Trimming method of stacked structure and stacked structure formed therefrom

A trimming method, comprising:

• providing a first wafer having a first surface and a second surface opposite to the first surface, wherein the first wafer has a first portion of a first thickness and closer to the first surface and a second portion of a second thickness, connected with the first portion and closer to the second surface;
• providing a second wafer having a third surface and a fourth surface opposite to the third surface;
• bonding the first surface of the first wafer with the fourth surface of the second wafer to form a stacked wafer structure;
• thinning the second wafer from the third surface;
• performing an edge trimming process to the stacked wafer structure to form a trench penetrating through the second wafer and extending into the first wafer with a first depth, wherein the first depth is larger than the first thickness;
• bonding semiconductor dies to the second wafer to form a stacked structure;
• forming a filling material over the stacked structure, wrapping around and filling between the semiconductor dies, covering the second wafer and covering a sidewall and a bottom surface of the trench without filling up the trench;
• flipping the stacked structure;
• and
• performing a wafer thinning process to partially remove the first wafer from the second surface and partially removing the filling material in the trench, wherein the second portion of the first wafer is removed and the first portion of the first wafer and a portion of the filling material on the sidewall of the trench are remained.

A stacked structure, comprising:

• a wafer having a first surface, a second surface opposite to the first surface and a sidewall connecting the first surface and the second surface;
• semiconductor dies stacked on the second surface of the wafer and bonded to the wafer;
• a filling material disposed on the second surface of the wafer, filling between and wrapping around sidewalls of the semiconductor dies, and covering the sidewall of the wafer,
• wherein the stacked structure includes first die units and second die units connected with one another, the first die units are located in a bordering region of the wafer surrounding the second die units in an inner mid region of the wafer,
• wherein the filling material covers the second surface and the sidewall of the wafer in the first die units, while the filling material covers only the second surface of the wafer in the second die units.