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Modulation capacitance voltage spectroscopy is applied to study the interaction between interface defect states and the conduction band of thermally oxidized n-type silicon wafers, which were prepared using a broad spectrum of preparation conditions. The modulation frequency response of metal oxide semiconductor samples is measured in depletion and accumulation as a function of temperature and of the position of the Fermi level at the interface. The data reveal two different sets of states, the capture cross sections of which differ by as much as 1–2 orders of magnitude. We assign these states to two types of defects which originate from silicon dangling bonds with three backbonded silicon atoms (Pb center) and silicon dangling bonds where one backbond is substituted by oxygen (PL center). Both capture cross sections decrease monotonically with decreasing energetic separation from the conduction band.

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A comparative investigation of the characteristics of the SiN x :H/Si interface has been undertaken by capacitance-voltage measurements and surface photovoltage spectroscopy. By each of these techniques, we have determined the distribution of the interface trap density within the silicon bandgap. The samples were grown by the electron-cyclotron resonance plasma method starting from SiH 4 and N 2 as precursor gases whose flow ratio was varied to produce films of three different compositions: silicon rich, near stoichiometric and nitrogen rich. Post-deposition rapid thermal annealing treatments were applied to observe the evolution of interface properties with the annealing temperature in the range from 300 to 1050 • C. For thin dielectrics, the interface state density has a U-shaped distribution dominated by band-tail states. The minimum of this distribution decreases significantly and shifts to midgap for moderate annealing temperatures. For higher annealing temperatures, the trend is reversed. In the silicon-rich films, the percolation of rigidity caused by the chains of Si-Si bonds impedes the initial decrease of the defect density. For thicker films, the strain of the SiN x :H film produces a higher density of defects that results in increased levels of leakage currents and poorer electrical characteristics.

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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/SiO x N y H z /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 (Q INS). 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 (N 3 ≡Si ↑) or the N dangling bond (Si 2 =N ↑), which may be present in a negatively charged state. For samples of SiO 2 composition, with a negligible N content, Q INS is positive. High densities of interface states (D it), above 10 12 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 Q INS from negative to positive and a decrease of its absolute value, as well as a decrease of D it 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 SiO x N y H z 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.

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