Characteristics of atomic-layer-deposited Al₂O₃ high- k dielectric films grown on Ge substrates

This paper describes the structural and electrical properties of Al2 O3 thin films grown through atomic layer deposition onto Ge substrates over a wide deposition temperature range (50-300°C). From grazing-incidence X-ray reflectivity and X-ray photoelectron spectroscopy, we found that increasing the deposition temperature improved the Al2 O3 film density and its dielectric stoichiometry; nevertheless, dielectric intermixing between main Al2 O3 and interfacial Ge O2 appeared at temperatures above 200°C, along with degradation of the Ge O2 Ge interface. Accordingly, a relatively large gate leakage current (Jg) and a high density of interfacial states Dit (> 1013 cm-2 eV-1) were observed as a result of deterioration of the entire Al2 O3 Ge structure at higher deposition temperatures. In addition, although subsequent high-temperature processing at 600°C in a N2 ambient could relieve the oxygen-excessive behavior further, i.e., to provide a more stoichiometric film, the accompanying Ge Ox volatilization close to the dielectric interface caused greater damage to the electrical performance. Only forming gas annealing (H2 N2, 1:10) at low temperature (300°C) improved the capacitance-voltage characteristics of the Pt Al2 O3 Ge structure, in terms of providing a lower value of Dit (ca. 6× 1011 cm-2 eV-1), a lower value of Jg, and a reduced hysteresis width.