Influence of activated polymer on the etching rate of silicon in CF4+H2 plasma

The reactive ion etching (RIE) of silicon in CF₄+H₂ plasma is considered. The influence of activated polymer on the RIE rate of silicon in CF₄+H₂ plasma is determined by extrapolation of experimentally measured kinetics of the etching rate. It is found that increased adsorption of CF₂ radicals suppresses the RIE rate of silicon in CF₄+H₂ plasma during the initial stages of the etching process. The formation of activated polymer becomes pronounced when adsorbed CF₂ radicals are slowly activated. The activated polymer intensifies the etching reaction and enhances the etching rate. C atoms, produced during the reaction, contribute to the formation of polymer on the surface. The increased concentration of the polymer suppresses the RIE rate of silicon in CF₄+H₂ plasma at later stages of the etching process.     

Simulation of Si and SiO2 etching in CF4 plasma

The reactive ion etching (RIE) of Si and SiO₂ in CF₄ plasma is considered. The dependences of RIE rates of Si and SiO₂ on pressure have maxima due to the presence of single-atom vacancies. The RIE rates approach the maximum values at different pressures but at the same concentration of SiF and SiOF molecules in the adsorbed layer. Using the obtained results Si/SiO₂ etching selectivity is investigated.     

Surface characteristics of parylene-C films in an inductively coupled O2/CF4 gas plasma

In this article, we report the results obtained from a study carried out on the inductively coupled plasma (ICP) etching of poly-monochloro-para-xylylene (parylene-C) thin films using an O₂/CF₄ gas mixture. The effects of adding CF₄ to the O₂ plasma on the etch rates were investigated. As the CF₄ gas fraction increases up to approximately 16%, the polymer etch rate increases in the range of 277-373 nm/min. In this work, the atomic force microscopy (AFM) analysis indicated that the surface roughness was reduced by the addition of CF₄ to the O₂ plasma. Contact angle measurements showed that the surface energy decreases with increasing CF₄ fraction. At the same time, X-ray photoelectron spectroscopy (XPS) demonstrated the increase in the relative F atomic content on the surface.     

Simulations of Si and SiO2 etching in SF6 + O2 plasma

Chemical etching of Si and SiO₂ in SF₆ + O₂ plasma is considered. The concentrations of plasma components are calculated using values extrapolated from experimental data. Resulting calculations of plasma components are used for the calculation of Si and SiO₂ etching rates. It is found that the reaction constants for reactions of F atoms with Si atoms and SiO₂ molecules are equal to (3.5 ± 0.1) × 10⁻² and (3.0 ± 0.1) × 10⁻⁴, respectively. The influence of O₂ addition to SF₆ plasma on the etching rate of Si is quantified.     

Ar + H2 plasma etching for improved adhesion of PVD coatings on steel substrates

Ar + H₂ plasma cleaning has been described for the surface modification of the steel substrates, which removes oxides and other contaminants from substrate surface effectively leading to a better adhesion of the physical vapor deposited (PVD) coatings. Approximately 1.1-1.3 μm thick TiAlN coatings were deposited on plasma treated (Ar and Ar + H₂) and untreated mild steel (MS) substrates. A mechanism has been put forward to explain the effect of plasma treatment on the substrate surface based upon the data obtained from X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The XPS measurements on untreated and Ar + H₂ plasma etched MS substrates indicated that the untreated substrate surface mainly consisted of Fe₃O₄, whereas, after etching the concentration of oxides decreased considerably. The FESEM and the AFM results showed changes in the surface morphology and an increase in the substrate roughness as a result of Ar + H₂ plasma etching. Removal of oxide/contaminants, formation of coarser surface and increased substrate surface roughness as a result of Ar + H₂ plasma etching facilitate good mechanical interlocking at the substrate surface, leading to a better adhesion of the deposited PVD coatings. The adhesion of TiAlN coating could be increased further by incorporating a very thin Ti interlayer.     

Anisotropic etching of silicon in SF6 plasma

The reactive ion etching of silicon in SF₆ plasma is considered. During the experiment, silicon substrates are etched in SF₆ plasma at different pressures and energies of incident ions. High etching anisotropy is achieved decreasing the pressure in the reactor and increasing the energy of the bombarding ions. The obtained experimental measurements are compared with theoretical calculations. It is determined that the temperature of the sidewalls decreases with the decrease of concentration of F atoms due to suppressed plasmochemical etching of silicon. The etching anisotropy increases with the decrease of concentration of F atoms due to decreased desorption of SiF₄ molecules.     

Comparison of dry etching of PMMA and polycarbonate in diffusion pump-based O2 capacitively coupled plasma and inductively coupled plasma

We report a comparison of dry etching of polymethyl methacrylate (PMMA) and polycarbonate (PC) in O₂ capacitively coupled plasma (CCP) and inductively coupled plasma (ICP). A diffusion pump was used as high vacuum pump in both cases. Experimental variables were process pressure (30-180 mTorr), CCP power (25-150 W) and ICP power (0-350 W). Gas flow rate was fixed at 5 sccm. An optimized process pressure range of 40-60 mTorr was found for the maximum etch rate of PMMA and PC in both CCP and ICP etch modes. ICP etching produced the highest etch rate of 0.9 μm/min for PMMA at 40 mTorr, 100 W CCP and 300 W ICP power, while 100 W CCP only plasma produced 0.46 μm/min for PMMA at the same condition. For polycarbonate, the highest etch rates were 0.45 and 0.27 μm/min, respectively. RMS surface roughnesses of PMMA and PC were about 2-3 nm after etching. Etch selectivity of PMMA over photoresist was 1-2 and that of PC was less than 1. When ICP power increased from 0 to 350 W, etch rates of PMMA and PC increased linearly from 0.47 to 1.18 μm/min and from 0.18 to 0.6 μm/min, while the negative self bias slightly reduced from 364 to 352 V. Increase of CCP power raised both self bias and PMMA etch rate. PMMA etch rates were about 3 times higher than those of PC at the same CCP conditions. SEM data showed that there was some undercutting of PMMA and PC after etching at 300 W ICP, 100 W CCP and 40 mTorr. The results also showed that the etched surface of PMMA was rough and that of PC was relatively smooth.     

CF4 plasma effect combined with rapid thermal annealing for high-k Er2O3 dielectrics

In this study, the influence of the duration of CF₄ plasma treatment of rapid thermal annealing on high-k Er₂O₃ dielectrics deposited on polycrystalline silicon was investigated using electrical and material analyses. Results demonstrate that Er₂O₃ dielectric films annealed at 800 °C and plasma treated with CF₄ for a period of 1 min exhibited excellent dielectric performance, including a higher breakdown electric field, lower charge trapping rate, and a larger charge-to-breakdown than the as-deposited sample. Performance improvements were caused by the incorporation of fluorine atoms and the reduction of dangling bonds and defect traps.     

Hydrogen etching of Si3N4 layers with plasma assisted hot wire CVD

In order to develop sustainable processes for clean manufacturing environment for thin film or other solar cell production, we studied the hydrogen etching of silicon nitride (Si₃N₄) films on flat crystalline silicon (c-Silicon) substrates. With an arrangement primarily constructed for hot wire CVD (HWCVD) deposition of thin silicon films also cleaning processes with atomic hydrogen were studied with a simplified three wire assembly. The three filaments could be biased independently by different potential. A variation of hydrogen pressure and flow was performed to find out conditions of high etching rates for the Si₃N₄ layers. The etching rate was simply determined by measuring the time for total removal of the film, since this could be easily detected by the change of the anti-reflection property. Etching rates of 0.1 nm/s have been obtained under 15 Pa and a flow of 50 sccm. An intensive study was carried out of the direct current (DC) plasma hot wire CVD conditions.     

Improvement in etch selectivity of SiO2 to CVD amorphous carbon mask in dual-frequency capacitively coupled C4F8/CH2F2/O2/Ar plasmas

Highly selective etching of a SiO₂ layer using a chemical vapor deposited (CVD) amorphous carbon (a-C) mask pattern was investigated in a dual-frequency superimposed capacitively coupled plasma etcher. The following process parameters of the C₄F₈/CH₂F₂/O₂/Ar plasmas were varied: the CH₂F₂/(CH₂F₂ + O₂) flow ratio (Q(CH₂F₂)), the high frequency power (P_HF), and the low frequency power (P_LF). It was found a process window exists to obtain infinitely high etch selectivity of the SiO₂ layer to the CVD a-C. The process parameters of Q(CH₂F₂), P_HF, and P_LF played critical roles in determining the process window for oxide/CVD a-C etch selectivity, presumably due to the disproportionate degree of polymerization on the SiO₂ and CVD a-C surfaces.     

Influence of plasma heating of wafer substrates on SiO2 deposition rate in a TEOS/O2 high-density plasma CVD system

The influence of plasma heating of the Si and glass wafer substrates on silicon dioxide (SiO₂) deposition rates by a tetraethylorthosilicate/O₂ supermagnetron (high-density) plasma CVD were investigated. With a fixed RF power of 100 W supplied to both upper and lower electrodes, the SiO₂ deposition rate on the Si wafer substrate decreased with increasing wafer-stage temperature, showing a negative activation energy for the deposition rate. When Si and glass wafers were attached to the electrode using adherent thermal conductors, the film thickness increased almost linearly with regard to the deposition time, and both deposition rates became almost the same (about 310 Å/min). When both wafers were simply laid on the electrode without an adhesive bond and hence with poor thermal contact, the film thickness increased nonlinearly with deposition time, showing a gradual decrease in deposition rate with time, being as low as 80 and 150 Å/min, respectively for Si and glass wafers, for a deposition time of 15 min. The difference between the two deposition rates on Si and glass wafers in the case of poor thermal contact to the lower electrode is thought to be caused by plasma heating and related mainly to differences in optical absorption characteristics of the two wafer substrates. Variations in measured thickness distributions across the substrate surface were attributed to an antisymmetric plasma density distribution in the direction perpendicular to the magnetic field lines caused by E×B electron drift.     

HfO2 etching mechanism in inductively-coupled Cl2/Ar plasma

Etching characteristics and the mechanism of HfO₂ thin films in Cl₂/Ar inductively-coupled plasma were investigated. The etch rate of HfO₂ was measured as a function of the Cl₂/Ar mixing ratio in the range of 0 to 100% Ar at a fixed gas pressure (6 mTorr), input power (700 W), and bias power (300 W). We found that an increase in the Ar mixing ratio resulted in a monotonic decrease in the HfO₂ etch rate in the range of 10.3 to 0.7 nm/min while the etch rate of the photoresist increased from 152.1 to 375.0 nm/min for 0 to 100% Ar. To examine the etching mechanism of HfO₂ films, we combined plasma diagnostics using Langmuir probes and quadrupole mass spectrometry with global (zero-dimensional) plasma modeling. We found that the HfO₂ etching process was not controlled by ion-surface interaction kinetics and formally corresponds to the reaction rate-limited etch regime.     

Fabrication of Co3O4 cubic nanoframes: Facet-preferential chemical etching of Fe ions to Co3O4 nanocubes

The novel Co₃O₄ cubic nanoframes, sized in ca. 30 nm, were firstly fabricated via a facile solvothermal route. Based on the transmission electron microscopy and the powder X-ray diffraction analyses of the time-dependent products, a mechanism of facet-preferential chemical etching of Fe³⁺ ions to the pre-synthesized Co₃O₄ nanocubes is proposed for the formation of Co₃O₄ cubic nanoframes. This synthetic strategy can probably be extended to fabricate nanoframes of some other binary metal oxides, by designing similar chemical etching process.     

Surface roughness of silicon carbide etching in a NF3 inductively coupled plasma

Silicon carbide was etched in a NF₃/CH₄ inductively coupled plasma. Surface roughness measured by atomic force microscopy was investigated as a function of process parameters. Both etch rate and dc bias were correlated to the surface roughness. To optimize the surface roughness, a 2⁴ full factorial experiment was conducted for 700-900 W source power, 50-150 W bias power, 0.80-1.60 Pa, and 20-100% NF₃ percentage. Main effect analysis revealed that the surface roughness is the most strongly affected by the bias power. For variations in the bias power or NF₃ percentage, decrease in the surface roughness was observed only as positive variations in the etch rate and dc bias are considerably large. The surface roughness with the pressure was chemically dominated as illustrated by its inverse relationship with the dc bias. For the variations in the NF₃ percentage, the radical variation was estimated to play a more dominant role. The smoothest surface roughness of 0.312 nm was obtained at 700 W source power, 150 W bias power, 1.60 Pa pressure, and 100% NF₃ percentage.     

Dry etching of TiN in N2/Cl2/Ar adaptively coupled plasma

We investigated the N₂ additive effect on the etch rates of TiN and SiO₂ and etch profile of TiN in N₂/Cl₂/Ar adaptively coupled plasma (ACP). The mixing ratio of Cl₂ and Ar was fixed at 75 and 25 sccm, respectively. The N₂ flow rate was increased from 0 to 9 sccm under the constant pressure of 10 mTorr. As N₂ flow rate was increased in N₂/Cl₂/Ar plasma, the etch rate of TiN was linearly increased, but that of SiO₂ was increased non-monotonically. The etch profile and the compositional changes of TiN was investigated with field emission-scanning electron microscope (FE-SEM), FE-Auger electron spectroscopy (FE-AES) and x-ray photoelectron spectroscopy (XPS). When 9 sccm N₂ was added into Cl₂/Ar, a steep etch profile and clean surface of TiN was obtained. In addition, the signals of TiN and Ti were disappeared in FE-AES and XPS when N₂ additive flow into Cl₂/Ar was above 6 sccm. From the experimental data, the increase in TiN etch rate was mainly caused by the increase of desorption and evacuation rate of etch by products because of the increased effective pumping speed. The etch mechanism of TiN in N₂/Cl₂/Ar ACP plasma can be concluded as the ion enhanced chemical etch.     

Fabrication of GaN nanorods by inductively coupled plasma etching via SiO2 nanosphere lithography

In this study, we present a facile route to fabricate GaN nanorods by employing the nanosphere lithography (NSL) technique. Compared to previous approaches, it was demonstrated that arrays of silica (SiO₂) nanospheres can be effectively used as etching masks for the inductively coupled plasma etching process. By adjusting the etching conditions between SiO₂ nanospheres and GaN substrates, well-defined nanorods, which were as long as a few microns with controllable diameters, were successfully fabricated. This method is much simpler than any other technique currently being used, and can be generally applied to fabricate various types of nanorods.     

Influence of reemission of neutrals on the shape of etched grooves

The plasmochemical etching of silicon in CF₄+O₂ plasma is considered. The chemical composition of plasma and values of reaction rate constants, determined in previous works, were used to calculate the etched groove profiles at real dimensions. The profiles of etched grooves are calculated as a function of mask dimensions, fluxes of chemically active components and reemission of chemically active components from the surface of groove. The etching anisotropy is reduced when the reemission of F and O atoms from the surface takes place. The increase of etching anisotropy at high O₂ content in the feed (>60%) is explained by the complete sidewall oxidation and decreased concentration of F atoms in the plasma. The influence of reemission of F and O atoms on the shape of etched grooves becomes pronounced for mask width >1 μm.     

Effect of doping elements on ZnO etching characteristics with CH4/H2/Ar plasma

Effect of doping elements on the etching characteristics of doped-ZnO (Ag, Li, and Al) thin films, etched with a positive photoresist (PR) mask, and an etch process window for infinite etch selectivity were investigated by varying the CH₄ flow ratio and self-bias voltage, V_dc, in inductively coupled CH₄/H₂/Ar plasmas. Increased doping of ZnO films decreased the etch rates significantly presumably due to lower volatility of reaction by-products of doped Li, Ag, and Al in CH₄/H₂/Ar plasmas. The etch rate of AZO (Al-doped ZnO) was most significantly decreased as the doping concentration is increased from 4 to 10 wt%. It was found that process window for infinite etch selectivity of the doped ZnO to the PR is closely related to a balance between deposition and removal processes of a-C:H (amorphous hydrogenated carbon) layer on the doped-ZnO surface. Measurements of optical emission of the radical species in the plasma and surface binding states by optical emission spectroscopy (OES) and X-ray photoelectron spectroscopy (XPS), respectively, implied that the chemical reaction of CH radicals with Zn atoms in doped-ZnO play an important role in determining the doped-ZnO etch rate together with an ion-enhanced removal mechanism of a-C:H layer as well as Zn(CH_x)_y etch by-products.     

The etching characteristics of Al2O3 thin films in an inductively coupled plasma

In this study, the etching characteristics of ALD deposited Al₂O₃ thin film in a BCl₃/N₂ plasma were investigated. The experiments were performed by comparing the etch rates and the selectivity of Al₂O₃ over SiO₂ as functions of the input plasma parameters, such as the gas mixing ratio, the DC-bias voltage, the RF power, and the process pressure. The maximum etch rate was obtained at 155.8 nm/min under a 15 mTorr process pressure, 700 W of RF power, and a BCl₃ (6 sccm)/N₂ (14 sccm) plasma. The highest etch selectivity was 1.9. We used X-ray photoelectron spectroscopy (XPS) to investigate the chemical reactions on the etched surface. Auger electron spectroscopy (AES) was used for the elemental analysis of the etched surfaces.