A workpiece (101) and a method of forming through holes (115) in substrate (100) are disclosed. The method of forming a through hole (115) in a substrate (100; 101) by drilling includes affixing an exit sacrificial cover layer (130) to a laser beam exit surface (112) of the substrate (100), positioning a laser beam (20) in a predetermined location relative to the substrate (100) and corresponding to a desired location for the through hole 8115), and forming the through hole 8115) by repeatedly pulsing the laser beam (20) into an entrance surface (110) of the substrate (100) and through a bulk of the substrate (100). The method further includes forming a hole (135) in the exit sacrificial cover layer (130) by repeatedly pulsing the laser beam (20) into the through hole (115) formed in the substrate (100) such that the laser beam (20) passes through the laser beam exit surface (112) of the substrate (100) and into the exit sacrificial cover layer (130).