Ultrahigh Resolution Titanium Deep Reactive Ion Etching

Reactive ion etching for fabrication of biofunctional titanium nanostructures

One of the major problems with the bone implant surfaces after surgery is the competition of host and bacterial cells to adhere to the implant surfaces. To keep the implants safe against implant-associated infections, the implant surface may be decorated with bactericidal nanostructures. Therefore, fabrication of nanostructures on biomaterials is of growing interest. Here, we systematically studied the effects of different processing parameters of inductively coupled plasma reactive ion etching (ICP RIE) on the Ti nanostructures. The resultant Ti surfaces were characterized by using scanning electron microscopy and contact angle measurements. The specimens etched using different chamber pressures were chosen for measurement of the mechanical properties using nanoindentation. The etched surfaces revealed various morphologies, from flat porous structures to relatively rough surfaces consisting of nanopillars with diameters between 26.4 ± 7.0 nm and 76.0 ± 24.4 nm and lengths between 0.5 ± 0.1 μm and 5.2 ± 0.3 μm. The wettability of the surfaces widely varied in the entire range of hydrophilicity. The structures obtained at higher chamber pressure showed enhanced mechanical properties. The bactericidal behavior of selected surfaces was assessed against Staphylococcus aureus and Escherichia coli bacteria while their cytocompatibility was evaluated with murine preosteoblasts. The findings indicated the potential of such ICP RIE Ti structures to incorporate both bactericidal and osteogenic activity, and pointed out that optimization of the process conditions is essential to maximize these biofunctionalities.

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

Recently, researchers have dedicated efforts toward producing large-area nanostructures using advanced lithography techniques and state-of-the-art etching methods. However, these processes involve challenges such as the diffraction limit and an unintended etching profile. In this work, we demonstrate large-area nanopatterning on a silicon substrate using the microscale metal mask by meticulous optimization of the etching process. Around the vertex of a microscale metal mask, a locally induced electric field is generated by a bias voltage applied on a silicon mold. We utilize this field to change the trajectory of reactive ions and their effect flux, thus providing a controllable bowing effect. The results are analyzed by both numerical simulations and experiments. Based on the field alignment by the metal mask for the etching (FAME) process, we demonstrate the fabrication of 378 nm-size nanostructure patterns which translate to a size reduction of 63% from 1 μm-size mask patterns on a wafer by optimization of the processes. This is much higher than the undercut (∼37%) usually achieved by a typical non-Bosch process under similar etching conditions. The optimized nanostructure is used as a mold for the transfer printing of nanostructure arrays on a flexible substrate to demonstrate that it enables the functionality of FAME-processed nanostructures.