Alignment mark used in wafer bonding process and wafer bonding method using the same

A wafer bonding method for aligning and bonding a first semiconductor wafer and a flipped second semiconductor wafer, the method comprising:

• forming a first alignment mark having a first center of symmetry in a predetermined region of the first semiconductor wafer;
• forming a second alignment mark having a second center of symmetry in a predetermined region of the second semiconductor wafer so as to overlap the first alignment mark in a flipped state when the first semiconductor wafer and the flipped second semiconductor wafer are bonded;
• aligning the first alignment mark and the second alignment mark;
• and
• bonding the first semiconductor wafer and the second semiconductor wafer,
• wherein the first center of symmetry and the second center of symmetry overlap when the first semiconductor wafer and the flipped second semiconductor wafer are aligned,
• a difference between the first center of symmetry and the second center of symmetry represents an alignment error between the first semiconductor wafer and the flipped second semiconductor wafer,
• the first alignment mark is rotationally symmetrical at 90 degrees and 180 degrees with respect to the first center of symmetry, and is asymmetrical with respect to a first axis passing through the first center of symmetry,
• the first alignment mark and the second alignment mark have the same shape and size,
• the first alignment mark and the second alignment mark comprises a plurality of bars, and
• a bar of the first alignment mark and a bar of the flipped second alignment mark, which belong to the same quadrant among quadrants divided by the first axis and a second axis orthogonal to the first axis, are perpendicular to each other.