Semiconductor memory device and method for forming semiconductor memory device

A method for fabricating a semiconductor memory device, comprising:

• providing a substrate;
• forming a plurality of word lines in the substrate;
• forming a plurality of bit lines on the substrate, wherein the bit lines extend along a first direction, and the word lines extend along a second direction;
• forming a plurality of filling patterns between the bit lines and at ends of the bit lines, and forming a plurality of first gaps surrounded by the filling patterns and the bit lines, wherein the filling patterns are separated from each other;
• depositing an insulating material to fill up the first gaps surrounded by the filling patterns and the bit lines, and forming a plurality of cavities surrounded by the insulating material in the first gaps respectively;
• etching the insulating material to form a strip-shaped isolation structure and a plurality of columnar isolation structures, wherein the cavity of the strip-shaped isolation structure is exposed to form a seam;
• after etching the insulating material, removing portions of the filling patterns to form a plurality of second gaps, wherein the second gaps are surrounded by the columnar isolation structures and the bit lines;
• and
• depositing a conductive material to fill up the second gaps and the seam concurrently.