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京都大学 / 新制・課程博士 / 博士(理学) / 甲第24074号 / 理博第4841号 / 新制||理||1692(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)教授 寺西 利治, 教授 島川 祐一, 教授 倉田 博基 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Electromigration (EM) and thermomigration (TM) reliability of Pb-free solder joints are emerging as critical concerns in advanced packages. In this study, EM and TM phenomena in Sn-2.5Ag solder joints with thick Cu or thin Ni under-bump metallurgy (UBM) were investigated. A series of EM tests were performed to obtain activation energy (Q) and current density exponent (n), and to understand failure mechanisms. Joule heating was also taken into account. Q and n values were determined as follows: for Cu UBM solders, Q = 1.0 eV and n = 1.5; for Ni UBM solders, Q = 0.9 and n = 2.2. Important factors limiting EM reliability of Pb-free solder joints were found to be UBM dissolution with extensive intermetallic compound (IMC) growth and current crowding. IMC growth without current stressing was found to follow the parabolic growth law whereas linear growth law was observed for Cu₆Sn₅ and Ni₃Sn₄ under high current stressing. For Cu UBM solders, the apparent activation energy for IMC growth was consistent with the activation energy for EM, which supports that EM failure was closely related to IMC growth. In contrast, for Ni UBM solders the apparent activation energy was higher than the EM activation energy. It was suggested that the EM failure in the Ni UBM solders could be associated with more than one mass transport mechanism. The current crowding effect was analyzed with different thicknesses of Ni UBM. It was found that the maximum current density in solder could represent the current density term in Black's equation better than the average current density. FEM studies demonstrated that current crowding was mainly controlled by UBM thickness, metal trace design, and passivation opening diameter. A large temperature gradient of the order of 10³ °C/cm was generated across the sample to induce noticeable TM and to compare its effect against that of EM. TM-induced voiding was observed in Ni UBM solders while UBM dissolution with IMC formation occurred in Cu UBM solders. However, the relative effect of TM was found to be several times smaller than that of EM even at this large temperature gradient. / text

Les fréquences de fonctionnement élevées des puces semi-conductrices génèrent des flux de chaleurs importants qu'il est nécessaire d'évacuer pour éviter la destruction de la puce. Un module standard dans le domaine de l'électronique de puissance est composé d'une puce en silicium, d'un isolant électrique (substrat) et d'un dissipateur thermique (drain) permettant l'évacuation de la chaleur. Cette chaleur induit des contraintes thermomécaniques dues à la dilatation différentielle des matériaux.Deux concepts nouveaux proposés permettent de palier ces problèmes et d'augmenter la fiabilité générale des systèmes électroniques. Le premier est la conception et l'élaboration d'un drain composite à propriétés thermiques adaptatives (coefficient de dilatation thermique et conductivité thermique). Dans le deuxième, une nouvelle méthode d'assemblage est présentée. Elle permet, au moyen d'un film métallique Sn ou Au, de créer des composés intermétalliques stables dans le temps. / The high operating frequencies of semiconductor chips generate heat fluxes it is important to be evacuated in order to avoid the destruction of the chip. A standard module in the field of power electronics is composed of a silicon chip, an electrical insulator (substrate) and a heat sink (drain) for the evacuation of heat. This heat induces thermomechanical stresses due to differential expansion of materials.Two new concepts proposed can overcome these problems and increase the overall reliability of electronic systems. The first is the design and development of a drain composite adaptive thermal properties (thermal expansion coefficient and thermal conductivity). In the second, a new assembly method is presented. It allows, by means of a metal film Sn or Au, intermetallic compounds to create stable over time.

This dissertation constitutes two major sections. In the first major section, a kinetic analysis was established to investigate the electromigration (EM), enhanced intermetallic compound (IMC) growth and void formation for Sn-based Pb-free solder joints to Cu under bump metallization (UBM). The model takes into account the interfacial intermetallic reaction, Cu-Sn interdiffusion, and current stressing. A new approach was developed to derive atomic diffusivities and effective charge numbers based on Simulated Annealing (SA) in conjunction with the kinetic model. The finite difference (FD) kinetic model based on this approach accurately predicted the intermetallic compound growth when compared to empirical observation. The ultimate electromigration failure of the solder joints was caused by extensive void formation at the intermetallic interface. The void formation mechanism was analyzed by modeling the vacancy transport under electromigration. The effects of current density and Cu diffusivity in Sn solder were also investigated with the kinetic model. The second major section describes the integration of Step and Flash Imprint Lithography (S-FIL®) into an industry standard Cu/low-k dual damascene process. The yield on a Back End Of the Line (BEOL) test vehicle that contains standard test structures such as via chains with 120 nm vias was established by electrical tests. S-FIL shows promise as a cost effective solution to patterning sub 45 nm features and is capable of simultaneously patterning two levels of interconnect structures, which provides a low cost BEOL process. The critical processing step in the integration is the reactive ion etching (RIE) process that transfers the multilevel patterns to the inter-level dielectrics (ILD). An in-situ, multistep etch process was developed that gives excellent pattern structures in two industry standard Chemical Vapor Deposited (CVD) low-k dielectrics. The etch process showed excellent pattern fidelity and a wide process window. Electrical testing was conducted on the test vehicle to show that this process renders high yield and consistent via resistance. Discussions of the failure behaviors that are characteristic to the use of S-FIL are provided. / text

The aim of the present work is to clarify the interplay between the complex technological chain of crystal preparation, chemical and structural perfection of grown crystals of intermetallic compounds and oxides and their physical properties. This technological chain includes detailed studies of unknown or insufficiently known phase diagrams, their correlation with growth conditions and optimisation of process parameters for obtaining single crystals with high chemical and physical perfection. The measurements of the physical properties of the grown crystals such as superconductivity, thermoelectric or dielectric properties not only show new features and properties for application of the materials obtained, but also allow conclusions of the crystal perfection. The studies are focused on the following systems: RENi2B2C borocarbides (RE=Y, Tb or Ho) displaying superconductivity, magnetic order and a strong interplay between magnetic and superconducting properties for YNi2B2C, TbNi2B2C, HoNi2B2C, respectively; CeSi2-?Ô and Ru2Si3 as examples of systems with magnetic and promising thermoelectric properties, respectively; MgB2 and LiBC to test of theoretical predictions of the new superconducting intermetallic compounds discovered in the last years; SrTiO3 and SrZrO3 oxide compounds with special dielectric and optical properties. For this wide spectrum of substances necessarily different growth techniques were applied. That is mainly the floating zone (FZ) or travelling solvent floating zone (TSFZ) techniques with optical heating. Flux techniques were used if the vapour pressure of composing elements is high such as for Mg and Li. The crucible free FZ technique is very attractive for the crystal growth of these intermetallic and oxide compounds to avoid contamination with the crucible material, if the melts have very high chemical reactivity, high melting temperatures and if a large crystal size (at least 3-5 mm) is desired for corresponding physical measurements. One special aim in the presented work is the optimisation of the preparation and growth process features with respect to crystal perfection, establishing new relationships between process parameters, crystal perfection, crystallographic structure, composition of grown crystals and the related physical properties. Optimisation of crystal growth process requires own constitutional studies of growth relevant parts of corresponding multicomponent phase diagrams. Therefore, parts of the phase diagrams were experimentally revealed by differential thermal analysis (DTA), optical metallography and EPMA and partially combined with CALPHAD calculations.

L'assemblage tridimensionnel des circuits microélectroniques et leur utilisation dansdes conditions environnementales extrêmement sévères nécessitent ledéveloppement d’alternatives plus robustes pour les contacts électriques. Unetechnique prometteuse est la transformation des contacts de brasure conventionnelleen composés intermétalliques (IMC). Ce processus est appelé « Transient LiquidPhase Soldering » (TLPS).Dans ce contexte, des tests accélérés permettant la formation d’IMC parélectromigration et thermomigration ont été effectués sur des structures « Packageon Package ». L'objectif principal est le développement d'un modèle généralpermettant de décrire la formation des IMC dans les joints de brasure. Combiné avecune analyse par éléments finis ce modèle pourra être utilisé pour prédire la formationdes IMC dans les joints de brasure pour des structures et des profils de missiondifférents. Le modèle de formation des IMC pourra être utilisé pour optimiser unprocessus TLPS. / A further miniaturization of microelectronic components by three dimensionalpackaging, as well as the use of microelectronic devices under harsh environmentconditions, requires the development of more robust alternatives to the existing Snbased solder joints. One promising technique is the diffusion and migration driventransformation of conventional solder bumps into intermetallic compound (IMC)connections. The related process is called transient liquid phase soldering (TLPS).Against this background an investigation of the IMC formation under consideration ofelectromigration and thermomigration was performed. For the stress tests Packageon Package structures are used. The final result is a general model for the IMCformation in solder joints. Combined with a Finite Element Analysis (FEA) this modelis used to predict the IMC formation in solder joints for a broad range of boundaryconditions. In future the model of the IMC formation can be used to optimize a TLPSprocess.

La demande en énergie ne cesse d'augmenter et elle satisfaite essentiellement par les énergies fossiles qui présentent une contrainte environnementale vue ses émissions de gaz à effet de serre. Considéré comme vecteur énergétique, l'hydrogène possède l'immense avantage de ne pas émettre de gaz à effet de serre et notamment du CO2. Son stockage dans des intermétalliques permet d’obtenir des capacités massiques et volumiques supérieures à celles obtenues en voie liquide ou sous pression. Dans ce travail, nous avons élaboré le composé intermétallique quaternaire LaCaMgNi9 par mécanosynthèse et ce selon différents schémas réactionnels. Ce procédés de synthèse est employé pour la première fois, pour la synthèse de cet intermétallique, afin de s'affranchir des difficultés que présentent les autres techniques de synthèse (co-fusion, frittage). Les caractérisations structurales et morphologiques des alliages obtenus ont été réalisées afin de tester leurs performances en tant que matériaux pour électrode négative d’accumulateur Ni-MH par divers techniques de caractérisation électrochimiques et solide-gaz / The increasing energy demand is mainly supplied by fossil sources which had environmental drawback essentially greenhouse gas emission. Considered as an energy carrier, hydrogen has the huge advantage to be clean. Its storage in intermetallic compound leads too higher hydration capacities than liquid and compressed storage. In this work, LaCaMgNi9 quaternary type alloy has been synthesized, for the first time, by mechanical alloying in order to avoid the inherent difficulties of the fusion technique. The structural and morphological characterization of the obtained alloys were performed. Their hydrogen related properties were examined (solid-gas and electrochemical reactions) in order to study their performance as negative electrode material in Ni-MH batteries

Standard crystalline silicon photovoltaic (PV) modules are designed to continuously convert solar energy into electricity for 25 years. However, the continual generation of electricity by the PV modules throughout their designed service life has been a concern. The key challenge has been the untimely fatigue failure of solder interconnections of solar cells in the modules due to accelerated thermo-mechanical degradation. The goal of this research is to provide adequate information for proper design of solar cell solder joint against fatigue failure through the study of cyclic thermo-mechanical stresses and strains in the joint. This is carried-out through finite element analysis (FEA) using ANSYS software to develop the solar cell assembly geometric models followed by simulations. Appropriate material constitutive model for solder alloy is employed to predict number of cycles to failure of solder joint, hence predicting its fatigue life. The results obtained from this study indicate that intermetallic compound thickness (TIMC); solder joint thickness (TSJ) and width (WSJ) have significant impacts on fatigue life of solder joint. The impacts of TIMC and TSJ are such that as the thicknesses increases solder joint fatigue life decreases. Conversely, as solder joint width (WSJ) increases, fatigue life increases. Furthermore, optimization of the joint is carried-out towards thermo-mechanical reliability improvement. Analysis of results shows the design with optimal parameter setting to be: TIMC -2.5μm, TSJ -20μm and WSJ -1000μm. In addition, the optimized model has 16,264 cycles to failure which is 18.82% more than the expected 13,688 cycles to failure of a PV module designed to last for 25 years.

Master’s thesis in the theoretical part analyses the heating factor (Q), which has significant share on quality of a solder joint. The practical part describes the design and production of test PCB and setting temperature profiles, SMD resistors soldering by using BiSn solder paste. Shear tests of SMD solder joints were realised and evaluated including isothermal ageing samples. At the end of master’s thesis solder joints visual aspects and defects were evaluated, measurement thickness of intermetallic compound by not only optical microscope but also SEM, discussion about results and Q was evaluated.