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 method of bonding wafers, 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;
• activating an alarm in response to a determination that the first wafer is misaligned with the second wafer.