4.3 Interface-Engineered Multilayer Structure
4.3.2 Re‡ectance Optimization with Di¤erent Barrier Layers in a Mo/Si
In extreme ultraviolet lithography, the multilayer re‡ectance and the thermal stability strongly depends on the di¤usion barrier thicknesses. In this research, we have inves-tigated to replace the original Mo/Si structure in one side layer or both layers by the barrier materials. Simulation results in Figure 4-7 show that regardless of the material as the barrier layer, the re‡ectance is over 70% for the barrier layer thickness d 1:2nm.
Nevertheless, a …nal decision has to consider the suitability of the particular material as an di¤usion and reaction between the individual layers of Mo and Si.
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Figure 4-7: Calculations of EUV re‡ectance depending on the thickness of B4C, C, and Ru barrier layers at the Mo-on-Si interface.
Consider the …eld intensity at the layer interfaces, the standing wave …eld has antin-odes at Si-on-Mo interfaces and therefore the absorption of barrier layers at this stack position will strongly a¤ect the EUV re‡ectance. We can do the similar calculation as Figure 4-7. From calculations, we can conclude that even materials with a lower EUV absorption like boroncarbide or carbon would cause a stronger loss to re‡ectance. Fig-ure 4-8 shows the 13.5-nm re‡ectance obtained for multilayers that have three kinds of interlayer thicknesses in the range of 0.1 1.8 nm. Note that the variable barrier layer thickness, combined with a …xed pair thickness, results in an optical response that has a maximum in the re‡ectance curve at varying wavelengths in the range of 12 15 nm.
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 30
35 40 45 50 55 60 65 70 75
B4C C Reflectance (%) Ru
Thickness of Barrier Layer (nm) Si-substrate / 54 (Mo / BL / Si)
dMo = 3.4 nm - 0.5dBL dSi = 3.6 nm - 0.5dBL
Figure 4-8: Calculations of EUV re‡ectance depending on the thicknesses of B4C, C, and Ru barrier layers at the Si-on-Mo interface.
The case that the barrier layer replaces the original absorption layer (dMo) or spacer layer (dSi) only are shown in Figures 4-9 to 4-12.
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Figure 4-9: Calculations of EUV re‡ectance depending on the thickness of B4C, C, and Ru barrier layers at the Mo-on-Si interface.
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Figure 4-10: Calculations of EUV re‡ectance depending on the thickness of B4C, C, and Ru barrier layers at the Mo-on-Si interface.
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Figure 4-11: Calculations of EUV re‡ectance depending on the thicknesses of B4C, C, and Ru barrier layers at the Si-on-Mo interface.
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Figure 4-12: Calculations of EUV re‡ectance depending on the thicknesses of B4C, C, and Ru barrier layers at the Si-on-Mo interface.
In this study, we used carbon, boroncarbide, and ruthenium as di¤usion barrier layers for enhancement of the re‡ectance. The detailed parameters and the corresponding re‡ectance of interface-engineered ML structures are tabulated in Tables 4.4 - 4.9. Based on the simulation results of Tables 4.4 - 4.9, it was suggested that boroncarbide is more suitable as the barrier layer for applying at the Si-on-Mo interface. Similarly, it was suggested that ruthenium is more suitable as the barrier layer for applying at the Mo-on-Si interfaces.
Table 4.4: The detailed parameters of interface-engineered B4C/Mo/Si ML structure at Mo-on-Si interface.
dB4C (nm) dM o (nm) dSi(nm) R = 13.5 nm (%) Rp eak (%) ( p eak)
0.2 3.4 3.6 31.51 72.86 (13.99 nm)
B4C/Mo/Si 0.2 3.2 3.6 71.53 73.56 (13.62 nm)
0.2 3.4 3.4 71.59 72.52 (13.59 nm)
0.2 3.3 3.5 71.60 72.87 (13.61 nm)
Table 4.5: The detailed parameters of interface-engineered C/Mo/Si ML structure at Mo-on-Si interface.
dC (nm) dM o (nm) dSi (nm) R = 13.5 nm (%) Rp eak (%) ( p eak)
0.2 3.4 3.6 31.76 72.83 (13.99 nm)
C/Mo/Si 0.2 3.2 3.6 71.54 73.14 (13.62 nm)
0.2 3.4 3.4 71.58 72.49 (13.59 nm)
0.2 3.3 3.5 71.61 72.84 (13.60 nm)
Table 4.6: The detailed parameters of interface-engineered Ru/Mo/Si ML structure at Mo-on-Si interface.
dR u (nm) dM o (nm) dSi(nm) R = 13.5 nm (%) Rp eak (%) ( p eak)
0.2 3.4 3.6 39.31 72.32 (13.96 nm)
0.2 3.2 3.6 71.76 72.72 (13.59 nm)
Ru/Mo/Si 0.2 3.4 3.4 71.47 71.85 (13.57 nm)
0.2 3.3 3.5 71.66 72.32 (13.57 nm)
1.4 2.0 3.6 73.04 73.74 (13.58 nm)
Table 4.7: The detailed parameters of interface-engineered Mo/B4C/Si ML structure at Si-on-Mo interface.
dM o(nm) dB4C (nm) dSi(nm) R = 13.5 nm (%) Rp eak (%) ( p eak)
3.4 0.2 3.6 31.31 72.42 (13.99 nm)
Mo/B4C/Si 3.2 0.2 3.6 71.09 72.71 (13.62 nm)
3.4 0.2 3.4 71.14 72.08 (13.59 nm)
3.3 0.2 3.5 71.16 72.42 (13.61 nm)
Table 4.8: The detailed parameters of interface-engineered Mo/C/Si ML structure at Si-on-Mo interface.
dM o(nm) dC (nm) dSi(nm) R = 13.5 nm (%) Rp eak (%) ( p eak)
3.4 0.2 3.6 31.30 71.84 (13.99 nm)
Mo/C/Si 3.2 0.2 3.6 70.53 72.12 (13.62 nm)
3.4 0.2 3.4 70.57 71.47 (13.59 nm)
3.3 0.2 3.5 70.60 71.81 (13.60 nm)
Table 4.9: The detailed parameters of interface-engineered Mo/Ru/Si ML structure at Si-on-Mo interface.
dM o(nm) dR u (nm) dSi(nm) R = 13.5 nm (%) Rp eak (%) ( p eak)
3.4 0.2 3.6 37.90 69.82 (13.96 nm)
Mo/Ru/Si 3.2 0.2 3.6 69.22 70.16 (13.59 nm)
3.4 0.2 3.4 68.90 69.30 (13.56 nm)
3.3 0.2 3.5 69.10 69.75 (13.57 nm)
Making these values was chosen to obtain good agreement between simulations, we have design a …ne structure Ru/Mo/B4C/Si. Calculations of the thickness with di¤erent barrier layers at every interface are listed in Table 4.10 as follows.
Table 4.10: The detailed parameters of interface-engineered Ru/Mo/B4C/Si ML we could achieve a higher re‡ectance 73.04% at 13.5-nm wavelength, a peak re‡ectance 73.74% at 13.58 nm with Ru/Mo/Si multilayer structure, and a FWHM of 0:829 nm as shown in Figure 4-13. Likewise, based on Table 4.7 with dB4C = 0:2 nm, dMo = 3:3nm, and dSi = 3:5 nm, we could achieve a higher re‡ectance 71.16% at 13.5-nm wavelength, a peak re‡ectance 72.42% at 13.61 nm with Mo/B4C/Si multilayer structure, and a FWHM of 0:708 nm as shown in Figure 4-13. Considering the practical process and using ruthenium and boron carbide as barrier layers at all interfaces as shown in Table 4.10 with dRu = 1:4 nm, dB4C = 0:2 nm, dMo = 1:8 nm, and dSi = 3:6 nm, we could achieve a higher re‡ectance 72.61% at 13.5-nm wavelength, a peak re‡ectance 73.64% at 13.60 nm with Ru/Mo/B4C/Si multilayer structure, and a FWHM of 0:837 nm as shown in Figure 4-13. These spectral re‡ectance comparison are all shown in Figure 4-13. We have also investigated re‡ectance dependency on each thin-…lm thickness, and the results are listed in Tables 4.11 - 4.15. With dRu = 1:4 nm, dB4C = 0:2nm, dMo = 1:9 nm, and dSi = 3:5 nm, we have achieved a higher re‡ectance 72.62% at 13.5-nm wavelength, a peak re‡ectance 73.30% at 13.58 nm with Ru/Mo/B4C/Si multilayer structure, and a FWHM of 0:828 nm as shown in Figure 4-14. The detailed parameters of ML structures are listed in Tables 4.16 and 4.17. Although the higher re‡ectance seems to be Ru/Mo/Si multilayer structure, we should consider the experimental process to choose the useful Ru/Mo/B4C/Si multilayer structure.
Table 4.11: The detailed parameters of interface-engineered Ru/Mo/B4C/Si ML struc-ture with thickness dependent.
dR u (nm) dM o (nm) dB4C(nm) dSi (nm) R = 13.5 nm (%) Rp eak (%) ( p eak)
1.2 1.8 0.2 3.8 72.29 74.12 (13.63 nm)
Ru/Mo/B4C/Si 1.2 1.9 0.2 3.7 72.48 73.87 (13.61 nm)
1.2 2.0 0.2 3.6 72.57 73.56 (13.59 nm)
1.2 2.1 0.2 3.5 72.55 73.20 (13.57 nm)
Table 4.12: The detailed parameters of interface-engineered Ru/Mo/B4C/Si ML struc-ture with thickness dependent.
dR u (nm) dM o (nm) dB4C(nm) dSi (nm) R = 13.5 nm (%) Rp eak (%) ( p eak)
1.3 1.8 0.2 3.7 72.50 73.91 (13.62 nm)
Ru/Mo/B4C/Si 1.3 1.9 0.2 3.6 72.60 73.61 (13.59 nm)
1.3 2.0 0.2 3.5 72.60 73.27 (13.58 nm)
1.3 2.1 0.2 3.4 72.48 72.86 (13.55 nm)
Table 4.13: The detailed parameters of interface-engineered Ru/Mo/B4C/Si ML struc-ture with thickness dependent.
dR u (nm) dM o (nm) dB4C(nm) dSi (nm) R = 13.5 nm (%) Rp eak (%) ( p eak)
1.4 1.7 0.2 3.7 72.49 73.91 (13.61 nm)
Ru/Mo/B4C/Si 1.4 1.8 0.2 3.6 72.61 73.64 (13.60 nm)
1.4 1.9 0.2 3.5 72.62 73.30 (13.58 nm)
1.4 2.0 0.2 3.4 72.51 72.91 (13.56 nm)
Table 4.14: The detailed parameters of interface-engineered Ru/Mo/B4C/Si ML struc-ture with thickness dependent.
dR u (nm) dM o (nm) dB4C(nm) dSi (nm) R = 13.5 nm (%) Rp eak (%) ( p eak)
1.5 1.6 0.2 3.7 72.45 73.88 (13.62 nm)
Ru/Mo/B4C/Si 1.5 1.7 0.2 3.6 72.58 73.62 (13.60 nm)
1.5 1.8 0.2 3.5 72.61 73.31 (13.58 nm)
1.5 1.9 0.2 3.4 72.52 72.93 (13.56 nm)
Table 4.15: The detailed parameters of interface-engineered Ru/Mo/B4C/Si ML
Table 4.16: The detailed parameters of interface-engineered Ru/Mo/Si, Mo/B4C/Si, and Ru/Mo/B4C/Si ML structures.
dBL (nm) dM o (nm) dSi (nm) R = 13.5 nm (%) Rp eak (%)
Ru/Mo/Si dR u = 1:4 2.0 3.6 73.04 73.74 (13.58nm)
Mo/B4C/Si dB4C = 0:2 3.3 3.5 71.16 72.42 (13.61nm)
Ru/Mo/B4C/Si dR u = 1:4 dB4C= 0:2 1.8 3.6 72.61 73.64 (13.60nm)
12.0 12.5 13.0 13.5 14.0 14.5 15.0
0
Figure 4-13: The spectral re‡ectance comparison of the Ru/Mo/Si ML structure, Mo/B C/Si ML structure, and Ru/Mo/B C/Si ML structure.
Table 4.17: The detailed parameters of interface-engineered Mo/Si ML structure and Ru/Mo/B4C/Si ML structure.
dBL(nm) dM o(nm) dSi(nm) R = 13.5 nm (%) Rpeak (%)
Mo/Si 0 3.4 3.6 71.65 72.91 (13.61 nm)
Ru/Mo/B4C/Si dRu= 1:4 dB4C= 0:2 1.9 3.5 72.62 73.30 (13.58 nm)
12.0 12.5 13.0 13.5 14.0 14.5 15.0
0 10 20 30 40 50 60 70 80
[Ru/Mo/B4C/Si]54 Rλ = 13.5 nm = 72.62 % FWHM = 0.828 nm [Mo/Si]54
Rλ = 13.5 nm = 71.65 % FWHM = 0.710 nm
Reflectance (%)
Wavelength (nm) Mo/Si ML
Ru/Mo/B4C/Si ML
Figure 4-14: The spectral re‡ectance comparison of the Mo/Si ML structure and Ru/Mo/B4C/Si ML structure.