Semiconductor device and manufacturing method thereof

A method of bonding substrates, comprising:

• forming a first connection electrode in a first substrate, the first connection electrode comprising a first metal;
• polishing the first semiconductor substrate using chemical mechanical polishing, the first metal having a polishing rate that is less than a polishing rate of a region surrounding the first metal, the chemical mechanical polishing thereby causing the first connection electrode to protrude from a surface of the first semiconductor substrate;
• forming a second connection electrode in a second substrate, the second connection electrode comprising a second metal;
• stacking the first and second substrates so that the first and second connection electrodes are opposed;
• pressing the first and second substrates so that the first and second connection electrodes are in contact;
• and
• heating the first and second substrates to a temperature at or below a melting point of the first metal and at or below a melting point of the second metal.

A semiconductor device, comprising:

• a first semiconductor substrate including a first connection electrode that protrudes from the first semiconductor substrate;
• and
• a second semiconductor substrate including a second connection electrode,
• wherein the first connection electrode is diffusion-bonded to the second connection electrode, and
• a bonding surface of the first connection electrode is flat or convex.