Effect of synchronized bias in the deposition of TiB2 thin films using high power impulse magnetron sputtering

Abstract

Titanium diboride thin films have been deposited from a compound TiB2 target on Si(001) substrates at a temperature of 500 °C using high power impulse magnetron sputtering (HiPIMS) at a frequency of 1000 Hz and pulse lengths of 20 and 40 μs. A −60 V bias pulse of different pulse length was applied at different time delay relative to the HiPIMS pulse. The average energy per deposited species, ⟨ED⟩ = Ei(Ji/Jt), where Ei is the average ion energy and Ji/Jt is the ratio of the ion bombarding flux to the total flux of deposited species, is strongly dependent on bias mode. A change in preferred orientation from (101) to (001) is observed when ⟨ED⟩ increase above 50 eV. The limited adatom mobility at ⟨ED⟩ below 50 eV promote growth of fast growing planes resulting in a (101) texture, while ⟨ED⟩ above 50 eV supply sufficient energy for development of the thermodynamically more favorable (001) texture. A linear increase in compressive residual stress with the increase in ⟨ED⟩ is also found, due to more intensive Ar+ ion bombardment. Analysis of charge-state-resolved plasma chemistry and ion energy shows that the total flux of bombarding ions contains a higher fraction of B+ when the bias is applied in synchronous with the HiPIMS pulse instead of after, resulting in a lower residual stress at similar values of ⟨ED⟩ (cf. −2.0 ± 0.2 and −2.6 ± 0.1 GPa). This study shows that use of a bias synchronized in different modes relative to the HiPIMS pulse, can be used as a tool to control ⟨ED⟩ and to some extent the type of bombarding species, and hence the microstructure of TiB2 thin films.