Method for improving FDSOI device leakage

A method for improving a Fully Depleted Silicon-on-Insulator (FDSOI) device leakage, at least comprising:

• step 1, providing a semiconductor structure, wherein the semiconductor structure comprises:
• a silicon substrate, a buried oxide layer, a silicon-on-insulator (SOI) layer, a first oxide layer, and a silicon nitride layer, formed sequentially from bottom to top on the silicon substrate;
• step 2, defining a non-bulk silicon region and a bulk silicon region on the semiconductor structure, wherein the defining the bulk silicon region on the semiconductor structure comprises forming by etching a recess area out of the semiconductor structure which includes a part of the silicon nitride layer, a part of the first oxide layer, a part of the SOI layer, a part of the buried oxide layer, and a part of the silicon substrate, wherein the etching is stopped at a pre-determined thickness in the silicon substrate, and wherein the non-bulk silicon region comprises areas outside of the recess area in the semiconductor structure;
• step 3, refilling the recess area of the bulk silicon region on the semiconductor structure with monocrystalline silicon, until the monocrystalline silicon reaches a same height as a height of the SOI layer of the non-bulk silicon region, and removing the silicon nitride layer and the first oxide layer in the non-bulk silicon region;
• step 4, forming a first shallow trench isolation (STI) region inside the non-bulk silicon region and a second STI region at a border between the non-bulk silicon region and the bulk silicon region;
• forming a photoresist layer over the bulk silicon region and the non-bulk silicon region, performing photolithography to expose the bulk silicon region and to keep the non-bulk silicon region covered by the photoresist layer;
• and performing ion implantation on the exposed bulk silicon region;
• and
• step 5, forming a device structure in the bulk silicon region after the ion implantation.