Etching Of GaN Research Articles

Passivating and low damaging plasma etching of GaN using Cl2 and SiCl4 for recessed gate MOSc-HEMT devices

Passivating and low damaging plasma etching of GaN using Cl2 and SiCl4 for recessed gate MOSc-HEMT devices

Enhanced etching of GaN with N2 gas addition during CVD diamond growth

Diamond on GaN materials processing is not straight-forward, as GaN is susceptible to a quasi-pure hydrogen CVD plasma etching. 1%, 3% and 5% N2 gas was gradually added to the H2 gas with fixed 6% CH4 in the recipe to promote the growth of diamond nanocrystals. Different types of microstructures were produced, with addition of nitrogen to the precursor gas recipe. Nitrogen gas changes the diamond film microstructure from faceted to spherical grains, with signs of GaN etching. The FWHM of the sp3 carbon Raman peak was calculated to be 6.5 cm−1, when there was no nitrogen gas in the precursor recipe, which deteriorates to a large extent after successive addition of N2. Fourier transform infrared spectroscopy (FTIR) showed a strong presence of the nitrogen related defects (peak positions at 1190 and 1299 cm−1) inside the nanocrystalline diamond (NCD) films grown with N2 addition. GaN layer etching from the base substrate by the CVD plasma was clearly evidenced by energy dispersive X-ray spectra (EDS) of the deposited films. Al elemental EDS peaks from the base sapphire substrate were observed for the films grown with nitrogen addition, but no Ga EDS peaks were detected. X-ray diffraction (XRD) micrographs further supported the enhanced GaN etching phenomenon. The electrical resistivity of the uncoated GaN was initially measured to be 22.2 Ω-cm. However, the resistivity rose to 1.59 × 106 Ω-cm after the nitrogen assisted film deposition; due to the GaN etching - thereby exposing the underlying insulating sapphire substrate.

Performance evaluation of GaN etching using Cl2-based plasma with bias pulsing

Reducing plasma-induced damage (PID) is one of the most challenging goals for the fabrication of GaN-based MOS-HEMT. In this paper, we propose a performance evaluation of a Cl2-based etching chemistry using bias pulsing mode for GaN applications. The plasma-induced damage using bias pulsing has been compared to conventional reactive ion etching (RIE) and atomic layer etching (ALE) processes using sheet resistance (Rsheet) measurements. This pulsing mode showed low plasma-induced damage, similar to ALE. In addition, it keeps an acceptable GaN etching rate, showing that pulsing mode has potential for industrial applications.

Demystifying metal-assisted chemical etching of GaN and related heterojunctions

GaN and related semiconductors have become an increasingly prominent material for a wide range of active and passive devices from optoelectronics to high frequency and power electronics as well as photocatalysis. Regardless of the application, anisotropic etching is required for micro and nano structuring, currently performed by reactive ion etching (RIE). Alternately, metal-assisted chemical etching (MacEtch) is an open-circuit plasma-free anisotropic etching method that has demonstrated high aspect ratio device structures devoid of plasma-induced damage found in RIE. This paper presents an in-depth study of the ensemble electrochemical mechanisms that govern the photo-enhanced MacEtch process of GaN and related heterojunctions. Through in-depth experimental investigations, modeling and simulations, the effects of local cathode and anode design, energy-band alignments, and solution chemistry on MacEtch are correlated with the underlying electronic mechanisms of carrier generation, annihilation, transport, and extraction, establishing a fundamental framework for parametrized prediction of system behavior. These findings carry profound implications for tailored design of photoelectrochemical processes employed not just for uniformly etching wide/ultrawide bandgap materials but more broadly for semiconductor-based photocatalytic reactions in general. One-pot photo-enhanced MacEtching of AlInGaN multi-heterojunction device structures including superlattices and multi-quantum wells are demonstrated.

Electrochemical etching of n-type GaN in different electrolytes

Nanosized pores were introduced into GaN epitaxial films via electrochemical (EC) etching in strong electrolytes including NaOH, HNO3, NaNO3, and NaCl. The growth behaviors of GaN nanopores show a strong correlation with the electrolyte types under the same applied bias and electrolyte concentration. Specifically, the resulting morphologies (e.g. pore growth direction and pore size) were mainly pertinent to the anions instead of cations. Pore sizes as small as a few nanometers and pore directions between the horizontal and vertical directions can be adjusted by selecting the electrolytes and etching voltages. The depletion model was employed to interpret the carrier flow pathways, and the pore propagation direction can be regarded as the sum of etch rate vectors of intended etching direction and preferential oxidation direction. Finally, the near-infrared nanoporous (NP) GaN distributed Bragg reflectors (DBRs) were manufactured by the EC etching in different electrolytes. Our study points out that the type of anions in electrolyte greatly impacts pore morphologies of EC etched GaN:Si, thereby affecting the future applications.

Faceting mechanisms of GaN nanopillar under KOH wet etching

This study presents strategies for achieving GaN pillars with the desired m- (or even a-) oriented nonpolar facets through a top-down approach that combines plasma etching followed by room temperature KOH wet treatment processes. Indeed, GaN etching in KOH solution is an anisotropic process, meaning that it allows the appearance of stable facets at the macroscopic scale, while atomic processes, such as step-flow, drive the fundamental mechanisms of the wet etching at the microscopic scale. Our study highlights the key role played by both the shape (circular or hexagonal, aligned with either the m-planes or the a-planes) and the roughness of the hard mask in determining the resulting crystalline facet formation and their associated roughness. Furthermore, it underscores the importance of the GaN pillar profiles (reentrant, straight, tapered) after plasma patterning, as they strongly influence the subsequent wet etching mechanisms. Ultimately, the article demonstrates that smooth m-oriented facets can be achieved by using room temperature wet KOH (44 wt%) on slightly sloped GaN profiles after plasma etching, in conjunction with the use of hexagonal m-oriented hard masks.

Depth Analyses of Mg‐Acceptor and Si‐Donor Concentrations in GaN by Combining Stepwise Etching and Photoluminescence

The depth profiles of the Mg‐acceptor or Si‐donor concentration in GaN are visualized using stepwise etching and photoluminescence (PL) measurements. Low‐damage etching techniques are applied: multistep‐bias inductively coupled plasma reactive ion etching for p‐type GaN and electrochemical etching for n‐type GaN. To determine the concentration calibration curve, the PL intensity ratios of Mg‐neutral acceptor or Si‐neutral donor‐bound excitons to free excitons are plotted against Mg or Si atomic concentrations in etched GaN epitaxial layers having depth distributions of dopant concentrations, as estimated by secondary ion mass spectrometry. The quantitative accuracy of the calibration curve is ensured by the appropriate sample temperature and excitation density ranges for PL. The stepwise dry etching and the Mg acceptor quantification by PL using this calibration curve are applied to Mg‐ion‐implanted GaN after ultra‐high‐pressure annealing at 1300 °C for 1 min. The obtained depth profile of the Mg‐acceptor concentration is consistent with the Mg atomic concentration profile in the region deeper than the implantation peak, whereas the acceptor concentration in the shallow region is lower than the Mg atomic concentration. This analysis is useful for revealing the site substitution ratio of dopants in GaN materials partially involving inactive dopants.

(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.

Analysis of Operational Characteristics of AlGaN/GaN MIS-HEMT with Different Slant-Recessed-Gate Structures

Purpose of WorkRecessed-gate metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs) have emerged as a promising technology for normally-off operation because of their ability to withstand high gate voltage sweeps while maintaining low levels of leakage current [1, 2]. Despite their excellent performance, the etch to leave nanometer-thin layers of AlGaN has proven to be a significant challenge due to difficulties in precisely controlling the etching process. Achieving a positive threshold voltage (Vth) while maintaining the high electron mobility characteristic of the two-dimensional electron gas (2DEG) requires atom-level etch control. Additionally, conventional dry etching techniques can potentially cause damage, presenting a second challenge [3]. However, atomic layer etching (ALE) offers a promising solution with its potential for low damage, uniformity, and high-resolution depth control [4]. In this work, we not only focus on the ALE process to leave nanometer-thin layers of AlGaN/GaN as recessed-gate structures but also analyze the breakdown voltage characteristics of the slant-recessed gate structure.ApproachNormally-off AlGaN/GaN MIS-HEMT with a recessed gate structure was fabricated on a 6-inch commercial Si substrate by MOCVD. The process involved mesa isolation by ICP-RIE, followed by the formation of the ohmic contact (Ti/Al/Ni/Au) at 825 °C annealing for source and drain metals, and the AlGaN/GaN recessed gate structure using ALE technology by O2/BCl3 multiple cycles of oxidation and etching [5]. After the recessed-gate process, the native oxide and carbon residue were removed by a wet cleaning process and O2 plasma treatment, and then the atom layer deposition (ALD) of about 12 nm thickness Al2O3 high-dielectric layer was also deposited. The backend process included gate field plate, SiNx passivation, and contact opening. Finally, the Ni/Au metal stack was deposited as pad electrodes, as shown in Fig. 1. The specific characteristics of the fabricated recessed MIS-HEMT were Lg of 3 μm, Lgs of 5 μm, Lgd of 10 μm, and Wg of 100 μm.Results and SignificanceIn Figure 2(a) and (b), TEM profiles of the recessed gate structure were presented. Following the ALE process for the recessed gate structure, the remaining thickness of AlGaN was approximately 5.1 nm and 5.6 nm for Slant A and Slant B, respectively. Although the thickness of AlGaN remaining was similar in both cases, the slant angle of the recessed gate structure differed, significantly. Specifically, Slant A had a 65-degree recessed gate structure, while Slant B had a 45-degree recessed gate structure. In order to analyze of operational characteristics of AlGaN/GaN MIS-HEMT with different slant-recessed gate structures (Slant A and Slant B), the three-terminal OFF-state breakdown voltage (BV) was measured, as shown in Fig. 3. Recessed gate MIS-HEMT feature design of Lg/Lgd/Lgd/Wg of 3/5/10/100 μm, and VG of -10 V was used as this BV measured condition. The Slant B structure demonstrated higher breakdown voltage (BV) performance compared to the Slant A structure. Specifically, the Slant B structure exhibited a BV of 470 V at 1 μA/mm and 750 V at 1 mA/mm, while the Slant A structure had a BV of only 70 V at 1 μA/mm and 140 V at 1 mA/mm. The reason for the superior BV performance of the Slant B structure (45-degree recessed gate structure) was attributed to the gradient of the AlGaN profile, which facilitates the thin film deposition process of materials such as Al2O3 and gate metal (Ni/Au). Additionally, the Slant B structure helps to reduce the high electric field effect between the gate and drain, further contributing to its improved BV performance.[1] Y. S. Lin, Y. W. Lain, and S. S. H. Hsu, "AlGaN/GaN HEMTs With Low Leakage Current and High On/Off Current Ratio," IEEE Electron Device Letters, vol. 31, no. 2, pp. 102-104, 2010.[2] Z. Tang et al., "600-V Normally Off SiNx/AlGaN/GaN MIS-HEMT With Large Gate Swing and Low Current Collapse," IEEE Electron Device Letters, vol. 34, no. 11, pp. 1373-1375, 2013.[3] T. H. Hung, P. S. Park, S. Krishnamoorthy, D. N. Nath, and S. Rajan, "Interface Charge Engineering for Enhancement-Mode GaN MISHEMTs," IEEE Electron Device Letters, vol. 35, no. 3, pp. 312-314, 2014.[4] T. Y. Yang et al., "A Normally-Off GaN MIS-HEMT Fabricated Using Atomic Layer Etching to Improve Device Performance Uniformity for High Power Applications," IEEE Electron Device Letters, vol. 43, no. 10, pp. 1629-1632, 2022.[5] I.-H. Hwang, H.-Y. Cha, and K.-S. Seo, "Low-Damage and Self-Limiting (Al)GaN Etching Process through Atomic Layer Etching Using O2 and BCl3 Plasma," Coatings, vol. 11, no. 3, p. 268, 2021. Figure 1

(Invited) Selective Area Growth, Etching, and Doping of GaN By MOCVD for Power Electronics

The lack of selective-area doping technique in GaN greatly hinders the demonstration of sophisticated device structures for high power application. We explored the possibility of using selective-area etching followed by selective area growth to achieve SAD. For the etching step, we explored the in-situ TBCl etching, where we achieved controlled etch rate and smooth trenches. The TBCl etching was proven to be a low-damage etching process compared to the conventional dry etching. Moreover, selective area growth of p-GaN in a patterned trench was analyzed by atom probe tomography (APT). We found Mg atoms cannot diffuse on the GaN surface, which led to an observed inverse proportionality between Mg concentration and local growth rate. However, it was discovered that Mg precursors, like Ga, exhibit inter-trench diffusion through the gas phase.

A novel mild etchant for photoelectrochemical etching of GaN with enhanced photoresponse

A novel mild etchant, i.e., taurine aqueous solution, was used to photoelectrochemical etching of GaN. The pore shape of etched GaN can be regulated via etching time, and the etching process had no influence on the crystal integration and stress property of GaN. The photocurrents of etched GaN were larger than that of as-grown planar GaN, demonstrating its potential for photoelectric fields.

Isotropic atomic layer etching of GaN using SF6 plasma and Al(CH3)3

GaN is an enabling material for light emitting diodes, advanced radio frequency, and power semiconductor devices. However, fabrication of GaN devices often relies on harsh etch processes, which can leave an etch damage layer, limiting final device performance. In this work, an isotropic atomic layer etching (ALE) process involving SF6 plasma and trimethylaluminium [Al(CH3)3] is presented for the controlled etching of GaN, which reduces oxygen and carbon contamination while smoothing the surface. The ALE chemistry was first examined with density functional theory. A comparison between proposed thermal and plasma-driven reactions is made by implementing Natarajan–Elliott analysis, highlighting that the plasma process is a good candidate for GaN ALE. Saturation was experimentally confirmed for both ALE half-cycles at 150 and 300 °C, with etch rates of 0.31 ± 0.01 and 0.40 ± 0.02 nm/cycle, respectively. Analysis of the films post-ALE shows that the RMS roughness of the films decreases from 2.6 ± 0.1 to 1.9 ± 0.1 nm after 25 nm of etching at 300 °C, in agreement with a previously developed curvature-dependent smoothing model. Taken together, this ALE process enables accurate GaN thickness tuning, surface cleaning, and surface smoothing, allowing for further development of GaN devices.

Hydrogen iodide (HI) neutral beam etching characteristics of InGaN and GaN for micro-LED fabrication

We investigated the etching characteristics of hydrogen iodide (HI) neutral beam etching (NBE) of GaN and InGaN and compared with Cl2 NBE. We showed the advantages of HI NBE versus Cl2 NBE, namely: higher InGaN etch rate, better surface smoothness, and significantly reduced etching residues. Moreover, HI NBE was suppressed of yellow luminescence compared with Cl2 plasma. InCl x is a product of Cl2 NBE. It does not evaporate and remains on the surface as a residue, resulting in a low InGaN etching rate. We found that HI NBE has a higher reactivity with In resulting in InGaN etch rates up to 6.3 nm min−1, and low activation energy for InGaN of approximately 0.015 eV, and a thinner reaction layer than Cl2 NBE due to high volatility of In-I compounds. HI NBE resulted in smoother etching surface with a root mean square average (rms) of 2.9 nm of HI NBE than Cl2 NBE (rms: 4.3 nm) with controlled etching residue. Moreover, the defect generation was suppressed in HI NBE compared to Cl2 plasma, as indicated by lower yellow luminescence intensity increase after etching. Therefore, HI NBE is potentially useful for high throughput fabrication of μLEDs.

Preferential crystal orientation etching of GaN nanopillars in Cl2 plasma

The ability to fabricate organized, dense arrays of GaN nanostructures with high aspect ratios is of great interest for improving light extraction and absorption in optoelectronic devices, such as light-emitting diodes (LEDs) and Lasers.However, achieving this requires a patterning method that allows for the fabrication of GaN nanostructures with a controlled final shape and specific crystallographic facets. Our study shows that a top-down approach combining lithography and Cl2-based plasma etching processes offers the possibility of anisotropically transferring a pattern while revealing smooth nonpolar facets.Although GaN etching in Cl2 is driven by ion-enhanced chemical etching mechanisms, the chemical component is very strong, and Cl2 plasma leads to preferential crystallographic orientation etching of GaN. The mechanisms that drive facet formation are very similar to those involved in wet KOH etching. The etching ability of a specific crystallographic plane by chlorine atoms depends on the planar density and the N dangling bonds present on the plane. Predictably, GaN crystallographic planes will be etched in Cl2 plasmas as follows: a-type semipolar > m-type semipolar planes > a nonpolar plane > m polar planes > c polar planes. Crystallographic etching usually reveals the slowest etching planes, meaning the m-planes. However, consistently with the wet mechanisms, our study shows that the final revealed plane in Cl2 plasma will strongly depend on the surface curvature: in concave surfaces, fast-etch facets persist, while in convex surfaces, slow-etch facets persist. Consequently, Cl2 plasma etching of pillars (convex surfaces) will result in a-type facets, while etching of holes (concave surfaces) result in m-type facets.

Atomic layer etching of gallium nitride using fluorine-based chemistry

Atomic layer etching (ALE) of GaN on silicon substrates has been investigated using fluorine-based chemistry. The ALE process used for this study consists of a modification step using SF6 plasma and a removal step using argon plasma. Two configurations were studied in which the distance between the sample and the plasma source was modified. The energy scan, synergy, selective etching of GaFx by Ar+ ion bombardment, and self-limiting etching regime of the ALE of GaN were first investigated. An etch per cycle of 0.50 nm/cycle averaged over 100 cycles was reached for GaN ALE. The self-limiting regime was also obtained for both SF6 and argon plasma steps. Moreover, a synergy rate as high as 78% was achieved. It was found that the GaFx-modified layer can be selectively sputtered by applying a self-bias voltage while the argon ion energy is maintained below the sputtering threshold of GaN.

A study of thermal etching of GaN by atmospheric argon inductively coupled plasma

GaN has a wide application in electronics and optoelectronics due to its excellent electrical properties. The thermal etching process is commonly used in the growth and subsequent process of GaN. As an easy-to-operate technique, atmospheric argon inductively coupled plasma (Ar-ICP) is first applied to the thermal etching of GaN in this study. Through the analysis of surface chemical composition and near-surface plasma spectroscopy, the etching principle and mechanism of the circular etching pit formation are revealed. The maximum material removal rate of Ar-ICP thermal etching can reach 18.72 μm/min. The optical properties of the sliced GaN after the Ar-ICP thermal etching and lapping process are evaluated by photoluminescence (PL), respectively. The PL intensity of the Ar-ICP thermally etched sample increases and the peak position of near-band emission shows a red shift compared to the lapped sample.

Highly efficient and atomic scale polishing of GaN via plasma-based atom-selective etching

Plasma-based atom-selective etching (PASE) of GaN is conducted to realize the highly efficient planarization of the GaN surface. Inductively coupled plasma with high temperature and high concentration of radicals is used as the source of PASE. The non-toxic carbon tetrafluoride is chosen over chlorine as the reaction gas, and the volatility of the etching products will be improved at high temperatures in the PASE of GaN. After 2 min of PASE, the GaN surface roughness is reduced from Sa 135.8 nm to Sa 0.527 nm. The material removal rate of PASE of GaN is measured to be 93.01 μm/min, thousands of times higher than that of the conventional chemical mechanical polishing method. The crystal structure of the GaN subsurface is well-ordered without any damage or defects. PASE is thus proven to be a non-destructive etching method. In this study, the effects of radio frequency power and reaction gas flow rate on PASE are also investigated. Surface temperature and concentration of radicals are found to be the critical factors in the PASE of GaN.

GaN damage-free cyclic etching by sequential exposure to Cl2 plasma and Ar plasma with low Ar+-ion energy at substrate temperature of 400 °C

Damage-free atomic layer etching (ALE) of GaN was demonstrated using a cyclic process in which the chlorinated layer formed by Cl2 plasma exposure was removed by exposure to Ar plasma with energy-controlled ions when the substrate temperature was maintained at 400 °C. The layer chlorinated at 400 °C by Cl2 plasma exposure was found to be thinner than that chlorinated at 25 °C. Therefore, in the case of an Ar+-ion energy of 70 eV, the “ALE synergy” parameter, which quantifies the degree to which a process approaches the ideal ALE regime, decreased from 86% at a substrate temperature of 25 °C to 24% at a substrate temperature of 400 °C. A substrate temperature of 400 °C promoted etching even at the lower ion energy of 40 eV, thereby resulting in a higher ALE synergy of 62%. The vertical etching profile with no degradation of photoluminescence near the band edge on the etched surface was then observed. The proposed high-temperature ALE method is promising for realizing a vertical pattern profile via damage-free etching of GaN.

Use of Laser Interferometry to Determine the End Time of the Plasma-Chemical Etching of p-GaN and AlGaN Layers of the p-GaN/AlGaN/GaN Heterostructure with Two-Dimensional Electron Gas

Regularities of the reflected signal intensity changing in time, recorded by the detector of the laser interferometer with the operating frequency of 670 nm during the inductively coupled plasma reactive ion etching in a Cl2/N2/O2 atmosphere of GaN, p-GaN and AlGaN in AlGaN/GaN and p-GaN/AlGaN/GaN heterostructures has been established by laser interferometry and scanning electron microscopy methods due to the changes in refractive indices and etching rates. During inductively coupled plasma reactive ion etching of GaN and p-GaN layers, the intensity of the reflected signal changes according to a periodic law with the thickness change period of about 144 nm, and for AlGaN layers about 148 nm, which is due to differences in their refractive indices and etching rates. During the crossing of the p-GaN/AlGaN and AlGaN/GaN interface, there is an abrupt change in the intensity of the reflected signal within 2.7–9.5 % for 20–40 s, due to changes in the aluminum concentration, refractive indices, and etching rate at the interfaces. The change in the periodicity of the interferogram, which is accompanied by a jump in intensity when passing through the etching front through the p-GaN/AlGaN and AlGaN/GaN interface, makes it possible to determine the end time of the inductively coupled plasma reactive ion etching of the AlGaN and p-GaN layers using laser interferometry in real time in AlGaN/GaN and p-GaN/AlGaN/GaN heterostructures with two-dimensional electron gas. The obtained results can be used to form microwave and power electronics devices elements which are based on the AlGaN/GaN heterostructures.

Influence of the Cl2 etching on the Al2O3/GaN metal–oxide–semiconductor interface

Controlling the plasma etching step involved in metal-oxide-semiconductor high-electron-mobility-transistor (MOSHEMT) GaN fabrication is essential for device performance and reliability. In particular, understanding the impact of GaN etching conditions on dielectric/GaN interface chemical properties is critically important. In this work, we investigate the impact of the carrier wafers (Si, photoresist, SiO2, and Si3N4) used during the etching of GaN in chlorine plasma on the electrical behavior of Al2O3/n-GaN metal–oxide–semiconductor (MOS) capacitors. X-ray Photoelectron spectroscopy (XPS) analyses show that the Al2O3/GaN interface layer contains contaminants from the etching process after the Al2O3 deposition. Their chemical nature depends on the plasma chemistry used as well as the chemical nature of the carrier wafer. Typically, Cl and C are trapped at the interface for all substrates. In the particular case of Si carrier wafer, a significant amount of SiOx is present at the Al2O3/GaN interface. The capacitance–voltage (C–V) characteristics of the MOS capacitors indicate that the presence of Si residues at the interface shifts the flat band voltage to negative values, while the presence of Cl or C at the interface increases the hysteresis. We demonstrate that introducing an in situ plasma cleaning treatment based on N2/H2 gas, before the atomic layer deposition, allows the removal of most of the residues except silicon and suppresses the hysteresis.