Method for in-cassette wafer center determination

A method for adjusting a relative position between a rounded workpiece supported on a support surface and a support tool adapted to support the rounded workpiece, the method comprising the steps of:

• providing a plurality of sensors on the support tool, the sensors configured so as to form an arc having a curvature similar to the curvature of an edge of the rounded workpiece and having an arc length no greater than half the circumference of said edge;
• moving the support tool toward the rounded workpiece on the support surface;
• sensing when a first of the plurality of sensors intersects with the edge of the rounded workpiece;
• and
• adjusting the relative position between the rounded workpiece and the support tool until three of the sensors detect the edge.

A method for positioning an end effector of a wafer handing robot in a predetermined position with respect to a notched semiconductor wafer, comprising the steps of:

• providing a plurality of sensors on the end effector, the sensors forming an arc having a curvature similar to that of the wafer and separated by a distance at least as great as the arc length of the notch in the wafer;
• moving the end effector toward the wafer;
• sensing when a first sensor of the end effector intersects an edge of the wafer;
• and
• adjusting the position of the end effector with respect to the wafer until three of the sensors intersects the edge.

A method for engaging a transportation member with a wafer, comprising the steps of:

• (a) providing a plurality of n sensors connected to the transportation member, said sensors being configured so as to form an arc having a curvature similar to the curvature of the edge of the wafer;
• (b) adjusting the position of the transportation member until n−1 sensors detect the edge of the wafer;
• and
• (c) engaging the transportation member with the wafer after said step (b).