A method of wafer bonding includes: forming a first hole in a first insulation layer disposed over a first substrate; performing a first deposition-self-etch process to deposit a first conductive material in the first hole to form a first conductive plug; forming a second hole in a second insulation layer disposed over a second substrate; performing a second deposition-self-etch process to deposit a second conductive material in the second hole to form a second conductive plug; and bonding the first conductive plug with the second conductive plug to form a first grain fusion layer between the first conductive plug and the second conductive plug.

A method of wafer bonding includes: forming a first hole in a first insulation layer disposed over a first substrate; performing a first deposition-self-etch process to deposit a first conductive material in the first hole to form a first conductive plug; forming a second hole in a second insulation layer disposed over a second substrate; performing a second deposition-self-etch process to deposit a second conductive material in the second hole to form a second conductive plug; and bonding the first conductive plug with the second conductive plug to form a first grain fusion layer between the first conductive plug and the second conductive plug.

A method of wafer bonding includes: forming a first hole in a first insulation layer disposed over a first substrate; performing a first deposition-self-etch process to deposit a first conductive material in the first hole to form a first conductive plug; forming a second hole in a second insulation layer disposed over a second substrate; performing a second deposition-self-etch process to deposit a second conductive material in the second hole to form a second conductive plug; and bonding the first conductive plug with the second conductive plug to form a first grain fusion layer between the first conductive plug and the second conductive plug.