Bruno M. LaFontaine

Advanced extreme ultraviolet resist testing using the SEMATECH Berkeley 0.3-NA microfield exposure tool

Microfield exposure tools (METs) continue to play a dominant role in the development of extreme ultraviolet (EUV) resists. Here we present an update on the SEMATECH Berkeley 0.3-NA MET and summarize the latest test results from high-resolution line-space and contact-hole printing. In practice, the resolution limit of contact-hole printing is generally dominated by contact size variation that is often speculated to originate form shot noise effects. Such observations of photon-noise limited performance are concerning because they suggest that future increased resist sensitivity would not be feasible. Recent printing data, however, indicates that the contact size variation problem is currently not a result of shot noise but rather attributable to the mask in combination with the resist-dominated mask error enhancement factor (MEEF). Also discussed is the importance of the contribution of the system-level line-edge roughness (LER) to resist LER values currently obtained with the SEMATECH Berkeley MET. We present the expected magnitude of such effects and compare the results to observed trends in LER performance from EUV resists over the past few years.

High power fiber laser driver for efficient EUV lithography source with tin-doped water droplet targets

In this paper we report the development of nanosecond-pulsed fiber laser technology for the next generation EUV lithography sources. The demonstrated fiber laser system incorporates large core fibers and arbitrary optical waveform generation, which enables achieving optimum intensities and other critical beam characteristics on a laser-plasma target. Experiment demonstrates efficient EUV generation with conversion efficiency of up to 2.07% for in-band 13.5-nm radiation using mass-limited Sn-doped droplet targets. This result opens a new technological path towards fiber laser based high power EUV sources for high-throughput lithography steppers.

Demonstration of fiber-laser-produced plasma source and application to efficient extreme UV light generation.

Efficient generation of extreme UV (EUV) light at lambda = 13.5 nm from a bulk Sn target has been demonstrated by using a fiber laser. The conversion efficiency from the 1064 nm IR to the EUV was measured to be around 0.9% into 2pi steradians within a 2% bandwidth. To the best of our knowledge, this is the first time an all-fiber system was used to generate EUV or soft x rays.

Progress in EUV photoresist technology

Resist resolution remains a significant issue for EUV. Strong concerns persist regarding the use of chemically amplified resists owing to their diffusion characteristics. Current EUV resist development is focused on a) large-scale screening efforts in an attempt to identify promising platforms and b) refinement and optimization of the processing of these formulations. Resolution arguably remains the parameter of highest importance at this time. The intrinsic resist resolution limit has been claimed to be determined by the resist diffusion length and various metrics have been proposed to characterize this diffusion length as well as resist resolution. Characterization of the intrinsic resolution limit of resists, however, is not a trivial issue due to practical complications such as pattern collapse and top-loss. Here we investigate a variety of resolution and diffusion length metrics and study the correlation between these metrics and observed resist performance when applied to a variety of leading EUV resists. The metrics we study include resist modulation transfer function, corner rounding, through-dose sub-resolution contact printing, iso-focal bias, line-edge-roughness correlation length, and mask error factor. We present an analogous study of resist process refinements. Process refinements are capable of significantly enhancing resolution, expanding process latitude, mitigating resist failure mechanisms, and attenuating line-edge and line-width roughness. Metrics used for correlation of resolution and diffusion length with resist performance show significant utility when applied to process refinement studies as well. Additionally, we show that LWR mitigation can be accomplished in selected EUV resists using post-development surface conditioner rinses. A similar post-development rinse apprach is also demonstrated to reduce pattern collapse at sub-40 nm CDs. Such strategies may become increasingly attractive as CDs shrink toward 32 nm and 22 nm nodes.