Electrical characteristics of Ta2O5 based capacitors with different gate electrodes

Al, W and TiN gate stacks using reactively sputtered thin (15–35 nm) Ta2O5 as a high-k dielectric have been investigated. It has been established that the type and the deposition technique of the gate electrode strongly affect the parameters of the structures. RF sputtered tungsten has been established as the most suitable electrode material (giving a nonreactive contact) providing a low leakage current (∼10-8 A/cm2 at 1 MV/cm) through capacitors and a high dielectric constant. The application of Al gate electrodes in the advanced DRAM devices is impeded by the chemical interaction of Al with the Ta2O5 films deteriorating the performance of the structures. The radiation-induced defects during the TiN deposition increase the leakage currents for TiN/Ta2O5/Si capacitors. A modified Poole–Frenkel conduction mechanism with a tendency for a reduction of the compensation level with increasing Ta2O5 thickness was found for W-gate capacitors. Schottky emission at low applied fields and modified Poole–Frenkel mechanism at high fields define the J–V characteristics of Al capacitors. The current through TiN capacitors is governed by ohmic and space charge limited conduction. The post metallization annealing in H2 reduces the oxide charge but deteriorates both the breakdown fields and the leakage currents for all capacitors studied. The effect is stronger for Al and TiN structures and is accompanied by a reduction of the dielectric constant.