Bonding apparatus and bonding method

A bonding method of preparing a combined substrate by bonding a first substrate and a second substrate by using a bonding apparatus,

• wherein the first substrate comprises a base substrate, and a device layer formed on a surface of the base substrate facing the second substrate,
• wherein the bonding method comprises:
• holding the first substrate with a first holder;
• holding the second substrate with a second holder;
• controlling a moving unit configured to move the first holder and the second holder relative to each other to align the first substrate and the second substrate;
• controlling the first holder and the second holder to bond the first substrate and the second substrate to form the combined substrate within the bonding apparatus;
• after bonding of the first substrate and the second substrate, measuring a total thickness of the combined substrate at multiple points within the bonding apparatus;
• and
• measuring a thickness of the base substrate at the multiple points,
• wherein the thickness of the base substrate is measured by a thickness detector that radiates light from above the base substrate, and measures the thickness of the base substrate from a phase difference between the light reflected from a top surface of the base substrate and the light reflected from the bottom surface of the base substrate, and
• wherein the thickness detector is fixed to a side surface of the first holder other than a holding surface of the first holder, or a side surface of the second holder other than a holding surface of the second holder.