Mass and energy measurements of the species responsible for $cBN$ growth in rf bias sputter conditions

Mass and energy measurements of ions and neutrals impinging on a substrate surface were performed during radio frequency (rf) bias sputter deposition of cubic boron nitride $(cBN)$ thin films in a pure Ar discharge. The sampling system was rf driven to measure the correct energy of ions impinging to the rf driven substrate. The ion energy distributions showed asymmetric bimodal shapes and the energy spreads varied with the masses of ions and the negative substrate bias voltage $(Vs).$ $Ar+$ was the most dominant ion, and the average energy and energy spread changed with $Vs$ from 90 to 310 eV and from 40 to 140 eV, respectively. The flux ratio of $Ar+$ to B $(Φi/ΦB)$ increased from 1.0 to 2.3 with a decrease in the target power input. $cBN$ could be deposited above a threshold of the total momentum transfer per depositing boron atoms; $138 (eV amu)1/2,$ which is comparable to the values reported in the ion beam assisted depositions. Therefore, argon ions with an energy of 135 to 380 eV are considered to be equally contributory for $cBN$ formation. Moreover, nucleation of $cBN$ depends on $Φi/ΦB,$ namely, the flux ratio of ion to boron, and requires accumulation of a certain surface state caused by ion bombardment effects, such as defects generation or densification.