Detection and handling of semiconductor wafers and wafer-like objects
View Patent ↗An end effector has one or more vortex chucks to support a wafer, and at least two detectors for detecting different portions of the wafer before the wafer is picked up. If one of the detectors detects a wafer and the other one does not, an alarm is generated to alert an operator that the wafer is possibly cross slotted in the wafer cassette. Each detector includes a light emitter and a light receiver. The light emitter emits a light beam at an angle to a surface defined by an ideally flat wafer when the wafer is supported by the end effector (the actual wafers do not have to be flat). The angle is not more than 45°, and is between 6° and 12° in some embodiments. Other features and embodiments are also provided.
1. An end-effector operable to pick up and support flat objects extending generally alone a plane, the end-effector comprising:
(1) a first detector mounted at a first side of the end-effector and comprising:
a first detector component for emitting a first light beam at an angle to said plane, the angle being greater than zero but not more than 45°; and
a second detector component for receiving the first light beam;
(2) a second detector mounted at a second side of the end-effector opposite to the first side and comprising:
a first detector component for emitting a second light beam at an angle to said plane, the angle being greater than zero but not more than 45°; and
a second detector component for receiving the second light beam;
wherein in the first detector, the first light beam's path from the first detector component to the second detector component passes at the first side of the end-effector but not at the second side of the end-effector, to detect the presence or absence of the object at the first side of the end-effector; and
in the second detector, the second light beam's path from the first detector component to the second detector component passes at the second side of the end-effector but not at the first side of the end-effector, to detect the presence or absence of the object at the second side of the end-effector.
2. The end-effector of claim 1 wherein the end-effector is suitable for picking up wafers from wafer cassette slots, a wafer cassette slot having a first shoulder for supporting a first portion of a wafer and a second shoulder for supporting a second portion of the wafer, wherein the end-effector is positionable with the first side adjacent to the first shoulder and the second side adjacent to the second shoulder, to cause the first light beam to travel adjacent to the first shoulder but not to the second shoulder, and to cause the second light beam to travel adjacent to the second shoulder but not to the first shoulder.
3. The end-effector of claim 2 in a system operable to generate an alarm if one of the detectors detects the presence of a wafer portion in a slot while the other one of the detectors does not detect the presence of a wafer portion in the slot.
4. The end-effector of claim 2 in combination with a wafer cassette having a plurality of the wafer cassette slots.
5. The end-effector of claim 2 wherein said angle is at least 6°.
6. The end-effector of claim 2 wherein each of the first and second detectors is operable to detect a respective portion of the wafer when the wafer is not supported by the end-effector.
7. The apparatus of claim 6 wherein said angle is at least 6°.
8. The apparatus of claim 2 wherein said angle is at most 12°.
9. The end-effector of claim 1 comprising a plurality of vortex chucks on the periphery of the end-effector, for emitting gas vortices towards the object.
10. An apparatus comprising the end-effector of claim 1 ,
wherein the apparatus is operable to generate an alarm if one of the first and second detectors detects the presence of an object while the other one of the first and second detectors does not detect the presence of an object.
11. The end effector of claim 10 wherein said angle is at least 6°.
12. The apparatus of claim 10 wherein the end-effector comprises at least one vortex chuck for emitting a gas vortex towards the object to support the object.
13. The end effector of claim 1 comprising at least one vortex chuck for emitting a gas vortex towards the object to support the object.
14. The apparatus of claim 2 wherein said angle is at least 6°.
15. The end-effector of claim 1 wherein said angle is at most 12°.
16. The end-effector of claim 15 wherein said angle is at least 6°.
17. The end-effector of claim 1 wherein said angle is at least 6°.