Nanostructure Fabrication by Ultra-High-Resolution Environmental Scanning Electron Microscopy

Abstract

Electron beam induced deposition (EBID) is a maskless nanofabrication technique capable of surpassing the resolution limits of resist-based lithography. However, EBID fabrication of functional nanostructures is limited by beam spread in bulk substrates, substrate charging, and delocalized film growth around deposits. Here, we overcome these problems by using environmental scanning electron microscopy (ESEM) to perform EBID and etching while eliminating charging artifacts at the nanoscale. Nanostructure morphology is tailored by slimming of deposits by ESEM imaging in the presence of a gaseous etch precursor and by pre-etching small features into a deposit (using a stationary or a scanned electron beam) prior to a final imaging process. The utility of this process is demonstrated by slimming of nanowires deposited by EBID, by the fabrication of gaps (between 4 and 7 nm wide) in the wires, and by the removal of thin films surrounding such nanowires. ESEM imaging provides a direct view of the slimming process, yielding process resolution that is limited by ESEM image resolution ( approximately 1 nm) and surface roughening occurring during etching.

Advances in gas-mediated electron beam-induced etching and related material processing techniques

“…3(a-h)). Sample applications include iterative editing of individual nanostructures [85,19], repair of photolithographic masks [27,28], fabrication of nanopores in membranes [30,35], etching of 3D in-plane features in photoresist [37], and re-shaping of tips used in scanning probe microscopy [33,38]. EBIE has also been used to improve the purity of materials grown by EBID.…”

“…For example, EBIE models are needed to improve present understanding of surface roughening that occurs during etching, and typically limits the spatial resolution and geometries of sub-10 nm features fabricated by EBIE [85] (see Fig. 3(a-d)).…”

Applications of ESEM on Materials Science: Recent Updates and a Look Forward

“…More importantly, as the research focus has changed a lot during this period, a great amount of seminal papers have been published with the help of ESEM. For example, Kiselev et al reported the direct observations of deposition growth of aligned ice crystals on feldspar; the in situ observations performed by Huang et al demonstrated the formation of nanowire arrays proceeds via a selective vaporization process of the bulk crystals; and Toth et al achieved fabrication and slimming of nanostructure by beam‐induced deposition and etching in ESEM . Actually, the total number of papers is over 3000 in the last 16 years.…”

Electron beam induced etching of carbon

“…EBIE has been used to etch numerous carbon materials including graphene 10,[12][13][14][15] , carbon nanotubes [16][17][18][19] , diamond 11,[20][21][22] , ultra nano-crystalline diamond 23 (UNCD), and amorphous carbon-rich nanowires 24,25 and films 18,24,[26][27][28] . At low electron beam energies ( 30 keV), where atomic displacements by knock-on collisions between electrons and carbon are negligible 14,29,30 , the removal of carbon is typically attributed TABLE I.…”