Low Etching Research Articles

Enhancing Performance and Function of Polymethacrylate Extreme Ultraviolet Resists Using Area-Selective Deposition

Extreme ultraviolet (EUV) lithography is a critical enabler in next-generation technology, although the low etch resistance of conventional organic EUV resists results in low resolution pattern transfer, particularly for smaller features. In this work, we integrate area-selective deposition (ASD), a bottom-up nanopatterning technique, with EUV resists of industrially relevant thicknesses (<50 nm thick) to form resist hardening or tone inverting layers for improved resolution. We utilize TiO2 ASD via atomic layer deposition on 25–35 nm thin photosensitive polymethacrylate-based EUV materials. By tuning the polymer structure and functionality, we enable different scenarios for selective deposition on top of the resist, infiltrated into the bulk resist, or selective to the resist. We find that a cyclohexyl protecting group causes TiO2 inhibition, thus showing promise for tone inversion applications with oxide underlayers. In contrast, resist materials containing a tert-butyl protecting group are good candidates for resist hardening because they enable TiO2 deposition on both EUV exposed and unexposed polymers. Furthermore, we report the integration of a dimethylamino-trimethylsilane inhibitor with the resists to inhibit TiO2 surface nucleation and facilitate subsurface diffusion, thus further broadening potential applications. The results described here establish an important baseline for utilizing ASD on various organic resists to achieve tone inversion or resist hardening and hence improve EUV pattern resolution.

Rate optimization of atomic layer etching process of silicon

With the shrink of critical dimensions of semiconductor devices to a few nanometers, atomic layer etching (ALE) has become an important technique to achieve single-atom resolution. The ALE can divide plasma etching into two self-limiting reaction processes: passivation process and etching process, allowing for the sequential removal of material atomic layer by layer. Therefore, it encounters the problem of low etch rate. In this work, the variation in surface substance coverage during the passivation process and the etching process are investigated numerically to optimize both the passivation duration and the etching duration. A coupled model integrating a two-dimensional inductively coupled plasma discharge chamber model, a one-dimensional sheath model, and a three-dimensional etching trench model is developed and used to investigate the optimal time for one single cycle ALE of silicon through the use of Ar/Cl&lt;sub&gt;2&lt;/sub&gt; gases under the condition of Ar inductively coupled plasma discharge. The results indicate that during the passivation stage, the surface coverage of SiCl and SiCl&lt;sub&gt;2&lt;/sub&gt; initially increase with time going by and then decrease, while the surface coverage of SiCl&lt;sub&gt;3&lt;/sub&gt; continuously increases, and eventually, the surface coverage of these three species stabilize. When the surface is predominantly covered by SiCl&lt;sub&gt;2&lt;/sub&gt;, it is the optimal time to trigger the etching process, which induces a relatively favorable surface state and a relatively short etching time. Comparing with typical ALE etching techniques, the time of our optimal ALE single cycle is shortened by about 33.89%. The ALE cycle time (etching rate) exhibits a linear relationship with the aspect ratio. Additionally, the duration of the passivation process and etching process increase linearly with the aspect ratio or etch depth increasing. Moreover, as the etch depth increases, the effect of the passivation process on the ALE rate becomes more significant than that of the etching process.

Rare-earth metals as effective getters for purification of germanium telluride glasses from oxygen impurities

The ability of rare-earth elements (REEs) to bind oxygen impurities in Ge20Te80 and Ga10Ge15Te75 telluride glasses is studied. Thermodynamic calculations and experiments show that REEs in glasses, with the exception of Eu, can significantly reduce the content of oxygen impurities chemically bound with germanium, tellurium, and gallium. The most promising oxygen getters are established to be Y, Gd, Lu, Tm, Dy, Tb, and Ho. The advantages of REEs as the getter compared to traditionally used aluminum are: more complete removal of the getter residue during the distillation of tellurium melt and chalcogenide glass; the absence of intense absorption oxide bands in the range of glass transparency; lower etching ability in relation to the silica-glass reactor.

Improved Superconducting Performance of YBCO-Coated Conductors by Low Energy Density Argon Ion Etching

Improved Superconducting Performance of YBCO-Coated Conductors by Low Energy Density Argon Ion Etching

Fabrication of High‐Quality Thin Single‐Crystal Diamond Membranes with Low Surface Roughness

Certain aspects before and during the fabrication of single‐crystal diamond (SCD) membranes are highlighted, which are decisive to obtain high‐quality membranes with low surface roughness values around 0.2 nm on a small area scale. In addition to the requirements for the starting material, including a high planarity and a moderate surface roughness, the importance of cleaning processes to minimize particles and impurities before and during the structuring is emphasized. With the help of a planarization procedure, consisting of a combination of different Ar/Cl2 recipes with low etch rates, surface defects like grooves due to polishing are minimized and smooth surfaces are acquired. Severe micro‐masking can be prevented by the application of a cyclic Ar/Cl2 + O2 recipe, allowing finally the fabrication of defect‐minimized and planarized SCD membranes in the thickness range between a few microns and a few hundred nanometers. The high quality of the structured SCD membranes is evidenced with a morphological as well as optical characterization via fiber‐based microcavity measurements.

Atomic layer etching of Sn by surface modification with H and Cl radicals

Sn is the one of the materials that can be used for next generation extreme ultraviolet (EUV) mask material having a high absorption coefficient and, for the fabrication of the next generation EUV mask, a precise etching of Sn is required. In this study, the atomic layer etching (ALE) process was performed for the precise etch thickness control and low damage etching of Sn by the formation SnHxCly compounds on the Sn surface using with H and Cl radicals during the adsorption step and by the removal of the compound using Ar+ ions with a controlled energy during the desorption step. Through this process, optimized ALE conditions with different H/Cl radical combinations that can etch Sn at ∼2.6 Å cycle−1 were identified with a high etch selectivity over Ru which can be used as the capping layer of the EUV mask. In addition, it was confirmed that not only the Sn but also Ru showed almost no physical and chemical damage during the Sn ALE process.

Compatibility between polymethacrylate-based extreme ultraviolet resists and TiO2 area-selective deposition

BackgroundExtreme ultraviolet (EUV) lithography is crucial to achieving smaller device sizes for next-generation technology, although organic resists face substantial challenges, such as low etch resistance, which limit the resolution of smaller features.AimEvaluate the potential for area-selective deposition (ASD) to improve EUV pattern resolution (e.g., by increasing etch resistance).ApproachWe evaluate thermal compatibility, atomic layer deposition growth rate, and selectivity for TiO2 ASD on various organic EUV resist materials using water contact angle, Rutherford backscattering spectrometry, and X-ray photoelectron spectroscopy. The effects of photo-acid generator (PAG) and EUV exposure on polymer properties and selectivity are considered.ResultsThe organic resist materials studied demonstrate thermal compatibility with TiO2 ALD (125°C for 60 min). The TiO2 ALD process from TiCl4 and H2O proceeds readily on poly(tert-butyl methacrylate), poly(p-hydroxystyrene), and poly(p-hydroxystyrene-random-methacrylic acid) polymers, with and without PAG incorporation, in either the as-formed or EUV exposed state. However, TiO2 is inhibited on poly(cyclohexyl methacrylate).ConclusionsWe demonstrate that as-formed EUV resists can serve as either the growth or nongrowth surface during TiO2 ASD, thereby enabling resist hardening and tone inversion applications, respectively. These results serve as a basis for further ASD studies on EUV resist materials to improve pattern resolution in next-generation devices.

(Digital Presentation) Selective SiGe Vapor Etching Using Br2 in View of Nanosheet Device Isolation

Forksheet transistors are lateral nanosheet devices with a forked gate structure [1,2]. The physical separation of N- and PFETs by a dielectric wall enables N-P space scaling and consequently sheet width maximization within the limited footprint of low-track-height standard cells. Bottom dielectric isolation has been proposed to circumvent the junction isolation trade-off between punch-through suppression on the one hand and junction leakage and capacitance on the other hand [3]. A typical fabrication scheme includes the epitaxial growth of Si/Si1-yGey/multi-{Si1-xGex/Si} epi stacks (y>x) where the bottom Si1-yGey layer is later replaced by a SiN/SiCO isolation [4]. The fabrication scheme relies on selective etching of the sacrificial Si1-yGey layer with respect to the {Si1-xGex/Si} multi-stack. Owing to the very small dimensions (e.g. sub-10 nm nanowire channel diameter), high etch selectivity towards both Si1-xGex and Si, and excellent process controls are mandatory. This sets stringent requirements on the epitaxial stacks (thicknesses and composition control, sharpness of interfaces, and absence of strain relaxation) [4] as well as on the etch process itself (high selectivity, limited Si1-xGex and Si consumption) [5-7].The selective Si1-yGey removal requires a great precision in its adjustment, with the risk of experiencing process variabilities and yield issues. Selective SiGe etching is typically done in advanced wet or dry chemistries and is sensitive to both strain in and oxidation of individual layers [4-6]. Also, HCl-based vapor etching has been reported for SiGe removal, with high selectivity towards Si [7]. The HCl vapor etching requires a sufficiently high process temperature (typically ≥ 600°C). This makes it less attractive for fabrication schemes with bottom isolations. The presence of the Ge-rich Si1-yGey layer in the as-grown epi stack results in an enhanced risk for unwanted layer relaxation.A low temperature Br2-based vapor etching process is proposed as an alternative for the selective Si1-yGey removal in the isolation fabrication. After initial process screening on blanket epi layers to compare etching behavior for different process gases as function of material composition and crystallinity, it is demonstrated on patterned test structures that Br2 etching enables high etch selectivity of Si0.5Ge0.5 towards Si and Si1-xGex (x=0.2, 0.23, and 0.3).Figure 1 compares the etching characteristics of HCl, HBr, and Br2 as obtained for blanket Si1-xGex layers where the Ge content was varied between 0.2 and 0.5. In all cases, the etching is kinetically controlled. The etching rates indeed show a clear exponential dependence as function of the process temperature. While the etching rates are similar for HCl and HBr, the Arrhenius plot is shifted to ~300°C lower temperatures for Si1-xGex etching with Br2. For each process gas, the etching rate increases with increasing Ge concentration. This difference in etching rate as function of layer composition is highest for Br2. Figure 2 reports the obtained etching selectivity between Si0.5Ge0.5 and Si1-xGex (x = 0.15 – 0.36) as obtained for Br2 etching on blanket wafers. Selective etch tests with Br2 as etching gas were conducted on fin patterned structures consisting of Si-substrate / 10 nm Si0.5Ge0.5 / 3x {9 nm Si1-xGex / 9 nm Si}. Different etching times have been applied to demonstrate the concept and to validate etch selectivity between Si0.5Ge0.5 and Si1-xGex/Si. Figure 3 displays low magnification X-TEM images of the structure with x=0.2, after fin patterning, 1 min, and 3 min Br2 etching. The selective etching of the Si0.5Ge0.5 layer is clearly demonstrated, although the shortest etching time is not sufficient for complete Si0.5Ge0.5 removal while the sample etched for 3 min was clearly over etched. Lateral material loss of the upper two Si0.8Ge0.2 layers is limited to 2-3 nm (Fig. 3b) and 3-4 nm (Fig. 3c), respectively. During lateral Si0.5Ge0.5 etching, the lowest Si0.8Ge0.2 layer gets exposed to the Br2 etching gas both from the side walls as well as from the bottom surface. The severe etching of this layer is also observed for other etching routines and can easily be avoided by adding a thin Si layer between the Si0.5Ge0.5 layer and the first Si0.8Ge0.2 layer.

(Digital Presentation) Fabrication of Strained Ge Microbridges with Mesh-Patterned Pads and Their Optical Properties

IntroductionRecently, Ge has attracted attention as a luminescent material on Si. As fabrication of Ge-on-Si structures can induce tensile strain into Ge owing to thermal mismatch between Si and Ge and resultantly modify its band structure, the direct transition probability can be improved, offering strong luminescence. However, amounts of the strain induced in the Ge-on-Si are quite small (~0.2 %) and the larger strain is highly desired. And then, microbridge structures have been studied to increase the tensile strain and luminescence intensity [1,2]. Usually, electron beam lithography, which is not suitable for mass production, is used for making sub mm scale microbridges. We attempt to fabricate relatively large, several mm scale, microbridges by simple photolithography process. To provide large tensile strain in the Ge microbridge, it is necessary to enlarge areas of the pad region (both side areas of the bridge) due to the relatively large bridge size. However, the lower etching rate of the (111) plane makes it difficult to completely remove the Si underneath the Ge in the pad area. Therefore, we attempt to fabricate microbridge structures with mesh-type holes on the pads to enhance the etching of the Si in the pad areas and obtain a significant increase in room temperature PL luminescence intensity.ExperimentalA low-temperature Ge layer (Tg=350℃,40 nm) and high-temperature Ge layer (Tg=600℃, 500nm) were grown on Si(100) substrates using solid source MBE, and annealed to improve crystallinity. Subsequently, microbridge structures with mesh holes on the pad areas were patterned with the bridge along <110> direction by standard photolithography. The Ge and Si were etched down by dry etching. Then the Si underneath the Ge was removed by selective etching with KOH to fabricate freestanding microbridges. In addition, since amounts of strain are expected to vary depending on the area of the holes in the pad area, samples with different areas of holes were fabricated and compared. PL measurements at room temperature (excitation wavelength: 980nm) were performed to evaluate luminescent characteristics. Moreover, Raman measurements were performed to evaluate the amounts of strain (Laser wavelength: 514.5nm).Results and discussionsLaser microscope measurements confirmed that microbridges with mesh-holes on the pads were fabricated and that the Si underneath the Ge in the pad areas was fully etched and the pad areas are freestanding. From the PL spectrum obtained from the central position of the microbridge, a strong PL peak is observed, and a PL intensity of the microbridge with the mesh structure is significantly higher than that without the mesh structure. The peak is seen to shift to longer wavelength around 1800 nm, indicating that the tensile strain in the Ge microbridge with the mesh pattern is larger than that without the mesh structure, which was confirmed by Raman measurements. It is notable that the Ge-on-Si without patterning hardly yield light emission, indicating that the fabrication of microbridges with mesh-pattern by the simple photolithography process is expected to realize Si-based high-efficiency light sources.This work was supported in part by Grant-in-Aid for Scientific Research (19H02175, 19H05616, 20K21009).Ref1.M.J.Süess et al. Nature Photonics7 46-472(2013) 2. F.T. Armand Pilon et al. Nature Communications10 2742 1-8(2019) Figure 1

(Digital Presentation) Selective SiGe Vapor Etching Using Br2 in View of Nanosheet Device Isolation

Both forksheet and CFET device layouts contain local dielectric isolation layers to circumvent junction isolation trade-offs which are specific for these designs. Typical fabrication schemes start with the epitaxial growth of complicated SiGe/Si multi stacks with at least two different Ge concentrations where a Ge-rich SiGe layer is later replaced by an isolating dielectric. This work proposes a low temperature Br2-based vapor etching process as an option for the selective SiGe removal in the isolation fabrication. After initial process screening on blanket epi layers to compare etching behavior for different process gases as function of material composition and crystallinity, it is demonstrated on patterned test structures that Br2 etching enables high etching selectivity of Si0.5Ge0.5 towards Si and Si1-xGex (x = 0.2 - 0.3).

(Digital Presentation) Epitaxially Grown of SiGe on Ge Microbridge and Observation of Strong Resonant Light Emission

We observe strong room-temperature photoluminescence from Ge microbridges formed on Ge-on-Si (110). The Si (110) substrate is employed to fabricate the bridge along [111] direction as uniaxial strain in the [111] direction is expected to be the most effective to bring direct transition. In this study, we grow Ge-on-Si with (110) orientation and fabricate MB along the [111] directions. Due to the low etching rate of the (111) plane, however, etching of the Si under the square-shaped pads is quite difficult. By contrast, we fabricate branch-like MB, where the underneath Si was fully etched owing to the various directions of the etching. As a result, we obtained very strong resonant light emission.

An ultra-flexible silicon substrate with light-trapping structures: The application for visible-NIR photodetectors

Flexible substrates have been widely used in Visible-NIR photodetectors in recent years. Flexible silicon wafers were prepared by alkali etching. Pyramids with reflectivity of 11.8%, inverted pyramid with reflectivity of 7.9% and nanowire with reflectivity of 1.9% light-trapping structures were prepared by low concentration alkali etching, one-step Cu-MACE and Ag-MACE, respectively. In addition, PEDOT: PSS films doped with 5 wt% DMSO successfully presented the highest conductivity of 580 S·cm−1. The PEDOT: PSS/UF-Si PDs with different light-trapping structures were prepared by spin-coating PEDOT: PSS films. Comparing the optoelectronic performance of different light-trapping structures of the photodetector, the PEDOT: PSS/UF-Si NWs device exhibited the best optoelectronic performance. The photoresponse range is 300–1100 nm and the responsivity at the peak of 650 nm is 0.62 A·W−1. Furthermore, bending measurements are performed on PEDOT: PSS/UF-Si NWs PDs to evaluate the bending performance of the flexible PDs. For PEDOT: PSS/UF-Si NWs PDs with a bending radius of 5.3 mm and a bending cycle of 500, the responsitivity of the device demonstrates very small degradation.

One-step in-situ low damage etching of SiC/SiC composites by high-temperature chemical-assisted laser processing

SiC/SiC composites have a promising application prospect in the fields of aero-engine turbine blades and other hot-end components due to their excellent properties. It is difficult to machine SiC/SiC composites by traditional mechanical processing because of the ultra-high hardness and anisotropic character. The routinely laser direct processing in the air produce thermal effect damage, resulting in heat-affected zones and microcracks. Here high-temperature chemical-assisted nanosecond laser processing was investigated to realize one-step in-situ fast etching without causing damage to the structure of SiC/SiC composites. Firstly, the chemical wet etching only occurred in the laser-induced local high-temperature region. There was no additional etching damage to the substrate material in the region where the temperature was relatively low. Secondly, chemical liquid served as a transparent constraint layer, the ablation pressure on the material increased in a liquid confined environment. In comparison with laser direct etching in the air, the exposed fiber was not a needle-like structure and tubular structure but turned into a thin and flat tongue-like structure. The etching behavior of 0° fiber layer, 90° fiber layer, and crossing regions of fibers of different directions at low and high laser intensities were studied. Further, the hardness and friction coefficient of SiC/SiC composites after laser direct etching in the air and high-temperature chemical-assisted laser etching were compared. The chemical elementary composition before and after etching was measured to reveal the oxidized and carbonized characteristics. It was concluded that the action mechanism was the combined result of high-temperature decomposition, laser-induced ablation pressure in the liquid confined region, and local chemical wet etching. The results demonstrate that high-temperature chemical-assisted laser etching has some advantages over traditional laser beam machining and is a potential processing method for SiC/SiC composites.

Effect and mechanism analysis of sarcosine on the chemical mechanical polishing performance of copper film for GLSI

With the decrease of integrated circuits feature size, chemical mechanical polishing (CMP) of copper (Cu) film for multilayer wiring is faced with new challenges. In order to reduce the step height of Cu film for cobalt-based Cu interconnect during CMP process, the selection of additives in the slurry is crucial. In this paper, sarcosine was used as an important additive in Cu slurry to improve the planarization properties. Through the polarization curves, dynamic polishing, static etching experiments and scanning electron microscopy (SEM) measurement, it was identified sarcosine as a complexing agent and trace functional reagent could improve the Cu planarization properties. Meanwhile, the adsorption and complexation mechanisms of sarcosine on Cu film surface were analyzed by electrochemical tests and X-ray photoelectron spectroscopy (XPS). The improvement of static etching and surface quality of Cu patterned wafers by sarcosine was verified by laser scanning confocal microscopy (LSCM). Low static etch rate (SER) (1658 Å/min), high removal rate (RR) (5091 Å/min), RR/SER of 3.07 and effective correction of the step height on Cu patterned wafers were achieved by the synergistic effect of sarcosine and benzotriazole (BTA). In this study, a green functional reagent for Cu film CMP in low-tech node multilayer wiring was provided, which is good practical application prospects.

Orientation dependent etching of polycrystalline diamond by hydrogen plasma

The p-type conducting hydrogen-terminated diamond obtained from hydrogen plasma has several applications in the field of power semiconductor devices. Therefore, clarifying the effects and role of hydrogen plasma on diamond surfaces is a critical aspect in the field of hydrogen-terminated diamond devices. In this study, we focused on diamond surface etching by hydrogen plasma and revealed the dependence of the diamond crystal orientation using scanning probe microscopy and electron backscatter diffraction. Crystal grains with a low etching rate were distributed around the {100} and {111} planes, and those with a high etching rate were distributed on the {110} plane. Furthermore, we found that the etching rate increased as the intermediate orientation grains tilted toward the {110} plane. Because the surface carbon atoms that compose the {110} plane have two of their three back bonds on the surface exposed to hydrogen plasma, we expected that the {110} orientation would have a high etching rate. Even for grains with intermediate orientations, the etching tendency corresponded to the location of the back bonds. Our research provides important systematic data on the crystal orientation in diamond electronics.

Si3N4 Etching with Carboxylic-Acid-Containing Superheated Water

Silicon nitride (Si3N4) has been widely used as an insulating or sacrificial layer in various electronic devices. A removal of Si3N4 is also required in the semiconductor manufacturing process. In particular, in the 3D NAND flash memory manufacturing processes, selective removal of Si3N4 from the Si3N4/SiO2 stack structure is one of the very critical processes. It is known that Si3N4 is etched in high temperature phosphoric acid (H3PO4). Si3N4 is etched by nucleophilic attack of H2PO4 - and H2O in H3PO4 solution [1]. However, as the number of Si3N4/SiO2 stacked layers increases to improve the memory density of 3D NAND, oxide regrowth on the SiO2 layer and non-uniform top-to-bottom etching performance during Si3N4 etching process are the issues that need to be solved [2]. In this study, a novel Si3N4 etching in superheated water is investigated.As the temperature of H2O increases, the self-ionization of H2O is accelerated, thus the concentrations of H3O+ and OH- ion increase. It was previously reported that Si3N4 is etched by nucleophilic attack of OH- in superheated water [3]. However, in general, superheated water produced a low Si3N4 etching rate with the attack of Si substrate, making it difficult to apply to the Si3N4 etching process. Therefore, in this study, various additives were added to superheated water to selectively etch Si3N4 without material loss of the SiO2 and Si substrate.LPCVD Si3N4 film was prepared on Si wafer. A patterned Si3N4/SiO2 multi-stack structure was prepared the selective etching of Si3N4. Deionized (DI) water with a resistivity of 18.25 M was used to prepare superheated water in the reactor. Acetic acid, butyric acid, citric acid, formic acid, hexanoic acid, lactic acid or tartaric acid was added to DI water before heating. The etching of process was conducted 160 °C for 20 min. The thickness of the Si3N4 film was measured using a spectroscopic ellipsometry and a field-emission scanning electron microscope.To increase Si3N4 etching rate and suppress the material loss of the Si substrate during the Si3N4 etching process, various carboxylic acids, which are acidic and nucleophiles, were added to superheated water. The etching rates of Si3N4 in 1 M carboxylic-acid-containing superheated water at 160 °C were shown in Fig. 1(a). To reduce the effect of OH- and investigate the effect of carboxylic acid on Si3N4 etching, HCl was added to superheated water, adjusting the pH of the solution at 1, 2 and 3. Etching rates of Si3N4 are shown in Fig. 1(a). When either of tartaric acid, citric acid, lactic acid, or acetic acid was added to superheated water, Si3N4 etching rate was increased at a given pH, as compared to that obtained in HCl-added superheated water. However, when butyric acid, hexanoic acid or formic acid was added to superheated water, similar or lower etching rates of Si3N4 were observed as compared to the HCl-added superheated water. The results in Fig. 1(a) suggest that Si3N4 etching kinetics differs depending on the type of carboxylic acid added to superheated water.To investigate the reason for different Si3N4 etching rate with the type of carboxylic acid, the concentrations of carboxylate (RCOO-) ion were calculated from the pK a values of carboxylic acids at 25 °C. As shown in Fig. 1(b), the etching rates of Si3N4 increased with the concentration of carboxylate ions. Based on these results, it is thought that carboxylate ions play an important role in Si3N4 etching in superheated water. To investigate the selective Si3N4 etching ability of carboxylic-acid-containing superheated water, a Si3N4/SiO2 multi pair-layered structure on Si wafer was etched in tartaric-acid-containing superheated water. The cross-sectional FE-SEM images before and after the Si3N4 etching process were shown in Fig. 2. It is clearly shown that Si3N4 was selectively etched without material loss of SiO2 and Si substrate. Finally, eco-friendly and environmentally friendly carboxylic-acid-containing superheated water process can be a strong candidate that can replace the conventional Si3N4 etching process.

Microdisk-Type Multicolor Semipolar Nitride-Based Light-Emitting Diodes

Recently, III-nitride semiconductors have gained immense attention for application in high-performance optoelectronic devices. However, in the device fabrication process, it is essential to develop a wet-etching process for conventional polar nitride-based devices to reduce the dry-etching damage. In this study, semipolar microdisk (MD)-type light-emitting diodes (LEDs) are fabricated using only a wet-etching process. The wet-etching rate of the n-type GaN film is the highest, followed by those of the undoped and p-type GaN films. The n- and p-type GaN films exhibit upward and downward surface-band-bending heights, respectively, because of which they can easily attract and repel OH– to form Ga2O3. In addition, the fully wet-etched MD-LED shows high light extraction efficiency from the etched nanofacets because of the increase in the escape cone angle with low etching damage. The smaller diameters of the MD-LEDs result in shorter emission wavelengths, allowing multicolor emission ranging from the violet (∼420 nm) to amber (∼620 nm) wavelengths to be achieved on a single LED wafer. Thus, monolithic multicolor emissions and increased light output power are achieved by fabricating parallel-connected MD-LED arrays using only a wet-etching process.

Effect of hydrofluorocarbon structure of C3H2F6 isomers on high aspect ratio etching of silicon oxide

In this study, using three isomers (1,1,1,3,3,3-hexafluoropropane (HFC-236fa), 1,1,1,2,3,3-hexafluoropropane (HFC-236ea), 1,1,2,2,3,3-hexafluoropropane (HFC-236ca)) having the same chemical composition of C3H2F6, effects of chemical branch structure of three C3H2F6 isomers on the plasma characteristics and etch characteristics of high aspect ratio ACL patterned SiO2 were investigated. During the etching of SiO2 and amorphous carbon layer (ACL) using the three isomers mixed with oxygen, different etch characteristics and plasma characteristics were observed. In the plasmas, more CF2 and H but, less F were related to the formation of a fluorocarbon polymer layer on the surface, while lower high mass ion species such as C3HF4+ and, C3H2F5+ were related to the ion bombardment in the order of HFC-236fa, HFC-236ea, and HFC-236ca consequently leading to a lower SiO2 etch rate. Therefore, when C3H2F6 was used, even with the same chemical composition, the chemical branch structure of the compound affected the plasma properties and etch characteristics significantly depending on chemical branches in the compound. We believe that, for other hydrofluorocarbon compounds mixed with a critical oxygen flow rate, plasma properties and SiO2 etch characteristics can be estimated through properties of chemical branches attached in these compounds.

Scalable, Nanometer‐Accurate Fabrication of All‐Dielectric Metasurfaces with Narrow Resonances Tunable from Near Infrared to Visible Wavelengths

Dielectric metasurfaces are a class of flat‐optical elements that provide new ways to manipulate light. Irrespective of the underlying operation principle, the realization of such nanometer‐sized structures requires a high fabrication accuracy, e.g., to match resonant conditions. While electron‐beam lithography (EBL) achieves feature sizes below 10 nm, transparent substrates, as used for transmission devices, are challenging due to proximity effects. Furthermore, EBL's sequential exposure limits the exposable area, making it unaffordable for applications. Here, a novel fabrication route is described based on a master template created by EBL, which is then replicated by nanoimprint lithography (NIL). A three‐layer process enables high‐resolution nanoimprint resists with low etching selectivity with respect to semiconductors yet to be used. The resulting structures are highly reproducible and defect‐free thanks to the selective removal of residual layers and a master not suffering from proximity effects. Exemplarily, elliptical Mie resonators are fabricated with tunable resonances from the near infrared (NIR) to the visible wavelength regime. They reveal a high uniformity and sensitivity toward dielectric changes. The generic fabrication approach enables upscaling of nanoscale metasurfaces to wafer scales by step‐and‐repeat techniques and deployment of the optical devices fabricated in real‐world applications due to massively reduced costs.

Purity Effect of High-Strength Steel on Failure Behavior of Automobile Front Axle

As unpredictable fracture of the front axle will lead to serious safety accidents, its failure behavior study is essential. This paper analyzes typical cracks on I-shaped and leaf springs of the front axle made by Steel A and Steel B. Steel B has a lower content of S, N, Cu, and Sn than Steel A. In order to identify the failure mechanism difference, the low magnification etch test, and metallographic and scanning electron microscope analyses were conducted. The results show that the microstructures are tempered sorbite, and the cracks are with intergranular fracture characteristics. The aggregated distribution of sulfide inclusions in the matrix of Steel A is higher than that of Steel B. Copper-rich particles are detected in the cracks of Steel A. The result indicates that the purity distinction of raw steel can have a big difference on the cracking rate of the front axle even under the same manufacturing process. Relevant suggestions to reduce the cracking are put forward from the aspects of raw materials and process conditions.