Substrate gripping apparatus, substrate gripping method and substrate releasing method

A robot hand having a hand body having a reference axis J is provided with fixed holding members and and a movable holding member The holding members and are arranged on the hand body at angular intervals about the reference axis J. Each of the fixed holding members and has a first guide part and a second guide part defining a V-shaped groove. The movable holding member has a first guide part and a second guide part defining a V-shaped groove. Peripheral parts of a wafer are fit in the V-shaped grooves of the holding members to to grip the wafer by the robot hand . The first guide parts and are provided at their lower ends with protrusions and protruding toward the reference axis J, respectively. The protrusions and prevent the wafer from slipping off the holding members to