Method for forming semiconductor device

A method for forming a semiconductor device, comprising:

• providing a substrate, having a NMOS region and a PMOS region defined thereon;
• forming a gate structure on the substrate within the NMOS region;
• forming at least two inner spacers on the gate structure;
• forming a disposal spacer on the at least two inner spacers;
• performing an oxygen treatment on the disposal spacers, thereby forming silicon seeds on the disposal spacers;
• forming a mask layer on the PMOS region to expose the NMOS region;
• forming a recess on two sides of the gate structure spaced from the gate structure by the disposal spacer within the NMOS region;
• removing the disposal spacer and the silicon seeds after the recess is formed while maintaining the at least two inner spacers;
• and
• forming an epitaxial layer into the recess after the disposal spacer is removed.