Nanoimprint

3D NIL from two-photon masters

While nano-imprint lithography (NIL) nears commercial viability for semiconductor applications, perhaps this is less true for nano-photonics. A preprint posted to the arXiv today outlines an apparently successful, albeit slow, demonstration of “three dimensional” NIL, starting from masters written by two-photon lithography. (Nanoscribe, for example, makes suitable equipment for this step.) The master has positive tone, while an intermediate replica of PDMS has negative tone. The latter is used to cast positive tone replicas on substrates.

The micrographs are quite impressive, revealing reproduction of even the sidewall texturing resulting from the two-photon lithography of the master.

Although the authors claim the technique could be used to print structures with overhangs, the examples shown are all strictly convex. For convex geometries, I see no advantage over electron-beam masters, except possibly capital outlay.

Reference: R Saive, C R Bukowsky, H A Atwater, “Three-dimensional nanoimprint lithography using two-photon lithography master samples”, arXiv:1702.04012

Advance in bit patterned media

HGST reports (13 June 2016) using template-assisted epitaxial growth to create 1 Tdot / in² bit-patterned media including servo patterning. The template is established by nano-imprinting on a carefully chosen materials stack such that subsequent processing induces oxide growth between platinum pillars, enhancing magnetic separation of the islands (bits) and ensuring single domains within each one. The pattern growth process takes advantage of both chemical and topological contrast.

Embedded servo patterning permits the final media to be manufactured without a separate servo writing step. The growth process results in topography favorable to flying head aerodynamics, while maintaining adequate magnetic contrast in the servo regions.

Reference: Yang et al., “Template-Assisted Direct Growth of 1 Td/in2 Bit Patterned Media”, Nano Lett. (2016), DOI: 10.1021/acs.nanolett.6b02345. [Also, arXiv:1606.05370.]

2016 NNI Strategic Planning Stakeholder Workshop

The U.S. National Nanotechnology Initiative is inviting participation in their planning workshop to be held 19-20 May 2016 in Washington, D.C.

Click here for the announcement.

SPIE 2015 – NIL

Toshiaki Ikoma-san, CTO (now retired) of Canon, gave an impressive presentation on Nano-Imprint Lithography. In addition to making a very strong statement about Canon’s commitment and ability, this paper was beautifully illustrated with photographs, many taken by Ikoma-san himself (using Canon cameras, of course).

Ikoma-san’s messages were quite simple:

At the present time, NIL is very low cost, but suffers from poor defect density. However, it is now more than adequate for NAND-flash production.
The trends on defect reduction, overlay (now 4.8 nm 3σ) and throughput (now 40 wph) show steady and rapid improvement since Canon took over.
Canon is committed at the highest level to returning to semiconductor lithography.

Alas, there is no corresponding paper in the proceedings at this time.

Long nanowires in bulk

Professor Jun-Bo Yoon’s group at KAIST has recently demonstrated bulk production of 200 mm long nanowires. The process begins with a silicon master template, which is used to fabricate many (thousands?) of disposable plastic templates. One then applies the nanowire material to the plastic template by PVD. It would appear that any material which can be deposited by PVD onto the plastic can be used, viz., metals, oxides and nitrides are demonstrated in the paper. Shadowing during PVD leads to the deposition being thinner in the trenches than on the peaks; a clean-up etch removes the trench material and leaves isolated wires atop each peak.

See the abstract (and select images) at ACS NanoLetters. The full paper can be found on Prof. Yoon’s website.