Diamond nanopatterns fabricated by room-temperature nanoimprinting technology with diamond molds using polysiloxane

Fabrication of diamond nanopatterns in room-temperature (RT) nanoimprint lithography (NIL) with chemical vapor deposited (CVD) diamond molds using polysiloxane as RT-imprint resist material was investigated. The diamond molds of a convex lattice with 1 μm line-width and 5 μm pitch, and a cylinder dot with 200 nm diameter and 1 μm pitch which has a height of 1 μm using RT-NIL process were fabricated with Bi₄Ti₃O₁₂ octylate (oxide) mask in electron beam lithography technology. The maximum radio frequency (RF) oxygen plasma-etching selectivity (diamond/polysiloxane) of 19 was obtained under the conditions of RF power of 100 W, oxygen gas flow rate of 10 sccm and background gas pressure of 30 Pa. It was found that the optimum imprinting pressure and its depth obtained after the press duration of 10 min were 0.8 MPa and about 0.5 μm, respectively. The resulting diamond nanopatterns of a concave lattice with 1 μm line-width and 5 μm pitch, and a concave cylinder dot with 200 nm diameter and 1 μm pitch which have a height of 1 μm after RF oxygen plasma-etching (100W, 10 sccm, 30 Pa, 40 min) were fabricated with diamond mold RT-NIL using polysiloxane.     

Effect of nanostructuration on the magnetic properties of CoPt films

We have nanostructured CoPt alloy layers prepared by molecular beam epitaxy, deposited directly on a MgO(0 0 1) substrate. The initial layer had the L1₀ tetragonal structure, ordered in the growth direction with an easy magnetization direction perpendicular to the layer plane. We realized by electron beam lithography and ion etching a network of dots spaced of 1 μm and lateral sizes of 1 μm, 500 nm and 300 nm, respectively. Whereas the continuous layers had a labyrinthine magnetic structure after perpendicular demagnetization, all the dots are monodomains with randomly distributed up and down magnetization. This is due to the fact that during the demagnetization the magnetic field is no longer sufficient to reach the nucleation field. Indeed, a single-dot hysteresis loop measured by field-dependent magnetic force microscopy shows a weak nucleation field distribution. However, the 3D micromagnetic calculations show a multidomain state for these dot sizes. This magnetic structure is similar to that observed on patterned samples, heated a short time (60 s) above the Curie temperature.     

Wet and dry etching of La0.67(Sr,Ca)0.33 MnO3 films on Si

We report etching processes of epitaxial La_0.67(Sr,Ca)_0.33 MnO₃ (LSCMO) colossal magnetoresistive (CMR) films grown on Bi₄Ti₃O₁₂/CeO₂/YSZ oxide-buffered Si using buffered HF (BHF), potassium hydroxide (KOH) and Ar ion beam etching (IBE) methods. LSCMO films demonstrate high resistivity against the KOH etchant whereas 22 nm/min etching rate was obtained in the BHF with high selectivity over photoresist and Si. Compared to 24 nm/min for Si, Ar IBE yields 16 nm/min etching rate for the LSCMO film and the oxide-buffer layers.     

Fabrication of sub-25 nm diameter pillar nanoimprint molds with smooth sidewalls using self-perfection by liquefaction and reactive ion etching

Self-perfection by liquefaction (SPEL) was used to fabricate nanoimprint molds with an array of sub-25?nm diameter pillars (200?nm period), resulting in nearly perfect cylindrical shape and smooth sidewalls. SPEL turned an array of irregularly shaped Cr polygons into an array of nearly perfect circular dots with small diameter. The Cr dot arrays were then transferred to SiO(2) or Si pillar arrays by means of reactive ion etching to produce imprint molds. High-fidelity nanoimprint lithography using the pillar molds was also demonstrated.     

EBL- and AFM-based techniques for nanowires fabrication on Si/SiGe

Two approaches for sub-100 nm patterning are applied to Si/SiGe samples.The first one combines electron beam lithography (EBL) and anisotropic wet etching to fabricate wires with triangular section whose top width is narrower than the beam size. Widths as small as 20 nm on silicon and 60 nm on Si/SiGe heterostructures are obtained.The second lithographic approach is based on the local anodization of an aluminum film induced by an atomic force scanning probe. Using atomic force microscopy (AFM) anodization and selective wet etching, aluminum and aluminum oxide nanostructures are obtained and used as masks for reactive ion etching (RIE). Sub-100 nm wide wires are fabricated on Si/SiGe substrates.     

Kinetics of cuprous oxide etching with β-diketones in Supercritical CO2

Cuprous oxide films (Cu₂O) supported on Cu or on SiO₂ were etched using solutions of β-diketones including 1,1,1,5,5,5-hexafluoroacetylacetone, 2,2,6,6-tetramethyl-3,5-heptanedione and 2,2,7-trimethyl-3,5-octanedione (TMOD) in supercritical carbon dioxide at temperatures between 80 and 150 °C and pressures between 20 and 27.5 MPa. The films and etched substrates were analyzed by X-ray photoelectron spectroscopy depth profiling, field emission scanning electron microscopy and spectroscopic ellipsometry. Each of the etching agents was effective. Etching kinetics using TMOD were measured at 100, 125 and 150 °C. At 150 °C the etch rate was 1.5 nm/min. Based on the activation energy obtained from the studies (66 kJ/mol), etching rates of greater than 10.0 nm/min can be obtained at 200 °C.     

Photoluminescence in the 1.55 μm wavelength range in the InGaAs/GaAs system with quantum dots and wells

It is demonstrated that longwave room-temperature photoluminescence (up to 1.65 μm) can be obtained using InGaAs/GaAs heterostructures of two types grown by low-temperature molecular beam epitaxy: (i) with InAs quantum dots formed at a low growth velocity and (ii) with an In_0.5Ga_0.5As quantum well grown in excess of the group III elements.     

Growth of β-FeSi2 thin films on β-FeSi2 (110) substrates by molecular beam epitaxy

We have investigated the preparation of β-FeSi₂ substrate and growth condition of β-FeSi₂ thin film on β-FeSi₂ (110) substrate by molecular beam epitaxy. The surface of the substrate was prepared by a wet-etching using HF(50%):HNO₃(60%):H₂O = 1:1:5 solution at 25 °C. It is clear that the optimal etching period to obtain a flat surface was 3 min. The β-FeSi₂ thin film with streak RHEED pattern was obtained at Si/Fe flux ratio of 2.9. Average surface roughness (Ra) of the β-FeSi₂ film was about 0.5 nm in 5 × 5 μm² area.     

Low energy O2 and N2O ion beam modification of polyimide for improving adhesive strength of Cu/PI in roll-to-roll process

To enhance the weak mechanical durability of directly deposited copper layers on polyimide (PI) film due to their poor adhesive strength, a continuous roll-to-roll process involving surface modification using a reactive ion beam irradiation and in-situ deposition process is studied. The polyimide film is modified by an ion source with a linear stationary plasma thruster (LSPT) in the vacuum roll-to-roll process. An O₂ ion beam, with beam energy of 214 eV and beam current density of 0.78 mA/cm², and N₂O ion beam, with 220 eV and 0.69 mA/cm², irradiate PI film in winding speed of 0.5 m/min. The surface energy increases from 38 mN/m for the pristine PI film to 80 mN/m after beam irradiation at an ion fluence of 3.5 × 10¹⁶ ions/s. After beam irradiation, a 10 nm thick tie layer and 200 nm thick copper layer are successively deposited by in-situ DC magnetron web coating. The peel strength of the copper layer on the PI film is enhanced from 0.4 kgf/cm without ion beam treatment to 0.71 kgf/cm after O₂ beam treatment and to 0.75 kgf/cm after N₂O beam treatment. This enhancement is closely related to the increase in the polar force originating from the formation of hydrophilic CO (carbonyl) groups on the modified PI surface.     

Seeded growth of ZnO nanorods from NaOH solutions

Perpendicularly aligned arrays of corrugated ZnO nanorods were grown onto gold patterned LiTaO₃ substrates, coated with a sputtered ZnO seed layer. During the growth process, these substrates were held submerged in an aqueous solution comprising a 1:40 mol ratio mix of zinc nitrate hexahydrate to sodium hydroxide. The substrates were placed in a custom apparatus residing in an autoclavable storage bottle. Scanning electron micrographs, which were taken at different deposition intervals, suggest that the growth mechanism of ZnO nanorods initiates with the etching of the ZnO sputtered seed layer into hexagonal bases (> 500 nm across), from where multiple protrusions (40 nm-100 nm in width) grow atop these hexagonal bases. Such nanoprotrusions later coalesce into larger nanorods. Uniformly distributed high density corrugated nanorods, with proximal spacing between adjacent nanorods of approximately 20 nm-50 nm, were observed over the entire surface.     

Dry etching of TaN thin film using CH4/Ar inductively coupled plasma

In this research, we investigated the TaN etch rate and selectivity with under layer (HfO₂) and mask material (SiO₂) in inductively coupled CH₄/Ar plasma. As the CH₄ content increased from 0% to 80% in CH₄/Ar plasma, the TaN etch rate was increased from 11.9 to 22.8 nm/min. From optical emission spectroscopy (OES), the intensities for CH [431 nm] and H [434 nm] were increased with the increasing CH₄ content from 0% to 100% in CH₄/Ar plasma. The results of x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) showed no accumulation of etch by-products from the etched surface of TaN thin film. As a result of OES, AES and XPS analysis, we observed the etch by-products from the surfaces, such as Ta-N-CH and N-CH bonds. Based on the experimental results, the TaN etch was dominated by the chemical etching with the assistance of Ar sputtering in reactive ion etching mechanism.     

Sb2S3:C/CdS p-n junction by laser irradiation

In this paper, we report laser irradiated carbon doping of Sb₂S₃ thin films and formation of a p-n junction photovoltaic structure using these films. A very thin carbon layer was evaporated on to chemical bath deposited Sb₂S₃ thin films of approximately 0.5 μm in thickness. Sb₂S₃ thin films were prepared from a solution containing SbCl₃ and Na₂S₂O₃ at 27 °C for 5 h and the films obtained were highly resistive. These C/Sb₂S₃ thin films were irradiated by an expanded laser beam of diameter approximately 0.5 cm (5 W power, 532 nm Verdi laser), for 2 min at ambient atmosphere. Morphology and composition of these films were analyzed. These films showed p-type conductivity due to carbon diffusion (Sb₂ S₃:C) by the thermal energy generated by the absorption of laser radiation. In addition, these thin films were incorporated in a photovoltaic structure Ag/Sb₂S₃:C/CdS/ITO/Glass. For this, CdS thin film of 50 nm in thickness was deposited on a commercially available ITO coated glass substrate from a chemical bath containing CdCl₂, sodium citrate, NH₄OH and thiourea at 70 °C. On the CdS film, Sb₂S₃/C layers were deposited. This multilayer structure was subjected to the laser irradiation, C/Sb₂S₃ side facing the beam. The p-n junction formed by p-Sb₂S₃:C and n-type CdS showed V_oc = 500 mV and J_sc = 0.5 mA/cm² under illumination by a tungsten halogen lamp. This work opens up a new method to produce solar cell structures by laser assisted material processing.     

Dry etching of TaN thin film using CH4/Ar inductively coupled plasma

In this research, we investigated the TaN etch rate and selectivity with under layer (HfO₂) and mask material (SiO₂) in inductively coupled CH₄/Ar plasma. As the CH₄ content increased from 0% to 80% in CH₄/Ar plasma, the TaN etch rate was increased from 11.9 to 22.8 nm/min. From optical emission spectroscopy (OES), the intensities for CH [431 nm] and H [434 nm] were increased with the increasing CH₄ content from 0% to 100% in CH₄/Ar plasma. The results of x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) showed no accumulation of etch by-products from the etched surface of TaN thin film. As a result of OES, AES and XPS analysis, we observed the etch by-products from the surfaces, such as Ta–N–CH and N–CH bonds. Based on the experimental results, the TaN etch was dominated by the chemical etching with the assistance of Ar sputtering in reactive ion etching mechanism.     

Oxygen ion beam assisted etching of single crystal diamond chips using reactive oxygen gas

The etching characteristics of single crystal diamond chips processed using an oxygen ion beam with reactive oxygen gas flux were investigated. The specific etching rate increased linearly with increasing ion energy in the range of 250 to 1000 eV. The specific etching rates processed in a 1000-eV oxygen ion beam with oxygen gas was approximately twice that processed only in a 1000-eV oxygen ion beam. The angular dependences of only a 500-eV oxygen ion beam (no assist), and a 500-eV argon ion beam with oxygen gas were quite different from that of the other conditions. The specific etching rates were almost constant as a function of ion incident angle in the range of 0 to 50°. Those for the other conditions first increased with increasing ion incident angle, and reached a maximum rate at an ion incident angle of 40° or 50°, and then decreased gradually with further increase in ion incident angle. The specific etching rates using an argon ion beam with oxygen gas first increased with increasing gas partial pressure and then reached a saturation level at a gas partial pressure above 0.015 Pa, whereas those for the other conditions increased linearly with increasing gas partial pressure in the range of 0 to 0.06 Pa. The specific etching rates using an oxygen ion beam increased linearly with increasing substrate temperature in the range of 100 to 500 °C. The specific surface roughness was almost constant as a function of the substrate temperature, in the range of 100 to 500 °C. The specific surface roughness after assisted etching using oxygen or hydrogen gases was approximately half that processed in only oxygen or argon ion beams (no assist). © 2001 Kluwer Academic Publishers     

Fibronectin modulates the morphology of osteoblast-like cells (MG-63) on nano-grooved substrates

Cell interactions with biomaterials are affected by surface topographic and chemical cues. Although it is well-known that nanometrical grooves/ridges structure modulates cellular spreading, elongation, and alignment, the combinational influence of surface topographic and chemical cues is not well studied. In this study, nano-textured silicon substrata with parallel ridges of 90, 250, or 500 nm wide, separated by grooves with equal width, were fabricated by electron beam lithography and dry etching techniques. Osteoblast-like cells, MG-63, were cultured on the patterned substrata with or without pre-adsorption of fibronectin. The cell morphology was imaged by scanning electron microscopy, and analyzed by image software. We found that FN coating initially modulated cellular spreading, length, and orientation on all types of grooved surfaces. However, after 24 h of culture, the cell morphology was not affected by FN coating on the 250-nm and 500-nm surfaces, while FN decreased cell alignment on the 90-nm surfaces. Our results suggest that surface chemical cues influence the initial cell-substratum contact, while the long-term cellular morphology is dictated by surface topographic cues.     

Nano patterning of cone dots and nano constrictions of negative e-beam resist for single electron transistor fabrication

We present an optimization of nano dot of negative tone e-beam resist which is a very important step in single electron transistor fabrication process. The optimum design of dot and nano constriction plays a significant role in determining optimum etching resolution and single electron transistor performance. In this research, we have optimized nano dot and nano constriction dimensions of resist by controlling some parameters, such as e-beam dose, spin speed, pre-bake time and image development time. However, a nano constriction design variety of 120–200 nm in width was carried out to reach the optimum design. In this paper, the fabrication process of cone nano dots using e-beam lithography with considering proximity effect is reported. As nano constriction design decreased, cone nano dot changed to pyramid nano dot and the compression effect on the dot also significantly increased as well.     

Influence of twice-deposited etching mask layers on verticality of nanostructures

The effects of single and double masks on focused ion beam (FIB) direct patterning and chlorine-based inductively coupled plasma reactive ion etching (ICP-RIE) were studied in order to determine the influence of twice-deposited mask layers on the verticality of the side wall of silicon-based nanostructures. When a single mask was used as the etching mask, an inclined plane with a large side angle on the top area was formed. When a double mask was used, the first mask layer of chromium (Cr) was deposited by RF (radio frequency) magnetron sputtering and then directly patterned by FIB. Then, the secondary mask layer of SiO₂, which was deposited to protect the side wall in order to retard etching and prevent the formation of an inclined plane, was deposited by RF magnetron sputtering. However, the SiO₂ on the top and bottom of the nanostructure was removed through anisotropic etching by ICP-RIE, and only SiO₂ on the side wall was retained. The experimental results show that the SiO₂ layer left on the side wall as an etching barrier can effectively maintain the verticality of the nanostructure. The measurement results show that the verticality and aspect ratio of the nanostructure are 90.8° and 5.08 (depth: 310 nm, width: 61 nm), respectively.     

Etch characteristics of TiN/Al2O3 thin film by using a Cl2/Ar adaptive coupled plasma

In this study, we carried out an investigation in the etching characteristics of TiN thin films in a C1₂/Ar adaptive coupled plasma. The maximum etch rate of the TiN thin films was 768 nm/min at a gas mixing ratio of C1₂ (75%)/Ar (25%). At the same time, the etch rate was measured as functions of the various etching parameters. The X-ray photoelectron spectroscopy analysis showed the efficient destruction of the oxide bonds by the ion bombardment as well as the accumulation of low volatile reaction products on the etched surface. Field emission Auger electron spectroscopy analysis was used to examine the efficiency of the ion-stimulated desorption of the reaction products.     

Etch characteristics of TiN/Al2O3 thin film by using a Cl2/Ar adaptive coupled plasma

In this study, we carried out an investigation in the etching characteristics of TiN thin films in a C1₂/Ar adaptive coupled plasma. The maximum etch rate of the TiN thin films was 768 nm/min at a gas mixing ratio of C1₂ (75%)/Ar (25%). At the same time, the etch rate was measured as functions of the various etching parameters. The X-ray photoelectron spectroscopy analysis showed the efficient destruction of the oxide bonds by the ion bombardment as well as the accumulation of low volatile reaction products on the etched surface. Field emission Auger electron spectroscopy analysis was used to examine the efficiency of the ion-stimulated desorption of the reaction products.     

Dry etch properties of IZO thin films in a CF4/Ar adaptively coupled plasma system

In this study, we investigated to the etch characteristics of indium zinc oxide (IZO) thin films in a CF₄/Ar plasma, namely, etch rate and selectivity toward SiO₂. A maximum etch rate of 76.6 nm/min was obtained for IZO thin films at a gas mixture ratio of CF₄/Ar (25:75%). In addition, etch rates were measured as a function of etching parameters, including adaptively coupled plasma chamber pressure. X-ray photoelectron spectroscopy analysis showed efficient destruction of the oxide bonds by ion bombardment, as well as accumulation of low volatile reaction products on the surface of the etched IZO thin films. Field emission Auger electron spectroscopy analysis was used to examine the efficiency of ion-stimulated desorption of the reaction products.