Inductively Coupled Plasma Etching in ICl- and IBr-Based Chemistries. Part I: GaAs, GaSb, and AlGaAs

High-density plasma etching of GaAs, GaSb, and AlGaAs was performed inICl/Ar and IBr/Ar chemistries using an Inductively Coupled Plasma (ICP)source. GaSb and AlGaAs showed maxima in their etch rates for both plamachemistries as a function of interhalogen percentage, while GaAs showedincreased etch rates with plasma composition in both chemistries. Etchrates of all materials increased substantially with increasing rf chuckpower, but rapidly decreased with chamber pressure. Selectivities >10 forGaAs and GaSb over AlGaAs were obtained in both chemistries. The etchedsurfaces of GaAs showed smooth morphology, which were somewhat better withICl/Ar than with IBr/Ar discharge. Auger Electron Spectroscopy analysisrevealed equirate of removal of group III and V components or thecorresponding etch products, maintaining the stoichiometry of the etchedsurface.     

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.     

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.     

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

Electron Cyclotron Resonance (ECR) discharges of CCl₂F₂ or PCl₃ have been used to etch InP, InAs, InSb, InGaAs and AlInAs. The etch rates of these materials increase linearly with additional RF power level applied to the cathode and are in the range 50–180 Å · min^–1 for 50 W (DC bias 308 V), 10 mTorr, 38 CCl₂F₂/2 O₂ plasmas. The etch rates fall rapidly with increasing pressure or increasing O₂-to-CCl₂F₂ ratio. Polymeric surface residues up to 40 Å thick are found on all of these semiconductors when using Freon-based gas mixtures. Etching at practical rates is possible with only 100 V self-bias when using PCl₃ discharges, and the addition of microwave excitation under these conditions enhances the etch rates by factors of 2–9. At higher self-biases (300 V) etch rates of 3500–8000 Å · min^–1 are possible with PCl₃ although the surface morphologies are significantly rougher and the etching less anisotropic than with CCl₂F₂-based mixtures.     

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.     

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.     

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.     

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.     

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.     

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.     

Heterogeneous reactions of HOI, ICl and IBr on sea salt and sea salt proxies

The heterogeneous chemistry of HOI, ICl and IBr on sea salt and sea salt proxies has been studied at 274 K using two experimental approaches: a wetted wall flow tube coupled to an electron impact mass spectrometer (WWFT-MS) and an aerosol flow tube (AFT) coupled to a differential mobility analyser (DMA) and a chemical ionisation mass spectrometer (CIMS). Uptake of all three title molecules into bulk aqueous halide salt films was rapid and controlled by gas phase diffusion. Uptake of HOI gave rise to gas-phase ICl and IBr, with the latter being the predominant product whenever Br(-) was present. Only partial release of IBr was observed due to high solubility of dihalogens in the film. ICl uptake gave the same yield of IBr as HOI uptake. Uptake of ICl on NaBr aerosol was accommodation limited with alpha = 0.018 +/- 0.004 and gas phase IBr product has a yield of 0.6 +/- 0.3. The results show that HOI can act as a catalyst for activation of bromine from sea-salt aerosols in the marine boundary layer, via the reactions: HOI(aq) + Cl + H--> ICl(aq) + H(2)O(l) and ICl(aq) + Br--> IBr(aq) + Cl.     

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.     

Photochemical reaction channels of OCS with Cl2, ICl, or IBr isolated together in an argon matrix: isolation of syn-iodocarbonylsulfenyl bromide

The photolytically induced reactions of a dihalogen XY (= Cl2, ICl, or IBr) with OCS isolated together in an Ar matrix at about 15 K lead to different photoproducts depending on the natures of X and Y. In addition to the known species ClCO*, OCCl2, syn-ClC(O)SCl, syn-ClC(O)SSCl, IC(O)Cl, IC(O)Br, and syn-BrC(O)SBr, syn-iodocarbonylsulfenyl bromide, syn-IC(O)SBr, has thus been identified for the first time as a photoproduct of the reactions involving IBr. The first product to be formed in the reactions with Cl2 or ICl is the ClCO* radical which reacts subsequently with halogen or sulfur atoms or other matrix guests to give the corresponding carbonyl dihalide (OCCl2 and IC(O)Cl), syn-ClC(O)SCl or syn-ClC(O)SSCl. The analogous reaction with IBr affords syn-BrC(O)SBr, IC(O)Br, and syn-IC(O)SBr. The changes have been followed, the products characterized experimentally by IR measurements, and the spectra analyzed in the light of the results of appropriate theoretical calculations.     

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.     

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.     

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.     

Effects of RF power on BZN thin‐film etching in SF6/Ar using surface analysis

Reactive ion etching (RIE) was used to etch bismuth zinc niobate (BZN) films in SF₆/ Ar plasma as a function of radio frequency (RF) power. Within the RF power range of choice, the etch rate of BZN films increases with increasing RF power. However, when RF power exceeds 200 W, the etch rate of films appears to increase at a slower rate. The structural properties of the BZN films before and after etching were characterized using X‐ray diffraction. As‐deposited film shows a cubic pyrochlore structure with preferential (222) plane orientation, but all the films etched at different reactive ion etching powers exhibit preferential (400) plane orientation. With increasing RF power, the ZnF₂ phase becomes evident. Also, the film surfaces before and after etching were analysed using XPS. Metal fluorides were found to remain on the surface, resulting in varying relative atomic percentages with RF power. Zn‐rich surfaces were formed because low‐volatile ZnF₂ residues were difficult to remove. Bi and Nb can be removed easily through chemical reactions because of their high volatility, whereas Bi–F and Nb–F, which were thought to be present in the form of a metal oxyfluoride, can still be detected using the narrow scan spectra. RF power has an effect on etch reaction through different plasma densities and particle energies, thus resulting in varying compositions and element chemical binding states. RF power also has an effect on the removal of residues. The minimum value of F atomic concentration is achieved at 150 W. Copyright © 2011 John Wiley & Sons, Ltd.     

On the effect of low-energy ion bombardment on polystyrene and polymethylmethacrylate etch rates in rf plasmas

The effect of low-energy ion bombardment on CD₄/O₂ and CF₃X (X=F, Cl, Br) plasma etching has been assessed by applying controlled rf bias voltages on polystyrene (PS) and polymethylmethacrylate (PMMA) samples. In both cases ion bombardment has been found to have a chemical effect. In the case of CF₄/O₂ discharges, ion bombardment has been found to change the relative etching efficiency of different mixtures. In the case of CF₃X plasmas, ion bombardment has been found to alter PMMA and PS etch rates in a different way. In particular, the ratios between CF₄ and CF₃X (X=Cl, Br) etch rates of PS have been found to decrease with increasing bias voltage. This effect has been tentatively attributed to an ion bombardment-induced enhancement of the reaction between the aromatic ring and halogen molecules formed in CF₃Cl and CF₃Br discharges.     

Synthesis and characterization of cyclopentadienyl transition metal halides,part I,vanadium halides

Summary Reactions between -Cp₂V and PX₃ (X=Cl, Br or I) yield the corresponding dihalogenated derivatives -Cp₂VX₂ (X=Cl, Br or I). The oxidative addition of ICl and IBr to -Cp₂V gives mixed halogenated derivatives -Cp₂VIX (X=Cl or Br). All the compounds have been characterized by elemental analyses, magnetic moment measurements and i.r. and e.p.r. spectra.     

Microwave-enhanced reaction rates for nanoparticle synthesis

Microwave reactor methodologies are unique in their ability to be scaled-up without suffering thermal gradient effects, providing a potentially industrially important improvement in nanocrystal synthetic methodology over convective methods. Synthesis of high-quality, near monodispersity nanoscale InGaP, InP, and CdSe have been prepared via direct microwave heating of the molecular precursors rather than convective heating of the solvent. Microwave dielectric heating not only enhances the rate of formation, it also enhances the material quality and size distributions. The reaction rates are influenced by the microwave field and by additives. The final quality of the microwave-generated materials depends on the reactant choice, the applied power, the reaction time, and temperature. CdSe nanocrystals prepared in the presence of a strong microwave absorber exhibit sharp excitonic features and a QY of 68% for microwave-grown materials. InGaP and InP are rapidly formed at 280 degrees C in minutes, yielding clean reactions and monodisperse size distributions that require no size-selective precipitation and result in the highest out of batch quantum efficiency reported to date of 15% prior to chemical etching. The use of microwave (MW) methodology is readily scalable to larger reaction volumes, allows faster reaction times, removes the need for high-temperature injection, and suggests a specific microwave effect may be present in these reactions.