Semiconductor device and fabrication method thereof

A method for fabricating a semiconductor device, comprising:

• providing a base substrate;
• forming gate structures over the base substrate;
• forming doped source/drain regions in the base substrate at two sides of each of the gate structures;
• forming an oxide layer on each of the doped source/drain regions;
• forming a metal layer on the oxide layer;
• and
• performing a reactive thermal annealing process, such that the metal layer reacts with a material of the oxide layer and a material of the doped source/drain regions to form a metal contact layer on each of the doped source/drain regions,
• wherein the metal contact layer includes a first metal contact layer on the doped source/drain region, an oxygen-containing metal contact layer on the first metal contact layer, and a second metal contact layer on the oxygen-containing metal contact layer,
• wherein the first metal contact layer is made of silicide, the oxygen-containing metal contact layer is made of oxysilicide, and the second metal contact layer is made of silicide.