In Situ Substrate Chemical Analysis during Sputter Deposition

Abstract

Recently, we introduced a new technique[1] which allows chemical analysis in situ during film growth provided that the discharge is in the capacitive mode (d.c. or r.f.). The principle of the technique is the following: under ion impact there is emission of neutrals, ions, photons and electrons from the target surface. The secondary electrons have a mean energy around a few eV but they are accelerated across the cathode sheath and enter the negative glow with an energy equivalent to the discharge voltage. These high energy electrons collide with the gas particles and produce atomic or molecular ionizations and excitations which attenuate their energy somewhat. However most arrive on the walls or on the substrate with a large part of their initial energy[2]. It is well known that in r.f. or d.c. diode sputtering, these high energy electrons account for the main part of substrate heating. However we have recently[1] shown that a fraction of the energy dissipated by electrons in the thin film or in the substrate goes to produce X—ray emission. The X—ray characteristic emission is intense enough to enable chemical analysis.