Bonding to alignment marks with dummy alignment marks

A method comprising:

• providing a first wafer comprising:
• a first alignment mark comprising a plurality of discrete metallic features having a first outer contour;
• and
• a first dummy alignment mark having a second outer contour, wherein the first outer contour and the second outer contour have an overlapped region;
• aligning the first wafer to a second wafer using the first alignment mark in the first wafer and a second alignment mark in the second wafer, wherein the second alignment mark is in a same chip area as a second dummy alignment mark in the second wafer;
• and
• bonding the first wafer to the second wafer through hybrid bonding, wherein after the bonding, the first alignment mark in the first wafer is directly bonded to the second dummy alignment mark in the second wafer.

A method comprising:

• forming a first alignment mark and a first dummy alignment mark in a first wafer, wherein the first alignment mark is in a same first area of the first wafer as the first dummy alignment mark;
• forming a second alignment mark and a second dummy alignment mark in a second wafer, wherein the second alignment mark is in a same second area of the second wafer as the second dummy alignment mark;
• searching for a first pattern of the first alignment mark in the first wafer to find the first alignment mark;
• searching for a second pattern of the second alignment mark in the second wafer to find the second alignment mark;
• using the first alignment mark and the second alignment mark that have been found to align the first wafer and the second wafer;
• and
• with the first wafer being aligned to the second wafer, bonding the second wafer to the first wafer.