Performance Optimization of a High-Repetition-Rate KrF Laser Plasma X-Ray Source for Microlithography

Area of Science:

• Applied Physics
• Materials Science
• X-ray Optics

Background:

• Industrial applications like x-ray lithography require high-intensity, high-repetition-rate x-ray sources.
• Existing laser plasma x-ray sources face challenges with target debris and prolonged operation.

Purpose of the Study:

• To develop a high-intensity laser plasma x-ray source suitable for industrial x-ray lithography.
• To address and mitigate problems associated with high-repetition-rate and prolonged operation of these sources.

Main Methods:

• Utilized a high-repetition-rate (40 Hz) excimer laser (249 nm, 300 mJ) with a power density of 2 × 10^13 W/cm^2.
• Investigated helium as a quenching gas to reduce atomic debris by over two orders of magnitude.
• Employed a tape target instead of a solid target to further reduce larger debris particles by a factor of 100.
• Used filters (aluminized plastic or beryllium) to block ultraviolet radiation and remaining debris.

Main Results:

• Reduced atomic debris by >100x and larger debris by another 100x using helium gas and tape targets.
• Successfully imaged x-ray transmission mask structures down to 0.3 μm onto photoresist.
• Measured a laser-to-x-ray conversion efficiency of 0.3% for resist-exposing x-rays into 2π steradians.
• Analyzed results using Scanning Electron Microscopy (SEM).

Conclusions:

• The developed laser plasma x-ray source effectively minimizes debris, making it suitable for industrial x-ray lithography.
• High-resolution imaging capabilities were demonstrated, validating the source's performance.
• The conversion efficiency indicates practical potential for lithographic applications.