Nanoscale physics

Influence of Low-Temperature Annealing on the Electrical Conductivity of SiOx Films
O.V. Pylypova 1, A.A. Evtukh1,2
1 Institute of High Technologies, Taras Shevchenko National University of Kyiv, Kyiv, Ukraine. E-mail: steblolia@gmail.com
2 V. Lashkaryov Institute of Semiconductor Physics NAS of Ukraine 41 pr. Nauki, 03028, Kyiv, Ukraine.

For the applications of the silicon-based nanostructures (single-electron transistor, cell of non-volatile nanocrystalline memory, resonance-tunneling diode, etc.), it is necessary to study the processes of superfine dielectric films deposition, to investigate the electrical properties of such films [1-3] and the effect of external influences on their parameters. 
In this paper the results on the influence of low temperature annealing at 450 ⁰C in the H2 and vacuum on the conductivity of silicon enriched SiOx films are presented. SiOx films were prepared on Si substrate by low pressure chemical vapor deposition (LP CVD) with using SiH4, N2O as the precursor gases and H2 as a carrier gas. The thicknesses of the deposited films were in the range of 10-30 nm. The influence of low temperature annealing on the electrical properties of SiOx films were investigated. The measurements of current-voltage characteristics were carried out in the wide temperature range 95-300K.
It was revealed that electron transport mechanism depends on as measurement temperature and applied voltage. The influence of low temperature annealing is also significant. In general case it was established that after the annealing of the initial film in the hydrogen the conductivity increases and after annealing in the vacuum decreases. Characteristic feature of all films (without and with annealing) is the conductivity according to the Mott's law at low voltages (U < 1V) in temperature range 295< T < 345 K. The calculated densities of electron states (traps) in bandgap near the Fermi level from slope of curves in Mott’s coordinate are equal to N = 6.62×1016 eV-1×cm- 3 (initial film), N = 2.12×1017 eV-1×cm-3 (H2), N = 4.14×1019 eV-1×cm-3 (vacuum). At higher voltages (U > 1V) and in the temperature range 150-334 K the space charge limited currents (SCLC) are observed for initial and annealing in vacuum films. But for films annealed in H2 the cubic dependence current on voltage I -U3 is characteristic. The cubic dependence points out on the limitation of current transport by injection of electrons and holes. Further increase of voltages (U > 4V) and lowering the temperature range to 95-170 K allowed to reveal Pool-Frenkel (P-F) mechanism of conductivity for the initial films. The height of energy barrier qB  0.68 еV was estimated from the slope of ln(I/U)=f(1/T) dependency. The value of this barrier can be interpreted as the level of traps in the oxide located at the distance qB from the bottom of the oxide conduction band. In case of films annealed in H2 and vacuum the tunneling transport of the charge is observed. 
The model for explanation of experimental results based on passivation of some types of traps by hydrogen at annealing in H2 and effusion of hydrogen from the film at annealing in vacuum has been proposed.

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