Wafer bonding method and wafer bonding apparatus

A method of aligning two wafers during a bonding process, the method comprising:

• aligning a first wafer with a second wafer;
• inserting a first plurality of flags between the first wafer and the second wafer;
• detecting a velocity of each of the first plurality of flags during removal of the first plurality of flags using at least one sensor;
• determining whether the first wafer remains aligned with the second wafer based on the detected velocity;
• and
• inserting a second plurality of flags between the first wafer and the second wafer in response to a determination that the first wafer is misaligned with respect to the second wafer.

A wafer bonding apparatus comprising:

• a first plate configured to support a first wafer;
• a second plate configured to support a second wafer, wherein the first plate is moveable relative to the second plate;
• a flag-out mechanism configured to remove a plurality of flags from between the first wafer and the second wafer;
• a sensor configured to detect movement of the plurality of flags during removal of the plurality of flags;
• and
• a controller configured to determine whether the first wafer is aligned with the second wafer based on the detected movement of the plurality of flags.