In summer, some people have to mow the lawn twice a week. Because grass grows about two centimeters a week. That's about two micrometers per minute or 30 nanometers per second. But what does the growth rate of grass have to do with Carl Zeiss? The smallest structure size of a high-performance microchip transistor is currently about 30 nanometers, the amount that grass grows per second. To project such fine patterns onto the microchips, optical lithography – the key technology for chip fabrication – also has to be increasingly exact. Carl Zeiss is the leading manufacturer of these lithography optics.
Much like a slide projector, lithography optics project the structures needed for what will later become a microchip onto a silicon disk, or wafer. The actual semiconductor structures are created in further processes. To achieve the extremely high resolution needed for the miniature structures, the lenses or mirrors in the imaging optics must be made with extreme precision. The manufacturing precision is so high that the highest elevation on a mirror in the latest lithography generation is barely one nanometer. To create such a smooth surface, the lenses and mirrors undergo numerous very complex processing steps, from grinding through various polishing processes to coating.
Humans can normally imagine sizes that are four to five magnitudes of the human body size. 100 micrometers – the thickness of a sheet of paper – or 1,000 kilometers, the stretch of road that we can normally cover in one day with a car. That’s something our powers of imagination can deal with. But how small is a nanometer? That’s where our imagination reaches its limits. Only comparisons can help here. If a mirror from the latest lithography generation were to be enlarged to the size of Germany, the largest deviation, i.e., the peak of the country’s highest mountain, would be less than one millimeter high.
So, let’s indulge in a bit of wishful thinking: if grass grew just one nanometer per second instead of 30, it would only need to be mowed once a year. Definitely a dream come true for some of us.
July 24, 2012