Tuomo Suntola, inventor of a technology that is responsible for massive advances in semiconductors and thin films, has been awarded the eighth Millennium Technology Prize in Finland this week for his work on atomic layer deposition (ALD).
Suntola, now 75 years old, began working on ALD at Instrumentarium Oy in 1974. It was the result of his development of a thin film humidity sensor at his previous company, Vaisala.
"That was very successful, and because Finland is a small country my reputation meant that I was moved to another company working with medical instruments", he told us. "They asked me to start inventing something for them, as well. It's a very strange challenge for a young scientist to propose something, but that happened to me."
Suntola devised ALD as a way of manufacturing flat panel displays, which no-one at the time had managed. The technique is used to manufacture ultra-thin material layers for a variety of products, including semiconductors. Its greatest strength is the uniformity of the layers created, which are built a single atom at a time through vapour deposition.
"I realised that if we really wanted to have well-controlled electronic properties, we needed a well-controlled material structure," he said. "That led me to the possibility of building up a structure of well-ordered material, moderated by time."
Suntola's work has been a major contributor to making IT equipment smaller, more powerful and cheaper - but the technique wasn't widely accepted by the chip industry until 2007.
"Originally everyone thought that it must be a very slow process because we had to build the material one atomic layer at a time," said Suntola. "That was the first reaction I generally heard from people: ‘It can't be practical at all!'"
Even senior researchers criticised the development after it was shown at the Society for Information Display (SID) conference in 1980: one even wrote to Suntola to say that he had proven that the claims were impossible.
Suntola solved the productional efficiency problem by running a gas flow containing two materials (known as precursors) through a substrate. These bond to the surface in layers, and although one end of the substrate is bombarded with far more material, the surface can only accept one layer of each precursor at a time.
The uniformity of ALD layers has proven important for the chip industry, which needs highly uniform, pinhole-free gate oxides on silicon to prevent leakage. Intel was the first manufacturer to introduce ALD, in 2007; this helped it to move from the existing 65nm nodes to 45nm, while keeping power consumption low. This has been vital in lengthening the life of Moore's Law. Today, every major chip manufacturer uses a form of ALD.
As for the eventual replacement of silicon and copper in chips, Suntola was hesitant to give an answer: "When we ask experts about the future they generally fail in their predictions," he pointed out. "They base their opinions on the existing technology."
"Many new parallel developments are needed to make completely new combinations possible," he added, "and that makes forecasting very very difficult."
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