Atomic Layer Deposition of BaTiO3 Thin Films - Effect of Barium Hydroxide Formation

摘要

Barium titanate thin films are grown by atomic layer deposition (ALD) at 340 ℃ from barium cyclopentienyl and titanium methoxide precursors. H2O is used as the oxygen source. Binary reactions of Ba(tBu3C5H2)2 and H2O are first studied separately in BaO deposition and are found to result in a hydration/dehydration cycle, which is strongly influenced by the process temperature. Self-limiting growth of amorphous barium titanate films becomes possible when Ti(OMe)4 - H2O growth cycles are mixed as well as possible with Ba(tBu3C5H2)2 - H2O cycles. The as-deposited amorphous films are crystallized by post-deposition annealing at 600 ℃. Permittivities of 15 and 70 are measured for as-deposited and post-deposition annealed films, respectively. A charge density of 1.9 μC cm-2 (equivalent oxide thickness of 1.8 nm) and leakage current density ≤ 1 * 10-7 A cm-2 were achieved at 1 V bias with a 32 nm thick Ba-Ti-O film in a Pt electrode stack annealed at 600 ℃.