Semiconductor History | Oberkochen — The Smoothest Surfaces Ever Made, in a Town of Eight Thousand

The mirrors inside an EUV lithography machine are polished until, by Zeiss's own comparison, scaling one up to the size of Germany would leave its largest bump about a tenth of a millimetre high.

They are made in Oberkochen, a town of roughly eight thousand people in Baden-Württemberg.

EUV light at 13.5 nanometres is absorbed by air and by glass, so the machine works in vacuum and cannot use lenses. Everything is done with mirrors, and a bare mirror at that wavelength reflects almost nothing.

The trick is a stack of up to a hundred alternating layers of molybdenum and silicon, each a few nanometres thick.

One layer returns about one per cent of the light. Only the whole stack, with the weak reflections adding in phase, gives a beam the machine can use.

Final figuring is done by ion beam, removing material atom by atom. A standard EUV mirror takes months; the larger mirrors for the High-NA generation take around a year each.

How the optics ended up in this particular town is a Cold War story.

Carl Zeiss opened a workshop for precision mechanics and optics in Jena on 17 November 1846, and Jena is where the company stayed for a century. At the end of the Second World War American troops removed seventy-seven selected employees from the Jena plant to Heidenheim in the south — the company's own figure; other accounts say eighty-four.

Opton Optische Werke Oberkochen GmbH was founded in 1946 as a subsidiary of the Carl Zeiss Foundation, and became Carl Zeiss soon after.

Jena and Oberkochen worked together until 1953 and then went separate ways, one in each Germany, both claiming the same name. West German products were sold as Opton inside the Eastern bloc; East German ones were sold as Zeiss Jena in the West. The two halves were reunited after 1990.

The company is still owned outright by the Carl Zeiss Foundation, which is why the most critical optical supplier in the semiconductor industry has no shareholders to answer to.

ASML bought a 24.9 per cent stake in Carl Zeiss SMT in 2016 for one billion euros in cash, specifically to fund High-NA optics.

The majority stayed with Zeiss. The deepest dependency in the most complex machine ever manufactured is therefore a relationship between two companies rather than something either one owns, and the company estimates its optics are involved in about eighty per cent of all chips made anywhere.

The headquarters is a plain modern block on the edge of a small Swabian town, visible from the road and closed to visitors.

There is a Zeiss museum in Oberkochen and another in Jena, and between them they cover microscopes, camera lenses and planetarium projectors — not the mirrors, which are the one thing here nobody outside gets to see.

Photo: Dwi Secundus, public domain, via Wikimedia Commons (Carl Zeiss headquarters, Oberkochen, 2008).