Method for preparing semiconductor memory device with air gaps between conductive features

Abstract

The present disclosure provides a method for preparing a semiconductor memory device with air gaps between conductive features. The method includes forming an isolation layer defining a first active region in a substrate; forming a first doped region in the first active region; forming a first word line buried in a first trench adjacent to the first doped region; and forming a high-level bit line contact positioned on the first doped region; forming a first air gap surrounding the high-level bit line contact. The forming of the first word line comprises: forming a lower electrode structure and an upper electrode structure on the lower electrode structure. The forming of the upper electrode structure comprises: forming a source layer substantially covering a sidewall of the first trench; forming a conductive layer on the source layer; and forming a work-function adjustment layer disposed between the source layer and the conductive layer.