Stress-induced leakage current and trap generation in HfO₂ thin films

Stress-induced leakage current (SILC) is studied in 10 nm HfO₂ metal-insulator-metal capacitors. Three regimes are observed in the current-time characteristics, namely, (1) an absorption current, (2) a quasi linear increase of current with time (SILC), and (3) thermal breakdown. Magnitude of SILC is strongly correlated to the nature of the cathode (being large for TiN and weak for Pt and Au), showing that SILC is governed by electron injection. Recovery is observed when short-circuiting the samples, pointing out that SILC is a reversible phenomenon. Desorption current and SILC are not correlated, which indicates that different defects control the absorption current and SILC. SILC is ascribed to the generation of oxygen vacancies upon hot electron injection, while recovery is ascribed to the recombination of oxygen ions with vacancies. In the SILC regime, the current varies as Ktⁿ (n = 1.15 at room temperature). Bias and temperature dependence of K and n are studied. The dependence of K on bias can be described either by a Fowler-Nordheim law or by an exponential law, while the exponent n is almost independent of bias. When temperature is increased, K increases according to an Arrhenius law and n decreases. SILC is modeled by considering the generation of oxygen vacancies by hot electron impact and subsequent electron trapping at vacancies (hopping conduction). An analytical expression for SILC growth is obtained from first order kinetics.