Reactive Ion Beam Etching Research Articles

Properties of Ion–Electron Emission from the Surface of Semiconductor Material During Reactive Ion–Beam Etching

The existing methods of diagnosis of solid surfaces in ion − plasma processes have been analyzed. We found that the most efficient method of estimating surface condition, determining the transition of the etching process from one layer to another and determining the end of the etching process is the registration of ion − electronic emission during ion − beam etching. Results on secondary electron current for ion beam etching of various semiconductors have been reported. We show the experimental setup and describe the electric circuit for the detection of secondary electrons. An experimental study has been carried out to determine the dependence of secondary electron current on the band gap E g and the height of the potential barrier (electron affinity) χ of Ge, Si, GaAs, GaP and SiC semiconductor materials. We found no clearly expressed dependence of integral signal of ion − electronic emission on E g and χ . We show that under the conditions of ion beam etching under the influence of the surface potential the electric field penetrates in the semiconductor volume, leading to a shift in the energy levels of electrons in the surface layer and a change in the secondary electron current due to the appearance of autoelectronic emission. We found that the signal of ion − electronic emission in n − type silicon is higher than in p − type silicon. A model of ion − electronic emission from the surface of semiconductors is presented for the conditions of ion − beam etching, consisting of: emission with the participation of conductivity band electrons, emission due to the direct transition of electrons in the ion – atom system, and autoelectronic emission under the influence of surface potential.

Reactive ion beam etching of fused silica using vertical lamellar patterns of PS-b-PMMA diblock copolymer masks

Nanostructured, functional materials attract increasing attention for various applications. Therefore, the fabrication of nanometer structures in polymers for masking purposes and their transfer into functional materials is highly requested. One promising approach is the transfer of vertical lamellas fabricated by self-assembling processes from 104k poly(styrene)-block-methyl methacrylate (PS-b-PMMA) block copolymer (DiBCP) into fused silica by dry etching. The ∼50nm high DiBCP lamellas were fabricated by a standard procedure comprising spin-on, thermal annealing, and wet developing in acetic acid. The perpendicular orientation of the lamellar DiBCP that is required for dry etching pattern transfer was verified and inclination angles of maximal 8° were found. These DiBCP lamellas that have a period of 48±1nm were transferred by a reactive ion beam etching process (RIBE) with CF3H into fused silica wafers. The etched fused silica lamellas feature a size of 21±4nm, a lamella period of 48±2nm, and a height of 81±3nm for 4min etching time. For 6min etching time we specified a lamella feature size of 18±4nm, a lamella period of 47±3nm, and a height of 114±4.5nm.

Fabrication of Niobium Nanobridge Josephson Junctions

To realize antenna-coupled Josephson detectors for microwave and millimeter-wave radiation, planar-type Nb nanobridge Josephson junctions were fabricated. Nb thin films whose thickness, the root mean square roughness and the critical temperature were 20.0 nm, 0.109 nm and 8.4 K, respectively were deposited using a DC magnetron sputtering at a substrate temperature of 700°C. Nanobridges were obtained from the film using 80-kV electron beam lithography and reactive ion-beam etching in CF4 (90%) + O2 (10%) gases. The minimum bridge area was 65 nm wide and 60 nm long. For the nanobridge whose width and length were less than 110 nm, an I-V characteristic showed resistively-shunted-junction behaviour near the critical temperature. Moreover, Shapiro steps were observed in the nanobridge with microwave irradiation at a frequency of 6 – 30 GHz. The Nb nanobridges can be used as detectors in the antenna-coupled devices.

High-density data recording via laser thermo-lithography and ion-beam etching

Pits 250 - 300 - nm wide were obtained on the surface of thin organic nanocomposite film using master-disc laser-burning station with 405 nm laser beam focused by 0.85 NA lens. The film with obtained pits was used as a mask for subsequent reactive ion-beam etching of glass substrate. Finally, 150 - 200-nm pits were performed on the substrate surface. Nanocomposite films were based on organic positive photoresist with a dye inclusions. This dye is characterized by wide absorption band within the spectral region 390-410 nm and can be evaporated by laser irradiation with the wavelength 405 nm.

Fabrication of high quality factor GaAs/InAsSb photonic crystal microcavities by inductively coupled plasma etching and fast wet etching

The authors demonstrate high quality factor GaAs-based L9 photonic crystal microcavities (PCMs) with embedded InAsSb quantum dots with emission in 1.3 μm at room temperature. The fabrication process uses reactive ion beam etching with a CHF3/N2 gas mixture and reactive ion etching with a BCl3/N2 gas mixture to form PCMs on air-suspended slabs. An optimum N2 partial flux content of 0.65 and a successful removal of deposits formed during the membrane release by a fast wet etching in HF provide optical quality factors (Q-factors) as high as ∼30 000.

Broadband trapeziform multilayer dielectric grating for femtosecond pulse compressor: design, fabrication, and analysis

Rectangular HfO2 grating fabrication is difficult, so a trapeziform multilayer dielectric pulse compression grating (PCG) has been designed using a genetic algorithm and the Fourier mode method. Simulation results show that a greater than 120 nm wavelength range multilayer dielectric grating (MDG) is obtained with a minus-first-order diffraction efficiency (DE) exceeding 95%. The bandwidth is 136 nm with the minus-first-order DE exceeding 90%. The trapeziform structure shows good tolerances for grating fabrication. The multilayer dielectric is deposited by e-beam evaporation, then the MDG is fabricated by reactive ion beam etching. A 128 nm bandwidth of the MDG for the transverse electric polarization with an efficiency exceeding 90% is obtained, and the maximum DE can reach up to 98.3%. The trapeziform MDG is an ideal PCG for chirped pulse amplification systems with high DE, broad bandwidth and good fabrication tolerances. Laser-induced damage thresholds of 0.53 J cm−2 under 40 fs pulses are experimentally reached with very high and uniform efficiency.

Fabrication of blazed grating by native substrate grating mask

The blazed grating is one of the key elements in a spectrometer. Hence we have adopted a new method of its fabrication. First, the combination of ion beam etching (IBE) and reactive IBE is used to fabricate a native substrate grating mask to replace the traditional photoresist grating mask. This is because the former mask allows for more accurate control of the profile than the latter. Then tilted IBE is used to etch the native substrate grating to ensure the precise control of the blazed angle and antiblazed angle. Therefore, an optimal blazed grating profile is successfully fabricated. Two types of blazed gratings with the same period of 833 nm have been fabricated: one with the blaze angle of 11 deg and the antiblaze angle of 72 deg; and one with the blaze angle of 20 deg and the antiblaze angle of 68.5 deg, respectively.

Rib and strip chalcogenide waveguides based on Ge–Sb–Se radio-frequency sputtered films

Rib and strip chalcogenide waveguides were demonstrated using photolithography technique and reactive ion beam etching method in a CF4/Ar atmosphere, based on Ge–Sb–Se films deposited by radio-frequency sputtering. The study of compositional, morphological and structural characteristics of the films was investigated, the propagation losses with different widths were measured and optical performance in rib and strip waveguides with different sizes were analyzed and compared. The thin films showed similar composition identical to the bulk glass targets with very low surface roughnesses. The fabricated waveguides by reactive ion beam etching had low surface roughnesses and reasonable vertical sidewalls. Propagation losses of rib and strip waveguides were measured at 1550nm with different widths, and the methods to decrease the propagation losses were introduced. The techniques were indicated feasible for fabricating rib and strip waveguides with potential applications of integrated optics fields in further study.

Modeling of altered layer formation during reactive ion etching of GaAs

The binary collision based SDTrimSP model has been used to simulate the reactive ion beam etching (RIBE) of GaAs in the presence of energetic Ar ions and thermal O atoms. It includes the collisional effects, diffusive processes and chemical reactions taking place in the system. The model parameters are fitted using the experimental observations of Grigonis and co-workers [1] and validated with the experimental results obtained during the GaAs ion etching presented in this paper. A detailed analysis is presented to understand the effect of the diffusive processes and the role of O during RIBE of GaAs. It is shown how the presence of damage caused by the energetic Ar coupled with the presence of thermal O opens up chemical reaction channels which eventually leads to the preferential sputtering of Ga observed at the ion etching facility at University of Greifswald.

Fabrication of optimized 3D microstructures with undercuts in fused silica for replication

The replication of 3D structures with undercuts by nanoimprint technologies needs appropriate, rigid masters. The fabrication of 3D microstructured masters with inclined, undercut structures by photolithography and reactive ion beam etching into fused silica is demonstrated. The ion beam incidence angle defines the sidewall inclination of the undercuts and the shape of the structures. Specific characteristics of 3D structures in particular of the undercuts and of the bottoms are the result of the competing processes of polymer deposition and silica etching and the alteration of the average ion current density distribution due to etching depth increasing and mask degradation during the cyclic etching from opposite directions. Optimized structures can be achieved with a high number of short etching cycles.

Possibility for the form correction of X-ray mirrors by reactive ion-beam etching

Key parameters for the reactive ion-beam etching of glass, quartz and silicon are studied. The dependence of the etching rate on chamber pressure and etching time is investigated. The etching zone has the form of a long (∼50 mm), narrow (∼1 mm) strip with depth homogeneity at a level of 0.2%. Such a zone is a handy tool for correcting the shape of cylindrical surfaces.

Single-layer resonant-waveguide grating for polarization and wavelength selection in Yb:YAG thin-disk lasers

A single-layer resonant-waveguide grating consisting of a sub-wavelength grating coupler etched into a waveguide is proposed in order to achieve high polarization and high spectral selectivity inside an Yb:YAG thin-disk laser resonator. The designed structure was fabricated with the help of a Lloyd's-mirror interference lithography setup followed by reactive ion beam etching down to the desired grating groove depth. The wavelength and polarization dependent reflectivity is measured and compared to the design results. The behaviour of the device at higher temperatures is also investigated in the present work. The device is introduced as the end mirror of an Yb:YAG thin-disk laser cavity. Output powers of up to 123 W with a spectral bandwidth of about 0.5 nm (FWHM) is demonstrated in a multimode configuration (M2~6). In fundamental-mode operation (TEM00 with M2~1.1) 70 W of power with a spectral bandwidth of about 20 pm have been obtained. Moreover, the degree of linear polarization was measured to be higher than 99% for both multimode and fundamental mode operation.

Direct patterning of functional interfaces in oxide heterostructures

We report on the direct patterning of high-quality structures incorporating the LaAlO3-SrTiO3 interface by an epitaxial-liftoff technique avoiding any reactive ion beam etching. Detailed studies of temperature dependent magnetotransport properties were performed on the patterned heterostructures with variable thickness of the LaAlO3 layer and compared to their unstructured thin film analogues. The results demonstrate the conservation of the high-quality interface properties in the patterned structures enabling future studies of low-dimensional confinement on high mobility interface conductivity as well as interface magnetism.

Fabrication of HfO2 patterns by laser interference nanolithography and selective dry etching for III-V CMOS application

Nanostructuring of ultrathin HfO2 films deposited on GaAs (001) substrates by high-resolution Lloyd's mirror laser interference nanolithography is described. Pattern transfer to the HfO2 film was carried out by reactive ion beam etching using CF4 and O2 plasmas. A combination of atomic force microscopy, high-resolution scanning electron microscopy, high-resolution transmission electron microscopy, and energy-dispersive X-ray spectroscopy microanalysis was used to characterise the various etching steps of the process and the resulting HfO2/GaAs pattern morphology, structure, and chemical composition. We show that the patterning process can be applied to fabricate uniform arrays of HfO2 mesa stripes with tapered sidewalls and linewidths of 100 nm. The exposed GaAs trenches were found to be residue-free and atomically smooth with a root-mean-square line roughness of 0.18 nm after plasma etching.PACS: Dielectric oxides 77.84.Bw, Nanoscale pattern formation 81.16.Rf, Plasma etching 52.77.Bn, Fabrication of III-V semiconductors 81.05.Ea

Glancing angle deposition of Ge nanorod arrays on Si patterned substrates

A periodic arrangement of Ge nanorods on a Si(111) substrate was realized by glancing angle deposition (GLAD) onto honeycomb-like arranged Au hillocks formed using a self-assembled monolayer of polystyrene nanospheres as an evaporation mask. Additionally, a honeycomb-like arrangement of Au dots was used as an etch mask in a reactive ion beam etching process for pattern transfer procedure. Resulting honeycomb patterns consisting of Si hillocks within the Si(111) substrates were utilized to deposit Ge nanorods. Effective morphological variations in shape and dimension of GLAD-grown nanorods on honeycomb-like patterned substrates with both Au dot and Si dot arrays are strongly influenced by interseed distances, seed heights, and consequently shadowing lengths. For a large pattern period, it was observed that the usual triangular shape of the nanorod changed to a hexagonal shape as an effect of additional particle flux that reached the growing nanorod from the direction of second and third-nearest neighbors due to inadequate shadowing lengths and increased interseed condensation.

The Fabrication of THz Emitting Mesas by Reactive Ion-Beam Etching of Superconducting Bi2212 with Multilayer Masks

Generation of powerful THz radiation from intrinsic Josephson Junctions (IJJs) of Bi2Sr2CaCu2O8+δ (Bi2212) may require mesas with large lateral dimensions. However, there are difficulties in fabrication of perfect rectangular mesas. The lateral angles of mesas should be close to 90 degrees to obtain IJJs with same planar dimensions for synchronization of IJJs. We patterned Ta/photoresist and photoresist/Ta/photoresist masks on Bi2212 and used selective ion etching to overcome the thick photoresist layer shading on the lateral dimension of mesa during the ion-beam etching. The reactive ion-beam etchings have been done with ion beams of Ar, N2 and O2, and we have obtained mesas about 1 μm with lateral angle of approximately 50 to 75°, which is better than the mesas fabricated with photoresist mask.

ChemInform Abstract: Surface Science Aspects of Etching Reactions

Abstract Basic studies of the surface science aspects of plasma-assisted etching were initiated over 10 years ago in laboratories throughout the world. Several approaches to this experimentally challenging problem have been taken: (1) simulate the reactive gas glow discharge environment with directed beams of energetic positive ions and thermal energy reactive molecules/radicals in a UHV environment; (2) simulate the reactive gas glow discharge by using a beam of reactive ions (reactive ion beam etching); and (3) carry out careful ex-situ analyses of surfaces etched in reactive gas glow discharges without air exposure. This report will be limited to a review of the work reported using the first of these approaches only and summarizes the status of this virtually unexplored field of surface chemistry. The report includes a discussion of the experimental aspects of this field and then focuses on the gas-solid system which has been studied most thoroughly; i.e., silicon-fluorine. A considerable quantity of new unpublished data is presented and a framework is proposed to explain the many observations associated with the spontaneous reaction of fluorine with silicon. The role of energetic ions in this reaction is then discussed in detail. Other materials combinations which are discussed are silicon-chlorine, silicon-bromine, silicon-hydrogen and SiO2-fluorine. The report concludes with a tabulation of the many other gas-solid systems which have been studied and also a discussion of the extent to which these basic studies relate to actual reactive gas processing environments.

A system for precision reactive ion-beam etching of nanostructures for field-emission devices

An system for precision selective ion-beam etching of nanostructures for field-emission devices is developed. The system is equipped with a Radikal-M160 multibeam ion source with a cold cathode and closed electron drift forming the ion beam of the working substance with a diameter of 160 mm and a microwave input for the supply of the microwave bias to the treated substrates. Technological possibilities of the system are investigated experimentally. The advantages of simultaneous ion-beam and microwave etching of the nanostructures are shown. The processes of precision etching of nanostructures through a mask up to 1 μm thick with diameters of orifices of 20–30 nm (aspect ratio of the structures of the mask ∼50: 1) are carried out.

Fabrication and Characterization of Vanadium Doped PbZr0.53Ti0.47O3 (PZTV) Force Sensors for Minimally Invasive Surgical Tools

Minimally invasive surgery (MIS) is the most exciting and rapidly developing area where force sensing is actually of central importance. Micro-machined piezoelectric sensors can be integrated onto MIS tools for improved diagnosis and treatment monitoring. A micro-machined freestanding vanadium doped-lead zirconate titanate (PZTV) force sensor is fabricated using five masks process incorporating deep reactive ion, ion beam and wet-chemical etching techniques. The PZTV sensor is designed as a parallel plate capacitor structure in which the sol-gel prepared 1-μ m thick PZTV film is sandwiched between top (Au/Cr) and bottom (Pt/Ti) metal electrodes mounted on a thin Si membrane. This paper also describes a new wet chemical approach for patterning vanadium doped-PbZr0.53Ti0.47O3 films. The etch recipe provided excellent etch control, minimized undercut, preserved the photoresist mask, and effectively removed the residues on the etched surfaces. A high etch rate (200 nm/min), high selectivity with respect to photoresist, and limited under-cutting (1.5:1, lateral : thickness) were obtained. The fabricated force sensor exhibited good ferroelectric properties. The current fabrication procedure and electrical analysis can be considered as a breakthrough for fabricating freestanding PZT force sensor in any desired shape and dimensions, as well as a good example of ferroelectric microdevices.

Fabrication of high quality factor photonic crystal microcavities in InAsP∕InP membranes combining reactive ion beam etching and reactive ion etching

The process of fabrication of high quality factor photonic crystal microcavities in slabs of InP with light emission at 1.5μm is reported. The process includes e-beam lithography, reactive ion beam etching with a CHF3∕N2 gas mixture, and reactive ion etching with a CH4∕H2 gas mixture and O2 cycling. An InGaAs sacrificial layer is removed by chemical wet etching in order to obtain the photonic crystal membrane. Microphotoluminescense measurements have been performed to assess the quality of the fabricated structures. Quality factors up to ≃30000 and laser emission with thresholds of excitation pump power around 34μW have been obtained.