Ahmed Rhallabi

Global model and diagnostic of a low-pressure SF6/Ar inductively coupled plasma

A global model has been developed for low-pressure (3–20 mTorr), radio-frequency (rf) (13.56 MHz) inductively coupled plasmas (ICPs), produced in SF6/Ar mixtures. The model is based on a set of mass balance equations for all the species considered, coupled to the discharge power balance equation and the charge neutrality condition. Simulations are used to show the impact of operating conditions, such as the rf power, the pressure and the percentage of argon in the mixture, on the evolution of charged and neutral species. Langmuir probe and optical emission spectroscopy measurements are used to determine the electron temperature and the densities of electrons, ions and atomic fluorine in the SF6/Ar ICPs under study. These data are compared with simulation results obtained from the global model. A satisfactory agreement is found between the simulation results and the measured values of the electron density and temperature, for rf powers in the range 900–1700 W, regardless of the percentage of argon in the mixture. Predictions for the atomic fluorine density (~1014 cm−3) are in good agreement with experiment, for various rf powers.

Etching studies of silica glasses in SF6/Ar inductively coupled plasmas: Implications for microfluidic devices fabrication

To fabricate microlaboratories, commercially available silica glasses represent a good alternative to the expensive quartz or fused silica substrates. Therefore, the authors have here investigated the behavior of four of them—Vycor, Pyrex, D263, and AF45—in SF6 and SF6/Ar inductively coupled plasmas. Using Vycor, a material close to pure SiO2, as a reference, they demonstrated that the etch rate negatively correlates with the global content in metallic oxides. However, no such clear trend was found for the surface roughness and they hypothesize that the large asperities (>500 nm) sometimes observed might be due to local variation in the glass surface composition. Furthermore, investigations on the influence of the plasma conditions (i.e., source power, dc self-bias, gas mixture, and pressure) on the etch rate, surface chemistry, and surface morphology, as well as positive ion current and fluorine concentration measurements, enable them to unravel an ion enhanced chemical etching mechanism, where stronger ...

Modelling of fluorine based high density plasma for the etching of silica glasses

An etching simulator has been developed to study the etching of commercial silica glass (Pyrex®, D263®, AF45®, and Vycor®) in a SF6/Ar inductively coupled plasma (ICP) discharge. The etching model is based on the development of the plasma kinetic model coupled to a two dimensional (2D) Monte Carlo cellular surface model to predict the etched surface morphology as a function of the operating conditions. The SF6/Ar plasma model allows us to predict the neutral and ion species fluxes, as well as the density and the temperature of electrons, as a function of the reactor operating conditions. Such output parameters are used as input parameters in both the sheath and etching models. The 2D Monte Carlo cellular model is based on the representation of both the substrate and the mask by uniform cells, which each represents a real number of sites. The preferential redeposition mechanism of the etched products on the metallic sites seems to play an important role on the formation and the propagation of the etched surface roughness. The results obtained by the model are compared with the experimental results for etching rate and roughness. A satisfactory agreement between the experimental results and the model concerning the etching rate and the etched surface morphology has been obtained for different glasses.

Modeling of inductively coupled plasma SF6/O2/Ar plasma discharge: Effect of O2 on the plasma kinetic properties

A global model has been developed for low-pressure, inductively coupled plasma (ICP) SF6/O2/Ar mixtures. This model is based on a set of mass balance equations for all the considered species, coupled with the discharge power balance equation and the charge neutrality condition. The present study is an extension of the kinetic global model previously developed for SF6/Ar ICP plasma discharges [Lallement et al., Plasma Sources Sci. Technol. 18, 025001 (2009)]. It is focused on the study of the impact of the O2 addition to the SF6/Ar gas mixture on the plasma kinetic properties. The simulation results show that the electron density increases with the %O2, which is due to the decrease of the plasma electronegativity, while the electron temperature is almost constant in our pressure range. The density evolutions of atomic fluorine and oxygen versus %O2 have been analyzed. Those atomic radicals play an important role in the silicon etching process. The atomic fluorine density increases from 0 up to 40% O2 where...

Process induced mechanical stress in InP ridge waveguides fabricated by inductively coupled plasma etching

Inductively coupled plasma (ICP) etching is suitable for producing semiconductor structures with a high aspect ratio. While the morphology of the structures is very satisfactory, less is known about other aspects related to the process, but with potential influence in the optical performance of the devices. We present herein a study of the mechanical stresses produced by the ICP process in the fabrication of ridge waveguides in InP. Stresses purely induced by the process are revealed by the spectral analysis of the cathodoluminescence. A dependence of the stress distribution on the aspect ratio of the waveguides is demonstrated.

Modeling of inductively coupled plasma Ar/Cl2/N2 plasma discharge: Effect of N2 on the plasma properties

A global kinetic model of Cl2/Ar/N2 plasma discharge has been developed, which allows calculation of the densities and fluxes of all neutral and charged species considered in the reaction scheme, as well as the electron temperature, as a function of the operating conditions. In this work, the results from the global model are first compared to the calculations given by other models. Our simulation results are focused on the effect of nitrogen adding to the Cl2/Ar plasma mixture, which impacts both neutral and charged species transport phenomena. The N2 percentage is varied to the detriment of Cl2 by keeping the total flow rates of Cl2 and N2 constant. In order to better understand the impact of N2 addition to the Cl2/Ar gas mixture, the authors analyzed the output plasma parameters calculated from the model for different N2 flow rate percentages. Indeed, the simulation results show a decrease in electron density and an increase in electron temperature with increasing percentage of N2. Particular attention is paid to the analysis of electronegativity, Cl2 and N2 dissociation, and positive ion to neutral flux ratio evolution by varying percentage of N2. Such parameters have a direct effect on the etching anisotropy of the materials during the etching process.

SF6 and C4F8 global kinetic models coupled to sheath models

Global kinetic models combined with Monte Carlo sheath models are developed for SF6 and C4F8 plasma discharges for silicon etching under the Bosch process. In SF6 plasma, the dominant positive ions are , , and F+ while in C4F8 the dominant positive ions are and . The simulation results show that the electrical parameters, such as the electron density and electron temperature, clearly affect the sheath dynamics and consequently the ion energy distribution function evolutions. In this context, we showed the effects of the operating conditions, such as the pressure and the radiofrequency power, on the electron density and electron temperature evolutions as well as the reactive particle fluxes (neutral and positive ions) involved in the plasma surface interactions for etching/deposition under the Bosch process. Ion energy distribution functions obtained from SF6 and C4F8 plasmas are compared with each other as regards the electrical properties of their associated plasmas. The simulation results show that the bimodal peaks of ion energy distribution functions are wider for SF6 plasma than for C4F8 plasma due to the high sheath thickness of SF6 compared to that of C4F8. This is explained by the low electron density due to the high electronegativity of SF6 in comparison to that of C4F8. The simulations also reveal that the bimodal peak of the ion energy distribution function is wider when the ion mass is low.

Modeling of inductively coupled plasma Ar/Cl{sub 2}/N{sub 2} plasma discharge: Effect of N{sub 2} on the plasma properties

A global kinetic model of Cl2/Ar/N2 plasma discharge has been developed, which allows calculation of the densities and fluxes of all neutral and charged species considered in the reaction scheme, as well as the electron temperature, as a function of the operating conditions. In this work, the results from the global model are first compared to the calculations given by other models. Our simulation results are focused on the effect of nitrogen adding to the Cl2/Ar plasma mixture, which impacts both neutral and charged species transport phenomena. The N2 percentage is varied to the detriment of Cl2 by keeping the total flow rates of Cl2 and N2 constant. In order to better understand the impact of N2 addition to the Cl2/Ar gas mixture, the authors analyzed the output plasma parameters calculated from the model for different N2 flow rate percentages. Indeed, the simulation results show a decrease in electron density and an increase in electron temperature with increasing percentage of N2. Particular attention is paid to the analysis of electronegativity, Cl2 and N2 dissociation, and positive ion to neutral flux ratio evolution by varying percentage of N2. Such parameters have a direct effect on the etching anisotropy of the materials during the etching process.

Defect formation during chlorine-based dry etching and their effects on the electronic and structural properties of InP/InAsP quantum wells

The general objective is the investigation of the defects formed by dry etching tools such as those involved in the fabrication of photonic devices with III–V semiconductors. Emphasis is put on plasma exposures with chlorine-based chemistries. In addition to identifying these defects and describing their effects on the electro-optic and structural properties, the long-term target would be to predict the impact on the parameters of importance for photonic devices, and possibly include these predictions in their design. The work is first centered on explaining the experimental methodology. This methodology starts with the design and growth of a quantum well structure on indium phosphide, including ternary indium arsenide/phosphide quantum wells with graded arsenic/phosphor composition. These samples have then been characterized by luminescence methods (photo- and cathodoluminescence), high-resolution transmission electron microscopy, and secondary ion mass spectrometry. As one of the parameters of importance in this study, the authors have also included the doping level. The samples have been exposed to the etching plasmas for “short” durations that do not remove completely the quantum wells, but change their optical signature. No masking layer with lithographic features was involved as this work is purely oriented to study the interaction between the plasma and the samples. A significant difference in the luminescence spectra of the as-grown undoped and doped samples is observed. A mechanism describing the effect of the built-in electric field appearing as a consequence of the doping profile is proposed. This mechanism involves quantum confined Stark effect and electric-field induced carrier escape from the quantum wells. In the following part, the effects of exposure to various chlorine-based plasmas were explored. Differences are again observed between the undoped and doped samples, especially for chemistries containing silicon tetrachloride. Secondary ion mass spectrometry indicates penetration of chlorine in the structures. Transmission electron microscopy is used to characterize the quantum well structure before and after plasma bombardment. By examining carefully the luminescence spectral properties, the authors could demonstrate the influence of the etching plasmas on the built-in electric field (in the case of doped samples), and relate it to some ionic species penetrating the structures. Etching plasmas involving both chlorine and nitrogen have also been studied. The etching rate for these chemistries is much slower than for some of the silicon tetrachloride based chemistries. Their effects on the samples are also very different, showing much reduced effect on the built-in electric field (for the doped samples), but significant blue-shifts of the luminescence peaks that the authors attributed to the penetration of nitrogen in the structures. Nitrogen, in interstitial locations, induces mechanical compressive stress that accounts for the blue-shifts. Finally, from the comparison between secondary ion mass spectrometry and luminescence spectra, the authors suggest some elements for a general mechanism involved in the etching by chloride-chemistries, in which a competition takes place between the species at the surface, active for the etching mechanism, and the species that penetrate the structure, lost for the etching process, but relevant in terms of impact on the electro-optic and structural features of the exposed materials.

Simulation of cryogenic silicon etching under SF6/O2/Ar plasma discharge

An etching simulator is developed to study the two-dimensional (2D) silicon etch profile evolution under SF6/O2 inductively coupled plasma discharge. The simulator is composed of three modules: plasma kinetic module, sheath module, and etching module. With this approach, the authors can predict the 2D etch profile evolution versus reactor parameters. Simulation results from the sheath model show that the shape of the bimodal ion energy distribution function for each incident angle depends on the ion mass. It is all the larger that the ion mass is low. As shown in the experiment, the simulation results reveal that the atomic oxygen plays an important role in the passivation process along the side-wall. Indeed, the simulation results show the decrease of the undercut when the %O2 increases. This improves the etching anisotropy. However, the decrease in the etch rate is observed for a high %O2. Moreover, for a moderate direct current (DC) bias (some 10 V), a low variation of the silicon etch profile versus D...