The layout dependence of process stress in Cu/low k interconnects are examined using various stress sources and layout patterns. The anisotropic grain growth stress model is compared with the conventional isotropic intrinsic stress model and the latter is found to underestimate stress concentrations in the dielectric regions near metal line ends. Both the grain growth stress in copper and the thermal mismatch stress in copper and low k dielectrics are considered in the layout dependence study. The results demonstrate that accurate stress evaluation in interconnect structures has to employ geometrical models that include layout variations. Capabilities are developed to extract these geometrical models directly from layout analysis.

Adhesion between abrasive particles and surfaces being polished plays an important role in chemical mechanical planarization (CMP) processes. The changes in particle - surface and particle – particle interactions can significantly influence the effectiveness of material removal and cleaning methods. To determine the adhesion between actual abrasive particles and different surfaces treated by the CMP process a method employing atomic force microscopy (AFM) technique is being developed.

The monolayer of silica abrasive nanoparticles was deposited on silicon wafer covered with polymer anchoring layer. High affinity of the thin polymer film to the particles and wafer ensures the stability of particles monolayer on the surface during measurements. AFM cantilever was modified with attachment of 20-40 microns hollow glass bead (representing a flat surface), which then was covered with copper using physical vapor deposition technique. Force-distance curves were collected employing AFM force volume mode and used to calculate the adhesion value. The effect of different factors (such as pH, presence of surfactants) on adhesion between copper surface and silica slurry has been studied.

We determined the most probable atomistic structure of an ultra-low-k material (k≅ 2.5) by computer simulations. Among the candidate structures generated by a molecular-dynamics calculation, the most probable one that reproduces the observed properties was selected using a first-principles density-functional-theory calculation. The candidate structures consisted of Si-O-Si network with some silicon atoms, each of which had a CH3 group or a hydrogen atom bonded. The structure with CH3 groups but no hydrogen atom reproduced the experimental properties best. This structure was then used to investigate the behaviors of the material irradiated with ultraviolet light.

This paper presents the evaluation of oxidizing and reducing plasmas for post etch pore-sealing treatments during patterning of interconnections in a porous Ultra Low-k (ULK) material. Morphological and chemical characterizations as well as electrical results (resistance, capacitance, leakage, yield) are presented for both single and dual-damascene integrations.

An automatic gas cell photoacoustic microscope has been used to characterize two laser machined air trenches in a silicon substrate from the back side. Both amplitude and phase images reveal the subsurface features. The frequency dependence of the photoacoustic signals with different laser spot sizes was compared with a 1-D model. The effect of lateral heat diffusion on subsurface defect characterization was investigated and the results can be applied to other photothermal techniques.

In this paper, two different air gap integration approaches are discussed in detail. Firstly, air gaps can be created using sacrificial materials, which are selectively removed through a capping layer either by wet- or dry-etching or by thermal decomposition. The second class benefits from the non-conformal deposition of different CVD dielectrics, which creates air gaps for narrow spaced lines. The benefit of air gaps in terms of capacitance reduction in multilevel interconnects is well known, therefore the authors will mainly concentrate on the challenges associated with the introduction of air gaps in interconnect systems. It will be shown that interconnect containing air gaps does not suffer more from reliability challenges than interconnects with porous low-k dielectrics. Therefore, air gaps can be considered as a viable option for the 32nm node and beyond.

We have observed the real-time behavior of electomigration-induced voids in both passivated and unpassivated copper interconnects in a Scanning Electron Microscope (SEM), and correlated void nucleation, growth, drift and stagnation with post-electromigration crystallographic microanalyses carried out using Electron Back-Scattered Diffraction (EBSD) analysis. Voids that nucleate at various locations along the interconnects often drift toward the cathode, where they grow, coalesce, and eventually cause electrical failure. In-situ SEM observations allowed for the tracking of void shapes and drift rates over long (multi-grain) distances. Changes in the size and the velocity of the voids were observed when the voids passed through different grains. These changes are attributed to the difference in diffusivity for different grain orientations. In passivated lines, voids were often trapped at individual grain boundaries, where they grew to cause failure, or de-trapped to continue to drift toward the cathode. In unpassivated lines, voids did not drift, but instead always nucleated and grew and grain boundaries. Locations at which voids grew in unpassivated lines, or at which voids were trapped and grew in passivated lines, were correlated with the crystallographic orientations of “upwind” and “downwind” grains. From these analyses, we find that the average electromigration interface diffusivities (z*D) as a function of grain orientation are ordered according to {100} > {111} > {110}. Quantitative analysis of void dynamics, correlated with crystallographic microanalyses, provides important data for modeling of electromigration-induced failure, and for process-optimization for improved reliability.

This study aims at assessing the role played by the coefficient of thermal expansion (CTE) and elastic modulus of low-k dielectric, in affecting the stress and deformation fields in copper interconnects. Parametric finite element analyses are conducted, varying one parameter at a time, for gaining fundamental understanding of the effect of individual properties. The analyses are based on a three dimensional model containing two levels of metal lines connected by a via. It is found that both the high CTE and low modulus values of the polymer-based dielectric contribute to the evolution of stress/strain fields in the metal structure. The low-k CTE plays a more significant role. Within certain limits, decreasing the low-k CTE and/or increasing the low-k modulus can help alleviate the plastic deformation, and thus the propensity of damage initiation, in the metal. Reducing the low-k CTE will be a more efficient and safer approach.

Plasma ash processes that cause surface damage in porous interlayer dielectric materials (ILDs) result in increased water absorption, permittivity, and metal intrusion. In this study, we employ mono-, di-, and tri-functional alkoxide silylation agents in supercritical CO2 to repair O2 ash damaged low-k methylsilsesquioxane (MSQ) films. Fourier transform infrared spectroscopy (FTIR) was performed using normal incidence transmission and attenuated total reflection (ATR) techniques to highlight differences in silylation efficiency based on agent functionality. Contact angle measurements reveal a significant change in hydrophobicity after functionalization of the O2 ashed samples with multifunctional agents. Atomic force microscopy (AFM) was utilized to determine changes in surface topography after ashing and repair.

Changing local electronic polarizability and chemical bonding in OSG in such a way that the effective permittivity - and consequently the electrical performance of the Cu/low-k structure - deteriorates only slightly and that adhesion and stiffness are improved significantly is an extremely challenging task [1], [2]. As the interconnect line spacings continue to shrink, optimization of the electrical and mechanical properties of the ILD material becomes increasingly important for Cu/low-k integration since the effect of thin regions that have been modified by special treatments on the effective material properties, e. g. keff, increases. Composition and chemical bonding, changed by plasma or beam treatments, effect the materials properties significantly. Plasma processes for resist stripping, trench etching and post-etch cleaning remove C and H containing molecular groups from the near-surface layer of OSG. Electron-beam interaction with OSG changes the chemical bonding in the low-k material. In this paper, the effect of chemical bonding on permittivity and elastic modulus is studied. Compositional analysis and chemical bonding characterization of structured ILD films with nanometer resolution is done with electron energy loss spectroscopy (EELS). The fine structure near the C-K electron energy loss edge, allows to differentiate between C-H, C-C, and C-O bonds, and consequently, between individual low-k materials and their modifications. Dielectric permittivity changes are studied based on VEELS (valence EELS) measurements and subsequent Kramers-Kronig analysis. The elastic modulus is determined with atomic force microscopy (AFM) in force modulation (FM) mode. Nanoindentation was applied as a complementary technique to obtain reference data.

This work investigates the effect of porogen loading on the fracture properties of methylsilsesquioxane (MSSQ) both before and after the porogen burnout process. The fracture behavior of the hybrid porogen/matrix materials differed significantly from that of the post-burnout materials. The most notable differences were alternative fracture paths and a trend of increasing fracture energy with increasing porogen loading. Characterization of the fracture surfaces indicate increasing amounts of carbon at the fracture interface corresponding to the increases in fracture energy and suggest bridging porogen molecules may be responsible for the increase in adhesion for the hybrid materials.

The use of porous ultra-low-k materials between interconnections for sub 45nm technologies has introduced some barrier diffusion and mechanical problems. In order to avoid the problems caused by the porosity, a hybrid dense material (porogen and matrix) can be used in an alternate integration scheme. In this approach, the porogen is removed after CMP steps by a thermal cure or UV assisted thermal cure. In this work, we have first characterized the impact of the temperature and the duration of the thermal cure on the material. The crosslinking degree increases and the porogen amount decreases with increasing cure temperature. The most important impact of the curing duration happens between 350°C and 400°C. The increase of the curing duration leads to an increase of the porogen loss and a decrease of the refractive index. Secondly, in order to assess the structure of the layer as a function of the depth, the material was etched in a 0.05% HF solution and then characterized. According to the temperature and duration of the cure, the etch-rate can vary as a function of the material depth. This variation is related to a complex gradient inside the material.

The Scanning X-Ray Submicron Diffraction (μ-SXRD) technique using focused synchrotron radiation white beam developed in the Beamline 7.3.3 at the ALS Berkeley Lab has been used to study the microstructural evolution at granular level of Cu polycrystalline lines during electromigration. Plastic deformation was observed in damascene Cu interconnect test structures during this in situ electromigration experiment and before the onset of visible microstructural damage (voiding, hillock formation). We show here that the extent of this electromigration-induced plasticity is dependent on the line width. In wide lines, plastic deformation manifests itself as grain bending and the formation of subgrain structures, while only grain rotation is observed in the narrower lines. The analysis of the Laue reflections allow for the determination of the geometrically necessary dislocation density in individual grains as well as for the misorientation angles between small angle boundaries generated by polygonization. The deformation geometry leads us to conclude that dislocations introduced by plastic flow lie predominantly in the direction of electron flow and may provide additional easy paths for the transport of point defects. Furthermore, we observe that the rotation axis of this plastic deformation coincides with one of the <112> line directions of the known slip systems for FCC crystal, and that it is always very close (within a few degrees) to the direction of the electron flow. This finding suggests a correlation of the proximity of certain <112> line directions to the direction of electron flow with the occurrence of plastic behavior. One important practical implication of this particular finding is that the grain texture of the line might thus play an important role in giving higher resistance towards early plastic response of the Cu line upon the electromigration loading.

As the dimensions of interconnects shrink, the confinement effects associated with a very small grain size lead to a significant increase in the resistivity of the metal. Cu resistivity models have been proposed using the classical Fuch and Sondheimer approach for surface effect, and the Mayadas and Shatzkes approach for the grain boundary effect. In these models, three adjustable parameters must be used. Good agreement between experimental data and models can easily be obtained. However, numerous fitting parameter sets can be used with equivalent fitting quality and opposite physical meaning. In this work, experiments dedicated to model parameter extraction are proposed and released. They are based on the used of Cu lines with various line widths and heights. Classical resistivity increase with line width and line height decrease is observed. The resistivity behaviour is modelled. In this case, limited fitting parameter options are obtained. For Cu narrow lines confined with Ta, these parameters suggest maximum surface effect, medium grain boundary effect and low impurity content inside the lines.

A novel design electroplating spring frame structure specimen is demonstrated here. The specimen can be fit into a specially designed microtensile apparatus which is capable of carrying out a series of tests on submicron scale freestanding thin films.

Certain thin films applicable in CMOS interconnect and low K materials were tested including sputtered Copper, Tantalum Nitride thin films. Metal specimens were fabricated by sputtering. For Tantalum Nitride film samples, Nitrogen gas was introduced into the chamber during sputtering Tantalum films on the silicon wafer.

We found the modulus of Copper and Tantalum Nitride thin films thin films with thickness of 200 to 800nm at room temperature.

As the industry develops processes for the 65 and 45 nm technology nodes, post etch/ash cleaning faces new challenges with far more stringent requirements on surface cleanliness and materials loss. The introduction and integration of new materials, such as metal hard mask, creates additional requirements for wafer cleaning due to the occurrence of new defect modes related to metal hard mask. These include organometallic residue and metal fluorite compounds precipitating with time. We have developed a novel aqueous solution (AQ) based single wafer cleaning process to address these new defect modes. Physical characterization results and process integration electrical data and reliability data (TEM cross section review of the vias) are presented in this paper.

The main conclusions can be summarized as follows: (1) In the dual damascene Cu/low-k process flow with hard mask, there are three typical residues after etch/ash: generic polymer residue, organometallic residue strongly bonded to metal maks, and time-dependent metal fluoride residue. (2) Generic polymer residue is very well characterized [1,2] and is usually easy to remove with solvent or aqueous solution [2,3]. (3)We developed an oxidizing chemistry based process to undercut the hard mask for the organometallic residue removal, which proved highly effective. (4)The time-dependent metal fluoride reside makes queue time control after etch/ash very critical (<1 hour). We developed a process with a fluorine based aqueous chemistry to address the metal fluoride residue, which proved highly effective. With this new process, queue time control is not required. (5) The post etch/ash cleaning for the Cu/low-k structure with metal hard mask typically employs the solvent/dry plasma ash multi-step procedure [4]. The new process developed in this research reduced the multi-step process to one wet clean step with two different aqueous chemistries in sequence. (6) The integration electrical data shows that the new single step aqueous cleaning process performance is comparable to, or even better than that from the solvent/dry plasma ash multi cleaning process. (7) Blanket Cu loss with the new process is about 23A/min, however TEM analysis of the vias after full integration shows Cu loss, we are working to improve the integration related Cu loss.

Spin-on glass organosilicate films are promising Ultra Low-ĸ (ULK) interlevel dielectric candidates in which porosity can be created by incorporating thermally labile porogens. The as-deposited film (called the hybrid film) consists of a methylsilsesquioxane (MSQ) matrix and an organic porogen. The standard porogen removal step consists of a 450°C thermal annealing. However, it leaves polymeric residues suspected to cause an incomplete matrix crosslinking and, consequently, to be detrimental to the porous film's electrical and mechanical properties. In this work, a supercritical fluid (SCF) treatment, performed on a 200 mm tool, was added before the thermal annealing with the intent of improving the dielectric properties. Electrical and mechanical properties were greatly enhanced: the dielectric constant was reduced from 2.5 to 2.1 and the Young's modulus was increased from 2 GPa to 3 GPa. Porogen residue removal and cross-linking improvements were investigated by Fourier Transform Infrared (FTIR) spectroscopy in transmission and multiple internal reflection (MIR) mode.

During the self-annealing in the copper electrodeposits for the copper metallization, an in-situ observation of grain growth of the copper at room temperature was performed by using EBSD (electron backscatter diffraction). The thin film structure of the copper electrodeposits after annealing was columnar. New twin was initiated at the front surface of growing twin and grew along the normal direction of the twin boundary between the new and parent twins. It was confirmed that the annealing twin in the copper electrodeposits during the self-annealing have an {111} growth front surface.

Chemical mechanical polishing (CMP) of copper was investigated in hydrogen peroxide and arginine slurries. Arginine was found to be a complexing agent for the copper in peroxide based slurries, in the alkaline region. The copper polish rate was measured in a Struers LaboPol-5 and LaboForce-3 CMP polishing tool. Static etch rate experiments of copper discs (25.4 mm Dia × 10 mm) were carried in 200 ml beakers with different combinations of hydrogen peroxide and arginine concentrations. Peroxide concentration was varied from 0 to 10 vol%, while the arginine concentration was varied from 0 to 1 wt% for both static etch and polish rate experiments. Fumed silica used as the abrasive medium for polishing.

The electrochemical processes involved in oxidative dissolution of copper were investigated by the Tafel corrosion plots and OCP measurements, using the Princeton Applied Research potentiostat. Three electrode corrosion flat cell was used for the electrochemical measurements. Corrosion current density and open circuit potentials (OCP) were used to elucidate the oxidative behavior of peroxide and the complexing role of arginine. Surface characteristics of the polished copper surface were analyzed with the Digital Instruments NanoScope AFM. Polishing with these chemicals resulted in smooth finish.

These results indicated that the arginine curtails the formation of oxidative layer on the copper surface and the removal rate was increased by forming complex with the copper.

Interaction of moisture with porous low-k films is evaluated by using in situ ellipsometry setup. The adsorbed water amount is calculated from change of refractive index measured during the adsorption. Pristine low-k films reversibly adsorb 2 - 5% of water that reflects presence of constitutive hydrophilic centrums. Plasma and thermal treatments increase the number of hydrophilic centrums. Once the amount of these centrums has reached a certain critical value sufficient to form a continuous water film, bulk water condensation is observed. Change of properties during the water adsorption in the damaged films is not fully reversible. Each additional adsorption cycle increases the dielectric function of the film because of decreasing porosity, increasing skeleton density and shrinkage. The pressure corresponding to the bulk condensation allows us to calculate internal contact angle (internal surface energy) of low-k materials. The water molecules adsorbed on separate OH groups play the role of a catalyst that hydrolyses the siloxane bridges initially present on hydrophobic surface.