Fluorocarbon Polymer Film Research Articles

Concentration of Fluorine Atoms and Kinetics of Reactive-Ion Etching of Silicon in CF4 + O2, CHF3 + O2, and C4F8 + O2 Mixtures

A comparative study of the electrophysical parameters of the plasma, the fluorine atom concentra-tions, and the kinetics of reactive-ion etching of silicon in CF4 + O2, CHF3 + O2, and C4F8 + O2 mixtures of a variable (0–75% O2) initial composition is carried out. It is shown that the dominant etching mecha-nism is always the ion-stimulated chemical reaction Si + xF → SiFx, whose rate has a maximum in the region of 20–50% O2. Based on the results of plasma diagnostics, it is found that the similar behavior of the concen-tration of fluorine atoms is typical only for mixtures of CF4 + O2 and CHF3 + O2, while in the C4F8 + O2 mix-ture, there is a nonmonotonic change in the probability of the interaction. It is assumed that the latter effect is caused by the competition between the processes of reducing the thickness of the fluorocarbon polymer film and the oxidation of the silicon surface by oxygen atoms.

On Relationships between Gas-Phase Chemistry and Reactive Ion Etching Kinetics for Silicon-Based Thin Films (SiC, SiO2 and SixNy) in Multi-Component Fluorocarbon Gas Mixtures.

This work summarizes the results of our previous studies related to investigations of reactive ion etching kinetics and mechanisms for widely used silicon-based materials (SiC, SiO2, and SixNy) as well as for the silicon itself in multi-component fluorocarbon gas mixtures. The main subjects were the three-component systems composed either by one fluorocarbon component (CF4, C4F8, CHF3) with Ar and O2 or by two fluorocarbon components with one additive gas. The investigation scheme included plasma diagnostics by Langmuir probes and model-based analysis of plasma chemistry and heterogeneous reaction kinetics. The combination of these methods allowed one (a) to figure out key processes which determine the steady-state plasma parameters and densities of active species; (b) to understand relationships between processing conditions and basic heterogeneous process kinetics; (c) to analyze etching mechanisms in terms of process-condition-dependent effective reaction probability and etching yield; and (d) to suggest the set gas-phase-related parameters (fluxes and flux-to-flux ratios) to control the thickness of the fluorocarbon polymer film and the change in the etching/polymerization balance. It was shown that non-monotonic etching rates as functions of gas mixing ratios may result from monotonic but opposite changes in F atoms flux and effective reaction probability. The latter depends either on the fluorocarbon film thickness (in high-polymerizing and oxygen-less gas systems) or on heterogeneous processes with a participation of O atoms (in oxygen-containing plasmas). It was suggested that an increase in O2 fraction in a feed gas may suppress the effective reaction probability through decreasing amounts of free adsorption sites and oxidation of surface atoms.

FEATURES OF SiO2 REACTIVE-ION ETCHING KINETICS IN CF4 + Ar + O2 AND C4F8 + Ar + O2 GAS MIXTURES

The effect of Ar/O2 mixing ratio on gas-phase characteristics and SiO2 etching kinetics in CF4 + Ar + O2 and C4F8 + Ar + O2 plasmas was studied under conditions of 13.56 MHz inductive RF discharge. The constant processing parameters were fraction of fluorocarbon component in a feed gas (50%) total gas pressure (6 mTorr), input power (700 W) and bias power (200 W). It was found that the full substitution of Ar for O2 in both gas systems results in non-monotonic (with a maximum at ~ 25% Ar + 25% O2) SiO2 etching rates as well as in monotonically increasing photoresist etching rate with higher absolute values for CF4-containing mixture. The steady-state densities of active species were determined using a combination of plasma diagnostics by Langmuir probes and 0-dimensional (global) plasma modeling. Corresponding results indicated that both gas systems are characterized by quite close parameters of electron and ion components while exhibit sufficient differences in the kinetics of neutral species, especially in the presence of O2. The latter produces opposite changes in F atom density as well as in effective probability of ion-assisted chemical reaction vs. Ar/O2 mixing ratio. Relationships between type of fluorocarbon component and heterogeneous process kinetics were analyzed through the set of gas-phase-related parameters (fluxes, flux-to-flux ratios) characterizing chemical etching pathways for SiO2 and formation/destruction balance for the fluorocarbon polymer film. It was suggested that the transition toward O2-rich plasma in the low-polymerizing CF4 + Ar + O2 plasma suppresses the effective probability for SiO2 + F reaction through decreasing efficiency for oxide bond breaking and desorption of etching products due to decreasing ion energy flux. Oppositely, an increase in O2 content in the high-polymerizing C4F8 + Ar + O2 mixture lifts up the effective reaction probability by decreasing fluorocarbon film thickness and providing better access of F atoms to the etched surface.

PLASMA PARAMETERS AND SiO2 ETCHING KINETICS IN C4F8 + Ar + O2 GAS MIXTURE

The effect of Ar/O2 mixing ratio on plasma parameters, steady-state densities of active species and SiO2 etching kinetics in the three-component C4F8+Ar+O2 gas mixture was studied under typical conditions of reactive ion etching process (inductive 13.56 MHz RF discharge, total gas pressure of 6 mTorr, input power of 700 W and bias power of 200 W). The investigation combined etching rate measurements, plasma diagnostics by Langmuir probes and 0-dimensional (global) plasma modeling in order to determine steady-state densities and fluxes of plasma active species. It was found that the full substitution of Ar for O2 at constant fraction of fluorocarbon gas (in fact, the transition from 50% C4F8 + 50% Ar to 50% C4F8 + 50% O2 gas system): 1) results in weakly non-monotonic (with a maximum) SiO2 etching rate with close values for both O2-free and Ar-free plasmas; 2) causes the monotonic decrease in both F atom flux and ion energy flux; and 3) suppresses the formation of the fluorocarbon polymer film on the etched surface through its oxidative destruction pathway. The model-based analysis of SiO2 etching kinetics allowed one to conclude that an increase in effective probability for SiO2 + F reaction contradicts with the behavior ion energy flux as well as demonstrate the agreement with the change in gas-phase parameters characterizing the fluorocarbon film thickness. Therefore, an increase in O2 content in a feed gas influences the effective reaction probability by decreasing fluorocarbon film thickness and providing better access of F atoms to the etched surface.

PLASMA PARAMETERS AND COMPOSITION IN CF4 + O2 + Ar AND CHF3 + O2 +Ar IN REACTIVE ION ETCHING PROCESSES

The comparative analysis of both CF4+O2+Ar and CHF3+O2+Ar plasma systems under the typical conditions of reactive ion etching of silicon and silicon-based compounds was carried out. The data on internal plasma parameters, plasma chemistry as well as the steady-state plasma composition were obtained using a description of Langmuir probe diagnostics and 0-dimensional (global) plasma modeling. As a presented in the literature, both experimental and modeling procedures were carried out at constant total gas pressure, input power, bias power. The obtained results allowed one 1) to figure out the influence of oxygen on steady-state densities of plasma active species through the kinetics of both electron-impact and atom-molecular reactions; 2) to understand the features of fluorine atoms and fluorocarbon radicals kinetics which determine chemical activity and polymerization ability of plasmas in respect to treated surfaces; 3) to perform the model-bases analysis of heterogeneous process kinetics (etching, polymerization, polymer destruction) which determine the overall etching regime and output parameters. It was found that the substitution of argon for oxygen in both gas mixtures 1) results in monotonic increase in fluorine atom density; 2) is accompanied by decreasing polymerization ability of a gas phase and 3) causes the rapid (by about two orders of magnitude at ~ 20% О2) decrease in fluorocarbon polymer film thickness with the higher values for CHF3+O2+Ar system.

Parameters of Plasma and Way of Etching Silicon in a CF4 + CHF3 + O2 Mixture

The effect of the CF4/CHF3 ratio in a CF4 + CHF3 + 9% O2 mixture on the parameters of the gaseous phase and kinetics of etching of silicon under the conditions of low-pressure inductively coupled plasma is investigated. It was found that substitution of CF4 by CHF3 at constant external parameters of the plasma (1) leads to a change of the temperature (average energy) and density of the electrons; (2) causes a decrease of the fluorine atom density followed by the majority of the molecules of HF; and (3) stimulates an increase of the rate of deposition and thickness of the fluorocarbon polymer film. By the analysis of the way of etching of silicon with the use of the calculated data on the fluxes of active particles, it was found that the observed change of the etching rate can be explained by heterogeneous reactions with the involvement of O, H, and HF. It was assumed that the process of etching silicon proceeds in the mode of limitation by the flux of chemically active particles F + HF and is characterized by the effective probability depending on the thickness of the fluorocarbon polymer film.

Gas-phase chemistry and etching mechanism of SiNx thin films in C4F8 + Ar inductively coupled plasma

In this study, we investigated the etching characteristics of non-stoichiometric SiNx thin films in C4F8 + Ar inductively coupled rf (13.56 MHz) plasma. The SiNx etching rates together with SiNx/Si and SiNx/SiO2 etching selectivities were measured as functions of the gas pressure (4–10 mTorr, or 0.53–1.33 Pa), input power (700–1000 W), bias power (100–400 W), and C4F8/Ar mixing ratio (0%–75% Ar). Data on internal plasma parameters and plasma chemistry as well as steady-state plasma composition were obtained by both Langmuir probe diagnostics and zero-dimensional plasma modeling. The etching mechanism of SiNx was analyzed through the relationship between the measured etching rates and model-predicted fluxes of active species (F atoms, CFx radicals, and positive ions). It was confirmed that within the given range of input process conditions, the SiNx etching process 1) appears in the steady-state etching regime, 2) exhibits the features of ion-assisted chemical reactions in the neutral-flux-limited mode, and 3) is influenced by the thickness of the fluorocarbon polymer film. It was shown that the influence of input process parameters on the effective probability of SiNx + F chemical reaction may be adequately characterized by the fluorocarbon radicals/fluorine atoms and fluorocarbon radicals/ion energy flux ratios.

Etching Mechanisms and Surface Conditions for SiOxNy Thin Films in CF4 + CHF3 + O2 Inductively Coupled Plasma

In this work, we investigated the etching characteristics of SiOxNy thin films in CF4 + CHF3 + O2 inductively coupled radiofrequency (13.56 MHz) plasma. SiOxNy etching rates were measured as functions of the CF4/CHF3 mixing ratio at constant O2 fraction, gas pressure (10 mTorr), input power (500 W) and bias power (100 W). The conditions of the etched surfaces were examined by X-ray photoelectron spectroscopy, atomic force microscopy and contact angle measurements. Data on internal plasma parameters and steady-state plasma composition were obtained by Langmuir probe diagnostics and zero-dimensional plasma modeling. It was found that the substitution of CF4 for CHF3 suppresses the SiOxNy etching rate as well as results in increasing both amount of residual fluorocarbon polymer and SiOxNy/Si etching selectivity. The SiOxNy etching mechanism was analyzed by considering the relationships between measured etching rates and model-predicted fluxes of active species (F atoms, CFx radicals and positive ions). It was proposed that the SiOxNy etching process: (1) exhibits features of ion-assisted chemical reactions in the neutral-flux-limited mode, and (2) involves the contributions of by HF molecules. The effective probability of the SiOxNy + F reaction is correlated with the amount of deposited fluorocarbon polymer while the hydrophobic nature of the plasma-treated SiOxNy surface confirms the presence of a continuous fluorocarbon polymer film.

PLASMA PARAMETERS, DENSITIES OF ACTIVE SPECIES AND ETCHING KINETICS IN C4F8+Ar GAS MIXTURE

In this work, we performed the combined (experimental and model-based) study of gas-phase plasma characteristics and etching kinetics for both Si and SiO2 in the C4F8 + Ar gas mixture. The experiments were carried out at constant total gas pressure (p = 6 mTorr), input power (W = 900 W) and bias power (Wdc = 200 W) while the C4F8/Ar mixing ratio was varied in the range of 0–75% Ar. The data on internal plasma parameters, plasma chemistry as well as the steady-state plasma composition were obtained by both Langmuir probe diagnostics and 0-dimensional plasma modeling. The etching mechanisms were investigated through the analysis of relationships between the measured etching rates and the model-predicted fluxes of active species (F atoms, polymerizing CFx radicals and positive ions). It was found that, under the given set of experimental conditions, the Si and SiO2 etching process 1) appears in the steady-state etching regime; 2) exhibits the features of the ion-assisted chemical reactions in the neutral-flux-limited mode; and 3) is influenced by the fluorocarbon polymer film thickness. It was shown that the influence of input process parameters on the effective probability of chemical reaction between Si, SiO2 and fluorine atoms may be adequately characterized by the fluorocarbon radicals/fluorine atoms and fluorocarbon radicals/ion energy flux ratios.

Achieving an acid resistant surface on magnesium alloy via bio-inspired design

Developing acid-resistant magnesium alloys is challenging because of the high chemical reactivity of magnesium in acidic media. In this work, a bio-inspired strategy by taking advantage of the super-hydrophobic effects on lotus leaves is described. The self-layered coating consisting of an inner compact layer and outer Mg-Al layered double hydroxide (LDH) microsheet-based layer prepared hydrothermally exhibits enhanced corrosion resistance in saline solutions but cannot resist corrosion in sulfuric acid. After depositing a fluorocarbon polymer film on the microsheets using a polytetrafluoroethylene (PTFE) target by magnetron sputtering, a super-hydrophobic surface is created on the magnesium alloy. Compared to the surface modified hydrothermally, the super-hydrophobic surface provides better corrosion protection in H2SO4 due to trapped air pockets in the microsheet array. The dual process offers a promising means to mitigate corrosion of magnesium alloys in acidic media.

Parameters of Plasma and Kinetics of Active Particles in CF4 (CHF3) + Ar Mixtures of a Variable Initial Composition

The electrophysical parameters of plasma and the kinetics of active particles in CF4 + Ar and CHF3 + Ar mixtures under induction RF (13.56 MHz) discharge are compared. It is shown that the CHF3 + Ar system containing 0–75% Ar is intrinsic for systematically lower concentrations and flow densities of fluorine atoms, while they are higher in the case of fluorocarbon radicals and positive ions. The set of formal parameters in the form of flux density ratios is suggested in order to describe the formation and destruction of a fluorocarbon polymer film. It is confirmed that the advantage of the CHF3 + Ar system according to the etching selectivity of SiO2/Si is caused by its higher polymerization ability.

On the Effect of the Ratio of Concentrations of Fluorocarbon Components in a CF4 + C4F8 + Ar Mixture on the Parameters of Plasma and SiO2/Si Etching Selectivity

The effect of the CF4/C4F8 ratio in a CF4 + C4F8 + Ar mixture on the parameters of the gaseous phase of a low-pressure inductively coupled plasma, defining the kinetics and selectivity of etching in an SiO2/Si system, is investigated. It is found that increasing the SiO2/Si etching ratio, with an increase of the quantity of C4F8 in the plasma-forming mixture, is determined by various changes of the effective interaction probabilities for these materials. It is demonstrated that, within the investigated range of conditions, the kinetics of the formation of the fluorocarbon polymer film on the processed surface exerts a decisive influence on the character of the variation of the effective interaction probability. The interrelationships between the gas-phase and heterogeneous characteristics of the etching process are revealed.

PLASMA PARAMETERS AND ACTIVE SPECIES KINETICS IN CF4+C4F8+Ar GAS MIXTURE

This work discusses the relationships between the initial composition of the CF4 + C4F8 + Ar gas mixture, gas-phase characteristics and heterogeneous process kinetics under the condition of low-pressure inductively coupled plasma. The goals were to investigate how the CF4/C4F8 mixing ratio influences internal plasma parameters (electron temperature, electron density and ion bombardment energy) and kinetics of plasma active species as well as to analyze how the changes in above parameters may influence the dry etching characteristics, such as etching rates and selectivities. The investigation was carried out using the combination of plasma diagnostics by double Langmuir probes and 0-dimensional plasma modeling. Both experiments and calculations were carried out at constant gas pressure (10 mTorr), input power (800 W) and bias power (150 W) while the CF4/C4F8 mixing ratio was varied through the partial flow rates for corresponding gases. It was shown that the substitution of CF4 for C4F8 in the CF4+C4F8+Ar feed gas lowers F atom formation rates and causes the decreasing F atom flux to the treated surface due to decreasing their volume density. It was proposed that an increase in the densities and fluxes of unsaturated CFx (x=1,2) radicals toward C4F8-rich plasmas at the nearly constant ion energy flux (i.e. at the nearly constant efficiency of ion bombardment) causes a decrease in the effective reaction probability for F atoms through the increasing thickness of the fluorocarbon polymer film on the treated surface.Forcitation:Efremov A.M., Murin D.B., Kwon K.H. Plasma parameters and active species kinetics CF4+C4F8+Ar gas mixture. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N4-5. P. 31-36

On the Etching Mechanisms of SiC Thin Films in CF4/CH2F2/N2/Ar Inductively Coupled Plasma

Etching mechanisms of SiC thin films in CF4/CH2F2/N2/Ar inductively coupled plasmas were studied based on the correlations between measured SiC etching rates and model-predicted fluxes of plasma active species. Plasma chemistry was analyzed using Langmuir probe diagnostics, optical emission spectroscopy and 0-dimensional (global) plasma modeling. It was found that, under the given set of process conditions, the SiC etching kinetics is not affected by the thickness of the fluorocarbon polymer film and corresponds to the steady-state ion-assisted chemical reaction with the domination of the chemical etching pathway. It was proposed that the reaction probability between SiC and F atoms depends on both ion energy flux and the flux of polymerizing radicals through the balance active surface sites acceptable for the adsorption of F atoms.

Area-Selective Atomic Layer Deposition Using an Inductively Coupled Plasma Polymerized Fluorocarbon Layer: A Case Study for Metal Oxides

Area-selective atomic layer deposition (AS-ALD) has attracted immense attention in recent years for self-aligned accurate pattern placement with subnanometer thickness control. Here, we demonstrate a methodology to achieve AS-ALD by using inductively couple plasma (ICP) grown fluorocarbon polymer film as hydrophobic blocking layer for selective deposition. Our approach has been tested for metal-oxide materials including ZnO, Al2O3, and HfO2. Contact angle, X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometer, and scanning electron microscopy (SEM) measurements were performed to investigate the blocking ability of plasma polymerized fluorocarbon layers against ALD-grown metal-oxide films. A considerable growth inhibition for ZnO has been observed on fluorocarbon coated Si(100) surfaces, while the same polymerized surface caused a relatively slow nucleation for HfO2 films. No growth selectivity was obtained for Al2O3 films, displaying almost the same nucleation behavior on Si and fluorocarbon ...

Application of Si and SiO2 Etching Mechanisms in CF4/C4F8/Ar Inductively Coupled Plasmas for Nanoscale Patterns.

An investigation of the etching characteristics and mechanism for both Si and SiO2 in CF4/C4F8/Ar inductively coupled plasmas under a constant gas pressure (4 mTorr), total gas flow rate (40 sccm), input power (800 W), and bias power (150 W) was performed. It was found that the variations in the CF4/C4F8 mixing ratio in the range of 0-50% at a constant Ar fraction of 50% resulted in slightly non-monotonic Si and SiO2 etching rates in CF4-rich plasmas and greatly decreasing etching rates in C4F8-rich plasmas. The zero-dimensional plasma model, Langmuir probe diagnostics, and optical emission spectroscopy provided information regarding the formation-decay kinetics for the plasma active species, along with their densities and fluxes. The model-based analysis of the etching kinetics indicated that the non-monotonic etching rates were caused not by the similar behavior of the fluorine atom density but rather by the opposite changes of the fluorine atom flux and ion energy flux. It was also determined that the great decrease in both the Si and SiO2 etching rates during the transition from the CF4/Ar to C4F8/Ar gas system was due to the deposition of the fluorocarbon polymer film.

UV-assisted modification and removal mechanism of a fluorocarbon polymer film on low-k dielectric trench structure.

In this study, we report the first chemical characterization of a plasma-deposited model fluoropolymer on low-k dielectric nanostructure and its decomposition in UV/O2 conditions. Carbonyl incorporation and progressive removal of fluorocarbon fragments from the polymer were observed with increasing UV (≥230 nm) irradiation under atmospheric conditions. A significant material loss was achieved after 300 s of UV treatment and a subsequent wet clean completely removed the initially insoluble fluoropolymer from the patterned nanostructures. A synergistic mechanism of UV light absorption by carbonyl chromophore and oxygen incorporation is proposed to account for the observed photodegradation of the fluoropolymer.

Dissolution of CF-Polymer Films at Ultra Low-k Surfaces Using Diluted HF

We report ab initio investigations about the dissolution of fluorocarbon polymer films at ultra low-k surfaces. In particular C-C and Si-C bond breaking mechanisms using diluted HF as cleaning chemical are investigated in detail. We found that the activation energy of C-C bond breaking reactions is mainly determined by the dissociation energy of the corresponding CF polymer. In contrast to this the activation energy of Si-C bond breaking reactions is much smaller. We conclude that industrial cleaner based on dHF cannot very efficiently dissolve pore sealing CF polymer films at ultra low-k surfaces. But with increasing porosity, increasing Si content or increasing dangling bond density of the CF polymer film the cleaning efficiency of dHF should increase.

Durability of nitrided fluorocarbon polymer films for nanoimprint lithography

Hydrophobic fluorocarbon polymer films have been used as anti-sticking and releasing coatings for templates in nano-imprint lithography, but have poor durability against repeated high pressure pressing processes. The addition of nitrogen into fluorocarbon-based gas plasma can provide nitrided fluorocarbon polymer films, as confirmed by Fourier-transform infrared spectroscopy. Fluorocarbon and nitrided fluorocarbon films have almost the same 110.0° contact angle with water drops. The nitrided fluorocarbon films are harder and significantly enhance durability as anti-sticking layers. Durability enhancement has been confirmed by fabricating replicas with silicon templates using nitrided fluorocarbon anti-sticking layers.

Preparation and UV Absorption Property of Hybrid Fluorocarbon/ZnO Thin Films Deposited by RF Magnetron Sputtering

Nanowire-mesoporous network structured fluorocarbon polymer films were prepared by radio-frequency (RF) magnetron sputtering of a polytetrafluoroethylene (PTFE) target on a poly(ethylene terephthalate) (PET) substrate. The fluorocarbon films were used as precursor materials to prepare fluorocarbon/ZnO double-layered hybrid films by reaction sputtering of a Zn target on the fluorocarbon films. The hybrid films had strong UV absorption that was far larger than the sum of the individual absorptions of fluorocarbon film and ZnO film because of a synergistic effect. The hybrid films exhibited multi-enhanced ultraviolet absorption due to the π-conjugated molecular structure, the nanoparticle-mesoporous reflection of fluorocarbon polymer films, and the absorption effect of nanosized ZnO particles.