Single-electron devices operating at room temperature require sub-5 nm quantum dots having tunnel junctions of comparable dimensions. Further development in nanoelectronics depends on the capability to generate mesoscopic structures and interfacing these with complementary metal–oxide–semiconductor devices in a single system. The authors employ a combination of two novel methods of fabricating room temperature silicon single-electron transistors (SETs), Fowler–Nordheim scanning probe lithography (F-N SPL) with active cantilevers and cryogenic reactive ion etching followed by pattern-dependent oxidation. The F-N SPL employs a low energy electron exposure of 5–10 nm thick high-resolution molecular resist (Calixarene) resulting in single nanodigit lithographic performance [Rangelow et al., Proc. SPIE 7637, 76370V (2010)]. The followed step of pattern transfer into silicon becomes very challenging because of the extremely low resist thickness, which limits the etching depth. The authors developed a computer simulation code to simulate the reactive ion etching at cryogenic temperatures (−120 °C). In this article, the authors present the alliance of all these technologies used for the manufacturing of SETs capable to operate at room temperatures.

The next generation of hard disk drive technology for data storage densities beyond 5 Tb/in will require single-bit patterning of features with sub-10 nm dimensions by nanoimprint lithography. To address this challenge master templates are fabricated using pattern multiplication with atomic layer deposition (ALD). Sub-10 nm lithography requires a solid understanding of materials and their interactions. In this work we study two important oxide materials, silicon dioxide and titanium dioxide, as the pattern spacer and look at their interactions with carbon, chromium and silicon dioxide. We found that thermal titanium dioxide ALD allows for the conformal deposition of a spacer layer without damaging the carbon mandrel and eliminates the surface modification due to the reactivity of the metal-organic precursor. Finally, using self-assembled block copolymer lithography and thermal titanium dioxide spacer fabrication, we demonstrate pattern doubling with 7.5 nm half-pitch spacer features.

Patterned chromium and its compounds are crucial materials for nanoscale patterning and chromium based devices. Here we investigate how temperature can be used to control chromium etching using chlorine/oxygen gas mixtures. Oxygen/chlorine ratios between 0% and 100% and temperatures between -100 °C and +40 °C are studied. Spectroscopic ellipsometry is used to precisely measure rates, chlorination, and the thickness dependence of n and k. Working in the extremes of oxygen content (very high or very low) and lower temperatures, we find rates can be controlled to nanometers per minute. Activation energies are measured and show that etch mechanisms are both temperature and oxygen level dependent. Furthermore, we find that etching temperature can manipulate the surface chemistry. One surprising consequence is that at low oxygen levels, Etching rates increase with decreasing temperature. Preliminary feature-profile studies show the extremes of temperature and oxygen provide advantages over commonly used room temperature processing conditions. One example is with higher ion energies at -100 °C, where etching products deposit.

Chromium and its oxides are valuable as functional materials and plasma-etching hard masks in micro- and nanofabrication. While the continuous decrease in feature sizes opens new opportunities for applications of patterned chromium, the demands placed on the patterning process require a new level of mechanistic understanding. In this work, we investigate plasma etching with chlorine/oxygen chemistry using temperature and oxygen concentration as a means to controllably pattern chromium at the nanometer level. Building on our previous studies on blanket film chromium etching, we look here at patterned trenches 15–100 nm wide in 20 and 10 nm thick chromium films. We vary oxygen concentrations from 1.5% to 81% at substrate temperatures of +20 and −50 °C, respectively. Feature and trench profiles are evaluated from high-resolution cross-sectional SEM images. The ternary chromium etch product shows very different profiles as oxygen, temperature, and feature size are varied. We find the highest anisotropy at −50 °C and 50% oxygen concentration. Etch results suggest that the redeposition of nonvolatile intermediate reaction compounds enhances anisotropy at low temperature, whereas re-emission of reactive species causes undercut at the higher etching temperature.

A new composite sample preparation method for high contrast cross-sectional SEM imaging.

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