Vincent Paillard

Oxide–nitride–oxide dielectric stacks with Si nanoparticles obtained by low-energy ion beam synthesis

Formation of a thin band of silicon nanoparticles within silicon nitride films by low-energy (1 keV) silicon ion implantation and subsequent thermal annealing is demonstrated. Electrical characterization of metal–insulator–semiconductor capacitors reveals that oxide/Si-nanoparticles-nitride/oxide dielectric stacks exhibit enhanced charge transfer characteristics between the substrate and the silicon nitride layer compared to dielectric stacks using unimplanted silicon nitride. Attractive results are obtained in terms of write/erase memory characteristics and data retention, indicating the large potential of the low-energy ion-beam-synthesis technique in SONOS memory technology.

On the influence of elastic strain on the accommodation of carbon atoms into substitutional sites in strained Si:C layers grown on Si substrates

Measurements of strain and composition are reported in tensile strained 10- and 30-nm-thick Si:C layers grown by chemical vapor deposition on a Si (001) substrate. Total carbon concentration varies from 0.62% to 1.97%. Strain measurements were realized by high-resolution x-ray diffraction, convergent-beam electron diffraction, and geometric phase analysis of high-resolution transmission electron microscopy cross-sectional images. Raman spectroscopy was used for the deduction of the substitutional concentration. We demonstrate that in addition to the growth conditions, strain accumulating during deposition, thus depending on a layer thickness, has an influence on the final substitutional carbon composition within a strained Si:C layer.

Measurement of stress gradients in hydrogenated microcrystalline silicon thin films using Raman spectroscopy

Raman spectroscopy is a powerful tool to measure stress in semiconductors. We show both large stress values and stress gradients in hydrogenated microcrystalline silicon thin films, by the use of different excitation wavelengths, from red to near-ultraviolet, allowing us to probe different film depths. For films deposited by standard radio frequency glow discharge at different substrate temperatures, we find that stress evolves from highly compressive in the bulk of the film, close to the glass substrate, to tensile near the film free surface. Moreover, the higher the substrate temperature, the higher the stress gradient.

Materials Science Issues for the Fabrication of Nanocrystal Memory Devices by Ultra Low Energy Ion Implantation

Nanocrystal memories are attractive candidate for the development of non volatile memory devices for deep submicron technologies. In a nanocrystal memory device, a 2D network of isolated nanocrystals is buried in the gate dielectric of a MOS and replaces the classical polysilicon layer used in floating gate (flash) memories. Recently, we have demonstrated a route to fabricate these devices at low cost by using ultra low energy ion implantation. Obviously, all the electrical characteristics of the device depend on the characteristics of the nanocrystal population (sizes and densities) but also on their exact location with respect to the gate and channel of the MOS transistor. It is the goal of this paper to report on the main materials science aspects of the fabrication of 2D arrays of Si nanocrystals in thin SiO2 layers and at tunable distances from their SiO2/interfaces.

Structural investigations of Inductively Coupled Plasma ultra-thin silicon nanowires

We demonstrated the high throughput production of ultra-thin SiNWs by the innovative Inductively Coupled Plasma (ICP) approach. Our investigations revealed that the vast majority (∼95%) of the ICP produced SiNWs grew according to the Oxide Assisted Growth mechanism, and the 5% through the Vapor-Liquid-Solid mechanism. These SiNWs present an intriguing internal nanostructure, that provides a new kind of nanocomposite, where quantum confinement effects are expected. Indeed, an intense photoluminescence emission in the near infra-red was observed. These results prove the ICP as a genuinely bulk process, which can be exploited for large scale production of thin SiNWs to be integrated into attractive large-area and flexible optoelectronic devices.

Localized Silicon Nanocrystals Fabricated by Stencil Masked Low Energy Ion Implantation: Effect of the Stencil Aperture Size on the Implanted Dose

In this paper, we develop a new method based on ultra-low-energy ion implantation through a stencil mask to locally fabricate Si nanocrystals in an ultrathin silica layer. We perform a 1 keV Si implantation with doses of 5x10 15 Si + /cm 2 , 7.5x10 15 Si + /cm 2 and 1x10 16 Si + /cm 2 in a 7 nm thick silicon oxide layer through stencil mask apertures ranging from 1μm up to 5 μm. After the mask removal the samples are furnace annealed at a temperature of 1050°C for 90 min under N2 atmosphere. The samples are then characterized by mapping the implanted and non-implanted areas by atomic force microscopy and photoluminescence spectroscopy. The intensity and the wavelength of the PL peak are found to depend on the implanted NCs cell size. A slight blue shift from 730 nm up to 720 nm is observed with decreasing cell size. Simultaneously, the PL intensity decreases and the signal vanishes for submicron features (which should contain 10 2 to 10 3 NCs). AFM microcopy performed on the implanted regions shows that the well-known oxide swelling usually observed after NCs synthesis decreases from 3.5 nm down to 0 as the cell size decreases. This result demonstrates that the effective implanted dose clearly decreases with the size of the cells. This effect is probably due to an electrostatic charging of the Si3N4 membrane despite the metallization treatments applied to the mask surface.

Determination of strain within Si 1-y C y layers grown by CVD on a Si Substrate

In this work, we performed quantitative measurements of strain in structures consisting of a 30 nm-thick Si 1-y C y layer grown by chemical vapour deposition (CVD) on a Si (001) substrate at 550 or 600°C. The total C concentration varies from 0.67 to 1.97% that was measured by SIMS. Geometric phase analysis (GPA) of high resolution transmission electron microscopy (HR TEM) cross-section images and convergent beam electron diffraction (CBED) were used to deduce the strain within these Si 1-y C y layers. Finite-element simulations were carried out to estimate the impact of strain relaxation in thin areas of a specimen. These results were compared with the data obtained by high resolution X-ray diffraction and Raman spectroscopy and with the predictions of elasticity theory. Particular interest is paid to the formation of the structural defects within Si 1-y C y layers as a function of a C concentration, growth temperature and incorporated strain. Both cross-sectional and plan-view TEM specimen configurations were used to obtain quantitative information on the defect size distribution, their density and structure.