Automatic system calibration for wafer handling

Method for automatically calibrating the position of a wafer handling robot relative to a wafer carrier, the method comprising:

• i) providing a semiconductor processing assembly comprising:
• a wafer handling robot having an end effector having a wafer support surface configured to carry a wafer;
• a wafer center finder configured to determine the center of a wafer which is placed on the end effector;
• a wafer carrier relative to which the position of the wafer handling robot has to be calibrated, the wafer carrier having wafer slots;
• and,
• an electronic controller for controlling at least the wafer handling robot and the wafer center finder and having a system memory;
• wherein for calibrating the wafer handling robot relative to the wafer carrier in a horizontal plane, the following method steps are automatically performed under control of the electronic controller of the semiconductor processing assembly:
• ii) placing a wafer in a start position on the wafer support surface of the end effector such that the wafer can be displaced over the wafer support surface when a lateral force is exerted on the wafer;
• iii) moving the end effector with the wafer to the wafer center finder and determine with the wafer center finder a determined position of the wafer relative to the end effector;
• iv) repeating the following horizontal calibration cycle of steps a) to d) until a set end criterion is met at least a number of cycles:
• a) determine on the basis of the determined position of the wafer relative to the end effector a defined entry angle of a movement path and a defined end position of the movement path of the end effector, wherein the defined end position is adjacent the wafer carrier;
• b) move the end effector with the wafer on its wafer support surface to the defined end position along the movement path with the defined entry angle;
• c) determine with the wafer center finder the position of the wafer relative to the end effector;
• and,
• d) check whether, due to the movement of the end effector along the movement path to the defined end position, the position of the wafer relative to the end effector has been displaced and whether a magnitude of the displacement meets the set end criterion, wherein, if the magnitude does not meet the set criterion, a subsequent cycle of steps a) to d) is performed, and wherein, if the magnitude does meet the set criterion at least a number of cycles, the method is continued at v);
• v) storing the entry angle and the end position which has been determined in the last cycle in the system memory as calibrated entry angle and calibrated end position for a calibrated movement path of the wafer handling robot relative to the respective wafer carrier.