High-Peak-Power Fiber-Laser Technology for Laser-Produced-Plasma Extreme-Ultraviolet Lithography.

Abstract

This dissertation studied and demonstrated, for the first time, the feasibility of using a fiber laser as a practical EUV driver for next generation lithography. Our specially-designed fiber laser successfully emulated the same conversion efficiency achieved by the solid-state lasers, which was not believed possible before this study. An innovative spectral combining scheme was also developed to accommodate the broad linewidth from a high-peak-power fiber-laser with concurrent MW-peak power and multi-kW average power, as required to reach the EUV power for high-volume manufacturing.

The concept of a single-emitter-fiber-integrated module (SEFIM) was realized. Using an 80-μm-core Yb-doped large-mode-area fiber, we achieved a record high peak power 6MW with 110-ps pulses and 6 mJ energy with 6-ns pulses, giving a near-diffraction-limited mode quality of M^2~1.3. These pulse parameters will provide sufficient intensities for optimal EUV generation using Sn targets. High average power 140 W is also achieved with proper forced cooling arrangements. Implementation of arbitrary waveform generator as the seed driver also provided pulse temporal-shaping capability, providing an instrumental tool for the study of plasma dynamics.

The first 13.5-nm EUV generation was demonstrated using our single emitter module, with a conversion efficiency 1% at a intensity of 1.0 × 10^10 W/cm2, using a solid-Sn planar target. Conversion efficiency was limited by the highest achievable laser intensity at the time. The second demonstration, using the improved SEFIM and Sn-doped water-droplet targets, achieved a conversion efficiency of 2.1% at a intensity of 8.8 × 10^10 W/cm2. The intrinsic advantages of this mass-limited target greatly are debris mitigation and compatibility with high repetition rate power scaling.

We developed a new high power spectral beam combing scheme based on sharp spectral- edge multi-layer dielectric filters, which does not use spectral spatial dispersion and, therefore, is free from the constraints on laser linewidth and beam size inherent in conventional diffraction-grating-based beam-combining approaches. This scheme is particularly well suited for high energy pulse power combining, as experimentally demonstrated in >91% efficient combination of three nanosecond-pulse fiber laser beams with a combined power and energy of 52 W and 4.0 mJ repectively.