Method for forming buried contact

A method for forming a buried contact, comprising the steps of:

• providing a substrate with an oxide layer, a first conductive layer and a first mask layer formed thereon;
• patterning the first mask layer, the first conductive layer and the oxide layer to form a first trench in the substrate;
• filling the first trench with an insulating layer;
• removing the first mask layer;
• forming a second mask layer with an opening over the substrate, wherein a portion of the insulating layer and a portion of the first conductive layer are exposed by the opening;
• performing an ion implantation process to form a buried contact within the substrate, with the second mask layer serving as a mask;
• removing the portion of the insulating layer exposed by the second mask layer to form a second trench;
• removing the second mask layer;
• forming a second conductive layer over the substrate to fill the second trench;
• forming a third mask layer over the substrate, wherein the third mask layer at least covers a portion of the buried contact and a region predetermined for forming a gate;
• removing a portion of the second conductive layer and the first conductive layer exposed by the third mask layer to form a conductive wire and a gate;
• removing the third mask layer;
• and
• forming a source/drain region in the substrate, wherein the source/drain region couples with the buried contact.