Smooth Etched Surface Research Articles

Reactive ion etching of trenches in 6H-SiC

In this paper, we report the reactive ion etching (RIE) of trenches in 6H-silicon carbide using SF6/O2. The plasma parameters: etchant composition, gas flow rate, chamber pressure, and radio frequency power were optimized to obtain a maximum etch rate of 360A/min. The etch rate of SiC was found to exhibit a direct correlation with the dc self bias except when the O2 percentage was varied. Trenches were fabricated using the optimized conditions. It was found that the trench surface was extremely rough due to the aluminum micromasking effect. To overcome this effect, a TeflonTM sheet was used to cover the cathode during the experiment. The trenches fabricated using this modification were found to have smooth etched surfaces and sidewalls. The angle of anisotropy of these trenches was approximately 80° which is suitable for device applications.

Ecr Etching of GaP, GaAs, InP, and InGaAs in Cl2/Ar, Cl2/N2, BCl3/Ar, and BCl3/N2

AbstractElectron cyclotron resonance (ECR) etching of GaP, GaAs, InP, and InGaAs are reported as a function of percent chlorine-containing gas for Cl2/Ar, Cl2/N2, BCl3/Ar, and BCl3/N2 plasma chemistries. GaAs and GaP etch rates were faster than InP and InGaAs, independent of plasma chemistry due to the low volatility of the InClx, etch products. GaAs and GaP etch rates increased as %Cl2 was increased for Cl2/Ar and Cl2/N2 plasmas. The GaAs and GaP etch rates were much slower in BCl3-based plasmas due to lower concentrations of reactive Cl, however enhanced etch rates were observed in BCl3/N2 at 75% BCl3. Smooth etched surfaces were obtained over a wide range of plasma chemistries.

Cl2-Based ECR Etching of InGaP, AlInP and AIGaP

AbstractHigh microwave power (1000W) Electron Cyclotron Resonance (ECR) Cl2/Ar plasma produce etch rates for In0.5Ga0.5P, Al0.5In0.5P and Al0.5Ga0.5P of ˜1um/min. at low pressure (1.5mTorr), moderate rf power levels (150W) and room temperature. Addition of Cl2 into Ar makes much smoother etched surface morphology as well as increasing the etch rate. All parameters, including microwave power, chamber pressure and rf power increase the etch rate of these alloys. Especially, there is at least a minimum rf power in order to get much higher etch rate with increasing microwave power. AlGaP in Cl2/Ar discharges has lower etch rates than InGaP or AlInP, which is similar to the results based on CH4/H2/Ar plasma chemistries. The Cl2/Ar chemistry enables smooth, high-rate etching without the need for polymer addition and thus simplifies the processing.

A comparative study of Cl2 and HCl gases for the chemically assisted ion beam etching of InP

Chemically assisted ion beam etching using an Ar ion beam and Cl2 and HCl gases was investigated for the etching of high quality facets in InP. The etch rate, anisotropy, and surface morphology for the Cl2 and HCl processes are compared for different conditions of substrate temperature and reactive gas flow rate. Elevated substrate temperatures above 150 °C were required due to the low volatility of InClx reaction products below this temperature. At higher substrate temperatures, etch rates in the range of 1–5 μm/min using Cl2 and 200–500 nm/min using HCl were obtained. Vertical etch profiles were obtained above 200 °C for Cl2 and above 300 °C using HCl. The HCl process provided very smooth etched surfaces under most conditions investigated. Surface analysis using Auger electron spectroscopy and secondary ion mass spectroscopy techniques was conducted. Auger electron spectroscopy indicated surface depletion of In using Cl2, HCl resulted in increased depletion of P. Secondary ion mass spectroscopy depth profiles carried out using deuterium gas indicated diffusion of deuterium greater than 10 μm at a process temperature of 325 °C, while a postetch anneal at 325 °C/10 min was demonstrated to reduce the level of deuterium near the surface.

Anisotropic Reactive Ion Etching of Silicon Using SF 6 / O 2 / CHF 3 Gas Mixtures

Reactive ion etching of silicon in an RF parallel plate system, using , plasmas has been studied. Etching behavior was found to be a function of loading, the cathode material, and the mask material. Good results with respect to reproducibility and uniformity have been obtained by using silicon as the cathode material and silicon dioxide as the masking material for mask designs where most of the surface is etched. Etch rate, selectivity, anisotropy, and self‐bias voltage have been examined as a function of flow, flow, flow, pressure, and the RF power, using response surface methodology, in order to optimize anisotropic etching conditions. The effects of the variables on the measured responses are discussed. The anisotropic etch mechanism is based on ion‐enhanced inhibitor etching. provides the reactive neutral etching species, supplies the inhibitor film forming species, and and generate ion species that suppress the formation of the inhibitor film at horizontal surfaces. Anisotropic etching of high aspect ratio structures with smooth etch surfaces has been achieved. The technique is applied to the fabrication of three‐dimensional micromechanical structures.

Selective etching of silicon in aqueous ammonia solution

Abstract The current-voltage ( I-V ) characteristics of silicon in aqueous ammonia have been studied. As the bias is swept to the cathodic direction and kept cathodic for a few minutes, clear passivation peaks in the I-V curves can be observed for both p- and n-type silicon. A linear current-voltage relation is observed for the n-Si/NH 4 OH contact. A rectifying current-voltage relation with large leakage current is found for the p-Si/NH 4 OH contact. These observations indicate that there is no potential barrier for the n-Si/NH 4 OH contact and only a very small potential barrier exists for the p-Si/NH 4 OH contact. This small potential barrier allows easy transfer of holes between silicon and aqueous ammonia and promotes the spontaneous formation of the oxide film. A systematic method to etch either the n- or the p-type region selectively on a silicon substrate has been proposed based on observed I-V curves and verified experimentally. Very good etching selectivity has been achieved in aqueous ammonia with a suitable applied external bias. If the external bias is between −0.85 and −0.6 V versus SCE, only the p-type region is etched. Smooth and hillock-free etched surfaces are achieved in this bias region. For a bias smaller than −1.4 V versus SCE, the etching rate for the n-type region is lower than that for the p-type region. A bias between −1.3 and −0.9 V versus SCE should be applied to the sample if a higher etching rate of the n-type region than that of the p-type region is required.

Deep Etched ZnSe‐Based Nanostructures for Future Optoelectronic Applications

AbstractBy electron beam lithography and a subsequent wet/dry etch process, optically active nanostructures are developed based on ZnSe with lateral extensions down to 35 nm. Dry etching using Ar+ ions is found to generate very smooth etch surfaces, while the photoluminescence efficiency of narrow wires is much higher in wet chemically etched structures. As a first application of deep etched nanostructures, index coupled distributed feedback laser structures of second order are realized with periods down to 185 nm on the base of (Cd, Zn)Se/ZnSe/(Mg, Zn) (Se, S) vertical waveguide heterostructures. A clear correlation between the resonator period and the emission wavelength is observed, indicating a high coupling coefficient of the structures. For optical pumping using a pulsed N2‐laser, the laser threshold at room temperature is about 100 kW/cm2.

Dead-time-free selective dry etching of GaAs/AlGaAs using BCl3/CHF3 plasma

A dead-time-free selective dry etching of GaAs/AlGaAs using mixed plasma of BCl3 and CHF3 has been developed. The selectivity of the etching for GaAs/AlGaAs is strongly dependent on the flow ratio R, where R=(flow of CHF3)/(flow of CHF3+ flow of BCl3). It was also found that the angle of the sidewall can be varied from overhanging to tapered by controlling R. No undercutting was observed. Complete vertical recess structures with sub-quarter micrometer width were obtained at R=40% where a selectivity of 30 was attained. The roughness of the etched surface was also strongly dependent on R. A smooth etched surface was obtained where R was larger than 40% even for bulk GaAs. Complete square-shaped vertical recessed structures with sub-quarter micrometer width were obtained in a GaAs/AlGaAs epitaxial wafer. This etching process is very applicable for the fabrication of GaAs/AlGaAs heterojunction devices such as the GaAs modulation doped field-effect transistor and the heterojunction bipolar transistor.

Reactive ion etching of gallium nitride usinghydrogen bromide plasmas

The characteristics of the reactive ion etching (RIE) of gallium nitride (GaN) have been investigated using HBr, 1:1 HBr:Ar, and 1:1 HBr:H/sub 2/ plasmas. Etch rates were found to increase with plasma self-bias voltage for all gas mixtures exceeding 60 nm/min at -400 V for pure HBr. Higher etch rates were obtained for pure HBr than for HBr mixtures with Ar and H/sub 2/. Chamber pressure was also found to slightly affect etch rates for the pressure ranges investigated. The anisotropy of etched profiles was found to improve with increasing pressure. Smooth etched surfaces are also demonstrated. >

Characteristics of chemically assisted ion beam etching of gallium nitride

Chemically assisted ion beam etching (CAIBE) characteristics of gallium nitride (GaN) have been investigated using a 500-eV Ar ion beam directed onto a sample in a Cl2 ambient. Enhanced etch rates were obtained for samples etched in the presence of Cl2 over those etched only by Ar ion milling at a substrate temperature of 20 °C. The CAIBE etch rates were further enhanced at higher substrate temperatures whereas etch rates for Ar ion milling were not influenced by substrate temperature. Etch rates as high as 210 nm/min are reported. The etch rates reported here are the highest so far reported for GaN. Anisotropic etch profiles and smooth etched surfaces in GaN have been achieved with CAIBE.

Interface analysis of dry etched and molecular beam epitaxial regrown AlGaAs

Many novel optoelectronic devices can be realized by the technique of molecular beam epitaxy regrowth on etched surfaces. A smooth etched surface free from contaminants is necessary as this surface determines the success of the regrowth and the etched/regrown interface affects the performance and reliability of the devices. We have systematically studied the contaminants at the etched and regrown interface of Al0.4Ga0.6As for various steps of our in situ process. Using secondary ion mass spectroscopy, transmission electron microscopy, and mass spectroscopic analysis we have pinpointed what we believe to be the sources of carbon, oxygen, and silicon contamination in the etch chamber and have taken steps to eliminate them.

Magnetron-enhanced reactive ion etching of GaAs and AlGaAs using CH4/H2/Ar

Magnetron reactive ion etching of GaAs and AlGaAs has been investigated in CH4/H2/Ar gas mixtures. Etch rate was determined as a function of gas composition, power density (0.4–1.0 W/cm2), pressure (6–25 mTorr), and total flow rate (20–40 sccm). Scanning electron microscope measurements revealed that anisotropic etching characteristics and smooth etched surfaces can be obtained. Transmission electron microscope measurements showed that the addition of Ar to the gas mixture enhanced surface smoothness, but increased the etch-induced defect depth and density. Hydrogen passivation effects of etched and rapid thermal annealed GaAs were studied for two anneal temperatures (300, 400 °C).

Reactive ion etching of β-SiC in CCl 2 F 2 /O 2

For the first time, the reactive ion etching (RIE) of β-SiC in CCI2F2/O2 gas mixture is reported. The addition of oxygen to the CC12F2 does not appear to enhance the etch rate, however, the RF power and the DC bias conditions prove to be the dominant factors for controlling the etch rate. In addition, fine line structures with vertical walls and smooth etched surfaces are achieved.

Formation of Long Wavelength InP Laser MESAS

ABSTRACTNarrow (1 μm), deep (3.5 μm) laser mesas have been formed on 2”φ InP wafers using stepper lithography and dry etching techniques for both dielectric and semiconductor patterning. Contrast enhancement techniques produce excellent edge acuity and vertical sidewalls on the initial photoresist lines. Pattern transfer to the underlying SiO2 regrowth mask is achieved by ECR SF6/Ar dry etching at 1 mTorr and –100V, conditions which also retain the verticality of the mesa. The semiconductor is etched using an ECR Cl2/CH4/H2/Ar discharge at 0.3 mTorr and –80V, with the sample held at ∼ 150°C. The etch rate under these conditions is ∼1 μm/min, with a selectivity of ≥10:1 for the semiconductor over the dielectric mask. The smooth etched surface and low degree of damage make this process ideal for epitaxial regrowth. The uniformity of each process step is also acceptable (≤7%). Comparison of the elevated temperature Cl2/CH4/H2/Ar mixture with the more conventional room temperature CH4/H2 plasma chemistry will be given.

Ultra-Smooth Dry Etching of GaAs Using a Hydrogen Plasma Pretreatment

AbstractWe have attained extremely smooth etched surfaces on GaAs using a hydrogen plasma pretreatment before etching. The resultant morphology exhibits smooth surfaces since the etching proceeds uniformly through the GaAs without micromasking effects arising from a nonuniform surface oxide. We report the effects of hydrogen plasma treatments before RIE of GaAs in two different reactors using a SiCI4 plasma. Optimization of H2 plasma pretreatments has produced improvements in RMS roughness greater than 1 order of magnitude (22.4 to 1.51 nm).

Oxygen based electron cyclotron resonance etching of semiconducting homoepitaxial diamond films

Oxygen-based electron cyclotron resonance (ECR) plasma etching of boron doped homoepitaxial diamond films with no de bias has been achieved. The process was developed to the point where it can provide a uniform and reproducible etching procedure that yields smooth damage-free etched surfaces. Etch rates attained under these conditions of smooth damage-free etched surfaced were about 86 Å/min.

Electron cyclotron resonance plasma etching using downstream magnetic confinement

We demonstrate that electron cyclotron resonance plasma etching with a magnetically confined plasma in the region of the sample produces an enhanced etch rate, an anisotropic etch profile, and low self-bias voltage. Results are presented for GaAs etch rates, etch profiles, and macroscopic etch uniformity using a SiCl4 plasma, comparing the effects of a confining magnetic field and a diverging magnetic field in the reactor. The etch rates and saturated ion current density to the sample are found to be correlated. An anisotropic near vertical etch profile with smooth-etched surfaces is obtained with a negative self-bias voltage of typically 5–25 V for electrically floating samples in a magnetically confined plasma. When the magnetic field lines are perpendicular to the sample surface, the measured macroscopic etch uniformity is ±6% across a 5 cm diam wafer.

Anodic Dissolution during Electrochemical Carrier‐Concentration Profiling of Silicon

The anodic dissolution process of silicon in aqueous ammonium‐bifluoride solution during electrochemical carrier‐concentration profiling has been investigated for samples of various crystal orientation as well as dopant type and concentration. The effective dissolution valence and the surface roughness of the etched crater bottom was measured in dependence on the electrode potential, the dissolution current density, the electrolyte concentration, and, as necessary for the anodic dissolution of n‐type material, the illumination intensity. Regions where well‐controlled electrochemical etching occurs producing smooth and flat etched surfaces were defined for all these parameters. An optimized set of parameters for electrochemical carrier‐concentration profiling leading to an effective dissolution valence of for silicon of both polarities is given.

Short-period gratings for long-wavelength optical devices

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.

Laser chemical etching of metals in sodium nitrate solution

A focused cw argon-ion laser has been used to etch several metals, including copper, molybdenum, nickel, niobium, and stainless steel in a 0.5M sodium nitrate neutral salt solution. Exceedingly smooth etch surfaces have been obtained for several of these metals with etch rates as high as 4 μm/s. Experiments were carried out as a function of laser intensity and laser dwell time to etch arrays of small holes, 100 μm or less in diameter on the different samples. From experiments performed in water under similar laser conditions we conclude that melt or near-melt temperatures are required to obtain etching in the salt solution. A comparison of the power required to produce incipient etching is made with calculated temperatures obtained for similar powers using a theory which approximates the experimental conditions. These calculated temperatures are reasonably close to the melt temperatures for most cases and offer supporting evidence for our etching model.