Fabrice Roqueta

Evaluation of mesoporous silicon thermal conductivity by electrothermal finite element simulation

The aim of this work is to determine the thermal conductivity of mesoporous silicon (PoSi) by fitting the experimental results with simulated ones. The electrothermal response (resistance versus applied current) of differently designed test lines integrated onto PoSi/silicon substrates and the bulk were compared to the simulations. The PoSi thermal conductivity was the single parameter used to fit the experimental results. The obtained thermal conductivity values were compared with those determined from Raman scattering measurements, and a good agreement between both methods was found. This methodology can be used to easily determine the thermal conductivity value for various porous silicon morphologies.

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...

Gettering on Cavities Induced by Helium Implantation in Si: The Case of Boron

In this paper, we shed light on the strong interaction between the cavity layer induced by helium implantation and boron. First, we present the impact of the He gettering step on a boron-diffused profile. In order to study the boron-cavity interaction, we used uniformly boron-doped wafers implanted with a high dose of helium and annealed using conventional furnace annealing as well as rapid thermal annealing. Then, to avoid any precipitation phenomena, conditions were chosen such that the boron solid solubility value was not exceeded. Our experimental results indicate a large trapping of boron within the cavity layer that occurs at the early stage of the annealing. A quantitative study of the gettered dopant fraction has been performed. These results enable us to have a better understanding of this interaction of the He-gettering step with boron atoms, which are of great interest for device applications.

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.

Properties of Cavities Induced by Helium Implantation in Silicon and their Applications to Devices

He implantation at high dose, followed by a thermal annealing, is a n interesting technique for metallic impurity gettering in silicon. In this paper, we first in roduce the extended defects encountered after this gettering stage. Then, we will focus on both t he metallic and the dopant gettering by emphasizing the strong interaction between the defe ct layer induced by helium implantation and these impurities. We will demonstrate that there is no competition between metal and dopant gettering and we will try to compare the mechanisms invol ved. Our results enlighten the effect of the He gettering step on the dopant such as segregation and its partial deactivation in presence of He induced defects. Finally, we will present the i ns rtion and the impact of helium implantation gettering step on a bi-directional device, showing its high interest for device fabrication.

Lateral gettering of iron and platinum by cavities induced by helium implantation in silicon

Abstract The aim of this study is to characterize the lateral gettering of iron and platinum atoms by introducing cavities at the periphery of large active device areas. Cavities have been obtained by helium implantation ( 5×10 16 He + / cm 2 , 40 keV) followed by a thermal treatment on samples previously contaminated by iron and platinum. These cavities are known to be efficient in trapping metallic impurities in silicon by chemisorption. The wafers were annealed in the range of 800–1000°C for several minutes in a neutral ambience (N 2 ). The metallic distribution has been monitored in each active device area by using current versus voltage and deep level transient spectroscopy techniques (DLTS). A symmetrical distribution of metallic impurities and current values has been observed in each active region. The influence of cavities extends laterally to several millimeters depending on the temperature and time of diffusion. This lateral gettering effect is suitable for the purification of transverse power devices.

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...

Gettering by helium implantation applied to a device: impact of metal and dopant segregation

In order to increase the performance of silicon-based devices, metal contaminants need to be gettered. Helium implantation followed by thermal treatment is a suitable gettering step. We show that its inclusion in a process induces a strong increase of the fabrication yield. However, we also found that this technique induces interactions with the dopants that can become a drawback. In this work, secondary ion mass spectrometry (SIMS) was used to study the dopant/metal/cavity layer system. We focus on the interactions of the defect layer with both metal and dopant impurities. Experimental results show that a large segregation of both species occurs during the annealing stage within the defect zone. Both species segregate simultaneously without interacting with each other. The number of gettering sites does not limit the trapping reactions.

Modeling of silicon etching using Bosch process: Effects of oxygen addition on the plasma and surface properties

The authors developed a tool using a multiscale approach to simulate the silicon etching using Bosch process. Their study is focused on the analysis of the effect of the oxygen addition to C4F8 plasma during the deposition pulse. This is the complementary study that the authors have recently published which was dedicated to the Bosch process under pure SF6 plasma used in etching pulse and pure C4F8 plasma used in polymer deposition pulse. Parametric study about the effect of the oxygen percentage on the reactive species flux evolution and their impact on the deposition kinetic during the deposition pulse has been performed. The simulation results reveal that for a low %O2 in a C4F8/O2 plasma mixture, the atomic fluorine density increases because of the volume reactions, especially recombinations between CFx and O which favor the production of fluorine. This leads to the decrease of CFx to F flux ratio. Ion energy distribution functions (IEDF) plotting reveals the impact of both %O2 and mass of the positive ions on the IEDF shape. Finally, both the experimental and simulation results show that in their pressure range, the addition of O2 to C4F8 plasma has a weak impact on the silicon etch profile and the etching rate, except for a high %O2 which the etch anisotropy begins to be degraded.The authors developed a tool using a multiscale approach to simulate the silicon etching using Bosch process. Their study is focused on the analysis of the effect of the oxygen addition to C4F8 plasma during the deposition pulse. This is the complementary study that the authors have recently published which was dedicated to the Bosch process under pure SF6 plasma used in etching pulse and pure C4F8 plasma used in polymer deposition pulse. Parametric study about the effect of the oxygen percentage on the reactive species flux evolution and their impact on the deposition kinetic during the deposition pulse has been performed. The simulation results reveal that for a low %O2 in a C4F8/O2 plasma mixture, the atomic fluorine density increases because of the volume reactions, especially recombinations between CFx and O which favor the production of fluorine. This leads to the decrease of CFx to F flux ratio. Ion energy distribution functions (IEDF) plotting reveals the impact of both %O2 and mass of the positiv...

Multiscale approach for simulation of silicon etching using SF6/C4F8 Bosch process

This study is dedicated to the development of a multiscale approach for the simulation of silicon etching using the Bosch process. The etching simulator is composed of three modules: plasma kinetic model, sheath model, and surface model. The top down connection of these three modules allows us to track the etch profile evolution through the mask versus the reactor parameters. Complex reaction schemes are used for both SF6 and C4F8 plasmas to quantify the neutral and ion species densities and fluxes. For the SF6 plasma used in the etching cycle and in our pressure and power ranges, the fluorine flux is still preponderant compared to the positive ion flux, indicating that the silicon etching is mainly ensured by the chemical processes. For the C4F8 plasma used in the deposition cycle, the simulation results reveal that CFx species are preponderant in comparison with atomic fluorine, confirming that, in our operating conditions, CFx species promote the deposition of a polymer layer instead of the chemical et...