Wafer to wafer bonding apparatuses

A wafer bonding apparatus includes lower and upper stages, lower and upper push rods, a position detection sensor, and processing circuitry. The stages may vacuum suction respective wafers on respective surfaces of the stages based on a vacuum pressure being supplied to respective suction holes in the respective surfaces from a vacuum pump. The push rods are movable through respective center holes in the stages to apply pressure to respective middle regions of the respective wafers. The position detection sensor may generate information indicating a bonding propagation position of the wafers based on detecting at least one wafer through a detection hole in at least one stage. The processing circuitry may process the information to detect the bonding propagation position and cause a change of at least one of a ratio of protruding lengths of the push rods, or a ratio of suction areas of the stages.