Abstract
We optimized the parameters of a laser-produced plasma source based on a solid-state Nd: YAG laser (λ = 1.06 nm, pulse duration 4 ns, energy per pulse up to 500 mJ, repetition rate 10 Hz, lens focus distance 45 mm, maximum power density of laser radiation in focus 9 × 1011 W/cm2) and a double-stream Xe/He gas jet to obtain a maximum of radiation intensity around 11 nm wavelength. It was shown that the key factor determining the ionization composition of the plasma is the jet density. With the decreased density, the ionization composition shifts toward a smaller degree of ionization, which leads to an increase in emission peak intensity around 11 nm. We attribute the dominant spectral feature centred near 11 nm originating from an unidentified 4d-4f transition array in Xe+10…+13 ions. The exact position of the peak and the bandwidth of the emission line were determined. We measured the dependence of the conversion efficiency of laser energy into an EUV in-band energy with a peak at 10.82 nm from the xenon pressure and the distance between the nozzle and the laser focus. The maximum conversion efficiency (CE) into the spectral band of 10–12 nm measured at a distance between the nozzle and the laser beam focus of 0.5 mm was CE = 4.25 ± 0.30%. The conversion efficiencies of the source in-bands of 5 and 12 mirror systems at two wavelengths of 10.8 and 11.2 nm have been evaluated; these efficiencies may be interesting for beyond extreme ultraviolet lithography.
Highlights
Projection extreme ultraviolet (EUV) lithography at 13.5 nm is becoming increasingly widespread in producing critical layers in chips.[1]
It was noted that productivity comparable to 13.5-nm lithography can be expected at 11 nm wavelength, with the resolution improving by about 20%
After optimizing τdel and τop times, we studied the dependence of the conversion efficiency on the xenon pressure at the valve inlet for different distances between the nozzle and the focus of the laser beam spot, which was measured with different filters and a two-mirror monochromator
Summary
Projection extreme ultraviolet (EUV) lithography at 13.5 nm is becoming increasingly widespread in producing critical layers in chips.[1]. An obvious solution to the problem is to reduce the wavelength. In articles,[4,5] a wavelength of about 7 nm was considered promising. The article[6] gives an overview of the actual results in developing effective radiation sources, multilayer mirrors, and EUV resists achieved at 6.7 nm wavelength. This article demonstrated that the productivity of the lithographic process at 6.7 nm is more than an order of magnitude lower than at 13.5 nm. It was noted that productivity comparable to 13.5-nm lithography can be expected at 11 nm wavelength, with the resolution improving by about 20%. The first wavelength is 10.8 nm, which corresponds to the peak position of the emission band excited from the Xe+ 10.
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