Cleaning of silicon surfaces by argon microwave multipolar plasmas excited by distributed electron cyclotron resonance

The cleaning of single-crystal silicon with an argon plasma produced by a microwave multipolar reactor has been studied as a function of the ion energy striking the surface (in the range 25–135 eV), the substrate temperature, and the ion dose. Two treatments have been applied. In the first one, the substrate is kept at room temperature, and the effect of the ion energy is studied before and after an anneal at 700 °C under high vacuum conditions. In the second case, the substrate is heated at 700 °C during the plasma treatment. In situ analysis (spectroscopic ellipsometry over the wavelength range 0.2–0.9 μm, low-energy electron diffraction, and Auger electron spectroscopy) and ex situ analysis (atomic force microscopy) allow us to define the surface state of the substrate and to follow its evolution as a function of the different parameters. We have shown that it is feasible to obtain a silicon surface exempt of contaminants (carbon and oxygen) by plasma treatment, even at low ion energy (<100 eV). However, the treated surface always shows a residual roughness due to the ion bombardment. The surface roughness increases with ion energy and treatment temperature. In the best case, the perturbed layer is still of the order of 30 Å. The temperature plays an important role as it can either increase or reduce the plasma-induced roughness according to the operating mode.