Showing papers on "Isotropic etching published in 1989"

Universal energy dependence of physical and ion-enhanced chemical etch yields at low ion energy

Abstract: Physical and ion‐enhanced chemical etch yields are shown to be a linear function of the square root of the ion energy down to the etching threshold for self‐sputtering of metals, sputtering of metals by noble gas ions, sputtering of Si and SiO2 by noble gas and reactive ions, and ion beam enhanced chemical etching of Si. The threshold energy must be taken into account for a quantitative description of etch yields even at intermediate ion energies. The relationship between the dependence of etch yields on ion energy and incident angle is also discussed.

Silicon-on-insulator wafer bonding-wafer thinning technological evaluations

Abstract: The realization of wafer-scale Silicon-on-Insulator by Van der Waals wafer bonding and subsequent thinning of one of the wafers is described for 100 mm wafers. The bonding of two silicon wafers is brought about by Van der Waals forces which are found to be sufficiently strong for a tight bond at wafer distances of less than 1 nm. This condition requires wafer surfaces which are extremely flat and free of dust particles. Usually the bonding susceptibility is enhanced by a short polishing step. Van der Waals bonding (dipole bonding) is sufficiently strong to withstand the thinning procedure, but bonding is often enhanced by an anneal step (chemical bonding) before thinning. Four thinning procedures are described: 1. Electroless chemical thinning: Selective etching of highly doped bulk material of an active wafer using an electrochemically controlled HF–HNO3–HAc–H2O etchant down to a low-dope, low etch-rate epilayer. 2. Chemical thinning: Electrochemically controlled chemical etching of p-type bulk material of an active wafer down to a p/n junction, where electrochemical passivation of an n-type silicon epilayer occurs. 3. Thinning down to a tribochemical polish stop: In this technique an active wafer is polished until grooves filled with Si3N4 are encountered. The removal rate then becomes small while SOI remains in the areas between the grooves. 4. Polish without stopper: By adapting the existing optical polishing technology, extreme control of flatness and parallelism of wafer surfaces can be achieved. It then becomes possible to polish homogeneously down to SOI layers a few microns thick over a 100 mm wafer. In procedures 1 and 2 an acceptable surface quality is obtained by applying a final tribochemical polishing step. Experimental results of the four technologies are presented. In these technologies, tribochemical polishing is crucial. The necessity of this polishing technology as an off-line facility is discussed in the broader context of ICs of the future.

Dry etching by alternately etching and depositing

Abstract: A dry etching method including the steps of introducing etching and deposition gases alternately into a reaction chamber at predetermined time intervals, etching the exposed surface of an article to be etched and applying deposition to the surface film thereof alternately by making plasma generated by applying power to the etching and deposition gases introduced into the reaction chamber come in contact with the article to be etched in the reaction chamber in order to etch the surface, is characterized in that the power is applied after the passage of predetermined time from the start of the introduction of the deposition gas and before the etching gas is introduced and cut off when the introduction of the etching gas is suspended.

Epitaxial Lateral Overgrowth of GaAs on a Si Substrate

Abstract: Epitaxial lateral overgrowth (ELO) of GaAs on a Si substrate was successfully achieved by a combination of LPE and MBE. To prevent meltback of the Si substrate by Ga solution, a thin GaAs layer (2.4 µm) was grown by MBE prior to the deposition of SiO2 by P-CVD. Uniform GaAs ELO layers with mirror surface were grown through a line-shaped window cut in SiO2 film on a Si substrate with a GaAs layer. Chemical etching with an RC-1 etchant showed that there were no etch pits observed in ELO layers except in the region just over the line seed. Although cracks are observed in ELO layers due to the difference in thermal expansion coefficients between GaAs and Si, it is concluded that this technique is promising for obtaining dislocation- free GaAs on a Si substrate.

Reactive ion etching of InP using CH4/H2 mixtures: Mechanisms of etching and anisotropy

Abstract: Reactive ion etching of InP with CH4/H2 mixtures, a promising process for optoelectronic device fabrication, has been studied to understand the mechanisms of etching and anisotropy. Special attention has been paid to the polymer film that deposits on inert surfaces in the discharge; deposition rates have been used as a monitor of the discharge chemistry as well as for process optimization. Surface analysis shows that under etching conditions that maximize the InP etch rate while minimizing polymer deposition, the hydrocarbon coverage on the InP surface equals typical ‘‘adventitious’’ carbon levels, and the surface is significantly depleted of P. The etch rate here is limited by the flux to the surface of hydrocarbon reactants responsible for In desorption. The absence of a significant hydrocarbon film on the vertical‐etched surfaces under conditions of 8:1 anisotropy precludes a surface inhibitor mechanism of anisotropy, implicating instead energy deposition via ion bombardment as the major contributor to...

In situ cleaning of silicon substrate surfaces by remote plasma-excited hydrogen

Abstract: We have demonstrated a low‐temperature cleaning technique for removing both carbon and oxygen from a Si surface. It uses a combination of ex situ wet chemical clean and an in situ remote rf plasma‐excited hydrogen clean in an ultrahigh vacuum chamber. Since a remote rf plasma is used, there is insignificant plasma damage or other deleterious effects on surface morphology. A combination of in situ Auger and RHEED analysis has been used to confirm the removal of surface contaminants and the reconstruction of the Si surface. From mass spectroscopy studies, we believe that the hydrogen cleaning is due to a chemical etching of the Si by atomic hydrogen produced by the plasma. This clean is compatible with UHV processing and yields Si substrates that can be used for successful very low temperature (220–400 °C) Si homoepitaxy by remote plasma‐enhanced chemical vapor deposition.

Ion bombardment of polyimide films

Abstract: Surface modification techniques such as wet chemical etching, oxidizing flames, and plasma treatments (inert ion sputtering and reactive ion etching) have been used to change the surface chemistry of polymers and improve adhesion. With an increase in the use of polyimides for microelectronic applications, the technique of ion sputtering to enhance polymer‐to‐metal adhesion is receiving increased attention. For this study, the argon‐ion bombardment surfaces of pyromellitic dianhydride and oxydianiline (PMDA–ODA) and biphenyl tetracarboxylic dianhydride and phenylene diamine (BPDA–PDA) polyimide films were characterized with x‐ray photoelectron spectroscopy (XPS) as a function of ion dose. Graphite and high‐density polyethylene were also examined by XPS for comparison of C 1s peak width and binding‐energy assignments. Results indicate that at low ion doses the surface of the polyimide does not change chemically, although adsorbed species are eliminated. At higher doses the chemical composition is altered and is dramatically reflected in the C 1s spectra where graphiticlike structures become evident and the prominent carbonyl peak is reduced significantly. Both polyimides demonstrate similar chemical changes after heavy ion bombardment. Atomic composition of PMDA–ODA and BPDA–PDA polymers are almost identical after heavy ion bombardment.

Method of fabricating semiconductor device

Abstract: A method of fabricating a semiconductor device which includes: (1) a step of forming an opening in a silicon substrate using a first silicon oxide film and a first silicon nitride film formed on the silicon substrate as masks, (2) a step of forming a second silicon oxide film and a second silicon nitride film on the side wall of the opening by the reduced pressure CVD method and anisotropic etching method, (3) a step of performing isotropic dry etching using the first and second silicon oxide films as masks, and (4) a step of performing heat treatment in an oxidizing atmosphere using the first and second silicon nitride films as masks. Thereby, uniform isotropic etching may be accomplished by use of the dry etching method.

Reactive–fast‐atom beam etching of GaAs using Cl2 gas

Abstract: GaAs dry etching using reactive–fast‐atom beam etching to obtain an etched mirrorlike surface is investigated. An etch rate of 0.1–0.6 μm/min is obtained when Cl2 gas is used, which is 50–100 times faster than when Ar gas is used. The etch rate ratio between GaAs and photoresist AZ‐1350J is more than 30. As a result, a trench with a depth of more than 10 μm and a width of less than 2 μm is easily fabricated under the etch conditions of a Cl2 gas pressure of 5–6.5×10−2 Pa, an accelerate voltage of 1.5–1.8 kV, and a substrate temperature of about 100 °C. The radiation damage caused by this etching is very small, and it is similar to that caused by wet chemical etching, in spite of the relatively higher accelerator voltage. The thickness of an induced damage layer is only 150 A. It is found that the radiation damage induced by reactive–fast‐atom beam etching decreased with an increase of the etch rate. It is confirmed that vertical, smooth, damage‐free etching can be easily attained with reactive–fast‐atom b...

Fabrication of silicon structures by single side, multiple step etching process

Abstract: Three dimensional silicon structures are fabricated from {100} silicon wafers by a single side, multiple step ODE etching process. All etching masks (26, 28) are formed one on top of the other prior to the initiation of etching, with the coarsest mask (28) formed last and used first. Once the coarse anisotropic etching is completed, the coarse mask is removed and the finer anisotropic etching is done. The three dimensional structure may be a thermal ink jet channel plate, in which case the etching process is a two-step process in which the coarse etching step provides the ink reservoir (30) and the fine etching step provides the ink channels (32).

Wet chemical etching of high-temperature superconducting Y-Ba-Cu-O films in ethylenediaminetetraacetic acid

Abstract: A new wet chemical etchant for high‐temperature superconducting films is reported, which leaves transition temperature unaffected within experimental accuracy (1 K) and does not require reoxygenation. The solution consists of ethylenediaminetetraacetic acid (EDTA) in water, and is suitable for micropatterning using standard photolithography. We have fabricated 3–50 μm patterns on laser‐deposited Y‐Ba‐Cu‐O films. The bulk of the films etches at 0.14 μm/min in a saturated solution at room temperature. Porous surface layers are removed three times faster than the dense portions of the films. Etch rate depends linearly on the solution concentration and exponentially on the solution temperature. These rates are reduced if etching is interrupted and the samples are exposed to atmosphere.

Strain-induced confinement of carriers to quantum wires and dots within an InGaAs-InP quantum well

Abstract: We describe a novel method of confining carriers by deliberately creating large inhomogeneous strain patterns in a quantum well The strain modulates the band gap to provide lateral quantum confinement for excitons Here, we generate strain confinement in an InGaAs quantum well by reactive ion beam assisted etching through an overlying compressed pseudomorphic quaternary layer using etch masks patterned by electron beam lithography Photoluminescence spectra of arrays of wires and dots show red‐shifted band gaps in direct evidence of lateral confinement We compare our results to finite element calculations of the inhomogeneous strain in an InP substrate from a compressed overlayer patterned into rectangular wires

Etching of thin SiO2 layers using wet HF gas

Abstract: The etching of SiO2 layers on silicon with HF/H2O vapor mixtures using a N2 gas flow as a carrier was studied. The differences between the etching process of SiO2 on silicon using HF in water solutions and the gaseous etching process were investigated using x‐ray photoelectron spectroscopy analysis. The experiments focused on the removal of thin (native) oxide layers. It is shown that HF gas etching yields a good and reproducible removal of the suboxide (SiOx) interface layer. Various parameters influencing the etching process are discussed. In our experiments the HF‐gas etch proved to be superior to the liquid‐HF etch with respect to the removal of the SiOx layer. After the HF gas etching process a logarithmic regrowth of an oxide layer in air occurs at a rate of 0.2 to 0.3 nm/decade (time in hours). Flashing HF gas etched samples to 700 °C for 2–3 min under ultrahigh vacuum conditions results in complete removal of oxygen.

Passivation of acceptors in InP resulting from CH4/H2 reactive ion etching

Abstract: Reactive ion etching of InP with CH4/H2 mixtures leads to hydrogen passivation of near‐surface Zn acceptors but not S donors. Secondary‐ion mass spectrometry (SIMS) measurements of CH4/D2 etched samples show deuterium diffuses to a depth of 2000 A in p‐InP (1.5×1018 cm−3) when etching at a rate of 520 A/min and a temperature of about 80 °C. Acceptor passivation occurs to the same depth. For n‐InP, no donor passivation is observed, even though SIMS shows deuterium diffusion to a depth of 7000 A. Annealing at 350 °C for 1 min restores carrier concentrations to near pre‐etched levels.

Method for recirculating high-temperature etching solution

Abstract: A method for recirculating a high-temperature etching solution according to the present invention comprises the steps of continuously removing, from a bath for etching a wafer for a semiconductor device, a portion of an etching solution contained in the etching bath, injecting a predetermined amount of pure water for adjusting the concentration of the etching solution into the removed etching solution, heating the resulting solution to a predetermined temperature, and recirculating the heated solution into the etching bath.

Chemical dry etching of GaAs and InP by Cl2 using a new ultrahigh‐vacuum dry‐etching molecular‐beam‐epitaxy system

Abstract: Damage and contamination‐free chemical dry etching of (100)GaAs and (100)InP by Cl2 was demonstrated using a new ultrahigh‐vacuum dry‐etching molecular‐beam‐epitaxy (MBE) system This system consists of a combined etching chamber, an MBE chamber, and a sample preparation chamber, all at ultrahigh vacuum A mirrorlike surface was obtained after etching at substrate temperatures ranging from 300 to 400 °C for GaAs, and from 200 to 400 °C for InP In situ reflection high‐energy electron diffraction observations were accomplished for GaAs, with a mirrorlike surface after etching, and (2×4) surface reconstruction was observed Results show that a smooth surface was formed at an atomic level

Dry etching with hydrogen bromide or bromine

Abstract: Plasma etching with hydrogen bromide or bromine as an etching gas allows a precise control of attaining vertical etching or taper etching with a desired taper angle by controlling a temperature of a mass to be etched, which mass is a phosphorus-doped n-type polycrystalline silicon, phosphorus-doped single crystalline or phosphorus-doped silicides semiconductor wafer.

Process for forming resist mask pattern

Abstract: A process for forming a resist mask pattern comprising the steps of forming a resist layer of organic material (a multilevel resist process) on a layer to be etched, and selectively etching, a planarizing lower layer (2) used in the resist layer by using an etching gas of oxygen under a plasma condition, characterized in that a compound gas of at least one element selected from the group consisting of B, Si, Ti, Al, Mo, W and S is added to the etching gas For example, the compound gas comprises BCl₃, BH₃, TiCl₄, S₂Cl₂, SiCl₄ or the like During the etching, a compound oxide (eg, B₂O₃, SiO₂ or the like) is deposited on sidewalls of the lower layer (2) to form a protective layer (10) which prevents undercutting

Uniformity of Etching in Parallel Plate Plasma Reactors

Abstract: A two‐dimensional transport and reaction model of a high pressure (~1 torr) high frequency (13.56 MHz) single‐wafer parallel plate plasma reactor was developed. The chemical etching uniformity was studied as a function of reactor operating conditions. The ratio of the reactivity of the surrounding electrode surface as compared to that of the wafer surface, , critically affected uniformity. A bullseye clearing pattern was predicted for , and the reverse pattern for , while etching was uniform for . In the case of , and for the parameter range studied, the absolute uniformity was found to improve by surrounding the wafer with a material of similar reactivity, by increasing the flow rate, or by decreasing the reactor pressure or power. However, such actions also served to decrease the etch rate. The oxygen plasma was used as a model experimental system to test the theoretical predictions. An experimental technique based on spatially resolved optical emission spectroscopy in concert with actinometry and the Abel transform was developed to obtain a three‐dimensional mapping of the reactant (O atom) concentration profile in the plasma reactor. When a reactive film was covering part of the substrate electrode, a profound decrease in the reactant concentration was observed over the film. At the same time, large concentration gradients developed, especially at the boundary of the reactive film with the surrounding electrode. Good quantitative agreement was found between the model predictions and the experimental reactant concentration data for the range of pressure, power, flow rate, and reactive film radius examined.

Dislocation nucleation and propagation in Si0.95Ge0.05 layers on silicon

Abstract: Defect reveal etching has been used to study the onset of relaxation in strained Si0.95 Ge0.05 layers grown by molecular beam epitaxy on (001) silicon substrates. Etch features corresponding to nucleation centers and to interfacial and threading segments of mismatch dislocations have been observed at thicknesses well below the expected critical thickness. From these it is deduced that mismatch dislocations take the form of half‐loops on {111} planes which glide approximately symmetrically outwards from existing defects along the 〈110〉 directions parallel to the interface.

Effect of Transport and Reaction on the Shape Evolution of Cavities during Wet Chemical Etching

Abstract: The effect of fluid flow, transport, and reaction on the shape evolution of two‐dimensional cavities during wet chemical etching was studied. Finite element methods were employed to solve for the fluid velocity profiles and for the etchant concentration distribution in cavities of arbitrary shape. A moving boundary scheme was developed to track the shape evolution of the etching cavity. In the case of pure diffusion and under mass‐transfer control, a mask with finite thickness resulted in significantly better etch factor (etch anisotropy) as compared to an infinitely thin mask, albeit the etch rate was essentially unaffected. With fluid flow past the cavity, the etch rate increased fourfold and the etch factor increased by 40% as compared to pure diffusion, under the conditions examined. In addition, the etch rate, etch factor, and cavity wall profiles showed a strong dependence on etch time as the cavity aspect ratio (depth/width) increased with time during etching.

Method of removing an oxide film on a substrate

Abstract: An oxide film such as native oxide film can be etched by forming a haloid or a liquid containing hydrogen halide, which is produced by a gas reaction such as one between a halogen-containing gas and a basic gas, on the oxide film The etching proceeds mainly in a chemical reaction So, the excellent etching selectivity of the oxide film with respect to underlying substrate is obtained, and the substrate receives no damage by the etching Furthermore, the etching can be carried out before processes such as etching, deposition, oxidation, diffusion, or epitaxial growth are carried out to the substrate The processed layer formed on the substrate, therefore, does not contain any useless native oxide

Reactive ion etching of GaAs with CCl2F2:O2: Etch rates, surface chemistry, and residual damage

Abstract: The reactive ion etching of GaAs with a CCl2F2:O2 discharge was investigated as a function of gas flow rate (10–60 sccm), total pressure (2–50 mTorr), power density (0.25–1.31 W cm−2), gas composition (0%–70% O2), and etch time (1–64 min). The etch rate decreases with increasing gas flow rate, increases with increasing power density, and goes through a maximum at a gas composition of 75:25 CCl2F2:O2 under our conditions. After etching at low‐power densities (0.56 W cm−2) and for high CCl2F2 ratios (19:1 to O2), carbon and chlorine could be detected in the GaAs to a depth of less than 15 A by x‐ray photoelectron spectroscopy. Under these conditions there was a Ga deficiency to a depth of ∼100 A, which we ascribe to surface roughening and the preferential vaporization of As2O3 over Ga2O3. At high‐power densities (1.31 W cm−2) a polymeric layer several hundred angstroms thick containing CCl and CF bonds was observed on the GaAs surface. Etching under O2‐rich conditions did not lead to any additional creation...

In situ pattern formation and high quality overgrowth by gas source molecular beam epitaxy

Abstract: We demonstrate a combination of focused Ga beam writing and dry etching techniques to pattern InP wafers in a common vacuum chamber. Surface steps on the order of 1000 A can be efficiently prepared using moderate Ga ion fluences. The implanted areas exhibit a faster etch rate, even for Ga doses below ∼1014 cm−2. The implantation damage is removed by the low‐energy Cl‐assisted ion beam etching as shown by the high quality of p‐n junctions grown on etched surfaces. GaInAs/InP heterostructures grown on in situ patterned substrates show excellent morphology and high luminescence efficiency.

Electron-Beam-Induced Cl2Etching of GaAs

Abstract: Electron-beam (EB)-induced Cl2 etching of GaAs is performed for the first time. Etching occurs only in the area exposed to both the Cl2 molecules and the EB. The etching rate is equal to that of a Cl2 gas phase etching. The morphologies of the etched surfaces are slightly rough, but the photoluminescence intensity of the processed sample does not change as compared with that of the unprocessed sample. The etching characteristics predict that surface adsorbates act as a mask for a gas phase etching and that the EB plays an important part in patterning of the adsorbate mask.

Method of producing ultrafine silicon tips for the AFM/STM profilometry

Abstract: A method is described for producing ultrafine silicon tips for the AFM/STM profilometry comprising: 1. providing a silicon substrate and applying a silicon dioxide layer thereto; 2. producing a mask in said silicon dioxide layer by photolithography and wet or dry etching; 3. producing a tip shaft by transferring the mask pattern, produced in step 2, by reactive ion etching into the silicon substrate; 4. thinning the shaft and forming a base by isotropic wet etching; and 5. removing the mask by etching. The resulting tip shaft with a rectangular end may be pointed by argon ion milling. In a second embodiment there is an anisotropic wet etching step, prior to step 5, through the intact silicon dioxide mask, producing a negative profile of the shaft immediately below the mask. After this etching step the mask is removed by etching.

Characterization of subsurface damage in GaAs processed by Ga+ focused ion‐beam‐assisted Cl2 etching using photoluminescence

Abstract: Subsurface damage in GaAs processed by a Ga+ focused ion‐beam‐assisted Cl2 etching is studied by photoluminescence (PL) measurement. The PL intensity of the processed sample decreased to (1)/(30) – (1)/(40) compared to that of the unprocessed sample. The recovery of PL intensity by a step removal of the damaged layer is observed as a function of the removed layer thickness. The removal of a 0.7‐μm‐thick surface layer enables the PL intensity to be recovered perfectly, which leads to the postulate that the damaged layer thickness is 0.7 μm at least, which is much larger than the ion range (about 0.01 μm). The recovery of PL intensity is analyzed on a one‐dimensional model in the direction normal to the sample surface. Computer simulations of PL intensity are carried out. The calculated result fully explains the experimental PL intensity recovery as a function of the removed layer thickness, which gives the profile of subsurface damage in the sample.

Reaction of silicon with chlorine and ultraviolet laser induced chemical etching mechanisms

Abstract: The reaction of 〈100〉Si with Cl2 and the excimer laser induced chemical etching process using 308 and 248 nm radiation have been investigated. Our results show that even at high Cl2 pressures, only a thin passivating chlorinated surface layer is built up which impedes further reaction. Pulsed excimer laser etching at high energy fluences is dominated by thermal evaporation. At lower energy fluences the melt depth decreases and good etch profiles with excellent spatial resolution are observed. At the lowest laser fluences nonthermal, wavelength dependent etching occurs. The laser etching at 308 nm is based on locally enhanced surface chlorination due to effective photodissociation of Cl2 in the gas phase. Photoinduced desorption, most likely due to nonradiative electron‐hole recombination, leads to etching. Conversely, at 248 nm, negligible gas phase photodissociation occurs and the surface reaction of Cl2 molecules limits the etch rate. However, the higher photon energy (5.0 eV for 248 nm) leads to effici...