Addition Of CF4 Research Articles

Influence of reactor walls on plasma chemistry and on silicon etch product densities during silicon etching processes in halogen-based plasmas

The absolute concentrations of SiClX (X = 0–2), SiFX (X = 1–2), SiClF, SiBr and SiO radicals were measured in an industrial silicon gate etching reactor with various halogen gas mixtures (HBr, Cl2, O2, CF4 mixtures). The influence of O2 gas flow in the HBr/Cl2 mixture, of the HB/Cl2 ratio, and of CF4 addition in HBr/Cl2 have been analysed systematically. These experimental results are the first quantitative information on the densities of silicon etch products in a high density Cl2-based plasma, and are useful to validate and improve numerical models. In addition, these results are correlated with the 200 mm diameter silicon wafer etch rate, and with the deposition rate of the layers deposited on the plasma chamber walls and with their chemical compositions. This allows us to discuss the production and loss mechanisms of silicon etching by-products during silicon etching processes. In Cl2-based plasmas, we show that the chamber walls are efficient for recycling silicon: SiCl2–4 radicals, initially produced from the etching of the wafer are ionized and dissociated by the plasma into reactive products Si, SiCl, Si+, SiCl+. These species can then undergo chemisorption on the reactor walls, where they can be either oxidized by O atoms from the plasma (leading to the formation and growth of SiOClX layers on the chamber walls) or be etched back into the gas phase by Cl atoms. Therefore, the deposition rate of SiOClX layers on the chamber wall results from a competition between these two reactions and is then limited by the amount of O atoms available. The other consequence of this competition is that reactor walls produce large amounts of SiCl2–4 radicals when the O2 flow is low. When CF4 is added to the plasma, the concentration of SiClX etch products decreases in favour of SiFX etch products. In addition, the presence of F atoms and CFX radicals and fluorine-based ions prevents the deposition of a SiOClX layer on the reactor walls.

Effects of CF4 addition on oxygen contamination of SiC films in hot filament chemical vapor deposition using CH4+SiH4+H2

The contamination of unwanted atoms such as oxygen that may originate from residual gas in reactant chambers is common in the deposition of SiC films. In this study, CF4 was introduced into a chamber while preparing SiC films by hot filament chemical vapor deposition using CH4, SiH4, and H2, and then the films were characterized by Fourier transform infrared (FTIR) spectrometer and x-ray photoelectron spectrometry (XPS). The FTIR and XPS results showed that the CF4 addition could reduce the oxygen content in the films. It is concluded that the reduction of oxygen is due to the reaction of active F* (or CFn*), O*, Si* (or SiHn*), and C* (or CHn*) in the process. Simultaneously, the results indicate also that the addition of CF4 could improve the degree of ordering of the Si–C bonds and lead to a decrease in the growth rate. The influence of CF4 addition on the ordering of the Si–C bonds and the growth rate of the films is discussed.

Enhancement of the recombination rate of Br atoms by CF4 addition and resist etching in HBr/Cl2/O2 plasmas

Mass spectrometry has been used to study the influence of the plasma chamber walls on the recombination rates of halogen atoms in a high density HBr/Cl2/O2/CF4 plasma used for silicon gate etching. In these plasmas, CF4 addition results in a transition from SiOx to CFx layer deposition on the chamber walls. We show that this is accompanied by an important enhancement of the surface recombination rate of halogen atoms (specially Br), whose gas phase concentration consequently drops. The same phenomenon is observed when photoresist is etched in an HBr/Cl2/O2 plasma resulting in carbon coating of the chamber walls. This demonstrates that the recombination coefficient of Br atoms on organic polymer surfaces is much larger than on SiO2-like surfaces, and that significant consequences on gate etch processes are expected.

Triple-GEM detector operation for high rate particle triggering

We report the results of a study of triple-GEM detectors for high rate charged particle triggering. This study was performed in the framework of an R&D activity on detectors for the Level-0 LHCb muon trigger and, in particular, for the inner regions (R1 and R2) of the first station (Ml), where particle rates up to 460 kHz/cmz are expected. A crucial requirement in this application is an efficiency higher than 99% per station (two detectors logically OR-ed) in a 25 ns time window. Results of the time performance are compared with the discharge probability per incident particle as results from a study performed with a high intensity hadron beam. We show here the considerable improvement obtained with the addition of CF4 and/or iso-C4H10 to the widely used Ar/CO2 mixture. Which allows to satisfy the experiment requirements.

Impact of chemistry on profile control of resist masked silicon gates etched in high density halogen-based plasmas

Critical dimension (CD) control during silicon gate etching has been investigated with state-of-the-art chemistries. In particular, we have compared the etched profile of both isolated and dense gates obtained after the main etch step of a gate etch process using HBr/Cl2/O2 and HBr/Cl2/O2/CF4 gas mixtures, and study the influence of the CF4/O2 ratio in this mixture. We demonstrate that the gate etch profile is mainly driven by the passivation layer deposited on the gate and mask sidewalls during the etching. Due to aspect ratio dependant etching effect the passivation layer formation is thinner in dense than in isolated structures resulting in significant profile microloading. However, CF4 addition to HBr/Cl2/O2 strongly minimizes the difference in passivation layer thickness between dense and isolated lines thus potentially improving the critical dimension control. These results will be discussed in terms of chemical composition of the passivation layer and deposition mechanisms, based on previous studies by x-ray photoelectron spectroscopy and mass spectrometry studies. Finally, we will discuss the influence of the soft-landing and overetch steps on the final profile of the gates, and show that aspect ratio dependant etch rate during the main etch step of the process can become an additional source of CD microloading.

Chemical topography analyses of silicon gates etched in HBr/Cl2/O2 and HBr/Cl2/O2/CF4 high density plasmas

We have used x-ray photoelectron spectroscopy (XPS) to analyze resist patterned silicon surfaces etched in a commercial 200 mm high density plasma etcher. After anisotropic etching using gate etching chemistries based on HBr/Cl2/O2 gas mixtures with or without CF4 addition, wafers are transferred under vacuum to perform chemical topography analysis using XPS in order to measure the element concentration on the silicon surfaces at the bottom of the trenches as well as the silicon sidewalls. Composition of the layers formed on the silicon sidewalls as a function of the plasma operating conditions is reported and discussed. The sidewall layer formation is mainly attributed to the oxidation of silicon etching by-products and the deposition of fluorocarbon species. Depending on the O2 and CF4 amount during a silicon gate main etch step, composition of the layer can be either SiOx-like or fluorocarbon rich. In all cases, the sidewall layer is transformed into a SiOx material during the subsequent fluorine free soft-landing step, as a result of the direct oxidation of silicon combined with the fluorocarbon species removal by oxygen in the plasma.

Integrated equipment-feature modeling investigation of fluorocarbon plasma etching of SiO2 and photoresist

As the microelectronics industry continues to shrink feature size and increase feature density in the back-end of integrated circuits, the traditional empirical approach to plasma etch process development is becoming prohibitively expensive and time consuming. Fundamental physics based models can prove useful in driving down process development time and cost. In this article, an integrated equipment-feature scale modeling infrastructure for SiO2 and photoresist (PR) etching in fluorocarbon based plasma discharges is described. The model correlates process conditions with plasma properties, surface interactions, and etch results. A validated plasma chemistry for Ar/c–C4F8/CF4 and detailed plasma–surface reaction mechanisms for SiO2/PR etching have been incorporated in the model. Major surface reactions for SiO2 etching include neutral surface passivation, fluorocarbon radical polymerization, and ion assisted etching of volatile products. The mechanism for PR erosion includes energy/angle dependent ion sputtering, ion activation, F atom etching with ion assistance, and fluorocarbon radical deposition. Computed SiO2 and PR etch profiles and rates have been validated by comparing with experimental results in a commercial inductively coupled plasma (ICP) etch tool. The validated model is used for a detailed investigation of SiO2/PR etching in a representative 300 mm wafer ICP tool. It is found that SiO2 etch rate is a nonlinear function of Ar/c–C4F8 ratio, where the highest etch rate is obtained when sufficient neutral passivation takes place while polymer deposition is still small. Deviating from this condition reduces SiO2 etch rate by either excessive polymerization or insufficient passivation. PR etch rate and facet size, however, increase monotonically with Ar/c–C4F8 ratio due to reduced polymer deposition. The effect of CF4 ratio in the Ar/c–C4F8/CF4 source gas on SiO2 etching depends on the Ar fraction. When Ar fraction is large, replacing c-C4F8 with CF4 reduces surface passivation and thereby decreases SiO2 etch rate. However, at small Ar fractions, CF4 addition reduces polymer formation and increases the SiO2 etch rate. For the range of conditions explored, SiO2 etch characteristics are insensitive to bias frequency as the ion energies are well above the threshold energy for etching. The plasma zone height (PZH) impacts the fluxes of etchants to the wafer and consequently the SiO2/PR etch rates. PZH, however, does not influence etch uniformity noticeably as diffusion is dominant at low gas pressures.

Effects of the polymer residues on via contact resistance after reactive ion etching

The effects of CF4 addition to O2 reactive ion etching (RIE) of a polyetherimide (Ultem®) surface and resultant via contact resistance were investigated using scanning electron microscopy (SEM), x-ray electron spectroscopy (XPS), and cross bridge Kelvin resistor (CBKR). In pure O2 RIE, the SEM micrograph showed that the originally smooth Ultem surface became rough and the rough features coarsened with increasing RIE time, resulting in residual particles on the metal pads. However, in the case of O2+CF4 RIE, the Ultem surface remained smooth throughout the etching process, and residue free metal pads were obtained. The XPS experiments identified that the origin of the Ultem surface roughening was organo-Si compound, which is easily converted to silicon oxide during O2 RIE. In contrast, the atomic fluorine in O2+CF4 RIE process etched out the silicon and the silicon oxide, resulting in smooth film surface and residue free metal pads. The metal to metal via contact resistance was measured by CBKR, and the pattern fabricated by O2+CF4 RIE showed lower contact resistance than those by O2 RIE. These results are discussed in the criterion of contact area and contact conformality differences.

Smooth and high-rate reactive ion etching of diamond

Diamond surfaces with patterned Al masks were etched by a reactive ion etching (RIE) system under conditions that the RF power was 100–280 W, the CF4/O2 ratio was 0–12.5% and the gas pressure 2–40 Pa. It was found that the roughness of the etched diamond surface decreased with an increase in the CF4/O2 ratio, although this reduced the selective etching ratio of diamond against Al. The gas pressure also affected the surface roughness and the etching anisotropy. The etching rate of diamond considerably increased upon a small addition of CF4 in O2. Based on these results, we were successful in an anisotropic etching of diamond at a very high rate (∼9.5 μm/h) with a smooth etched surface (Ra<0.4 nm), a high selective etching ratio of diamond vs. Al, and a high aspect ratio (the height/diameter was ∼8 for array structures and ∼25 for exceptional cases) by choosing appropriate etching conditions.

Fluorocarbon polymer formation, characterization, and reduction in polycrystalline–silicon etching with CF4-added plasma

Addition of CF4 into HBr-based plasma for polycrystalline–silicon gate etching reduces the deposition of an etch byproduct, silicon oxide, onto the chamber wall but tends to generate organic polymer. In this work, a detailed study has been carried out to analyze the mechanism of polymerization and to characterize the polymer composition and quantity. The study has shown that the polymer formation is due to the F-radical depletion by H atoms dissociated from HBr. The composition of the polymer changes significantly with CF4 concentration in the gas feed, and the polymer deposition rate depends on CF4% and other process conditions such as source power, bias power, and pressure. Surface temperature also affects the polymer deposition rate. Adding O2 into the plasma can clean the organic polymer, but the O2 amount has to be well controlled in order to prevent the formation of silicon oxide. Based on a series of tests to evaluate polymer deposition and oxide cleaning with O2 addition, an optimized process regime in terms of O2-to-CF4 ratio has been identified to simultaneously suppress the polymer and oxide deposition so that the etch process becomes self-cleaning.

Decrease in Deposition Rate and Improvement of Step Coverage by CF4 Addition to Plasma-Enhanced Chemical Vapor Deposition of Silicon Oxide Films

The low dielectric constant of F-doped silicon dioxide film makes it suitable for use as an intermetal film to improve the performance of ultra-large scale integrated circuits (ULSIs). One of the properties required by an intermetal film is good gap filling. It is known that fluorine addition to silicon oxide decreases the film deposition rate and improves the step coverage. In order to investigate these phenomena, we study the reaction mechanism of plasma-enhanced chemical vapor deposition (PECVD) silicon oxide film and its change by fluorine addition. Using a two film-forming species model, we explain the dependence of the deposition rate and the step coverage on the residence time for a SiH4/N2O-based PECVD system. The precursor produced by the dissociation of SiH4 has a relatively high sticking probability (≈0.5), while an intermediate species has a low (<10-4) sticking probability. The concentration of each species for deposition is changed by the residence time of the gas, thus the deposition rate and the step coverage show dependence on the residence time. The deposition rate of silicon oxide films is decreased and the step coverage is improved by CF4 addition during SiH4/N2O-based PECVD. From the estimation of the sticking probability, we suggest that the reason for the improvement of the step coverage by fluorine addition is not the etching effect by CF4 addition, but the decrease in sticking probability of the precursor produced by the dissociation of SiH4.

Probe measurements and global model of inductively coupled Ar/CF4 discharges

The electron energy distribution function (EEDF) is measured with a Langmuir probe in an inductively-coupled radio frequency (RF, 13.56 MHz) Ar/CF4 discharge over a pressure range 3-30 mTorr by changing the CF4 content from 0 to 20%, while keeping the power injected into the plasma at about 50 W. EEDFs measured at a pressure lower than 10 mTorr are bi-Maxwellian distributions over the measured CF4 content, while those at a pressure of 30 mTorr are Druyvesteyn ones in the presence of a small amount of CF4. The average electron energy slightly increases with CF4 content, while the electron density decreases. The decrease in the electron density with addition of CF4 is more prominent as the total pressure increases. Dependences of the electron density and the averaged electron energy on CF4 content are predicted in the global model.

Effect of CF4 Addition on Downflow Ashing under Atmospheric Pressure

We studied the rate increase of ozone ashing under atmospheric pressure. It was verified that when an ozonizer discharge was used under atmospheric pressure, the ashing rate increased to up to one and a half times the original rate with the addtion of CF4. F element and C–F bonds, which might appear as a result of the addition of CF4, were not detected on the resist surface by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) analyses. On the other hand, the formation of HF and an increase in CO and CO2 were observed by FT-IR analysis of the excited gas. Therefore, the increased ashing rate with the addition of CF4 is likely due to the active decomposition product which contains fluorine radicals produced in the discharge. These active species are transported under atmospheric pressure and cause H extraction from –OH groups which exist in the resist and result in improved oxidative decomposition.

Investigation into the Analytical Utility of Plasma Etching in Reactive Glow Discharge Plasmas

Tetrafluoromethane (CF4, 1.01% by weight) was added to the argon support gas of a hollow cathode glow discharge to investigate the analytical utility of etch atomization. When a conducting copper cathode was analyzed, the sputtering rate (as measured by weight loss) was reduced by a factor of five compared to operation with pure argon. Copper atomic absorbance and copper atomic emission intensity were also reduced by factors of seven and two, respectively. When a nonconducting sample was analyzed, the stainless steel ring that held the sample acted as an auxiliary cathode, supporting the discharge processes. Radical fluoride species formed in this discharge reacted with the nonconducting substrate (silica) to produce volatile SiF4 that spontaneously evolved into the gas phase, carrying with it copper and uranium. This approach is analogous to plasma etching, a well-established technique for semiconductor processing. Atomic emission data were obtained with a pure argon discharge and an argon/CF4 discharge. With the addition of CF4, a 30% enhancement was observed for uranium in glass and a 50% enhancement for copper in glass. Scanning electron microscopy (SEM) was used to support the supposition that etching of the silica matrix on the inner surface of the hollow cathode contributed to this enhancement.

Effects of CF4 Addition on the Growth of Amorphous CNx Films by Plasma Decomposition of CH4-N2 Gas Mixtures

ABSTRACTHydrogenated amorphous carbon nitride (α-CNx:H) films are deposited at 50–300°C by radio-frequency plasma decomposition of CH4-CF4-N2 gas mixtures. Effects of fluorine radicals on the deposition rate, composition, and on chemical bonding are investigated. When CF4 gas is added as partial replacement of CH4 gas, the deposition rate at 200°C steeply increases with increasing flow rate ratio RCF = [CF4]/([CH4]+[CF4]) up to ∼0.3, and then it decreases gradually. It is found that the nitrogen content, x, increases from 0.22 to 0.46 when RCF increases from 0 to 0.75. The inclusion of fluorine atoms into the films is less than 5 at%. The infrared absorption spectra shows strong enhancement of the absorption bands related to various forms of C—N bonding by the CF4 addition. It is found that the addition of CF4enhances the formation of C–N bonds in PECVD α-CNx:H films.

Reactive Ion Etching Mechanism of RuO2 Thin Films in Oxygen Plasma with the Addition of CF4, Cl2, and N2

In this study, we thoroughly investigated the reactive ion etching mechanism of RuO2 film in oxygen plasma with the addition of CF4, Cl2, and N2. The etch rate of RuO2 was examined as functions of flow rates of input gases, substrate temperature, DC bias applied to the substrate, and pressure. The concentrations of the etching species in the plasma were determined using optical emission spectroscopy (OES) and a quadrupole mass spectrometer (QMS). The etch products were determined with a QMS and the etched surface of RuO2 film was examined with X-ray photoelectron spectroscopy (XPS). RuO4 and RuO3, which are formed by the reactions between RuO2 film and oxygen radicals, are the only etch products regardless of the kind of additive gas. The additive gases (CF4, Cl2, and N2) are not directly involved in the chemical reaction with the RuO2 film, but they increase the concentration of oxygen radicals and accordingly, appreciably increase the etch rate of the RuO2 films. The etch rate is limited by the formation rate of the etch products, which is enhanced by the bombardment of energetic ions. Therefore, the etch rate depends not only on the concentration of oxygen radicals, but also on the flux and energy of the ions bombarding the film surface. In this study, for the first time, we introduced the use of the O2/N2 plasma system in RuO2 etching.

Gas phase study with CF4 and CCl2F2 addition in microwave CVD diamond growth

The effects of halogenated precursor associated with O 2 addition in the gas phase for diamond growth have been studied. Optical emission spectroscopy (OES) and exhaust gas mass spectrometry (MS) were used in a microwave plasma-assisted chemical vapor deposition (MWPACVD) reactor. The relative emission intensity of atomic hydrogen line H α (656.3 nm) has been measured with CF 4 and CCl 2 F 2 concentrations in the range of 0–5%. Our results show an increase of atomic hydrogen concentration up to 80 and 200% when CF 4 and CCl 2 F 2 are added in the mixture, respectively. The input gases were chosen in order to discern the oxygen effects for mixtures with different concentrations of CF 4 and CCl 2 F 2 . An additional increase of 50% H generation was observed when O 2 was added in the range of 0–3% for both mixtures with 3% of CF 4 or CCl 2 F 2 . Mass spectrometry was used to analyze the dissociation process of CF 4 and CCl 2 F 2 associated with HF and HCl formation. These dissociation processes are correlated with the increase of atomic hydrogen concentration. For oxygen addition, CO formation is the main final product from the halocarbon. The higher thermodynamic stability of CO enables us to obtain a gas phase with a high concentration of atomic hydrogen and inhibits the formation of solid non-diamond carbon observed in mixtures with high halocarbon concentrations.

0.1 μm WSiN-gate fabrication of GaAs metal-semiconductor field effect transistors using electron cyclotron resonance ion stream etching with SF6–CF4–SiF4–O2

We investigate etching characteristics of WSiN gates using electron cyclotron resonance ion stream etching with a SF6–CF4–SiF4–O2 gas mixture, and we fabricate 0.1 μm WSiN gates for ultrahigh speed GaAs metal-semiconductor field effect transistors (MESFETs). A vertical WSiN gate etched pattern is obtained as a result of CF4 addition. Moreover, uniform etching over the entire wafer can be attained with high selectivity between the WSiN and the GaAs and with accurate control of the gate length. A current-gain cutoff frequency (fT) of 131.4 GHz with a 3σ value of 5.0 GHz in whole wafer has been obtained for 0.1 μm gate GaAs MESFETs.

H actinometry with CF4 addition in microwave plasma-assisted chemical vapor deposition of diamond

Abstract Optical emission spectroscopy (OES) and exhaust gas mass spectrometry were used to study the gas phase during diamond growth in microwave plasma-assisted chemical vapor deposition (MPACVD). Mixtures with CF 4 addition in H 2 /Ar and H 2 /Ar/CH 4 have been studied. The relative emission intensity of atomic hydrogen line H α has been measured by actinometry. This work presents a systematic study that has been performed with regard to the dependence of the relative intensity of the H α line (656.3 nm) with CF 4 addition. CF 4 concentrations in the range of 0–5% have been studied. We also investigated the influence of oxygen addition on the relative intensity of the H α line for fixed mixtures with H 2 /Ar/CH 4 and H 2 /Ar/CF 4 . Our results have shown that CF 4 and O 2 addition increases considerably the atomic hydrogen concentration. These results suggest that the CF 4 and O 2 addition can promote diamond growth using systems with lower activation power.

Diamond growth with CF4 addition inhot-filament chemical vapour deposition

Tetrafluoromethane (CF4) was added to standard CH4/H2 mixtures for diamond growth in hot-filament-assisted chemical vapour deposition. CF4 concentrations in the range of 0.3%–3% were studied. Mass spectrometry of the exhaust gas showed that only a small fraction (< 15%) of CF4 was thermally dissociated for filament temperatures over 1800 °C. The observed stable products of its dissociation were mainly C2H2, CH4 and HF. This CF4 addition considerably enhanced the nucleation and growth characteristics on silicon and molybdenum. Diamond growth was observed with substrate temperature as low as 390 °C. A comparative study for the growth dependence on substrate temperature with and without CF4 addition in the gas mixture is presented. The growth rate was measured by post-growth weighing with a micro balance. An activation energy of 11 kcal mol-1 for growth with CF4 addition was obtained. Raman spectra and atomic force microscopy were used to characterize the diamond films.