The present disclosure provides to a method for manufacturing a semiconductor memory device. The method includes receiving a substrate including a cell area and a peripheral area; forming a first bit line structure on a surface of the cell area; depositing a landing pad above the barrier layer and on the top surface of the first bit line structure; removing a top corner of the landing pad to form an inclined surface connecting a top surface of the landing pad to a sidewall of the landing pad; etching the nitride layer of the first bit line structure and the spacer nitride layer from the top opening so as to form a concavity;
etching the spacer oxide layer from the concavity to form an air gap; and depositing a silicon nitride layer to seal the air gap.