Etching of As- and P-based III–V semiconductors in a planar inductively coupled BCl<Subscript>3</Subscript>/Ar plasma

A parametric study of the etch characteristics of Ga-based (GaAs, GaSb, and AlGaAs) and In-based (InGaP, InP, InAs, and InGaAsP) compound semiconductors in BCl₃/Ar planar inductively coupled plasmas (ICPs) was performed. The Ga-based materials etched at significantly higher rates, as expected from the higher volatilities of the As, Ga, and Al trichloride, etch products relative to InCl₃. The ratio of BCl₃ to Ar proved critical in determining the anisotropy of the etching for GaAs and AlGaAs, through its effect on sidewall passivation. The etched features in In-based materials tended to have sloped sidewalls and much rougher surfaces than for GaAs and AlGaAs. The etched surfaces of both AlGaAs and GaAs have comparable root-mean-square (RMS) roughness and similar stoichiometry to their unetched control samples, while the surfaces of In-based materials are degraded by the etching. The practical effect of the Ar addition is found to be the ability to operate the ICP source over a broader range of pressures and to still maintain acceptable etch rates.     

New wet etching solution molar ratio for processing T2SLs InAs/GaSb nBn MWIR infrared detectors grown on GaSb substrates

Mid-wave infrared (MWIR) technology is dominated by HgCdTe. However, in terms of performance, InAs/GaSb type-II superlattice (T2SL) has shown the theoretical potential to compete with HgCdTe. T2SLs InAs/GaSb technology is under development, where proper detector’s architecture formation must be considered as one of the most important steps of the fabrication process. The paper presents experimental results related to chemical etching of the T2SLs InAs/GaSb with bulk AlGaSb barriers, mesa type nBn MWIR detectors. Although, we attempted to transfer HgCdTe etching solutions: Br₂+C₂H₆O₂ into T2SLs InAs/GaSb technology, H₃PO₄+C₂H₈O₇+H₂O₂+H₂O (molar ratio: 1:1:4:16) at temperature ~21 °C was estimated to have optimal parameters in terms of the mesa profile and current–voltage characteristics. Repeatability of the mesa profiles and surface uniformity was reached. Overetching close to the mesa sidewalls was not observed.     

Conduction- and Valence-Band Energies in Bulk InAs1−x Sb x and Type II InAs1−x Sb x /InAs Strained-Layer Superlattices

The energy gaps were studied in two types of structures: unrelaxed bulk InAs_1?x Sb _x layers with x = 0.2 to 0.46 grown on metamorphic buffers and type II InAs_1?x Sb _x /InAs strained-layer superlattices (SLS) with x = 0.225 to 0.296 in the temperature range from T = 13 K to 300 K. All structures were grown on GaSb substrates. The longest wavelength of photoluminescence (PL) at low temperatures was observed from bulk InAs_0.56Sb_0.44 with a peak at 10.3 μm and full-width at half-maximum (FWHM) of 11 meV. The PL data for the bulk InAs_1?x Sb _x materials of various compositions imply an energy gap bowing parameter of 0.87 eV. A low-temperature PL peak at 9.1 μm with FWHM of 13 meV was observed for InAs_0.704Sb_0.296/InAs SLS. The PL spectrum of InAs_0.775Sb_0.225/InAs SLS under pulsed excitation revealed a second peak associated with recombination of electrons in the three-dimensional (3D) continuum with holes in the InAs_0.775Sb_0.225. This experiment determined the conduction-band offset in the InAs_0.775Sb_0.225/InAs SLS. The energies of the conduction and valence bands in unstrained InAs_1?x Sb _x and their bowing with respect to the Sb composition are discussed.     

Dry Etching Characteristics of MOVPE-Grown CdTe Epilayers in CH<Subscript>4</Subscript>, H<Subscript>2</Subscript>, Ar ECR Plasmas

Dry etching characteristics of single crystal (100) CdTe epitaxial layers grown on GaAs substrates were studied using CH₄, H₂, and Ar as process gases in an electron cyclotron resonance plasma. A smooth and anisotropic etching was obtained with CH₄, H₂, and Ar. No hydrocarbon polymer was found on the etched surface, which was confirmed by x-ray photoelectron spectroscopy measurement. Etching of the CdTe surface was also possible with H₂ and Ar; however, no etching was observed in the absence of H₂. Dependence of the etch rate on plasma gas composition and flow rates was studied. Mechanisms of etching with and without CH₄ supply were also studied. Etched CdTe layers also showed no deterioration of electrical properties, which was confirmed by photoluminescence measurement at 4.2 K and Hall measurement at 300 K.     

Reactive-ion etching of Ge2Sb2Te5 in CF4/Ar plasma for non-volatile phase-change memories

Etching of Ge₂Sb₂Te₅ (GST) is a critical step in the fabrication of chalcogenide random access memories. In this paper, the etch characteristics of GST films were studied with a CF₄/Ar gas mixture using a reactive-ion etching system. We observed a monotonic decrease in etch rate with decreasing CF₄ concentration indicating its importance in defining the material removal rate. Argon, on the other hand, plays an important role in defining the smoothness of the etched surface and sidewall edge acuity. We have studied the importance of gas mixture and RF power on the quality of the etched film. The smoothest surfaces and most vertical sidewalls were achieved using a CF₄/Ar gas mixture ratio of 10/40, a background pressure of 80 mTorr, and power of 200 W.     

Molds and Resists Studies for Nanoimprint Lithography of Electrodes in Low-Voltage Polymer Thin-Film Transistors

A low-cost patterning of electrodes was investigated looking forward to replacing conventional photolithography for the processing of low-operating voltage polymeric thin-film transistors. Hard silicon, etched by sulfur hexafluoride and oxygen gas mixture, and flexible polydimethylsiloxane imprinting molds were studied through atomic force microscopy (AFM) and field emission gun scanning electron microscopy. The higher the concentration of oxygen in reactive ion etching, the lower the etch rate, sidewall angle, and surface roughness. A concentration around 30 % at 100 mTorr, 65 W and 70 sccm was demonstrated as adequate for submicrometric channels, presenting a reduced etch rate of 176 nm/min. Imprinting with positive photoresist AZ1518 was compared to negative SU-8 2002 by optical microscopy and AFM. Conformal results were obtained only with the last resist by hot embossing at 120 °C and 1 kgf/cm² for 2 min, followed by a 10 min post-baking at 100 °C. The patterning procedure was applied to define gold source and drain electrodes on oxide-covered substrates to produce bottom-gate bottom-contact transistors. Poly(3-hexylthiophene) (P3HT) devices were processed on high-κ titanium oxynitride (TiO _x N _y ) deposited by radiofrequency magnetron sputtering over indium tin oxide-covered glass to achieve low-voltage operation. Hole mobility on micrometric imprinted channels may approach amorphous silicon (～0.01 cm²/V s) and, since these devices operated at less than 5 V, they are not only suitable for electronic applications but also as sensors in aqueous media.     

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

The etching characteristics of Al_xGa_1-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 Al_xGa_1-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 1000?. 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 1000?. 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 Al_xGa_1-xAs(x ≥ 0.45) etch stop layer provides a reasonably simple, safe, and reliable process for gate recessing in the fabrication of pseudomorphic MODFETs.     

Plasma and wet chemical etching of In0.5Ga0.5P

Dry and wet chemical etching of epitaxial In_{0, 5}Ga_0.5P layers grown on GaAs substrates by gas-source molecular beam epitaxy have been investigated. For chlorine-based dry etch mixtures (PCl₃/Ar or CC1₂F₂/Ar) the etching rate of InGaP increases linearly with dc self-bias on the sample, whereas CH₄/H₂-based mixtures produce slower etch rates. Selectivities of ≥500 for etching GaAs over InGaP are obtained under low bias conditions with PCl₃/Ar, but the surface morphologies of InGaP are rough. Both CC1₂F₂/Ar and CH₄/H₂/Ar mixtures produce smooth surface morphologies and good (≥10) selectivities for etching GaAs over InGaP. The wet chemical etching rates of InGaP in H₃PO₄:HC1:H₂O mixtures has been systemically measured as a function of etch formulation and are most rapid (∼1 μn · min⁻¹) for high HCl compositions. The etch rate,R, in a 1:1:1 mixture is thermally activated of the formR ∝ , whereE _a = 11.25 kCal · mole⁻¹. This is consistent with the etching being reaction-limited at the surface. This etch mixture is selective for InGaP over GaAs.     

用于非易失性相变存储器中Si2Sb2Te5在CF4/Ar等离子体下的反应离子刻蚀

Phase change random access memory（PCRAM） is one of the best candidates for next generation nonvolatile memory,and phase change Si₂Sb₂Te₅ material is expected to be a promising material for PCRAM.In the fabrication of phase change random access memories,the etching process is a critical step.In this paper,the etching characteristics of Si₂Sb₂Te₅ films were studied with a CF₄/Ar gas mixture using a reactive ion etching system.We observed a monotonic decrease in etch rate with decreasing CF4 concentration,meanwhile,Ar concentration went up and smoother etched surfaces were obtained.It proves that CF4 determines the etch rate while Ar plays an important role in defining the smoothness of the etched surface and sidewall edge acuity.Compared with Ge₂Sb₂Te₅, it is found that Si₂Sb₂Te₅ has a greater etch rate.Etching characteristics of Si₂Sb₂Te₅ as a function of power and pressure were also studied.The smoothest surfaces and most vertical sidewalls were achieved using a CF₄/Ar gas mixture ratio of 10/40,a background pressure of 40 mTorr,and power of 200 W.     

Characterization of Plasma Etching Process Damage in HgCdTe

Microstructural and electrical damage to n-type long-wavelength infrared Hg_1?x Cd _x Te (MCT) following CH₄-H₂-based inductively coupled plasma etching has been investigated. While the damage from such etching processes to MCT has previously been characterized for planar full-wafer etching, in this communication we present the results of an investigation of the damage incurred to etched sidewalls, whose faces constitute the majority of the etched surface in novel architectures. Auger electron spectroscopy was used to monitor the evolution of X _Cd beneath etched surfaces. So far, no X _Cd evolution has been detected underneath etched surfaces within a ΔX _Cd = 0.02 resolution. Conductivity and minority-carrier lifetime have been studied on patterned photoconductors, from which it is possible to extract a surface recombination velocity (SRV). These studies have shown surface conductivity variations and SRV shifts of several orders of magnitude, depending on the etching process used.     

Reactive ion etching of SiC using C2F6/O2 inductively coupled plasma

The inductively coupled plasma-reactive ion etching (ICP-RIE) of SiC single crystals using the C₂F₆/O₂ gas mixture was investigated. It was observed that the etch rate increased as the ICP power and bias power increased. With increasing sample-coil distance, O₂ concentration, and chamber pressure, the etch rate initially increased, reached a maximum, and then decreased. Mesas with smooth surfaces (roughness ≤1 nm) and vertical sidewalls (∼85°) were obtained at low bias conditions with a reasonable etch rate of about 100 nm/min. A maximum etch rate of 300 nm/min could be obtained by etching at high bias conditions (≥300 V), in which case rough surfaces and the trenched sidewall base were observed. The trenching effect could be suppressed by etching the samples on anodized Al plates, although mesas with sloped (60–70°) sidewalls were obtained. Results of various surface characterization indicated little contamination and damage on the etched SiC surfaces.     

Wet Etching of (0001) GaN/Al2O3 grown by MOVPE

H₃PO₄, NaOH, and KOH solutions are found to be useful for removing nitrogen depleted layers or damage induced by high temperature annealing or dry etching of metalorganic chemical vapor deposition-grown (0001)GaN/Al₂O₃. Solutions are selective to the (0001)plane of GaN. However, certain flat planes etched without etch pits are exposed by wet etching.     

Reactive sputter etching of Al in BCl3

Etching of Al is studied in pure BCl₃ as well as in mixtures with other gases in the reactive sputter etching mode in a cryopumped system. Etch rate, selectivity with respect to positive photoresist, SiO₂ and Si and etch profiles are investigated as a function of gas composition, gas pressure, flow rate and plasma power. Plasma chemical processes are monitored by quadrupole mass spectroscopy as well as by optical emission spectroscopy. Perfectly square Al-profiles can be etched if etch rates are kept below 1000 A/min. Al-patterns running over steep steps can also be clearly defined if a certain amount of overetching can be tolerated. The experimental data indicate that the etch process is reactant supply limited. Anisotropic etching is achieved by either a ‘surface inhibitor mechanism’ or the formation of a sidewall protecting film.     

Luminescent chemically-etched porous poly-crystalline silicon on insulating substrates

Polycrystalline silicon deposited on insulating substrates has been chemically-etched to form thin films of porous material exhibiting room temperature visible photoluminescence with emission wavelengths of around 650 nm. Material of 4000 ? thickness was quickly converted to porous silicon within 15 s of etching, with an etch rate of 1–1.5 μm/h. In contrast to anodization, chemical-etching parameters have little effect on modulating the resultant peak wavelength. Peak photoluminescence intensity was achieved 8–12 s of etching in 1:3:5 parts HF:HNO₃:H₂O at room temperature with ambient lighting. The chemical etching process and its etch characteristics have been discussed in relation to its suitability for large area thin film devices.     

Carbon etching with a high density plasma etcher

Generating suitable passivation on the carbon sidewall is a major challenge facing carbon etching especially for films thicker than 500 nm. Patterning carbon hard mask stacks for sub 90 nm technologies was tested for three different O₂-based chemistries using an inductively coupled plasma etch tool. The results show that the etched carbon profiles are highly dependant upon the O₂ flow and the total time of the etch process. Extended over etch times quite often initiates lateral etching and rapid loss of profile and critical dimension. An HBr/O₂/N₂ chemistry has been shown to provide the best options for profile control and more resistance to profile loss during extended over etching than the other chemistries which were tested during this study.     

SiCl4-based reactive ion etching of ZnO and MgxZn1−xO films on r-sapphire substrates

SiCl₄-based reactive ion etching (RIE) is used to etch Mg_xZn_1−xO (0≤x≤0.3) films grown on r-plane sapphire substrates. The RIE etch rates are investigated as a function of Mg composition, RIE power, and chamber pressure. SiO₂ is used as the etching mask to achieve a good etching profile. In comparison with wet chemical etching, the in-plane etching anisotropy of Mg_xZn_1−xO (0≤x≤0.3) films is reduced in RIE. X-ray photoelectron spectroscopy measurements show that there is no Si and Cl contamination detected at the etched surface under the current RIE conditions. The influence of the RIE to the optical properties has been investigated.     

ECR plasma etch fabrication of C-doped base InGaAs/InP DHBT structures: A comparison of CH4/H2/Ar vs BCl3/N2 plasma etch chemistries

We compare ECR plasma etch fabrication of self-aligned thin emitter carbondoped base InGaAs/InP DHBT structures using either CH₄/H₂/Ar or BCl₃/N₂ etch chemistries. Detrimental hydrogen passivation of the carbon doping in the base region of our structure during CH₄/H₂/Ar dry etching of the emitter region is observed. Initial conductivity is not recovered with annealing up to a temperature of 500°C. This passivation is not due to damage from the dry etching or from the MOMBE growth process, since DHBT structures which are ECR plasma etched in BCl₃/N₂ have the same electrical characteristics as wet etched controls. It is due to hydrogen implantation from the plasma exposure. This is supported with secondary ion mass spectroscopy profiles of structures which are etched in CH₄/D₂/Ar showing an accumulation of deuterium in the C-doped base region.     

InAs/GaSb超晶格探测器台面工艺研究

InAs/GaSb SLs探测器台面刻蚀常用的工艺有干法刻蚀和湿法刻蚀.研究了三种等离子刻蚀气体(Cl2基, Ar基和CH4基)对超晶格的刻蚀效果,SEM结果表明,CH4基组分能够得到更加平整的表面形貌和更少的腐蚀坑;之后采用湿法腐蚀工艺,用于消除干法刻蚀带来的刻蚀损伤,分别研究了酒石酸系和磷酸系两种腐蚀溶液的去损伤效果,结果表明,磷酸系腐蚀液的去损伤效果更好,且腐蚀速率更加稳定.采用优化的台面工艺制备了InAs/GaSb SLs探测器,其I-V特性曲线表明二极管具有较低的暗电流,其77 K时动态阻抗R0A =1.98104 cm2.     

Wet chemical etching of NiFe,NiFeCo AND NiMnSb for magnetic device fabrication

Thin film NiMnSb is found to be wet chemically etched in a range of solutions, including HNO₃, H₂SO₄:H₂O₂, FeCl₃ and HF, with activation energies in the range 10–23 kCal mol⁻¹, i.e. a reaction-limited regime. The degree of sidewall undercut is a function of solution type. Both NiFe and NiFeCo can be etched in H₂SO₄ and HNO₃, with reaction-limited characteristics, while HCl at 25°C is completely selective for NiFe over NiFeCo, even for 7% Co alloys. The degree of sidewall undercut on NiFe is also a strong function of solution type.     

Reactive Ion Etching of GaAs, GaSb, InP and InAs in Cl2／Ar Plasma

Reactive ion etching characteristics of GaAs,GaSb,InP and InAs using Cl_2/Ar plasma have been investigated,it is that,etching rates and etching profiles as functions of etching time,gas flow ratio and RF power.Etch rates of above 0.45 μm/min and 1.2 μm/min have been obtained in etching of GaAs and GaSb respectively, while very slow etch rates (<40 nm/min) were observed in etching of In-containing materials,which were linearly increased with the applied RF power.Etched surfaces have remained smooth over a wide range of plasma conditions in the etching of GaAs,InP and InAs,however,were partly blackened in etching of GaSb due to a rough appearance.