Seiichi Iwamatsu, the Inventor of Atomic Layer Etching: The Conception of Cycled Exposures of Silicon to Halogens and Pulses of Heat, Ions, and More
Authors: Roozeboom Fred , Sundqvist Jonas , Suyatin Dmitry B. , Kakushima Kuniyuki 
Published: December 2024

The history of Atomic Layer Deposition (ALD) has been extensively researched in the VPHA-project (www.vph-ald.com/) initiated in 2013 by R. Puurunen [1]. It is commonly accepted that Atomic Layer Deposition (ALD) was conceived in the Baltic area as a unique ultrathin-film growth method based on the repeated, self-terminating gas-solid half-reactions of at least two volatile compounds on a solid substrate surface. Originally, in the 1960’s, the Russians Alekskovski and Kol'tsov [2]) named this method Molecular Layering and exactly 50 years ago, in 1974 the Finnish inventors Suntola and Antson [3] patented the method as Atomic Layer Epitaxy. This fact has been officially celebrated at the 24th ALD Conference in Helsinki (Aug. 5, ’24 ald2024.avs.org).
Atomic Layer Etching (ALE) has lagged behind ALD. For long [4,5] the first patent published on ALE was thought to have been initiated by Max Yoder [6]. In 1987 he conceived the idea on diamond etching with intermittent pulsing of nitrogen dioxide and noble gas ions mixed with hydrogen gas. However, it was Seiichi Iwamatsu (Fig. 1) of Seiko Epson, Japan, who filed in 1981 an application on Si-etching by repeated exposure to iodine (I2) chemistry at moderate temperatures (20 °C to 100 °C) followed by a light or heat pulse up to ~ 300 °C [7]; see Fig. 2. This patent was followed by several others on ALE [8]. One of these patents disclosed quasi-ALE (named “digital etching”) via Si-surface modification by “lamination” of 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” [9].
This presentation will highlight the groundbreaking work and background of the Japanese inventor Seiichi Iwamatsu. Born in 1939 in Kyoto to a family of doctors - his father being a practicing physician- he grew up and studied in Osaka, after which he spent many years as a ‘master inventor’ (over 1200 patents filed in his name) for Seiko Epson (~1970-1990) and others afterwards. He played key roles in thin-film technology and e-beam lithography. He also contributed to the success story of Seiko’s quartz watch, a masterpiece in micromachining a miniature tuning fork from crystalline fused silica, tuning/trimming it to 32,768 Hz (=215 Hz), packaging it in a hermetically sealed case and integrating it with flip-flop frequency dividing and counting electronic circuitry and a step motor [10].
From the above it is clear that Mr. Iwamatsu can be recognized as the original inventor of Atomic Layer Etching.
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Acknowledgement
The authors would like to thank Dr. Masanobu Honda (Tokyo Electron Miyagi Ltd., Japan) for his support in retrieving some of the historic facts mentioned herewith about Dr. Iwamatsu.
References
[1] R.L. Puurunen, Chem. Vap. Deposition 20, pp. 332–344 (2014); doi:10.1002/cvde.201402012.
[2] V.B. Alekskovski and S. I. Kol'tsov, Some characteristics of molecular layering reactions, Abstract of
Scientiﬁc and Technical Conference, Goskhimizdat, Leningrad, 1965, p. 67 (in Russian).
[3] T. Suntola and J. Antson, FIN 52359, priority Nov. 29, 1974, US Patent 4,058,430, Nov. 15, 1977.
[4] K.J. Kanarik, et al., J. Vac. Sci. Technol. A33, 020802 (2015); doi/10.1116/1.4913379.
[5] W.M.M. Kessels, www.atomiclimits.com/ March 2, 2020.
[6] M.N. Yoder, Atomic Layer Etching, US Patent 4,756,794, July 12, 1988; assigned to US Navy.
[7] S. Iwamatsu, Atomic Layer Etching Method, JPS5898929A / JPH0379862B2; priority Dec. 9, 1981,
published June 13, 1983; assigned to Seiko Epson Corp.
[8]
https://worldwide.espacenet.com/patent/search/family/016189802/publication/JPH0472726A?q=iwamatsu%20seiichi%20atomic%20layer%20etching
[9] S. Iwamatsu, Digital Etching Process, JPH0472726A, priority: July 13, 1990, published March 6, 1992;
assigned to Seiko Epson Corp.
[10] https://corporate.epson/en/technology/search-by-products/wearable/quartz-watch.html

Figure 1