Inductively Coupled Plasma Etching in ICl- and IBr-Based Chemistries. Part II: InP, InSb, InGaP, and InGaAs

A parametric study of Inductively Coupled Plasma (ICP) etching of InP, InSb, InGaP, and InGaAs has been carried out in ICl/Ar and IBr/Ar chemistries. Etch rates in excess of 3.1 for InP, 3.6 for InSb, 2.3 for InGaP, and 2.2 m/min for InGaAs were obtained in IBr/Ar plasmas. The ICP etching of In-based materials showed a general tendency: The etch rates increased substantially with increasing ICP source power and rf chuck power in both chemistries, while they decreased with increasing chamber pressure. The IBr/Ar chemistry typically showed higher etch rates than ICl/Ar, but the etched surface morphologies were fairly poor for both chemistries.     

Plasma etching of III–V semiconductors in BCl3 chemistries: Part I: GaAs and related compounds

BCl₃/Ar discharges provide rapid, smooth pattern transfer in GaAs, AlGaAs, GaP, and GaSb over a wide range of plasma conditions. At high BCl₃-to-Ar ratio there is significant surface roughening on GaSb, which is correlated with the presence of B- and Cl-containing residues detected by Auger electron spectroscopy. BCl₃/N₂ discharges provide similar etch rates to BCl₃/Ar, but when used with photoresist masks lead to rough morphologies on the semiconductor materials due to enhanced dissociation and redeposition of the resist. Etch rates with electron cyclotron resonance discharges are up to two orders of magnitude higher than for rf-only conditions.     

Plasma etching of III–V semiconductors in BCl3 chemistries: Part II: InP and related compounds

BCl₃/Ar and BCl₃/N₂ plasma chemistries were compared for patterning of InP, InAs, InSb, InGaAs, InGaAsP, and AlInAs. Under electron cyclotron resonance conditions etch rates in excess of 1 μm/min can be achieved at room temperature with low additional rf chuck power (150 W). The etch rates are similar for both chemistries, with smoother surface morphologies for BCl₃/Ar. However, the surfaces are still approximately an order of magnitude rougher (as quantified by atomic force microscopy) than those obtained under the same conditions with Cl₂/Ar. InP surfaces etched at high BCl₃-to-Ar ratios have measurable concentrations of boron-and chlorine-containing residues.     

Temperature-dependent dry etching characteristics of III–V semiconductors in HBr- and HI-based discharges

Microwave discharges of HBr/H₂/Ar and H/H₂/Ar with additional do biasing of the sample were used to etch InP, GaAs, and AlGaAs at temperatures between 50–250°C. The etch rates increase by factors of 3–50 and 5–9, respectively, for HBr-and HI-based discharges over this temperature range, but display non-Arrhenius behavior. The etched surfaces became very rough above 100°C for InP with either discharge chemistry due to preferential loss of P, while GaAs and AlGaAs are more tolerant of the elevated temperature etching. The near-surface electrical properties of InP are severely degraded by etch temperatures above 100°C, while extensive hydrogen in-diffusion occurs in GaAs and AlGaAs under these conditions, leading to dopant passivation which can be reversed by annealing at 400°C.     

Etching Mechanism of Pb(Zr,Ti)O3 Thin Films in Cl2/Ar Plasma

The etching mechanism of Pb(Zr,Ti)O₃ (PZT) thin films in Cl₂/Ar plasma was investigated through the analysis of gas mixing ratio on volume and surface chemistries. Experiments showed that PZT etch rate keeps a constant value up to 40% of Ar addition into Cl₂/Ar plasma. Langmuir probe measurement showed the noticeable influence of Cl₂/Ar mixing ratio on electron temperature and electron density. The modeling of volume kinetics for neutral and charged particles indicated monotonic changes of both densities and fluxes of active species such as chlorine atoms and positive ions. The analysis of surface kinetics showed that PZT etch rate behavior may be explained by the combination of spontaneous and ion-assisted etch mechanisms.     

Characteristics of vinyl iodide microwave plasma etching of GaAs/AlGaAs and InP/InGaAs heterostructures

Vinyl iodide (C₂H₃I) microwave discharges with additions of H₂ and Ar are found to provide faster etch rates than conventional CH₄/H₂/Ar discharges for InP, InGaAs, GaAs, and AlGaAs. This is a result of the relatively high volatilities of indium, gallium, and aluminum iodide species. The etched features are smooth and anisotropic over a wide range of do self-biases (–150 to –350 V), process pressures (1–20mTorr), and microwave powers (150–500 W). The polymer that forms on the mask during the plasma exposure can be readily removed in O₂ discharges. Electron spectroscopy for chemical analysis (ESCA) showed that the etched surfaces are slightly deficient in the group V elements under most conditions, but changes to the optical properties of the semiconductors are minimal. No defects are visible by transmission electron microscopy (TEM) in GaAs or InP samples etched at dc biases –250 V.     

Dry etching characteristics of III–V semiconductors in microwave BCl3 discharges

Electron cyclotron resonance (ECR) BCl₃ discharges with additional rf biasing of the sample position have been used to etch a variety of III–V semiconductors. GaAs and Al_xGa_1–xAs (x = 0–1) etch at equal rates in BCl₃ or BCl₃/Ar discharges, whereas SF₆ addition produces high selectivities for etching GaAs over AlGaAs. These selectivities are in excess of 600 for dc biases of –150 V, and fall to 6 for biases of –300 V. If the dc biases are kept to – 100 V, there is no measurable degradation of the optical properties of the GaAs and AlGaAs. The AlF₃ formed on the AlGaAs surface during exposure to BCl₃/SF₆ plasmas can be removed by sequential rinsing in dilute NH₄OH and water. In-based materials (InP, InAs, InSb, InGaAs) etch at slow rates with relatively rough morphologies in BCl₃ plasmas.     

Use of CF3,Br/Al,discharges for reactive ion etching of III-V semiconductors

The reactive ion etching of GaAs, InP, InGaAs, and InAlAs in CF₃Br/Ar discharges was investigated as a function of both plasma power density (0.56-1.3 W - cm^–2) and total pressure (10-40 mTorr) The etch rate of GaAs in 19CF₃Br:1Ar discharges at 10 m Torr increases linearly with power density, from 600 Å min^–1 at 0.56 W · cm^–2, to 1550 Å · min at 1.3 W · cm^–2. The in-based materials show linear increases in etch rates only for power densities above – 1.0 W · cm^–2. These etch rates are comparable to those obtained with CCI₂F₂:O₂ mixtures under the same conditions. Smooth surface morphologies and vertical sidewalls are obtained over a wide range of plasma parameters. Reductions in the near-surface carrier concentration in n-type GaAs are evident for etching with power densities of >0.8 W cm^–2, due to the introduction of deep level trapping centers. At 1.3 W· cm^–2, the Schottky barrier height of TiPtAu contacts on GaAs is reduced from 0.74 to 0.53 eV as a result of this damage, and the photoluminescent intensity from the material is degraded. Alter RIE, we detect the presence of both F and Br on the surface of all of the semiconductors. This contamination is worse than with CCl₂F₂-based mixtures. High-power etching with CF₃Br/Ar together with Al-containing electrodes can lead to the presence of a substantial layer of aluminum oxide on the samples if the moisture content in the reactor is appreciable.     

Low-temperature dry etching of tungsten,dielectric, and trilevel resist layers on GaAs

Dry etching of common masking materials used in GaAs device technology, was examined down to temperatures of –30°C. The etch rates of SiN_x, SiO₂, and W in SF₆/Ar are reduced below 0°C, but the anisotropy of the etching is improved at low temperature. Microwave enhancement of the SF₆/Ar discharges produces increases in etch rates of several times at 25°C, but much lower increases at –30°C substrate temperature. The underlying GaAs surface shows increased S and F coverage after low-temperature etching, but these species are readily removerd either by anex-situ wet chemical cleaning step or an in-situ H₂ plasma exposure. Photoresist etching is less sensitive to temperature, and anisotropic profiles are produced between –30 and +60°C in pure O₂ discharges.     

Low-temperature plasma etching of GaAs,AlGaAs, and AlAs

Dry etching of compound semiconductors is becoming increasingly important as design ruler shrink for electronic devices. For photonic device applications, dry or plasma etching is used fin- device isolation, fine-line pattern transfer, and fabrication of optical quality interfaces. As has been well established for Si and W. plasma etching at reduced temperatures can provide superior critical dimension control and obviate the need for operating at high bias voltages that produce excessively energetic ion bombardment t. In this work, we explore low-temperature (–60 C to +60 C) etching of the compound semiconductors GaAs, AlGaAs, and AlAs, In addition to improving etch anisotropy, which provides critical dimension control, rye find thut processing at lower temperatures improves microuniformity and reduces loading effects. At high lemperaturcs, where larger samples are observed to etch more slowly than smaller pieces (loading effect), etching rates appear limited bv reactant transport to the wafer. In this regime, both microuniformity and macrouniformity arc poor. As the temperature is reduced, the etching rate becomes limited by surfitce processes us a residue containing the semiconductor elements, etchant gases, and residual background gases forms on the surface. hi this regime, the etch rare becomes independent of surface area and uniformity is improved.     

A Comparative Study of HBr-Ar and HBr-Cl<Subscript>2</Subscript> Plasma Chemistries for Dry Etch Applications

The effects of HBr/Ar and HBr/Cl₂ mixing ratios in the ranges of 0–100% Ar or Cl₂ on plasma parameters, densities of active species influencing the dry etch mechanisms were analyzed at fixed total gas flow rate of 40 sccm, total gas pressure of 6 mTorr, input power of 700 W and bias power of 300 W. The investigation combined plasma diagnostics by Langmuir probes and the 0-dimensional plasma modeling. It was found that the dilution of HBr by Ar results in maximum effect on the ion energy flux with expected impact on the etch rate in the ion-flux-limited etch regime, while the addition of Cl₂ influences mainly the relative fluxes of Br and Cl atoms on the etched surface with expected impact on the etch rate in the reaction-rate-limited etch regime.     

Hybrid electron cyclotron resonance-radio-frequency plasma etching of III–V semiconductors in Cl2-based discharges. Part I: GaAs and related compounds

A systematic study has been performed of the dry etching characteristics of GaAs, Al_0.3Ga_0.7As, and GaSb in chlorine-based electron cyclotron resonance (ECR) discharges. The gas mixtures investigated were CCl₂F₂/O₂, CHCl₂F/O₂, and PCl₃. The etching rates of all three materials increase rapidly with applied RF power, while the addition of the microwave power at moderate levels (150 W) increases the etch rates by 20–80%. In the microwave discharges, the etch rates decrease with increasing pressure, but at 1 m Torr it is possible to obtain usable rates for self-bias voltages 100 V. Of the Freon-based mixtures, CHCl₂F provides the least degradation of optical (photoluminescence) and electrical (diode ideality factors and Schottky barrier heights) properties of GaAs as a result of dry etching. Smooth surface morphologies are obtained on all three materials provided the microwave power is limited to 200 W. Above this power, there is surface roughening evident with all of the gas mixtures investigated.     

Effect of Wafer Temperature on High Aspect Ratio Hardmask Etching

Fluorocarbon-based chemistries were used to study the effect of wafer temperature on the etch of high aspect ratio hardmasks composed of SiO₂ and SiN_x layers. It is found that etch stop can occur easily at high temperature. The rate of polymer deposition plays an important role in etch stop. The etching rates were found to be inversely proportional to the wafer temperature. Such a relation indicates a negative activation energy in the rate expression of hardmask etching using fluorocarbon plasma. It also implies that in hardmask etching, complicated gas-surface, but not simple one-step, reactions are involved. Different wafer surface temperature can provide different degree of activation for etching reactions. Analysis of etching rate and optical emission trends indicates that CF_x may contribute more than F does in the etch of SiO₂ and SiN_x, since polymer-rich etching chemistries were used. Based on the temperature-dependent etching rate, we propose a reaction mechanism for the reaction trends observed in hardmask etching.     

Dry etching of InGaP and AlInP in CH4/H2/Ar

Electron cyclotron resonance (ECR) plasma etching with additional rf-biasing produces etch rates 2,500 A/min for InGaP and AlInP in CH₄/H₂/Ar. These rates are an order of magnitude or much higher than for reactive ion etching conditions (RIE) carried out in the same reactor. N₂ addition to CH₄/H₂/Ar can enhance the InGaP etch rates at low flow rates, while at higher concentrations it provides an etch-stop reaction. The InGaP and AlInP etched under ECR conditions have somewhat rougher morphologies and different stoichiometries up to 200 Å from the sur face relative to the RIE samples.     

Highly Selective and Low Damage Etching of GaAs/AlGaAs Heterostructure using Cl2/O2 Neutral Beam

Highly selective and low damage etching of the GaAs cap layer on AlGaAs is essential in fabricating GaAs/AlGaAs high electron mobility transistors. The GaAs on AlGaAs was etched using a low energy Cl₂/O₂ neutral beam and the Schottky device characteristics fabricated on the exposed AlGaAs were compared with those fabricated after the etching using wet etching and a Cl₂/O₂ ion beam. Using a low energy Cl₂/O₂ ion beam or a Cl₂/O₂ neutral beam, highly selective etching of the GaAs cap layer to AlGaAs similar to wet etching could be achieved through the formation of Al₂O₃ on the exposed AlGaAs during the etching. When the electrical characteristics of the Schottky devices were compared, the devices fabricated after the etching using the neutral beam showed the best electrical characteristics such as electrical stability, low leakage current, higher barrier height, etc. by showing low damage to the exposed AlGaAs surface.     

Iodine- and Bromine-Based Dry Etching of LaCaMnO3

Two novel plasma chemistries, BI ₃ and BBr ₃ , have been employed for dry etching of LaCaMnO ₃ thin films. For both mixtures there is some chemical enhancement of etch rates at low halide compositions in the discharge, and the rates are a strong function of ion/neutral ratio. Maximum rates are obtained at ratios near 0.02. Etch yields are typically low (<0.3) under inductively-coupled plasma (CICP) conditions. Smooth _d surface morphologies are obtained over a wide range of conditions, with high-fidelity pattern transfer using SiO ₂ or SiN _x masks.     

Studies of GaAs surface roughness and organic masks resistance depending on the ion-beam energy

Summary The development of A^III–B^V semiconductor surfaces exposed to ion-beam irradiation in the ion energy range from 100 to 1000 eV and the ion current density of 1 mA/cm² (max) is investigated. The ion-beam etching with an ion energy of 1 keV results in sharp cones and needles on the semiconductor surface due to the surface contamination and unevenness. Etching with ion-beam energies in the order of 300 eV and with etch rates higher than 1000 /min produces relatively even GaAs surfaces. In case of reactive gases (i.e. CCl₂F₂ and the mixture of CCl₂F₂+Ar) ion-beam etching results in significantly higher etch rates; however, the mask residue contains Cl and F. In studies on the ion-beam resistance of organic masks selectivities as high as 13:1 for the photoresist CM-79 with an ion energy of 180 eV and an ion current density of approximately 0.3 mA/cm² were achieved.     

Etching Characteristics and Mechanisms of TiO2 Thin Films in HBr/Ar and Cl2/Ar Inductively-Coupled Plasmas

The TiO₂ etching characteristics and mechanisms in HBr/Ar and Cl₂/Ar inductively-coupled plasmas were investigated under fixed gas-mixing ratio and bias power conditions. It was found that in both systems, an increase in gas pressure from 4 to 10 mTorr results in a non-monotonic TiO₂ etching rate, while a variation of input power in the range 500–800 W causes a faster-than-linear acceleration of the etching process. Plasma diagnostics performed by Langmuir probes and zero-dimensional plasma modeling provided data on plasma parameters, steady-state densities, and fluxes of the active species on the etched surface. The model-based analysis of the etching mechanism showed that for the given set of processing parameters, the TiO₂ etch kinetics correspond to the transitional regime of ion-assisted chemical reaction in which a chemical-etch pathway dominates.     

Analysis of AlGaAs/GaAs superlattices by means of sputter-assisted AES,SEM and TEM

This paper reports the developments of evaluation methods on epitaxially grown superlattices by means of sputterassisted Auger electron spectroscopy (AES), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). AlGaAs/GaAs semiconductor superlattics were grown epitaxially by metal–organic chemical vapour deposition (MOCVD). The layer thickness of the superlattices ranged from a few to ten nanometers. Firstly, developments of Auger depth profiling were tried by using: (1) a differential pumping-type ion gun instead of a static pressure type to reduce the oxygen adsorbates on the AlGaAs layer; (2) low-energy Auger signals instead of high-energy ones to shorten the escape depth; and (3) the lowest ion etching energy of 0.2 keV instead of 1 keV to reduce the surface roughening effects. It is shown that the depth resolution of sputter-assisted AES is attainable to 1.5 nm. Secondly, high-resolution SEM can be used as an easy evaluation method by observing the cleaved surface of superlattices, since the layers can be distinguished by signal contrast. Also, TEM can be used as an evaluation method by observing the (110) cross-section thinned sample. The dark field image has a high contrast between AlGaAs and GaAs using the (002) diffraction. It is confirmed from these AES, SEM and TEM evaluations that the hetero-interface abruptness of AlGaAs/GaAs superlattices grown by MOCVD is of the order of one monoatomic layer.     

Photoreflectance characteristic about AlGaAs/GaAs heterostructure

We investigated the photoreflectance (PR) spectra of as-grown, etched AlGaAs/GaAs heterostructure sample. As etching time increases, the electric fields are reduced. And the surface and interface electric field calculated for the AlGaAs/GaAs sample, respectively.