Improvements for Chip-Chip Interconnects and MEMS Packaging Through Materials and Processing Research Erdal Uzunlar 129 Pages Directed by Dr. Paul A. Kohl The work presented in this dissertation focuses on improvements for ever-evolving modern microelectronic technology. Specifically, three topics were investigated in this work: electroless copper deposition on printed wiring boards (PWBs), polymer-based air-gap microelectromechanical systems (MEMS) packaging technology, and thermal stability enhancement in sacrificial polymers, such as poly(propylene carbonate) (PPC). In the electroless copper deposition study, Ag-based catalysts were identified as a low-cost and equally active alternative to expensive Pd-based catalysts. Hot H2SO4 treatment of PWBs was found as a non-roughening surface treatment method to minimize electrical losses. In MEMS packaging study, a sacrificial polymer-based air-gap packaging technique was improved in terms of identification and simplification of air-gap formation process options, optimization of thermal treatment steps, assessing air-gap formation performance, and analyzing the chemical composition of residue. It was found that non-photosensitive PPC leaves less residue, and creates more reliable air-gaps. The mechanical strength of air-gaps was found to come from residual stress in benzocyclobutene (BCB) caps. In thermal stability of PPC study, the mechanism of thermal stability increase on copper (Cu) surfaces was found as the complex formation between Cu(I) and iodonium of the photoacid generator (PAG), leading to hindrance of acid formation by PAG and restriction of acid-catalyzed decomposition of PPC.

In this work, adhesion between electrolessly deposited copper and dielectric materials for use in microelectronic devices is investigated. The microelectronics industry requires continuous advances due to ever-evolving technology and the corresponding need for higher density substrates with smaller features. At the same time, adhesion must be maintained in order to preserve package reliability and mechanical performance. In order to meet these requirements two approaches were taken: smoothing the surface of traditional epoxy dielectric materials while maintaining adhesion, and increasing adhesion on advanced dielectric materials through chemical bonding and mechanical anchoring. It was found that NH3 plasma treatments can be effective for increasing both catalyst adsorption and adhesion across a range of materials. This adhesion is achieved through increased nitrogen content on the polymer surface, specifically N=C. This nitrogen interacts with the palladium catalyst particles to form chemical anchors between the polymer surface and the electroless copper layer without the need for roughness. Chemical bonding alone, however, did not enable sufficient adhesion but needed to be supplemented with mechanical anchoring. Traditional epoxy materials were treated with a swell and etch process to roughen the surface and create mechanical anchoring. This same process was found to be ineffective when used on advanced dielectric materials. In order to create controlled roughness on these surfaces a novel method was developed that utilized blends of traditional epoxy with the advanced materials. Finally, combined treatments of surface roughening followed by plasma treatments were utilized to create optimum interfaces between traditional or advanced dielectric materials and electroless copper. In these systems adhesion was measured over 0.5 N/mm with root-mean-square surface roughness as low as 15 nm. In addition, the individual contributions of chemical bonding and mechanical anchoring were identified. The plasma treatment conditions used in these experiments contributed up to 0.25 N/mm to adhesion through purely chemical bonding with minimal roughness generation. Mechanical anchoring accounted for the remainder of adhesion, 0.2-0.8 N/mm depending on the level of roughness created on the surface. Thus, optimized surfaces with very low surface roughness and adequate adhesion were achieved by sequential combination of roughness formation and chemical modifications.

In this work, all-copper connections between silicon microchips and substrates are developed. The semiconductor industry advances the transistor density on a microchip based on the roadmap set by Moore's Law. Communicating with a microprocessor which has nearly one billion transistors is a daunting challenge. Interconnects from the chip to the system (i.e. memory, graphics, drives, power supply) are rapidly growing in number and becoming a serious concern. Specifically, the solder ball connections that are formed between the chip itself and the package are challenging to make and still have acceptable electrical and mechanical performance. These connections are being required to increase in number, increase in power current density, and increase in off-chip operating frequency. Many of the challenges with using solder connections are limiting these areas. In order to advance beyond the limitations of solder for electrical and mechanical performance, a novel approach to creating all-copper connections from the chip-to-substrate has been developed. The development included characterizing the electroless plating and annealing process used to create the connections, designing these connections to be compatible with the stress requirements for fragile low-k devices, and finally by improving the plating/annealing process to become process time competitive with solder. It was found that using a commercially available electroless copper bath for the plating, followed by annealing at 180 C for 1 hour, the shear strength of the copper-copper bond was approximately 165 MPa. This work resulted in many significant conclusions about the mechanism for bonding in the all-copper process and the significance of materials and geometry on the mechanical design for these connections.

The microelectronics industry requires continuous advances due to ever-evolving technology and the corresponding need for higher density substrates with smaller features. Specifically, new dielectric materials with enhanced electrical properties are needed. At the same time, adhesion must be maintained in order to preserve package reliability and mechanical performance. As a result, this research investigates the use of thin glass sheets as an alternative substrate material as it offers a number of advantages including coefficient of thermal expansion similar to silicon, good dielectric properties and optical transparency to assist in the alignment of buried features. As part of this project it was necessary to deposit metallic coatings onto the glass sheets to create electrical tracks, pads and microvias. In order to meet these requirements, the metallisation of both smooth as received glass surfaces and surfaces roughened by laser machining using electroless copper and nickel deposition were investigated. This study resulted in a number of important conclusions about the roles of chemical bonding and mechanical anchoring in both the adhesion and catalyst adsorption, that are key factors in the electroless metallisation process.....

Cheminio variavimo tirpalai bei cheminio variavimo procesai tiriami jau nuo XX a. vidurio iki šių dienų, ieškant vis efektyvesnių parametrų dangų funkcinėms bei dekoratyvinėms savybėms pagerinti. Pastaruoju metu vis didesnis dėmesys krypsta ne tik į nusodinamų dangų funkcionalumą, bet ir į ekologiškai nekenksmingus ar mažiau kenksmingus technologinius procesus, pzv., vykdoma ekologiškai nekenksmingų ligandų paieška. Kaip alternatyva šiuo metu siūlomos dvi cheminių junginių klasės t.y. alditoliai (polihodroksiliai alkoholiai) ir hidroksikarboksirūgštys. Pagrindinis darbo tikslas: ištirti cheminio variavimo sistemas ir jose vykstančius procesus, vario(II) jonų ligandais naudojant ekologiškai nekenksmingas citrinų ir vyno rūgštis. Cheminio variavimo sistemose panaudoti du nauji Cu(II) jonų ligandai t.y. citrinų rūgštis ir vyno rūgšties D-izomeras. Atliktų tyrimų duomenys rodo, kad minėti ligandai sėkmingai gali būti naudojami cheminio variavimo sistemose, kur reduktoriumi naudojamas formaldehidas. Nustatyta, kad 2-hidroksipropan-1,2,3-trikarboksirūgštis (citrinų rūgštis) ir 2,3-dihidroksibutano-1,4-dirūgštis (vyno rūgštis) šarminėje terpėje sudaro pakankamai patvarius kompleksus su vario(II) jonais ir yra tinkamas ligandas vario(II) kompleksinimui šarminiuose (pH > 12) cheminio variavimo tirpaluose. Ištirta vario(II)-citrato ir Cu(II)-D-, L- ir DL-tartratų kompleksų redukcija hidratuotu formaldehidu, apibūdintos gautosios vario dangos. Optimaliomis proceso vykdymo sąlygomis... [toliau žr. visą tekstą] / Electroless metal coating technique is one of the elegant ways of metal coating by controlling the temperature and pH of the plating bath in which there is no usage of electric current. The industrial electroless copper plating solution containing formaldehyde as reducing agent are known from the middle of the last century and are widespread in the practice up to now. However many chemical compounds used in such kind technological processes are hazardous for total environment, therefore the efforts are made to displace those substances with less hazardous or purely harmless compounds. Generally two classes of chemical compounds were proposed as EDTA alternative, namely alditols (polyhydroxylic alcohols) and hydroxypolycarboxylic acids. The aim of the work was to investigate peculiarities of formaldehyde containing alkaline electroless copper deposition systems using environment friendly hydroxycarboxylic acids as Cu(II) ligands. Two new Cu(II) ligands, namely citric acid and D-isomer of tartaric acid, were applied for the systems of electroless copper deposition. The results of the investigations show that the ligands mentioned can be successful applied in the processes of electroless copper deposition using formaldehyde as reducing agent. Citric acid (2-hydroxypropane-1,2,3-tricarboxylic acid) and different isomers of tartaric acid (2,3-dihydroxybutanedioic acid), namely L- and D-tartrate, and their racemic mixture DL-tartrate, forming sufficiently stable complexes with... [to full text]

Electroless metal coating technique is one of the elegant ways of metal coating by controlling the temperature and pH of the plating bath in which there is no usage of electric current. The industrial electroless copper plating solution containing formaldehyde as reducing agent are known from the middle of the last century and are widespread in the practice up to now. However many chemical compounds used in such kind technological processes are hazardous for total environment, therefore the efforts are made to displace those substances with less hazardous or purely harmless compounds. Generally two classes of chemical compounds were proposed as EDTA alternative, namely alditols (polyhydroxylic alcohols) and hydroxypolycarboxylic acids. The aim of the work was to investigate peculiarities of formaldehyde containing alkaline electroless copper deposition systems using environment friendly hydroxycarboxylic acids as Cu(II) ligands. Two new Cu(II) ligands, namely citric acid and D-isomer of tartaric acid, were applied for the systems of electroless copper deposition. The results of the investigations show that the ligands mentioned can be successful applied in the processes of electroless copper deposition using formaldehyde as reducing agent. Citric acid (2-hydroxypropane-1,2,3-tricarboxylic acid) and different isomers of tartaric acid (2,3-dihydroxybutanedioic acid), namely L- and D-tartrate, and their racemic mixture DL-tartrate, forming sufficiently stable complexes with... [to full text] / Cheminio variavimo tirpalai bei cheminio variavimo procesai tiriami jau nuo XX a. vidurio iki šių dienų, ieškant vis efektyvesnių parametrų dangų funkcinėms bei dekoratyvinėms savybėms pagerinti. Pastaruoju metu vis didesnis dėmesys krypsta ne tik į nusodinamų dangų funkcionalumą, bet ir į ekologiškai nekenksmingus ar mažiau kenksmingus technologinius procesus, pzv., vykdoma ekologiškai nekenksmingų ligandų paieška. Kaip alternatyva šiuo metu siūlomos dvi cheminių junginių klasės t.y. alditoliai (polihodroksiliai alkoholiai) ir hidroksikarboksirūgštys. Pagrindinis darbo tikslas: ištirti cheminio variavimo sistemas ir jose vykstančius procesus, vario(II) jonų ligandais naudojant ekologiškai nekenksmingas citrinų ir vyno rūgštis. Cheminio variavimo sistemose panaudoti du nauji Cu(II) jonų ligandai t.y. citrinų rūgštis ir vyno rūgšties D-izomeras. Atliktų tyrimų duomenys rodo, kad minėti ligandai sėkmingai gali būti naudojami cheminio variavimo sistemose, kur reduktoriumi naudojamas formaldehidas. Nustatyta, kad 2-hidroksipropan-1,2,3-trikarboksirūgštis (citrinų rūgštis) ir 2,3-dihidroksibutano-1,4-dirūgštis (vyno rūgštis) šarminėje terpėje sudaro pakankamai patvarius kompleksus su vario(II) jonais ir yra tinkamas ligandas vario(II) kompleksinimui šarminiuose (pH > 12) cheminio variavimo tirpaluose. Ištirta vario(II)-citrato ir Cu(II)-D-, L- ir DL-tartratų kompleksų redukcija hidratuotu formaldehidu, apibūdintos gautosios vario dangos. Optimaliomis proceso vykdymo sąlygomis... [toliau žr. visą tekstą]

As the world has woken up to the change in climate in recent years, people's environmental concerns are forcing companies to change and find ways to manufacture products without harming nature. One area of serious concern is the electronics industries where an ever-increasing number of products gets updated with sensors and microcomputers to be part of the internet of things. Wen more things are upgraded with electronics, it's important that the production process is as environmentally friendly as possible and that the techniques used introduces a minimum amount of disturbance to the circuits in them.  To tackle this problem, this thesis presents a novel way of manufacturing PCBs without the need for soldering components, a method that increases performance and has substantial environmental benefits. When comparing conventional soldering to the electroless copper plating process presented in this thesis, electroless copper plating uses 67 times less metal and also reduces the parasitic capacitance in the PCB that comes from the solder joints. Utilizing the solder-free method means 67 times less metal needs to be mined, transported, and recycled. Moreover, since lead is a toxic heavy metal that is often part of the solder, decreasing its use in the industry is beneficial for human health and the environment. Nowadays, when the world steadily moves toward products that use technologies like 5G, technologies where higher frequencies are required, their sensitivity to capacitive disturbances from parasitics increases. In this thesis, when comparing the conventional solder method to the non-solder method to attach a capacitor, a significant reduction in phase shift of 0.9° is measured; this change is directly related to the removal of the solder and the parasitic capacitance that comes with it.

The recent developments in Low Temperature Co-fired Ceramic (LTCC) as a substrate material enable it to be used in the micro and millimetre wave range providing low dissipation factors at high frequencies, good dielectric properties and a high degree of integration for further miniaturised devices. The most common metallisation method used in LTCC technology is screen printing with high cost noble metals such as silver and gold that are compatible with the high sintering temperatures (850°C). However, these techniques require high capital cost and maintenance cost. As the commercial world requires convenient and low cost process technologies for mass production, alternative metallisation methods should be considered. As a result, electroless copper plating of fired LTCC was mainly investigated in this research. The main goals of this project were to carry out electroless plating of fired LTCC with sufficient adhesion and to extend the process to metallise closed LTCC channel structures to manufacture Substrate Integrated Waveguide (SIW) components. The objectives were focused on electroless copper deposition on fired LTCC with improved adhesion. Electroless deposits on the Sn/Pd activated LTCC surface showed poor adhesion without any surface pre-treatments. Hence, chemical etching of fired LTCC was carried out using concentrated NaOH solution. NaOH pre-treatment of LTCC led to the formation of flake like structures on the LTCC surface. A number of surface and chemical analysis techniques and weight measurements were used to investigate the mechanism of the modification of the LTCC surface. The results showed that the flake like structures were dispersed in the LTCC material and a material model for the LTCC structure was proposed. SEM EDX elemental mapping showed that the flake like structure consisted of aluminium, calcium, boron and oxygen. Further experiments showed that both the concentration of NaOH and the immersion time affect the surface morphology and the roughness of fired LTCC. The measured Ra values were 0.6 μm for untreated LTCC and 1.1 μm for the LTCC sample treated with 4M NaOH for 270 minutes. Adhesion tests including peel test and scratch test were carried out to examine the adhesion strength of the deposited copper and both tests indicated that the NaOH pre-treatment led to an improvement, with the best results achieved for samples treated with 4M NaOH. A second aspect of the research focused on the selective metallisation of fired LTCC. Excimer laser machining was used to pattern a resist film laminated on the LTCC surface. This process also roughened the substrate and created channels that were characterised with respect to the laser operating parameters. After patterning the resist layer, samples were activated using Sn/Pd catalyst solution followed by the electroless copper deposition. Electroless copper was selectively deposited only on the patterned LTCC surface. Laser parameters clearly affected the copper plating rate. Even with a similar number of shots per area, the tracks machined with higher repetition rate showed relatively more machining depth as well as good plating conditions with low resistance values. The process was further implemented to realize a complete working circuit on fired LTCC. Passive components including a capacitor and an inductor were also fabricated on LTCC using the mask projection technique of the excimer laser system. This was successful for many designs, but when the separation between conductor lines dropped below 18 μm, electroless copper started to deposit on the areas between them. Finally, a method to deposit copper films on the internal walls of closed channel structures was developed. The method was first demonstrated by flowing electroless copper solutions through silane treated glass capillaries. A thin layer (approx. 60 nm) of electroless copper was deposited only on the internal walls of the glass capillaries. The flow rate of the electroless copper solution had to be maintained at a low level as the copper deposits tended to wash away with higher flow rates. The structures were tested for transmission losses and showed low (<10dB) transmission losses in the terahertz region of the electromagnetic spectrum. The process was further applied to deposit electroless copper on the internal walls of the LTCC closed channel structures to manufacture a LTCC Substrate Integrated Waveguide (SIW).

Neste trabalho, diferentes tipos de microestruturas foram geradas por torneamento com ferramenta de diamante de ponta única e microendentação para serem replicadas através da prensagem a quente. Testes foram realizados para ser avaliada a geração destas microestruturas por dois métodos distintos: microdeformação e microusinagem, planejados para observar a replicação gerada por marca de endentação Vickers (piramidal) e, remoção de material (torneamento com ferramenta de diamante de ponta única). Uma revisão no processo de manufatura aplicada para a replicação de microestruturas é apresentada. Os materiais usados como molde e réplica foram o cobre eletrolítico e o polimetilmetacrilato (PMMA), respectivamente. Inicialmente, a usinabilidade do cobre eletrolítico foi avaliada sob diferentes condições de corte, a fim de determinar parâmetros apropriados de torneamento para obter um fino revestimento de superfície final (rugosidade). Observou-se que para avanços (f) de 10 mícrons por revolução e profundidade de corte (ap) de 5 mícrons, a superfície apresentou um baixo valor de rugosidade, isto é, 2,81 nm para rugosidade média (Ra) e 13,4 nm para rugosidade teórica (Rt). Além disso, observou-se que a microestrutura do material mostrou-se de fundamental papel na rugosidade, por conta da recuperação elástica dos grãos devido a anisotropia da estrutura policristalina do cobre. As microestruturas geradas para a replicagem foram: a) lente esférica, b) perfil senoidal e sulcos concêntricos. Os resultados mostraram que é viável a reprodução, com boa conformidade das microestruturas, por meio de prensagem a quente. Observou-se que as bordas e as superfícies finas com rugosidade em torno de 10 nm rms foram bem replicadas. / In this work, different types of microstructures were generated by single point diamond turning and microindentation for will replicated through the hot embossing. Tests were carried to evaluate the generation these microstructures by two distinct methods: micro-deformation and micro-machining, planned to observe the replication of the mark generated by the Vickers indenter (Pyramidal) and the latter by material removal (single point diamond turning). A review on several manufacturing processes applied to replication of microfeatures, is presented. The materials used as mould and replication workpiece were electroless copper and polymethylmethacrylate (PMMA), respectively. Initially, the machinability of electroless copper was evaluated under different cutting conditions to determinate appropriate turning parameters to obtain very fine surface finish (roughness). It was observed that for f = 10 microns of revolution (feed rate) and ap = 5 microns (depth of cut), the surface presented the roughness’ lowest value, i.e., 2,81 nm to medium roughness (Ra) and 13,4 nm to theoretical roughness (Rt). Moreover, it was observed that the microstructure of the material plays a fundamental role on roughness, because of the elastic recovery of grains due to the anisotropy of the polycrystalline structure of copper. The microfeatures generated were the following: a) spherical lens, b) sinusoidal profile and concentrical grooves. The results showed that it is feasible to reproduce, with good agreement, the microfeatures by means of hot embossing. It was observed that thin edges and fine surfaces with roughness around 10 nm rms were well replicated.

Neste trabalho, diferentes tipos de microestruturas foram geradas por torneamento com ferramenta de diamante de ponta única e microendentação para serem replicadas através da prensagem a quente. Testes foram realizados para ser avaliada a geração destas microestruturas por dois métodos distintos: microdeformação e microusinagem, planejados para observar a replicação gerada por marca de endentação Vickers (piramidal) e, remoção de material (torneamento com ferramenta de diamante de ponta única). Uma revisão no processo de manufatura aplicada para a replicação de microestruturas é apresentada. Os materiais usados como molde e réplica foram o cobre eletrolítico e o polimetilmetacrilato (PMMA), respectivamente. Inicialmente, a usinabilidade do cobre eletrolítico foi avaliada sob diferentes condições de corte, a fim de determinar parâmetros apropriados de torneamento para obter um fino revestimento de superfície final (rugosidade). Observou-se que para avanços (f) de 10 mícrons por revolução e profundidade de corte (ap) de 5 mícrons, a superfície apresentou um baixo valor de rugosidade, isto é, 2,81 nm para rugosidade média (Ra) e 13,4 nm para rugosidade teórica (Rt). Além disso, observou-se que a microestrutura do material mostrou-se de fundamental papel na rugosidade, por conta da recuperação elástica dos grãos devido a anisotropia da estrutura policristalina do cobre. As microestruturas geradas para a replicagem foram: a) lente esférica, b) perfil senoidal e sulcos concêntricos. Os resultados mostraram que é viável a reprodução, com boa conformidade das microestruturas, por meio de prensagem a quente. Observou-se que as bordas e as superfícies finas com rugosidade em torno de 10 nm rms foram bem replicadas. / In this work, different types of microstructures were generated by single point diamond turning and microindentation for will replicated through the hot embossing. Tests were carried to evaluate the generation these microstructures by two distinct methods: micro-deformation and micro-machining, planned to observe the replication of the mark generated by the Vickers indenter (Pyramidal) and the latter by material removal (single point diamond turning). A review on several manufacturing processes applied to replication of microfeatures, is presented. The materials used as mould and replication workpiece were electroless copper and polymethylmethacrylate (PMMA), respectively. Initially, the machinability of electroless copper was evaluated under different cutting conditions to determinate appropriate turning parameters to obtain very fine surface finish (roughness). It was observed that for f = 10 microns of revolution (feed rate) and ap = 5 microns (depth of cut), the surface presented the roughness’ lowest value, i.e., 2,81 nm to medium roughness (Ra) and 13,4 nm to theoretical roughness (Rt). Moreover, it was observed that the microstructure of the material plays a fundamental role on roughness, because of the elastic recovery of grains due to the anisotropy of the polycrystalline structure of copper. The microfeatures generated were the following: a) spherical lens, b) sinusoidal profile and concentrical grooves. The results showed that it is feasible to reproduce, with good agreement, the microfeatures by means of hot embossing. It was observed that thin edges and fine surfaces with roughness around 10 nm rms were well replicated.