Semiconductor memory device and method for manufacturing the same

A method for manufacturing a semiconductor memory device, comprising:

• forming a stacked body on a substrate by alternately stacking a first insulating layer and a first layer;
• forming a first trench in the stacked body, the first trench surrounding a part of the stacked body;
• forming a protection film and a first film in the first trench;
• removing a first portion of the first film by etching in a first direction opposite to a stacking direction of the stacked body;
• removing a part of the first layer by etching in a second direction crossing the stacking direction, the first layer being exposed by the removal of the first portion of the first film;
• removing a second portion of the first film by etching in the first direction;
• further removing a part of the first layer and a part of another first layer by etching in the second direction, the another first layer being exposed by the removal of the second portion of the first film;
• and
• embedding an insulating film in hollow spaces provided by the removal of the parts of the first layer and the another first layer,
• the first trench having a first portion and a second portion, the first portion extending in a third direction crossing the second direction with a first width in the second direction, the second portion extending in the second direction with a second width in the third direction,
• the second width being smaller than the first width,
• the first width being not less than 3 times a thickness of the protection film, and
• the second width being not more than 2 times the thickness of the protection film.