Barrier layers: TEM investigations

• Starting point: pure Mo/Si with G=d_Mo/d_period=0.4
• Introduction of 0.5nm B₄C on Si-on-Mo (Fig. 4a), Mo-on-Si (Fig. 4b) and both interfaces (Fig. 4c)

Fig. 4: TEM cross sections of of Mo/Si multilayers with B₄C on Si-on-Mo (a), Mo-on-Si (b) and both interfaces (c).

Analysis of TEM investigations and EUV reflectivity measurements:

• B₄C on Si-on-Mo: polycrystalline Mo layer, amorphous interlayer on Mo-on-Si interface, steep density gradient on Si-on-Mo interface, R_EUV=67.9%
• B₄C on Mo-on-Si: amorphous Mo layer, amorphous interlayer on Si-on-Mo interface with increased thickness compared to pure Mo/Si, steep density gradient on Mo-on-Si interface, R_EUV=67.3%
• B₄C on both interfaces: amorphous Mo and Si layer without interdiffusion layers

CONCLUSION: Barrier layers are necessary on both interfaces!