At the 65 nm node, silicide faces formidable challenges. Co is the current process of record for most integrated circuit manufacturers and thus becomes baseline silicide for 65 nm. However, Ni is the likely replacement. Both silicides are challenged to meet the requirements at the 65 nm node. This manuscript reviews the current CoSi2 challenges (dopant interactions, Ge interactions, linewidth extendibility, impurity effects, agglomeration issues, etc). Ni consumes less Si but has its own challenges, including issues with contact leakage and thermal budget, excessive diffusion and oxidation, interactions with dopant and impurities. Both silicides have formation and stability issues in the presence of Ge. Additions of Ge increase the temperature at which a low resistance CoSi2 is formed due to film segregation into CoSi2 and Ge-rich Si-Ge grains. With Ni, additions of Ge decrease the temperature at which NiSi converts to a NiSi2, lead to agglomeration at a lower temperature and lead to germanosilicide formation.

Organofluorosilicate glass (OFSG) films with the composition Si:O:C:H:F were deposited via plasma-enhanced CVD from mixtures of trimethylsilane (3MS), silicon tetrafluoride (SiF4), and oxygen (O2). OFSG films have significantly enhanced mechanical strength, thermo-oxidative stability, and adhesion compared with OSG films deposited from 3MS and O2 alone. We propose that the increased density of OFSG, which helps improve mechanical strength, is balanced by the presence on non-polarizable Si-F functionalities, which serve to lower the dielectric constant.

We report on our work to develop a process for depositing nanoporous organosilicate (OSG) films via plasma enhanced chemical vapor deposition (PECVD). This approach entails codepositing an OSG material with a plasma polymerizable hydrocarbon, followed by thermal annealing of the material to remove the porogen, leaving an OSG matrix with nano-sized voids. The dielectric constant of the final film is controlled by varying the ratio of porogen precursor to OSG precursor in the delivery gas. Because of the need to maintain the mechanical strength of the final material, diethoxymethylsilane (DEMS) is utilized as the OSG precursor. Utilizing this route we are able to deposit films with a dielectric constant of 2.55 to 2.20 and hardness of 0.7 to 0.3 GPa, respectively.

New synchrotron x-ray microbeam methodology is used to analyze and test the reliability of interconnects. The early stage of plastic deformation induced by electromigration before any damages become visible has been recently revealed by white beam scanning X-ray microdiffraction during an accelerated test on Al interconnect lines. In the present paper, we provide a quantitative analysis of the dislocation structure generated in several micron-sized Al grains in both the middle region and ends of the interconnect line during an in-situ electromigration experiment. We demonstrate that the evolution of the dislocation structure during electromigration is highly inhomogeneous and results in the formation of randomly distributed geometrically necessary dislocations as well as geometrically necessary boundaries. The orientation of the activated slip systems and rotation axis depends on the position of the grain in the interconnect line. The origin of the observed plastic deformation is considered in view of constraints for dislocation arrangements under applied electric field during electromigration. The coupling between plastic deformation and precipitation in the Al (0.5% wt. Cu) is observed for the grains close to the anode/cathode end of the line.

The evidence of copper (Cu) ion drift in low-dielectric-constant (low-k) interlayer films is clearly shown by transient capacitance measurements for the first time. The bias-temperaturestress (BTS) was applied to the copper electrode of Cu/low-k/p-Si metal-insulator-semiconductor capacitors. After injecting photoelectrons into the low-k film from the substrate, time-dependence of the capacitance was measured. When BTS-applied samples were measured, a decrement of the capacitance was observed, whereas not observed without BTS. The decrement of the capacitance was attributed to thermal emission of electrons from copper-related electronic states. By assuming an attempt-to-escape frequency of the charge from the electronic states, the energy level of Cu was estimated to be 0.8–0.9 eV below the conduction band edge.

Low dielectric fluoro-containing poly(silsesquioxanes) (PSSQs) have been synthesized using trifluoropropyl trimethoxysilane (TFPTMS), methyl trimethoxysilane (MTMS), and 2, 4, 6, 8-tetramethyl-2, 4, 6, 8-tetra(trimethoxysilylethyl) cyclotetrasiloxane. The properties of fluorocontaining PSSQs based thin films were studied by electrical, mechanical, and structural characterization. Film was spun on a silicon substrate, baked at 150°C and 250°C for 1 minute, respectively, and cured in the furnace at 420°C for 1 hour under vacuum condition. Thermally decomposable trifluoropropyl groups of the fluoro-containing PSSQ were served as a pore generator and partially contributed to lower a dielectric constant. â-cyclodextrin (CD) was also employed as a pore generator. The concentration of the pore generator in the film was varied from 0 to 30 %. The dielectric constants of the porous PSSQ films were found to be in the range of 2.7 – 1.9 (at 100 kHz). Hardness and Young's modulus of the films were measured by nano-indentation. The elastic modulus and hardness of the porous films were well correlated with the concentration of the pore generators. Positronium Annihilation Lifetime Spectroscopy (PALS) was employed to characterize a pore size of the porous fluoro-containing PSSQ film. The pore size of the film was less than 2.2 nm. The nanoporous films showed quite promising properties for commercial application.

Electromigration measurements of dual-damascene VLSI copper interconnect with sputtered TiN barrier was performed to measure both long-line (Jmax) performance and EM threshold (JLmax). Wafer-level stress of via chains with various segment lengths was combined with a statistical efficient experiment design to explore various conditions with minimum sample size. Resistance saturation was observed with exponential time constant corresponding to vacancy diffusivity. Time to opens failure by resistance increase follows Black's equation with current exponent n=1.90 and activation energy Ea=0.94 eV. Thermal gradients due to high current stress were characterized and accounted-for in acceleration models.

Electromigration reliability in Cu dual-damascene interconnects with a CVD MSQ low k dielectric was investigated. Statistical studies were carried out using the critical length (LC) test structures containing multi-link line/via elements with varying line lengths. EM lifetime characteristics, critical current density-length product (jL)c, and failure mechanisms were discussed and compared with Cu/oxide structures. Our results suggested that the diffusion at the cap layer interface was the dominant mechanism for EM mass transport. The confinement effect, in terms of an effective modulus B, can be used to account for the shorter EM lifetime and smaller critical current density-length product (jL)c observed for Cu/CVD MSQ low k interconnects. Failure analysis by FIB confirmed the presence of multiple failure modes including voiding at the via bottom, Cu extrusion and delamination at Cu/cap layer interface.

For a diffusion barrier against Cu, tantalum nitride (TaN) films have been successfully deposited by both conventional thermal atomic layer deposition (ALD) and plasma assisted atomic layer deposition (PAALD), using pentakis (ethylmethlyamino) tantalum (PEMAT) and ammonia (NH3) as precursors. The growth rate of PAALD TaN at substrate temperature 250° was slightly higher than that of ALD TaN (0.80 Å/cycle for PAALD and 0.75 Å/cycle for ALD). Density of TaN films deposited by PAALD was as high as 11.0 g/cm3, considerably higher compared to the value of 8.3 g/cm3 obtained by ALD. The N: Ta ratio for ALD TaN was 44: 37 in composition and the film contained approximately 8∼10 atomic % carbon and 11 atomic % oxygen impurities. On the other hand, the ratio for PAALD TaN layers was 47: 44 and the respective carbon and oxygen contents of TaN layers decreased to 3 atomic % and 4 atomic %. The stability of 10 nm-thick TaN films as a Cu diffusion barrier was tested through thermal annealing for 30 minutes in N2 ambient and characterized by XRD, which proves the PAALD deposited TaN film to maintain better barrier properties against Cu below 800°.

It has been discovered that the incorporation of small amounts of hydrogen silsesquioxaneco-octadecyl silsesquioxane resin into hydrogen silsesquioxane films results in a significant modification of the thermally processed thin film properties compared to standard hydrogen silsesquioxane (HSQ) films derived from FOx ® solutions. These modifications included a doubling of the modulus and significant reduction in the remaining silyl hydride level. Key to the change in properties was an accelerated oxidation of the film during a one-minute hot plate bake step under a partial oxygen atmosphere. A systematic examination of a series of 5 to 30 weight percent resin additive formulations showed improved mechanical properties at lower additive levels but these were neutralized at higher levels by increasing levels of nanoporosity. It is hypothesized that the enhanced oxidation effect is the result of increased oxygen diffusivity into the film facilitated by the hydrocarbon component of the resin additive.

The microstructure of interconnect material is know to influence its electromigration and stress-voiding properties. In addition to many factors responsible for the microstructure development, the barrier layer could be a major contributing factor as it forms the substrate for the copper films above. The microstructure of the barrier films based on its deposition technique could determine the final microstructure of the copper film. In the present work we examine the effect of two different barrier layers (Ta and TaN) and different stackings of these two materials on the microstructure on the copper seed (PVD) and electroplated films using EBSD, AFM and XRD. The results show that the plated films have a predominantly (111) texture and uniform grain size. But the (111) texture maximum varied with the barrier layer stacking underneath the plated film.

Subcritical debonding of Cu films from silicate glass substrates has been studied using a driver film method. In this method, a highly stressed Cr overlayer is imposed to debond the target Cu film from the substrate. Substrates included a commercial flat panel display glass and glasses having composition (2SiO2)x(CaO·Al2O3)1-x. A range of strain energy densities for driving interfacial crack growth was provided by depositing Cr driver layers with varying thickness. The film debond velocity was obtained experimentally. The stresses in Cu and Cr were measured and used to obtain the strain energy release rate. The effect of oxygen concentration and substrate composition on subcritical debonding was studied. A kinetic crack model previously developed for bulk ceramics was modified and applied. Differences in adhesion could be attributed to differences in density of strong Cu-O bonds across the interface.

Electromigration (EM) is a major reliability issue in VLSI. Many physical processes are involved simultaneously in an EM process, namely atom migration due to electron wind force, thermal migration due to temperature gradient, stress migration due to stress gradient, and surface migration (just when free surface is available) due to surface tension. In this work, the intrinsic EM damages of Al and Cu, that is without the effect from the surrounding materials, was investigated and compared based on the finite element analysis (FEA). The FEA results show that, in the intrinsic Al EM damage, electron wind force induced flux divergence is always the main cause of void growth; however, in the intrinsic Cu EM damage, dominant flux divergence varies with time, with the final dominant flux divergence due to electron wind force. It is also found that current density and temperature gradient are the most important factors affecting flux divergence. These simulation predictions agree with experimental observation and theoretical analysis.

Electromigration in upper M2 and lower M1 Cu lines in dual damascene interconnects was investigated by using two types of via terminated structures. Two different types of failures termed as abrupt and gradual failures were observed. Electromigration failures in M2 were mostly by gradual failures, while abrupt failures dominated in M1. Significantly different types of voids were observed in M1 as compared to those in M2, though similar resistance change was observed. Experimentally calculated activation energies for M1 and M2 indicated interfacial electromigration. Activation energy of M1 was found to be much lower than that of M2. This clearly demonstrates the asymmetry of electromigration in M2 and M1 Cu lines in dual damascene interconnects.

The film properties of WNxCy films deposited by atomic layer deposition (ALD) using WF6, NH3, and triethylboron source gases were characterized as diffusion barrier for Cu metallization. It is noted that the as-deposited film shows an extremely low resistivity of about 350 μΔ-cm with a film density of 15.37 g/cm3. The film composition measured from Rutherford backscattering spectrometry shows W, C, and N of approximately 48, 32, and 20 at.%, respectively. Transmission electron microscopy analyses show that the as-deposited film is composed of face-centered-cubic phase with a lattice parameter similar to both β-WC1-x and β-W2N with an equiaxed microstructure. The barrier property of this ALD-WNxCy film at a nominal thickness of 12 nm deposited between Cu and Si fails only after annealing at 700°C for 30 minutes while the sputter-deposited Ta (12 nm) and ALD-TiN (20 nm) fail at 650 and 600°C, respectively. It is thought that the superior diffusion barrier performance of ALD-WNxCyfilm is the consequence of both nanocrystalline equiaxed grain structure and the formation of high density film.

Elastic properties of electroplated copper films fabricated under different plating and annealing conditions have been characterized with laser-generated surface acoustic waves. For acoustic wavelengths longer than the characteristic copper grain size, the effective elastic modulus of copper was found to be unaffected by variations of the plating current as well as by the grain size variation due to different annealing temperatures. Consequently, copper thickness measurements with surface acoustic waves have been found to be more stable with respect to process variations than electrical sheet resistance measurements. For short acoustic wavelengths (∼ 2 νm), grain growth results in a significant increase of acoustic attenuation and a shift in the measured velocity. This finding opens an opportunity for copper structure monitoring by surface wave-based optoacoustic metrology.

This work presents a novel approach using supercritical carbon dioxide (SCCO2) to selectively extract poly(propylene glycol) (PPG) porogen from a poly(methylsilsesquioxane) (PMSSQ) matrix, which results in the formation of nanopores. Nanoporous thin films were prepared by spin-casting a solution containing appropriate quantities of PPG porogen and PMSSQ dissolved in PM acetate. The as-spun films were thermally cured at temperatures well below the thermal degradation temperature of the organic polymer to form a cross-linked organic/inorganic polymer hybrid. By selectively removing the CO2 soluble PPG porogen, open and closed pore structures are possible depending upon the porogen load and its distribution in the matrix before extraction. In the present work, two different loadings of PPG namely 25 wt.% and 55 wt.% were used. Both static SCCO2 and pulsed SCCO2/cosolvent treatments were used for PPG extraction. The initial results indicate that the pulsed SCCO2/cosolovent treatment was more efficient. Fourier transform infrared spectroscopy (FTIR) and refractive index measurements further corroborate the successful extraction of the porogens at relatively low temperatures (2000C). For the pure PMSSQ film, the k value is 3.1, whereas it is 1.46 and 2.27 for the open and closed pore compositions respectively after the static SCCO2 extraction and 430°C subsequent annealing. The reduction in the k-value is attributed to the formation of nanopores. The pore structure was verified from transmission electron microscopy (TEM), and from small-angle x-ray scattering (SAXS) measurements, the pore size was determined to be 1-3 nm for these films.

Polysilsesquioxanes (PSSQs) with the empirical formula (RSiO3/2)n have become very important as low-dielectric insulators for copper interconnects in the next-generation logic devices, but the detailed structure-property relationships were completely lacking. We have investigated the microstructure and functional properties of PSSQs with varying alkyl substituents and also PSSQ copolymers. As a result, significant advances have been made in the scientific understanding of PSSQ structures and significant improvements of key properties such as the crack resistance, mechanical modulus and hardness, and incorporation of nanometer-sized (<4 nm) porosity for ultra-low dielectric constants (<2.0).

The continual drive for faster interconnects requires the development of new interlayer dielectricmaterials with k values less than 2.1. Porous SiLKTM semiconductor dielectric resin wasdeveloped to achieve these low dielectric constants by introducing nanometer-sized pores intothe dense SiLK resin matrix. A quantitative description of the nano-porous morphology in low-kinterlayer dielectrics can be difficult to achieve for many reasons, including: complexities in theporous structure (size range, geometry, pore/pore interaction), inadequate mathematicaldescriptors, limitations of existing metrology technology, and availability of “tailor-made” experimental samples with a wide range of pore morphologies. On-wafer quantification of poremorphology is even more difficult as data must be obtained from extremely limited samplevolumes (thin films of ∼100-500 nm) residing on thick silicon (Si) wafer substrates.

This paper will focus on the design, development and successful application of on-wafer smallangle x-ray scattering (SAXS) technology to characterize the morphology of porous SiLK resin.It will be demonstrated, by example, that this technology is able to deliver rapid quantificationover the entire pore size range for these systems. Recently developed data acquisition, reductionand analysis tools will be described. Direct evaluation of the strengths and challenges of severalmodels used to generate average pore size and pore size distribution will be reviewed. Finally,additional capabilities offered by this technology (wafer mapping and detection of “killer” pores)will also be discussed.

In the present work, a novel method is proposed to re-construct voids in passivated metal interconnections. In this method, the conventional SEM and EBIC systems are assembled and utilized without much modification. In principle, a constant current is applied to the metal interconnections while an electron beam is scanning and impinging upon the surface of the sample. The voltage at the terminals is monitored simultaneously during electron beam scanning. Resistance change, and hence voltage perturbation are expected when the electron beam approaches the defective area, caused by uneven electron beam heating (EBH) and heat transmission. Information on defects or voids is thus obtained by analyzing the voltage alteration. Finite element simulation showed that the recorded voltage perturbation is not dependent of the length of the interconnect, but a linear function of the void volume. Thus, the method is essentially useful as the metal length has increased tremendously in copper technology. In addition, it can provide the void size and depth, with the possibility to reconstruct the entire void shape in 3D.