New applications of excimer lamps to the low temperature photo-deposition of thin films

Over the last decade, the requirement for low temperature processing in the semiconductor industry has become apparent due to the continued reduction in device geometry and the emergence of temperature sensitive materials. Of the low temperature techniques available, photo-enhanced processing of materials is very promising since the growing films are not subject to damaging ionic bombardment which is present in plasma assisted systems. Here is presented the development of a flexible large area, low temperature photo enhanced chemical vapour deposition reactor (photo-CVD) for applications to low temperature thin films processing. The development of novel excimer lamps has opened up the field of direct photo- CVD. Such lamps are a cheap and intense source of visible, UV and vacuum ultraviolet radiation (VUV: below 200nm). The major breakthrough with the development of these lamps is that they offer a large number of wavelengths that can be used for selective photo-CVD. The fabrication and characterisation of those light sources were conducted, and various devices generating up to a few watts are presented. Applications of the available radiation are also presented such as for the direct VUV enhanced generation of ozone and various metal-organic depositions (MOD). For the first time, the 172nm radiation of a xenon excimer lamp has been used to deposit silicon dioxide (SiO2), silicon nitride (Si3N4), and silicon oxynitride films from the photo-CVD of gas mixtures of silane with nitrous oxide and ammonia, and at temperatures as low as 300°C. Fast deposition (up to 500A/min) of SiO2 was also achieved by irradiating silane and oxygen gas mixtures. Investigations into the deposition photochemistry are reported, together with the characterisation of the deposited material properties. Good SiO2 and Si3N4 film quality was obtained, as well as a very good control of the stoichiometry in the case of silicon oxynitride film deposition, therefore providing interesting perspectives for electronic and optical applications

Laser-processed three dimensional graphitic electrodes for diamond radiation detectors

International audienceWe have used an original approach for diamond detectors where three dimensional buried graphitic electrodes are processed in the bulk of a diamond substrate via laser-induced graphitization. Prototype made of polycrystalline chemical vapor deposition diamond was fabricated using a nanosecond UV laser. Its charge collection efficiency was evaluated using a-particles emitted by a 241-Americium source. An improved charge collection efficiency was measured proving that laser micro-machining of diamond is a valid option for the future fabrication of three dimensional diamond detector

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International audienceWe propose to use the non-electronic grade (nitrogen content 5 ppb < [N] < 5 ppm) single crystal (sc) chemical vapour deposited (CVD) diamond as a thin-membrane radiation detector. Using deep Ar/O$_2$ plasma etching it is possible to produce self-supported few micrometres thick scCVD membranes of a size approaching 7 mm × 7 mm, with a very good surface quality. After metallization and contacting, electrical properties of diamond membrane detectors were probed with 5.486 MeV $\alpha$-particles as an ionization source. Despite nitrogen impurity, scCVD membrane detectors exhibit stable operation, charge collection efficiency close to 100%, with homogenous response, and extraordinary dielectric strength up to 30 V/$\mu$m

Simultaneous detection of indole and 3-methylindole using boron-doped diamond electrodes

International audienceThe simultaneous electrodetection of indole and 3-methylindole was investigated in this paper. The detection was performed using a boron-doped diamond ( BDD) electrode to take advantage of its remarkable electrochemical properties ( Fujishima et al., Diamond Electrochemistry ( Elsevier, 2005) [ 1]. In order to improve the selectivity between indole and 3-methylindole, square-wave voltammetry ( SWV) was used. We showed that BDD electrodes fouled either from oxidation of indole or 3-methylindole could be efficiently reactivated in LiClO4 aqueous solutions using trains of short anodic and cathodic pulses applied to the working electrode. We were able with this approach to measure simultaneously both indole and 3-methylindole in aqueous solutions in the range of 10-500 mu M with the limits of detection ( LOD) found to be 3 x 10(-2) mu M for indole and 5 x 10(-2) mu M for 3-methylindole. Both indoles were also detected successfully following extraction from pork fat. This work opens up the way toward systematic detection of indole and 3-methylindole in processed foodstuffs, with a strong industrial interest for the detection of boar taint in pork meat

Porous diamond with high electrochemical performance

International audienceSynthetic diamond materials are currently attracting attention for applications such as thin films supercapacitors or medical implantable electrodes where chemically stable materials featuring high double layer capacitance as well as low electrochemical impedance are sought. Those properties may be reached with high aspect ratio diamond provided that current collection is done efficiently through the diamond layer. In this paper, we introduce a very novel material, namely SPDiam (TM), based on boron-doped diamond grown on a highly porous polypyrrole scaffold prepared by chemical vapour deposition. This composite was first characterised by SEM and Raman spectroscopy to check the diamond crystallinity and the structural evolution of the polypyrrole during the CVD process. Then cyclic voltammetry and electrochemical impedance spectroscopy were performed to assess its electrochemical reactivity. It was found to exhibit remarkable properties, that include a large double layer capacitance with values reaching up to 3 mF cm(-2) in aqueous LiClO4 and a low electrochemical impedance, thus highly competitive with respect to other nanostructured diamond materials as recently reported

Optical Analysis of p-Type Surface Conductivity in Diamond with Slotted Photonic Crystals

International audience2D slotted diamond‐based photonic crystals (PhCs) with Q factors up to 6500 are fabricated and optically characterized at 1550 nm in order to probe surface molecular modifications. This study focuses on the simplest surface modifications that can modify the diamond PhC optical properties, namely, hydrogenation and oxidation. Depending on the chemical surface termination, these diamond PhCs exhibit a strong modification of their spectral features. When the surface is tuned from oxidized to hydrogenated, a resonance wavelength shift of the cavity occurs and is accompanied by a decrease of the Q factor. Moreover, experimental evidence is given that this phenomenon is reversible, as the initial value of the Q factor is recovered when the surface is re‐oxidized. This is attributed to the subsurface conductive layer that is due to transfer doping in hydrogenated diamond and which is absent from oxidized diamond. Thanks to 3D finite differences in time domain (FDTD) simulations, an estimate of the effective refractive index of the surface conductive layer at 1.5 μm is given as a function of its thickness. This result highlights the high sensitivity of slotted diamond PhC and the importance of surface control for biosensing with diamond

Realisation and characterisation of mass-based diamond micro-transducers working in dynamic mode

International audienceWe report on novel MEMS micro-transducers made of diamond and targeted for bio-sensing applications. To overcome the non-straightforward micromachining of diamond, we developed a bottom up process for the fabrication of synthetic diamond micro-structures involving the patterned growth of diamond using the CVD (chemical vapour deposition) technique, inside micro-machined silicon moulds. Here typical resonant MEMS structures including cantilevers fabricated using this method were characterized by measuring their first mode resonance (frequency and Q-factor) by Doppler laser interferometry. The experimental data matched the simulation data. Data from bare diamond cantilevers and from diamond cantilevers with actuation gold track on the surface were compared and showed a significant decrease in the resonant frequency in the presence of gold tracks. Nevertheless, comparisons with equivalent silicon structures demonstrated the superior performances of diamond cantilevers: the resonance frequencies were twice higher and the Q-factors 2.5 times higher for the diamond transducers. Diamond cantilevers sensitivity were measured using PMMA deposition and values as high as 227.4 Hz ng−1 were found. It was shown that diamond mass sensitivity values are typically two times higher than identical silicon devices. Finally, the limit of detection (LOD) of diamond cantilevers was found experimentally to be as low as 0.86 pg using our set up. This is suitable for many bio-sensing applications

Realization and characterization of diamond micro-transducers for bio-chemical sensing

International audienceWe report on novel MEMS micro-transducers made of diamond and used for bio-sensing applications. To overcome the non straightforward micro-machining of diamond, we developed an original process involving the patterned growth of diamond using the CVD (chemical vapour deposition) technique, inside micro-machined silicon moulds.Typical MEMS structures were successfully fabricated and include cantilevers and bridges. They were actuated using Laplace forces. The structures were characterized by measuring their first mode resonance (frequency and Q-factor) using laser interferometry. The measured data fitted the simulated data and comparison with equivalent silicon structures showed the superior resonant properties of diamond cantilevers. It implies that the later are potentially more sensitive transducers than their silicon counterpart

Fabrication and micromechanical characterization of polycrystalline diamond microcantilevers

International audienceThe exceptional chemical, mechanical and thermal properties of diamond make this material the ideal choice for resonant MEMS. Cantilevers designed for biochemical applications have been fabricated using CVD diamond. In this work, the mechanical properties of these cantilevers were investigated by two different techniques: bending test using a Contact Surface Profilometer and resonant test, using a Laser Doppler Vibrometer. The Young's Modulus mean value of polycrystalline diamond cantilever was estimated from these tests at 950-1100GPa