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Abstract

The photoluminescence properties of silicon nanocrystals in SiO2, prepared by low-pressure chemical vapour deposition and subsequent annealing have been studied. A comprehensive range of combinations of film compositions and annealing conditions were tested. The use of two-step annealing (a rapid annealing, followed by a conventional one) used instead of the common one-step conventional annealing, enhances emission. Annealing conditions are key to the photoluminescence and structural properties of the obtained film and have been investigated in detail. Film composition is also an important parameter, which allows tuning of the emission in a wide spectral range in the near infrared.

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A 3-D electrical finite-element model (FEM) for the design of an ultra-low on-state resistance power MOSFET device is presented. Model building and layer conductivity are discussed to take into account microscopic, technological, and electrical effects, such as metal step coverage and MOS behavior of each elementary cell of the transistor. Model simplifications are also presented to ensure time-efficient simulations. FEM gauging is then achieved, by comparing simulation results to electrical measurements, on devices subjected to top metallization debiasing effects. Simulations show a good agreement with measurements for result errors at less than 2%. The aim of this paper is to provide an accurate estimation of the contribution of parasitic elements such as the shape and number of power bonding wires or top metallization thickness to power device on-state resistance (RON). The 3-D electrical FEM is a mandatory first step towards an accurate electrothermal FEM for the design of efficient power products.

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We have studied the matrix effects in Si1-xGex structures under O2+ and Cs+ bombardments. Matrix effects are practically suppressed with Cs2Ge+ secondary ions, for Ge concentrations between 0 and 100 at. %. A procedure for the accurate quantification of the Ge concentration in Si1-xGex alloys using Cs2Ge+ and CsGe+ clusters has been proposed. For structures in which the Ge content is constant over several hundreds of nanometers, both methods provide very similar results, with an excellent agreement between the Ge concentrations measured by secondary ions mass spectrometry and x-ray diffraction. However, for continuously varying Ge concentration profiles, the nonlinear response of the CsGe+ normalized intensity and the persistence of strong matrix effects for CsSi+ ions lead to differences between the Ge concentration profiles measured with the CsGe+ method compared to the Cs2Ge+ one. The latter is therefore the only reliable method for the study of Ge indiffusion into Si from a pure Ge layer grown by chemical vapor deposition. An application of this method to the analysis of Ge indiffusion in Si at 900 °C is also reported.

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A modeling study is presented involving calculations at continuum and atomistic (DFT, Density Functional Theory) levels so as to better understand mechanisms leading to silicon nanocrystals (NC) nucleation and growth on SiO2 silicon dioxide surface, by Low Pressure Chemical Vapor Deposition (LPCVD) from silane SiH4. Calculations at the industrial reactor scale show that a promising way to improve reproducibility and uniformity of NC deposition at short term could be to increase deposition time by highly diluting silane in a carrier gas. This dilution leads to a decrease of silane deposition rate and to a marked increase of the contribution to deposition of unsaturated species such as silylene SiH2. This result gives importance to our DFT calculations since they reveal that only silylene (and probably other unsaturated species) are involved in the very first steps of nucleation i.e. silicon chemisorption on silanol SiOH or siloxane SiOSi bonds present on SiO2 substrates. Saturated molecules such as silane could only contribute to NC growth, i.e. chemisorption on already deposited silicon bonds, since their decomposition activation barriers on SiO2 surface are as high as 3 eV.

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A method based on the failure analysis of power MOSFET devices tested under extreme electrothermal fatigue is proposed. Failure modes are associated to several structural changes that have been investigated through acoustic, electron and ion microscopy. The main aging mode is related to the exponential increase in drain resistance due to delamination at the die attach. Earlier failures are observed when very local defects due to electrical over stresses (EOS) occur at the source metallization or at the wire bonding. Aging models were elaborated to account for the die attach delamination, but are still lacking to take in account the structural evolution of the Al metallization. This new methodology, based on accelerated tests and structural observations aims at designing a new generation of power components that will be more reliable.

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The main goal of this work is to realize a metal oxide gas sensor with stable operating temperature. This article describes our approach and the technological process used to reach a high and stable operating temperature (650-700°C), with low consumption (100mW) and good thermal homogeneity all over the active area.

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