Method for producing SiGe-based zones at different concentrations of Ge

A method for forming at least two SiGe-based regions in a silicon-based layer, comprising steps of:

• providing a substrate comprising the silicon-based layer;
• defining at least a first enrichment region by exposing a first portion of the silicon-based layer;
• forming, by epitaxial growth, a first Ge-based layer with an initial Ge concentration [Ge]0 on the first portion, at the first enrichment region;
• diffusing, during a first diffusion by oxygen annealing, in a first direction z perpendicular to the first Ge-based layer, germanium of the first Ge-based layer in the first portion corresponding to the first enrichment region, the first portion thus becoming a first SiGe-based portion having a first Ge concentration [Ge]1, and the first Ge-based layer thus becoming a first oxide layer;
• defining at least a second enrichment region where the silicon-based layer is exposed, the at least one second enrichment region being separate from the first enrichment region;
• forming a grating of masking patterns on the exposed silicon-based layer within the at least one second enrichment region, so as to define a plurality of transient portions of the silicon-based layer;
• forming, by epitaxial growth, a second Ge-based layer with the initial Ge concentration [Ge]0 on the transient portions of the silicon-based layer, at the second enrichment region;
• diffusing, by oxygen annealing, in the first direction z, germanium of the second Ge-based layer into the transient portions, such that the transient portions become SiGe-based transient portions each having the first Ge concentration [Ge]1;
• and
• after the diffusing of the germanium by oxygen annealing in the first direction z, diffusing, during a second diffusion, in a second direction x parallel to the silicon-based layer, the germanium of the SiGe-based transient portions within the silicon-based layer, beneath the grating of masking patterns, so as to form at least a second SiGe-based portion having a second Ge concentration [Ge]2 that is lower than [Ge]1, at the second enrichment region.