Silver localization on polyimide using microcontact printing and electroless metallization

Metal oxides have recently been fabricated in solutions without high-temperature sintering in order to reduce energy consumption and allow application for various substrates having low heat resistance. The fabrication of metal oxide thin films from solutions has been encouraged by the development of environment-friendly chemistry such as Green & sustainable chemistry1-6, Bioinspired materials chemistry7, Biomimetic materials chemistry7, Soft-solution processing8-10, Soft chemistry (“Chimie douce” in French)11, Liquid phase deposition7,12, Chemical bath deposition (CBD)12,13, Electroless deposition (ED) with catalyst12,13, Successive ion layer adsorption and reaction (SILAR) 12,13, Sol-gel process14,15, Hydrothermal reaction16, Electrodeposition17,18 and so on. Solution processing of metal oxides allows us to prepare metal oxide thin films on the surface of solids such as substrates, particles, and fibers. Metal oxide nano/microstructures can also be fabricated by applying these solution systems to electronic or photonic devices. Many kinds of lithography or patterning techniques have been developed to prepare patterns of thin films, for instance, X-ray/electronbeam lithography and photolithography,19 microcontact printing,20,21 wet etching,22 ink-jet printing,23 embossing,24,25 slip-pressing,26 charge-based printing,27 micromolding,28 and cold welding29. However, etching or lift-off processes are required in many of these methods, which causes degradation of performance, increases waste and energy consumption, and makes the process complicated. Additionally, etching or lift-off processes cannot be applied to corrosion-resistant metal oxides. The deposition of metal oxides only on desired areas of a substrate is thus required for the pattering of metal oxide thin films. In this section, Liquid Phase Patterning (LPP) of metal oxides was reported 30. Selfassembled monolayer (SAM), which can modify the surface of solids with various functional groups, was used as the template to enable molecular recognition for LPP. Solution systems were developed and applied to LPP of ceramic thin films on patterned SAMs by the proposed novel LPP processes.

'Invited'Starting from critical dimensions below 10 nm, the continuation of CMOS scaling requires the Cu replacement as an IC interconnect material by a barrierless metal with lower resistivity and better electromigration performance than Cu, such as Co and Ru. In addition, narrow dimensions of interconnect features require implementation of bottom-up metal fill schemes to mitigate defects in metal structures. At the same time, significant technological improvements are required to mitigate the pattern overlays and litho-based edge placement errors when forming multilevel structures with a half-pitch at or below 10 nm. The transition from standard multiple litho-etch deposition schemes to bottom-up area-selective deposition (ASD) is a very promising way to enable self-alignment of multilevel structures. The approaches to achieve ASD can be classified in three categories: i) intrinsic selectivity, ii) selectivity enabled by passivation of the “non-growth area” and iii) selectivity enabled by activation of the “growth area”. Among selective deposition processes, electroless deposition (ELD) and atomic layer deposition (ALD) can be effectively used due to their chemical nature and surface sensitivity. This work explores all three categories of ASD approaches for BEOL technology application, utilizing the above listed techniques for Co and Ru deposition.Intrinsically selective metal deposition can be realized for very limited number of material combinations used in IC manufacturing. Part of this work focuses on various H-based plasma treatments, which allow forming appropriate surface functionalities enabling ASD. Among various material combinations, the focus was set on amorphous carbon (a-C) as “non-growth” surface and Si-based materials, such as SiCN, as “growth” surface. An interaction of various compounds of H-based plasma, namely: H ions and H radicals with a-C was investigated experimentally. In order to support experimental observations, molecular dynamic modeling of a-C interaction with H plasma was performed, which allowed to understand the mechanisms of a-C chemical modification by H ions and radicals. Effectivity of H plasma treatment on ALD selectivity was studied for the case of selective Ru ALD using (ethylbenzyl)(1-ethyl-1,4-cyclohexadienyl)Ru(0) (EBECHRu) precursor with O2 co-reactant. In addition, an initial study of Ru ASD integration into patterned structures of technological relevant dimensions was performed.Direct implementation of intrinsically selective processes into production is a rare case in microelectronic technology. In most of the cases, however, blocking layers can be used. This work explores self-assembled monolayers (SAMs) as blocking layers for ALD. Screening of various siloxane-SAM precursors was performed to study the impact of SAM’s functional group, length of alkyl chain and deposition conditions on surface density of SAM molecules and, specifically, passivation properties of SAM against Ru ALD. An additional study was performed in order to analyze modification of (3-trimethoxysilylpropyl)diethylenetriamine (DETA)-derived SAM under ALD conditions (250 °C and O2 co-reactant). In-situ XPS as well as molecular-dynamic modelling were employed to investigate the mechanisms of DETA modification. Lastly, a removal of DETA-derived SAM from Cu “growth area” selectively with respect to SiO2 “non-growth area” using acetic acid was investigated to mitigate defectivity.Further, surface functionalization by SAMs can also be used to form appropriate surface terminal groups for further attachment of a metal catalyst or metal seed, used in subsequent selective ELD deposition. ELD is based on redox reactions on the metal substrate; therefore, it can be used for intrinsically selective metal deposition on metal substrates or metal seeds. SAMs-enabled selectivity can be used for metal growth on a dielectric surface selectively with respect to another type of the dielectric material. In the case of ELD bottom-up growth in a trench, the metal catalyst should be selectively deposited at the trench bottom dielectric layer. In this work, the selectivity of Pd metal catalyst promoted by selective surface functionalization by SAMs was investigated. It has been shown that SAMs with amino functional groups form covalent bonds with Pd catalyst, which is commonly used as a seed for subsequent ELD of various metals including Co on the Pd seed. Since the electrical properties of interconnect material are of crucial importance, an additional study of ELD Co resistivity was performed, including in-depth analysis of Co recrystallization revealing Co grain size dependency on the film resistivity.In conclusion, area-selective metal deposition processes are an important part of future microelectronic technology. This work explores ASD of Ru and Co, as the most promising Cu replacement metals. For the deposition of these metals, surface sensitive techniques are used, namely ALD and ELD. For the cases, where intrinsic selectively of the deposition technique cannot be realized for the combination of materials used in the process flow, SAM-based passivation and SAM-based activation layers were investigated.

Surface modification of polyethylene naphthalate substrates by ultraviolet light-irradiation and assembling multilayers and their application in electroless deposition: The chemical and physical properties of the stratified structure

Integrated electroceramic thin-film devices on semiconducting or insulating substrate materials offer a wide variety of attractive attributes, including high capacitance density, nonvolatile memory, sensor/actuator ability, and other unique electrical, electromechanical, magnetic and optical functions. Thus the ability to pattern such electroceramic thin films is a critical technology for future device realization. Patterned oxide thin-film devices are typically formed by uniform film deposition followed by somewhat complicated post-deposition ion-beam or chemical etching in a controlled environment i.e., a subtractive method. We review here an upset technology, a different way of patterning, by an additive approach, which allows for the selective deposition of electroceramic thin layers without such post-deposition etching. In this method, substrate surfaces are selectively functionalized with hydrophobic self-assembled monolayers to modify the adhesion of subsequently deposited solution-derived electroceramics. The selective functionalization is achieved through microcontact printing (μ-CP) of self-assembled monolayers of the chemical octadecyltrichlorosilane on substrates of current technical interest. Subsequent sol-gel deposition of ceramic oxides on these functionalized substrates, followed by lift-off from the monolayer, yields high quality, patterned oxide thin layers only on the unfunctionalized regions. A variety of micron-scale dielectric oxide devices have been fabricated by this method, with lateral resolution as fine as 0.5 μm. In this paper, we review the monolayer patterning and electrical behavior of several patterned electroceramic thin films, including Pb(Zr,Ti)O3 [PZT], LiNbO3, and Ta2O5. A multilevel example is also given which combines selective MOCVD deposition of metal electrodes and sol-gel patterned PZT for Pt//PZT//Pt//Si(100) ferroelectric memory cells.

A self-assembled microarray (SAMA) of organic light-emitting diodes (OLEDs) has been fabricated using self-assembled monolayers (SAMs) by microcontact printing (μCP). The hydrophobic methyl-terminated SAMs modify the surface properties of the substrates to become hydrophobic, i.e., with low surface energy. Thus, the hydrophobic SAMs pattern, by the μCP, can be applied to form SAMAs on the patterned SAMs since the difference of the local surface energy modifies the patterns on the substrates. In this study, octadecyltrichlorosilane based hydrophobic methyl-terminated SAMs have been used and the fabricated OLEDs, with the SAMAs show local light emissions on the micron scale with efficient performances.

Self-assembled monolayers (SAM) formed on gold or hydroxylated surfaces are well ordered organic surfaces that enable the control of interface property at the molecular scale. Microcontact printing is a simple technique that can pattern the formation of SAM in the plane with dimensions on the micron scale. The combination of SAM and microcontact printing makes a technique useful for studying a variety of fundamental phenomena in bio-interfacial science such as cell adhesion. However, the existence of surface roughness tends to impede the effectiveness of the method in generating the desirable interface properties. Studies have shown that surface roughness significantly changes adhesion of SAM coated material. The current study tries to understand the roughness effects on bio-adhesion of cell-SAM substratum. A current model of cell adhesion considers the effects of nonspecific and specific interactions between adhesion molecules and the substrate assuming an isotropic Gaussian distributed roughness. Simulation results show the change of pull-off force and contact area due to different scales of roughness. The reduction rate of cell adhesion due to roughness and chemical-mechanical factors are then compared to show the significance of roughness effects on SAM adhesion. Results suggest that caution must be taken in quantitative interpretation of protein and cell adsorption strength by using SAM device as a biosensor.

Fabrication of micro- and submicrometer silver patterns by microcontact printing of mercaptosilanes and direct electroless metallization

One of the major challenges for nanofabrication, in particular microcontact printing (mu-CP), is the control of molecular diffusion, or "ink spreading", for the creation of nanopatterns with minimized "smudging" at pattern boundaries. In this study, fully atomistic computer simulations were used to measure the impact of naturally occurring domain boundaries on the diffusion of excess alkanethiol ink molecules on printed alkanethiol self-assembled monolayers (SAM). A periodic unit cell containing approximately one million atoms and with a surface area of 56 nm x 55 nm was used to model a hexadecanethiol SAM on Au(111), featuring SAM domain boundaries and a range of concentrations of excess hexadecanethiol ink molecules diffusing on top. This model was simulated for a total of approximately 80 ns of molecular dynamics. The simulations reveal that domain boundaries impede the diffusion of excess ink molecules and can, in some cases, permanently trap excess inks. There is competition between ink spreading and ink trapping, with the ink/SAM interaction strongly dependent on both the ink concentration and the SAM orientation at domain boundaries. SAM defects thus provide potential diffusion barriers for the control of excess ink spreading, and simulations also illustrate atom-scale mechanisms for the repair of damaged areas of the SAM via self-healing. The ability of domain boundaries to trap excess ink molecules is accounted for using an accessible volume argument, and trapping is discussed in relation to experimental efforts to reduce molecular spreading on SAMs for the creation of ultrahigh resolution nanopatterns.

Individual multi-walled carbon nanotubes (CNTs) were deposited onto microelectrodes and embedded in nickel to achieve low-ohmic contact resistances. Electroless deposition of nickel onto gold/iron, palladium, and cobalt microelectrodes was used to form electrically stable bonds at the interfaces between the electrodes and CNTs. Resistance measurements showed that the contact resistances of the CNTs on gold/iron and palladium were significantly improved by nickel embedding, whereas no further improvement was found for the CNTs on cobalt. Electroless metal deposition is a parallel process providing stable electrical and mechanical contacts between CNTs and metallic microelectrodes.

This work presents a simple and versatile approach for the growth of in-situ contacted single-walled carbon nanotubes (SWCNTs) and subsequent improvement of the contacts using a self-aligned process. We investigated the conditions for the thermal CVD growth of SWCNTs and developed a variety of multilayered metal systems for SWCNT growth at temperatures between 650 °C and 900 °C. The catalytically active layers were either an Fe/Mo bilayer or a Co layer. Further, we report that some of the multilayer systems presented allow lithography free contact improvement by electroless metal deposition.

This paper reports on a new method for the production of metallic microstructures with high aspect ratios that combines the advantages of injection moulding with the high precision replication of surfaces by galvanic and electroless metal deposition. LIGA made moulding tools are used to produce plastic “lost forms”, which are partially metallized by a silver cluster beam of high directionality to achieve electrical conductivity. For structures with an interconnected Ag layer at the bottom, galvanic metal deposition is used to form massive microstructures without voids. For isolated structures where contacting is not possible, chemical deposition was used for metal build-up starting from the metallized areas. However, massive electroless deposition beyond about 3 μm was not yet possible due to problems with internal stress in the deposited metal layer that cause delamination from the template. This stress must be reduced by appropriate modifications of the electrolyte.

Arrays of silicon nanowire/multiwalled carbon nanotube nanocomposite have been synthesized by wet etching through electroless metal deposition and chemical vapor deposition. Vertically aligned Si nanowire arrays with controlled diameter and length were fabricated by Ag nanodendrite-assisted wet chemical etching of n-type or p-type silicon wafers using HF/ AgNO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> solution. The composite structure was synthesized by formation of a sheath of carbon multilayers on a Si nanowire template surface through a thermal CVD process under various conditions. The results of Raman spectroscopy, scanning electron microscopy and high resolution transmission electron microcopy reveal that the obtained nanocomposite has a silicon nanowire core/carbon nanotube shell structure. Nanocomposite arrays showed good electrochemical properties.

Microcontact printing (μCP) of lipophilic self-assembled monolayers (SAMs) has been used to fabricate micron dimensioned patterned surfaces that can be used as a means of attaching lipid bilayers to solid surfaces. This communication addresses how variation in the patterned SAM geometry affects vesicle adsorption. The substrates consisted of circular hydrophilic regions functionalized with mercaptoethanol surrounded by octadecanethiol (ODT). Three geometries were studied in which the diameter of the hydrophilic portion was varied between 4 and 16 μm and the center-to-center separation was varied between 10 and 40 μm. Thus, it was possible to study lipid adsorption on SAM systems with the same total hydrophilic surface area, but with different sized hydrophilic patches. Impedance spectroscopy showed that for the films of the same total hydrophilic area greater lipid coverage was obtained for SAMs with smaller diameter hydrophilic patches. To understand this observation, tapping mode AFM and surface plasmon...

Microcontact printing is incorporated with electroless plating to fabricate the micrometer (and submicrometer) scale pattern of copper on poly(ethylene terephthalate) surfaces. Copper patterns with featured sizes ranging from 0.45 to are fabricated by two different procedures: the printing adhesion layer (PAL) and printing masking layer (PML) methods. The PAL method applies to directly print the siloxane-containing functional group for further catalyst adhesion and electroless plating. The PML method uses to print the octadecyltrichlorosilane self-assembled monolayer as a masking layer, which prevents the stamped regions from any further catalyst adhesion. Therefore, the catalyst adhesion would occur in the unstamped regions. Consequently, copper would deposit in these catalyst-adsorbed regions via electroless plating. The PML method has a better selectivity of copper deposition than the PAL method. In addition, the variation in deposited copper properties as a function of the plating time and temperature is discussed.

Chemoselective deposition of alane and patterned deposition of alane and aluminum oxide on ultrathin organic selfassembled monolayers (SAMs) were investigated. Information about elementary steps of the interaction of trimethyl amine alane (TMAA) with appropriately functionalized HO- and HOOC-terminated SAMs under UHV conditions is presented. The self-terminated growth of an alane bilayer on HO-terminated SAMs was established on the basis of quantitative X-ray photoelectron spectroscopy (XPS) analysis. A patterned deposition of 2 nm of aluminum oxide on patterned SAMs obtained by microcontact printing is demonstrated.