Wafer-to-wafer direct bonding method

A method for directly bonding a first microelectronic device on a second microelectronic device comprising the following steps:

• a provision of a first microelectronic device having a first flat surface and of a second microelectronic device having a second flat surface
• a treatment of at least one from among the first and second surfaces with a plasma gas comprising at least one fluorinated gas, having an atomic percentage F of fluorine,
• a transfer of the first and second devices to a bonding equipment,
• an immersion of the first and second surfaces in a bonding atmosphere having a controlled relative humidity RH,
• a bonding of the first and second surfaces disposed facing one another, using the bonding equipment under the bonding atmosphere, in which a partial adhesion of the first and second surfaces is initiated and propagates in the form of a bonding wave at a speed Vc called bonding speed,
• wherein the atomic percentage F of fluorine during the treatment step, and the relative humidity RH during the bonding step, are synergistically controlled, such that the bonding speed Vc is less than or equal to 15 mm/s.