Decrease In Etch Rate Research Articles

Plasma etching of SiO2 using remote-type pin-to-plate dielectric barrier discharge

Atmospheric pressure plasma etching of SiO2 was examined using a modified remote-type dielectric barrier discharge (DBD), called “pin-to-plate DBD.” The effect of adding four gases CF4, C4F8, O2, and Ar to the base gas mixture containing N2 (60 slm) (slm denotes standard liters per minute)/NF3 (600 SCCM) (SCCM denotes cubic centimeter per minute at STP) on the SiO2 etch characteristics was investigated. The results showed that the SiO2 etch rate decreased continuously with increasing C4F8 (200–800 SCCM) addition, whereas the SiO2 etch rate increased with increasing CF4 (1–10 slm) addition up to 7 slm CF4. This increase in the SiO2 etch rate up to 7 slm CF4 was attributed to the effective removal of Si in SiO2 by F atoms through the removal of oxygen in SiO2 by carbon in the CFX in the plasma. However, the decrease in SiO2 etch rate with further increases in CF4 flow rate above 7 slm was attributed to the formation of a thick C–F polymer layer on the SiO2 surface. A SiO2 etch rate of approximately 243 nm/min was obtained with a gas mixture of N2 (60 slm)/NF3 (600 SCCM)/CF4 (7 slm), and an input voltage and operating frequency to the source of 10 kV and 30 kHz, respectively. The addition of 200 SCCM Ar to the above gas mixture increased the SiO2 etch rate to approximately 263 nm/min. This is possibly due to the increased ionization and dissociation of reactive species through penning ionization of Ar.

Comparative study of carbide-derived carbons obtained from biomorphic TiC and SiC structures

Biomorphic carbide ceramics, TiC and SiC, derived from paper performs by chemical vapor infiltration were converted into high porous carbon by carbide-derived carbon (CDC) approach using selective etching in chlorine or hydrogen/chlorine gas mixture in a temperature range of 400–1200 °C. A comparative study of both carbide precursors was performed regarding reaction kinetics, influence of hydrogen as well as microstructure of the resulting carbon. SiC showed lower reactivity than TiC. Temperatures below 650 °C are not sufficient to remove Si from SiC. Addition of hydrogen to the reactive gas inhibits the chlorination reaction. A linear decrease of etching rate with increasing hydrogen/chlorine ratio was observed for both carbide precursors. A critical ratio, where no etching takes place, was estimated to be 0.72 for TiC–CDC and 0.66 for SiC–CDC. The etching rate of TiC is independent from the temperature. In the case of SiC activation energy of the chlorination reaction of about 50 kJ/mol was estimated in the temperature range 650–800 °C. The structural ordering of CDC with increasing synthesis temperature affects also its oxidation resistance as shown by thermo gravimetric analysis.

Reactive-ion etching of Ge 2Sb 2Te 5 in CF 4/Ar plasma for non-volatile phase-change memories

Etching of Ge 2Sb 2Te 5 (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 CF 4/Ar gas mixture using a reactive-ion etching system. We observed a monotonic decrease in etch rate with decreasing CF 4 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 CF 4/Ar gas mixture ratio of 10/40, a background pressure of 80 mTorr, and power of 200 W.

The optical properties of porous silicon produced by metal-assisted anodic etching

Porous silicon (PS) was obtained from n-type (100) mono-crystalline silicon wafers with different metal using two different illumination conditions. The visible photoluminescence (PL) may come from defect-related radiative centers on PS surface and adsorbed hydrogen atoms may be associated to the elimination of irradiative centers on PS surface, which can be proved by the infrared absorption spectra. The metal can be used as catalytic role to increase the etching rate under back illumination, but under front illumination, the metal can cancel light-generated carrier leading to the decrease of etching rate during anodic etching. Furthermore, the change of minority carrier lifetime is opposite to the change of PL efficiency of PS, which can be Confirmed by the results of μ-PCD measurements.

ETCH CHARACTERISTICS OF COFESIB MAGNETIC FILMS USING INDUCTIVELY COUPLED PLASMA REACTIVE ION ETCHING FOR MAGNETIC RANDOM ACCESS MEMORY

ABSTRACT Inductively coupled plasma reactive ion etching of CoFeSiB magnetic thin films was studied in a Cl2/O2/Ar gas mix. The etch rate, etch selectivity and etch profile of this magnetic film were examined on varying gas concentration, coil rf power, gas pressure and dc-bias voltage. As the Cl2 gas increased, the etch rate monotonously decreased and etch residues decreased but etch slope was slanted. The use of the TiN hard mask gave rise to high selectivity of CoFeSiB to the TiN mask due to large decrease in etch rate of TiN in Cl2/O2/Ar gas mix. The addition of O2 into the gas mix led to the anisotropic etching of CoFeSiB films without the etch residues.

High-density plasma etching of CoFeSiB magnetic films with hard mask

High-density plasma etching of amorphous CoFeSiB magnetic films was carried out in a Cl 2/Ar and Cl 2/O 2/Ar gas mixes. In a Cl 2/Ar gas, as the Cl 2 concentration increased, the etch rate of CoFeSiB films decreased, and etch residues decreased but the etch slope was slanted. However, in Cl 2/O 2/Ar gas mix, the etch characteristics of CoFeSiB films with TiN hard mask was enhanced. The etch rate and selectivity of CoFeSiB films were investigated as a function of O 2 concentration. The use of TiN hard mask gave rise to high etch selectivity of CoFeSiB to TiN mask due to large decrease in etch rate of TiN in Cl 2/O 2/Ar chemistry. The addition of O 2 into the gas mix led to the anisotropic etching of CoFeSiB films without the etch residues.

Reactive ion etching of glass for biochip applications: Composition effects and surface damages

Due to its insulating properties, transparency, and well known surface chemistry, glass represents an interesting alternative to silicon or polymers for biochip processing. However, high aspect-ratio posts for DNA electrophoresis have only been reported in expensive quartz substrates. Therefore, we investigate here metal mask transfer by fluorocarbon plasma etching in nine silica or glasses of different grades. With increasing amounts of non-SiO 2/non-B 2O 3 oxides in the material, the etch rate decreases and, in some cases, strong surface roughening appears. Furthermore, even for fused silica, surface damages such as cone-like defects were observed. Consequently, soda-lime slides coated with silica by plasma enhanced chemical vapor deposition (PECVD) were used as a good compromise between etching quality and cost. Electrophoresis chips with features down to 100 nm and aspect-ratio up to 10 could then be fabricated.

Effect of hydrogen peroxide on hydrofluoric acid etching of high- k materials: ESR investigations

Oxides and silicates of zirconium and hafnium are being actively considered for use as gate dielectrics in MOS devices. Because of their higher dielectric constant ( k ∼ 16–22), they permit the use of thicker layers without sacrificing the capacitance value. Wet chemical etching is the method of choice for patterning these oxides. The etching process has to be selective to zirconium/hafnium oxides over silicon dioxide, which may be present in other areas. In this paper, work done on HF etching of ZrO 2 and HfO 2 in presence of hydrogen peroxide is presented and discussed. It was found that addition of hydrogen peroxide to HF solutions lower the etch rate of ZrO 2 and HfO 2 films. Electron spin resonance (ESR) spectroscopy was used to probe the reasons for the decrease in etch rates in this solution.

Effect of gas mixing ratio on MgO etch behaviour in inductively coupled BCl 3/Ar plasma

The etching behaviour of MgO thin films in BCl 3/Ar plasma was investigated. It was found that the increasing Ar mixing ratio under the constant total pressure conditions causes the monotonic decrease of MgO etch rate, which falls from 93 to 17 nm/min. Plasma diagnostics combined with a 0-dimensional plasma model showed the noticeable sensitivity of both electron temperature and electron density to the process parameters as well as monotonic changes of both densities and fluxes of active species. The analysis of etching kinetics and mechanisms was performed. The results showed in the BCl 3-rich plasma the etching process is dominantly supplied by the chemical pathway through the ion-assisted chemical reaction.

Etching of porous SiOCH materials in fluorocarbon-based plasmas

This work focuses on the etching of different porous methylsilsesquioxane materials (spin on SiOCH, k=2.2) with different porosity (30%, 40% and 50%) in fluorocarbon-based plasmas (CF4∕Ar). The etching of these materials is performed on blanket wafers in a magnetically enhanced reactive ion etcher. The surface and bulk modification after partial etching are studied using different surface analysis techniques such as quasi-in-situ x-ray photoelectron spectroscopy (XPS), infrared spectroscopy (FTIR), and attenuated total reflection spectroscopy (FTIR-ATR). Similar to nonporous SiOCH materials, a decrease in etch rate of porous SiOCH films is observed with either increasing Ar dilution or polymerizing gas addition (CH2F2), which can lead in this last case to an etch stop phenomenon. The etch rate increases with higher porosity in the SiOCH film, since less material per unit thickness needs to be removed as the porosity increases. The XPS results show that a fluorocarbon layer is formed at the surface of the porous material and complementary angle resolved XPS analyses reveal that fluorocarbon species diffuse through the pores into the material. After partial etching, FTIR and ATR analyses reveal a carbon depletion in the remaining film, which indicates that the porous material is altered during plasma exposure. The film degradation is more important as the porosity increases. The etch rate evolution and film degradation are discussed and interpreted in terms of etching mechanisms and plasma surface interaction.

SiO2 films fabricated by F2 laser-induced chemical deposition using silicone rubber

Silicon dioxide (SiO2) films were selectively fabricated on a Si substrate at room temperature by illuminating both the silicone rubber target and the substrate with an F2 laser (157 nm). The laser fluence was much less than the ablation threshold. Absorption due to absorbed water (H2O) and hydrogen-bonded silanol (SiOH) groups were observed in addition to absorption due to Si-O-Si stretching mode in the Fourier transform infrared spectroscopy (FT-IR) spectra of the films. The illumination with higher laser fluence caused an increase of Si-O-Si/OH peak ratio in the FT-IR spectra, a decrease of etching rate in hydrofluoric acid (HF) solution, and an increase in the refractive index close to the value of a thermal SiO2 film. These results indicate that the quality of the grown SiO2 films was improved. The high photon energy of F2 laser induced photodissociation of main chains and side chains of silicone and oxygen (O2), and bonds between the ejected gaseous molecules including Si and O(1D) to form SiO2 films.

Many-hit model calculations for track etch rate in CR-39 SSNTD using confocal microscope data

The present work studied an important part of ion tracks: the Bragg peak region. Information about the microscopic nature of ion-energy dissipation based on zero-approximation in frame of the many-hit model of the track structure theory was studied. The detector response, Vt, was calculated in terms of Poisson’s distribution as a function of the ion’s linear energy transfer (LET). This approach can be considered to be a zero-approximation since LET is a special case of restricted energy losses with a cut off energy wcutoff=∞: LET=REL∞. Confocal microscopic data allows the visualising and analysing of the etched tracks one by one with high precision. A three-dimensional track image was observed and the track etch rate was measured. On the basis of χ2 analysis of the experimental track etch rate (square of the least deviation), with respect to that of the theoretical value, information about the energy transfer process can be obtained. Light ions of little MeV energy were slowed down in the CR-39 detector and the detectors responses close to the Bragg peak region were studied. It was shown that in the zero-approximation no one to one relation can be found between the primary linear energy transfer (LET) and the measured specific track etch rate. The statistical analysis can be split into two separate parts; before the Bragg peak (Bethe–Bloch) and after the Bragg peak (Thin Down). The two parts analysed reflect the separated domains where the etching rate increases or decreases, due to the different role of the delta-electrons in each of these domains. The main aim of this study is to develop a method for any ion describing Vt in this very sensitive Bragg region. This would allow ion identification at low velocities on the one hand, and on the other hand to have a better understanding of the physical processes involved during high velocity ion stopping.

Etch characteristics of CoZrNb and CoTb magnetic thin films in a high density plasma

The dry etching of CoZrNb and CoTb magnetic thin films was carried out using Cl2 and C2F6 etch gases in an high density plasma. These new magnetic materials exhibited the etching characteristic of monotonous decrease in etch rate with increasing gas concentration. The etch rates of CoZrNb and CoTb films were faster in Cl2 gas than in C2F6 gas. The etch rates of CoZrNb and CoTb films were in the range of 30 ∼ 60 nm/min for Cl2 gas while in the case of C2F6 gas, CoZrNb and CoTb films showed the etch rate of less than 20 nm/min. The etch profiles of CoZrNb and CoTb films exhibited clean without any etch residues but the etch slopes were shallow. As the concentration of Cl2 gas increases, the etch slope became slanted. At the etch conditions used in this study, it is thought that the concentration of 20 ∼ 40% Cl2/Ar gas is optimum to give fast etching and clean profiles. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Dynamic transition in etching with poisoning.

We study a lattice model for etching of a crystalline solid including the deposition of a poisoning species. The model considers normal and lateral erosion of the columns of the solid by a flux of etching particles and the blocking effects of impurities formed at the surface. As the probability p of formation of this poisoning species increases, the etching rate decreases and a continuous transition to a pinned phase is observed. The transition is in the directed percolation (DP) class, with the fraction of the exposed columns as the order parameter. This interpretation is consistent with a mapping of the interface problem in d+1 dimensions onto a d-dimensional contact process, and is confirmed by numerical results in d=1 and d=2. In the etching phase, the interface width scales with Kardar-Parisi-Zhang (KPZ) exponents, and shows a crossover from the critical DP behavior (W approximately t) to KPZ near the critical point, at etching times of the order of (pc-p)(-nu(||)). Anomalous roughening is observed at criticality, with the roughness exponent related to DP exponents as alphac=nu(||)/nu(perpendicular)>1. The main differences from previously studied DP transitions in growth models and isotropic percolation transitions in etching models are discussed. Investigations in real systems are suggested.

Effects of nitrogen addition on methane-based ECR plasma etching of gallium nitride

The effects of nitrogen addition on methane-based ECR plasma etching of GaN were studied. The etch rate 30 nm/min and r.m.s. roughness 2.6 nm were obtained when the GaN sample was etched by a methane-based gas mixture without N 2. The addition of N 2 gas resulted in a decrease of etch rate and a smoother etched surface. The r.m.s. roughness became less than 0.4 nm even only 1.5 sccm N 2 gas was added to the mixture. In situ XPS measurements showed that, without N 2, heavy N-depletion took place on the etched surface, resulting in appearance of Ga metal on the surface. In contrast, the loss of N was compensated when the N 2 gas was added, and the etched surface approached the stoichiometric one with the increase of N 2 gas flow. This suppression of preferential loss of N was considered to be the main reason that improved the etched surface morphology.

Micromachining of copper using Nd:YAG laser radiation at 1064, 532, and 355 nm wavelengths

The interaction phenomena of nanosecond time period Q-switched diode-pumped Nd:YAG laser pulses using 1064, 532 and 355 nm with 0.25 mm thick pure-copper foil was investigated at an incident laser intensity range of 0.5– 57.9 GW/ cm 2 . For each sample, etch rate and surface structure were determined. Analysis of the results of the tests included scanning electron microscopy (SEM). A maximum etch rate of 13.3 μm per pulse was obtained for the etch rate tests carried out at 532 nm . The maximum etch rate obtainable for 1064 nm was 2.21 μm per pulse, and for 355 nm , 6.68 μm per pulse. The dramatic decrease in etch rate observed when processing at 1064 nm is thought to occur due the highly reflective nature of copper as the interaction wavelength is increased, plus the nature of the plasma formed above the material during the high-intensity laser–material interaction. This plasma then imparts energy to the surface of the processed area leading to surface melting of the area surrounding the hole as can be seen by the SEM photographs.

Analysis and Modeling of Decontamination Experiments of Depleted Uranium Dioxide in RF Plasma

ABSTRACT: Analysis was performed of the results of UO2 etching experiments, which used NF3 RF glow discharge. In the experiments, the gas pressure was varied from ∼10 ‐ 40 Pa and the absorbed power was varied from 24 ‐ 210 W. The UO2 etch reactions to form volatile UF6 were strongly dependent on the absorbed power and, to a lesser extent, on pressure. At and below 50 W absorbed power, UO2 etching increased with pressure up to ∼ 23 Pa, then decreased with further increase in pressure. At higher power, however, UO2 etching increased monotonically with pressure. The UO2 etching process was self‐limiting, due to the formation of non‐volatile products UF2–5, UO2F, and UO2F2. The accumulation of UF6 and O2 in the plasma sheath also reduced the diffusion coefficient of atomic fluorine radicals to the UO2 surface thereby contributing to the decrease in etch rate with immersion time.

In Situ Measurements of the Resist Etch Rate for Submicron Patterns

A resist film is etched by oxygen-based plasmas, and fine grating patterns of the resist are fabricated. During etching, a laser beam is irradiated onto the sample and the reflection intensity from the sample is measured in order to determine the etching depth. The reflection intensities are calculated by solving the Maxwell equations for electromagnetic wave propagation. The dependence of the reflection intensity on the etching depth varies greatly with the ratio of the space width to the grating period. The absolute etch rate can be obtained by comparison between the experimental and simulated reflection intensities. The fabricated gratings are 0.5 µm in period and the ratios of the space width to the grating period are between 0.4 and 0.7. The reflection intensities obtained from the experiments agree very well with those from the simulations. The etch rate decreases as the etching depth increases, but it is almost independent of the aspect ratio of the fabricated patterns. The etch rate decrease is not caused by an increase in the aspect ratio of the etched pattern, but may be induced by the time variation of plasma conditions.

Modern Applications of Plasma Etching and Patterning in Silicon Process Technology

Besides plasma etching of through-wafer interconnects in wafer stacks for vertical integration of chips, fabrication of platinum (Pt) electrodes with non-tapered sidewalls for the storage node in modern memories (DRAMs and FeRAMs) is one of the most challenging tasks of plasma process technology today. This paper describes the achievement of vertical integration of chips by plasma etching of high aspect ratio interchip vias. The etching processes for dielectrics, single crystal silicon, and the organic glue layer were all optimized for minimum reactive ion etching (RIE) lag i.e. for minimum decrease of etch rate with increasing etch depth. Furthermore the fabrication of perfect Pt electrodes for modern DRAMs and FeRAMs is reported. Vertical Pt profiles were achieved by plasma processing with resist mask. In this novel approach, the build-up of thin redepositions of Pt onto the sidewalls of the resist, obtained as a result of processing in pure Ar plasmas, is utilized to achieve a sidewall steepness of the patterned Pt film which is determined by the steepness of the pre-etch resist profile. After pattern transfer and resist stripping, the portion of the redepositions protruding above the fabricated storage node was completely removed by chemical mechanical polishing.

Cl 2-based dry etching of the AlGaInN system in inductively coupled plasmas

Cl 2-Based inductively coupled plasmas with low additional d.c. self-biases (−100 V) produce convenient etch rates (500–1500 Å·min −1) for GaN, AlN, InN, InAlN and InGaN. A systematic study of the effects of additive gas (Ar, N 2, H 2), discharge composition and ICP source power and chuck power on etch rate and surface morphology has been performed. The general trends are to go through a maximum in etch rate with percent Cl 2 in the discharge for all three mixtures and to have an increase (decrease) in etch rate with source power (pressure). Since the etching is strongly ion-assisted, anisotropic pattern transfer is readily achieved. Maximum etch selectivities of approximately 6 for InN over the other nitrides were obtained.