Wafer bonding apparatus and the wafer bonding method

A wafer bonding method is provided with a step of holding a first substrate by an upper holding mechanism (7) by applying a voltage to the upper holding mechanism (7); a step of forming a bonded substrate by bonding the first substrate and a second substrate held by a lower holding mechanism (8); and a step of dechucking the bonded substrate from the upper holding mechanism (7) after applying a voltage, which attenuates while alternating, to the upper holding mechanism (7). Residual attracting force between the bonded substrate and the upper holding mechanism (7) is reduced when the voltage, which attenuates while alternating, is applied to the upper holding mechanism (7), and the bonded substrate can be dechucked from the upper holding mechanism (7) more surely in a shorter time. As a result, a wafer bonding apparatus (1) can bond the first substrate and the second substrate in a shorter time.