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— Presentation at the 232nd ECS Meeting —
October 31, 2017
The 232nd Electrochemical Society (ECS) Meeting was held in National Harbor, Maryland, from October 1 to 5, 2017. The ECS Meeting is a biannual international conference organized by the ECS, which was founded 115 years ago. The meeting covered various topics related to electrochemistry, including semiconductor fabrication processes, lithium-ion batteries, fuel cells, corrosion science, and semiconductor cleaning and etching. More than 2300 papers were presented at the meeting. Attendees came from the United States, Japan, South Korea, European countries, and many other places.
Fig. 1 Applications and devices in IoT era
At this conference, we were invited to give a presentation entitled "Thermal Cyclic Atomic-Level Etching of Nitride Films: A Novel Way for Atomic-Scale Nanofabrication." We presented our method for atomic-level etching of nitride films such as titanium nitride and silicon nitride. This novel type of etching enables precisely controlled lateral etching of nitride films with atomic-scale precision. This precision is essential for fabricating miniaturized three-dimensional (3D) semiconductor devices that will be used in the Internet of things (IoT) era.
IoT applications continue to increase: 50 billion devices will be connected by 2020. Further, because of the increase in enterprise applications, data traffic will exceed two zettabytes. To handle increased data traffic, semiconductor devices have come to require lower power consumption and higher storage capacity. To meet these requirements, the structures of semiconductor devices are shifting from 2D to miniaturized 3D. The next generation of this technology will be based on high-aspect-ratio structures with very narrow gaps. Atomically precise etching will thus be required to manufacture this next generation of devices (Fig. 1).
In 2016, we developed a method of atomic-level etching of nitride films in collaboration with Hitachi High-Technologies and Nagoya University. The development of atomic-level etching for nitride films is important because these films are widely used in semiconductor-device manufacturing: titanium nitride films are used as gate-electrodes and barrier metals, and silicon nitride films are used as dielectric materials and passivation layers. The etching process is composed of cyclic repetitions of plasma exposure and infrared (IR) irradiation. The first step of the etching cycle for silicon nitride is exposing the material surface to hydrofluorocarbon-based plasmas that form ammonium hexafluorosilicate on the material's surface. The second step is thermal annealing by IR irradiation to sublimate the ammonium hexafluorosilicate (Fig. 2). This etching method has many useful capabilities, such as atomic-level control of the amount etched, high selectivity with respect to silicon dioxide, and isotropic etched profiles for patterned samples (Fig. 3).
A potential application of atomic-level etching of nitride films is lateral etching for the fabrication of 3D NAND flash memory. In addition to flash memory, this technology could also be applied to next-generation logic devices such as nanowire field-effect transistors. Thus, this atomic-level etching of nitride films can provide a novel method of atomic-scale nanofabrication for the next generation of semiconductor manufacturing. We will provide a product for atomic-level etching in collaboration with Hitachi High-Technologies to contribute to the development of IoT technologies.