Method for fabricating semiconductor memory device

A method for manufacturing a semiconductor memory device, comprising the steps of:

• forming an insulating layer on a semiconductor substrate;
• forming an adhesion layer on the insulating layer;
• forming a capping layer on the adhesion layer;
• forming a contact hole exposing the semiconductor substrate by selectively etching the capping layer, the adhesion layer and the insulating layer;
• forming a first diffusion barrier on the capping layer and in the contact hole;
• forming a conductive layer on the first diffusion barrier;
• forming a conductive plug in the contact hole by removing the conductive layer until the first diffusion barrier on the insulating layer is exposed, thereby obtaining a first recess in the contact hole, wherein the first recess is surrounded by the conductive layer in the contact hole;
• etching the first diffusion barrier on the capping layer thereby forming a second recess in the contact hole, wherein a portion of the conductive plug is surrounded by the second recess and the second recess is surrounded by the capping layer, adhesion layer and the insulating layer;
• removing the portion of the conductive plug surrounded by the second recess thereby forming a third recess in the contact hole, wherein the third recess is surrounded by the capping layer, adhesion layer and the insulating layer and bottom of the of the third recess expose the first diffusion barrier and the conductive plug in the contact hole;
• and
• forming a second diffusion barrier in the third recess and removing the capping layer on the adhesion layer.