Wafer platform

Wafer platforms (in English " wafer stage ") are used in the context of micro and nano structuring for positioning and position control of the wafer during processing ( photolithography ).

general structure

Wafer platforms differ in their design depending on the manufacturer. However, they are always connected to a laser interferometer (the mirrors of the interferometer, for example, are directly connected to the platform). The exact position of the platform is determined via the interferometer.

In general, however, a distinction can be made between two basic concepts: on the one hand, the division into two platforms for fine and coarse adjustment of the wafer and, on the other hand, the use of a single platform for fine and coarse adjustment.

In the first case, the division into two differently mounted platforms, the rough positioning takes place by means of the rough drive . This is usually moved using stepper motors and adjusting screws . The more precise positioning is done by means of the fine drive , which is mounted on air cushions or magnetic bearings.

An alternative concept combines the coarse and fine drives in a massive platform that is supported by magnetic fields. On the platform also always the restraint (is Chuck ) of the wafer. This can generally rotate in order to compensate for errors in the alignment of the wafer (what is meant here is errors in the prealigner ). The exposure or exposure of the wafer can then take place statically or during the movement ( step-and-scan ).

supporting documents

• Kazuaki Suzuki, Bruce W. Smith: Microlithography. Science and Technology . 2nd edited edition. CRC Press, Boca Raton, Fla. 2007, ISBN 978-0-8247-9024-0 (English).