US Patent 7919725 Via hole forming method

A method of forming a via hole reaching a bonding pad in a wafer having a plurality of devices on the front surface of a substrate and bonding pads on each of the devices, by applying a laser beam from the rear surface side of the substrate, comprising the steps of forming an annular groove by applying a laser beam to an annular area surrounding a via hole forming area on the rear surface of the substrate; and forming a via hole reaching a bonding pad by applying a laser beam to the via hole forming area surrounded by the annular groove from the rear surface side of the substrate.