April 25th, 2013
Two recent articles show very surprising mechanisms for transporting nanoparticles through nanotubes. In the first, Xu and Chen at Columbia embed a single water molecule inside a fullerene cage, which was placed inside a carbon nanotube. An applied electrical field parallel to the tube causes the fullerene to migrate, even though the cage and its entrapped water molecule are electrically neutral. This phenomenon seems to be due to conservation of energy and momentum: the initially randomly oriented water molecule largely aligns with the electrical field. Leftover momentum provides the kick needed to move the whole cage forward. There’s a nice summary here.
In the second, the Cohen group at Berkeley show that an iron nanoparticle migrates through a carbon nanotube with an applied electrical field. In this case, electromigration within the nanoparticle induces something like a plastic flow of the particle through the tube.
April 3rd, 2013
Hoffrogge et al. recently posted a pre-print to the arXiv describing a laser-heated field emission source demonstrating sub-100 femtosecond pulsed electron emission. There have been previous disclosures of laser-heated field emission cathodes (see, for example US 6,828,996 and references therein), but none have been designed for pulsed emission.
The new source should find application in time-resolved electron diffraction. The coherence of the source has apparently not yet been established. The implementation shown operates at 30 keV.
Another application comes to mind – pump-probe spectroscopy. In the usual scheme, a femto-second laser pulse is used to excite a target molecule, while a second, time-delayed pulse measures the decay product. One can envision replacing the pump laser pulse with a pump electron beam pulse. Since the selection rules for energy absorption are entirely different for photons and electrons, the excited states and resultant decay channels will also differ. Comparing photo-pumped and electron-pumped systems could, for example, clarify why EUV resists are generally not particularly good electron-beam resists and vice versa.
A recent advance in laser pump-probe spectroscopy, involving a third photon pulse, would be very useful here as well, since we know that electron impact with resist yields a vast number of excited states.
September 28th, 2012
Built up field emission electron sources, while bright, have limited angle over which they are spatially coherent. For purposes such as electron holography and low-energy electron point source (LEEPS) microscopy, this angular limitation has long been a fundamental stumbling block. In a major advance, Mutus et al. demonstrate a tip which opens the spatial coherence angle to ~14 degrees. The tip is formed by field assisted nitrogen etch of tungsten to expose a single tungsten atom, while enveloping the remainder of the tip in a TiN sheath. The authors claim that the tip is extra-ordinarily stable.
The paper may be found on the arXiv. For an interesting application, see this paper (also on the arXiv).
September 26th, 2012
In a paper coming out of Kamerlingh Onnes Laboratorium, Schramm et al. remind us that instability is inherent in aberration corrected electron microscopes. They propose that the system designer use a stability budget to trade off stability and resolution. The stability budget is somewhat orthogonal to the usual error budget. They further point out that real-time control is required to further advance TEM (and SEM, LEEM, etc. for that matter), but that suitable measurement parameters from which to derive feedback are presently unknown.
The paper is on the arXiv. It would appear that there’s an entrepreneurial opportunity here.
June 15th, 2012
A group at NIST reports that they have created single electron transistors in a CMOS process. These are meant to support electrometry, thermometry, and quantum information processing. As experimental devices, they are rather large but they do work over temperatures ranging from 30 mK to 300 K. The nanowire and gates at the heart of the devices were formed by e-beam lithography in HSQ and chlorine etch.
Details may be found on the arXiv as arXiv:1206.2872v1.
April 4th, 2012
The papers presented at SPIE’s 2012 Advanced Lithography Conference are beginning to appear on line. Follow these links:
Metrology & Inspection, …
March 14th, 2012
Chris Mack gave an insightful talk on line edge roughness (LER). One of the points he made is that talking about σ_LER is not enough. Consider the power spectral density (PSD) plots in the figure. Which curve shows “better” LER? If both curves integrate to the same area, they cannot be distinguished by the variance (σ^2). We must also consider the correlation length and roughness exponent. The correlation length influences where the “break” of the curve appears, while the roughness exponent influences how rapidly the curve declines from there. (The PSD plot of white noise would be a horizontal line.)
A recent article in JMM attempts to quantify just this effect, that the impact of LER is not constant with constant variance. One must instead specify the PSD at least to the level of the three parameters: variance, correlation length, and roughness exponent.
February 29th, 2012
Carl Zeiss SMS has introduced the RegC® process for registration error correction on photomasks. In their PMJ paper, they report using the same femtosecond laser technology as in their previously announced CDC32 product, which corrects CDU error. [The PMJ paper was presented at BACUS, since PMJ was cancelled due to the after-effects of the earthquake and tsunami.]
In these instruments, femtosecond laser pulses create local changes in the refractive index of the photomask substrate (in the case of CDU correction) or bulk strain (in the case of registration error correction). Zeiss claims correction of up to 50% of the total placement error contribution of the photomask.
Zeiss also claims that the treated photomasks are stable. Privately they claim that there is no induced flare. One wonders how this is possible after introducing millions of small pockets of color centers and high strain throughout the exposure field.
[Sorry - I neglected to "Publish" this one last fall. - Richard L]
February 29th, 2012
REBL has undergone big changes since the last report. The rotary stage is now gone. We recall that an early KLA-Tencor proposal was to have multi-column clusters arrayed on opposing sides of a circle as in Figure 1.
Fig. 1 Previous REBL stage concept.
Entire wafer areas can be covered by moving the stage along one axis in addition to rotating. However, throughput was found to be inadequate, necessitating the addition of more column clusters. Unfortunately, with more clusters arrayed around the circle, one cannot cover the wafer areas by a simple one-dimensional stage motion. Instead, one must move each column cluster in and out radially. This is clearly not possible mechanically.
Fig. 2 New REBL stage concept.
K-T’s latest proposal shows two X/Y maglev stages moving side by side in opposing directions. Each stage carries multiple wafers. (See Figure 2.) Obviously, this configuration suffers stage turn-around overhead. Because K-T targets the 16 nm node, and expects a higher dose requirement, they claim that the overhead is negligible.
K-T claims to have “some” functional modulator chips, but clearly continues to have difficulties here. The next column design (Column 4) due this year will operate at 100 kV and will have 100X demagnification. K-T expects 5 nm to 12 nm beam blur. Throughput will be limited to a few wafers per hour. Importantly, K-T may be targeting the cut pattern market rather than fully general patterning.
February 24th, 2012
Nanoscribe GmbH has an impressive technology for 3D patterning. Based on non-linear two-photon lithography, the instrument builds up (nearly) arbitrary three-dimensional structures at the micron to sub-micron scale. Take a look at the pictures in their newsletter and in their company booklet.