Semiconductor storage device and method for manufacturing semiconductor storage device

A semiconductor storage device comprising:

• a first stacked body in which a plurality of first conductive layers are alternately stacked with an insulating layer interposed therebetween;
• a second stacked body in which a plurality of second conductive layers are alternately stacked on a part of the first stacked body with an insulating layer interposed therebetween;
• and
• a third stacked body in which a plurality of third conductive layers are alternately stacked on the first stacked body with an insulating layer interposed therebetween on a part of an area where the second stacked body is not provided,
• wherein the second stacked body includes a plurality of pillars extending in a stacking direction of the second stacked body in the second stacked body, and a first stair portion in which the second conductive layers provided in the second stacked body are formed in a stair shape,
• the first stacked body includes a plurality of pillars extending in a stacking direction of the first stacked body in the first stacked body, and a second stair portion in which the first conductive layers lower than the conductive layers forming the first stair portion are formed in a stair shape,
• the third stacked body includes a third stair portion in which the third conductive layers are formed in a stair shape to face the first stair portion, an upper surface of the third stacked body located at a position identical to an upper surface of the second stacked body in the stacking direction, and
• the number of the first conductive layers included in one step in the first stair portion is smaller than the number of the third conductive layers included in one step in the third stair portion.

A method for manufacturing a semiconductor storage device, the method comprising:

• forming a stacked body in which a plurality of first layers are stacked on each other with a second layer interposed therebetween;
• forming a first stair portion in which a third layer group out of the plurality of first layers in an upper layer part of the stacked body is formed in a stair shape;
• forming a second stair portion in which a fourth layer group, located at a stacking position identical to the third layer group, out of the plurality of first layers is formed in a stair shape;
• forming a third stair portion between the first stair portion and the second stair portion such that the fourth layer group is formed in a stair shape and is arranged to face the first stair portion;
• a first process of extending the first stair portion to a lower layer part of the stacked body while retracting a position of an uppermost step relative to a lowermost step of the first stair portion;
• a second process of extending the second stair portion to the lower layer part of the stacked body while retracting a position of an uppermost step relative to a lowermost step of the second stair portion;
• a third process of extending the third stair portion to the lower layer part of the stacked body without retracting a position of an uppermost step relative to a lowermost step of the third stair portion;
• and
• a process of etching the second stair portion in a stacking direction of the stacked body while maintaining a difference in level of the second stair portion to form a fourth stair portion in which a fifth layer group, lower than the third layer group, out of the plurality of first layers is formed in a stair shape.