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The growth of tungsten nitride carbide (WNxCy) films obtained by atomic layer deposition using triethylboron, tungsten hexafluoride, and ammonia precursors is determined by the density and type of reactive sites. The film properties change as a function of thickness. On silicon dioxide and silicon carbide, growth is initially nonlinear such that the transient regimes are characterized by island formation, as evidenced by a parabolic tungsten growth curve extending to film thicknesses of up to 5 nm. Such films have low densities of ∼4–6 g cm-3 corresponding to only ∼30%–45% of the bulk density of ∼13.1 g cm-3 determined for a WN0.45C0.55 composition. X-ray reflectivity, thermal desorption, and elastic recoil detection spectroscopies reveal surface roughening and compositional and density differences close to the substrate surface. The offset from linear growth in the case of WNxCy films deposited on silicon dioxide is induced by the initial reaction of silanol and siloxane groups with triethylborane resulting in passivating ethylsilyl groups on the surface. A transient regime is not observed for WNxCy growth on hydrogen-terminated silicon with the initial growth being dominated by the reduction of tungsten hexafluoride to tungsten. On silicon nitride a short transient regime is observed relative to the carbide and oxide surfaces attributed to the enhanced binding of the triethylboron precursor. [ABSTRACT FROM AUTHOR]

The short-ranged bonding structure of organosilicate glasses can vary to a great extent and is directly linked to the mechanical properties of the thin film material. The combined action of ultraviolet (UV) radiation and thermal activation is shown to generate a pronounced rearrangement in the bonding structure of thin organosilicate glass films involving no significant compositional change or film densification. Nuclear magnetic resonance spectroscopy indicates loss of –OH groups and an increase of the degree of cross-linking of the organosilicate matrix for UV-treated films. Fourier transform infrared spectroscopy shows a pronounced enhancement of the Si–O–Si network bond structure, indicating the formation of more energetically stable silica bonds. Investigation with x-ray reflectivity and ellipsometric porosimetry indicated only minor film densification. As a consequence, the mechanical properties of microporous organosilicate dielectric films are substantially enhanced while preserving the organosilicate nature and pristine porosity of the films. UV-treated films show an increase in elastic modulus and hardness of more than 40%, and a similar improvement in fracture energy compared to untreated films. A minor increase in material dielectric constant from 3.0 to 3.15 was observed after UV treatment. This mechanism is of high relevance for the application of organosilicate glasses as dielectric materials for microelectronics interconnects, for which a high mechanical stability and a low dielectric constant are both essential film requirements. [ABSTRACT FROM AUTHOR]

Gaseous precursors for the atomic layer deposition (ALD) process can penetrate and deposit inside porous dielectrics. Understanding the relationship between the substrate porosity and the size and shape of precursor molecules used for the ALD of dielectric or metal films on these substrates is crucial for the formation and fabrication of reliable nanostructures. Sealing the surface pores is highly desirable to prevent the deposition of gaseous ALD precursors inside the porous network. In this study, in-diffusion of precursors is investigated using x-ray reflectivity, transmission electron microscopy, and Rutherford backscattering spectrometry for different porous substrates and binary (TaN) and ternary (WNC) ALD systems. Experimental observations are complemented with computational molecular modeling performed in the framework of the density-functional-theory formalism to determine the size and shape of ALD precursors. Pore sealing treatments are used to prevent a precursor penetration and to provide a suitable starting surface for the nucleation and growth of ALD films. [ABSTRACT FROM AUTHOR]

On nanoscale laminate structures, the interface cannot be identified any longer as the separation between two films of bulk materials. The formation of the interface defines the final composition and structure of the laminate structure. As such, the characterization of the interface becomes an important challenge. In this work the nanoscale laminate structures were formed by atomic layer deposition (ALD) of tungsten nitride carbide and tantalum nitride thin films on dense dielectrics [silicon carbide and silicon oxide (SiO2)]. The laminates were studied using x-ray reflectivity. The starting substrate surface is a primary factor in determining the density of the ALD layer. Moreover, in some cases, electron-density perturbations are observed in the vicinity of the interfacial region. A characterization strategy, using a density contrast layer between the silicon substrate and the SiO2 dielectric is presented. Depending on the chemical nature of precursors and substrate, ALD processes can either form specific interfacial organization or induce dielectric modifications, in any case, leading to unexpected metal-dielectric interactions. [ABSTRACT FROM AUTHOR]

Abstract: In order to enable an oxide-free Cu-to-Cu bonding in a (dual) damascene process, 3-aminopropyltrimethoxysilane- and decanethiol-derived self-assembled monolayers are selectively deposited in a dielectric-Cu based metal–insulator–metal (MIM) capacitor used as a test vehicle, which represents a dual damascene architecture environment. A two-steps SAM coating sequence is investigated for this purpose. In a first step, a “sacrificial” SHSAM is deposited on the Cu areas at the bottom of the vias. In a second step, a “barrier” NH2SAM is deposited on the dielectric areas in the field region and via’s sidewalls. This deposition sequence followed by the selective thermal ablation of the “sacrificial” SAM vs. the “barrier” SAM, enable an oxide-free Cu-to-Cu connection at via’s bottom. The differential in thermal stability between the amino and thiol SAMs has been studied by water contact angle and cyclic voltammetry. While the sacrificial SAM is selectively desorbed by thermal ablation already at ∼200°C, the barrier SAM on the dielectric sidewall and field regions withstands a thermal budget as high as ∼350°C. The substrate-selective SAMs depositions are revealed by XPS chemical characterization on the Cu and dielectric areas of the MIM structures supported by the SEM visualization of the Au nanoparticles that selectively decorate the NH2 functionalities of the barrier SAM. [Copyright &y& Elsevier]

Abstract: This article describes less explored solutions to improve interconnect performance without changing established steps (etch, strip, clean, CMP) in a sub-100nm integration route. Process conditions of the porogen-based low-k are adjusted by (1) varying the curing time (2) adding a thermal anneal step prior to CuO reduction or (3) depositing a capping layer on top of the low-k after curing. The low-k material examined in this study is Aurora® ELK HM (k ∼2.5). The integration process was robust against these variations, showing good electrical yield for all process splits. RC-product was improved when using a shorter curing time and when an anneal step prior to CuO reduction was performed. The use of a thicker capping layer decreased capacitance, showing an improved protection against damage. [Copyright &y& Elsevier]

Abstract: This paper describes a simple and novel approach to calculate the line resistance of copper interconnects. The proposed methodology is simply based on a linear representation of the Cu resistivity vs. 1/S Cu (S Cu is the Cu cross-sectional area) in which the slope captures the net result of scattering phenomena in Cu. [Copyright &y& Elsevier]

Abstract: Interfaces play a crucial role in determining the ultimate properties of nanoscale structures. However, the characterization of such structures is difficult, as the interface can no longer be defined as the separation between two materials. The high sensitivity of electron density to surface and interface reactions has attracted increasing interest in application of X-ray reflectivity (XRR) as probing technique. In this study, the nanolaminate structures were formed by atomic layer deposition (ALD) of tungsten nitride carbide (WNC) and tantalum nitride (TaN) thin films on silicon carbide (SiC), silicon oxide (SiO2) and silicon oxynitride (SiON) substrates and subsequently characterized by XRR. The goal is to establish a relationship between surface chemistry, interface properties and density of the final structure. To achieve this objective, the density variations at the interfaces between ALD TaN and ALD WNC with SiC, SiO2 and SiON films will be quantified by modeling analysis of XRR reflection spectra. From these modeled electron density profiles, specific mechanisms leading to surface dependent structural behavior are proposed. [Copyright &y& Elsevier]

Abstract: The thermal stability of Ni silicide, in comparison to the more conventionally used Co silicide, is studied by X-ray reflectivity. These data were complemented by sheet resistance measurements, transmission electron microscopy, time-of-flight Rutherford backscattering spectrometry, X-ray diffraction and time-of-flight elastic recoil detection analysis. [Copyright &y& Elsevier]

The impact of material/process interactions on low temperature CVD-O3 low-k dielectric film properties are presented. The film under investigation is deposited following a three-step process consisting of a low temperature chemical vapor deposition (CVD), an ex situ high temperature cure in a controlled ambient and a plasma treatment to seal the porous surface of the dielectric. In this paper, the extent to which the air break exposure, the cure, the nature of the plasma and the substrate can affect the material properties is investigated. The influence of the resist stripping plasmas on the material sealing and the mechanical properties during integration is also discussed. Finally, the dielectric k-value as extracted from damascene structures using Raphael™ simulations is presented and discussed. [Copyright &y& Elsevier]

Abstract: Surface hydrophilisation and effective k-value degradation have been reported in literature after direct-CMP of high porosity SiOC films (without a protective capping layer). In the sequel, attempts to restore ultra low-k (ULK) material initial properties after a standard CMP and post-CMP cleaning process are reported. Annealing treatment has shown to be valuable to remove residual organics and water absorbed at the ultra low-k material surface after direct-CMP. However, as the hydrophilicity of the polished surface remains unchanged, it does not prevent moisture uptake, leading to an increase in k-value with time. Therefore, in order to restore hydrophobic properties and to stabilize the surface in time, three silylating agents – containing chlorosilane reactive groups (–SiMe n Cl3−n ) as well as hydrophobic methyl functions (–CH3) in their structure – have been employed in liquid, gas or dense CO2 phases on the CMP-induced damaged ULK layers. While each of these organic treatments is efficient to restore hydrophobicity on post-CMP ULK surfaces, only one of them proved to be able to keep the k-value low (comparable to the ULK pristine k-value) and stable in time, without inducing significant change in porosity of the ULK material. [Copyright &y& Elsevier]

Abstract: Ultraviolet (UV)-assisted cure has recently been reported as an efficient method to enhance the mechanical properties of organosilicate glasses (OSG) at the expense of only minor film densification. In this work we show that, depending on the OSG material, the effect of UV-cure on fracture and thermal conductivity properties can vary to a large extent even though the same extent of stiffness enhancement is obtained. When the increase of elastic modulus is mostly due to the rearrangement of the silica matrix into more stable silica bonds, the film cohesion strength and thermal conductivity are also improved. Conversely, these properties remain unaffected when the dominant UV-cure mechanism is the increase of matrix connectivity. In the latter case, film adhesion is enhanced. The dominant UV-cure mechanism depends on the initial degree of cross-linking and on the mobility of the OSG matrix. [Copyright &y& Elsevier]

Abstract: In this paper we will highlight key integration issues that were encountered during the development of the 3D-stacked IC Through Silicon Via (TSV) module and present solutions to achieve a robust copper TSV. Electrical performance of the obtained TSV module is discussed based on a lumped RC model for 3D ring oscillators containing TSVs between bottom and top tiers. [Copyright &y& Elsevier]

Abstract: Through-silicon vias (TSVs) are critical components in most 3D architectures. In this paper, fully filled cylindrical Cu TSVs with a diameter of 5μm and a depth of 25μm were used to demonstrate quantitative assessment of the fabrication process and the interfacial adhesion of the TSVs. For TSV fabrication, the coverage of barrier and seed layers was respectively examined through dilute HF dipping and copper decoration plating. The adhesion between the TSVs and the substrate, which is of great importance for the functionality and long-term reliability of the TSVs, was characterized by four-point bending in combination with fractographic analysis. The scanning electron microscopic (SEM) images of the fracture indicate that the top of a TSV has better adhesion than the rest. This can be due to the non-uniformity of sidewall roughness and barrier thickness. A degradation of adhesion at the top was observed after thermal cycling tests, which seems to confirm the hypothesis of the influence of the roughness. These reliability tests should be taken as additional criteria for the assessment of TSV properties. [Copyright &y& Elsevier]

Abstract: A sacrificial material deposited by CVD is used to demonstrate air gap formation in single damascene structures by UV-assisted decomposition. The material is removed through a porous low-k cap, after completion of the damascene scheme. The porosity of the low-k cap is shown to be critical for efficient air gap formation. Capacitance reduction of ∼50% is demonstrated using this technique compared to conventional SiOC(H) interconnects and an effective dielectric constant of 1.7 is extrapolated. [Copyright &y& Elsevier]

Abstract: A ternary WN x C y system was deposited in a thermal ALD (atomic layer deposition) reactor from ASM at 300°C in a process sequence using tungsten hexafluoride (WF6), triethyl borane (TEB) and ammonia (NH3) as precursors. The WC x layers were deposited by a novel ALD process at a process temperature of 250°C. The WN x layers were deposited at 375°C using bis(tert-butylimido)-bis-(dimethylamido)tungsten ( t BuN)2(Me2N)2W (imido–amido) and NH3 as precursors. WN x grows faster on plasma enhanced chemical vapor deposition (PECVD) oxide than WC x does on chemical oxide. WN x C y grows better on PECVD oxide than on thermal oxide, which is opposite of what is seen for WN x . In the case of the ternary WN x C y system, the scalability towards thinner layers and galvanic corrosion behavior are disadvantages for the incorporation of the layer into Cu interconnects. ALD WC x based barriers have a low resistivity, but galvanic corrosion in a model slurry solution of 15% peroxide (H2O2) is a potential problem. Higher resistivity values are determined for the binary WN x layers. WN x shows a constant composition and density throughout the layer. [Copyright &y& Elsevier]

Abstract: The introduction of ultra low-k materials in copper technology has been much slower than anticipated in the ITRS Roadmap. The introduction of porosity in low-k materials has increased the level of complexity tremendously. In this paper, the challenges appearing during the integration of ultra low-k dielectrics will be discussed, since a proper understanding of these issues is essential for downscaling of the interconnect system. The inferior mechanical and thermal properties were always identified as main showstoppers for low-k integration. However, the extreme vulnerability of porous low-k to produces-induced damage (accompanied with the loss of dielectric performance and reliability) demands a continuous innovation of materials, processes and integration approaches. [Copyright &y& Elsevier]

Severe mechanical loads during multilevel metallization manufacturing, such as repeated thermal cycles and chemical–mechanical planarization processes, can induce high stresses in interconnect structures. It is shown that such stresses in ultra-low-k-based interconnect structures can experience relaxation either through interfacial adhesion failure or through the compliance of the porous dielectrics. Adhesion quality can be improved by careful interface engineering aimed at enhancing both the fundamental and the practical work of adhesion. However, the low stiffness of porous ultra-low-k films limits the range of loads in which mechanical responses remain elastic. Moreover, such films can show a time-dependent response (creep). Therefore, stresses in device fabrication and operation need to be kept under control to ensure structural stability. [Copyright &y& Elsevier]