Structural changes in nanometer-thick silicon-on-insulator films during high-temperature annealing

The thermal stability of silicon-on-insulator films with a thickness of 4.7 and 2.2 nm is studied as a function of annealing temperature in the range of $T$ = 800–1200$^\circ$C by scanning electron microscopy and spectral ellipsometry. No signs of film melting were found; the films remain continuous over this annealing temperature range. A decrease in the thickness of the films and a change in their phase composition with an increase in temperature are discovered. According to the data of spectral ellipsometry, as the annealing temperature is increased, the content of the crystalline phase in the films decreases and the content of the amorphous phase increases. The activation energy of the process of film amorphization is estimated. The revealed properties are discussed from the viewpoint of diffusion of oxygen atoms into a silicon film and rearrangement of Si–Si bonds.