Method of assembly by direct bonding between two elements, each element comprising portions of metal and dielectric materials

A method of assembly of a first element and a second element each having a back face and an assembly surface by direct bonding, at least the assembly surface of the first element comprising at least one first portion with at least one first metal part surrounded by at least one dielectric material, said first metal part having a free surface recessed from the dielectric material at said assembly surface, said method comprising:

• a step A) to bring the two assembly surfaces into contact such that direct bonding is obtained between the assembly surfaces, said step taking place at ambient temperature, said first and second elements forming a stack with a thickness, and
• a step B) taking place after step A), said step B) comprising
• B1) a step to hold the back faces of the first and the second elements in position so that they are immobilized,
• B2) a step to apply a heat treatment to said stack, wherein
• during a first phase of the heat treatment, the back faces of the first and second elements are held in place and a first heat treatment temperature between 50° and 400° C. is constantly applied to the stack for a first time period, and
• during a second phase of the heat treatment, the first and second elements are no longer held in place and a second heat treatment temperature between 50° and 400° C. is constantly applied to the stack for a second time period.