In the present paper the evolution of the dislocation structure duringelectromigration in different regions along the Al(Cu) interconnect line isconsidered. It is shown that plastic deformation increases in the regionsclose to cathode end of the interconnect line. A coupling between thedissolution, growth and re-precipitation of Al2Cu precipitates and theelectromigration-induced plastic deformation of grains in interconnects isobserved. Possible mechanism of the Cu doping effect on the improvedelectromigration resistance of the Al(Cu) interconnects is discussed.

Stereoscopic and electron tomographic observation methods using TransmissionElectron Microscope (TEM) were examined to characterize three-dimensionallya shape and size of pores and spatial distribution in porous low dielectricconstant (low-k) films. In a case of TEM observation, nm size pores in anamorphous film are difficult to be imaged since contrast from the amorphouslayer affect the pore imaging. An optimum image capture method at a modifiedelectron beam condition was studied in which the amorphous contrast from theporous low-k film is weakened to enhance scattering contrast from the poresand a matrix. As a result, a stereoscopic observation and 3-D reconstructionimages clarified that the shape of pores was not spherical but distorted andalmost pores were partially connected. For measuring pore size and spatialdistribution, connected pores were segmented into smaller pores byseparating at the narrowest part. From images after segmentation, it isindicated that there existed more and larger pores at interfaces than acenter area. It was found that the pores did not homogeneously distribute inthe film but concentrated at the interfaces.

Evaluation of quasi-closed cavities connected with air through narrow necksis discussed. These cavities behave as closed pores when they are studied byPositron Annihilation Lifetime Spectroscopy (PALS). The reason is a shortlifetime of o-positronium (Ps) and energy barrier that exist for Psdiffusion from large pores (d>3 nm) to small ones (d<3 nm). It isshown that more comprehensive information can be obtained using adsorptionporosimetry. Standard adsorptives used in adsorption porosimetry haveinfinite lifetime allowing complete penetration and filling all the cavitiesduring the measurement. Calculation of the neck and cavity sizes is based onthe theory of metastable adsorption phases developed by Derjagin, Broekhoffand de Boer (DBdB). Results of evaluation are in good agreement with dataobtained by SEM and TEM.

TiAl based thin-films possess high oxidation-resistance and high meltingpoints, making them possible candidates for application in electronics. Thebehavior of the films upon exposure to various temperatures is of interestfor such application. In the present study, Ti37Al63thin films were deposited onto SiO2 substrates using RF magnetronsputtering from a compound target. Anneals were performed in vacuum attemperatures ranging from 400 °C to 700 °C. The phases and microstructuralbehavior of the films were evaluated as a function of annealing.Microstructural behavior was correlated with resistivity changes in thefilms. The behavior of Ti-Al films as potential under-layers for silvermetallization was also evaluated. The Ti-Al was observed to enhance thethermal stability of pure Al thin-films. The results are relevant forpotential application of the films to electronics.

Two particularly important reliability issues facing the integration of low-κ dielectric films are the fracture energy of the barrier-dielectricinterface and the barrier layer integrity during processing. We have noticedthat the compressive stresses in the barrier layers on low- κ dielectricslead to spontaneous delamination and formation of telephone-cord likemorphologies. These morphologies allow the measurement of fracture energyand are advantageous over artificially contrived features to yield realisticdebonding parameters. The fracture energy of common barrier films, TaN andTa, was determined using this method for varying porosity nanoporous silicaand MSQ. Detailed characterization of the telephone cord morphology using acombination of Optical Microscopy, SEM and Profilometry was done. Thefracture energy for Ta on different low-κ dielectrics was evaluated using a1-D model for straight buckles. The kinetic coefficient of buckling was alsoevaluated.

In this study, we developed a system allowing interfacial adhesionmeasurements as a function of mode-mixity, from pure tension to pure shear.Results show that the debonding energy increases, by a factor of 3 to 10, asthe amount of shear stress increases, approaching mode II conditions. Forlow k dielectrics, the debonding energy was found to decrease withincreasing porosity and increase with increasing plasticity. The crackpropagation is also dependent on mode-mixity.

Periodic 2-dimensional (2-D) hexagonal and the disordered pore structuresilica films have been developed using nonionic surfactants as thetemplates. The pore structure was controlled by the static electricalinteraction between the micelle of the surfactant and the silica oligomer.No X-ray diffraction peaks were observed for the disordered mesoporoussilica films, while the pore diameters of 2.0-4.0 nm could be measured bysmall angle X-ray scattering spectroscopy. By comparing the properties ofthe 2-D hexagonal and the disordered porous silica films which have the sameporosity, it is found that the disordered porous silica film has advantagesin terms of the dielectric constant and Young's modulus as well as thehardness. The disordered porous silica film is more suitable for theinterlayer dielectrics for ULSI.

The kinetics of copper deposition by the hydrogen-assisted reduction ofbis(2,2,7- trimethyloctane-3,5-dionato)copper in supercritical carbondioxide was studied as a function of temperature and precursorconcentration. The growth rate was found to be as high as 31.5 nm/min.Experiments between 220 °C and 270 °C indicated an apparent activationenergy of 51.9 kJ/mol. The deposition kinetics were zero order with respectto precursor at 250 °C and 134 bar and precursor concentrations between0.016 and 0.38 wt.% in CO2. Zero order kinetics over this largeconcentration interval likely contributes to the exceptional step coverageobtained from Cu depositions from supercritical fluids.

In-situ SEM electromigration studies were performed atfully embedded via/line interconnect structures to visualize thetime-dependent void evolution in inlaid copper interconnects. Voidformation, growth and movement, and consequently interconnect degradation,depend on both interface bonding and copper microstructure. Two phases aredistinguished for the electromigration-induced interconnect degradationprocess: In the first phase, agglomerations of vacancies and voids areformed at interfaces and grain boundaries, and voids move along weakinterfaces. In the second phase of the degradation process, they merge intoa larger void which subsequently grows into the via and eventually causesthe interconnect failure. Void movement along the copper line and voidgrowth in the via are discontinuous processes, whereas their step-likebehavior is caused by the copper microstructure. Directed mass transportalong inner surfaces depends strongly on the crystallographic orientation ofthe copper grains. Electromigration lifetime can be drastically increased bychanging the copper/capping layer interface. Both an additional CoWP coatingand a local copper alloying with aluminum increase the bonding strength ofthe top interface of the copper interconnect line, and consequently,electromigration-induced mass transport and degradation processes arereduced significantly.

Pore characteristics including pore size distribution, porosity, and poreinterconnectivity of PECVD SiCOH inter- layer dielectric (ILD) materialswith different dielectric constant (κ) values have been studied. Oxygenplasma damage to SiCOH low-κ films increases dramatically as the κ valuedecreases. Simulations showed that, compared to the ILD film, the overheaddielectric films have a significant impact on the overall effective κ (κeff) of the BEOL interconnects. Reducing the κ values ofthese overhead films helps to alleviate the pressure on the κ valuerequirement of the ILD materials while still meeting the κeff target. Ultralow-κ (ULK) PECVD hydrogenated silicon carbide (H:SiC) films with a κ of 3.0have been studied for the etch-stop applications. Studies of the chemicalcomposition and bonding structure suggest that less Si-C networκs are formedand more micro-porosity are incorporated in the ULK H:SiC film. The leakagecurrent of the ULK H:SiC film is found to be about 5 times lower than theH:S iC and H:SiCN films with higher κ values. The etch rate of ULK H:SiCfilm using a standard SiCOH ILD etch chemistry has been found to benegligible. Such an extremely high etch selectivity maκes these films verygood etch-stop layers.

A previously developed metal-organic atomic layer deposition (ALD) tantalumnitride (TaNx) process was employed to investigate the growth of TaNx liners on low dielectric constant (low-k) materials forliner applications in advanced Cu/low-k interconnect metallization schemes.ALD of TaNx was performed at a substrate temperature of 250°C byalternately exposing low-k materials totertbutylimido-tris(diethylamido)tantalum (TBTDET) and ammonia (NH3), separated by argon purge steps. The dependence of TaNx film thickness on the number of ALD cycles performed onboth organosilicate and organic polymer-based low-k materials was determinedand compared to baseline growth characteristics of ALD TaNx on SiO2. In order to assess the effect of the deposition of TaNx on surface roughness, atomic force microscopy (AFM)measurements were carried out prior to and after the deposition of TaNx on the low-k materials. The stability of the interfacebetween TaNx and the low-k materials after thermal annealing at350°C for 30 minutes was studied by examining interfacial roughness profilesusing cross-sectional imaging in a high-resolution transmission electronmicroscope (HR-TEM). The wetting and adhesion properties of Cu/low-k werequantified using a solid-state wetting experimental methodology afterintegration of ALD TaNx liners with Cu and low-k dielectrics.

A non-contact optical technique based on laser-generated surface acousticwaves (SAWs) was used to characterize elastic properties of two types ofthin (150-1100 nm) low-k films: more traditional non-porous organosilicateglass PECVD films (k=3.0) and novel mesoporous silica films fabricated insupercritical CO2 (k=2.2). The acoustic response of thenon-porous samples is well described by a model of an elastically isotropicmaterial with two elastic constants, Young's modulus and Poisson's ratio.Both parameters can be determined by analyzing SAW dispersion curves.However, the isotropic model fails to describe the SAW dispersion in themesoporous samples. Modifying the model to allow a difference betweenin-plane and out-of plane properties (i.e., a transversely isotropicmaterial) results in good agreement between the measurements and the model.The in-plane compressional modulus is found to be 2-3 times larger than theout-of plane modulus, possibly due to the anisotropic shape of the pores.Elastic anisotropy should therefore be taken into account in modelingmechanical behavior of low-k materials.

NANOGLASS®E (NGE) ultra low-k (ULK) dielectric material, with a k-value of∼2.2, was integrated for 130 nm Cu/ULK interconnect process technology. Thiswork deals with the characterization of reactive ion etching (RIE) and wetchemical processing of this film. Blanket films were characterized for etchrate, surface roughness, k-value change and chemical compatibility. Trenchetching and post etch wet clean processes were developed and optimizedenabling process integration for single damascene structures. Trench etchprocesses were evaluated for two etch schemes viz., etching under - photoresist and etching under hardmask. The details of each scheme will bedescribed and advantages observed will be discussed. To evaluate effect ofwet clean processes three different formulations were used. After formationof single damascene wafers, metal comb and serpentine structures weremeasured for metal continuity and bridging. Electrical continuity wasachieved for long serpentine structures with 0.18μm/0.18μm linewidth/spacing. Based on voltage ramp test results the film was found to besensitive to certain plasma etch conditions.

Our understanding of the role of the initial surface on atomic layerdeposition (ALD) of Cu diffusion barrier materials is limited by thecomplexity of the sequential reactions and the heterogeneous nature oftypical dielectric substrates. The atomically controlled surface chemistryof self-assembled monolayers (SAMs) provides a means of creating modelsubstrates for ALD. Here we report on ALD of WCxNyfilms on SAMs derived from bromoundecyltrichlorosilane adsorbed on silicondioxide. The as-prepared SAM is macroscopically ordered with the expectedBr-termination and has a well-defined chemical composition as determined bycontact angle measurements and X-ray photoelectron spectroscopy,respectively. Temperature programmed desorption spectroscopy confirms thatthe SAM is stable to 550°C. It survives multiple cycles of ALD at 300°C asevidenced by the detection of mass fragments characteristic of the alkylchain and supported by the persistence of a Br 2p peak at 71 eV. X-rayfluorescence, ellipsometry and atomic force microscopy reveal that theunderlying SAM influences WCxNy film coverage, thickness, andmorphology.

Ultra low dielectric constant (κ) material is needed as the inter-metaldielectrics to reduce RC delay when device dimension is scaled to sub-100nm.Porous dielectric films have been considered as good candidates for theapplication as inter-metal dielectrics due to their ultra low-k properties.Identifying proper dielectric copper diffusion barrier on the porous low-kfilms is critical for the low-k/Cu damascene fabrication process. In thisstudy, we have evaluated the compatibility of plasma-deposited amorphousBoron Nitride film as a dielectrics copper diffusion barrier on a MSQ-basedporous low-k LKD5109 film (from JSR). Both microwave plasma enhanced CVD(2.45 GHz) and radio-frequency plasma enhanced CVD (13.56 MHz) were appliedfor the BN deposition in order to evaluate the compatibility of the twoplasma processes with the porous film. Growth parameters were optimized tominimize the boron diffusion and carbon depletion in the porous low-k films,which were found to have deleterious effects on the dielectric properties ofthe low-k films. FTIR and micro-Raman were employed for analyzing thechanges in chemical structure of the low-k films after BN growth.Capacitance-voltage measurement was used to characterize the dielectricconstants of BN film on Si and the BN-deposited porous low-k film. SIMScharacterization was carried out to evaluate the performance of the BN filmagainst copper diffusion.

Electromigration (EM) failure statistics and the origin of the lognormaldeviation (σ) for Cu interconnects have been investigated by analyzing thelifetime statistics and void size distributions at various stages during EMtesting. Experiments were performed on 0.18 μm wide Cu interconnects withtests terminated after specific amounts of resistance increases, or after aspecified test time. Void size distributions of resistance-based, as well astime-based EM tests were obtained using focused ion beam (FIB) microscopy.The lifetime and void size distributions were found to follow lognormaldistribution functions. The σ values of EM lifetime and time-based void sizedistributions decrease with higher percentages of resistance increase,reaching an asymptotic value of σ ∼ 0.14. In contrast, σ values ofresistance-based void size distributions are significantly smaller and donot show an obvious dependence on time. The statistics of resistance-basedvoid size distributions can mainly be accounted for by geometricalvariations of the void shape, while the statistics of time-based void sizedistributions requires consideration of kinetic aspects of the EM process.The σ values of EM lifetime distributions at long times can be simulatedbased on measured void size distributions, taking into account geometricaland experimental factors of EM. In contrast, for short times the statisticsof initial void formation and the kinetics of interfacial mass transporthave to be considered.

Beams of nitrogen and hydrogen radicals were investigated as surfacepre-treatment and process enhancement techniques for atomic layer deposition(ALD) of tantalum nitride barrier layer on a dense organosilicate (OSG) lowk film. In-situ x-ray photoelectron spectroscopy (XPS)studies of the evolution of the low k surface chemistry revealed an initialtransient growth region controlled mainly by the substrate surfacechemistry. Pre-treatment of the low k surface with radical beams,particularly with nitrogen radicals, was found to enhance significantly thechemisorption of the TaCl5 precursor on the OSG surfaces. Theenhancement was attributed to the dissociation of the weakly bonded methylgroups from the low k surface followed by nitridation with the nitrogenradicals. In the subsequent linear growth region, atomic hydrogen specieswas able to reduce the chlorine content under appropriate temperature andwith sufficient purge. The role of the atomic hydrogen in this processenhancement is discussed.

This paper introduces a low-k dielectric material, a novel epoxy siloxanepolymer, made by Polyset Co. Inc, which has promising properties. Thepolymer was spin-deposited, and thickness and optical properties weremeasured using variable-angle spectroscopic ellipsometry (VASE). Fouriertransform infrared (FTIR) spectra of as deposited and cured polymers showedthat the polymer is fully cured at 165 °C. The low curing temperature of thepolymer lowers stress in back-end-of-line (BEOL) stack and thus improves thereliability. The polymer is thermally stable up to 400 °C. The polymer hasYoung's modulus of ∼5 GPa and hardness of greater than 0.4 GPa. Aftermultiple stress cycles up to 300 °C, the residual stress in the polymer atroom temperature is less than 60 Mpa. The polymer has good adhesion withsemiconductor and dielectrics such as Si, SiC, and SiO2, metalssuch as Al, Cu, Co, and W, and barrier materials such as TaN. The bulkdielectric constant of the polymer is 2.4 - 2.7. The leakage current densityin the polymer at the applied electrical field of 1 MV/cm is in 10−9 A/cm2 range and the breakdown field of thepolymer is ranging from 5 to 7 MV/cm. The polymer when subjected tobias-temperature stress (BTS) conditions of 150 °C and 0.5 MV/cm shows noC-V shift for up to 100 min indicating that the polymer resists Copperdiffusion. The current density under stress conditions of 150 °C and 0.5MV/cm was less than 10−9 A/cm2 for up to 7 hrs.

A novel organosiloxane-vapor-annealing method has been developed forimproving the mechanical strength of porous silica films with a lowdielectric constant. Treatment of a porous silica film with1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS) under atmospheric nitrogenabove 350 °C significantly enhanced the mechanical strength (i.e., elasticmodulus and hardness) of the film. Results of Fourier transform infraredspectroscopy (FT-IR) and thermal desorption spectroscopy (TDS) suggested theformation of cross-linked poly(TMCTS) network on the porous silica internalwall surfaces by the TMCTS treatment. Such TMCTS cross-linked network isthought to enhance the mechanical strength of the low-k film.