Edge structure for multiple layers of devices, and method for fabricating the same

An edge structure for multiple layers of devices, wherein the multiple layers of devices comprises a plurality of unit layers being stacked, comprising:

• a first stair structure at a first direction of the multiple layers of devices where contacts for the devices are to be formed, including first edge portions of the unit layers at the first direction, wherein borders of the first edge portions gradually retreat with increase of a level height thereof, and an elevation angle from the border of the first edge portion of the bottom unit layer to the border of the first edge portion of the top unit layer is a first angle (θ1);
• and
• a second stair structure, including second edge portions of the unit layers at a second direction, wherein variation of border position of the second edge portion with increase of the level height is irregular, and an elevation angle from the border of the second edge portion of the bottom unit layer to the border of the second edge portion of the top unit layer is a second angle (θ2) that is larger than the first angle θ1,
• wherein a number of the unit layers is 16 or more,
• the first direction is orthogonal with the second direction, and
• the second stair structure has a first part and a second part above the first part, wherein
• in the first part, variation of border position of the second edge portion with increase of the level height is regular,
• in the second part, borders of the second edge portions of a corresponding part of the unit layers are aligned with each other, and
• a height of the second part is over a half of a total height of the second stair structure.