ZEISS systems in wafer steppers

The wafer stepper (as well as its more advanced descendant, the wafer scanner) is a product that unites numerous top technological achievements. Lithography optics by ZEISS make up the core of the scanner. Other components, known as mirror blocks, form part of the wafer stage, holding and positioning the wafer during the exposure process. The light source also includes optical components by ZEISS. The technologies involved in the photomask systems are used before the exposure process: these guarantee that defect-free structures can be created with the photomask.

Copyright © ASML

Copyright © ASML

How a wafer stepper works

Wafer steppers and wafer scanners are among the most important production machines for chip manufacture. The functional principle is comparable to that of an oversized slide projector: in the wafer stepper, the structures of the later semiconductor components are transferred from a mask (reticle) to the wafer, which is coated with photoresist. This step, known as lithography, is a particularly important production process in the manufacture of semiconductor components.

The core of a wafer stepper consists of optical systems for exposure and projection. The Starlith® systems by Carl Zeiss SMT GmbH are the world’s leading wafer stepper and scanner optics.

The exposure optics (comparable to the condenser of a slide projector) ensures the even lighting of the mask (corresponds to the slide) and the targeted guidance of the beam into the projection lens. The lithographic lens projects the mask structures onto the wafer (however, reduced by a factor of four, in contrast to the slide projector). The wafer is shifted below the optical system after each exposure by precisely the size of the image field, and completely exposed step by step – hence the name “wafer stepper”.

To obtain even better process parameters, wafer scanners are used, with which the mask is continuously scanned. In steppers, on the other hand, the mask is exposed in a single step.
 

 

Exposure wavelengths

The higher the performance of a chip is to be, the finer the structures generated by the optical systems must be. Thus, progress in miniaturization and the resulting continuous increase in the performance of integrated circuits depend directly on the resolution of the optical systems. Like the ever more delicate brushes used in painting to bring out fine and finest details on canvas, ever shorter wavelengths are used in optical lithography to further reduce the structural dimensions. The Semiconductor Manufacturing Technology segment at ZEISS accomplishes this with EUV lithography optics, among other things.