MOS Capacitance Measurements for PEALD TiO2 Dielectric Films Grown under Different Conditions and the Impact of Al2O3 Partial-Monolayer Insertion

Abstract

In this paper, we report the plasma-enhanced atomic layer deposition (PEALD) of TiO₂ and TiO₂/Al₂O₃ nanolaminate films on p-Si(100) to fabricate metal-oxide-semiconductor (MOS) capacitors. In the PEALD process, we used titanium tetraisopropoxide (TTIP) as a titanium precursor, trimethyl aluminum (TMA) as an aluminum precursor and O₂ plasma as an oxidant, keeping the process temperature at 250 °C. The effects of PEALD process parameters, such as RF power, substrate exposure mode (direct or remote plasma exposure) and Al₂O₃ partial-monolayer insertion (generating a nanolaminate structure) on the physical and chemical properties of the TiO₂ films were investigated by Rutherford backscattering spectroscopy (RBS), Raman spectroscopy, grazing incidence X-ray diffraction (GIXRD), and field emission scanning electron microscopy (FESEM) techniques. The MOS capacitor structures were fabricated by evaporation of Al gates through mechanical mask on PEALD TiO₂ thin film, followed by evaporation of an Al layer on the back side of the Si substrate. The capacitors were characterized by current density-voltage (J-V), capacitance-voltage (C-V) and conductance-voltage (G-V) measurements. Our results indicate that RF power and exposure mode promoted significant modifications on the characteristics of the PEALD TiO₂ films, while the insertion of Al₂O₃ partial monolayers allows the synthesis of TiO₂/Al₂O₃ nanolaminate with well-spaced crystalline TiO₂ grains in an amorphous structure. The electrical characterization of the MOS structures evidenced a significant leakage current in the accumulation region in the PEALD TiO₂ films, which could be reduced by the addition of partial-monolayers of Al₂O₃ in the bulk of TiO₂ films or by reducing RF power.