During the transition to sub-20nm nodes before EUV was ready, lithography engineers had to rely on immersion deep ultraviolet (DUV) machines combined with multi-patterning techniques. One elegant process avoided multiple expensive masking steps by depositing a conformal spacer layer over a sacrificial mandrel, then directionally etching it away to double the spatial frequency of the lines. This process goes by a variety of acronyms (SADP, SAQP), but the foundational mechanism relies entirely on a conformal technique pioneered in 1977 by Finnish physicist Tuomo Suntola to create thin-film electroluminescent displays.
What is the name of this highly precise deposition technique?
CLUES:
The film grows one atomic layer per cycle, because each precursor reacts only with the surface and then stops (self-limiting).
Suntola first called it “Atomic Layer Epitaxy.” The modern name swaps out the last word.