Process for bonding by molecular adhesion

A method for bonding two substrates together by molecular adhesion of their surfaces comprising:

• supporting a first substrate and placing a second substrate upon the first substrate, each substrate having a first surface that has a flatness sufficient to facilitate bonding by propagation of a bonding front when the first surfaces of the substrates are placed in contact with each other, and a second surface that is opposite to the first surface;
• initiating bonding of the substrates by applying a force upon the surface of the second substrate;
• modifying, prior to adhesion, the surface state of one or both of the substrates to be bonded by applying heating directly to one or both substrates to regulate propagation speed of the bonding front to reduce bubble or voids between the substrates after bonding.