Abstract: End effector pads are provided that may be used to secure substrates to an end effector on a wafer handling robot. An end effector may have a plurality of end effector pads. Each of the end effector pads may have a thin diaphragm that allows a peripheral ring of the pad to tilt slightly to allow the ring to seal against a bottom surface of a bowed substrate. A vacuum may be used to pull down the substrate against a hard-stop on each end effector pad and hold the substrate more securely. The hard-stop may be used to consistently locate the z-position of the bottom surface of the substrate relative to the end effector.