Wafer-to-wafer bonding structure and image sensor including the same

An image sensor comprising:

• a first substrate including a pixel array, a first multilayer wiring, a first insulation layer and a plurality of first metal pads arranged apart from one another in a horizontal direction to each be buried in the first insulation layer;
• and
• a second substrate on the first substrate,
• wherein the second substrate comprises a logic circuit, a second multilayer wiring, a second insulation layer facing the first insulation layer and a plurality of second metal pads arranged apart from one another in a horizontal direction to each be buried in the second insulation layer, and
• wherein a plurality of second steps formed in the second junction surface respectively engage with a plurality of first steps respectively contacting the plurality of second steps in a symmetrical slope shape to form direct bonding between the first substrate and the second substrate.

An image sensor comprising:

• a lower substrate;
• and
• an upper substrate stacked on and bonded to the lower substrate,
• wherein the lower substrate comprises:
• a pixel array;
• a lower multilayer wiring;
• a lower insulation layer formed on an upper surface of the lower substrate;
• a lower metal pad buried in the lower insulation layer;
• and
• a lower step formed in the lower metal pad,
• wherein the upper substrate comprises:
• an upper insulation layer formed on a lower surface of the upper substrate;
• a logic circuit;
• a multilayer wiring;
• an upper metal pad buried in the upper insulation layer;
• and
• an upper step formed in the upper metal pad, and
• wherein the upper step engages with the lower step in a symmetrical slope shape to form direct bonding between the upper substrate and the lower substrate.