Investigation of the interlayer characteristics of Ta 2O 5 thin films deposited on bare, N 2O, and NH 3 plasma nitridated Si substrates

Abstract

Low-temperature N 2O and NH 3 plasma nitridations on Si surfaces are conducted to prevent the thermodynamic instability at the Ta 2O 5/Si interface. The surface and interface of the Ta 2O 5/Si systems, without or with nitridation, were examined by x-ray photoelectron spectroscopy (XPS), atomic force microscopy, transmission electron microscopy, and secondary ion mass spectrometry. Capacitance-voltage (C-V) measurements were carried out to investigate the electric/defect characteristics of the Ta 2O 5/Si systems. For the non-nitrided Si substrate XPS detects no surface oxide formed prior to Ta 2O 5 deposition. In contrast, NH 3 plasma nitridation forms a nitrogen-rich SiO xN y layer, while N 2O plasma nitridation produces an oxygen-rich SiO xN y layer on Si. C-V measurement reveals high densities of fixed charges, trapping sites, and interface states in the Ta 2O 5/non-nitrided Si sample, indicative that a defective interlayer was formed during Ta 2O 5 deposition. Ta 2O 5 on both nitrided systems exhibits a reduced amount of fixed charges and trapping sites. Nevertheless, NH 3 plasma nitridation is not as effective as N 2O plasma nitridation in diminishing the density of interface states. The different electric/defect characters between the NH 3 and N 2O nitrided systems are attributed to the further oxidation of the nitrogen-rich SiO xN y layer produced by NH 3 plasma nitridation, which induces defects at the dielectric/Si interface. Effectiveness of the nitridation process, therefore, depends on the stability of the nitrided layer during deposition of Ta 2O 5. © 2002 American Institute of Physics.