Papers by Author: Emmanuel Collard

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Authors: Nicolas Thierry-Jebali, Olivier Ménard, Arnaud Yvon, Emmanuel Collard, Miao Zhe, Olivier Dezellus, Christian Brylinski, Jean Claude Viala
Abstract: Ohmic contacts represent a major technological brick for the development of high power devices on Gallium Nitride. Al(200 nm) Ti(70 nm) metallization on n+-GaN, annealed at 650 °C, provides a “Specific Contact Resistivity” (SCR) in the range mid 10-5 Ω.cm², which is low enough for the main switching power applications. However, the Al-Ti metallic compound phases formed during the annealing step result from solid-solid reactions, which may lead to high stress and / or poor cohesion, possibly deleterious to contact reliability. In this work, we have investigated several configurations of Ti-Al-Si based contacts, aiming at favoring liquid-solid reactions and / or Si element diffusion, in order to get better SCR and / or morphology and cohesion of the metallic phase. Surprisingly, only contacts annealed at low temperature (450 °C) provide low contact SCR, comparable to that of Ti-Al only contact, but systematically higher.
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Authors: Francois Templier, Pierre Ferret, Lea Di Cioccio, Emmanuel Collard, André Lhorte, Thierry Billon
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Authors: Xi Song, Jérôme Biscarrat, Anne Elisabeth Bazin, Jean François Michaud, Frédéric Cayrel, Marcin Zielinski, Thierry Chassagne, Marc Portail, Emmanuel Collard, Daniel Alquier
Abstract: In this paper, we studied the influence of nitrogen implantation dose on both physical and electrical properties in 3C-SiC grown on Si (100) substrate. Scanning Transmission Electron Microscopy characterizations prove that high dose is responsible for amorphization of the implanted layer and the high defect density after annealing. A high V-shape defect density is still found in the implanted layer after an annealing at 1350°C. By lowering the dose, the layer is less damaged and no amorphization is observed. For the different doses, low Specific Contact Resistances are measured using Ti/Ni contacts. The Specific Contact Resistance value decreases from 8x10-6 Ω.cm2 for the high dose to 3.2x10­6 Ω.cm2 with decreasing the dose. Furthermore, the dopant activation ratio, evaluated by quantitative SSRM measurements, is improved at the same time from 17% (for the high dose) to 60% (for the low dose). This work demonstrates that high activation ratio can be achieved consecutively to a nitrogen implantation at reasonable implantation fluence.
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Authors: Xi Song, Anne Elisabeth Bazin, Jean François Michaud, Frédéric Cayrel, Marcin Zielinski, Marc Portail, Thierry Chassagne, Emmanuel Collard, Daniel Alquier
Abstract: Two electrical characterization methods were used to study 3C-SiC epilayers doped by nitrogen implantation: circular Transfer Length Method (c­TLM) which allows extracting the specific contact resistance and Scanning Spreading Resistance Microscopy (SSRM) used to measure activated doping concentration. 3C-SiC samples were implanted at room temperature with different energies (ranging from 30 to 150keV) and doses (from 1 to 5.4x1015cm-2) in order to obtain a 300nm thick box-like profile at 5x1020cm-3. To activate the dopant, the samples were then annealed from 1150°C to 1350°C for 1h to 4h. Titanium-nickel c-TLM contacts annealed at 1000°C under argon showed the best results in terms of specific contact resistance (8x10-6.cm2) after a 1350°C–1h annealing. For this annealing condition, the activation rate was assessed by SSRM around 13%. This value confirms the difficulty to activate the dopants introduced into the 3C-SiC as the temperature is limited by the silicon substrate. However, this work demonstrates that low resistance values can be achieved on 3C-SiC, using nitrogen implantation at room temperature.
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Authors: Stéphane Berckmans, Laurent Auvray, Gabriel Ferro, François Cauwet, Véronique Soulière, Emmanuel Collard, Jean Baptiste Quoirin, Christian Brylinski
Abstract: The crystal growth of 3C-SiC onto silicon substrate by Vapour-Liquid-Solid (VLS) transport has been investigated. In the studied growth configuration, propane feeds a SiGe liquid phase contained in 10 µm-deep etched trenches on the Si substrate. Before SiGe deposition, the substrate surface and the trench walls were coated with a thin (100 - 200 nm) CVD-grown 3C-SiC seeding layer. For the VLS growth, the temperature was increased up to 1280°C, above the SiGe alloy melting point, at which point propane was added to start VLS growth. X-ray diffraction shows that some SiC is grown epitaxially onto the CVD seeding layer. However, cross-section SEM observations have evidenced that SiC has grown as trapezoidal islands and not as an uniform layer. Backscattered electron images also clearly show a deep penetration of germanium into the substrate through the SiC seeding layer. This penetration was found to be strongly reduced when increasing the seeding layer thickness from 100 to 200 nm.
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Authors: Jerome Biscarrat, Jean François Michaud, Emmanuel Collard, Daniel Alquier
Abstract: Due to its inert chemical nature, plasma etching is the most effective technique to pattern SiC. In this paper, dry etching of 4H-SiC substrate in Inductively Coupled Plasma (ICP) has been studied in order to evaluate the impact of process parameters on the characteristics of etching such as etch rate and trenching effect. Key process parameters such as platen power and ICP coil power prove to be essential to control the SiC etch rate. On the other hand, the ICP coil power and the working pressure mainly master the trenching effect. Our results enlighten that high etch rate with minimal trenching effect can be obtained using high ICP coil power and low working pressure.
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Authors: Stéphane Berckmans, Laurent Auvray, Gabriel Ferro, François Cauwet, Davy Carole, Véronique Soulière, Jean Claude Viala, Emmanuel Collard, Jean Baptiste Quoirin, Christian Brylinski
Abstract: In this work, the growth by Vapour-Liquid-Solid (VLS) mechanism of 3C-SiC on silicon substrate is reported. Firstly, a germanium layer is deposited on the substrate. Then the temperature of the sample is increased above Ge melting point in order to form a SiGe liquid phase by reaction with the substrate. Upon reaching the target temperature (1100-1300°C) the VLS growth starts with the injection of propane in the reactor. Both Raman spectrometry and X-Ray diffraction analyses evidenced the formation of 3C-SiC on every sample. However, this SiC deposit, a few micrometers thick, is always found to be polycrystalline though textured. In parallel, the presence of an epitaxial Si-Ge alloy, whose composition depends on the growth temperature, was systematically detected between Si and SiC.
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Authors: Nicolas Thierry-Jebali, Olivier Ménard, Christiane Dubois, Dominique Tournier, Emmanuel Collard, Christian Brylinski, Frédéric Cayrel, Daniel Alquier
Abstract: This work reports of investigation on the origin of the ohmic behavior for Ti/Al basedcontacts on n-GaN. Indeed, last publications tend to prove that the ''nitrogen vacancy'' theory is notconfirmed by the experimental ground available. To find new answers, we first made electrical charac-terizations on some Al/Ti/n+-GaN contacts with different annealing conditions. Then, we performedSIMS depth profiles of annealed TiN/Ti/n+-GaN samples. Results developed in this paper tend todemonstrate that the ohmic behavior of Ti/Al based contact is mainly due to an increase of the dop-ing concentration. Moreover, the high doping level can be explained by an in-diffusion of Ti and anexo-diffusion of Si elements close to the metal / semiconductor interface.
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Authors: Anne Elisabeth Bazin, Thierry Chassagne, Jean François Michaud, André Leycuras, Marc Portail, Marcin Zielinski, Emmanuel Collard, Daniel Alquier
Abstract: In this work, ohmic contacts, formed by 100nm Ni layer RTA annealed or not, were investigated on 3C-SiC epilayers exhibiting different nitrogen doping levels. The epilayers were grown on (100) silicon. Doping level (N) and eventual dopant contamination (Al) were analyzed by C-V and/or SIMS. The specific contact resistance was determined by using Transmission Line Model (TLM) patterns for each condition (doping and annealing). Our results clearly evidence that very low specific contact resistance (~10-51.cm²) is obtained on highly doped 3C-SiC epilayers, enlightening the interest of both material and Ni contacts for future devices fabrication.
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Authors: Olivier Ménard, Frédéric Cayrel, Emmanuel Collard, Daniel Alquier
Abstract: In this work, Ti/Al bilayer sputtered ohmic contacts on n-type Gallium Nitride films were studied as a function of process parameters such as Ti thickness, surface cleaning procedure or annealing temperature. Epilayers, with doping concentration of 5.8x1018 at.cm-3, were grown on sapphire using AlN buffer layer. Electrical characterizations were made using circular Transfer Length Method (cTLM) patterns with a four probes equipment. Specific Contact Resistance (SCR) was then extracted for all the process conditions. Our results show that surface treatment is not a critical step in the ohmic contact process while annealing temperature has a larger impact. Finally, SCR values of 1x10-5 Ω.cm2 can be reproducibly achieved, which is of high interest for future devices fabrication using this material.
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