EUV Plasma Source Shaping for Anamorphic Lithography
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Solution Overview
Problem
Current lithographic systems face challenges in reducing the critical dimension of features due to limitations in numerical aperture and wavelength, particularly in achieving efficient filling of the anamorphic projection system's elliptical pupil with EUV radiation.
Innovation Solution
The use of a radiation source that generates an EUV radiation emitting plasma with an elongate form, matched to the anamorphic projection system's pupil, is achieved through a pre-pulse laser that causes a fuel droplet to expand unevenly and tilt, and multiple lasers that provide overlapping beam waists to optimize irradiance and plasma formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional circular plasma source is used, then the radiation source is simple to generate, but the anamorphic projection system's elliptical pupil cannot be efficiently filled, limiting numerical aperture and resolution
Solution Approach 1:
The patent applies asymmetry by transforming the conventional circular plasma source into an elongate plasma source. This is achieved through a pre-pulse laser that creates an asymmetric pressure distribution within the fuel droplet, causing it to expand preferentially in one direction. The resulting elongate plasma geometry efficiently fills the anamorphic projection system's elliptical pupil, enabling higher numerical aperture and improved critical dimension without excessive system complexity
Solution Approach 2:
The patent employs preliminary action through the use of a pre-pulse laser that acts on the fuel droplet before the main plasma-generating laser pulse. This pre-pulse creates an asymmetric pressure distribution and initiates directional expansion of the droplet, preparing it in advance to form an elongate plasma source. This preliminary shaping action enables the main pulse to generate the desired elongate plasma geometry, resolving the contradiction between source simplicity and pupil-filling efficiency
2Manufacturing precision
If the numerical aperture is increased on the mask side to improve resolution, then the critical dimension decreases, but the illumination requirements and system complexity increase
Solution Approach 1:
The patent applies local quality by concentrating the plasma emission in a specific elongate region that corresponds to the elliptical pupil geometry. The pre-pulse laser creates localized asymmetric heating and expansion in the fuel droplet, generating a plasma source with non-uniform spatial distribution. This localized plasma emission optimally fills the anamorphic projection system's pupil, improving energy utilization efficiency and enabling higher numerical aperture on the substrate side without proportionally increasing mask side illumination requirements
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 enhances the conversion efficiency of fuel to EUV radiation, matches the radiation shape to the projection system's pupil, and increases the numerical aperture on the substrate side without increasing it on the mask side, thereby reducing the critical dimension of features.
Implementation Method 1
a pre-pulse laser which is configured to provide a laser pulse which causes a fuel droplet to expand
Implementation Method 2
causes a fuel droplet to expand by more in a first direction than in a second direction
Implementation Method 3
a radiation source configured to generate an EUV radiation emitting plasma at a plasma formation location
Implementation Method 4
the EUV radiation emitting plasma having an elongate form in a plane substantially perpendicular to an optical axis of the radiation source
Data Source
AI summary
A lithographic system including a lithographic apparatus with an anamorphic projection system, and a radiation source configured to generate an EUV radiation emitting plasma at a plasma formation location, the EUV radiation emitting plasma having an elongate form in a plane substantially perpendicular to an optical axis of the radiation source.