【公開日：2025.06.10】【最終更新日：2025.05.17】

課題データ / Project Data

課題番号 / Project Issue Number

24KT2287

利用課題名 / Title

Fabrication and Application of Diamond Nanoresonator Devices

利用した実施機関 / Support Institute

京都大学 / Kyoto Univ.

機関外・機関内の利用 / External or Internal Use

内部利用（ARIM事業参画者以外）/Internal Use (by non ARIM members)

技術領域 / Technology Area

【横断技術領域 / Cross-Technology Area】（主 / Main）加工・デバイスプロセス/Nanofabrication（副 / Sub）-

【重要技術領域 / Important Technology Area】（主 / Main）高度なデバイス機能の発現を可能とするマテリアル/Materials allowing high-level device functions to be performed（副 / Sub）マルチマテリアル化技術・次世代高分子マテリアル/Multi-material technologies / Next-generation high-molecular materials

キーワード / Keywords

diamond,nano,resonator,電子線リソグラフィ/ EB lithography,スパッタリング/ Sputtering,膜加工・エッチング/ Film processing/etching

利用者と利用形態 / User and Support Type

利用者名（課題申請者）/ User Name (Project Applicant)

Banerjee Amit

所属名 / Affiliation

京都大学　大学院工学研究科

共同利用者氏名 / Names of Collaborators in Other Institutes Than Hub and Spoke Institutes

宇野将生

ARIM実施機関支援担当者 / Names of Collaborators in The Hub and Spoke Institutes

利用形態 / Support Type

（主 / Main）機器利用/Equipment Utilization（副 / Sub）-

利用した主な設備 / Equipment Used in This Project

KT-101：高速高精度電子ビーム描画装置
KT-201：多元スパッタ装置（仕様Ａ）
KT-212：シリコン酸化膜犠牲層ドライエッチングシステム

報告書データ / Report

概要（目的・用途・実施内容）/ Abstract (Aim, Use Applications and Contents)

Nanofabrication technologies have been evolving at an astonishing pace to enable device miniaturization, high integration, high sensitivity, and low power consumption. Nanoelectromechanical Systems (NEMS) integrate nanoscale mechanical components with electronic circuits on a semiconductor substrate. NEMS has various functions such as acceleration sensing, pressure sensing, mass sensing, charge sensing, etc. These technologies are widely applied in fields such as sensing, signal processing, and artificial intelligence. NEMS can play an essential role in our modern lives. Until now, nanofabrication processes have primarily developed around silicon-based semiconductors. However, the growing demand for NEMS devices with superior performance and versatility has driven some research for materials beyond conventional silicon semiconductors.
Diamond, with its unique mechanical, electrical, thermal, and chemical properties, has promised as a superior material for many NEMS applications. Notably, diamond’s biocompatibility and stability in extreme environments open new possibilities for NEMS applications. By developing scalable fabrication processes for diamond NEMS, it may become possible to realize innovative devices for applications in biology, medicine, mining, heavy industry, and planetary exploration. Although some research is conducted for diamond fabrication in microscale, scalable nanofabrication of diamond is not sufficiently studied. In particular, metal nanopatterning on diamond surfaces and etching of diamond for nanostructure formation has not been explored extensively. Achieving scalable diamond NEMS fabrication requires extensive experimental investigations that consider multiple factors impacting these processes.
In this study, we develop nanoscale Cr patterning as hard mask by electron beam lithography (EBL) through lift-off process and also reactive ion etching (RIE) of diamond thin film (thickness ~ 2 μm) with O₂ plasma to create nanoscale suspended diamond structures for diamond NEMS devices. As a result of this study, we can achieve the nanopatterning of ~ 100nm thickness Cr on diamond film. Additionally, identify the challenges in diamond RIE process for nanofabrication. We report a partial success in creating nanoscale diamond resonators device (beam with a triangular cross-section, a base width of 300–1000 nm and a height of 0.5–1.5 µm, beam length 100–200 µm, gap between beam and electrode is 4 μm) and successfully induce electromechanical oscillation.

実験 / Experimental

⓪ Prepare a 10 mm × 10 mm diamond-on-insulator chip.
① Coating the resist layer on the diamond chip.
② Expose the positive resist in electron beam lithography (EBL) (KT-101) , immerse it in developing solution to develop, and remove the resist at the exposed areas. In this step, the resist at the area exposed by electron beam is removed, while the resist at the area unexposed remains on the substrate.
③ Perform descumming with oxygen plasma to remove the resist residue remaining in the exposed regions.
④ Deposit a metal layer on top. As a result, in the areas where the resist was removed, the metal will be deposited on the diamond surface. On the other hand, in the areas where the resist remained, the metal will be deposited on top of the resist.
⑤ Immerse the chip in NMP (N-Methyl-2-pyrrolidone) to dissolve the resist. This will remove the resist and the metal on top of resist from the substrate. And, in the electron beam exposed areas, the metal directly adheres to the diamond surface. In this way, we complete the process of metal nanopatterning on the diamond film.
⑥ Use the metal nanopatterns on the diamond as a hard mask and perform reactive ion etching (RIE). This process will remove the diamond in areas where no Cr is present, while the diamond beneath the Cr will be preserved
⑦ Finally, release the diamond beam structures. Since the diamond beam is fixed by the underlying SiO₂ layer, use VHF (Vapor Hydrofluoric Acid) etching (KT-212)  to remove the SiO₂ layer and release the diamond beams

結果と考察 / Results and Discussion

In this study, we investigate suitable methods for Cr nanopatterning on CVD diamond thin films as a hard mask and for diamond nanostructure etching, aimed at the scalable and mass-producible fabrication process of diamond NEMS. Specifically, the research was conducted to achieve the following three objectives:
①To realize nanopatterning of Cr thin films (a few hundreds of nm width) on diamond. (Figure1)
②To study the reactive ion etching of diamond (using the Cr nanopatterns as hard mask) for the fabrication of diamond nanostructures.
③To develop diamond NEMS resonator devices. (Figure2)                 
Regarding the first objective, the adhesion between the diamond film and the Cr film was poor, resulting in the Cr film detaching from the diamond film during the lift-off process. To counter this issue, we implemented several strategies in the EB deposition device. By applying these strategies, the adhesion of the Cr film became sufficient to endure IPA immersion and strong N₂ blow. In other words, the 100 nm thick Cr nanopatterning using electron beam deposition was successful (with line widths ranging from approximately 100 nm to 1000 nm). On the other hand, sputtering deposition is not suitable for our process because lift-off was successful in only about 70% of the devices.              
Regarding the second objective, the reduction of the Cr mask during RIE occurred not only from the top but also from the sides, and the reduction from the sides was more severe. The Cr mask on the beam portion was completely removed from the sides before the diamond film was fully etched. As a result, the cross-sectional shape of the beam became triangular instead of rectangular. We could successfully etch the diamond, however, the top parts of the nanostructures got damaged by the plasma once the Cr mask was removed.              
Regarding the third objective, we fabricated the devices (a triangular cross-section a base 300–1000 nm and height 0.5–1.5 µm, length 100–200 µm and gap is 4 μm) and using 400–800 nm width Cr mask. We could successfully release the resonator structures and we could observe electromechanically induced low frequency oscillation (~ 1 Hz) in the fabricated devices.

図・表・数式 / Figures, Tables and Equations

Figure1 Nanopatterning of Cr thin films (a few hundreds of nm width) on diamond.

Figure2 Diamond NEMS resonator devices.

その他・特記事項（参考文献・謝辞等） / Remarks(References and Acknowledgements)

成果発表・成果利用 / Publication and Patents

論文・プロシーディング（DOIのあるもの） / DOI (Publication and Proceedings)

口頭発表、ポスター発表および、その他の論文 / Oral Presentations etc.

特許 / Patents

特許出願件数 / Number of Patent Applications：0件
特許登録件数 / Number of Registered Patents：0件