現在主流の電子感材に集束電子ビームを露光する電子ビームリソグラフィ(EBL)を使った、材料パターン化技術がますます微細化することが、ナノテクノロジー分野における進歩を駆り立て続けています。材料のfeature size(フューチャサイズ、加工寸法)が、マイクロスケールからナノスケールへ縮小されると、一つ一つの原子と分子は、カラー、化学反応性、電気伝導度、光相互作用などの材料特性を劇的に変化させる目的で操作可能になります。



Scientists set record resolution for drawing at the one-nanometer length scale

In the ongoing quest to pattern materials with ever-smaller feature sizes, scientists at the Center for Functional Nanomaterials (CFN) — a U.S. Department of Energy (DOE) Office of Science User Facility at Brookhaven National Laboratory — have recently set a new record. Performing EBL with a scanning transmission electron microscope (STEM), they have patterned thin films of the polymer poly(methyl methacrylate), or PMMA, with individual features as small as one nanometer (nm), and with a spacing between features of 11 nm, yielding an areal density of nearly one trillion features per square centimeter. These record achievements are published in the April 18 online edition of Nano Letters.

微細化を続けるフィーチャサイズを使った材料パターン化の、さらなる微細化を追求する研究において、米エネルギー省ブルックヘブン国立研究所にある科学局ユーザー施設の機能性ナノ材料センター(CFN)の研究者たちが、現在までの微細化新記録を樹立しています。走査型透過電子顕微鏡(STEM)によるEBLを行い、彼らは、ポリメタクリル酸メチル樹脂(PMMA、アクリル樹脂)の薄膜に、1平方センチメートル当たり、約1兆フューチャの面密度を達成可能な、各フューチャが最小1nmで11nmのフューチャー間隔でパターン化しています。この記録的な大偉業に関する論文は、4月18日、Nano Lettersのオンライン版に掲載されました。

“Our goal at CFN is to study how the optical, electrical, thermal, and other properties of materials change as their feature sizes get smaller,” said lead author Vitor Manfrinato, a research associate in CFN’s electron microscopy group who began the project as a CFN user while completing his doctoral work at MIT. “Until now, patterning materials at a single nanometer has not been possible in a controllable and efficient way.”





“We converted an imaging tool into a drawing tool that is capable of not only taking atomic-resolution images but also making atomic-resolution structures,” said coauthor Aaron Stein, a senior scientist in the electronic nanomaterials group at CFN.


Their measurements with this instrument show a nearly 200 percent reduction in feature size (from 5 to 1.7 nm) and 100 percent increase in areal pattern density (from 0.4 to 0.8 trillion dots per square centimeter, or from 16 to 11 nm spacing between features) over previous scientific reports.




The team’s patterned PMMA films can be used as stencils for transferring the drawn single-digit nanometer feature into any other material. In this work, the scientists created structures smaller than 5 nm in both metallic (gold palladium) and semiconducting (zinc oxide) materials. Their fabricated gold palladium features were as small as six atoms wide.





“The resolution of EBL can be impacted by many parameters, including instrument limitations, interactions between the electron beam and the polymer material, molecular dimensions associated with the polymer structure, and chemical processes of lithography,”




An exciting result of this study was the realization that polymer films can be patterned at sizes much smaller than the 26 nm effective radius of the PMMA macromolecule. “The polymer chains that make up a PMMA macromolecule are a million repeating monomers (molecules) long–in a film, these macromolecules are all entangled and balled up,” said Stein. “We were surprised to find that the smallest size we could pattern is well below the size of the macromolecule and nears the size of one of the monomer repeating units, as small as a single nanometer.”


Next, the team plans to use their technique to study the properties of materials patterned at one-nanometer dimensions. One early target will be the semiconducting material silicon, whose electronic and optical properties are predicted to change at the single-digit nanometer scale.