This work is supported by the National Science Foundation and the Department of Energy under Grant No. DMR-9712988.
Ionized physical vapor deposition is currently used to deposit metal seed layers (copper) and diffusion barrier layers (TiN, TaN) into high aspect ratio microstructures encountered in the contact and metallization layers of modern integrated circuits.
The ionization process begins with sputtering metal atoms into a high density plasma. The sputtering process accelerates argon ions from the plasma region into a solid target. Atoms are ejected from the target with a cosine angular velocity distribution. At a moderate gas pressure (10-50 mTorr or 1-5 Pa), the atoms are slowed to near thermal velocities by collisions with the argon background gas. Once slowed, the metal atoms are ionized by energetic electron impact. The ions finally diffuse to the wafer where they are collimated by the electric field in the plasma sheath.
Above is a SEM image of a 1 um wide trench that is lined with titanium using I-PVD: