Thermodynamic Theory of Phase Separation in Nonstoichiometric Si Oxide Films Induced by High-Temperature Anneals

Abstract

High-temperature anneals of nonstoichiometric Si oxide (SiOx, x < 2) films induce phase separation in them, with the formation of composite structures containing amorphous or crystalline Si nanoinclusions embedded in the Si oxide matrix. In this paper, a thermodynamic theory of the phase separation process in SiOx films is proposed. The theory is based on the thermodynamic models addressing various aspects of this process which we previously developed. A review of these models is provided, including: (i) the derivation of the expressions for the Gibbs free energy of Si oxides and Si/Si oxide systems, (ii) the identification of the phase separation driving forces and counteracting mechanisms, and (iii) the crystallization behavior of amorphous Si nanoinclusions in the Si oxide matrix. A general description of the phase separation process is presented. A number of characteristic features of the nano-Si/Si oxide composites formed by SiOx decomposition, such as the local separation of Si nanoinclusions surrounded by the Si oxide matrix; the dependence of the amount of separated Si and the equilibrium matrix composition on the initial Si oxide stoichiometry and annealing temperature; and the correlation of the presence of amorphous and crystalline Si nanoinclusions with the presence of SiOx (x < 2) and SiO2 phase, respectively, in the Si oxide matrix, are explained.

Percolation threshold in annealed ultrathin SiOx films by 2D Monte Carlo simulations

“…The presence of isolated Si nanoparticles in the real annealed SiO 0.7 films may point to incomplete phase separation due to the appearance of internal mechanical stresses hindering this process. 35,36 Despite this, a generally good correspondence between the experimental and the simulation results of the percolation threshold of non-stoichiometric Si oxide films may be inferred, which supports the application of the 2D-MC approach for modelling the characteristics of the phase separation process in ultrathin SiO x films and their resulting structure.…”