29Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy was employed to characterize short-range atomic structure modifications to low k dielectric films that were subjected to post-deposition plasma exposure or UV curing. Comparison of spectra from single thick depositions of a CVD low k film (k∼3.0) with sequential thin depositions of the same film revealed ∼3% increase in Si-O crosslinking that was attributed to interfacial plasma damage. Comparison of a second CVD low k film (k∼3.0) before and after UV curing revealed ∼11% increase in Si-O crosslinking with commensurate losses of Si-OH and Si-CH3 groups. UV curing was believed to result in bulk modification. This crosslinking was found to increase the Young's modulus of the film from 11 to 16 GPa as measured on 700 nm films by nanoindentation. NMR analysis was found to provide significant information beyond that provided by FTIR but required special sample preparation and extensive data collection.

Water adsorption by porous low-k silica films results in increased dielectric constants and is often due to silanol groups on the pore surfaces. Reacting the silanols with silylating agents (e.g., hexamethyldisilazane (HMDS) and trimethylchlorosilane (TMCS)) in supercritical CO2 (SC-CO2) can increase film hydrophobicity and can remove adsorbed water. In porous methylsilsesquioxane (MSQ) films (average pore size ∼ 3-4nm), it has been determined that supercritical silylation reactions do not substantially penetrate beyond the film surface.1,2 In this work we have examined the supercritical penetration behavior of silylating agents in low-k films with larger pore sizes (5-10nm). The depth and extent of reactants was determined by in situ infrared spectroscopy (FTIR), and surface hydrophobicity was examined by contact angle experiments.

It is of importance to understand cracking behavior in low dielectric constant, low modulus materials. Nanoindentation method is presented as a tool to estimate the critical film thickness, thickness above which spontaneous cracking could occur, for ILD films used in the BEOL. The critical film thickness was then used to calculate cohesive energies and fracture toughness of the films. Materials were investigated using nanoindentation combined with AFM imaging. The results were compared to data acquired by four point bend methods.

A novel process of TMCTS vapor annealing combined with a plasma treatment has been developed for improving the mechanical strength of porous silica films having ultralow dielectric constant. When porous silica films annealed under 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS) vapor were treated with argon plasma and then re-treated with TMCTS vapor, the mechanical strength (i.e., elastic modulus, hardness) of the films increased significantly. Results of Fourier transform infrared spectroscopy (FT-IR) suggested an accelerative effect resulted from the plasma treatment on the conversion of Si-CH3 and Si-H groups to Si-OH groups. The latter group appears to react faster with TMCTS from the second annealing to form cross-linked polymer network on the porous silica wall surfaces. The resulting cross-linked network is thought to keep the low permittivity and enhance the mechanical strength of the low-k films.

The thermal oxidation of Cu interconnects, at 350°C in air, has been studied as a function of thickness of a CoWP capping layer. For thin CoWP layers (25 nm), a thick oxide layer (200 nm) is formed which is mainly composed of Cu20. For thick CoWP layers (50 nm), the oxide layer is much thinner (36 nm) and is mainly composed of CoO. For both CoWP thicknesses, depletion of the underlying Cu is often observed after oxidation and whisker growth is often observed on the surface. The results are consistent with an oxidation mechanism where metal is the dominant diffusing species. For thin CoWP layers, Cu diffuses more quickly to the surface than Co, and therefore mainly Cu oxides are formed. For thick CoWP layers, the Cu diffusion to the surface is greatly reduced, and as a result, mainly Co oxides are formed. These results indicate that CoWP is not a good barrier for thermal oxidation, so high temperature exposure to oxidizing ambients must be minimized during processing of integrated circuits where CoWP is used instead of a dielectric barrier.

A high-temperature nanoindentation measurement method has been developed for evaluating the hardness and modulus of low-k films when the temperature is raised from R.T. to 200°C. Thermal stability and chemical changes due to heating were investigated by Raman spectroscopy, Fourier transform infrared spectroscopy and thermogravimetry-differential thermal analysis, and by thermal desorption spectroscopy, respectively. Two different classes of low-k materials, organic polyarylence ether film and methyl-hydrogen-silsesquioxane film, were examined. The hardness and modulus of the former film during heating increased due to water desorption in the lower temperature range, and then decreased due to the evolution of hydrocarbon gas from some unreacted components or solvent residuals in the higher temperature range. In regard to the latter film, the hardness and modulus of a specimen (A) having a higher hydrocarbon content decreased during heating and reached the lowest value at 200°C and then constantly remained at the lowest levels during cooling. In contrast, no significant changes in hardness and modulus were observed for a specimen (B) having a lower hydrocarbon content in either the heating or cooling process. The reduction of the hardness and modulus of specimen A was attributed to thermal decomposition of most of its Si-CH3 and SiH/SiH2 chains. These results revealed that the temperature dependence of the hardness and modulus of low-k films is significantly affected by physical and/or chemical changes during heating due to moisture absorption, thermal evolution of organic residuals and thermal decomposition, rather than other factors such as thermal stress.

In this work we report the adhesion of a thin Tantalum (Ta) barrier films deposited on nanoporous dielectric substrates (Xerogel and Methyl Silesquioxanes (MSQ)). The high compressive stresses in the Ta barrier layer lead to spontaneous delamination from the underlying substrate resulting in a telephone cord like morphology, which allows the measurement of critical interfacial adhesion (fracture) energy. The fracture energy of Ta barrier films on different porous substrates is evaluated using the above two methods and the resulting differences are explained. Fracture energy varies inversely as a power law with the dielectric pore size indicating pores are essential to delamination in the barrier-dielectric interface. The observed trend of fracture energy is related to other mechanical properties of the porous substrate offering insights into the underlying mechanisms governing fracture of films deposited on porous substrates.

Positronium annihilation lifetime spectroscopy (PALS) using a positron beam is a proven technique to characterize porosity in amorphous thin film materials. The capability to control the depth of the implanted positrons is unique to beams as compared to traditional bulk PALS techniques. By increasing the positron beam energy, positrons are implanted deeper into the film. Control of the positron implantation depth in beam-PALS allows analysis of sub- micron films, investigation of depth-dependent film inhomogeneities, determination of pore interconnection lengths, and access to buried films under barrier layers. Details on PALS depth profiling and an example of applying the technique to a plasma-enhanced-chemical-vapor- deposited (PECVD) porous film are presented.

Two level metal structures were fabricated to test the efficacy of using an organic low K etch stop layer (OESL) in order to lower the effective dielectric constant for intralayer capacitance. The organic etch stop layer's intrinsic capacitance of 3.3 compares with that of silicon carbide (∼ 5) which constitutes the control of the experiment. This reduction represents a reduction of effective dielectric constant for the stack of about 10% to about 3.0. The process was optimized so as to achieve yield of via chains of a million 130 nm diameter vias, and effective K was measured. The target of 3.0 was achieved using this process. Interpenetration of the organic etch stop with the MSQ porous low K material was observed.

Structure evolution in plated Cu films is a function of sublayer stacking, film thickness, plating chemistry, plating parameters, and temperature. The present work examines grain growth and texture evolution in annealed plated Cu on a 25 nm thick Ta sublayer for films of 480 and 750 nm in thickness. These results are compared against those obtained from damascene Cu lines fabricated from a similar process, using a series of line widths. The results show that the initial structures of the plated films are similar, with slightly weaker (111) texture, a higher fraction of twin boundaries, and larger grains in the thicker films. The microstructure of the Cu within the trench constraints is a strong function of line geometry with the propensity for twin boundary development controlling structural evolution.

This communication describes the results of a potential spin-on glass (SOG) solution for narrow and high aspect ratio trench fill in both shallow trench isolation (STI) and premetal dielectric (PMD) applications. We have focused our development work on a hydrogen silsesquioxane (HSQ, (HSiO3/2)n) material, which offers the advantage of a carbon free gap fill solution. The main challenge for carbon-free SOG materials is to achieve material densification in the nano-scale gaps during thermal processing that of the gap filled material during the wet cleaning steps. This paper reports some approaches and findings on material densification in the nano-scale gaps and the results of subsequent wet etch tests.

In this paper, we investigate the effect of copper diffusion barrier integrity on the leakage behavior and dielectric reliability of copper/micro porous organo-silica-glass (OSG) interconnects. Significant differences in the field dependence of TDDB median-time-to-failure are observed when comparing sub-critical and sealing barriers. Also for the temperature acceleration of TDDB, a significant difference is found which is reflected in the thermal activation energies. With fast voltage ramp measurements, I-V curves of samples with subcritical and sealing barriers are compared before and after constant current stresses. Above 1.4 MV/cm, the dominant leakage mechanism is found to be Frenkel-Poole emission regardless of barrier treatments and stress times. Below 1.4 MV/cm, however, the I-V characteristic is modulated by the barrier integrity, which can be attributed to copper diffusion into the intermetal dielectric.

A plasma-assisted atomic layer deposition (PA-ALD) process of titanium nitride (TiN) using TiCl4 precursor dosing and H2/N2 plasma exposure is presented. In situ spectroscopic ellipsometry revealed a growth rate at 400 °C of ∼0.7 A/cycle independent of precursor dosing. Varying the plasma exposure time changed the stoichiometry [N]/[Ti] of the films within the range ∼0.93-1.15. At 100 °C a relatively low chlorine impurity level (∼2 at. %) and low resistivity (∼200 νΔcm) were obtained for a ∼45 nm thick film. The growth rate was found to be considerably lower (∼0.3 Å/cycle) at this temperature. Using TEM imaging we found that PAALD TiN films can be deposited conformally in 20:1 aspect-ratio features (1.5 Êm width) but that the step coverage still needs to be improved, probably by a prolonged plasma exposure step.

Due to a rapid shrinkage in memory devices, backned of the line process experiences great difficulties, especially Al metallization. Furthermore, there is a continuous demands in low line resistance in order to promote device performances. In this article, Al damascene process is proposed as compared to Al patterning process, which suffers from inherent pattering issue at a fine pitch under 70nm. The most difficulties in the development of Al damascene process were to form a stable and void free Al in fine trench and to obtain scratch and corrosions free Al surface. In this study, 50nm beyond fill was successfully achieved by “bottom up growth” of CVD Al. For the process, CVD Al by using Methylpyrroridine Alane (MPA) precursor was deposited on a stacked film of CVD TiN and PVD TiN as a wetting layer, which was followed by PVD Al and reflow, then the Al surface was polished with colloidal silica based slurry.

In addition, electrical property of Al scheme and W scheme was compared with damascene pattern, along with which we demonstrated that around 36% decrease in parasitic capacitance is achievable by decrease of metal line height from 3500A to 1000A on simulation test implying that device performance could be enhanced.

Poly(p-xylylene) (also known as parylene N) has previously been used to pore seal ultralow k (≤ 2.2) (ULK) dielectrics. The parylene polymers may facilitate the integration of ULK dielectrics by: substantially improving their fracture toughness, hermetically sealing the pores, being able to use standard wet chemical cleans, and minimally impacting the observed dielectric constant, while minimally disrupting current process flow integrations. This paper introduces a new cross-linkable polymer that is deposited using thermal chemical vapor deposition (CVD) on the same tool that is used for parylene N deposition. The polymer, poly(ethynyl-p-xylylene) (parylene X), was deposited at room temperature. A series of 30 min post-deposition anneals in helium shows that the deposited material cross-linked between 200°C and 300°C with full conversion at 380°C for a ~300 A film. After the low molecular weight species out-gassed during anneals at 200°C, there was less than a percent weight loss to 450°C with no change in the optical constants and no optical loss. Previous work with poly(ethyl-p-xylylene) suggests that the dielectric constant of parylene X will be significantly lower than parylene N.

The most frequent failure of wireless, handheld, and movable consumer electronic products is an accidental drop to the ground. The impact may cause interfacial fracture of wire-bonds or solder joints between a Si chip and its packaging module. Existing metrologies, such as ball shear, and pull test cannot well represent the shock reliability of the package. In this study, a micro-impact machine is utilized to test the impact reliability of three kinds of lead-free solders: 99Sn1Ag, 98.5Sn1Ag0.5Cu and 97.5Sn1Ag0.5Cu1In (hereafter called Sn1Ag, Sn1Ag0.5Cu, and Sn1Ag0.5Cu1In). The effect of thermal aging on the impact toughness is also evaluated in this study. We find a ductile-to-brittle transition in SnAg (Cu) solder joints after thermal aging. The impact toughness is enhanced by the thermal aging. This is a combination effect of the growth of intermetallic compound (IMC) at the interface provided strong bonding, and the softening of the solder bulk during the thermal aging absorbed more energy during plastic deformation.

Recently, we showed that thin film stresses can be used to form well aligned and complex nanowire structures [1]. Within this approach we used stress to introduce cracks in a thin film. Subsequent vacuum deposition of metal leads to the formation of a metal layer on the thin film and of metal nanowires in the cracks of the film. Removal of the thin film together with the excess metal cover finishes the nanowire fabrication on the substrate. As stress can be intentionally introduced by choosing an appropriate thin film geometry that leads to a stress concentration, the cracks and consequently the nanowires can be well aligned. Meanwhile, we have demonstrated how to form thousands of parallel aligned nanowires, x-and y-junctions or nanowires with macroscopic contacts for sensor applications, simply by applying fracture mechanics in thin films. Christiansen and Gösele called this approach “constructive destruction” in a comment in Nature Materials [2]. This gives a hint how to overcome some problems of the approach, arising from the limits of thin film fracture. A generalization of the fracture approach by being “more destructive” can overcome this limitations. For example, it is difficult to form pairs of parallel wires with a nanometer distance of the pair, but a micrometer separation between the individual pairs. Structures like this are useful for many contact applications including sensor arrays or field effect transistors. As well as thin film fracture, thin film delamination can be well controlled by fracture mechanics. Our latest experiments show that the combination of both, fracture and delamination, forms an ideal shadow mask for vacuum deposition. Cracks with delaminated sides were used as templates for the deposition of pairs of parallel wires consisting out of different materials with only a few 10 nm separation. First, a metal was sputter deposited under an angle of approx. 45° through the delaminated crack, which was used as a shadow mask. Afterwards, a second deposition metal is deposited under the opposite 45° angle with respect to the sample normal, having the crack located in the middle between both deposition sources. The angle, the delamination height and the crack width determine the separation of the nanowire contacts. We present several examples which show how these mechanisms of mechanical failure of thin films can be turned into useful templates for various nanostructures. We will focus here on two thin film systems, that can be easily deposited in every lab. These are wet chemically deposited photo-resist and flash evaporated amorphous carbon. These examples are compared with finite element simulations of the thin film stress with the ANSYS program. Moreover, we show how the delamination cracks can be also used as masks for the removal of material. Channals with a width down to 20 nm produced by ion beam sputtering are shown.

Surface modification of a p-SiOC film induced by Helium (He) plasma was investigated using various measurements. Differential Fourier transform infrared absorption (FT-IR) spectra and the etch-depth measurements with the immersion in the mixed hydrofluoric acid (HF) indicate that the almost all of Si-CH3 bonds are broken in the modification layer, resulting in carbon-depletion, an SiO2-like composition. The x-ray photoelectron spectroscopy (XPS) measurements at different take-off angles reveal that the modified surface forms a double-layered structure, a thin carbon-rich top layer (about 1 nm thick) on a thick carbon-depletion layer (about 20 nm thick) with the irradiation of He plasma over 300 W. Atomic force microscopy (AFM) observations show that the modified surface is the smoothest in the case of the carbon-depletion surface.

Blanket porous methyl silsesquioxane (pMSQ) films on a Si substrate were studied with the intent to seal the pores and prevent penetration of a metallic precursor during barrier deposition. The blanket pMSQ films studied were approximately 220 nm thick and had been etched and ashed. When tantalum pentafluoride (TaF5) is exposed to an unsealed pMSQ sample, X-ray photoelectron spectroscopy (XPS) depth profiling and secondary ion mass spectroscopy (SIMS) depth profiling reveal penetration of Ta into the pores all the way to the pMSQ / Si interface. Boron carbo-nitride films were grown by thermal chemical vapor deposition (CVD) using dimethylamine borane (DMAB) precursor with Ar carrier gas and C2H4 coreactant. These films had a stoichiometry of BC0.9N0.07 and have been shown in a previous study to have a k value as low as 3.8. BC0.9N0.07 films ranging from 1.8 to 40.6 nm were deposited on pMSQ and then exposed to TaF5 gas to determine the extent of Ta penetration into the pMSQ. Ta penetration was determined by XPS depth profiling and sometimes SIMS depth profiling. XPS depth profiling of a TaF5 / 6.3 nm BC0.9N0.07 / pMSQ / Si film stack indicates the attenuation of the Ta signal to < 2 at. % throughout the pMSQ. Backside SIMS of this sample suggests that trace amounts of Ta (< 2 at. %) are due to knock-in by Ar ions used for sputtering. An identical film stack containing 3.9 nm BC0.9N0.07 was also successful at inhibiting Ta penetration even with a 370°C post-TaF5 exposure anneal, suggesting the stability of BC0.9N0.07 to thermal diffusion of Ta. All BC0.9N0.07 films thicker than and including 3.9 nm prevented Ta from penetrating into the pMSQ.