Negative-ion production on carbon materials in hydrogen plasma: influence of the carbon hybridization state and the hydrogen content on H− yield

International audienceHighly oriented polycrystalline graphite (HOPG), boron-doped diamond (BDD), nanocrystalline diamond, ultra-nanocrystalline diamond and diamond-like carbon surfaces are exposed to low-pressure hydrogen plasma in a 13.56MHz plasma reactor. Relative yields of surface-produced H− ions due to bombardment of positive ions from the plasma are measured by an energy analyser cum quadrupole mass spectrometer. Irrespective of plasma conditions (0.2 and 2 Pa), HOPG surfaces show the highest yield at room temperature (RT), while at high temperature (HT), the highest yield (∼3-5 times compared to HOPG surface at RT) is observed on BDD surfaces. The shapes of ion distribution functions are compared at RT and HT to demonstrate the mechanism of ion generation at the surface. Raman spectroscopy analyses of the plasma-exposed samples reveal surface modifications influencing H− production yields, while further analyses strongly suggest that the hydrogen content of the material and the sp3/sp2 ratio are the key parameters in driving the surface ionization efficiency of carbon materials under the chosen plasma conditions

Surface production of negative ions from pulse-biased nitrogen doped diamond within a low-pressure deuterium plasma

International audienceThe production of negative ions is of significant interest for applications including mass spectrometry, materials surface processing, and neutral beam injection for magnetic confined fusion. Neutral beam injection sources maximise negative ion production through the use of surface production processes and low work function metals, which introduce complex engineering. Investigating materials and techniques to avoid the use of low work function metals is of interest to broaden the application of negative ion sources and simplify future devices. In this study, we use pulsed sample biasing to investigate the surface production of negative ions from nitrogen doped diamond. The use of a pulsed bias allows for the study of insulating samples in a preserved surface state at temperatures between 150 ∘ C and 700 ∘ C in a 2 Pa, 130 W, (n e ∼ 10 9 cm −3 , T e ∼ 0.6 eV) inductively coupled deuterium plasma. The negative ion yield during the application of a pulsed negative bias is measured using a mass spectrometer and found to be approximately 20% higher for nitrogen doped diamond compared to non-doped diamond. It is also shown that the pulsed sample bias has a lower peak negative ion yield compared to a continuous sample bias, which suggests that the formation of an optimum ratio of defects on its surface can be favourable for negative ion production

Enhancing surface production of negative ions using nitrogen doped diamond in a deuterium plasma

The production of negative ions is of significant interest for applications including mass spectrometry, particle acceleration, material surface processing, and neutral beam injection for magnetic confinement fusion. Methods to improve the efficiency of the surface production of negative ions, without the use of low work function metals, are of interest for mitigating the complex engineering challenges these materials introduce. In this study we investigate the production of negative ions by doping diamond with nitrogen. Negatively biased ($-20$ V or $-130$ V), nitrogen doped micro-crystalline diamond films are introduced to a low pressure deuterium plasma (helicon source operated in capacitive mode, 2 Pa, 26 W) and negative ion energy distribution functions (NIEDFs) are measured via mass spectrometry with respect to the surface temperature (30$^{\circ}$C to 750$^{\circ}$C) and dopant concentration. The results suggest that nitrogen doping has little influence on the yield when the sample is biased at $-130$ V, but when a relatively small bias voltage of $-20$ V is applied the yield is increased by a factor of 2 above that of un-doped diamond when its temperature reaches 550$^{\circ}$C. The doping of diamond with nitrogen is a new method for controlling the surface production of negative ions, which continues to be of significant interest for a wide variety of practical applications

Gravure en plasma dense fluorocarboné de matériaux organosiliciés à faible constante diélectrique (SiOCH, SiOCH poreux) (étude d'un procédé de polarisation pulsée)

L'objet de ce travail est la gravure en plasma ICP fluorocarboné de matériaux à faible constante diélectrique que sont les méthylsilsesquioxanes SiOCH et SiOCH poreux, utilisés comme isolant intermétallique dans la réalisation de circuits intégrés en microélectronique. La gravure de matériaux utilisés comme masque dur ou couche d'arrêt, SiO2, SiCH, est aussi étudiée. Une vitesse de gravure élevée pour le low- SiOCH poreux, associée à une forte sélectivité de gravure vis à vis de SiO2 et SiCH, sont recherchées. Dans cet objectif, le procédé de gravure est modifié : la tension de polarisation, et donc l'énergie des ions, est pulsée. Pour comprendre les mécanismes de gravure de Si, SiCH, SiO2, SiOCH, et SiOCH poreux en polarisation continue et pulsée, les analyses de surface (XPS, ellipsométrie) sont couplées aux analyses plasma (spectrométrie de masse, spectroscopie d'émission optique, sonde plane). Un modèle est développé pour décrire la vitesse de gravure en polarisation pulsée.This study concerns the etching of low permittivity methylsilsesquioxane materials, SiOCH and porous SiOCH, used as intermetal dielectric in microelectronics devices, with fluorocarbon inductively coupled plasma. Etching of SiO2 and SiCH, used as hard mask or etch stop layer is also studied. The aim is to obtain a high porous SiOCH etch rate with a high selectivity versus SiCH and SiO2. To reach this goal, the etching process has been modified : the bias voltage, and so the ion energy, is pulsed. This process provides excellent results concerning both etch rate and selectivity. To understand etch mechanisms of Si, SiCH, SiO2, SiOCH, and porous SiOCH in continuous and pulsed modes, surface analyses (XPS, ellipsometry) are coupled to plasma analyses (mass spectrometry, optical emission spectroscopy, planar probe). A model describing etch rates when a pulsed bias voltage is applied has been developed.NANTES-BU Sciences (441092104) / SudocSudocFranceF

Développement d'un procédé de dopage de matériaux semi-conducteurs par plasma (caractérisation du plasma et de son interaction avec les matériaux)

Le but de ce travail est de caractériser le plasma de trifluorure de bore (BF3) et son interaction avec les matériaux pendant le procédé de dopage des jonctions fines pour les semi-conducteurs utilisant un procédé de plasma pulsé (PLAD). Afin de mesurer in-situ la distribution en énergie des ions présents dans le plasma, accéléré par le pulse négatif et implantés dans le substrat de silicium, une cathode spéciale a été conçue avec un spectromètre de masse installé en son centre. La mesure de ces distributions donne des informations sur les processus de collision qui surviennent à l intérieur de la gaine. Grâce à une meilleure compréhension de ces processus, nous proposons des solutions pour optimiser le procédé de dopage. Nous avons développé une méthode de prédiction du profil de dopage en profondeur; cette méthode a été validé par comparaison avec des profils SIMS. Le plasma peut être régulé, afin d obtenir une distribution de dopage moins profonde dans le silicium.The aim of this work is to characterize the boron trifluoride plasma and its interaction with the materials during the ultra-shallow-junction doping process for semiconductors using a pulsed plasma doping system (PLAD). In order to measure in situ the ion energy distribution of the various ions present in the plasma, accelerated by the negative pulse and implanted into the silicon wafer, a special cathode was designed with a mass spectrometer installed in its center. The measurement of the composition of the bulk plasma ions as well as the composition of the ions provides some information on the collision processes that occur inside the sheath. Thanks to a better understanding of these processes, the doping process can be optimized. Based on the ion energy distributions measured with the mass spectrometer, the dopant depth profile can be predicted and the plasma can be tuned in order to obtain shallower dopant depth distribution in the silicon after plasma doping implantation.NANTES-BU Sciences (441092104) / SudocSudocFranceF

Mesure du travail de sortie de matériaux en environnement plasma par spectroscopie de seuil de photoémission

International audienc

Investigating the possible origin of Raman bands in defective sp2/sp3 carbons below 900 cm−1: Phonon density of states or double resonance mechanism at play?

This article belongs to the Special Issue Characterization of Disorder in Carbons.Multiwavelength Raman spectroscopy (325, 514, 633 nm) was used to analyze three different kinds of samples containing sp2 and sp3 carbons: chemical vapor deposited diamond films of varying microstructure, a plasma-enhanced chemical vapor deposited hydrogenated amorphous carbon film heated at 500 °C and highly oriented pyrolytic graphite exposed to a radio-frequent deuterium plasma. We found evidence that the lower part of the phonon density of states (PDOS) spectral region (300–900 cm−1) that rises when defects are introduced in crystals can give more information on the structure than expected. For example, the height of the PDOS, taken at 400 cm−1 and compared to the height of the G band, depends on the sp2 content, estimated by electron energy-loss spectroscopy. This ratio measured with 633 nm laser is more intense than with 514 nm laser. It is also correlated for diamond to the relative intensity ratio between the diamond band at 1332 cm−1 and the G band at ≈1500–1600 cm−1 when using 325 nm laser. Moreover, it is found that the shape of the PDOS of the exposed graphite samples is different when changing the wavelength of the laser used, giving evidence of a double resonance mechanism origin with the rise of the associated D3, D4 and D5 bands, which is not the case for a-C:H samples.R.A. gratefully acknowledges the support from the Spanish Ministerio de Economia y Competitividad (MAT2016-79776-P) and from the European Union H2020 program “ESTEEM3” (823717).".Peer reviewe