Method of forming wafer-to-wafer bonding structure

A method of forming a semiconductor structure, the method comprising:

• obtaining a composite wafer comprising a substrate, an insulation layer on the substrate, and a first active layer on the insulation layer, wherein an etch stop layer is formed in the substrate at a distance from a bottom surface of the substrate;
• forming a first device in a first active region on a top surface of the first active layer;
• forming a first oxide layer over the first device and the first active layer;
• forming a second oxide layer over a first carrier, and attaching the first carrier over the first device through a bonding of the first oxide layer and the second oxide layer;
• removing a portion of the substrate under the etch stop layer and removing the etch stop layer so that a remaining portion of the substrate under the insulation layer forms a second active layer;
• obtaining a position of the first active region of the first active layer using an optical alignment method from a bottom surface of the second active layer, which comprises emitting a light passing through the second active layer, the insulation layer and the first active layer to reach the top surface of the first active layer, and then receiving a reflected light form the top surface of the first active layer, and determining a position of a second active region on the bottom surface of the second active layer using the optical alignment method, wherein the second active region is aligned with the first active region;
• forming a second device in the second active region on the bottom surface of the second active layer, and a second interconnection structure below and coupled to the second device;
• forming a third oxide layer below the second interconnection structure;
• forming a fourth oxide layer over a second carrier, and attaching the second carrier to the second interconnection structure through a bonding of the third oxide layer and the fourth oxide layer;
• removing the first carrier, the first oxide layer, and the second oxide layer;
• forming a via cavity through the first active layer, through the insulation layer, through the second active layer, and to one conductive feature of the second interconnection structure;
• filling the via cavity with a metal material to form a via structure;
• and
• forming a first interconnection structure over and coupled to the first device, wherein the via structure connects the first device to the second device.

A method of forming a semiconductor structure, the method comprising:

• obtaining a composite wafer comprising a substrate, an insulation layer on the substrate, and a first active layer on the insulation layer, wherein obtaining the composite wafer comprises:
• providing a first wafer and a second wafer, wherein an oxide layer is formed around the first wafer;
• implanting hydrogen ions into the first wafer to embrittle the first wafer beneath the oxide layer;
• bonding the first wafer to the second wafer through the oxide layer;
• and
• after bonding the first wafer to the second wafer, splitting the first wafer at a peak location of the implanted hydrogen ions by using an annealing process, wherein a remaining portion of the first wafer forms the first active layer of the composite wafer, the oxide layer forms the insulation layer of the composite wafer, and the second wafer forms the substrate of the composite wafer;
• implanting ions into the substrate to form an etch stop layer in the substrate;
• forming a first device on a top surface of the first active layer;
• attaching a first carrier over the first device;
• removing a portion of the substrate under the etch stop layer and removing the etch stop layer so that a remaining portion of the substrate under the insulation layer forms a second active layer;
• forming a second device on a bottom surface of the second active layer, and a second interconnection structure below and coupled to the second device;
• attaching a second carrier over the second interconnection structure;
• removing the first carrier;
• forming a via structure extending through the first active layer, the insulation layer and the second active layer and coupled to one conductive feature of the second interconnection structure;
• and
• forming a first interconnection structure over and coupled to the first device, wherein the via structure connects the first interconnection structure and the second interconnection structure.