Method for forming recess and filling epitaxial layer in situ

A method for forming a recess in a semiconductor device, comprising a plurality of steps:

• step 1:
• providing a silicon substrate, performing a first etching in a selected region of the silicon substrate to form a recess, wherein the first etching is a dry etching, and wherein the recess has either a U-shape or a ball-shape;
• and
• step 2:
• placing the silicon substrate in an epitaxial process chamber, and performing a second etching to the recess by introducing reaction gases comprising HCl and GeH4 in the epitaxial process chamber to form the recess into a diamond-shape;
• wherein in step 1, a top surface of the silicon substrate is a surface of crystal (100);
• wherein in step 2, etching rates of the second etching to a surface of crystal (110), the surface of crystal (100) and a surface of crystal (111) decrease sequentially;
• wherein step 1 further comprises forming a gate structure on a top surface of the silicon substrate;
• wherein in step 1, the selected region of the silicon substrate is source and drain forming area at two sides of the gate structure;
• wherein the gate structure comprises a gate dielectric layer and a polysilicon gate, wherein the gate dielectric layer comprises silicon oxide;
• wherein the gate structure further comprises a metal gate, wherein the gate dielectric layer comprises a high-dielectric-constant material;
• wherein step 1 further comprises forming a pseudo gate structure in a forming region of the gate structure on the top surface of the silicon substrate, wherein the pseudo gate structure comprises a pseudo gate dielectric layer and a pseudo polysilicon gate;
• and
• wherein the pseudo gate structure is replaced by the gate structure in a subsequent process.