Plasma-assisted atomic layer deposition of Ta2O5 from alkylamide precursor and remote O2 plasma

Tantalum oxide (Ta2O5) films were synthesized by plasma-assisted atomic layer deposition from pentakis(dimethylamino)tantalum (Ta[N(CH3)2]5), precursor and remote O2 plasma as oxidation source. Film growth was monitored in situ by spectroscopic ellipsometry, and film properties were investigated for deposition temperatures between 100 and 225°C. Saturated precursor dosing conditions and plasma exposure times were identified and growth rates ranging from 0.8Å∕cycle at 225°Cto0.87Å∕cycle at 100°C were obtained. The deposited films were found to be stoichiometric (Ta:O=2:5). Moreover, no N incorporation was detected, and the C content was below the detection limit of the Rutherford backscattering measurement (<2at.%) for all films studied. The mass density of the films, ranging from 7.8gcm−3 at 100°Cto8.1gcm−3 at 225°C, was found to be close to the bulk Ta2O5 density. The deviation could partly be accounted for by the amount of H detected with elastic recoil detection analysis, varying from 2at.% at 225°Cto4.6at.% at 100°C. X-ray diffraction revealed that all films were amorphous, independent of deposition temperature. The reaction mechanisms, in particular, during the plasma step, were investigated by using quadrupole mass spectrometry and optical emission spectroscopy. During the plasma step, combustion products such as CO, CO2, and H2O were detected. This indicates that combustionlike processes occur, in which the alkylamide N(CH3)2 ligands are oxidized by the O radicals generated in the plasma. Additionally, the presence of excited CN* molecules in the plasma was observed in the plasma emission.