Integral characteristics of spectra of ions important for EUV lithography

Abstract

The emission spectrum corresponding to the 4p54dN+1 + 4p64dN–14f → 4p64dN transition array is concentrated in a narrow interval of wavelengths. That is due to the existence of an approximate selection rule and quenching of some lines by configuration mixing. Thus such emission of elements near Z = 50 is considered to be the main candidate for the EUV lithography source at λ = 13.5 nm. In the present work the regularities of these transition arrays are considered using their integral characteristics: average energy, total line strength, variance and interval of array containing some part of the total transition probability. Calculations for various ions of elements In, Sn, Sb, Te, I and Xe have been performed in a two-configuration pseudorelativistic approximation, which describes fairly well the main features of the spectra. The variation in the values of the main integral characteristics of the spectra with atomic number and ionization degree gives the possibility of comparing quantitatively the suitability of the emission of various ions for EUV lithography.

Intensity enhancement in the emission spectra of Sb, Sn, and W ions due to the mixing of configurations with symmetric exchange of symmetry

“…In the present work the calculation results for these ions are specific in two ways: relativistic Dirac-Fock functions are used instead of quasirelativistic wave functions and the additional integral characteristicshalfwidth of the intense group of lines and total transition probability -are given (Table 1). More accurate relativistic calculations do not change the main conclusions made in [10], but improve the values of average wavelength, which are diminished by 0.13-0.23 nm. For Sn 12+ the obtained result corresponds better to that of semiempirical spectrum.…”

“…As it was shown in [10], the two-configuration approximation (1) enabled us to describe correctly the formation of a narrow group of intense lines in photoabsorption and emission spectra and to obtain rather accurate values of the main characteristics for this group of lines. Recently the probabilities of transitions (2) at N = 2 for Sn 12+ have been calculated semiempirically, taking into account configurations 4p 6 4d nl (n ≤ 6, l = s, p, d, f ), 4p 5 4d 3 , 4p 6 5s 2 , 4p 5 4d 2 5s and scaling down various integrals to different extent [17].…”

“…On the grounds of calculations of integral characteristics for transitions in two-configuration approximation using quasirelativistic wave functions the conclusion was made that from the atomic point of view the strongest emitters in the narrowest interval around 13.5 nm are ions Sn 9+ -Sn 11+ and Sb 10+ -Sb 11+ [10]. In the present work the calculation results for these ions are specific in two ways: relativistic Dirac-Fock functions are used instead of quasirelativistic wave functions and the additional integral characteristicshalfwidth of the intense group of lines and total transition probability -are given (Table 1).…”

“…For the purpose of investigating which ions are most suitable as the required source of EUV emission, the calculation of integral characteristics of these transitions for a wide interval of ionization degrees and atomic numbers around Z = 50 was performed in [10], and the ions with the optimal set of atomic characteristics were determined.…”

Spectroscopy of Ionized Atoms for Nanotechnology

“…The other possible reason is reflected in a formation of so called "emissive zone" [16,17]. Figure 3 is an illustration to resent calculations [18] based on our experimental data.…”