Studies on the stress and thermal properties of Mo/B₄C and Mo_xC_1-x/B₄C multilayers

Abstract

A comparative study of Mo/B 4 C and Mo x C 1-x /B 4 C multilayers deposited by DC magnetron sputtering technology was presented in this paper. Using a homemade real-time stress measure instrument, the stress of two kinds of multilayers was investigated. Characterizations of the multilayers before and after annealing were performed by grazing incident and at-wavelength near-normal incident x-ray reflectivity. Experimental results show that after replacing Mo by Mo x C 1-x , Mo x C 1-x /B 4 C multilayers obtain relatively smaller compressive stress compared with Mo/B 4 C multilayers. The corresponding stress value changes from −0.99 GPa to −0.36 Gpa. Mo x C 1-x /B 4 C multilayers have also proven to have better thermal stability up to 600°C. After repeatedly annealing from 100°C to 600°C, Mo/B 4 C multilayers had a ∼2% decrease in near-normal incident reflectivity, while Mo x C 1-x /B 4 C multilayers had a smaller 1.4% loss of reflectivity and a higher stability temperature.

Multilayer Reflective Coatings for BEUV Lithography: A Review

“…The computer modeling signified that the Mo/B PMMs should display a reflectivity of ⁓53% at a working λ=6.7 nm (Figure 5) [44]. Such reflectivity is many times higher than one of the B4C structures reported by other researchers [34,40,51]. Table 1 gives the summary of the recent achievements of PMMs reflectivity in the BEUV range.…”

“…For comparison, the best B4C-based PMMs such as La/B4C, Mo/B4C, Sb/B4C, etc., demonstrated the reflectivity of around 20-40% at the wavelength of 6.6 nm [32] [26,33]. In the recent study published by Zhu et al in 2020, the peak reflectivity of 10% was recorded for Mo/B4C PMMs [34]. In general, the low reflectivity of B4C-based PMMs should be attributed to the relatively high absorption of Carbon at the 6.6 nm wavelength and various structural imperfections.…”

“…Despite high expectations, these PMMs showed a low reflectivity because of the intermixing of the layers and the high interface roughness. Besides, the active chemical properties of La make it challenging to preserve the reflectivity of La-based PMMs [34]. To improve the reflectivity of La/B PMMs, the nitridation of the interfaces between La and B was recommended [10].…”

“…However, for PMMs with B4C ≥ 2 nm, it was reported that the higher diffusion of B and C (the mobilities of B and C atoms are higher than Mo atoms) into the interlayers led to the formation of low-density compounds resulting in a thickness period expansion. In place of Mo, Zhu et al [34] use MoxC1-x to grow 100 bilayers MoxC1-x/B4C PMMs on Si substrate to compare the effect of stress and thermal treatment. After repeated thermal treatment from 100 °C to 600 °C, the Mo/B4C multilayers showed a ∼2% decrease in reflectivity near-normal incident, whereas MoxC1-x/B4C multilayers proved to be more stable with a 1.4% decrease in reflectivity.…”

Multilayer Reflective Coatings for BEUV Lithography: A Review

“…Thus, Boron in the PMMs was replaced mainly by the less efficient B 4 C. For comparison, the best B 4 C-based PMMs, such as La/B 4 C, Mo/B 4 C, and Sb/B 4 C, demonstrated the reflectivity of around 20-40% at the wavelength of 6.6 nm [26,32,33]. In the recent study published by Zhu et al in 2020, the peak reflectivity of 10% was recorded for Mo/B 4 C PMMs [34]. In general, the low reflectivity of B 4 C-based PMMs should be attributed to the relatively high absorption of carbon at the 6.6 nm wavelength and various structural imperfections.…”