Plasma-Enhanced Atomic Layer Deposition of Silver Thin Films

Thermal properties of various silver precursors known in the literature were evaluated in order to discover which precursor is the most suitable one for plasma-enhanced atomic layer deposition (PEALD) of silver thin films. Ag(fod)(PEt3) (fod = 2,2-dimethyl-6,6,7,7,8,8,8-heptafluorooctane-3,5-dionato) was found to be the best choice. Using Ag(fod) (PEt3) together with plasma-activated hydrogen, silver thin films were deposited at growth temperatures of 120-150 degrees C, and ALD-type saturative growth was achieved at 120-140 degrees C. At 120 degrees C, the growth rate was 0.03 nm per cycle. The plasma exposure time had also an effect on the growth rate: with shorter exposure times, the growth rate was lower over the whole deposition area. The films deposited at 120 degrees C contained relatively small amounts of impurities, but these still affected the electrical properties of the films. The resistivities were relatively low: about 20 nm thick films had a resistivity of 6-8 mu Omega . cm. The morphology and the crystal structure of the films were analyzed as well.