Influence of the thickness of Si and Ge films deposited on Si$_3$N$_4$/SiO$_2$/Si substrates on their structure and diffusion of hydrogen atoms from Si$_3$N$_4$ layers

Abstract

The results of RHEED, FTIR and Raman spectroscopy study of silicon and germanium films with the thickness up to 200 nm grown from molecular beams on dielectric Si$_3$N$_4$/SiO$_2$/Si(001) substrates are presented. Noticeable changes of the intensity of the N$-$H and Si$-$N absorption bands have been observed in the IR absorbance spectra as a result of the deposition of the silicon and germanium films. The thicker was the deposited film, the more considerable were the decrease of N$-$H absorption band intensity and the increase in that of the Si$-$N band. This tendency has been observed during the growth of both amorphous and polycrystalline Si or Ge films. The reduction of IR absorption at the band assigned to the N$-$H bond vibration is explained by breaking of these bonds followed by the diffusion of the hydrogen atoms from the Si$_3$N$_4$ layer into the growing film of silicon or germanium. The effect of the deposited film thickness on the diffusion of hydrogen is discussed within a model of the diffusion of hydrogen atoms controlled by the difference in chemical potentials of hydrogen atoms in the dielectric Si$_3$N$_4$ layer and the growing silicon or germanium film. Hydrogen atoms escape from the Si$_3$N$_4$ layer only during the deposition of a Si or Ge film when its thickness gradually grows. The interruption of the film growth stops the migration of hydrogen atoms into the film because of the decline in the chemical potential difference.