Epitaxial growth of Ge thick layers on nominal and 6° off Si(0 0 1); Ge surface passivation by Si

Abstract

We have grown various thickness Ge layers on nominal and 6° off Si(0 0 1) substrates using a low-temperature/high-temperature strategy followed by thermal cycling. A combination of ‘mounds’ and a perpendicular cross-hatch were obtained on nominal surfaces. On 6° off surfaces, three sets of lines were obtained on top of the ‘mounds’: one along the ⟨1 1 0⟩ direction perpendicular to the misorientation direction and the other two at ∼4.5° on each side of the ⟨1 1 0⟩ direction parallel to the misorientation direction. The surface root mean square roughness was less than 1 nm for 2.5 µm thick nominal and 6° off Ge layers. Those slightly tensily strained Ge layers (R ∼ 104%) were characterized by 5 × 107 cm−2 (as-grown layers) −107 cm−2 (annealed layers) threading dislocation densities, independently of the substrate orientation. We have then described the 550 °C/650 °C process used to passivate nominal Ge(0 0 1) surfaces with Si prior to gate stack deposition. An ∼5 Å thick SiGe interfacial layer is self-limitedly grown at 550 °C and then thickened at 650 °C (5 Å min−1) thanks to SiH2Cl2 at 20 Torr. Such a Ge surface passivation yields state-of-the-art p-type metal oxide semiconductor field effect transistors provided that 15 Å Si layer thickness is not exceeded. For higher thickness, elastic strain relaxation (through the formation of numerous 2D islands) occurs, followed by plastic relaxation (for a 35 Å thick Si layer).