Monolayer-Mediated Patterning of Integrated Electroceramics

Integration of oxide thin films with semiconductor substrates is a critical technology for a variety of microelectronic memory and circuit applications. Patterned oxide thin film devices are typically formed by uniform deposition followed by postdeposition ion‐beam or chemical etching in a controlled environment. This paper reports details of an ambient atmosphere technique which allows selective deposition of dielectric oxide thin layers without postdeposition etching. In this method, substrate surfaces are selectively functionalized with hydrophobic self‐assembled monolayers of octadecyltrichlorosilane by microcontact printing (μ‐CP). Sol‐gel deposition of ceramic oxides on these functionalized substrates, followed by mild, nonabrasive polishing, yields high‐quality, patterned oxide thin layers only on the unfunctionalized regions. A variety of micrometer‐scale dielectric oxide devices have been fabricated by this process, with lateral resolutions as fine as 4 μm. In this paper, we describe the solution chemistry, evolution of microstructure, and electrical properties of Ta2O5 thin films, as well as the stress‐related mechanism which enables selective de‐adhesion and resultant patterning. Selectively deposited, 80‐120 nm thick Ta2O5 thin film capacitors were crystallized on platinized silicon at 700‐800°C, and had dielectric constants of 18‐25 depending upon the processing conditions, with 1 V leakage current densities as low as 2 × 10−8 A/cm2. The ability to selectively deposit Ta2O5 and other electrical ceramics (such as LiNbO3 and PbTiO3) on a variety of technologically important substrate materials suggests broad potential for integrated circuit and hybrid microelectronics applications.

'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.

In situ patterning of iron oxide thin layers were fabricated via microcontact printing (μCP) and selective area deposition. μCP is used to pattern two different surface moieties of self-assembled organic monolayers (SAMs) on Au/Cr/Si substrates. An elastomeric stamp is used to transfer hydrophobic (hexadecanethiol (HDT)) SAMs that are to sustain deposition of iron oxide precipitates. Hydrophilic (dithiothreitol, DTT) SAMs were used to induce crystalline iron oxide films. 0.05 M of iron nitrate (Fe(NO3)3·9H2O) aqueous solutions containing urea under nitric acid (pH ≤ 2) were used. Selective depositions were realized through precipitation of crystalline iron oxides at ambient temperature (80°C) onto the mixed SAM surfaces.

Selective vapor deposition of conductive poly(3,4-ethylenedioxythiophene) (PEDOT), thin films has been carried out on self assembled monolayers patterned oxide substrate. Since the 3,4-ethylenedioxythiophene(EDOT) monomer can be polymerized only in the presence of oxidant such as <TEX>$FeCl_3$</TEX>, the PEDOT thin film is selectively deposited on patterned <TEX>$FeCl_3$</TEX>, which only adsorbs on the partly removed SAMs region due to the inability of <TEX>$FeCl_3$</TEX> to adsorb on SAMs. Therefore, the partly removed SAMs can act as an adsorption layer for the <TEX>$FeCl_3$</TEX> and also as a glue layer for the deposition of PEDOT, resulting in the significantly increased adhesion of PEDOT to <TEX>$SiO_2$</TEX> substrate. The use of UV lithography and Cr patterned quartz mask provided the formation of SAMs patterns on oxide substrates, which allowed for the selective deposition of conductive PEDOT thin films.<TEX>$^{oo}The$</TEX> new process was successfully developed for the selective deposition of PEDOT thin films on SAMs patterned oxide substrate, providing a new way for the patterning of vapor phase deposition of PEDOT thin films with accurate alignment and addressing the inherent adhesion issues between PEDOT and dielectrics.

We present a novel process to gain selective deposition and generate high feature edge acuity micropatterns of TiO2 thin films from a gas phase. Self-assembled monolayers (SAMs) of octadecyltrichloro-silane were modified to produce a methyl/silanol pattern and applied as templates to deposit TiO2 through the use of titanium dichloride diethoxide. Patterned SAMs showed high selectivity for nucleation and growth of TiO2, plus a feature edge acuity of the TiO2 pattern well below 2.1%. Moreover, we developed a novel process to realize a two-dimensional arrangement of TiO2 particles onto a SAM from a gas phase.

Selective deposition holds promise to simplify next-generation device fabrication and bring down economic cost. In this work, selectively depositing polymers on metal/dielectric patterns was achieved by spin dewetting, a phenomenon that refers to the dewetting of polymers during spin coating. Our strategy utilizes self-assembled monolayers (SAMs) to induce dewetting of polymers over some areas. Line patterns of Cu/SiO2 were investigated. A hydrophobic SAM, octyltrichlorosilane (OTS, Cl3Si–C8H17), was selectively formed on SiO2 in the presence of Cu to render SiO2 non-wettable. During a subsequent spin coating step, polymers dewet from OTS-functionalized SiO2 and coat Cu exclusively. The spin dewetting process is strongly dictated by the spin coating kinetics. A systematic study of the processing conditions revealed strong dependence of polymer film coverage on spin speed, solution concentration, polymer molecular weight, casting solvent, and SAM hydrophobicity.

Microcontact printing and selective surface dewetting for large area electronic applications

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.

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.

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.

Atomic Layer Deposition (ALD) has garnered significant interest within the scientific community owing to its exceptional ability to deposit ultra-thin films with meticulous control over thickness and uniformity. By capitalizing on self-limited surface reactions, ALD represents a versatile technique for depositing a diverse array of materials encompassing semiconductors, insulators, and metals. However, traditional top-down methodologies, particularly those reliant on lithographic patterning, present inherent complexities characterized by a multitude of process steps, thereby giving rise to challenges such as misalignment, particularly pronounced in intricate three-dimensional (3D) and multilayer structures.In response to these challenges, the emergence of Area-Selective ALD (AS-ALD) heralds a promising paradigm shift towards bottom-up approaches, offering the promising prospect of selective deposition on patterned substrates. The allure of AS-ALD lies in its potential to streamline manufacturing process steps by confining material deposition exclusively within predetermined regions, thereby refining pattern precision while concurrently curtailing process steps. The operationalization of AS-ALD hinges upon the deployment of a non-reactive polymer film as a strategic barrier layer, effectively impeding precursor penetration into undesired regions. In this context, Self-Assembled Monolayers (SAM) are organic monolayers films that are spontaneously formed via complex interactions of van der Waals forces and densely populated on the substrate surface, making them a pivotal component in achieving AS-ALD.SAM, characterized by head, tail, and chain groups, confer a diverse functionality whereby the head group organized substrate reactivity modulation, the tail group modulates penetration of metal precursors into the substrate via end-group manipulation, and the chain group regulates SAM packing density. The strategic harnessing of SAM facilitates selective deposition by impeding precursor diffusion and penetration, thereby endowing a finely calibrated tool for SAM deposition. The controllability of surface properties through modification of molecular structure underscores ALD blocking efficiency as contingent upon factors such as alkyl chain length, with elongated chains fostering augmented Van der Waals attraction and packing density. Generally, empirical evidence substantiates the adequacy of a 12-carbon alkyl chain length for ALD blocking efficacy.A pivotal facet of our investigation revolves around the optimization of SAM coatings on tungsten (W)-deposited silicon (Si) substrates, a crucial endeavor aimed at fortifying substrate adhesion while ensuring seamless compatibility with ALD processes. To this end, phosphonic acid-based SAM materials, boasting the capacity to form up to three bonds with metal surfaces, were judiciously selected to withstand the rigors of high-temperature, low-pressure ALD operations without decomposition. Furthermore, pretreatment of the metal surface with a basic solution served to enhance SAM coating uniformity and coverage, thereby affording a robust processability for subsequent ALD operations. Tailoring the alkyl chain length emerged as an additional aspect, with sophisticated adjustments tailored to fortify SAM coatings against structural degradation, thereby engendering enhanced stability and uniformity. Subsequent heat treatment emerged as a pivotal refinement step, efficaciously optimizing SAM coating uniformity and extending its application range, thereby endowing a versatile toolkit for material deposition.Comprehensive characterization of SAM coatings via a suite of analytical techniques encompassing Atomic Force Microscopy (AFM), Water Contact Angle (WCA) measurements, and X-ray Photoelectron Spectroscopy (XPS) analyses provided invaluable insights into substrate coverage, adhesion, and thermal stability. Quantitative assessments facilitated by frictional force measurements, contact angle analyses, and bond reorganization studies emphasized the efficacy of SAM coatings in facilitating selective ALD, with enhancements in AS-ALD performance attributed to SAM optimization strategies. Collectively, these findings highlight the pivotal role of SAM coatings in advancing the frontiers of AS-ALD technology, offering the imperative optimization strategies in future process developments towards greater efficacy and efficiency.

Thermal stability of self-assembled octadecyltrichlorosilane monolayers on planar and curved silica surfaces

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.

Selective deposition and micropatterning of titanium dioxide thin film on self-assembled monolayers

Self-Assembled Monolayer (SAM) is a single layer of ordered molecules absorbed on a surface by chemical bonding between the molecular head group and the surface. The surface properties can be controlled by the terminal functional group of the SAM layer. In order to utilize SAM layers for device applications, SAM layer needs to be patterned as a sub-micron size. Patterning of SAM layer in sub-micron size has been done by various techniques including direct-writing by dip-pen nano lithography, selective etching with UV photons, and selective deposition of SAM layer by &amp;-contact printing. In this study, silane based SAM layer was patterned to the sub-micron size using zero residual Nano imprint Lithography, which is regarded as next generation lithography technique due to its simplicity, high throughput and high resolution pattern transferring capability. Using zero-residual layer imprinting, 300nm~2um sized SAM patterns can successfully fabricated. In order to check the surface property of patterned SAM layer, a solution containing nano Ag particles was spin-coated on the SAM patterned substrate and nano Ag particles were selectively deposited on the substrate.