Interpretation of hydrogen incorporation into radio frequency sputtered amorphous silicon based on Berg modelling

Abstract

Incorporated hydrogen and its bonding configuration have an effect on the electrical and structural properties of hydrogenated amorphous silicon (a-Si) thin films. On one hand hydrogenization is known to be very efficient in reducing the density of dangling bonds responsible for deep levels in the bandgap; the technological process that carries out the incorporation of hydrogen improves the device parameters. On the other hand, the H–Si–H bonding configuration may negatively affect the microstructure of the amorphous lattice and promote the creation of voids.In this work the incorporation of hydrogen into radio frequency sputtered amorphous silicon thin films is interpreted by means of Berg-model handling the hydrogen incorporation as a reactive sputtering process involving ionization of molecular hydrogen followed by reactions between elemental target atoms to compound molecules. This approach is suitable for the interpretation of hydrogen incorporation into a-Si films based on the fact that the amount of incorporated hydrogen is proportional to the current. The imaginary and the real part of the dielectric function deduced from spectroscopic ellipsometry are investigated as a function of hydrogen flow. Using the results of spectroscopic ellipsometry and elastic recoil detection analysis presented earlier, as well as the equations of Berg model, the metal and compound sputtering rate and the sticking coefficient between silicon and hydrogen atoms are calculated.