Inductively Coupled Plasma Etching Research Articles

Modeling of surface evolution in plasma etching for SiC microgroove fabrication

Monocrystalline silicon carbide (SiC) has attracted attention for applications in devices operating in harsh environments due to its excellent physicochemical properties. However, it is difficult to obtain extremely small-feature sizes with undamaged surfaces due to its extremely high hardness. Herein, a novel method to fabricate SiC microgrooves is proposed that combines molding with inductively coupled plasma (ICP) etching process. First, a Ni–P microgroove master mold was fabricated by ultraprecision cutting and replicated on a polydimethylsiloxane (PDMS) surface, which was then used as the microgroove mold for hot embossing. Then, the patterned mask fabricated by hot embossing was transferred to the SiC substrate by ICP etching. To obtain customized microgrooves, an interface-evolution model based on angular dependence theory was established. A numerical method based on a string algorithm approach is developed for interface-evolution simulations. During ICP etching, the characteristic size d of homogeneous materials and the sidewall angle in heterogeneous materials varied with the sidewall angle of the SU-8 mask due to the angular dependence of etch rate. Finally, seven sets of microgrooves were machined on SU-8 to study the interface-evolution process. Variations in the characteristic size Δd and sidewall angle θ for each unit in homogeneous material, as well as the variations in sidewall angle before and after etching in heterogeneous materials are described. The high accuracy of the proposed interface-evolution model was experimentally validated.

(Invited) In-Situ MOCVD Etching of GaN Using XeF2 for Selective-Area-Epitaxial-Regrowth of p-Type GaN for High Voltage PN Diodes

PN diodes with multi-kilovolt breakdown voltages have been demonstrated to great than 6 kV in GaN, validating the device potential predicted by the intrinsic material properties of III-nitride semiconductors. However, power control circuits also require switching transistors such as junction field effect transistors (JFETs) and practical diodes such as merged PIN Schottky (MPS) diodes. Such devices usually employ selective areas of p-type semiconductor surrounded by n-type material and require the formation of PN junctions with low reverse leakage current. Selective-area p-type doping in Si and SiC based power devices is typically achieved using implantation and thermal annealing to form the p-type areas. Ion implantation of Mg in GaN has demonstrated p-type conductivity, but this process requires specialized equipment for the high-pressure and high-temperature activation of Mg dopants. We have investigated selective-area-regrowth (SArG) to epitaxially grow p-type GaN as an alternative to dopant implantation. Successful PN diode formation by SArG requires a process to remove residual crystalline damage resulting from the ex-situ inductively coupled plasma (ICP) etch typically used to form the p-well, as well as a method to remove the elevated level of Si found at the regrowth interface of a surface that had been exposed to air. For the case of SArG of p-GaN on air-exposed, blanket ICP etched n-type GaN, we present the novel use of a fluorine-based precursor (XeF2) for in-situ etching of GaN in the MOCVD chamber. Unlike chlorine (TBCl and CCl4) and bromine (CBr4) -based precursors we have studied; we obtained a smooth surface following in-situ fluorine etching of air-exposed GaN. Schottky barrier diodes (SBDs) formed by shadow mask evaporation on in-situ fluorine etched n-GaN that had been previously ICP etched showed reverse leakage currents to -40 V that are equal to those of SBDs formed on as-grown n-GaN layers. The in-situ fluorine/ICP etched Schottky diodes had reverse leakage currents more than 3 orders of magnitude lower than those formed on n-GaN layers that had only experienced ICP etching. This suggests that the in-situ fluorine etch was effective at removing the residual damage from the ICP etch process. Furthermore, we discuss the use of in-situ fluorine etching to reduce the concentration of Si at the regrowth interface required to form PN junctions with low reverse leakage current. This work was supported in part by the Advanced Research Projects Agency – Energy (ARPA-E), U.S. Department of Energy under the PNDIODES program directed by Dr. Isik Kizilyalli, and in part by the US Department of Energy (DOE) Vehicle Technologies Office (VTO) under the Electric Drive Train Consortium. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525. The views expressed in the presentation do not necessarily represent the views of the U.S. Department of Energy or the United States Government.

Enhanced light extraction efficiency of GaN-based green micro-LED modulating by a thickness-tunable SiO2 passivation structure.

Green micro-light emitting diodes (micro-LEDs) is one of the three primary color light sources as full-color display, which serves as a key research object in the field of micro-LED display. As the micro-LED size decreases, the surface-area-to-volume ratio of the device increases, leading to more serious damage on the sidewall by inductively coupled plasma (ICP) etching. The passivation process of SiO2 provides an effective method to reduce sidewall damage caused by ICP etching. In this work, green rectangular micro-LEDs with passivation layer thickness of 0∼600 nm was designed using the finite-difference time-domain (FDTD) simulation. In order to verify the simulation results, the micro-LED array was fabricated by parallel laser micro-lens array (MLA) lithography in high speed and large area. The effect of the SiO2 passivation layer thickness on the performance of the green micro-LED was analyzed, which shows that the passivation layer thickness-light extraction efficiency curve fluctuates periodically. For the sample with 90 nm thickness of SiO2 passivation layer, there exists a small leakage current and higher operating current density, and the maximum external quantum efficiency (EQE) is 2.8 times higher than micro-LED without SiO2 passivation layer.

Selective Wet and Dry Etching of NiO over β-Ga2O3

In this study, a reaction-limited chemical wet etching process of NiO by an HNO3-based solution, with a complete selectivity over β-Ga2O3 was investigated. The threshold ion energies for inductively coupled plasmas (ICP) dry etching of NiO in BCl3 discharges, its selectivity to β-Ga2O3, and the cleaning effect for chlorine-based residues remaining on the surface after plasma exposure was also examined. One of the major drawbacks of β-Ga2O3 device design is the lack of p-type dopants. An alternative approach is to use a p-type oxide, NiO, to form heterojunctions with n-type Ga2O3. Therefore, a selective wet and dry etching process development is in demand for the optimized pattern transfer process. A solution of 1 HNO3: 4 H2O exhibited measurable etch rates for NiO above 40°C and wet etching activation energy of 172.9 kJ.mol-1 (41.3 kCal.mol-1, 1.8 eV/atom), which is firmly in the reaction-limited regime. The selectivity over β-Ga2O3 was infinite for temperatures up to 55 °C. The strong negative enthalpy for producing the etch product Ga(OH)4 suggests that HNO3-based wet etching of NiO occurs via the formation and dissolution of hydroxides. The BCl3/Ar ICP etching produced maximum etch rates up to 300 Å.min-1 for NiO and 800 Å.min-1 for β-Ga2O3 under moderate plasma power conditions. The selectivity for NiO: Ga2O3 was < 1 under all conditions. The ion energy threshold for the initiation of etching NiO was between 35-60 eV, depending on the plasma power conditions. And its etching mechanism was ion-driven, as determined by the linear dependence between etch rate and the square root of ion energy incident on the surface. By sharp contrast, the etching of Ga2O3 had a stronger chemical component without a well-defined ion energy threshold. After being exposed to BCl3 plasmas, both NiO and Ga2O3 surfaces show chlorine residues, which can both be removed by the standard 1NH4OH: 10H2O or 1HCl: 10H2O solution used for native oxide removal. In addition, according to the location of the Cl 2p3/2 peak in the XPS analysis on the surface, the chlorine particles were ionically bonded. Figure 1

High-Efficiency and Reliable Value Geometric Standard: Integrated Periodic Structure Reference Materials.

Integrated periodic structure reference materials are crucial for calibration in optical instruments and micro-computed tomography (micro-CT), yet they face limitations concerning a restricted measurement range, a single pattern type, and a single calibration parameter. In this study, we address these challenges by developing integrated periodic structure reference materials with an expanded measurement range, diverse pattern types, and multiple calibration parameters through a combination of photolithography and inductively coupled plasma (ICP) etching process. These reference materials facilitate high-efficiency and multi-value calibration, finding applications in the calibration of optical instruments and micro-CT systems. The simulations were conducted using MATLAB (R2022b) to examine the structure-morphology changes during the single-step ICP etching process. The variation rules governing line widths, periods, etching depths, and side wall verticality in integrated periodic structure reference materials were thoroughly evaluated. Linewidths were accurately extracted utilizing an advanced image processing algorithm, while average period values were determined through the precise Fast Fourier Transform method. The experimental results demonstrate that the relative errors of line widths do not exceed 17.5%, and the relative errors of periods do not exceed 1.5%. Furthermore, precise control of the etching depth was achieved, ranging from 30 to 60 μm for grids with line widths 2-20 μm. The side wall verticality exhibited remarkable consistency with an angle of 90° ± 0.8°, and its relative error was found to be less than 0.9%.

Controllable Fabrication of Silicon Nanopore Arrays by Two-Step Inductively Coupled Plasma Etching Using Self-Assembled Anodic Aluminum Oxide Mask

Silicon nanopore arrays (SiNPs) were prepared by a two-step inductively coupled plasma (ICP) etching process using a self-assembled anodic aluminum oxide film mask. The influence of etching parameters (first-step etching time, Cl2 proportion in the etching gas, etching pressure, ICP power, and radio frequency (RF) power) on the morphology of the SiNPs were systematically investigated. The results revealed that the first step of ICP etching can effectively remove the barrier layer of the mask. Higher Cl2 proportion and lower etching pressure increase the chemical corrosion and physical bombardment of ICP etching, respectively, which may damage the porous morphology. ICP power affects both chemical reaction etching and physical bombardment, but the RF power mainly affects physical etching. The etching rate is positively correlated with Cl2 proportion and RF power, and negatively correlated with etching pressure. The optimized first-step etching time, Cl2/Ar ratio, etching pressure, ICP power and RF power for high-quality SiNPs are approximately 10 s, 60%, 7 mTorr, 900 W and 100 W, respectively. Precise control of the pore size and depth of the SiNPs can be achieved using this controllable growth process. These results demonstrate a simple and controllable way to achieve good quality SiNPs with desired sizes.

Redeposition-free inductively-coupled plasma etching of lithium niobate for integrated photonics

Abstract Lithium niobate on insulator is being established as a versatile platform for a new generation of photonic integrated devices. Extensive progress has been made in recent years to improve the fabrication of integrated optical circuits from a research platform towards wafer-scale fabrication in commercial foundries, and optical losses have reached remarkably low values approaching material limits. In this context, argon etching of lithium niobate waveguides has been shown to provide the best optical quality, yet the process is still challenging to optimise due to its physical nature. Namely, the micro-masking effects introduced by the material redeposition and a close to one etch mask selectivity for deep etches. We present a workflow to identify the parameter set offering the best etching results independent of the plasma system being used. We show how to reach the redeposition-free regime and propose three methods to achieve redeposition-free lithium niobate etching with good quality sidewalls without need of wet chemistry for cleaning.

Effect of RF power and gas ratio on the sidewall of β-Ga2O3 films via inductively coupled plasma etching

The beveled mesa structure of β-Ga2O3 has attracted wide attention because it can significantly weaken the peak electric field and increase the breakdown voltage. In this study, β-Ga2O3 beveled mesa has been modulated via inductively coupled plasma (ICP) etching with the etching precursors of BCl3 and Ar. And the morphology of the sidewall has been investigated by properly adjusting the etching parameters, realizing different beveled angles owing to the different ratios of chemical etching and physical etching. The effect of ICP etching on the sidewall morphology of the β-Ga2O3 beveled mesa was also studied. This study provides important guidance for the realization of higher-power devices based on β-Ga2O3.

Tuning the Plasma Etching Mode for the Atomic-Scale Smoothing of Single-Crystal Silicon

Atomic-scale smooth surfaces of single-crystal silicon (Si) are indispensable for cutting-edge applications, such as semiconductor chips, quantum devices, and X-ray optics. Here, we vary the CF4/O2 reactant gas ratio to tune the etching mode from isotropic and orientation-selective etching to atom-selective etching in an atmospheric inductively coupled plasma (ICP). At low CF4/O2 ratios, the diffusion of the etching species dominates, resulting in isotropic etching. By contrast, the kinetics of ICP etching becomes dominant upon increasing the CF4/O2 ratio to between 1:1 and 2:1, inducing orientation-selective etching. Notably, CF4/O2 ratios above 2:1 result in atom-selective etching, whereby atoms around rough surface sites can be selectively removed. The atom-selective etching mode was used to achieve an atomically smooth surface with a Sa roughness of 0.14 nm. The results of this study demonstrate that atom-selective etching is an efficient and effective approach for manufacturing Si atomic surfaces.

Synchrotron X-Ray Topography Characterization of Power Electronic GaN Materials

Synchrotron X-ray topography techniques are used to characterize the microstructures in gallium nitride materials being developed for selective area doping for power electronic applications. Bulk substrates grown by different methods, epitaxial layers that are subject to ion implantation, annealing, etching and regrowth are characterized by X-ray topography in grazing incidence geometry and X-ray rocking curve topography. Strain and tilt maps of ion implanted epitaxial layers and etched and regrown wafers are generated. From the X-ray topographs, it is concluded that ammonothermal grown substrates show the highest quality among other types and most suitable for high-end electronic applications. It is also revealed that epitaxial growth, ion implantation and the annealing process do not change the dislocation distribution, but ion implantation introduces damage, strain and lattice bending effect, which are removed after annealing. Inductively coupled plasma (ICP) etching gives rise to strain variations in the wafer, while using tertiary butyl chloride (TBCl) to etch the wafer does not affect the strain distribution and can remove some damage from a preceding ICP etching process.

Performance-enhanced NiO/β-Ga2O3 heterojunction diodes fabricated on an etched β-Ga2O3 surface

In this study, performance-enhanced NiO/β-Ga2O3 heterojunction diodes (HJDs) were realized on an etched β-Ga2O3 surface through applying a surface preparation process involving a BCl3/Cl2-based inductively coupled plasma (ICP) etch followed by a hot tetramethylammonium hydroxide (TMAH) treatment. Atomic force microscopy scan and X-ray photoelectron spectroscopy analysis revealed that the ICP etch process created a rough β-Ga2O3 surface with high density small peaks associated with Boron-related etch by-product, which resulted in a dramatic decrease of the HJDs’ breakdown voltage from 1.43 kV to 0.92 kV in average. On the other hand, the TMAH treatment effectively removed the etch-induced damages and contaminations from the β-Ga2O3 surface, therefore obviating its surface instability issue. Consequently, on the processed β-Ga2O3 surface high-quality NiO/β-Ga2O3 heterojunctions with a fully recovered breakdown voltage and an improved turn-on property were successfully formed.

Local pressure calibration method of inductively coupled plasma generator based on laser Thomson scattering measurement

Based on laser Thomson scattering (TS) measurements and finite element method (FEM) simulations of electron density in inductively coupled plasma (ICP), the simulated local pressure calibration curves of ICP generator are obtained by comparing the experimental and simulated electron density distributions and maxima. The equation coefficients of theoretical model associated with the ICP generator experimental system can be obtained by fitting the simulation curve with the least square method, and the theoretical pressure calibration curves under different absorbed powers can be further obtained. Combined with the vacuum gauge measurements, both the simulated and theoretical pressure calibration curves can give the true local pressure in the plasma. The results of the local pressure calibration at the different absorbed powers show that the density gradient from the vacuum gauge sensor to the center of the coil in ICP generator cavity becomes larger with the increase of electron density, resulting in a larger gap between the measured value and the pressure calibration value. This calibration method helps to grasp the local pressure of ICP as an external control factor and helps to study the physicochemical mechanism of ICP in order to achieve higher performance in ICP etching, material modification, etc.

Investigation of SiO2 Etch Characteristics by C6F6/Ar/O2 Plasmas Generated Using Inductively Coupled Plasma and Capacitively Coupled Plasma.

The etching properties of C6F6/Ar/O2 in both an inductively coupled plasma (ICP) system and a capacitively coupled plasma (CCP) system were evaluated to investigate the effects of high C/F ratio of perfluorocarbon (PFC) gas on the etch characteristics of SiO2. When the SiO2 masked with ACL was etched with C6F6, for the CCP system, even though the etch selectivity was very high (20 ~ infinite), due to the heavy-ion bombardment possibly caused by the less dissociated high-mass ions from C6F6, tapered SiO2 etch profiles were observed. In the case of the ICP system, due to the higher dissociation of C6F6 and O2 compared to the CCP system, the etching of SiO2 required a much lower ratio of O2/C6F6 (~1.0) while showing a higher maximum SiO2 etch rate (~400 nm/min) and a lower etch selectivity (~6.5) compared with the CCP system. For the ICP etching, even though the etch selectivity was much lower than that by the CCP etching, due to less heavy-mass-ion bombardment in addition to an adequate fluorocarbon layer formation on the substrate caused by heavily dissociated species, highly anisotropic SiO2 etch profiles could be obtained at the optimized condition of the O2/C6F6 ratio (~1.0).

Strain mapping of GaN substrates and epitaxial layers used for power electronic devices by synchrotron X-ray rocking curve topography

Strain and tilt maps of gallium nitride (GaN) materials including substrates, ion-implanted and annealed epilayers, and etched and regrown epilayers by different etching methods have been generated from synchrotron X-ray rocking curve topography. The strain map of the ammonothermal grown GaN substrate shows uniform low strain values, while that of the patterned hydride vapor phase epitaxy (HVPE) grown substrate shows high strain centers as well as uniformly distributed low strain between them. Strain variations within the as-implanted wafers and the annealed wafers are similar, while the tilt levels are significantly decreased for the annealed wafers. The inductively coupled plasma (ICP) etched and then regrown sample gives rise to the significant variations in strain values within the imaged region, while using tertiary butyl chloride (TBCl) to etch the sample does not affect the strain distribution compared to the continuously grown sample without etching and can remove some damage from a preceding ICP etching process.

Ion energy control in an industrial ICP etch chamber without bias power usage

This investigation focuses on process control for commercial inductively coupled plasma (ICP) etchers under manufacturing conditions. Plasma processes close to active zones of surface-sensitive devices are critical, demanding minimal damage caused by ion bombardment and so an excellent process understanding and control. In order to get the ion energy below the surface damage limit, RF biasing at the substrate is switched off. The plasma process then works in a downstreamlike mode. Without Faraday shielding, capacitive coupling must always be considered. Also with very low bias power, the ion energy can still be too high. Without bias power, bias matchbox capacitances are used as control elements for the ion energy. To ensure a high reliability for this control solution in a running production line, a combined RF and plasma model of the entire system with this special setup is presented and validated. The etch rate shows that the RF peak voltage measurement in the bias matchbox does not represent the ion energy at the substrate. The sheath voltage provided by the model is closely related to the ion energy and shows a reasonable correlation with the etch rate of the photoresist on test wafers. This relation shows the transition of chemical etching at low ion energies to ion-assisted etching with increasing sheath voltage.

A Selective Etching Route for Large-Scale Fabrication of β-Ga2O3 Micro-/Nanotube Arrays.

In this paper, based on the different etching characteristics between GaN and Ga2O3, large-scale and vertically aligned β-Ga2O3 nanotube (NT) and microtube (MT) arrays were fabricated on the GaN template by a facile and feasible selective etching method. GaN micro-/nanowire arrays were prepared first by inductively coupled plasma (ICP) etching using self-organized or patterning nickel masks as the etching masks, and then the Ga2O3 shell layer converted from GaN was formed by thermal oxidation, resulting in GaN@Ga2O3 micro-/nanowire arrays. After the GaN core of GaN@Ga2O3 micro-/nanowire arrays was removed by ICP etching, hollow Ga2O3 tubes were obtained successfully. The micro-/nanotubes have uniform morphology and controllable size, and the wall thickness can also be controlled with the thermal oxidation conditions. These vertical β-Ga2O3 micro-/nanotube arrays could be used as new materials for novel optoelectronic devices.

(Invited) The Application of ALD and ALE Passivated MicroLED Display

Micro LED has been engaged to the next generation display technology and evolved for various applications from several electronic manufacturers and institutions. The less than 10×10 μm2 area of micro-LEDs is desired for the high pixel per inch (PPI) of micro display but the sidewall effect from etching process will drop the quantum efficiency. Therefore, a good passivation process is essential to be introduced into micro-LED process to overcome the efficiency droop issue. The passivation technique of atomic layer deposition (ALD) enables to improve the sidewall damages from dry etching and hence the quantum efficiency of micro-LEDs can be enhanced [1, 2]. Furthermore, the improvement can be enhanced within smaller size of micro LEDs. In particular, due to the excellent uniformity and step coverage passivation by ALD Al2O3 thin films, the interest in efficient ALD equipment has gradually increased. The atomic layer etching (ALE) is an advance etching process that promises an excellent depth control in shallow device structures. This paper provides an overview of ALD and ALE process for improving the micro-LED performance.The epitaxial structure of the micro-LED structures was grown on a c-plane sapphire substrate using metal-organic chemical vapor deposition (MOCVD). Following the development of MOCVD, a transparent and ohmic p-contact of indium tin oxide (ITO) with a thickness of 100 nm was deposited by electron-beam evaporation as a transparent and ohmic p-contact. The ITO layer can result in efficient electrical current spreading and provide a transparent emission window for topside emitting devices. N-type GaN, p-type GaN, and the multiple quantum wells (MQWs) active region, which consists of twelve pairs of InGaN wells and a GaN barrier with an emission wavelength of around 445 nm, are the major epitaxial layers. The growth phases of micro-LED processing included mesa etching, ohmic contact metallization, sidewall passivation deposition using Al2O3 of thickness 21.3 nm and SiO2 of thickness 300 nm, and interconnects. The inductively coupled plasma (ICP) dry etching process is used for the mesa etching method, and SiO2 and Al2O3 passivation layers are deposited using PECVD and ALD techniques. Since Al2O3 and SiO2 are well-known dielectric materials for photonic applications, they were selected. Because of the field effect passivation produced by negative fixed charges, Al2O3 has emerged as a unique passivation material for commercial solar cells. The passivation layers tend to prevent surface recombination and reabsorption of emitted light near the etched surface during forward-biased activity. Following the deposition of the dielectric passivation layers, a hole was created using the ICP etching technique for the deposition of metal contacts. The electrode metal consisted of 50/300 nm of Ti/Au for p- and n- metal contacts deposited using electron-beam evaporation followed by rapid thermal annealing. The process flow of ALD passivated micro-LED is shown in Fig. 1(a).Fig. 1(b) showed the effect of the ALD-Al2O3 passivation technique on the EQE enhancement of µ-LEDs. According to the literature, the peak EQE of a small LED is considerably small due to the surface and nonradiative recombination of the mesa layer caused by plasma-assisted dry etching. ALD sidewall passivation is an important method for reducing plasma damage in LEDs. We can observe the 21.3 nm Al2O3 passivation on micro-LED in Fig.1(a). Therefore, Fig. 1 (b) presents the EQEs of 10 × 10-µm2 µ-LEDs with and without an Al2O3 passivation layer deposited using the ALD technology for reducing plasma damage. Compared with the device not subjected to ALD-Al2O3 passivation, the 10 × 10-µm2 array subjected to ALD-Al2O3 passivation exhibited an EQE enhancement of 37.5%. This result proves that ALD sidewall passivation can effectively reduce the sidewall damage caused by SRH nonradiative recombination and thus increase the EQE of small LEDs.

Activation of buried p-GaN through nanopipes in large-size GaN-based tunnel junction LEDs

In GaN-based light-emitting diodes (LEDs), tunnel junctions offer a way of replacing the highly resistive p-type GaN (p-GaN) ohmic contact with a low-resistance n-GaN ohmic contact. However, the p-GaN would be re-passivated by hydrogen atoms during the subsequent growth of n-GaN in a metal-organic chemical vapor deposition (MOCVD) chamber. The n-GaN layer, acting as a hydrogen diffusion barrier, hinders the thermal activation of the underlying p-GaN. Here, we report a method to thermally activate the buried p-GaN in tunnel junction LED (TJ-LED) through vertically aligned nanopipe arrays across the top n-GaN layer, which provides a hydrogen outgassing passage. The fabrication of nanopipes is realized via inductive coupled plasma etching using a mask prepared by self-assembled nanosphere arrays. As a result, we attain large-size TJ-LED chips, exhibiting nearly equivalent p-GaN activation and superior light extraction compared to conventional LEDs. Specifically, the light extraction efficiency is boosted by 44% relative to conventional LEDs at an injection current density of 100 A cm−2.

Characterization of AlN and AlScN film ICP etching for micro/nano fabrication

We investigate the inductively coupled plasma (ICP) etching characteristics of (0002) Aluminum Nitride (AlN) and Aluminum Scandium Nitride (Al0.94Sc0.06N) piezoelectric thin films as well as the implementation on piezoelectric lamb wave resonators. A profile of 84° is obtained on AlN thin film, with an etching rate of approximately 230 nm/min, and a selectivity of 0.77:1 relative to photoresist mask. A nearly 80° profile and over 30:1 selectivity are accomplished using Ni film as the etching mask. Al0.94Sc0.06N film has achieved a profile of 77° by optimizing the RF power. Finally, AlN contour mode resonators (CMRs) are fabricated and characterized, and a CMR operating at about 400 MHz with a quality factor exceeding 1600 has been demonstrated.

The dual-suppression of peak electric field in AlGaN/GaN HEMT with sandwich structure

To improve the power and RF performance of the high electron mobility transistors (HEMTs) based on AlGaN/GaN heterostructure junction, in this paper, a sandwich structure consisting of gate field plate, SiN passivation layer, and notch structure is proposed. The notch structure at the AlGaN barrier layer between the gate and drain is formed by the Inductively Coupled Plasma etching system (ICP), and the notch has a depth of 15 nm. The dual-suppression of the peak electric field contributes to the breakdown voltage of 91 V, which is a 152.8% improvement compared with the conventional HEMT. The decrease of C gd due to increase of distance between the gate electrode and the lower surface of the depletion layer contributes to the cut-off frequency of 24.1 GHz, which is an 8% improvement. Thus, this composite-structure HEMT has a JFOM of 2.2 THz V, it is an 84.6% improvement compared with the conventional gate field plate HEMT. A well suppression of current collapse is also achieved. It has potential in high power and RF applications. • The Sandwich structure manufacturing process is compatible with the conventional process for AlGaN/GaN HEMTs. • The Sandwich structure has a good suppression on the peak electric field, and it can decrease the capacitance between the gate and drain. • The Sandwich structure not only improves the breakdown characteristic but also improves the cut-off frequency characteristics. • The manufacturing process of the notch structure at AlGaN barrier layer does not cause the surface damage.