RF Reactive Magnetron Sputter Deposition of Silicon Sub-Oxides

Abstract

RF reactive magnetron plasma sputter deposition of silicon sub oxide E.D. van Hattum Department of Physics and Astronomy, Faculty of Sciences, Utrecht University The work described in the thesis has been inspired and stimulated by the use of SiOx layers in the direct inductive printing technology, where the SiOx layer is used as the charge retention layer on the drums for copying and printing devices. The thesis describes investigations of the plasma and of processes taking place on the sputter target and on the SiOx growth surface in the room temperature, RF reactive magnetron plasma sputter deposition technology. The sputtering target consists of silicon and the reactive atmosphere consists of an Ar/O2 mixture. The composition of the grown SiOx layers has been varied between x=0 and x=2 by variation of the O2 partial pressure. The characteristics of the growth process have been related to the nanostructural properties of the grown films. The deposition system enables the characterisation of the plasma (Langmuir probe, energy resolved mass spectrometer) and of the growing film (Elastic Recoil Detection (ERD), Fourier transform infrared absorption spectroscopy) and is connected to a beamline of a 6MV tandem van de Graaff accelerator. Also Rutherford Backscattering Spectrometry and X-ray Photoelectron Spectroscopy have been applied. It is shown how ERD can be used as a real-time in-situ technique. The thesis presents spatially resolved values of the ion density, electron temperature and the quasi-electrostatic potential, determined using a Langmuir probe. The plasma potential has a maximum about 2 cm from the cathode erosion area, and decreases (more than 200 V typically) towards the floating sputter cathode. The potential decreases slightly in the direction towards the grounded growth surface and the positive, mainly Ar+, ions created in the large volume of the plasma closest to the substrate are accelerated towards the growth surface. These ions obtain a few eV of kinetic energy in the plasma and around 30-50 eV in the anode sheath, and bombard the growing film. Some of them are incorporated in the grown material. The flux of ions on the growth surface hardly depends on the power injected into the plasma. Since the growth rate increases strongly with increasing injected power, at the same time the relative ion bombardment (about 10-20 ions per deposited atom) decreases strongly. The hypothesis that the microstructure of the grown material depends on the ion bombardment is not supported by the results, as deduced from the infrared analysis. The oxygen, incorporated in the growing SiOx, originates for ~65 % from O2 and for about 30 % from atomic oxygen produced in the plasma. A minority contribution is from SiO sputtered from the cathode. The oxygen coverage in the sputter erosion area appears low for all oxygen partial pressures leading to x<2. This explains why the silicon growth rate does not depend on the O2 partial pressure in the range where x < 2 is grown. It is discussed how this observation relates to the details of the rf plasma deposition setup.