Plasma-enhanced ALD of platinum with O₂, N₂ and NH₃ plasmas

Platinum thin films were grown by plasma-enhanced atomic layer deposition (PEALD) using (methylcyclopentadienyl)- trimethylplatinum (MeCpPtMe₃) as precursor and respectively an oxygen, nitrogen and ammonia plasma as reactant. For each process the film thickness was found to be linearly dependent on the number of reaction cycles. Saturation curves and temperature windows were defined and growth rates of 0.45 Å cycle-1, 0.30 Å cycle-1 and 0.40 Å cycle-1 were obtained for the oxygen, nitrogen and ammonia process respectively. All the films were metallic platinum, crystalline, uniform and closed, with low surface roughness and low impurity levels. At a pressure of 1 × 10-3 mbar, nucleation on SiO₂ was remarkably faster with the NH3 and N₂ processes than with the O₂ process. In-situ OES and MS measurements showed a fundamental difference between the NH₃ and N₂ processes and the O₂ process. Based on these measurements we propose a reaction mechanism for the N₂ and NH ₃ PEALD processes where nitrogen will unstably adsorb on the substrate during the plasma pulse and be used during the subsequent precursor pulse to remove part of the precursor ligands.