the target with the prepulse laser light, and a main pulse laser configured to generate extreme ultraviolet light by irradiating the diffusion target with main pulse laser light having an intensity distribution of a Gaussian distribution shape.