High Aspect Ratio Nanotip Research Articles

A non-lithographic plasma nanoassembly technology for polymeric nanodot and silicon nanopillar fabrication

In this work, we present plasma etching alone as a directed assembly method to both create the nanodot pattern on an etched polymeric (PMMA) film and transfer it to a silicon substrate for the fabrication of silicon nanopillars or cone-like nanostructuring. By using a shield to control sputtering from inside the plasma reactor, the size and shape of the resulting nanodots can be better controlled by varying plasma parameters as the bias power. The effect of the shield on inhibitor deposition on the etched surfaces was investigated by time-of-flight secondary ion mass spectroscopy (ToF-SIMS) measurements. The fabrication of quasi-ordered PMMA nanodots of a diameter of 25 nm and period of 54 nm is demonstrated. Pattern transfer to the silicon substrate using the same plasma reactor was performed in two ways: (a) a mixed fluorine-fluorocarbon-oxygen nanoscale etch plasma process was employed to fabricate silicon nanopillars with a diameter of 25 nm and an aspect ratio of 5.6, which show the same periodicity as the nanodot pattern, and (b) high etch rate cryogenic plasma process was used for pattern transfer. The result is the nanostructuring of Si by high aspect ratio nanotip or nanocone-like features that show excellent antireflective properties.

Sharp Needles: Fabrication of Tungsten Nanotips by AC Electrochemical Etching and Laser Enhanced Etching for Nanoprobing on Interconnects of Advanced Technology Nodes.

ABSTRACTSharper nanotips are required for application in nanoprobing systems due to a shrinking contact size with each new transistor technology node. We describe a two-step etching process to fabricate W nanotips with controllable tip dimensions. The first process is an optimized AC electrochemical etching in KOH to fabricate nanotips with a radius of curvature (ROC) down to 90 nm. This was followed by a secondary nanotip sharpening process by laser irradiation in KOH. High aspect ratio nanotips with ROC close to 20 nm were obtained. Finally we demonstrate the application of the fabricated nanotips for nanoprobing on advanced technology SRAM devices.

Fabrication of zinc nanotip arrays by ion beam sputtering

Zinc nanotip arrays were fabricated on polycrystalline zinc foils using capillaritron ion beam sputtering. The geometry and structure of the nanotip are found to be dependent on the ion species, beam energy, and exposure fluence. After 12keV argon ion beam sputtering, zinc nanotips with end radii less than 5nm and aspect ratios larger than 20 were obtained. Cone-shaped nanostructures with an aspect ratio of 3 and tip radius of 25nm were found after oxygen ion beam sputtering. Energy dispersive x-ray spectroscopy and scanning electron microscopy analysis indicate that the high aspect ratio nanotip formation mechanism after argon ion beam sputtering is due to differential erosion and anisotropic hardness of zinc nanocrystal, while the formation mechanism of cone-shaped nanostructures after oxygen ion beam sputtering is due mainly to the formation of ZnO on the apex, acting as an etch stop. The field emission properties of zinc nanotips are presented.

Three-dimensional microfabrication in bulk silicon using high-energy protons

We report an alternative technique which utilizes fast-proton irradiation prior to electrochemical etching for three-dimensional microfabrication in bulk p-type silicon. The proton-induced damage increases the resistivity of the irradiated regions and acts as an etch stop for porous silicon formation. A raised structure of the scanned area is left behind after removal of the unirradiated regions with potassium hydroxide. By exposing the silicon to different proton energies, the implanted depth and hence structure height can be precisely varied. We demonstrate the versatility of this three-dimensional patterning process to create multilevel free-standing bridges in bulk silicon, as well as submicron pillars and high aspect-ratio nanotips.

EXTREMELY SHARP {111}-BOUND, SINGLE-CRYSTALLINE SILICON NANO TIPS

This paper presents (111) nano tips made using (111) single crystalline silicon. Many research efforts have reported on the fabrication methods of micro and nano tips in silicon. Most of the developed fabrication methods are based on (100) or (110) silicon. However, (111) silicon will give the sharpest {111}-bounded nano tips, and in addition, (111) silicon has the best mechanical properties compared with other types of silicon. In this paper, we use (111) silicon wafers to fabricate two type of nano tip. One type is the sharpest nano tip that can be fabricated by using only {111} silicon planes. The other type is a high aspect ratio nano tip, which is composed of one {111} plane and two vertical passivation planes. In the first case, the tip height is 5 μm and the total cone angle of the tip is 54.7°, which represents the sharpest angle for a nano tip bounded only by {111} planes on silicon. In the second case, the nano tip height is 15 μm, and the aspect ratio is greater than 3:1. The cone angle of the nano tip is only 19.5°. The tip radius is less then 10 nm, which is of the sharpest {111}-bound, single-crystalline-silicon nano tips.