Fabrication of Sub-micron Active Layer SSOI Substrates using Ion Splitting and Wafer Bonding Technologies

This paper reports the fabrication of SSOI (Silicon on Silicide On Insulator) substrates with active silicon regions only 0.5mum thick, incorporating LPCVD low resistivity tungsten silicide (WSix) as the buried layer. The substrates were produced using ion splitting and two stages of wafer bonding. Scanning acoustic microscope imaging confirmed that the bond interfaces are essentially void-free. These SSOI wafers are designed to be employed as substrates for mm-wave reflect-array diodes, and the required selective etch technology is described together with details of a suitable device.

Mécanismes de recuit dans le silicium implanté par faisceau d’ion caractérisés par nanocalorimétrie

Nous présenterons le procédé de fabrication, la caractérisation, ainsi qu’un modèle numérique permettant l’optimisation d’un nouveau dispositif permettant d’effectuer des mesures de nanocalorimétrie sur un échantillon de silicium monocristallin. Ce dernier possède entre autre des propriétés thermiques nous permettant d’effectuer des mesures à des températures supérieures à 900 C, avec une résolution meilleure que 16 C. Ceci nous a permis d’étudier la dynamique des défauts induits par implantation ionique dans le silicium monocristallin. Deux comportements différents sont observés dans la germination de la phase amorphe induite par implantation à 10 et 80 keV. Ces résultats ont été confrontés à des simulations Monte-Carlo basées sur le modèle des paires lacunesinterstitiels. La comparaison entre les simulations et les mesures expérimentales ont montré que ce modèle est incomplet car il ne reproduit qualitativement que certaines caractéristiques observées expérimentalement. Des mesures réalisées à partir de -110 C dans le silicium monocristallin et amorphisé implanté avec des ions légers, ont mis en évidence des différences claires entre la relaxation dans le silicium amorphe et le recuit des défauts dans le silicium monocristallin. Deux processus à des énergies d’activation de 0.48 et 0.6 eV ont été observés pour les implantations réalisées dans le silicium monocristallin tandis qu’un relâchement de chaleur uniforme ne révélant qu’un spectre continu d’énergie d’activation a été observé dans le silicium amorphe.

Réduction de la durée de vie des porteurs de charge dans le silicium noir par implantation ionique

Le but de ce projet est d’étudier l’effet des défauts cristallins sur les propriétés optoélectroniques de photodétecteurs fabriqué à partir de « silicium noir », c’est-à-dire du silicium dopé et microstructuré par impulsions laser femtoseconde, ce qui lui donne une apparence noire mate caractéristique. Des échantillons de silicium noir ont été recuits puis implantés avec des ions ayant une énergie de 300 keV (Si+), 1500 keV (Si+) ou 2000 keV (H+). Trois fluences pour chaque énergie d’implantation ont été utilisées (1E11, 1E12, ou 1E13 ions/cm2) ce qui modifie le matériau en ajoutant des défauts cristallins à des profondeurs et concentrations variées. Neuf photodétecteurs ont été réalisés à partir de ces échantillons implantés, en plus d’un détecteur-contrôle (non-implanté). La courbe de courant-tension, la sensibilité spectrale et la réponse en fréquence ont été mesurées pour chaque détecteur afin de les comparer. Les détecteurs ont une relation de courant-tension presque ohmique, mais ceux implantés à plus haute fluence montrent une meilleure rectification. Les implantations ont eu pour effet, en général, d’augmenter la sensibilité des détecteurs. Par exemple, l’efficacité quantique externe passe de (0,069±0,001) % à 900 nm pour le détecteur-contrôle à (26,0±0,5) % pour le détecteur ayant reçu une fluence de 1E12 cm-2 d’ions de silicium de 1500 keV. Avec une tension appliquée de -0,50 V, la sensibilité est améliorée et certains détecteurs montrent un facteur de gain de photocourant supérieur à l’unité, ce qui implique un mécanisme de multiplication (avalanche ou photoconductivité). De même, la fréquence de coupure a été augmentée par l’implantation. Une technique purement optique a été mise à l’essai pour mesurer sans contacts la durée de vie effective des porteurs, dans le but d’observer une réduction de la durée de vie causée par les défauts. Utilisant le principe de la réflexion photo-induite résolue en fréquence, le montage n’a pas réuni toutes les conditions expérimentales nécessaires à la détection du signal.

Étude de la formation et de l'évolution de nanostructures par méthodes Monte Carlo

Cette thèse, composée de quatre articles scientifiques, porte sur les méthodes numériques atomistiques et leur application à des systèmes semi-conducteurs nanostructurés. Nous introduisons les méthodes accélérées conçues pour traiter les événements activés, faisant un survol des développements du domaine. Suit notre premier article, qui traite en détail de la technique d'activation-relaxation cinétique (ART-cinétique), un algorithme Monte Carlo cinétique hors-réseau autodidacte basé sur la technique de l'activation-relaxation nouveau (ARTn), dont le développement ouvre la voie au traitement exact des interactions élastiques tout en permettant la simulation de matériaux sur des plages de temps pouvant atteindre la seconde. Ce développement algorithmique, combiné à des données expérimentales récentes, ouvre la voie au second article. On y explique le relâchement de chaleur par le silicium cristallin suite à son implantation ionique avec des ions de Si à 3 keV. Grâce à nos simulations par ART-cinétique et l'analyse de données obtenues par nanocalorimétrie, nous montrons que la relaxation est décrite par un nouveau modèle en deux temps: "réinitialiser et relaxer" ("Replenish-and-Relax"). Ce modèle, assez général, peut potentiellement expliquer la relaxation dans d'autres matériaux désordonnés. Par la suite, nous poussons l'analyse plus loin. Le troisième article offre une analyse poussée des mécanismes atomistiques responsables de la relaxation lors du recuit. Nous montrons que les interactions élastiques entre des défauts ponctuels et des petits complexes de défauts contrôlent la relaxation, en net contraste avec la littérature qui postule que des "poches amorphes" jouent ce rôle. Nous étudions aussi certains sous-aspects de la croissance de boîtes quantiques de Ge sur Si (001). En effet, après une courte mise en contexte et une introduction méthodologique supplémentaire, le quatrième article décrit la structure de la couche de mouillage lors du dépôt de Ge sur Si (001) à l'aide d'une implémentation QM/MM du code BigDFT-ART. Nous caractérisons la structure de la reconstruction 2xN de la surface et abaissons le seuil de la température nécessaire pour la diffusion du Ge en sous-couche prédit théoriquement par plus de 100 K.

Magnetic and topographical modifications of amorphous Co–Fe thin films induced by high energy Ag7+ ion irradiation

We have investigated the effects of swift heavy ion irradiation on thermally evaporated 44 nm thick, amorphous Co77Fe23 thin films on silicon substrates using 100 MeV Ag7+ ions fluences of 1 1011 ions/ cm2, 1 1012 ions/cm2, 1 1013 ions/cm2, and 3 1013 ions/cm2. The structural modifications upon swift heavy irradiation were investigated using glancing angle X-ray diffraction. The surface morphological evolution of thin film with irradiation was studied using Atomic Force Microscopy. Power spectral density analysis was used to correlate the roughness variation with structural modifications investigated using X-ray diffraction. Magnetic measurements were carried out using vibrating sample magnetometry and the observed variation in coercivity of the irradiated films is explained on the basis of stress relaxation. Magnetic force microscopy images are subjected to analysis using the scanning probe image processor software. These results are in agreement with the results obtained using vibrating sample magnetometry. The magnetic and structural properties are correlated

Strained Silicon on Silicon by Wafer Bonding and Layer Transfer from Relaxed SiGe Buffer

We report the creation of strained silicon on silicon (SSOS) substrate technology. The method uses a relaxed SiGe buffer as a template for inducing tensile strain in a Si layer, which is then bonded to another Si handle wafer. The original Si wafer and the relaxed SiGe buffer are subsequently removed, thereby transferring a strained-Si layer directly to Si substrate without intermediate SiGe or oxide layers. Complete removal of Ge from the structure was confirmed by cross-sectional transmission electron microscopy as well as secondary ion mass spectrometry. A plan-view transmission electron microscopy study of the strained-Si/Si interface reveals that the lattice-mismatch between the layers is accommodated by an orthogonal array of edge dislocations. This misfit dislocation array, which forms upon bonding, is geometrically necessary and has an average spacing of approximately 40nm, in excellent agreement with established dislocation theory. To our knowledge, this is the first study of a chemically homogeneous, yet lattice-mismatched, interface.

Plasma polymerization of C[subscript 4]F[subscript 8] thin film on high aspect ratio silicon molds

High aspect ratio polymeric micro-patterns are ubiquitous in many fields ranging from sensors, actuators, optics, fluidics and medical. Second generation PDMS molds are replicated against first generation silicon molds created by deep reactive ion etching. In order to ensure successful demolding, the silicon molds are coated with a thin layer of C[subscript 4]F[subscript 8] plasma polymer to reduce the adhesion force. Peel force and demolding status are used to determine if delamination is successful. Response surface method is employed to provide insights on how changes in coil power, passivating time and gas flow conditions affect plasma polymerization of C[subscript 4]F[subscript 8].

A Two-level Prediction Model for Deep Reactive Ion Etch (DRIE)

We contribute a quantitative and systematic model to capture etch non-uniformity in deep reactive ion etch of microelectromechanical systems (MEMS) devices. Deep reactive ion etch is commonly used in MEMS fabrication where high-aspect ratio features are to be produced in silicon. It is typical for many supposedly identical devices, perhaps of diameter 10 mm, to be etched simultaneously into one silicon wafer of diameter 150 mm. Etch non-uniformity depends on uneven distributions of ion and neutral species at the wafer level, and on local consumption of those species at the device, or die, level. An ion–neutral synergism model is constructed from data obtained from etching several layouts of differing pattern opening densities. Such a model is used to predict wafer-level variation with an r.m.s. error below 3%. This model is combined with a die-level model, which we have reported previously, on a MEMS layout. The two-level model is shown to enable prediction of both within-die and wafer-scale etch rate variation for arbitrary wafer loadings.

Chemical bonding and composition of silicon nitride films prepared by inductively coupled plasma chemical vapor deposition

Thin silicon nitride films were prepared at 350 degrees C by inductively coupled plasma chemical vapor deposition on Si(100) substrates under different NH(3)/SiH(4) or N(2)/SiH(4) gas mixture. The chemical composition and bonding structure of the deposited films were investigated as a function of the process parameters, such as the gas flow ratio NH(3)/SiH(4) or N(2)/SiH(4) and the RF power, using X-ray photoelectron spectroscopy (XPS). The gas flow ratio was 1.4, 4.3, 7.2 or 9.5 and the RF power, 50 or 100 W. Decomposition results of Si 2p XPS spectra indicated the presence of bulk Si, under-stoichiometric nitride, stoichiometric nitride Si(3)N(4), oxynitride SiN(x)O(y), and stoichiometric oxide SiO(2), and the amounts of these compounds were strongly influenced by the two process parameters. These results were consistent with those obtained from N 1s XPS spectra. The chemical composition ratio N/Si in the film increased with increasing the gas flow ratio until the gas flow ratio reached 4.3, reflecting the high reactivity of nitrogen, and stayed almost constant for further increase in gas flow ratio, the excess nitrogen being rejected from the growing film. A considerable and unexpected incorporation of contaminant oxygen and carbon into the depositing film was observed and attributed to their high chemical reactivity. (C) 2010 Elsevier B.V. All rights reserved.

Effect of electron magnetic trapping in a plasma immersion ion implantation system

In this work we describe a two-dimensional computer simulation of magnetic field enhanced plasma immersion implantation system. Negative bias voltage of 10.0 kV is applied to a cylindrical target located on the axis of a grounded vacuum chamber filled with uniform nitrogen plasma. A pair of external coils creates a static magnetic field with main vector component along the axial direction. Thus, a system of crossed ExB field is generated inside the vessel forcing plasma electrons to rotate in azimuthal direction. In addition, the axial variation of the magnetic field intensity produces magnetic mirror effect that enables axial particle confinement. It is found that high-density plasma regions are formed around the target due to intense background gas ionization by the trapped electrons. Effect of the magnetic field on the sheath dynamics and the implantation current density of the PIII system is investigated. By changing the magnetic field axial profile (varying coils separation) an enhancement of about 30% of the retained dose can be achieved. The results of the simulation show that the magnetic mirror configuration brings additional benefits to the PIII process, permitting more precise control of the implanted dose.

Corrosion resistance enhancement of SAE 1020 steel after Chromium implantation by nitrogen ion recoil

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Helium ion irradiation of polymer films deposited from TMS-Ar plasmas

Polymer films synthesized from plasmas of a tetramethylsilane - Ar mixture were modified by irradiation with 170 keV He ions at fluences ranging from 1 x 10(14) to 1 x 10(16) cm(-2). As revealed by infrared spectroscopy, the ion beam produced intense bond rearrangements, such as the depletion of bonding groups (C-H and Si-H), and induced the formation of new ones, such as O-H and Si-O. From the nanoindentation measurements, a remarkable increase in the surface hardness of the films was observed as the ion fluence was increased. The increases in hardness were accompanied by an increase in the film compaction as shown by using a combination of RBS and film thickness measurements. From both hardness and infrared measurements A was concluded that, under the He ion bombardment, the polymer structure is transformed into a silicon oxycarbide network.

Effects of ion beam on nanoindentation characteristics of glassy polymeric carbon surface

Glassy polymeric carbon (GPC) is a useful material for medical applications due to its chemical inertness and biocompatible characteristics. Mitral and aortic and hydrocephalic valves are examples of GPC prosthetic devices that have been fabricated and commercialized in Brazil. In this work, ion beam was used to improve the mechanical characteristics of GPC surface and therefore to avoid the propagation of microcracks where the cardiac valves are more fragile. A control group of phenolic resin samples heat-treated at 300, 400, 700, 1000, 1500, and 2500 degrees C was characterized by measuring their hardness and Young's reduced elastic modulus with the depth of indentation. The control group was compared to results obtained with samples heat-treated at 700, 1000, and 1500 degrees C and bombarded with energetic ions of silicon, carbon, oxygen, and gold at energies of 5, 6, 8, and 10 MeV, respectively, with fluences between 10x10(13) and 10x10(16) ions/cm(2). GPC nonbombarded samples showed that hardness depends on the heat treatment temperature (HTT), with a maximum hardness for heat treatment at 1000 degrees C. The comparison between the control group and bombarded group also showed that hardness, after bombardment, had a greater increase for samples prepared at 700 degrees C than for samples prepared at higher temperatures. The Young's elastic modulus presents an exponential relationship with depth. The parameters obtained by fitting depend on the HTT and on the ion used in the bombardment more than on energy and fluence. The hardness results show clearly that bombardment can promote carbonization, increase the linkage between the chains of the polymeric material, and promote recombination of broken bonds in lateral groups that are more numerous for samples heat-treated at 700 degrees C. (c) 2004 Elsevier B.V. All rights reserved.

Modification of surface properties of Ti-16Si-4B powder alloy by plasma immersion ion implantation

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Polymer treatment by plasma immersion ion implantation of nitrogen for formation of diamond-like carbon film

Nitrogen ions were implanted by plasma immersion in Kapton, Mylar and polypropylene, with the objective of forming a diamond-like carbon layer on these polymers. The Raman spectrum of the implanted polypropylene showed typical Diamond-Like Carbon (DLC) graphite (G) and disorder (D) peaks, with an sp 3/sp2 hybridization ratio of approximately 0.4 to 0.6. The XPS analysis of the three implanted polymers also showed peaks of C-C and N-C bonds in the sp3 configuration, with hybridization ratios in the same range as the Raman result. The implanted polymers were exposed to oxygen plasma to test the resistance of the polymers to oxygen degradation. Mass loss rate results, however, showed that the DLC layer formed is not sufficiently robust for this application. Nevertheless, the layer formed can be suitable for other applications such as in gas barriers in beverage containers. Further study of implantation conditions may improve the quality of the DLC layer.