Tilted EUV Collector Mirror for Non-Vertical Beam Delivery
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Solution Overview
Problem
Existing EUV light sources face challenges in maintaining the cleanliness and protection of collector mirrors from plasma-generated debris and achieving a non-vertical EUV output beam, which is desirable for certain photolithography processes to minimize optical aberrations and obscurations.
Innovation Solution
The system includes an EUV reflective optic with a surface of revolution positioned at a nonzero angle to the horizontal plane, a target material delivery system with a release point outside the optic's projection area, and a catch mechanism to protect the optic from stray material, allowing for a non-vertical droplet stream and efficient EUV light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a vertical droplet stream is used with a collector mirror positioned out of the droplet path, then the mirror is protected from contamination, but the EUV output beam becomes cone-shaped and aligned horizontally, which may not be desirable for certain photolithography processes
Solution Approach 1:
The patent reorients the entire system by tilting the collector mirror and droplet delivery apparatus relative to the horizontal plane. This dimensional change allows the droplet stream to remain vertical (protecting the mirror) while the collected EUV beam emerges at a desired non-horizontal angle, solving both the contamination protection and beam orientation requirements simultaneously.
Solution Approach 2:
The patent employs asymmetric positioning where the collector mirror is tilted at a specific angle relative to the horizontal plane, creating an asymmetric configuration. This asymmetric arrangement allows the mirror to stay out of the vertical droplet path while directing the collected EUV radiation at a non-horizontal angle, resolving the contradiction between mirror protection and beam orientation.
2Use of energy by moving object
If the collector mirror is positioned close to the plasma to efficiently collect EUV light, then light collection efficiency is improved, but the mirror surface is more exposed to plasma-generated debris and contamination
Solution Approach 1:
The patent introduces a tilted intermediate optical path between the plasma and the collector mirror. The droplet delivery system and optical components are angled relative to the horizontal plane, creating an intermediate configuration that allows efficient light collection while the tilted mirror positioning acts as a protective measure against direct exposure to falling debris.
Solution Approach 2:
By tilting the collector mirror and optical path away from the horizontal plane, the system moves the mirror into a different spatial dimension relative to the vertical debris fall path. This dimensional change maintains close proximity for efficient collection while reducing direct exposure to contamination.
3Ease of operation
If a horizontal EUV beam path is used to match the workpiece orientation, then handling and clamping of the workpiece is facilitated, but additional optics are required that reduce light intensity and may introduce aberrations
Solution Approach 1:
The patent tilts the entire optical system and collector mirror relative to the horizontal plane, creating a three-dimensional beam path that is neither purely horizontal nor vertical. This dimensional change allows the beam to reach the wafer at an angle, potentially reducing the number of horizontal optics required while maintaining workpiece accessibility.
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 configuration reduces contamination of the collector mirror, enables a non-vertical EUV output beam, and minimizes obscurations, improving the stability and efficiency of the EUV light source for photolithography applications.
Implementation Method 1
irradiating a target material having the required line-emitting element, with a laser beam... the required plasma can be produced by irradiating a target material... with a laser beam... creating a highly ionized plasma
Implementation Method 2
The energetic radiation generated during de-excitation and recombination of these ions is emitted from the plasma in all directions
Implementation Method 3
a near-normal-incidence mirror (often termed a 'collector mirror') is positioned at a relatively short distance... from the plasma to collect, direct (and in some arrangements, focus) the light
Data Source
AI summary
Devices are disclosed herein which may comprise an EUV reflective optic having a surface of revolution that defines a rotation axis and a circular periphery. The optic may be positioned to incline the axis at a nonzero angle relative to a horizontal plane, and to establish a vertical projection of the periphery in the horizontal plane with the periphery projection bounding a region in the horizontal plane. The device may further comprise a system delivering target material, the system having a target material release point that is located in the horizontal plane and outside the region, bounded by the periphery projection and a system generating a laser beam for irradiating the target material to generate an EUV emission.