Inflight electron impact excitation in ionized metal physical vapor deposition

Ionized metal physical vapor deposition (IMPVD) is a process in which sputt ered metal atoms from a magnetron target are ionized by a secondary plasma before depositing onto the substrate. The sputtered metal atoms and neutral ized ions reflected from the target have higher kinetic energies than the b uffer 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 significa ntly contribute to excitation and ionization. To investigate these processe s, a model was developed to include the inflight electron impact excitation (IEIE) of sputtered species during IMPVD. Results for Cu IMPVD indicate th at the predicted Cu+ density at low pressure (2 mTorr) significantly increa sed when IEIE was taken into account. As the pressure increases, the rate o f thermalization increases and the importance of IEIE decreases. (C) 2001 A merican Institute of Physics.