MOLTEN METAPHOR

Dick Pountain /Idealog 328/ 05 Nov 2021 09:03

The little-known corollary to Moore’s Law is that computer columnists have to mention it in a column at least once a decade, and I am no exception. The miracle of digital search tells me that I’ve covered it here in 1996, 2004, 2005, 2009 and 2019 (the numerate among you will deduce that it’s a pretty rough sort of law). That first date is significant because it was in PC Pro issue 18, two years before the most popular piece I ever wrote for Byte, ‘The Limits Of Computing’ in 1998, about how and when Moore’s Law would end. In that piece I talked about the difficulty of getting down to 0.1 micron feature sizes in silicon CPUs: it would require short wavelength UV light from exotic krypton/fluorine lasers to illuminate the masks whose reduced images create the circuit patterns via the lithographic fabrication process. Getting much smaller would require X-rays which are intractable for many reasons.

Skip forward one quarter of a century, Moore’s Law is still at work and Intel and Apple’s latest chip families are pushing feature sizes down toward 10 nanometres (0.01 microns in old money). They do that by using EUV (Extreme UV) illumination, the last stop before those dreaded X-rays, and these are very, very difficult indeed to generate. I found myself getting interested in fab tech again, and decided to read up on EUV. 

There’s only one firm in the world that makes the EUV machines for this chip generation. It’s a Dutch firm called ASML (nothing at all to do with ASMR) and you can have one of their machines for somewhere around $180,000,000 depending on what bell and whistles you need. You’ll need to rent a new garage, around the size of a football field, and a couple of cranes to house it, and your electricity bill may rise. The reason for this price and size is that 13.5nm EUV radiation is totally absorbed by both glass and air, so everything has to be performed in the highest possible vacuum and with mirrors rather than lenses. The mirrors, by Zeiss, are the flattest ever made, flatter even than the ones in space telescopes. A whole array of vacuum pumps employ little rotors spinning at 30,000rpm that bat air molecules away one at a time like ping-pong balls. Oh, and you can’t use any old incandescent lamp to generate these rays. In fact the only way they found to generate 13.5nm EUV is by blasting a tiny drop of molten tin with two hits from a powerful laser microseconds apart, which explodes it into a tiny ball of glowing plasma. Over and over again, like a sort of hot, tinny ink-jet printer. Phew.

I’ve always been fascinated by molten metal. I love the stuff, perhaps because my father worked in the steel industry. As a small boy I watched Bessemer Converters blowing, the best firework display in the world, from just far enough so I didn’t catch fire (health-and-safety was loose back then). At home I melted down all my lead soldiers in a pan on the gas stove, poured them into two small alloy jelly moulds in the shape of tortoises which became our doorstops for years (I did spill at bit on the kitchen floor, which remained a burned-in silver splatter for years too). 

My favourite movie was ‘The Hunchback of Notre Dame’ in which Charles Laughton as Quasimodo, stands on the roof of a Gothic cathedral chanting “Molten Metal! Molten Metal” while he pours boiling lead onto the soldiers below. Studying chemistry in London I was often faced with molten metal, often sodium, not always on purpose. When later I became a magazine publisher I used to visit marvellous old printing plants in the East End that still employed Linotype machines, in which a small vat of molten lead gets poured into the lines of lead type. 

You get the picture. I just find the image of some sort of expensive ink-jet printer that fires drops of molten tin that get blasted into plasma very, very powerful indeed. It’s a bit of a cliché to compare the silicon chip industry to the building of Gothic cathedrals, in both effort and ambition, but ASML’s EUV machine makes it a very tempting metaphor. It’s certainly as costly, and getting on for a similar sized floor-plan. Instead I’ll deflate the rhetorical atmosphere slightly with a more humble metaphor. Predicting the end of Moore’s Law is very like making a long car journey with a small child, who keeps asking “Are We There Yet!, Are We There Yet!”. And I can now tell you that the answer is a resounding “Not Yet!...Soon!”.