【公開日：2023.07.28】【最終更新日：2023.05.23】

課題データ / Project Data

課題番号 / Project Issue Number

22TU0209

利用課題名 / Title

Evaluation of physical properties of Al whiskers

利用した実施機関 / Support Institute

東北大学 / Tohoku 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）計測・分析/Advanced Characterization（副 / Sub）-

【重要技術領域 / Important Technology Area】（主 / Main）次世代ナノスケールマテリアル/Next-generation nanoscale materials（副 / Sub）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

キーワード / Keywords

ウィスカー,集束イオンビーム/Focused ion beam,ナノワイヤー・ナノファイバー/ Nanowire/nanofiber

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)

LUDWIG THOMAS

所属名 / Affiliation

東北大学大学院 工学研究科

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

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）技術補助/Technical Assistance（副 / Sub）,技術代行/Technology Substitution

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

TU-507：集束イオンビーム加工装置
TU-508：集束イオンビーム加工装置

報告書データ / Report

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

The objective of this project was to prepare samples of Al whiskers for TEM observation. Al whiskers can be fabricated by heating a passivated Al thin film on an Si wafer via the mechanism of stress induced atomic migration. Al whiskers are expected to improve performance of sensors and to be used in MEMS, micro electro- mechanical systems. In order to investigate mechanical properties of the fabricated Al whiskers, tensile tests were conducted on whiskers fabricated under two different conditions. The crystal structure of each whisker is considered to have a great impact on its tensile strength. The FIB machines Quanta and Versa were used to prepare thin slices of tested Al whiskers for TEM observation of crystal structure.

実験 / Experimental

One of three tested Al whiskers was transferred onto a Cu TEM grid via a micromanipulator and attached to the surface by SEM glue from the company Kleindiek. The other 2 tested Al whiskers were transferred to an AFM cantilever chip. The SEM glue used is designed to harden after electron beam exposure at acceleration voltages above 20kV and provides firm fixation of the whisker to the substrate. Afterwards, whiskers were covered with a protection layer of Pt and C. When depositing C, it was essential to create a flat top surface for better stability during ion beam etching. In a next step, the area above and below the whisker was removed and the whisker was cut free from its surroundings except for one part; this is called J cut. After attaching the lamella to an Omniprobe via C deposition, it was transferred from the substrate to the post of a TEM half grid and fixated via C deposition at 6 points. The post was carved out prior to lamella transfer, so that only 2um on each side of the lamella would touch the post. Then the lamella was thinned until a thickness below 70nm. Measuring the exact thickness is a difficult task, which is why the actual thickness is estimated from the degree of translucence during observation at 2kV acceleration voltage in SEM mode. The whisker appears then in light grey, with white surroundings.

結果と考察 / Results and Discussion

When using the Cu TEM grid, the difference in etching speed between Cu and Al, or Cu and SEM glue would lead to preferential etching of Al and the SEM glue. This resulted in a visible step at the whisker Cu interface. Special care had to be taken to remove the step. Therefore, using an AFM cantilever chip made from Si was found to achieve a greater ease of preparation. Furthermore, not covering the whole whisker, but leaving a small portion of 2 um on the side uncovered helped greatly to find and keep the right spot during slicing. By this approach much thinner lamellas could be fabricated. Finally, best results were achieved with perfectly straight whiskers. Even a slight curvature of the whisker of 4 degree reduces the area which can later be observed in TEM by half. Therefore, special care shall be taken when attaching the whisker to the AFM cantilever chip. In summary, three whiskers of two different conditions were successfully prepared in FIB for TEM observation.

図・表・数式 / Figures, Tables and Equations

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

We thank Mrs. Takenaka for her great, valuable technical support in sample preparation.

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