Method for reducing contact resistance

A method for reducing contact resistance in a gate structure, comprising following steps:

• step 1:
• providing a semiconductor structure comprising a silicon substrate, metal gates located separately from each other on the silicon substrate, and a source and drain structure located between the metal gates, on an upper surface of the silicon substrate, wherein a height of the source and drain structure is lower than a height of the metal gates;
• a recess formed by using an outer side wall of the metal gates as a side wall and an upper surface of the source and drain structure as a bottom of the recess;
• a silicon nitride layer provided at the bottom of the recess;
• an oxide provided within the recess;
• wherein upper surfaces of the metal gates and an upper surface of the oxide are covered with a silicon oxide layer;
• step 2:
• forming contact holes connected with the upper surface of the source and drain structure and the upper surfaces of the metal gates, respectively, wherein the contact holes connected with the source and drain structure are formed by etching the silicon oxide layer above the recess, the oxide within the recess and the silicon nitride layer at the bottom of the recess;
• wherein the contact holes connected with the upper surfaces of the metal gates are formed by etching the silicon oxide layer above the metal gates;
• step 3:
• clearing by-products resulting from etching the contact holes by applying ion bombardment;
• step 4:
• depositing a Ti layer and TiN layer sequentially on the contact holes;
• step 5:
• forming a seed layer of Co on surfaces of the Ti layer and the TiN layer in the contact holes, depositing a Co layer on the Co seed layer in the contact holes and an upper surface of the silicon oxide layer;
• step 6:
• performing chemical mechanical polishing for Co at the upper surface of the silicon oxide layer and the upper portion of the contact holes after filling with Co, until the Ti layer and the TiN layer at the upper surface of the silicon oxide layer are removed;
• step 7:
• forming a cap layer covering the upper surface of Co within the contact holes and the upper surface of the silicon oxide layer;
• and
• step 8:
• performing laser annealing, wherein the Ti layer located at the bottoms of the contact holes in the source and drain structure reacts with silicon in the source and drain structure to form TiSi during the laser annealing process.