Room temperature desorption of Self Assembled Monolayer from Copper surface for low temperature & low pressure thermocompression bonding

In this paper the utility of Self Assembled Monolayer (SAM) of Propanethiol (C3) for Copper protection from oxidation and subsequent desorption of the Thiol layer from Copper surface by using cold Helium plasma has been investigated. The major bottleneck of achieving low temperature and low pressure bonding is the presence of contamination and oxidation on the Copper surface. Use of Thiol can protect the freshly deposited Copper surface from oxidation and other contamination. Removal of this Thiol layer by Helium plasma just prior to bonding can bring down the required temperature of bonding to 200° and pressure to 4kN. This technique can open up a whole new platform for low temperature bonding for 3D ICs

Investigation of Cu‑Cu bonding for 2.5D and 3D system integration using self‑assembled monolayer as oxidation inhibitor

Das Cu-Cu-Bonden ist eine vielversprechende lötfreie Fine-Pitch-Verbindungstechnologie für die 2,5D- und 3D-Systemintegration. Diese Bondtechnologie wurde in den letzten Jahren intensiv untersucht und wird derzeit für miniaturisierte mikroelektronische Produkte eingesetzt. Allerdings, stellt das Cu‑Cu-Bonden zum einen sehr hohe Anforderungen an die Oberflächenplanarität und -reinheit, und zum anderen sollten die Bondpartner frei von Oxiden sein. Oxidiertes Cu erfordert erhöhte Bondparameter, um die Oxidschicht zu durchbrechen und zuverlässige Cu-Cu-Verbindungen zu erzielen. Diese Bondbedingungen sind für viele sensible Bauelemente nicht geeignet. Aus diesem Grund sollten alternative Technologien mit einer einfachen Technik zum Schutz von Cu vor Oxidation gefunden werden. In dieser Arbeit werden selbstorganisierte Monolagen (SAMs) für den Cu-Oxidationsschutz und die Verbesserung der Cu-Cu-Thermokompression- (TC) und Ultraschall- (US) Flip-Chip-Bondtechnologien untersucht. Die Experimente werden an Si-Chips mit galvanisch aufgebrachten Cu-Microbumps und Cu-Schichten durchgeführt. Die Arbeit beinhaltet die umfassende Charakterisierung der SAM für den Cu-Schutz, die Bewertung der technologischen Parameter für das TC- und US-Flip-Chip-Bonden sowie die Charakterisierung der Cu-Cu-Bondqualität (Scherfestigkeitstests, Bruchflächen- und Mikrostrukturanalysen). Eine Lagerung bei tiefen Temperaturen (bei ‑18 °C und ‑40 °C) bestätigte die langanhaltende Schutzwirkung der kurzkettigen SAMs für das galvanisch abgeschiedene Cu ohne chemisch-mechanische Politur. Der Einfluss der Tieftemperaturlagerung an Luft und der thermischen SAM-Desorption in einer Inertgasatmosphäre auf die TC-Verbindungsqualität wird im Detail analysiert. Die Idee, mit Hilfe der US-Leistung SAM mechanisch zu entfernen und gleichzeitig das US-Flip-Chip-Bonden zu starten, wurde in der Literatur bisher nicht systematisch untersucht. Die Methode ermöglicht kurze Bondzeiten, niedrige Bondtemperaturen und das Bonden an Umgebungsluft. Sowohl beim TC- als auch beim US-Flip-Chip-Bonden zeigt es sich, dass die Scherfestigkeit bei den Proben mit SAM-Passivierung um ca. 30 % höher ist als bei unbeschichteten Proben. Das Vorhandensein von Si- und Ti-Bruchflächen nach den Scherfestigkeitstests ist für die Proben mit der SAM-Passivierung typisch, was auf eine höhere Festigkeit solcher Verbindungen im Vergleich zu ungeschützten Proben schließen lässt. Die Transmissionselektronenmikroskopie (TEM) zeigt keine SAM-Spuren im zentralen Bereich der Cu-Cu-Grenzfläche nach dem US-Flip-Chip-Bonden. Die Ergebnisse dieser Arbeit zeigen die Verbesserung der Bondqualität durch den Einsatz von SAM zum Schutz des Cu vor Oxidation im Vergleich zum üblicherweise angewandten Cu-Vorätzen. Das gefundene technologische Prozessfenster für das US-Flip-Chip-Bonden an Luft bietet eine hohe Bondqualität bei 90 °C und 150 °C, bei 180 MPa, bei einer Bonddauer von 1 s an. Die in dieser Arbeit gewonnenen Erkenntnisse sind ein wichtiger Beitrag zum Verständnis des SAM-Einflusses auf Chips mit galvanischen Cu-Microbumps, bzw. Cu-Schichten, und zur weiteren Anwendung der Cu-Cu-Fine-Pitch-Bondtechnologie in der Mikroelektronik.Cu-Cu bonding is one of the most promising fine-pitch interconnect technologies with solder elimination for 2.5D and 3D system integration. This bonding technology has been intensively investigated in the last years and is currently in application for miniaturized microelectronics products. However, Cu-Cu bonding has very high demands on the sur-face planarity and purity, and the bonding partners should be oxide-free. Oxidized Cu requires elevated bonding parameters in order to break through the oxide layer and achieve reliable Cu-Cu interconnects. Those bonding conditions are undesirable for many devices (e.g. due to the temperature/pressure sensitivity). Therefore, alternative technologies with a simple technique for Cu protection from oxidation are required. Self-assembled monolayers (SAMs) are proposed for the Cu protection and the improvement of the Cu-Cu thermocompression (TC) and ultrasonic (US) flip-chip bonding technologies in this thesis. The experiments were carried out on Si dies with electroplated Cu microbumps and Cu layers. The thesis comprises the comprehensive characterization of the SAM for Cu protection, evaluation of technological parameters for TC and US flip-chip bonding as well as characterization of the Cu-Cu bonding quality (shear strength tests, fracture surface and microstructure analyses). The storage at low temperatures (at ‑18 °C and ‑40 °C) confirmed the prolonged protective effect of the short-chain SAMs for the electroplated Cu without chemical-mechanical polishing. The influence of the low-temperature storage in air and the thermal SAM desorption in an inert gas atmosphere on the TC bonding quality was analyzed in detail. The approach of using US power to mechanically remove SAM and simultaneously start the US flip-chip bonding has not been systematically investigated before. The method provides the benefit of short bonding time, low bonding temperature and bonding in ambient air. Both the TC and US flip-chip bonding results featured the shear strength that is approximately 30 % higher for the samples with SAM passivation in comparison to the uncoated samples. The presence of Si and Ti fracture surfaces after the shear strength tests is typical for the samples with the SAM passivation, which suggests a higher strength of such interconnects in comparison to the uncoated samples. The transmission electron microscopy (TEM) indicated no SAM traces at the central region of the Cu-Cu bonding interface after the US flip-chip bonding. The results of this thesis show the improvement of the bonding quality caused by the application of SAM for Cu protection from oxidation in comparison to the commonly applied Cu pre-treatments. The found technological process window for the US flip-chip bonding in air offers high bonding quality at 90 °C and 150 °C, at 180 MPa, for the bonding duration of 1 s. The knowledge gained in this thesis is an important contribution to the understanding of the SAM performance on chips with electroplated Cu microbumps/layers and further application of the Cu-Cu fine-pitch bonding technology for microelectronic devices

Metal-Alloy Cu Surface Passivation Leads to High Quality Fine-Pitch Bump-Less Cu-Cu Bonding for 3D IC and Heterogeneous Integration Applications

In this paper, we report a low temperature, fine-pitch, bump-less, damascene compatible Cu-Cu thermocompression bonding, using an optimized ultra-thin passivation layer, Constantan, which is an alloy (Copper-Nickel) of 55% Cu and 45% Ni. Surface oxidation and its roughness are the major bottlenecks in achieving high quality, low temperature, and fine-pitch Cu-Cu bonding. In this endeavor, we have used Cu rich alloy (Constantan) for passivation of Cu surface prior to bonding. We have systematically optimized the constantan passivation layer thickness for high quality low temperature, low pressure, bump-less Cu-Cu bonding. Also, we have studied systematically the efficacy of Cu surface passivation with optimized ultra-thin constantan alloy passivation layer. After rigorous trial and optimization, we successfully identified 2 nm passivation layer thickness, at which very high quality Cu-Cu bonding could be accomplished at sub 200 °C with a nominal contact pressure of 0.4 MPa. Post-bonding, electrical and mechanical characterization were validated using four-probe IV measurement and bond strength measurement respectively. Furthermore, Cu-Cu bonding interface was analyzed using IR wafer bonder inspection tool. Very high bond strength of 163 MPa and defect free interface observed by WBI-IR clearly suggests, Cu-Cu finepitch bonding with optimized ultra-thin alloy of 2 nm thick constantan, is of very high quality and reliable. Moreover, this novel bonding approach with alloy based interconnect passivation technique is the prime contestant for future heterogeneous integration

DENSE 3D HETEROGENEOUS INTEGRATION USING SELECTIVE COBALT ALD DEPOSITION AND RECONSTITUTED TIERS

In this thesis, a new fine-pitch low-temperature bonding technology using selective Cobalt (Co) ALD deposition is presented. The benefits of selective Co ALD bonding are nanometer-scale controllability, low planarity requirement, low bonding temperature (200 oC) and potential for ultra-high-density bonds. To demonstrate selective Co ALD bonding, a Cu/Gap/Cu three-layered structure, which emulates 3D ICs stacking, is fabricated and carefully characterized. The testbed shows seamless Co interconnection between the Cu pads after Co ALD deposition for 1000 cycles. The electrical measurements demonstrate over 90% yield, which prove the Co connectivity between the Cu pads. Moreover, in this thesis, a new type of SiO2-reconstituted-tier stacking technology is proposed. The SiO2-reconstituted-tier stacking technology utilizes low-temperature ICP- PECVD SiO2 to encapsulate multi-sized chiplets. After ICP-PECVD SiO2 encapsulation, the through-oxide-vias and the pads are formed on the SiO2 to complete the reconstituted tier before stacking. Compared with conventional epoxy-molding-compound-based stacking, the SiO2 approach can have smaller loss tangent (10x), lower CTE mismatch (3x) and the higher via density (>400x). The thickness of the proposed technology can be over 10 times smaller than conventional epoxy molding. The two technologies, with further analysis and studies, open up exciting new opportunities for future 3D IC heterogeneous integration.M.S

Low-Molecular Weight Molecules as Selective Contacts for Perovskite Solar Cells

La tecnologia fotovoltaica és una de les fonts d'energia neta i renovable més prometedores per reduir l'impacte ambiental dels combustibles fòssils en les últimes dècades. en aquest context, les perovskites són un material que ha atret recentment una atenció important a causa de la seva capacitat per aconseguir eficiències de conversió molt elevades. Les capes de càrrega selectiva juguen un paper crucial en el ràpid augment del rendiment del dispositiu i en l'estabilitat de les cel·les solars de perovskita. Recentment, l'aplicació de mono-capes auto-assemblades formades per molècules orgàniques que funcionen com a capes selectives de càrrega en cel·les solars de perovskita ha atret una gran atenció a causa d'avantatges com la rendibilitat, l'estabilitat i l'absència d'additius. L'objectiu d'aquesta tesi és el disseny i la síntesi de noves molècules que formen mono-capes auto-assemblades que funcionin com a capes selectives de forats en cel·les solars de perovskita per aconseguir una eficiència de conversió d'alta d'energia i una vida d'envelliment d'alt rendiment feta a mida.La tecnología fotovoltaica es una de las fuentes de energía limpia y renovable más prometedoras para reducir el impacto ambiental de los combustibles fósiles en las últimas décadas. en este contexto, las *perovskites son un material que ha atraído recientemente una atención importante a causa de su capacidad para conseguir eficiencias de conversión muy elevadas. Las capas de carga selectiva juegan un papel crucial en el rápido aumento del rendimiento del dispositivo y en la estabilidad de las celdas solares de *perovskita. Recientemente, la aplicación de *mono-capes auto-asemejadas formadas por moléculas orgánicas que funcionan como capas selectivas de carga en celdas solares de *perovskita ha atraído una gran atención a causa de ventajas como la rentabilidad, la estabilidad y la ausencia de aditivos. El objetivo de esta tesis es el diseño y la síntesis de nuevas moléculas que forman *mono-capes auto-asemejadas que funcionen como capas selectivas de agujeros en celdas solares de *perovskita para conseguir una eficiencia de conversión de alta de energía y una vida de envejecimiento de alto rendimiento hecha a medida.Photovoltaic technology is one of the most promising clean and renewable energy sources to reduce the environmental impact of fossil fuels in recent decades. In this context, perovskites are a material that has recently attracted significant attention due to their ability to achieve very high conversion efficiencys. Selective charge layers play a crucial role in rapidly increasing device performance and in the stability of perovskite solar cells. Recently, the application of self-assembly mono-caps made up of organic molecules that function as selective layers of charge in solar perovskite cells has attracted great attention due to advantages such as profitability, stability and the absence of additives. The goal of this thesis is the design and synthesis of new molecules that form self-assembly mono-layers that function as selective layers of holes in solar perovskite cells to achieve high-energy conversion efficiency and a high-performance aging life tailored to size

Heterogeneous Integration on Silicon-Interconnect Fabric using fine-pitch interconnects (≤10 �m)

Today, the ever-growing data-bandwidth demand is pushing the boundaries of the traditional printed circuit board (PCB) based integration schemes. Moreover, with the apparent saturation of semiconductor scaling, commonly called Moore's law, system scaling warrants a paradigm shift in packaging technologies, assembly techniques, and integration methodologies. In this work, a superior alternative to PCBs called the Silicon-Interconnect Fabric (Si-IF) is investigated. The Si-IF is a silicon-based, package-less, fine-pitch, highly scalable, heterogeneous integration platform for wafer-scale systems. In this technology, unpackaged dielets are assembled on the Si-IF at small inter-dielet spacings (≤100 �m) using fine-pitch (≤10 �m) die-to-substrate interconnects. A novel assembly process using a solder-less direct metal-metal (gold-gold and copper-copper) thermal compression bonding was developed. Using this process, sub-10 �m pitch interconnects with a low specific contact resistance of ≤0.7 Ω-�m2 were successfully demonstrated. Because of the tightly packed Si-IF assembly, the communication links between the neighboring dies are short (≤500 �m) with low loss (≤2 dB), comparable to on-chip connections. Consequently, simple buffers can transfer data between dies using a Simple Universal Parallel intERface for chips (SuperCHIPS) at low latency (<30 ps), low energy per bit (≤0.03 pJ/b), and high data-rates (up to 10 Gbps/link), corresponding to an aggregate bandwidth up to 8 Tbps/mm. The benefits of the SuperCHIPS protocol were experimentally demonstrated to provide 5-90X higher data-bandwidth, 8-30X lower latency, and 5-40X lower energy per bit compared to existing integration schemes. This dissertation addresses the assembly technology and communication protocols of the Si-IF technology

Nanotemplate creation and self-assembly on the (111) surface of gold

Self-assembly on strained metallic interfaces is an attractive option for growing highly ordered, multi-functional nanopatterns. I performed a series of studies in UHV to investigate the processes of ordered growth and self-assembly on Au(111). I did a combined AES/STM study of the formation of ordered networks of Co islands on Au(111) and obtained the conditions for growing uniform, bi-layer Co-terminated clusters. In another STM study I obtained novel results which reveal the particular complexity of CH3SH self-assembly on Au(111). I observed dimerization of the molecules on the FCC areas of an unperturbed Au(111) reconstruction network and the formation of two new continuous ordered phases--an in-plane oriented stripe phase (beta-phase) and an out-of-plane pointing, close-packed phase (&phgr;-phase). These results complement recent theoretical investigations and contribute to an ongoing DFT study of the energetics of the assembly. The cluster growth and the self-assembly processes are successfully combined in achieving selective adsorption of CH 3SH on Co/Au(111) network--a prototype nanotechnology for directed self-assembly of molecular elements on large, multifunctional templates with a nm size unit cell. The thermal evolution of Co/Au(111) system is established, and CH3SH is shown to exhibit a novel interaction which leads to non-dissociative dimerization and to the formation of new ordered phases

Nanocrystal

We focused on cutting-edge science and technology of Nanocrystals in this book. "Nanocrystal" is expected to lead to the creation of new materials with revolutionary properties and functions. It will open up fresh possibilities for the solution to the environmental problems and energy problems. We wish that this book contributes to bequeath a beautiful environment and valuable resources to subsequent generations

Synthesis and Characterization of Films and Membranes of Metal-Organic Framework (MOF) for Gas Separation Applications

Metal-Organic Frameworks (MOFs) are nanoporous framework materials with tunable pore size and functionality, and hence attractive for gas separation membrane applications. Zeolitic Imidazolate Frameworks (ZIFs), a subclass of MOFs, are known for their high thermal and chemical stability. ZIF-8 has demonstrated potential to kinetically separate propane/propene in powder and membrane form. ZIF-8 membranes propane-propene separation performance is superior in comparison to polymer, mixed matrix and carbon membranes. The overarching theme of my research is to address challenges that hinder fabrication of MOF membranes on a commercial scale and in a reproducible and scalable manner. 1. Current approaches, are specific to a given ZIF, a general synthesis route is not available. Use of multiple steps for surface modification or seeding causes reproducibility and scalability issues. 2. Conventional fabrication techniques are batch processes, thereby limiting their commercialization. Here we demonstrate two new approaches that can potentially address these challenges. First, we report one step in situ synthesis of ZIF-8 membranes on more commonly used porous α-alumina supports. By incorporating sodium formate in the in situ growth solution, well intergrown ZIF-8 membranes were synthesized on unmodified supports. The mechanism by which sodium formate promotes heterogeneous nucleation was investigated. Sodium formate reacts with zinc source to form zinc oxide layer, which in turn promotes heterogeneous nucleation. Sodium formate promotes heterogeneous nucleation in other ZIF systems as well, leading to ZIF-7, Zn(Im)2 (ZIF-61 analogue), ZIF-90, and SIM-1 films. Thus one step in situ growth using sodium formate provides a simplified, reproducible and potentially general route for ZIF film fabrication. One step in situ route, although advantageous; is still conventional in nature and batch process with long synthesis time. This limits commercialization, due to scalability and manufacturing cost issues. Taking advantage of coordination chemistry of MOFs and using temperature as driving force, continuous well-intergrown membranes of HKUST-1 and ZIF-8 in relatively short time (15 min) using Rapid Thermal Deposition (RTD). With minimum precursor consumption and simplified synthesis protocol, RTD provides potential for a continuous, scalable, reproducible and commercializable route for MOF membrane fabrication. RTD-prepared MOF membranes show improved separation performances, indicating improved microstructure