We present a stochastic model which simulates electromigration damage in metallic interconnects by biased percolation of a random resistor network. The main features of experiments including Black's law and the log-normal distribution of the times to failure are well reproduced together with compositional effects showing up in early stage measurements made on Al-0.5%Cu and Al-1%Si lines.

The influence of stress-induced voiding on the electromigration (EM) behavior has been investigated on narrow via-line structures. For this purpose the EM performance of metal lines containing stress-induced voids already before the electrical operation has been compared with samples without stress-induced voids. We found, that pre-existing stress voids in the metal lines do not affect the activation energy Ea and lead only to a small decrease of the EM median time to failure, but cause a relevant reduction of the current density exponent down to n = 1. As a consequence, a tremendous decrease of the electromigration limited life time is obtained.

Processible poly(methylsilsesquioxane)s (PMSSQs) were prepared in THF solution under nitrogen atmosphere in the presence of HCl catalyst. It was found that various reaction parameters such as concentration, temperature, reaction time, the amount of water, and the amount of acid catalyst could affect the molecular weight and the amount of functional end groups of PMSSQ samples. Thin films prepared from our PMSSQ samples by spin-coating followed by curing to 420°C exhibited a much better crack resistance than those presented in the literature, while the dielectric constant remained practically the same, i.e., ca. 2.7.

In previous studies, low-k carbon-doped silicon oxide (SiOC) films were deposited using organosilicon precursor: (CH3)xSiH4−x. In this paper, we present the properties of PECVD low-k SiOC films produced by using conventional SiH4 based gas precursors. The SiH4 based SiOC films have similar gross physical and electrical characteristics to those of (CH3)xSiH4−x based SiOC. Since the precursors are inexpensive, commercially available and convenient to operate for existing tools, the process should not require additional cost as compared with that of PECVD silicon dioxide. We demonstrate the feasibility of integrating Cu with SiOC on damascene interconnection. The evaluation on electrical performance of the Cu/SiOC based damascene structure will be discussed.

One of the important reliability challenges in integrating copper/Low-K dielectric technology has been adhesion between the Low-K dielectric and barrier metal. This investigation explored the applicability of the four-point bend technique for determining the adhesion strength of a fluorine doped low dielectric constant oxide in contact with tantalum barrier layer. Time of flight secondary ion mass spectroscopy (ToFSIMS) was used for surface chemical analyses of the delaminated surfaces to identify the fractured interface and its chemical compositions. The effect of annealing on mechanical strength was coupled with chemical analysis to discern the adhesion properties. Experimental results suggested that fluorine rich interfacial layer formation was associated with degraded adhesion characteristics between Low-K dielectric and tantalum barrier metal.

Effects of H irradiation on purifying Cu films and improving their surface roughness as well as size and orientation of Cu grains in the films have been examined using a newly developed plasma CVD reactor equipped with an H atom source, in which Cu(hfac)2 is supplied as the source material. The H irradiation is effective in purifying the Cu films, increasing the grain size, and reducing the surface roughness, while it has no effect on the grain orientation. The decrease in dissociation degree of material gas leads to reduction of the surface reaction probability of Cu- containing radicals, which is important to realize conformal deposition in fine trenches. Using the control of dissociation degree of material gas independent of H irradiation, we have demonstrated conformal deposition of smooth Cu films in the trench using the developed plasma CVD reactor.

The structures and properties of the HSQ film during the cage/network transformation were studied by curing at 300°C for 1 hour. The experimental results show that the ratio of the network/cage structure of the cured HSQ film increases from 0.21 to 0.39 by curing. The porosity of the cured film increases from 10.0% to 12.3 %, while the refractive index decreases from 1.413 to 1.376 during curing. These results suggest that the dependence of the structure and properties of the HSQ film by curing. The CMP characteristics of HSQ were studied by using different kinds of slurries and surfactant. The CMP results of polishing HSQ suggest that the hardness and charge status of the abrasive, the interaction of the surfactant with the abrasive and film surface significantly affect the polishing results.

Fluorinated silica has a dielectric constant lower than that of F-free SiO2 and is a potential interlayer dielectric. We investigate the F-doped SiO2 with ab-initio modeling and various characterization techniques searching to explain the dielectric constant reduction. FTIR transmission and spectroscopic ellipsometry give us information about the ionic and electronic contributions to ε. Nuclear reaction analysis and Auger spectrometry measure F composition. XPS and FTIR provide information on the atomic structure of the film. We use several cells of cristobalite to model fluorinated silica using the electronic structure theory. The ground state geometry, vibrational density of states, electronic band structure, and Born effective charges are analyzed. The calculations suggest that it is the ionic component of the dielectric constant that is mostly effected by the F incorporation.

Convergent beam electron diffraction (CBED) was used to measure localized lattice strains in damascene copper interconnects. This method provides data from areas of approximate diameter 20 nm, enabling evaluation of strain states within individual grains. Lattice parameters were determined by measuring the deficient higher order Laue zone (HOLZ) line positions in experimental zone axis patterns and subsequently comparing them to kinematical and dynamical simulations. Quantitative comparison was accomplished using a least squares analysis of distances between line intersections. Deposition-induced strains between 0.06% and 0.14% were measured in 2.0 µm wide lines. The uncertainty in strain determination was approximately 0.02%, as limited by the precision in HOLZ line detection. In addition to enabling localized analysis of strain states, another advantage of using CBED is that the microstructure can be fully evaluated. Used in conjunction with global methods such as X-ray diffraction, CBED may provide unique insight into localized failure phenomena such as electromigration void formation in damascene copper.

The present work describes the process principles of “Spin-Etch Planarization” (SEP), an emerging method of planarization of dual damascene copper interconnects. The process involves a uniform removal of copper and the planarization of surface topography of copper interconnects by dispensing abrasive free etchants to a rotating wafer. The primary process parameters comprise of (a) Physics and chemistry of etchants, and (b) Nature of fluid flow on a spinning wafer. It is evident, that unlike conventional chemical-mechanical planarization, which has a large number of variables due to the presence of pads, normal load, and abrasives, SEP has a smaller number of process parameters and most of them are primary in nature. Based on our preliminary works, we have presented the basic technical parameters that contribute to the process and satisfy the basic requirements of planarization such as (a) Uniformity of removal (b) Removal rate (c) Degree of Planarization (d) Selectivity. The anticipated advantages and some inherent limitations are discussed in the context of process principles. We believe that when fully developed, SEP will be a simple, predictable and controllable process.

Porous silica exhibits attractive dielectric properties, which make it a potential candidate for use as insulator into interconnect structures. A new way of preparation of highly porous silica layers by the sol-gel route was investigated and is presented. The synthesis strategy was based on the use of common and low toxicity reagents and on the development of a simple process without gaseous ammonia post-treatment or supercritical drying step. Defect free layers were deposited by spin coating on 200 mm silicon wafers and characterized. Thin layers with a total porosity larger than 70% and an average pore size of 5 nm were produced. The dielectric constant measured under nitrogen flow on these highly porous layers is equal to ∼ 2.5, which can be compared to the value calculated from the measured porosity, ∼ 1.9. This difference is explained by the presence of water adsorbed on the hydrophilic surface of the unmodified silica.

Tantalum nitride (TaN) films were deposited using pentakis-diethylamido-tantalum [PDEAT, Ta(N(C2H5)2)5] as a precursor. During film growth, N- and Ar-ion beams with an energy of 120 eV were supplied in order to improve the film quality. In case of thermallydecomposed films, the deposition rate is controlled by the surface reaction up to about 350 °C with an activation energy of about 1.07 eV. The activation energy of the surface reaction controlled regime is decreased to 0.26 eV when the Ar-beam is applied. However, in case of Nbeam bombarded films, the deposition is controlled by the precursor diffusion in gas phase at the whole temperature range. By using Ar-beam, the resistivity of the film is drastically reduced from approximately 10000 µω-cm to 600 µω-cm and the density of the film is increased from 5.85 g/cm3 to 8.26 g/cm3, as compared with thermally-decomposed film. The use of N-beam also considerably lowers the resistivity of films (∼ 800 µω-cm) and increases the density of the films (7.5 g/cm3). Finally, the diffusion barrier properties of 50-nm-thick TaN films for Cu were investigated aftre annealing by X-ray diffraction analysis. The films deposited using N- and Arbeam showed the Cu3Si formation after annealing at 650 °C for 1 hour, while thermallydecomposed films showed Cu3Si peaks firstly after annealing at 600 °C. It is considered that the improvements of the diffusion barrier performance of the films deposited using N- and Ar-ion beam are the consequence of the film densification resulting from the ion bombardment during film growth.

The effect of fatigue loading on microelectronic thin film interfaces has until now been difficult to quantify. Most industrial fatigue testing uses HAST (Highly Accelerated Stress Testing) protocols, which inherently convolutes the effects of mechanical fatigue and the test environment. Our work focuses on isolating the deleterious effects of mechanical fatigue on interfaces, which we have found to be substantial. In this study, the integrity of a low-k polymer interface involving benzocyclobutene (BCB) and silica was examined under a variety of loading conditions. Critical (fast fracture) adhesion values were measured using standard interface fracture-mechanics geometries. Experiments were then conducted to measure the debond growth rate as a function of the applied strain energy release rate under both static and cyclic loading conditions. Our results show that even under room temperature conditions, debond growth rates measured under cyclic fatigue are considerably faster than those observed under static loading. Results are presented detailing the effects of interface chemistry (adhesion promoters), environmental moisture, and test temperature on the resistance of the interfaces to subcritical debonding. Strategies for increasing resistance of dielectric interfaces to fatigue debonding are outlined.

Fluorine-doped silicon dioxide, a dielectric material compatible with copper integration, has received considerable attention for applications requiring a k value in the 3.5 to 4.0 range. Given the influence of structure on desired properties, convenient experimental structural probes of this type of material are of widespread interest. This work focuses on Raman spectroscopic analyses of ring defects in fluorine-doped silicon dioxide films prepared by plasma enhanced chemical vapor deposition (PECVD) as well as high density plasma methods (HDP). These measurements are complemented by ab initio computational simulations of the ring defects in these films and the impact of nearby fluorine on their stability. The impact of aging on these structures and correlations of observed trends with experimental techniques such as X-ray fluorescence are also described.

We report low temperature (25-200°C) photo-assisted sol-gel processing for the formation of porous silicon dioxide films on Si (100) substrates using 172 nm radiation from an excimer lamp. The effects of substrate temperature and irriadation time on the properties of the films formed have been studied using ellipsometry, Fourier transform infrared spectroscopy (FTIR), and electrical measurements. The FTIR spectra revealed the presence of a Si-O-Si stretching vibration peak at 1070 cm-1 after UV irradiation at 200°C. This is similar to that recorded for oxides grown by thermally oxidation of silicon at temperatures between 600-1000°C. Capacitance measurements indicated that the dielectric constant values of the films, found to be between 1.7-3.3, strongly depended on the substrate temperature during irradiation. Dielectric constant values as low as 1.7 were readily achievable at room temperature. These results show that the photochemical induced effects initiated by the UV radiation enable both reduced processing times and reduced processing temperatures to be used.

Spin-on mesoporous silica films were prepared on eight-inch wafers at SEMATECH by condensation of a silicate network around surfactant micellar structures. Copper single-damascene one-level test structures were built using mesoporous silica as the intermetal dielectric. No major structural failures were observed after chemical mechanical planarization on both blanket films and patterned wafers, indicating relatively good mechanical integrity for a highly porous structure. A simple silane spin-coating step used at SEMATECH on the films appears to be insufficient for complete dehydroxylation and silylation. The electrical test results on the metal comb structures showed good capacitance and leakage current distributions. However, capacitance and leakage current changes were observed after each post-CMP process step, and these changes could be correlated to moisture desorption/outgassing, which was also noted during k measurement. With controlled film synthesis and dehydroxylation conditions, mesoporous silica films with k ≤2.0 and elastic modulus of 4.0 GPa have been synthesized at PNNL. The results of the Cu one-level metal screening tests at SEMATECH combined with properties obtained at PNNL indicate that mesoporous molecularly-templated silicate films hold promise as ultra low k intermetal dielectrics.

Tungsten nitride (WNx) thin films can be used as Schottky barriers in high power, high temperature semiconductor devices or as diffusion barriers between Cu, low-k dielectric and silicon because each application requires a thermally stable film. Therefore, it is important to understand the thin film properties of WNx as a function of deposition conditions and elevated temperature exposure. In this investigation, the influence of nitrogen content and post deposition annealing on the stress and microstructure of reactive dc magnetron sputter deposited WNx films was analyzed. With an increasing N2 to Ar flow ratio, the as-deposited crystal structure of the films changed from α-W to β-W to amorphous WNx and finally to W2N. Rapid thermal anneals up to 650°C resulted in large tensile stress increases and phase transformations to W2N in the nitrogen-containing films. Grain growth during annealing decreased as the concentration of nitrogen in the film increased. The nitrogen content in the films was determined using x-ray photoelectron spectroscopy (XPS).