Tin Deposition and Tin Cleaning for EUVL

April 1, 2024

Extreme ultraviolet lithography (EUVL) is one of the cutting-edge leading technologies in a semiconductor industries. For tin Cross Section Measurements, the mean free path of an ion as it travels through the EUV source is dependent on the cross section. For tin Diffusion Coefficient Measurements, tin vapor, generated as ions neutralize, diffuses throughout the system. Deposition rate depends on tin flux. Tin can be cleaned by H2 etching, forming SnH4 vapor. SnH4 sticking coefficients for other EUV relevant surfaces need to be measured. Tin exposed to H radicals can become brittle and eject solid particles (tin spitting). Size, velocity, and rate of particle ejection need to be characterized to ensure they will not damage other EUV components.

CO2 Laser Enhancement for EUV lithography

April 1, 2024

CO2 drive lasers are a vital component of current EUV lithography tools. Up to 60-80% of the CO2 dissociates into CO and O during operation of ICP. Oxygen creates parasitic species (Ox, NOX) which lower laser efficiency. Auxiliary plasmas are being studied to dissociate parasitic species and preferentially recombine CO and O into CO2. We installed Au o Cu catalyst to see the effect on CO2 recombination after ICP discharge.

Liquid Metal Work

April 1, 2024

CPMI is a big proponent of lithium as the most promising fusion PFC with both Dr. Ruzic and Dr. Andruczyk having extensive experience and current projects working with lithium or its alloys. 

Lithium Corrosion

April 1, 2024

•Material Attacked by Lithium Corrosion Experiment (MALiCE).

•Extended static molten lithium exposure.

•6 individual canisters.

•Canisters held at 1 to 5 PSI of Ar during exposure.

•Spinning Lithium Attacked Potential Substrates (SLAPS).

•Extended dynamic molten lithium exposure.

•8 samples in 1 experimental session.

•Corrosion tests conducted under high vacuum.

Liquid Metal Infused Trenches (LiMIT) in a SLiDE Lithium Loop

April 1, 2024

The Solid/Liquid Divertor Experiment (SLiDE) chamber is used to expose divertor concepts to fusion relevant heat fluxes to test their viability.

•Solid/Liquid Divertor Experiment (SLiDE) chamber to test divertor concepts under representative heat fluxes.

•SLiDE generates a E-beam or a ECR plasma.

•Focuses on liquid metal divertor concepts.

•Loop allows liquid metal flow for extended periods without substantial contamination build-up. 

•Lithium engineering and de-risking is additional goal for Li loop construction and operation.

•Modular Li loop allows components to be added or removed as needed for testing, cleaning or any planned upgrades/modifications.

Extreme Ultraviolet Light

April 1, 2024

Extreme ultraviolet (EUV) light at the desired wavelength, 13.5 nm, is created through very high energy releases of photons due to the de-excitation of heavily ionized tin, Sn14+. This degree of ionization is only possible in a strong plasma, which in industry is created by irradiating tin droplets with a high-power laser. A large problem associated with this type of EUV source is tin debris buildup on the mirror, leading to reduced EUV intensity over time as the mirror gets dirtier. Previously, work has been done at the Center for Plasma-Material Interactions (CPMI) to use a hydrogen plasma to etch the tin off the surface of the mirror, effectively cleaning it in-situ. Although effective for cleaning, debris can still damage the mirror due to high energies. A small scale EUV source has been created, allowing for less intensive experimentation on tin debris within the chamber. This source is called MK-III and is shown on the right. The laser is pulsed at various powers, creating varying intensities of EUV as plotted below. After laser pulses, the tin target is irradiated, creating EUV light and creating tin debris within the chamber. Hydrogen gas is flowed in the chamber at 100 sccm at various pressures, finding better debris removal at lower pressures as shown in the SEM images.

Pellet Radical Probes

April 1, 2024

Radicals are very important for many of the processes that occur during the production of computer chips and other processes involving plasmas. However, the direct measurement of radical density is difficult due to their reactivity and tendency to recombine with themselves. Instead, by catalyzing the recombination process and measuring the heat released, one can infer the density of radicals present in a system at equilibrium. For probes not at equilibrium, the temperature time derivatives become important, treating the probes as 0D objects with heating and cooling terms. F-radical measurement is especially difficult due to catalyst fouling and low F-F recombination coefficients. Etching-based probes use the high etch rates of fluorine to improve measurement signal. Since thin coatings etch too quickly, pellets containing thermocouples that measure dT/dt can be used instead, allowing for the calculation of density. Al and W pellet probes were placed in SF6 and NF3 plasmas, comparing measurements of F radical density to spectroscopy. Comparing probes made of al, the aluminum probe is only heated by the plasma, whereas the tungsten turns red hot due to the creation of WF6, showing material sensitivity.

Etching Degradation of Elastomer O-rings

April 1, 2024

• Elastomer O-rings are commonly used as vacuum seals, O-ring degradation and particulate generation has been observed in some plasmas systems
• Mechanistic understanding of O-ring degradation from plasma exposure could enable new, resilient elastomer development
• Degradation tests conducted in semiconductor industry relevant gases and chamber layout
• Etching species diagnostic experiments
• Prototype radical probes designed and tested to measure F radicals in SF6 and NF3 plasmas

Time, Mass, and Energy Resolved Diagnostics

April 1, 2024

•Time and Energy resolved Mass Spectroscopy, allows for differentiation between metal and gas ions
• Ion Energy Distribution Functions (IEDF)
• Time resolved measurement of ion energy during a HiPIMS pulse showing energy increase during the kick
• Electron Energy Distribution Functions (EEDF)
• Shows the evolution of the electron energy as well as plasma density during the discharge

High Power Impulse Magnetron Sputtering (HiPIMS)

April 1, 2024

Pulsed deposition technique
• Up to 100’s of kW peak power for the same average power as direct current magnetron sputtering (DCMS)
• High peak power means electron density can be 2 orders of magnitude higher for HiPIMS than DCMS
• Higher electron density leads to higher ionization fraction which improves film density, hardness, and conformality
• Positive voltage pulse (kick ) following the main pulse enables control over the ion energy