Nikon 2006 Annual Report Download - page 10

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PRECISION EQUIPMENT
REVIEW OF OPERATIONS
Introduction of
tandem stage realizes
practical application
of immersion scanner
The newly developed tandem
stage consists of an exposure
stage and a calibration stage.
As the name suggests, the
exposure stage occurs when
the wafer is placed on the stage
for exposure, while the calibra-
tion stage is used to calibrate
the tool between each wafer
exchange. Previously, the calibration tool was loaded onto the apparatus after
the wafer was placed on the stage (wafer stage). Thus, with frequent calibra-
tion checks, accuracy increased, but productivity declined.
With Nikon’s tandem stage, the calibration stage is moved into position
as exposure is completed in a closely overlapping sequence. Next, both stages
move simultaneously until the immersion area is positioned above the calibra-
tion stage. Following this, only the exposure stage is moved to allow for wafer
exchange, while the exposure stage on the replaced wafer closely overlaps
the calibration stage, and the circuit pattern is exposed. During this time,
purifi ed water is continuously transferred. The calibration stage replaces the
wafer and the space between the projection lens and the calibration stage
is fi lled with purifi ed water. With the tandem stage method, purifi ed water
is supplied continuously during wafer exchange, so the temperature remains
stable and no time is lost.
It has traditionally been thought that immersion would reduce throughput,
but the tandem stage dismisses this as myth. Calibration at every wafer exchange
ensures optimum accuracy including alignment. The NSR-S609B boasts alignment
accuracy far superior to conventional systems at a level of 7nm or better.
Tandem stage
Reticle stage
08