Annealing effects on the interface and insulator properties of plasma-deposited Al/SiOxNyHz/Si devices

Abstract

We have studied and compared the effects of conventional annealing in a forming gas atmosphere (430 °C, 20 min) and rapid thermal annealing (RTA) in an inert Ar atmosphere (400–1000 °C, 30 s) on Al/SiOxNyHz/Si devices. The samples were deposited by the electron cyclotron resonance plasma method at low temperature (T = 200 °C). The devices were characterized by surface photovoltage measurements before applying contacts and by capacitance–voltage measurements.All the as-deposited samples containing N had positive flat-band voltage, which corresponds to negative charge in the insulator and/or in the interface states (QINS). Additionally, trapping of positive charge is observed when measuring from inversion to accumulation after measuring from accumulation to inversion. This behaviour is tentatively attributed to the presence of defects related to N, such as the K centre (N3≡Si↑) or the N dangling bond (Si2=N↑), which may be present in a negatively charged state. For samples of SiO2 composition, with a negligible N content, QINS is positive. High densities of interface states (Dit), above 1012 eV−1 cm−2, are observed in the as-deposited samples.Both the annealing in a forming gas atmosphere and the RTA result in the change of the sign of QINS from negative to positive and a decrease of its absolute value, as well as a decrease of Dit of about one order of magnitude. The trapping of positive charge is also greatly reduced. These improvements of the electrical properties are attributed to the passivation of defects by H present in the forming gas atmosphere or in the SiOxNyHz film itself in a non-bonded state. For RTA temperatures above 700 °C the properties of the devices degrade due to the release of H. The combination of RTA and annealing in a forming gas atmosphere results in the best properties.