Semiconductor memory device and method for manufacturing the same

A method for manufacturing a semiconductor device, comprising:

• forming a stack assembly over a substrate, the stack assembly including dielectric layers and sacrificial layers which are disposed to alternate with the dielectric layers;
• etching the stack assembly such that the etched stack assembly has a main structure and a staircase structure;
• forming an inter-metal dielectric (IMD) layer over the staircase structure;
• patterning the etched stack assembly to form trenches which are disposed to alternate with stack units, each of the stack units including a portion of the IMD layer, a portion of the staircase structure and a portion of the main structure;
• depositing a strut layer to fill the trenches;
• patterning the strut layer to form openings such that two side surfaces of each of remaining sacrificial layers in the stack units are exposed to the openings;
• performing a replacement process to replace the remaining sacrificial layers respectively with conductive features through the openings;
• and
• forming repeating units respectively in the openings, each of the repeating units including
• a channel film which is made of a semiconductor material, and
• a gate dielectric film which is disposed to separate the channel film from the conductive features,
• wherein, after the etched stack assembly is patterned, each of the remaining sacrificial layers further has an upper surface and a lower surface, the two side surfaces each interconnecting the upper surface and the lower surface,
• wherein, before the replacement process, the gate dielectric film is not formed over one of the two side surfaces of each of the remaining sacrificial layers, and
• wherein, after the replacement process, and after the gate dielectric film is formed, the gate dielectric film interfaces the conductive features which are positioned in place of the remaining sacrificial layers.

A method for manufacturing a semiconductor device, comprising:

• forming a first stack unit and a second stack unit over a substrate, the first stack unit and the second stack unit extending lengthwise along a first direction and being spaced apart from each other along a second direction, each of the first stack unit and the second stack unit including a sacrificial feature and a dielectric feature which are stacked on each other;
• forming a first strut structure in a first trench which is located between the first stack unit and the second stack unit, the first strut structure bridging the first stack unit and the second stack unit and being formed with first openings to expose the sacrificial feature of each of the first stack unit and the second stack unit;
• removing the sacrificial feature of the first stack unit to form a first space, and removing the sacrificial feature of the second stack unit to form a second space, the first space and the second space being in spatial communication with the first openings;
• forming a first conductive feature in the first space, and forming a second conductive feature in the second space;
• and
• forming first repeating units respectively in the first openings, each of the first repeating units including
• a first channel film which is made of a semiconductor material,
• a first gate dielectric film which is disposed to separate the first channel film from one of the first conductive feature and the second conductive feature, and
• a first bit line and a first source line which are separated from each other by a first isolation region,
• wherein the sacrificial feature has an upper surface, a lower surface, and two side surfaces each interconnecting the upper surface and the lower surface, and
• wherein, before removing the sacrificial feature, each of the first bit line, the first source line and the first gate dielectric film is not formed over one of the upper surface, the lower surface and the two side surfaces of the sacrificial feature.