The present invention relates to an apparatus and method for transferring a substrate, such as a wafer or flat panel display, from a robotic transfer arm to a desired location, such as on a processing tool, and in particular for transferring a substrate from a robotic edge grip arm to a chuck on a processing tool. 
Substrates, such as semiconductor wafers or flat panel displays, are typically moved from one processing station to the next using robotic transfer arms.  The newest type of arm is an edge grip arm, which grips only the leading and trailing edges of the substrate as it is transported.  By gripping only the leading and trailing edges of the substrate, there is only a small amount of contact and, thus, possibility of particulate contamination is reduced.  One such edge grip arm is manufactured by, e.g., Kensington Laboratories, Inc, located in Richmond Calif.
Many processing tools, e.g., integrated metrology tools, use a chuck as a substrate holding device.  Unfortunately, many new edge grip arms cannot place a substrate on a conventional chuck because the configuration of the edge grip arms interferes with the chuck.  Redesigning chucks to cooperate with the edge grip arms is undesirable due to the expense and time that would be required. 
Thus, what is needed is a substrate lift mechanism that cooperates with edge grip arms and may be integrally included in new products as well as easily mounted to existing processing tools. 
A substrate lift mechanism in accordance with the present invention includes a plurality of fingers, e.g., at least three fingers and preferably four fingers, controlled by an actuator or actuators to transfer a substrate, such as a wafer or a flat panel display, from an edge grip arm to a chuck on a processing tool, such as integrated metrology tools.  The plurality of fingers, in one embodiment, are mounted on a hoop controlled by an actuator.  The substrate lift mechanism includes a base, an actuator positioned in the base, and at least two arms coupled to the actuator with the arms moving in an upward and downward direction by the actuator.  The substrate lift mechanism also includes a plurality of fingers extending from the arms with the fingers positioned such that an edge grip arm may pass between two of the fingers.  The fingers are configured to gravitationally support the substrate.  The fingers include positioning nipples to precisely position the substrate over the fingers.  The actuator is ideally a small sized actuator, such as a pneumatic actuator, to minimize the size of the base.  Consequently, the footprint of the substrate lift mechanism is minimized.  The actuator may be controlled, e.g., by a micro-switch that is activated from movement of the Z stage of the processing tool itself. 
A method of using the substrate lift mechanism includes positioning the fingers mounted on hoop in an up position; positioning a substrate held on an edge grip arm over the plurality of fingers; lowering the edge grip arm to place the substrate on the plurality of fingers; retracting the edge grip arm from between two of the plurality of fingers; and lowering the hoop to a down position to place the substrate on a chuck of a processing tool to which the substrate lift mechanism is mounted.  The substrate is unloaded by raising the hoop to the up position to place the substrate on the fingers; extending the edge grip arm between two of the fingers; raising the edge grip arm to place the substrate on the edge grip arm; and retracting the edge grip arm to remove said substrate from said processing tool. 
With the use of the substrate lift mechanism in accordance with the present invention, existing tools may be adapted to be used with the new edge grip arms without requiring a redesign of the chuck system and without a substantial increase in the footprint of the device.