Ionized physical vapor deposition of Ti and Al

Summary form only given. One method of directional deposition currently under investigation is ionized physical vapor deposition (I-PVD). In this technique sputtered atoms are thermalized by 10-40 mTorr argon gas, ionized by a high-density plasma, and subsequently collimated by the plasma sheath near the wafer. Both experiments and models indicate that up to 80% of the depositing flux in ionized. The dominant physical mechanism responsible for the ionization of sputtered metal atoms is shown to be electron impact ionization, rather than Penning ionization. The high degree of ionization is due to a number of factors: (1) the average ionization potential in the argon plasma is much greater than that of metals, (2) the metal ions are preferentially extracted from the plasma by the presheath region while metal atoms simply diffuse to the wafer, and (3) metal ions are generated in the entire plasma volume and are rather uniformly distributed; metal atoms, however, originate only at the sputter target´s surface-the density of metal neutrals therefore decays significantly downstream near the wafer. Experiments and simple models that support these conclusions will be presented.