Exposure – a key technology

The “exposure” or “printing” process is of central importance because the ability of the objective in wafer steppers to reproduce the finest details and smallest structures has influenced the progress of microelectronics. The smaller the structures are, the faster the processes. In other words, the processor’s tact rate increases, electricity consumption decreases, and productivity significantly improves because the single chip requires less room on the wafer.

One look at the objectives shows just how enormous progress has been from the beginnings of lithography at the end of the 1960s. In the early days they were based on simple photographic objectives. By the 1970s they were composed of a good dozen individual lenses weighing up to 50 kilograms. The latest product generations have up to 30 individual lenses and weigh up to 400 kilograms.

Improving the optical resolution can generally be achieved in two ways: either you increase the diameter of the lens, or you use light with shorter wavelengths. But both options have their limits. Once they reach a certain size, individual lenses begin to be awkward and unhandy. To use shortwave light you need light sources and optical materials that are transparent for this radiation.

For this reason, many experts already began predicting the end of optical lithography ten years ago. However, new developments such as the calcium fluoride crystals from SCHOTT LITHOTEC that are transparent for 157 nanometers still outperform any alternative technologies.