EUV Viewport Assembly With Sapphire Shield Against Thermal Lensing
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Solution Overview
Problem
Thermal lensing in viewport assemblies of extreme ultraviolet (EUV) light sources distorts light transmission and imaging, reducing the efficiency and reliability of EUV light production and system performance.
Innovation Solution
A viewport assembly comprising a window with a high thermal conductivity material, such as sapphire, and a protector with a reflective coating to shield the window from thermal effects, reducing thermal lensing by dissipating thermal gradients and reflecting unwanted radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a window is used to allow optical access to the EUV light source vessel interior, then optical access is enabled, but thermal lensing occurs due to thermal gradients in the window material
Solution Approach 1:
A protector made of sapphire is introduced as an intermediary component between the window and the EUV light source vessel interior. The protector absorbs thermal radiation and protects the window from direct thermal exposure, thereby reducing thermal gradients and thermal lensing while maintaining optical access through the window
Solution Approach 2:
The system uses a composite structure combining a window (made of material transparent to EUV light) with a protector (made of sapphire). This composite arrangement allows the window to provide optical access while the sapphire protector manages thermal loads, resolving the contradiction between optical access and thermal stability
2Reliability
If the window material has high thermal conductivity to reduce thermal gradients, then thermal lensing is reduced, but the window may absorb more radiation and overheat
Solution Approach 1:
The sapphire protector serves as a thermal intermediary that absorbs the bulk of the thermal radiation from the EUV plasma. By placing this high thermal conductivity material between the heat source and the window, the system manages thermal gradients effectively while preventing excessive heat accumulation in the window itself
3Reliability
If a protector is added to shield the window from thermal effects, then thermal lensing is reduced, but device complexity increases
Solution Approach 1:
The protector is implemented as a thin sapphire sheet or plate that can be integrated into the existing viewport assembly structure. This thin-film approach provides effective thermal protection while minimizing the increase in device complexity and maintaining a compact design
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 effectively minimizes thermal lensing, allowing for higher efficiency in EUV light production and reducing the risk of system failure by maintaining clear optical access and improving operational stability.
Implementation Method 1
the sheet comprising a material having a thermal conductivity in the range of 10 to 2000 W/(m·K)
Implementation Method 2
a coating on the window-facing surface of the sheet, wherein the coating reflects at least some radiation having wavelengths longer than the wavelengths encompassed by the transmission band
Data Source
AI summary
An assembly includes a window useful for optical access to an interior of an extreme ultraviolet (EUV) light source vessel, the window having a transmission band and a protector configured to shield the window from the interior of the EUV light source vessel, the protector comprising a sheet with a surface facing the window across a gap, the sheet having a thermal conductivity in the range of 10 to 2000 W/(m·K). The sheet can be a sapphire sheet, and can have an optical coating on the surface facing the window, the coating reflecting at least some radiation outside the transmission band, and the opposite side of the sheet can be bare sapphire.