Method for germanium enrichment around the channel of a transistor

A method for making a transistor structure comprising, in this order, the following steps of:

• providing a gate block and insulating spacers on either side of the gate block over a determined region of a surface semiconductor layer of a semiconductor-on-insulator type substrate, the surface semiconductor layer being based on a first semiconductor material, in particular Si or Si1-aGea with a>0, the determined being adapted to accommodate a channel structure of said transistor opposite said gate block,
• forming semiconductor blocks over said surface semiconductor layer and on either side of the spacers by growth of a second semiconductor material based on SixGe1-x with x>0, the semiconductor blocks having lateral facets forming a non-zero angle with a normal to the surface semiconductor layer, the lateral facets defining cavities between said facets and said insulating spacers,
• deposition of a silicon layer over the semiconductor blocks, so as to fill the cavities located between said facets and said insulating spacers, the deposition of the silicon layer over the semiconductor blocks being carried out so as to completely fill said cavities,
• thermal oxidation of said semiconductor blocks and of said silicon layer, so as to carry out a germanium enrichment of a portion of the surface semiconductor layer, said portion being disposed around the channel and the spacers.