Cooled Buffer Gas Debris Suppression in EUV Radiation Sources
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Solution Overview
Problem
Current lithographic systems face challenges in effectively suppressing debris from plasma-based extreme ultraviolet radiation sources, as increasing buffer gas pressure or distance is difficult due to limitations in plasma expansion and source size constraints.
Innovation Solution
Introducing a cooled buffer gas into the radiation source, which can be compressed and introduced in a liquid state to evaporate and expand, increasing the number of gas atoms for a given pressure and volume, thereby enhancing debris suppression without increasing operating pressure or source size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If buffer gas pressure is increased to suppress debris, then debris suppression is improved, but plasma expansion is inhibited and radiation output decreases
Solution Approach 1:
The patent changes the temperature parameter of the buffer gas from ambient to cryogenic (e.g., liquid nitrogen temperature of 77K or liquid helium temperature of 4K). This parameter change increases the number density of gas atoms by a factor of 10-100 times compared to ambient temperature gas at the same pressure, thereby enhancing debris suppression without increasing the pressure that would inhibit plasma expansion and reduce radiation output.
Solution Approach 2:
The patent utilizes phase transition by introducing buffer gas in its liquid state (e.g., liquid nitrogen or liquid helium) which then evaporates to form a cold gas cloud. This phase transition from liquid to gas provides a high density of cold gas atoms in a compact volume, achieving effective debris suppression while maintaining a compact source design and avoiding the need to increase system pressure.
2Object-affected harmful factors
If distance between radiation emitter and collector is increased to suppress debris, then debris suppression is improved, but source size increases
Solution Approach 1:
The patent changes the temperature parameter of the buffer gas to cryogenic levels, which increases the number density of gas atoms at the same pressure. This allows effective debris suppression to be achieved in a shorter distance between the radiation emitter and collector, thereby maintaining a compact source size while still providing sufficient debris suppression.
Solution Approach 2:
The patent introduces a cold buffer gas cloud that replicates the debris suppression function of a much longer interaction path at ambient temperature. The cold gas cloud acts as a dense medium that provides equivalent or superior debris suppression in a compact volume, effectively 'copying' the protective function of a long interaction path without requiring the physical space.
3Temperature
If additional cooling arrangements are added to the radiation source, then temperature control is improved, but device complexity and cost increase
Solution Approach 1:
The patent employs the buffer gas itself to provide cooling to the radiation source components through which it passes. The cold buffer gas (at 77K or 4K) absorbs heat from the plasma emission region and surrounding components as it flows through the source, providing self-cooling without requiring separate active cooling systems. This eliminates the need for additional cooling arrangements and reduces device complexity and cost.
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 improves debris suppression while allowing the radiation source to operate at higher power with increased radiation output, without the need for additional cooling arrangements within the source, thus reducing complexity and cost.
Implementation Method 1
Debris repeatedly collides with constituent parts (e.g., atoms or molecules) of the buffer gas, and these collisions cause the debris to slow down and/or be deflected from their original path.
Implementation Method 2
The buffer gas is often characterized in terms of the integrated pressure along the trajectory of the debris. The suppression can be improved by increasing the integrated pressure.
Implementation Method 3
Extreme ultraviolet radiation and beyond EUV radiation may be produced using a plasma. The plasma may be created for example by directing a laser at particles of a suitable material (e.g., tin), or by directing a laser at a stream of a suitable gas or vapor, such as Xe gas or Li vapor.
Data Source
AI summary
A radiation source may include a radiation emitter for emitting radiation, a collector for collecting radiation emitted by the radiation emitter, and an outlet configured, in use, to introduce a cooled gas into the radiation source.