Etching characteristics of LiNbO3 crystal by fluorine gas plasma reactive ion etching

The etching characteristics of a LiNbO₃ single crystal have been investigated using plasma reactive ion etching (RIE) with a mixture of CF₄/Ar/H₂. The etching rate of LiNbO₃ with the mixture of CF₄/Ar/H₂ gases was evaluated. The etching surface was evaluated by atomic force microscopy, X-ray diffraction and X-ray photoelectron spectroscopy methods. The rate-determining process of RIE is the supply of F radicals in RIE. The surface morphology of the etched LiNbO₃ changed with the increase in the H₂ gas flow ratio. The surface profile became flat, on optimizing the etching conditions, similar to the surface of non-etched LiNbO₃. The X-ray diffraction peakfor etched LiNbO₃ using the mixture of CF₄ and Ar gases did not appear, because a non-crystalline layer was formed. It was found that the crystallinity of the surface is dependent on both, the flow rate of H₂ gas and the etching time. F atoms exist in the contamination layer of the sample etched, using the mixture of CF₄, Ar and H₂ gases. Optimum etching conditions, considering both the surface flatness and the crystallinity, were determined.     

Etching characteristics of LiNbO3 crystal by fluorine gas plasma reactive ion etching

The etching characteristics of a LiNbO₃ single crystal have been investigated using plasma reactive ion etching (RIE) with a mixture of CF₄/Ar/H₂. The etching rate of LiNbO₃ with the mixture of CF₄/Ar/H₂ gases was evaluated. The etching surface was evaluated by atomic force microscopy, X-ray diffraction and X-ray photoelectron spectroscopy methods. The rate-determining process of RIE is the supply of F radicals in RIE. The surface morphology of the etched LiNbO₃ changed with the increase in the H₂ gas flow ratio. The surface profile became flat, on optimizing the etching conditions, similar to the surface of non-etched LiNbO₃. The X-ray diffraction peak for etched LiNbO₃ using the mixture of CF₄ and Ar gases did not appear, because a non-crystalline layer was formed. It was found that the crystallinity of the surface is dependent on both, the flow rate of H₂ gas and the etching time. F atoms exist in the contamination layer of the sample etched, using the mixture of CF₄, Ar and H₂ gases. Optimum etching conditions, considering both the surface flatness and the crystallinity, were determined.     

Inductively coupled plasma reactive ion etching of ZnO films in HBr/Ar plasma

The etching characteristics of ZnO thin films were examined in an HBr/Ar gas mix using an inductively coupled plasma reactive ion etching system. The etch rate and etch profile were systematically investigated as a function of gas concentration. In addition, the effects of etch parameters such as coil rf power, dc-bias voltage, and gas pressure were studied. As the HBr concentration increased, the etch rate of the ZnO films gradually decreased while the etch profile was improved. Surface analyses including X-ray photoelectron spectroscopy and atomic force microscopy were employed to elucidate the etch mechanism of ZnO in an HBr/Ar chemistry.     

Effect of inductively-coupled plasma assist on the crystal orientation of magnesium oxide thin films produced by reactive sputtering

High-performance reactive sputter-deposition of magnesium oxide (MgO) thin films is investigated. In this research, planar magnetron (PM) sputtering of Mg target in argon/oxygen mixture is assisted by an inductively coupled plasma (ICP) that is located between the target and the substrate and is driven by an internal RF coil antenna at 13.56 MHz. The changes in deposition rates and X-ray diffraction patterns due to the independent power control of PM and ICP are investigated. As a result, we found that deposition rate of MgO films was predominantly controlled by the PM discharge power and that the crystallinity of deposited MgO films was controlled by the ICP-RF power.     

Refractive sapphire microlenses fabricated by chlorine-based inductively coupled plasma etching

We have fabricated refractive sapphire microlenses and characterized their properties for what we believe to be the first time. We use thermally reflown photoresist lenslet patterns as a mask for chlorine-based dry etch of sapphire. Pattern transfer to the mechanically hard and chemically inert sapphire substrate is made possible by an inductively coupled plasma etch system that supplies a high-density plasma gas. Processed sapphire microlenses exhibit properties close to the ideal and operate nearly in the diffraction limit.     

Argon ion etching in a reactive gas

It is shown that the sputtering yield of various materials submitted to argon ion (1 ke V) bombardment decreases strongly with increase of oxygen pressure in the atmosphere of the sputtering chamber. The sputtering yields are plotted against the “poisoning ratio” (the poisoning ratio is defined as the ratio of the rate of arrival of oxygen molecules at the target surface to that of the rate of removal of sputtered atoms). On the curves representing the sputtering yield versus the poisoning ratio, two particular values are pointed out for each material. Between these two values the sputtering yield decreases as the poisoning ratio increases, out of these values the sputtering yield is quite independent of the poisoning ratio. In the region of high poisoning ratio value, the spread of the sputtering yield for investigated materials is wider than in the region of low poisoning ratio value. Thus, we observed, in terms of etching rate, a ratio of 7 between silica and chromium and a ratio of 10 between silica and vanadium when the oxygen pressure introduced in the target chamber is 10⁻⁴ Torr. These results are used in order to obtain deep grooves in silica, when such metals are used as masking materials. New data on the sputtering yield of various materials is provided.     

Evolution of etch profile in etching of CoFeB thin films using high density plasma reactive ion etching

Inductively coupled plasma reactive ion etching of CoFeB magnetic thin films patterned with Ti hard mask was studied in a CH₃OH/Ar gas mix. As the CH₃OH concentration increased, the etch rates of CoFeB thin films and Ti hard mask decreased but the etch profiles improved with high degree of anisotropy. The effects of coil rf power, dc-bias voltage and gas pressure on the etch characteristics were investigated. The etch rate increased with increasing coil rf power, dc-bias voltage and decreasing gas pressure. The degree of anisotropy in the etch profile of CoFeB films improved with increasing coil rf power and dc-bias voltage. X-ray photoelectron spectroscopy revealed that the chemical compounds containing Co and Fe components were formed during the etching. However, it was expected that the formation of these compounds could not increase the etch rates of the films due to low volatile compounds despite the improvement in etch profile.     

Irregular shaping of polystyrene nanosphere array by plasma etching

The morphology of nanospheres is crucial for designing the nanofabrication in the nanosphere lithography. Here, by plasma etching, the controllable tailoring of the nanosphere is realized and its morphology dependence on the initial shape, microscopic roughness, and the etching conditions is investigated quantitatively. The results show that the shape evolution strongly depends on the etching gas, power, and process duration. Particularly, the aspect ratio (diameter/height) significantly increases with violent etching, turning the spherical shape into tiny ellipsoidal nanoparticles. The findings are practical to the protocol of non-uniform etching of nanoobjects and provide the useful design tool for the device fabrication at nanoscale.     

Structurally perfect silicon layers produced on sapphire by oxygen ion implantation

We demonstrate that the structural perfection of silicon layers on sapphire can be improved through high-temperature solid-state recrystallization after preamorphization of the most imperfect silicon layer near the silicon/sapphire interface by high-energy oxygen ions, followed by high-temperature recrystallization in an inert atmosphere.     

Etch characteristics of FePt magnetic thin films using inductively coupled plasma reactive ion etching

Etch characteristics of L10 FePt thin films masked with TiN films were investigated using an inductively coupled plasma (ICP) reactive ion etching in a CH₃OH/Ar plasma. As the CH₃OH gas was added to Ar, the etch rates of FePt thin films and TiN hard mask gradually decreased, and the etch profile of FePt films improved with high degree of anisotropy. With increasing ICP rf power and dc-bias voltage to substrate and decreasing gas pressure, the etch rate increased and the etch profile becomes vertical without any redepositions or etch residues. Based on the etch characteristics and surface analysis of the films by X-ray photoelectron spectroscopy, it can be concluded that the etch mechanism of FePt thin films in a CH₃OH/Ar gas does not follow the reactive ion etch mechanism but the chemically assisted sputter etching mechanism, due to the chemical reaction of FePt film with CH₃OH gas.     

Submicron-patterning of bulk titanium by nanoimprint lithography and reactive ion etching

Nanopatterns on titanium may enhance endosseous implant biofunctionality. To enable biological studies to prove this hypothesis, we developed a scalable method of fabricating nanogrooved titanium substrates. We defined nanogrooves by nanoimprint lithography (NIL) and a subsequent pattern transfer to the surface of ASTM grade 2 bulk titanium applying a soft-mask for chlorine-based reactive ion etching (RIE). With respect to direct write lithographic techniques the method introduced here is fast and capable of delivering uniformly patterned areas of at least 4 cm(2). A dedicated silicon nanostamp process has been designed to generate the required thickness of the soft-mask for the NIL-RIE pattern transfer. Stamps with pitch sizes from 1000 nm down to 300 nm were fabricated using laser interference lithography (LIL) and deep cryogenic silicon RIE. Although silicon nanomachining was proven to produce smaller pitch sizes of 200 nm and 150 nm respectively, successful pattern transfer to titanium was only possible down to a pitch of 300 nm. Hence, the smallest nanogrooves have a width of 140 nm. An x-ray photoelectron spectroscopy study showed that only very few contaminations arise from the fabrication process and a cytotoxicity assay on the nanopatterned surfaces confirmed that the obtained nanogrooved titanium specimens are suitable for in vivo studies in implantology research.     

反应离子刻蚀工艺仿真模型的研究

以ＳＦ６／Ｎ２混合气体对Ｓｉ反应离子刻蚀工艺研究为例提出干法刻蚀计算机工艺模拟的方法：在分段拟合优化工艺条件下采用人工神经网络该当建立干法刻蚀仿真模型,可以预测绘定射频功率、总气流量下刻蚀速率和纵横比,并且以仿真实验数据训练模型学习,模型具有通用性,与设备无关。     

Deep reactive ion etching and focused ion beam combination for nanotip fabrication

We have studied the fabrication of high-aspect ratio silicon tips by a combination of deep reactive ion etching and focused ion beam. The reactive ion etching is used to obtain so-called “rocket tips” which can be fabricated with a high aspect ratio. The rocket tips are further processed by using a focused ion beam to obtain nanotips at their apex. Typical results obtained are nanotips with a basis radius of 200 nm and a height of 2.5 μm, with an apex radius of 5 nm, located on top of a 3 μm wide and 9 μm high silicon column. The process would allow however obtaining column heights of several tens of microns.     

The formation of volume elements for microelectromechanical systems in polyimide by method of reactive ion beam etching

The main problem related to the creation of microelectromechanical systems—the formation of an anisotropic profile with vertical side walls and clean flat bottom in a thick resist film—is experimentally solved by optimizing the parameters of the reactive ion beam etching process for polyimide (PI) layers with a thicknesses up to 50 μm. The optimized technique was used to form the volume parts of a microelectromotor structure by etching a PI film with an oxygen ion beam (beam current density j=0.5 mA/cm²; ion extraction energy U=800 V).     

HfO2 etching mechanism in inductively-coupled Cl2/Ar plasma

Etching characteristics and the mechanism of HfO₂ thin films in Cl₂/Ar inductively-coupled plasma were investigated. The etch rate of HfO₂ was measured as a function of the Cl₂/Ar mixing ratio in the range of 0 to 100% Ar at a fixed gas pressure (6 mTorr), input power (700 W), and bias power (300 W). We found that an increase in the Ar mixing ratio resulted in a monotonic decrease in the HfO₂ etch rate in the range of 10.3 to 0.7 nm/min while the etch rate of the photoresist increased from 152.1 to 375.0 nm/min for 0 to 100% Ar. To examine the etching mechanism of HfO₂ films, we combined plasma diagnostics using Langmuir probes and quadrupole mass spectrometry with global (zero-dimensional) plasma modeling. We found that the HfO₂ etching process was not controlled by ion-surface interaction kinetics and formally corresponds to the reaction rate-limited etch regime.     

Growth control of carbon nanotubes by plasma-enhanced chemical vapor deposition and reactive ion etching

A novel process for growth of carbon nanotubes using plasma processes is reported. This process consists of formation of nanotips on substrate and growth of carbon nanotubes on it. The formation of the nanotips, which were formed under an intention to control formation of catalyst nanoparticles, was carried out on substrates by reactive ion etching. After the nanotips formation, the carbon nanotubes were grown on the substrate by plasma-enhanced chemical vapor deposition. Our results showed that the introduction of the nanotips on surface gave lower density and smaller diameter growth of carbon nanotubes than those without the structure.     

Influence of incident ion beam angle on dry etching of silica sub-micron particles deposited on Si substrates

Large surface area nanopatterning using colloidal lithography (CL) processed by dry-etching was investigated by comparing the effect of the etching angle on the subsequent nanostructured sample. The particles, produced from an alkoxide precursor by sol-gel process, were spherical with a size about 300 nm. They were self-assembled in closed-packed 2D crystal monolayers by means of the Langmuir-Blodgett (LB) technique, which controls the surface compactness of the colloidal crystals as well as the number of the particle layers deposited on the substrate. Afterwards, the structure was transferred on silicon wafers by CL: further nanostructuring of monolayer films was made by etching with Ar⁺ ion beam at 550 eV, 7 · 10^− 2 Pa and room temperature over areas of about 4 cm² of the particle film. The incident beam angle was fixed at 0° and 45° with respect to the normal of the substrate in order to change the morphology of the etched 2D crystal. The shape of the sub-micron particles was altered and the particle size was reduced but the original close-packed structure was conserved. The etching process affected both the particles and the interstitial uncovered substrate. The substrate etching was more pronounced for long time and high etching angle: this resulted from a higher physical sputtering yield at higher angle. Moreover the oblique incidence of ion beam introduced anisotropy to the sample. The particle shadowing effect accentuated the nanostructuring of the substrate at 45°.     

Copper nanoparticles synthesized in sapphire by ion implantation

Sapphire-based composite layers implanted with 40-keV Cu⁺ ions to a total dose of 1.0×10¹⁷ cm⁻² at an ion beam current density varied from 2.5 to 10 μA/cm² were studied using Rutherford backscattering and optical reflectance methods. The appearance of optical plasma resonance lines in the reflectance spectra indicates that ion implantation allows copper nanoparticles to be synthesized in the subsurface region of the dielectric crystal studied.     

Voltage-gated ion transport through semiconducting conical nanopores formed by metal nanoparticle-assisted plasma etching

Nanopores with conical geometries have been found to rectify ionic current in electrolytes. While nanopores in semiconducting membranes are known to modulate ionic transport through gated modification of pore surface charge, the fabrication of conical nanopores in silicon (Si) has proven challenging. Here, we report the discovery that gold (Au) nanoparticle (NP)-assisted plasma etching results in the formation of conical etch profiles in Si. These conical profiles result due to enhanced Si etch rates in the vicinity of the Au NPs. We show that this process provides a convenient and versatile means to fabricate conical nanopores in Si membranes and crystals with variable pore-diameters and cone-angles. We investigated ionic transport through these pores and observed that rectification ratios could be enhanced by a factor of over 100 by voltage gating alone, and that these pores could function as ionic switches with high on-off ratios of approximately 260. Further, we demonstrate voltage gated control over protein transport, which is of importance in lab-on-a-chip devices and biomolecular separations.