The 83rd JSAP Autumn Meeting 2022 Highlighted Presentations
October 24, 2022

Surface Reaction Mechanisms to Realize High-throughput SiN ALE

Etching Technology to Support Future Atomic-Scale
Semiconductor Manufacturing
High-throughput SiN ALE: a step toward realization
Sony Semiconductor Solutions Corporation(1), Graduate School of Engineering, Osaka University(2)Akiko Hirata (1), Masanaga Fukasawa (1), Katsuhisa Kugimiya (1), Yoshiya Hagimoto (1), Hayato Iwamoto (1)J. U. Tercero(2), Kazuhiro Karahashi(2), Satoshi Hamaguchi(2)Summary• Demonstrated high-throughput atomic layer etching of silicon nitride (SiN ALE), using
high ion energy to reduce the process time of the argon desorption step to one-fifth.
• The high-throughput SiN ALE and conventional ALE etching were characterized, and it
was confirmed that their etching characteristics were equivalent while realizing a shortertime.
• This research affords a technological innovation that will support the manufacturing ofnext-generation semiconductors and may lead to shorter manufacturing process times
and lower costs.

A research group led by Akiko Hirata, Masanaga Fukasawa, Katsuhisa Kugimiya, Yoshiya Hagimoto, Hayato
Iwamoto (Sony Semiconductor Solutions Corp.), J. U. Tercero, Kazuhiro Karahashi, Satoshi Hamaguchi(Osaka University), and their colleagues have achieved a high-throughput atomic layer etching of silicon
nitride (SiN ALE), which is a highly anticipated next-generation semiconductor manufacturing technology,
utilizing high ion energy, and this reduces the process time of argon desorption step to one-fifth. Accordingly,
the etching amount was approximately the same as that of conventional ALE, even though the process time
was shortened by high ion energy. Furthermore, it was confirmed that the etching amount depended on thenumber of cycles and the etched amount per cycle (EPC) was stable at approximately 0.5 nm/cycle. This
research is a groundbreaking discovery regarding the SiN ALE, which has been anticipated for practicalapplications in recent semiconductor manufacturing, where ultra-high-precision processing is required, as
well as technological innovation that will support future atomic-scale semiconductor manufacturing.
Detailsdetail

Creating manufacturing technologies to support the next generation ofsemiconductors beyond Moore's Law
Moore's Law, a widely known standard proposed by Dr. Gordon Moore, one of the founders ofIntel, has long guided the development of semiconductor technology, and semiconductor devices
have been scaled down in accordance with it. However, it is believed that Moore's law has alreadybroken down. This is because the miniaturization of semiconductors approaches the size of anatom, the smallest unit of matter, which is considered as the endpoint of Moore's law. In recentyears, semiconductor processes have been scaled down to 10 nm or less, and what lies ahead isthe realization of atomic-level semiconductors.
Semiconductor miniaturization is achieved via a series of technological innovations insemiconductor manufacturing processes. Dr. Akiko Hirata and her research group at Sony
Semiconductor Solutions have reported on a technology for achieving high throughput in atomic
layer etching (ALE), a new etching process that is expected to support further miniaturization ofsemiconductors.
The heart of a semiconductor device is formed by transferring a circuit pattern onto a wafer andthin plate made of silicon single crystals. The main processes are lithography, which transfers
minute circuit patterns onto the wafer, and etching, which processes the material according to thepatterns and these are positioned as the front-end processes of semiconductor manufacturing.
Currently, ALE is envisioned as a new technology that is capable of atomic-scale etching. Dr.
Hirata and her group have established a high-throughput atomic layer etching of silicon nitride (SiNALE), which is indispensable in industrialization, and has succeeded in significantly reducing thetime of the work process.

SiN ALE, the next-generation etching technology, can be widely utilized with higher
speed and lower cost.
The SiN ALE process can be roughly divided into three steps: "adsorption," wherein a polymer isutilized to form a reaction layer; "desorption," wherein a plasma is utilized to desorb the reaction
layer; and "ashing," wherein the remaining polymer from the adsorption step is removed (Figure 1).
The main result of the research by Dr. Hirata and her group is a reduction in the time required forthe "desorption" process.
In the conventional ALE process, the adsorption step takes several seconds, while the desorption
step takes 10 s to several minutes. In the actual manufacturing process, this process is repeatedseveral dozen times, which means that it takes more than 10 min to etch a single semiconductor
device. Shortening the processing time is an issue that must be addressed to realize low-cost
manufacturing.
In conventional ALE, the desorption step involves a long processing time with low ion energy(Eion:100–280 V, 10 s), which has been a bottleneck that reduces the work process time.
Therefore, Dr. Hirata's group introduced and evaluated a high-throughput ALE (Eion:140–900 V, 2s) with a short processing time at high ion energy (Fig. 2).

Hence, when examining the etching amount (amount of material desorbed), it was determined thateven in the case of high-throughput ALE, the ALE window was approximately the same as that ofconventional ALE. Furthermore, when the etching characteristics were evaluated based on cycle
number dependence, no significant difference was observed between conventional ALE and highthroughput ALE. These results indicate that the time required for the desorption step can bereduced to one-fifth (from 10 s to 2 s) by increasing the ion energy, without altering the etching
characteristics.
The increased processing time of conventional ALE is a major challenge in terms of productivity andhigh cost; however, if the time required for the desorption step can be reduced, the overall
processing time for the entire manufacturing process can be significantly shortened and costs canbe lowered.
Shorter and less expensive manufacturing processes for semiconductor devices will lead toimproved performance and lower costs in the development of supercomputers and other devices.
High-throughput ALE is an indispensable technology in the future of semiconductor manufacturing.
FiguresFigure 1. Process of SiN ALE CH3F/Ar gas is utilized to generate plasma and adsorb the adsorbed layer ofhydrofluorocarbon polymer (adsorption). Simultaneously, a reaction layer of hydrofluorocarbon polymer and SiN isformed. Furthermore, only the reaction layer is desorbed by argon plasma (desorption), and finally, the residual polymer
is removed by O2 plasma (ashing).
Figure 2. Etching amount per cycle (vertical axis) versus ion energy (horizontal axis) for conventional ALE (a) and highthroughput SiN ALE (b). Evidently, the etch amount is approximately the same as that of conventional ALE, while theprocess time is shortened using high ion energy.
Figure 3. Dependence of SiN etch amount on the number of cycles. The close agreement between conventional ALE(yellow) and high-throughput SiN ALE (green) on the number of cycles (horizontal axis) and amount of SiN etch (verticalaxis) indicates that the cycle dependence is approximately the same.