Method of manufacturing a three-dimensionally integrated structure having a clamping surface and a wafer stack with a chamfered surface

A method for fabricating a three-dimensionally integrated structure, comprising:

• obtaining a wafer stack having a surface that includes an active device region and a peripheral region surrounding the active device region, wherein the wafer stack comprises at least three wafers;
• forming a chamfered surface adjacent to and surrounding the active device region by performing a first trimming process in the peripheral region, wherein each wafer of the wafer stack comprises a sub-chamfered surface, wherein the sub-chamfered surface is a curved surface without angular transition, thereby allowing a smooth transition at an interface between the sub-chamfered surfaces of adjacent wafers;
• and
• forming a clamping surface by performing a second trimming process at an edge of the peripheral region, wherein the clamping surface is for clamping the wafer stack and is adjacent to and surrounds the chamfered surface, wherein a thickness of the wafer stack along the chamfered surface gradually decreases from an edge of the active device region outward, and the thickness further decreases at the clamping surface.