Semiconductor memory device and method of manufacturing semiconductor memory device

A method of manufacturing a semiconductor memory device, the method comprising:

• forming a stacked body in which a plurality of first insulating layers and a plurality of second insulating layers are alternately stacked one by one;
• forming a stepped portion in which the plurality of first insulating layers is processed into a stepped shape;
• forming a plurality of plate-like portions that extends in the stacked body in a stacking direction of the stacked body and a first direction intersecting the stacking direction and divides the stacked body and the stepped portion of the stacked body in a second direction intersecting the stacking direction and the first direction;
• when the stepped portion is formed,
• forming a first mask pattern across first to third regions that are to be divided by the plurality of plate-like portions and are adjacent in an order of the first to third regions in the second direction, the first mask pattern being formed so as to have a width in the second direction that is less than a width of the first to third regions in the second direction;
• removing a pair of first and second insulating layers of the plurality of first and second insulating layers from a surface of the stacked body exposed from the first mask pattern;
• after removing the first mask pattern, forming a second mask pattern across the second and third regions and a fourth region adjacent to the third region on an opposite side of the second region, the second to fourth regions being to be divided by the plurality of plate-like portions, the second mask pattern being formed so as to have a width in the second direction that is less than a width of the second to fourth regions in the second direction;
• removing the pair of first and second insulating layers from a surface of the stacked body exposed from the second mask pattern;
• when the first mask pattern is formed,
• forming the first mask pattern by shifting a center position in the second direction toward the second region with respect to a boundary between the second and third regions;
• and
• when the second mask pattern is formed,
• forming the second mask pattern by shifting a center position in the second direction toward the third region with respect to the boundary between the second and third regions.