Substrate bonding with diffusion barrier structures

A method of bonding substrates comprising:

• providing a first substrate including a first metal pad predominantly embedded in a first silicon oxide layer;
• providing a second substrate including a second metal pad predominantly embedded in a second silicon oxide layer;
• introducing a dopant metal into surface regions of at least one of said first substrate and said second substrate, wherein said dopant metal is selected from elemental metals having a greater oxygen-affinity than copper;
• bonding said first metal pad with said second metal pad, wherein a metal silicate material layer comprising said dopant metal is formed between said first silicon oxide layer and said second silicon oxide layer, said metal silicate material layer laterally surrounding said first and second metal pads and contacting a horizontal surface of said first silicon oxide layer and a horizontal surface of said second silicon oxide layer, wherein said metal silicate material layer comprises a silicate of said dopant metal, and a vertically contacting pair of said first metal pad and said second metal pad is formed within a bonded structure including said first and second substrates, and said metal silicate material layer contacts a horizontal surface of a peripheral portion of each of said first and second metal pads and a sidewall surface of each of said first and second metal pads;
• and
• forming a dopant metal rich portion within each of said first and second metal pads underneath said horizontal surface of said peripheral portion of each of said first and second metal pads by diffusion of said dopant metal into each of said first and second metal pads.