Luis J. Bernardez

High-power extreme ultraviolet source based on gas jets

We report on the development of a high-power laser plasma extreme UV (EUV) source for EUV. The source is based on the plasma emission of a recycled jet beam of large Xe clusters and produces no particular debris. The source will be driven by a pulsed laser delivering 1500 W of focused average power to the cluster jet target. To develop condensers and to optimize source performance, a low-power laboratory cluster jet prototype has been used to study the spectroscopy, angular distributions, and EUV source images of the cluster jet plasma emission. In addition, methods to improve the reflectance lifetimes of nearby plasma-facing condenser mirrors have been developed. The resulting source yields EUV conversion efficiencies up to 3.8 percent and mirror lifetimes of approximately 109 plasma pulses, with further improvement anticipated.

Scale-up of a cluster jet laser plasma source for extreme ultraviolet lithography

A high-average-power extreme UV (EUV) source based on a laser plasma cluster jet is being developed for EUV lithography. The source employs a cooled supersonic nozzle expansion to produce a dense beam of Xe clusters as the plasma source target. The cluster beam is irradiated with a pulsed laser to create a high-temperature plasma radiating efficiently in the EUV spectral region. To accommodate drive laser repetition rates of up to 6000 Hz, a continuous jet expansion with full Xe gas recycling is employed, rather than earlier pulsed jet expansions. The continuous jet employs an efficient high-throughput pumping scheme to minimize the ambient pressure highly-attenuating Xe gas. Source power scale-up is achieved by increasing laser repetition rate, keeping laser pulse parameters nominally fixed. In the first phase of EUV power scale-up, the continuous cluster jet source has been integrated with a 200 W laser driver operating at repetition rates up to 500 Hz. With this system, a laser-to-EUV conversion efficiency of 0.69 percent is achieved. In the second phase, the jet is being integrated with a 1700 W diode-pumped solid sate laser driver operating at repetition rates up to 6000 Hz. A brief description of the 1700 W laser system and its integration with the continuous cluster jet are discussed.

In situ Raman spectroscopy of diamond during growth in a hot filament reactor

We report a system capable of obtaining Raman spectra during growth of carbon films in a hot filament reactor. A gated, multichannel detection system was used to discriminate against the high levels of background radiation produced by the hot substrate and the hot filament. The ability to detect and distinguish between diamond and nondiamond carbon films during growth is shown. Diamond was grown on silicon substrates at 925 °C, with a filament temperature of 2100 °C and with CH4/H2 ratios between 0.002 and 0.008. A nondiamond carbon film was produced with CH4/H2 ratio of 0.016. In order to estimate the sensitivity of the system to detect diamond during growth, the average particle size and fractional coverage of the substrate were determined when a diamond Raman signature was first observed. Currently, the system is capable of detecting diamond particles about 0.5 μm in diameter covering about 3/4 of the surface.

Absorption of extreme ultraviolet light in a laser produced gas-jet plasma source

Laser produced plasmas (LPPs) provide a stable source of extreme ultraviolet (EUV) light making them well suited for use in next-generation lithography tools. The plasma is generated by directing a laser at a target composed of a partially condensed gas after it undergoes a supersonic expansion through a nozzle and enters a vacuum chamber. The expansion process results in very cold temperatures such that the gas partially condenses forming a mixture of gas and small clusters. The clusters absorb the laser energy leading to the formation of the plasma, but the excess gas absorbs some of the emitted EUV light reducing the net output of the LPP. Calculations were carried out to determine the amount of EUV light absorbed by the gaseous xenon that surrounds the plasma. The Navier–Stokes equations were solved to obtain the gas density field. Observations from experiments were used for the shape of the plasma, which showed it to be approximately that of a prolate spheroid. The relative EUV signal strength was ob...

High-power source and illumination system for extreme ultraviolet lithography

A clean, high-power Extreme Ultraviolet (EUV) light source is being developed for Extreme Ultraviolet Lithography (EUVL). The source is based on a continuous jet of condensable gas irradiated with a diode-pumped solid state laser producing a time-averaged output power of 1700 W at 5000 - 6000 Hz. An illumination system is being assembled to collect and deliver the EUV output from the source and deliver it to a reticle and projection optics box to achieve an EUV exposure rate equivalent to ten 300-mm wafers per hour.

System and process learning in a full-field, high-power EUVL alpha tool

Full-field imaging with a developmental projection optic box (POB 1) was successfully demonstrated in the alpha tool Engineering Test Stand (ETS) last year. Since then, numerous improvements, including laser power for the laser-produced plasma (LPP) source, stages, sensors, and control system have been made. The LPP has been upgraded from the 40 W LPP cluster jet source used for initial demonstration of full-field imaging to a high-power (1500 W) LPP source with a liquid Xe spray jet. Scanned lithography at various laser drive powers of >500 W has been demonstrated with virtually identical lithographic performance.

Lithographic evaluation of the EUV engineering test stand

Static and scanned images of 100 nm dense features were successfully obtained with a developmental set of projection optics and a 500W drive laser laser-produced-plasma (LPP) source in the Engineering Test Stand (ETS). The ETS, configured with POB1, has been used to understand system performance and acquire lithographic learning which will be used in the development of EUV high volume manufacturing tools. The printed static images for dense features below 100 nm with the improved LPP source are comparable to those obtained with the low power LPP source, while the exposure time was decreased by more than 30x. Image quality comparisons between the static and scanned images with the improved LPP source are also presented. Lithographic evaluation of the ETS includes flare and contrast measurements. By using a resist clearing method, the flare and aerial image contrast of POB1 have been measured, and the results have been compared to analytical calculations and computer simulations.

Recent advances in the Sandia EUV 10x microstepper

The Sandia EUV 10x microstepper system is the result of an evolutionary development process, starting with a simple 20x system, progressing through an earlier 10x system, to the current system that has full microstepper capabilities. The 10x microstepper prints 400-micrometers -diameter fields at sub- 0.10-micrometers resolution. Upgrades include the replacement of the copper wire target with a pulsed xenon jet target, construction of an improved projection optics system, the addition of a dose monitor a d an aerial image monitor, and the addition of a graphical user interface to the system operation software. This paper provides an up-to-date report on the status of the microstepper.

EUV absorption in a laser-produced plasma source

Laser produced plasmas (LPP) provide a stable source of EUV making them well suited for use in next-generation lithography tools. The plasma is generated by directing a laser at a target composed of a partially condensed gas after it undergoes a supersonic expansion through a nozzle and enters a vacuum chamber. The expansion process results in very cold temperatures such that the gas partially condenses forming a mixture of gas and small clusters. The clusters absorb the laser energy leading to the formation of the plasma, but the excess gas absorbs some of the emitted EUV reducing the net output of the LPP. Calculations were carried out to determine the amount of EUV absorbed by the gaseous xenon that surrounds the plasma. The Navier-Stokes equations were solved to obtain the gas density field. Observations from experiments were used for the shape of the plasma, which showed it to be approximately that of a prolate spheroid. The relative EUV signal strength was obtained as a function of the direction angle by calculating the absorption of EUV in the gas surrounding the plasma and integrating over the plasma surface. Calculated results for the normalized EUV energy distribution compare well with measurements of the EUV angular distribution obtained in experiments.