Inflight electron impact excitation in ionized metal physical vapor deposition

Ionized metal physical vapor deposition (IMPVD) is a process in which sputtered metal atoms from a magnetron target are ionized by a secondary plasma before depositing onto the substrate. The sputtered metal atoms and neutralized ions reflected from the target have higher kinetic energies than the buffer gas and so are not in thermal equilibrium. These nonthermal (inflight) species can dominate the total metal species density at low pressures (<5 mTorr). As a result, electron impact of the inflight species may significantly contribute to excitation and ionization. To investigate these processes, a model was developed to include the inflight electron impact excitation (IEIE) of sputtered species during IMPVD. Results for Cu IMPVD indicate that the predicted Cu+ density at low pressure (2 mTorr) significantly increased when IEIE was taken into account. As the pressure increases, the rate of thermalization increases and the importance of IEIE decreases.