Method of forming gate-all-around structures

A method of forming gate-all-around structures for FinFET devices including the following steps:

• S01, providing a semiconductor substrate;
• forming a composite layer on the semiconductor substrate and patterning the composite layer;
• wherein, the composite layer comprises a dielectric layer, a buried gate layer and a barrier layer from bottom to top;
• S02, forming a sidewall layer on four sides of the patterned composite layer, then forming an epitaxial layer surrounding the sidewall layer;
• planarizing the epitaxial layer so that a top surface of the barrier layer, a top surface of the sidewall layer and a top surface of the epitaxial layer are at the same level;
• S03, removing the barrier layer;
• depositing a first high-k dielectric layer having the same thickness with the barrier layer;
• S04, forming a fin layer;
• patterning the fin layer to expose the buried gate layer, so as to form a fin structure;
• S05, forming a dielectric isolating layer on the epitaxial layer;
• S06, forming a second high-k dielectric layer on sidewalls and a top surface of the fin structure;
• S07, forming a second gate layer, patterning the second gate layer to form a gate structure traversing and surrounding the fin structure.