The reactive ion etching characteristics of gallium nitride (GaN) in silicon tetrachloride plasmas (SiCl4, 1:1/SiCl4:Ar, and 1:1/SiCl4:SiF4) in the pressure range between 20 and 80 mTorr have been investigated. For the pressure range investigated, etch rates are found to be essentially identical for the different gas mixtures and also invariant with pressure. However for all gas mixtures, etch rates increased monotonically with increasing plasma self‐bias voltage exceeding 50 nm/min at 400 V. This is one of the highest etch rate ever reported for GaN. Smooth and anisotropic etch profiles are demonstrated for structures of submicrometer dimensions. The slight overcut observed in the etch profiles is attributed to the significant role of physical ion bombardment in the etching mechanism. Auger electron spectroscopy show that a wet etch in dilute HF is needed to clear the Si (in the form of SiOx) embedded in the near surface of GaN during etching thereby restoring etched surfaces to their virgin state.

Reactive ion etching of gallium nitride in silicon tetrachloride plasmasa)

In this paper, general aspects of the reactive ion etching (RIE) technique will be described, such as anisotropy, loading effect, lag effect, RIE chemistries and micro-masking, followed by a brief overview of etching dielectrics (SiOx, SiNx) and crystalline Si. The second section of the paper is dedicated to etching III–V compound semiconductors where, based on RIE results of GaN material, a simple and practical thermodynamic approach is exposed, explaining the criteria for selecting the best chemistry for etching a specific material and explaining the GaN etching results. Finally, a comprehensive study of etching InP-based materials using various chemistries will be discussed, as well as their various photonic applications.

https://iopscience.iop.org/article/10.1088/0022-3727/47/23/233501/pdf

A practical approach to reactive ion etching

The etching characteristics of AlxGa1-xAs in citric acid/H2O2 solutions and SiCl4/SiF4 plasmas have been studied. Using a 4:1 solution of citric acid/H2O2 at 20° C, selectivities of 155, 260, and 1450 have been obtained for GaAs on AlxGa1-xAs withx = 0.3,x = 0.45, andx = 1.0, respectively. Etch rates of GaAs in this solution were found to be independent of line widths and crystal orientations for etched depths up to 1000A. GaAs etch profiles along [110] and [110] directions displayed different slope angles as expected. Selective reactive ion etching (SRIE) using SiCl4/SiF4 gas mixtures at 90 mTorr and -60 V self-biased voltage yielded selectivities between 200 and 500 forx values ranging from 0.17 to 1.0. SRIE etch rates for GaAs were relatively constant for etch depths of less than 1000A. At greater etch depths, etch rates varied by up to 76% for line widths between 0.3 and 1.0µm. Both selective wet etch and dry etch processes were applied to the fabrication of pseudomorphic GaAs/AIGaAs/lnGaAs MODFETs with gate lengths ranging from 0.3 to 2.5 µm on heterostructures with an embedded thin AlAs etch stop layer. A threshold voltage standard deviation of 13.5 mV for 0.3 µ gate-length MODFETs was achieved using a 4:1 citric acid/H2O2 solution for gate recessing. This result compares favorably with the 40 mV obtained using SRIE, and is much superior to the 230 mV achieved using the nonselective etch of 3:1:50 H3PO4: H2O2: H2O. This shows that selective wet etching using citric acid/H2O2 solutions in conjunction with a thin AlxGa1-xAs(x ≥ 0.45) etch stop layer provides a reasonably simple, safe, and reliable process for gate recessing in the fabrication of pseudomorphic MODFETs.

A comparative study of wet and dry selective etching processes for GaAs/AIGaAs/InGaAs pseudomorphic MODFETs

Semiconductor nanowaveguides are the key structure for light-guiding nanophotonics applications. Efficient guiding and confinement of single-mode light in these waveguides require high aspect ratio geometries. In these conditions, sidewall verticality becomes crucial. We fabricated such structures using a top-down process combining electron beam lithography and inductively coupled plasma (ICP) etching of hard masks and GaAs/AlGaAs semiconductors with Al concentrations varying from 0 to 100%. The GaAs/AlGaAs plasma etching was a single-step process using a Cl2/BCl3/Ar gas mixture with various fractions of N2. Scanning electron microscope (SEM) observations showed that the presence of nitrogen generated the deposition of a passivation layer, which had a significant effect on sidewall slope. Near-ideal vertical sidewalls were obtained over a very narrow range of N2, allowing the production of extremely high aspect ratios (>32) for 80 nm wide nanowaveguides.

https://iopscience.iop.org/article/10.1088/0957-4484/21/13/134014/pdf

Extremely high aspect ratio GaAs and GaAs/AlGaAs nanowaveguides fabricated using chlorine ICP etching with N2-promoted passivation

This letter introduces a novel inductively coupled plasma-reactive ion etching (ICP-RIE) technique based on a BCl3/SiCl4/Ar chemistry for fabricating sub-20 nm diameter InGaAs nanowires with smooth, vertical sidewall and high aspect ratio (>10). To mitigate dry-etch damage, RIE is followed by a digital etch method comprised of multiple cycles of self-limiting low power O2 plasma oxidation and diluted H2SO4 rinse. Using these technologies, we demonstrate vertical InGaAs gateall-around nanowire MOSFETs with 30 nm diameter. Digital etch improves both the subthreshold swing and peak transconductance, indicating enhanced sidewall interfacial quality. The combination of RIE and digital etch techniques proposed here is promising for future 3-D III-V MOSFETs.

Nanometer-Scale Vertical-Sidewall Reactive Ion Etching of InGaAs for 3-D III-V MOSFETs

Nanometer‐scale gratings have been fabricated in InP and InGaAs/InP heterostructures using electron‐beam lithography and reactive‐ion etching in methane‐hydrogen plasmas. It is shown that the slight overcut obtained in the etch profiles during a single‐step etch in CH4/H2 is due to polymer formation on inert mask surfaces and edges. Intermittent removal of the deposited polymer film is shown to be effective in obtaining anisotropic profiles. Highly anisotropic 35‐nm‐wide InP lines at 70‐nm pitch demonstrate the potential of this fabrication process. The formation of 100‐nm‐wide free‐standing InP wires is also presented.

Nanostructure fabrication in InP and related compounds

Selective reactive ion etching of GaAs over AlxGa1−xAs using SiF4/SiCl4 gas mixtures is studied. Etch rates of GaAs and AlxGa1−xAs are measured versus pressure, etch gas ratio, and plasma self‐bias voltage. A selectivity ratio of 500:1 has been obtained for GaAs over Al0.35Ga0.65As at a gas composition ratio of SiCl4/SiF4=0.25, a pressure of 60 mTorr, and a self‐bias voltage of −60 V. The etch stop mechanism is studied using Auger electron spectroscopy. Auger surface scan spectra indicate a high concentration of fluorine at the surface of etched AlGaAs samples suggesting the formation of an AlF3 etch stop layer.1 It is also shown that the AlF3 layer is easily removed with a very short dip in HCl/H2O or NH4OH/H2O. Hall effect measurements at 300 and 77 K are made on etched GaAs/Al0.3Ga0.7As modulation doped heterostructures to determine the effect of low‐power etching on two‐dimensional electron gas (2‐DEG) sheet concentrations and carrier mobility. Slight reduction in both 2‐DEG sheet carrier concentratio...

Characterization of GaAs/AlxGa1−xAs selective reactive ion etching in SiCl4/SiF4 plasmas

Selective reactive ion etching of GaAs on AlGaAs in SiCl4/SiF4 plasma is reported. A selectivity ratio of 350:1 has been obtained at low power. A small decrease in the saturation current of gateless MODFET structures has been observed after etching the GaAs cap layer and has been ascribed to be due to low‐power ion damage of the AlGaAs layer. This process was applied to the fabrication of 0.2 μm T‐gate pseudomorphic MODFET’s. The dc and microwave performance of reactive‐ion‐etched devices and wet‐etched devices were identical. However, for these short‐gate‐length devices a threshold voltage standard deviation of 30 mV was obtained for the reactive‐ion‐etched devices as compared to 230 mV for the wet‐etched devices.

Selective reactive ion etching for short-gate-length GaAs/AlGaAs/InGaAs pseudomorphic modulation-doped field-effect transistors

The reactive ion etching in InGaAsP and InP have been characterized in methane‐based plasma. The role of H2, He, and Ar as diluents have been investigated. Highly anisotropic short‐period gratings with periods as small as 0.2 μm and with smooth etched surfaces are presented. Auger electron spectroscopy has been used to delineate a proper processing sequence to obtain etched surfaces as clean as the surface of control samples. The CH4/He gas mixture is suggested for the fabrication of gratings as a compromise for achieving good etched profiles as well as to minimize hydrogen passivation of donors in etched samples.

E. Andideh

Papers

Nanostructure fabrication in InP and related compounds

Characterization of GaAs/AlxGa1−xAs selective reactive ion etching in SiCl4/SiF4 plasmas

Selective reactive ion etching for short-gate-length GaAs/AlGaAs/InGaAs pseudomorphic modulation-doped field-effect transistors

Short‐period gratings for long‐wavelength optical devices