In-band Emission Research Articles

Heating dynamics and extreme ultraviolet radiation emission of laser-produced Sn plasmas

The impact of 1.064 μm laser absorption depth on the heating and in-band (2% bandwidth) 13.5 nm extreme ultraviolet emissions in Sn plasmas is investigated experimentally and numerically. In-band emission lasting longer than the laser pulse and separation between the laser absorption and in-band emission region are observed. Maximum efficiency is achieved by additional heating of the core of the plasma to allow the optimal temperature to expand to a lower and more optically thin density. This leads to higher temperature plasma that emits less in-band light as compared to CO2 produced plasma sources for the same application.

Interference effects of 24 GHz UWB automotive short-range radar to broadcasting and fixed satellite services in Ku and Ka bands

The introduction of the automotive radar was a challenge for spectrum engineering and management primarily because of its out-of-band emissions, and not due to its in-band emissions. The SRR will have a large operating bandwidth of up to 5 GHz and could potentially cause interference to broadcasting and fixed satellite services operating/planned in the nearby Ku and Ka bands. The emissions from 24 GHz systems on-board a vehicle should not cause unwanted interference to these services. Accompanying the market introduction of 24 GHz ultrawide band (UWB) short automotive radar (short-range radar), extensive co-existence studies have been performed between 24 GHz UWB short-range radar and different present and planned RF services. In this paper, an estimate of the interference due to direct-coupled fields from the SRR's on a single vehicle to BSS and FSS systems in Ku and Ka bands, is studied. In addition, aggregate interference from multiple SRR's mounted on single/multiple vehicles are also analysed. This paper introduces a methodology for coexistence studies between 24 GHz UWB SRR and BSS/FSS services.

Optimization of a gas discharge plasma source for extreme ultraviolet interference lithography at a wavelength of 11 nm

In this work, we report about the optimization of the spectral emission characteristic of a gas discharge plasma source for high-resolution extreme ultraviolet (EUV) interference lithography based on achromatic Talbot self-imaging. The working parameters of the source are optimized to achieve a required narrowband emission spectrum and to fulfill the necessary coherence and intensity requirements. The intense 4f-4d transitions around 11 nm in a highly ionized (Xe8+–Xe12+) xenon plasma are chosen to provide the working wavelength. This allows us to increase the available radiation intensity in comparison with an in-band EUV xenon emission at 13.5 nm and opens up the possibility to strongly suppress the influence of the 5p-4d transitions at wavelengths between 12 and 16 nm utilizing a significant difference in conditions for optical thickness between 4f-4d and 5p-4d transitions. The effect is achieved by using the admixture of argon to the pinch plasma, which allows keeping the plasma parameters approximately constant while, at the same time, reducing the density of xenon emitters. It is demonstrated that with this approach it is possible to achieve a high intensity 11 nm EUV radiation with a bandwidth of 3%–4% without the use of multilayer mirrors or other additional spectral filters in the vicinity of the working wavelength. The achieved radiation parameters are sufficient for high-performance interference lithography based on the achromatic Talbot effect.

Optimization of the size ratio of Sn sphere and laser focal spot for an extreme ultraviolet light source

The effect of the ratio of Sn sphere diameter to laser focal spot size (SD/FSS) on conversion efficiency (CE) from laser to in-band (2%) 13.5nm extreme ultraviolet (EUV) light was investigated by fixing the laser spot size and irradiating variable diameter spheres. It was found that a minimum SD/FSS, i.e., 2.5, is necessary to produce high in-band CE, which is 15% higher than planar targets. Two-dimensional plasma density profile maps showed that the density of the dominant in-band EUV emission region and the size of the surrounding absorbing plasma can be manipulated by geometric effects of the SD/FSS ratio.

Two dimensional expansion effects on angular distribution of 13.5nm in-band extreme ultraviolet emission from laser-produced Sn plasma

The angular distribution of extreme ultraviolet emission at 13.5nm within 2% bandwidth was characterized for laser irradiated, planar, Sn targets at prototypic conditions for a lithography system. We have found that two dimensional plasma expansion plays a key role in the distribution of in-band 13.5nm emission under these conditions. The angular distribution was found to have two peaks at 45° and 15°. This complex angular distribution arises from the shape of both the emitting plasma and the surrounding absorbing plasma. This research reveals that the detailed angular distribution can be important to the deduction of conversion efficiency.

Extreme-ultraviolet spectral purity and magnetic ion debris mitigation by use of low-density tin targets

We investigate the extreme-ultraviolet (EUV) emission from targets that contain tin as an impurity and the advantages of using these targets for ion debris mitigation by use of a magnetic field. The EUV spectral features were characterized by a transmission grating spectrograph. The in-band EUV emission energy was measured with a calorimeter of absolute calibration. The ion flux coming from the plume was measured with a Faraday cup. Our studies indicate that 0.5% Sn density is necessary to obtain a conversion efficiency very close to that of full-density Sn. The use of Sn-doped low-Z targets provides a narrower unresolved transition array and facilitates better control of energetic ions in the presence of a moderate magnetic field of 0.64 T.

Spectral control of emissions from tin doped targets for extreme ultraviolet lithography

We have investigated the unresolved transition array (UTA) emission around 13.5 nm from solid density tin and tin doped foam targets. Extreme ultraviolet (EUV) spectral measurements were made in the wavelength region 11–17 nm using a transmission grating spectrograph and the EUV in-band conversion efficiency was measured using an absolutely calibrated EUV calorimeter. The aim of this work was to optimize the UTA emission with the proper density of tin dopant in low-Z foam targets. The addition of tin as an impurity leads to a reduction in the plasma continuum and narrowing of the UTA compared with fully dense tin targets. Our studies indicate that the required percentage of tin for obtaining bright in-band spectral emission is less than 1%.