Surface structure of Si(001) treated by hydrogen and argon electron cyclotron resonance plasmas

Abstract

Si(001) surfaces subjected to H 2 or Ar ECR plasma irradiation are studied, in situ, from the standpoints of both impurity removal and induced crystallographic damage. The atomic cleanliness is checked by XPS (X-ray photoelectron spectroscopy) and UPS (ultra-violet photoelectron spectroscopy), while surface crystallographic information given by LEED and XPD (X-ray photoelectron diffraction) experiments. As an H ion-source, the ECR plant appears to be a convenient hydrogenation source, with low damage, able to passivate the surface in the usual hydrogenated LEED phases (dihydride 1 × 1 or monohydride 2 × 1) depending on the employed substrate temperature T. It presents nevertheless poor etching properties concerning the dioxide overlayer in our low plasma pressure domain (<5×10 −4 mbar). On the other hand, as an Ar ion source, the ECR plasma is more efficient to etch physically and clean, particularly at low working pressure and aided by a DC negative bias voltage and T s increase but suffers from more crystallographic perturbations checked by the LEED disappearance and quantified by the decrease of the anisotropy factor related to the XPD contrast. Finally, a procedure which combines exposures to the cleaning Ar ions followed by a refinement Si etching of the damaged overlayers using the H plasma allows the attainment of clean reconstructed 2 × 1 surfaces with processing temperatures limited at 500°C and suitable for subsequent epitaxial growths.