Ar Ion Beam Milling Research Articles

Precise Final Specimen Thinning by Concentrated Argon Ion Beam Milling of Plan View TEM Specimens Prepared in the Xenon Plasma FIB

Abstract Xenon plasma focused ion beam specimen preparation is ideal for preparing plan view TEM specimens due to its large-volume-milling capabilities. This article describes concentrated Ar ion beam milling using low energy as a post-pFIB final thinning step of plan view TEM specimens from a phase change memory device. Precise control of specimen thinning is achieved, which results in high-quality specimens with pristine surfaces and a large field of view for TEM characterization.

Aluminum Josephson Junction Formation on 200mm Wafers Using Different Oxidation Techniques

This work focuses on the manufacturing of Al/AlOx/Al Josephson junctions (JJs), which are essential components of many quantum circuits. Two processes were studied to understand the oxidation of the aluminum surface. Static oxidation was performed by removing native AlOx in a cluster system with Ar-ion beam milling and controlling the final tunneling oxide by applying a specific O2 pressure in the chamber. Controlled plasma oxidation was performed by removing native AlOx with a H2 plasma followed by a defined reoxidation with an oxygen plasma. The resulting oxides had thicknesses up to 10 nm and their electrical properties were analyzed on wafer level, providing insight into the structure and composition of the aluminum oxides and their applicability for Qubits. This work is crucial for reliable industrial manufacturing on full-scale 200 mm wafers with a very high uniformity level.

Site-specific preparation of plan-view samples with large field of view for atomic resolution STEM and TEM studies of rapidly solidified multi-phase Al Cu thin films

The present work describes application of a method for site-specific plan-view sample preparation for atomic column resolution scanning transmission and transmission electron microscopy (STEM and TEM) from free-standing thin films of multi-phase Al-alloys after laser irradiation induced rapid solidification (RS). The electron-transparent multilayer thin film samples (amorphous Si3N4 substrate plus metal alloy layer) had a total initial thickness of ≈ 130–200 nm. At such large total sample thickness frequently multiple grains of the same or different phases overlap along the electron beam path in the RS microstructures of the alloys. Consequently, accurate atomic resolution images in TEM and STEM mode, and composition sensitive analytical data of the metastable microstructural features presenting in the RS microstructures cannot be obtained with confidence. Using low-energy concentrated Ar ion beam milling, locally thinned regions with thickness of 20–30 nm with large fields of view ≥ (30 μm)2 suitable for high-resolution TEM/STEM studies have been created with micron-scale site-specificity. As example application, atomic scale resolution TEM/STEM imaging has been performed of the banded grain regions of the RS microstructure established in multi-phase AlCu alloy thin films. The sample preparation strategy described here appears to be readily applicable to freestanding thin film specimens in general.

Elemental depth profiles and plasma etching rates of positive-tone electron beam resists after sequential infiltration synthesis of alumina

By scanning transmission electron microscopy and energy dispersive X-ray spectroscopy (STEM–EDS), we investigated the elemental depth profiles of organic electron beam resist films after the sequential infiltration synthesis (SIS) of inorganic alumina. Although a 40-nm-thick poly(methyl methacrylate) (PMMA) film was entirely hybridized with alumina, an uneven distribution was observed near the interface between the substrate and the resist as well as near the resist surface. The uneven distribution was observed around the center of a 100-nm-thick PMMA film. The thicknesses of the PMMA and CSAR62 resist films decreased almost linearly as functions of plasma etching period. The comparison of etching rate among oxygen reactive ion etching, C3F8 reactive ion beam etching (RIBE), and Ar ion beam milling suggested that the SIS treatment enhanced the etching resistance of the electron beam resists to chemical reactions rather than to ion collisions. We proposed oxygen- and Ar-assisted C3F8 RIBE for the fabrication of silica imprint molds by electron beam lithography.

Depth profiling organic light-emitting devices by gas-cluster ion beam sputtering and X-ray photoelectron spectroscopy

The composition depth profile in organic light-emitting devices (OLEDs) is investigated using X-ray photoelectron spectroscopy (XPS) coupled with gas-cluster Ar-ion beam milling (Ar-GCIB). The XPS technique gives precise information about the surface chemistry of the organic thin films and is capable of differentiating the various charge transport, host and guest materials used in an OLED. The use of large Ar ion clusters (∼1500–2500atoms/cluster) in the milling process allows for small amounts of the organic thin film to be sputtered away without contaminating the surface or damaging the underlying material chemistry. By probing OLEDs as a function of depth, key parameters including emissive layer composition and interface quality can be assessed directly. It is found that the depth profile for graded-composition emissive layer OLEDs closely matches the intended deposition profiles, maintaining both the composition gradient and the intended endpoint compositions. The ability to resolve and correlate subtle changes in film composition to variations in device performance will help inform efforts in device design, while also serving as a diagnostic tool to better understand the mechanisms for device degradation and failure.

Manufacturing Over Many Scales: High Fidelity Macroscale Coverage of Nanoporous Metal Arrays via Lift‐Off‐Free Nanofabrication

A low-cost, high-throughput, lift-off-free nanolithographic method is developed for creating hexagonal arrays of sub-30-nm-sized pores on a metal film, achieving uniform coverage over an entire wafer of 10 cm in diameter. Spherical nanodomains of poly(methyl methacrylate) are demonstrated to be well-controlled and self-aligned within a polystyrene matrix layer on a metal thin film without any intermediary coating. After removal of PMMA, the porous PS thin film acts as an etch mask for defining nanoscale pores in the metal underlayer by Ar ion beam milling, resulting in wafer-scale patterning with great fidelity.

Nanoscale Rings from Silicon-Containing Triblock Terpolymers

Nanoscopic ring arrays of various materials show promise for both technological applications and fundamental studies. In this work we report the preparation of sub-50 nm diameter ring arrays from metallic thin films using a block polymer lithographic pattern transfer approach. We prepared a triblock terpolymer that adopts a core-shell cylindrical morphology where the shell is an oxidizable polydimethylsiloxane block. Solvent annealed thin films of this terpolymer produce cylindrical features oriented perpendicular to the substrate surface. The polydimethylsiloxane shell is then converted into SiOx rings by an oxygen reactive ion etch. The resultant hard mask pattern is then transferred into Au, Ni80Fe20, and Ni80Cr20 thin films via Ar ion beam milling, demonstrating the generality of the approach.

Josephson junctions fabrication in multi-layer deposition and post annealing MgB<sub>2</sub> thin films

Josephson junctions are fabricated by focused ion beam in MgB₂ thin films. The films were prepared by deposite multi-layer Mg and B films at room temperature first and then annealed at about 700°C. These films have <italic>T</italic>_c of 32 K. Strips and SQUID loops were defined by photolithography and Ar ion beam milling. Then nanobridges of 150-300 nm wide were made by focused ion beam etching. The <italic>R-T</italic> characteristics of the strip is the same as that of the raw film while SQUIDs have a “foot” near the critical temperature. The <italic>I-V</italic> curve of one of the SQUIDs is hysteretic below about 10 K. Nanobridges show features of the resistively shunted junction like, and the temperature dependence of the critical current turns out to be of SINS weaklink. At 9.8 K, the critical current density is about 1.5×10⁷ A/cm².

The kinetics of conductivity type conversion in HgCdTe by ion beam milling

It is well established that dry etching of HgCdTe by Ar ion-beam milling (IBM) converts vacancy-doped p-type HgCdTe to n-type. Less well established is the understanding of the observed rate of conversion. This paper shows that the observed variations of the depth of conversion with milling time can be accounted for in terms of two rate processes operating in tandem. The first process is the diffusion of Hg interstitials from the surface to the conversion boundary followed by the second, or conversion, process that is the capture of the Hg interstitials by cation vacancies. Assuming steady-state conditions exist a quadratic equation is derived for the conversion depth and its milling-time dependence for two cases: when the initial p-type layer is electrically intrinsic at the milling temperature and when it is extrinsic. Good agreement is found with the available experimental Ar-ion-milling data. Good agreement is also found for type conversion due to etching with a radio-frequency Ar plasma. The effect of capture of Hg interstitials by traps, in addition to capture by cation vacancies, is also considered.

Magnesium diboride nanobridges fabricated by electron-beam lithography

MgB 2 nanobridges were fabricated by e-beam lithography and Ar-ion beam milling. Nanobridges of widths ranging from 60 nm to 1μm and 3μm in length were realized by Ar-ion beam milling using amorphous carbon as etching mask. The processing did not harm the superconducting properties appreciably. High values of the critical current density, more than 10MA∕cm2, were measured for bridges with widths down to 60 nm. Current-voltage (I-V) characteristics showed a behavior typical of a bridge going normal, after the critical current is exceeded, and remaining normal as the current is decreased to a lower switch back value due to Joule heating. We could also observe switching behavior in some bridges indicating formation of normal hotspots in the bridges before they returned to their superconducting state. Alternative explanations may include natural grain boundaries in the film or the movement of Abrikosov vortices. The current-voltage (I-V) characteristics showing critical current densities up to 5×107⁢A∕cm2 indicates excellent film properties in the nanobridges.

Ｘ７Ｒ特性積層セラミックコンデンサ材料の焼結過程における微細構造変化

Transmission Electron Microscopy and Scanning Transmission Electron Microscopy were applied to study sintering process of the X7R MLCC materials, BaTiO3-MgO-Y2O3-(BaCa)SiO3. Though the materials were porous at the intermediate state of sintering process, the Ar-ion beam milling technique was employed for specimen preparation of electron microscopy. Succeeding in preparation, structural changes in microscopic scale have become visible. It has found that at rather low firing temperatures where the materials would not show any shrinkage in the macroscopic scale, the additives such as yttria, were already active. It was confirmed that thin Y layers of a few nanometers in thickness were formed at the surface of BaTiO3 Particles. The macroscopic shrinkage could progress, as yttria or calcia begins to diffuse toward the inner part of BaTiO3 particles. After the shrinkage, so-called core-shell structures could be observed.

Superconductivity in magnesium diboride thin films

Mg–B thin films were grown in situ on (1 0 0) SrTiO 3 substrates by pulsed laser deposition. Targets pressed from a commercial MgB 2 powder had a superconducting transition temperature of 37 K. Films were characterized by atomic force microscopy and susceptibility measurements. First samples showed superconducting onset at 30 K and became superconducting at about 20 K. Films were patterned into microbridges 4–100 μm wide by Ar ion beam milling. Films had large contact resistances, of the order of 500 Ω cm 2 in the temperature range 4.2–300 K.

Fabrication of ramp-edge type junctions with different high- Tc superconductor electrodes

We have fabricated ramp-edge type junctions with different high- T c superconductor electrodes; YBa 2Cu 3O 7− y (YBCO) and Bi 2Sr 2CaCu 2O 8+ y (BSCCO). Thin films were prepared on SrTiO 3 (1 0 0) substrates by a pulsed laser deposition method. YBCO was selected as a base electrode and BSCCO as a counter electrode, by considering the growth conditions for these thin films. The samples were etched by Ar ion-beam milling to pattern the shape of the ramp-edge type junction. We have prepared several junctions with and without a PrBa 2Cu 3O 7− y barrier. In case of the junction without a barrier material, T c's of YBCO and BSCCO electrodes were about 90 and 60–70 K, respectively, and it was found that the maximum supercurrent between the ab planes of YBCO (RE123 superconductor) and BSCCO (Bi-based superconductor) was about 1 mA at 4.2 K. Shapiro steps were also observable.

Investigation of the microstructure of ramp-typeYBa2Cu3O7-δ structures

We studied the morphology of ramps in YBa2Cu3O7-δ films and, subsequently, the barrier layer. The ramps have beenfabricated by Ar ion beam milling using standard photoresist masks. SEM andAFM showed the formation of tracks along the slope of the ramp, originatingfrom the irregular shape of the edge of the photoresist mask. A proposedmodified reflowed resist and pre-annealing process show a significantly smootherramp surface, important for the fabrication of reproducible Josephson junctions.

Optimization and magnetic field behavior of sputtered submicron YBa/sub 2/Cu/sub 3/O/sub 7/ step-edge Josephson-junctions

YBa/sub 2/Cu/sub 3/O/sub 7/ step-edge junctions with widths down to 0.5 /spl mu/m are fabricated on SrTiO/sub 3/-substrates by Ar ion-beam milling of the steps, high-pressure on-axis magnetron sputtering and, finally, electron beam patterning and ion-beam etching of the microbridge. For ratios of film thickness to step height of about 1/2 the current-voltage characteristics show Shapiro steps under microwave irradiation and RSJ (resistively shunted junction)-like behavior. The periodic dependence of the critical current upon the magnetic field resembles a Fraunhofer-pattern. The period of the current variation /spl Delta/B/sub 0/ depends upon the width w of the junction according to the theoretical prediction for planar thin Josephson junctions: /spl Delta/B/sub 0/=1.84/spl phi//sub 0//w/sup 2/. Junctions with widths of 0.7 /spl mu/m possess a large magnetic field stability with /spl Delta/B/sub 0//spl ap/100 G. Small junctions (w<1 /spl mu/m) exhibit voltage jumps in the Fraunhofer pattern, which are explained by flux penetration of single vortices into the superconducting electrodes.

Magnetic field behavior of small sputtered step-edge junctions

YBa2Cu3O7 step-edge junctions with widths down to 0.5 μm are fabricated on SrTiO3 substrates by Ar ion-beam milling of the steps, high-pressure on-axis magnetron sputtering, electron beam patterning and ion-beam etching of the microbridge. For ratios of film thickness to step height of ∼1/2 the current-voltage characteristics show Shapiro steps under microwave irradiation and resistively shunted junction like behavior. The periodic dependence of the critical current upon the magnetic field resembles a Fraunhofer pattern. The period of the current variation ΔB0 depends upon the width w of the junction according to the theoretical prediction for planar thin Josephson junctions: ΔB0=1.84φ0/w2. Junctions with widths of 0.7 μm possess a large magnetic field stability with ΔB0≊100 G. Small junctions (w&amp;lt;1 μm) exhibit voltage jumps in the Fraunhofer pattern, which are explained by flux penetration of single vortices into the electrodes.