Method for positioning a wafer

1. Method for positioning a wafer ( 3 ) with a reference marker ( 6 ) in a vacuum process installation with a transport chamber comprising a transport device ( 2 , 20 , 21 ) for moving the wafer ( 3 ) in a plane to a process chamber disposed at the transport chamber and with a single sensor ( 1 ), which is disposed in front of the process chamber within the transport chamber for acquiring the position of the wafer ( 3 ) through the acquisition on its edge at a first detection point ( 4 ) and a second detection point ( 5 ), such that with electronic evaluation of the two measured detection points ( 4 , 5 ) the true position of the wafer ( 12 ), with the diameter of the wafer known, is determined and the transport device ( 2 , 20 , 21 ) actively guides the wafer ( 3 ) to a desired nominal position, characterized in that the wafer ( 3 ) with respect to its reference marker ( 6 ) is deposited on the transport device ( 2 , 20 , 21 ) with respect to its reference marker ( 6 ) aligned in predetermined position and the projection of the reference marker ( 6 ) along a motion direction determines on the wafer ( 3 ) a disallowable zone ( 22 ) and thereby the remaining circular region of the wafer ( 3 ) defines a free zone, the sensor ( 1 ) being disposed in the transport chamber such that the disallowable zone ( 22 ) is reliably not swept over and the sensor ( 1 ) thereby can only acquire the circular region of the wafer edge and no portion of the reference marker ( 6 ).

2. Method as claimed in claim 1 , characterized in that the positioning is a centering process of the wafer ( 3 ) for the active guiding of the wafer center ( 12 ) onto the predetermined desired nominal position.

3. Method as claimed in claim 1 , characterized in that first a measurement is carried out on a first wafer ( 3 ) and with further succeeding transport steps with further wafers, correction to a nominal position takes place.

4. Method as claimed in claim 1 , characterized in that translatory dislocation errors are corrected.

5. Method as claimed in claim 1 , characterized in that the transport device carries out a rotational motion and about a center of rotation ( 20 ) and a radial motion away and toward this center for the transport and/or positioning of a wafer ( 3 ) into a process chamber and/or a lock chamber.

6. Method as claimed in claim 5 , characterized in that the vacuum process installation is a cluster configuration.

7. Method as claimed in claim 1 , characterized in that only two detection points ( 4 , 5 ) on the wafer edge are acquired for each wafer ( 3 ) to be measured.

8. Method as claimed in claim 1 , characterized in that the wafer ( 3 ) through a rotational movement and/or linear movement in the transport plane is guided with its edge to the sensor ( 1 ) for the acquisition of the detection points ( 4 , 5 ).

9. Method as claimed in claim 1 , characterized in that the position of the detection points ( 4 , 5 ) are chosen to be far apart, however less far than the wafer diameter to be measured.

10. Method as claimed in claim 1 , characterized in that the wafer mounting is implemented such that it does not disturb the measuring procedure and is positioned beneath the disallowable zone ( 22 ).

11. Method as claimed in claim 1 , characterized in that each wafer ( 3 ) is deposited with the reference marker ( 6 ) aligned identically onto the mounting of the transport device ( 2 , 20 , 21 ), put in place with the alignment in the direction of the radial lateral motion ( 21 ) toward the center of rotation ( 20 ).

12. Method as claimed in claim 1 , characterized in that the tolerance bands of the positioning accuracy of the transport device ( 2 , 20 , 21 ) are simultaneously calculated for the determination of the disallowable zone ( 22 ).

13. Method as claimed in claim 1 , characterized in that a multiplicity of wafer sizes are taken into consideration and such wafer sizes, starting from the same position of their reference markers ( 6 ), form an overlap zone ( 9 ) which represents the free zone ( 7 ).

14. Method as claimed in claim 1 , characterized in that the measured discrepancies from the nominal position of the wafers ( 3 ), are acquired and stored for the acquisition of the system state for the deduction of corrective measures.

15. Method as claimed in claim 1 , characterized in that the wafer ( 3 ) is first worked in the process chamber and subsequently is transported from the process chamber into the transport chamber and here is measured with the single sensor ( 1 ) and the measured values are processed with electronic means and, upon reaching and/or exceeding a predetermined value, corrective measures are taken in one of the subsequent process steps.

16. Method as claimed in claim 15 , characterized in that several measuring steps are processed and a trend analysis regarding the type of error is determined and subsequently measures are determined for the further operating manner of the vacuum process installation, for actuating the transport device ( 2 , 20 , 21 ).

17. Method as claimed in claim 16 , characterized in that the contacting of the wafer ( 3 ), due to error setting of the transport device with the wafer ( 3 ), is acquired by the trend analysis.

18. Method as claimed in claim 16 , characterized in that the trend analysis acquires the local displacement of the wafer ( 3 ) on the mounting ( 10 ) of the transport device based on layer growths on masking parts during the process.

19. Method as claimed in claim 16 , characterized in that the trend analysis acquires the loss of efficiency of an electrostatic wafer mounting over the operating time.