Ultrahigh Resolution Titanium Deep Reactive Ion Etching

Abstract

Titanium (Ti) represents a promising new material for microelectromechanical systems (MEMS) because of its unique properties. Recently, this has been made possible with the advent of processes that enable deep reactive ion etching (DRIE) of high-aspect-ratio (HAR) structures in bulk Ti substrates. However, to date, these processes have been limited to minimum feature sizes (MFS) ≥750 nm. Although this is sufficient for many applications, MFS reduction to the deep submicrometer range opens potential for further device miniaturization and an opportunity for endowing devices with unique functionalities that are derived from precisely defined structures within this length scale regime. Herein, we report results from studies seeking to create means for realizing such opportunities through extension of Ti DRIE to the deep submicrometer scale. The effects of key process parameters on etch performance were investigated, and the understanding gained from these studies formed the development of a new ultrahigh resolution (UHR) Ti DRIE process. Using this process, we demonstrate, for the first time, fabrication of HAR structures in bulk Ti substrates with 150 nm MFS, smooth vertical sidewalls (88°), good etch rate (587 nm/min), and mask selectivity (11.1). This represents a fivefold or greater improvement in MFS relative to our previously reported processes and a 29-fold or greater improvement over more recent processes reported by others. As such, the UHR Ti DRIE process extends the state-of-the-art considerably, and it opens important new opportunities for Ti MEMS, particularly in the implantable medical device realm.

Bactericidal Anisotropic Nanostructures on Titanium Fabricated by Maskless Dry Etching

“…The thinner ridge walls also suggest that as more reactive species became available, the tendency for isotropic etching increased, which led to increased etching of the wall surface. Similar trends have been reported by other researchers ,, and were also observed with nanopillars in this study. While at 30 sccm flow, thick and free-standing pillars were obtained, as the flow rate was increased to 40 sccm, the pillars became relatively thinner.…”

“…At 50 sccm, the pillars became wirelike, much thinner, and with a greater tendency to clump together, which likely results from increased mechanical instability (Figures a and S2b). This reduction in diameter is similar to the increased sidewall etching in the patterned etching of titanium …”

“…This reduction in diameter is similar to the increased sidewall etching in the patterned etching of titanium. 36 Therefore, taken together, the gas flow rate and chamber pressure decide the availability of reactive ions that interact with the substrate, their incoming energy (mean free path), and the duration of their stay in the chamber (residence time) (Figures 2c and 3c). Inside a clean chamber, this leads to similar trends on the morphology and etch rate of nanostructures for both these parameters, whereas opposite trends are observed inside an unclean chamber due to a higher concentration of masking species.…”

Reactive ion etching for fabrication of biofunctional titanium nanostructures

“…the most common areas of applications for such profiles) 50 . Furthermore, the resulting nanostructures of the Cl 2 gas have vertical sidewalls and smoother surfaces 51 . We therefore chose Cl 2 /Ar chemistry and studied the effects of gas flows on the Ti structures.…”

Large-Area Nanopatterning Based on Field Alignment by the Microscale Metal Mask for the Etching Process

“…Most wet etching methods produce isotropic shapes on the target materials. However, when we used potassium hydroxide (KOH), ethylenediamine pyrocatechol, tetramethylammonium hydroxide, or metal-assisted chemical etching, anisotropic shapes could be formed. − For anisotropic etching, a dry etching process is usually preferred. − It avoids the use of hazardous and toxic solutions that may be required in wet etching. Dry etching can also be used to change the surface properties such as the hydrophilicity and surface profile (shape and roughness) by controlling the pressure, type of etching gas, and voltage and power of the bias in the plasma electrode. − However, undercutting, profile tilting, notching, bowing effects, loading effects, and charging effects during the surface treatment or surface etching must be overcome to produce a purposed nanostructure while maintaining their anisotropic shape and purposed surface profile. − …”