A New Alternative to Self-Aligned Double Patterning: Pitch Splitting by Atomic Layer Etching

For the past decade (1,2) the first patent published on Atomic Layer Etching (ALE) was thought to have been conceived by Max Yoder (3), who in 1987 filed the concept on etching diamond by saturating its surface with alternated pulses of NO2 and ionized noble gas / H2 gas mixtures. This date of conception still holds for plasma-assisted ALE of diamond. Surprisingly, we needed extensive A.I.-assisted patent searches to find out that thermal ALE of silicon was conceived as early as in 1981 by dr. Seiichi Iwamatsu (Fig. 1) of Seiko Epson, Japan. He stands out as concept inventor of ALE with his first application that was filed for the application on Si-etching by exposures to iodine (I2) vapor at moderate temperatures (20-100 °C), followed by a light or heat pulse up to ~300 °C (4) ; see Fig. 2. A few more patents on ALE in his name appeared shortly after (5), one of them being disclosed on plasma-assisted quasi-ALE, which he described as “digital etching” (6). The process steps comprised the modification of the Si-surface by “lamination” with a single Cl-atomic layer from exposure to Cl2 gas, followed by a removal step carried out by Ar+-ion bombardment to etch off “one atomic layer or at most three atomic layers by controlling the kinetic energy”. Other researchers in Japan can be recognized as the concept demonstrators who, soon after, published on digital etching of GaAs, with similar two-step physico-chemistry recipes (7). Fueled by early-leading groups, who worked on thermal and plasma ALE of metals, metal oxides, metal nitrides, semiconductors, and their oxides, ALE is now an established technique in the commercial manufacture of 3D logic and memory devices in single-digit nanometer technology nodes; see the reviews in refs. (8,9).

This presentation follows our earlier presentation (10) and will highlight our continued quest on the groundbreaking work and background of the Japanese inventor. Seiichi Iwamatsu was born in 1939 in Kyoto to a family of physicians, grew up in Osaka and studied there. Next, he worked for some 20 years as a ‘master inventor’ and created over 1200 patents in his name for Seiko Epson (~1970-1990), and for other employers, including Japan’s renowned VLSI Lab. He played key innovative roles in thin-film technology and e-beam lithography, and contributed also this way to the success story of Seiko’s quartz watch (11), a masterpiece in micromachining and hermetic sealing of the quartz resonator and its heterogeneous integration with microelectronics. Dr. Iwamatsu is still active: earlier this year he contributed chapters to the newly published book on the Japanese consortium (“VLSI Lab”) in the 1970's (12), for which he also worked; Fig. 1c.

We intend to include a short interview with Dr. Iwamatsu, now 86 years old, and conclude that he can and should be widely recognized as the original inventor of Atomic Layer Etching of silicon.