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In this paper we examine the relationship between precursor structure and material properties for films produced from several leading organosilicon precursors on a common processing platform. Results from our study indicate that for the precursors tested the nature of the precursor has little effect upon film composition but significant impact on film structure and properties.
The growing importance of copper in the semiconductor industry has led to a renewed interest in the properties and growth modes of copper oxides under a variety of conditions. While thermal oxidation of copper has been studied extensively over the last decades, recent surface studies seem to ignore the possible formation of Cu3O2. It has been shown earlier that thermal oxidation of copper leads to multilayer structures, which consist of CuxO, Cu2O, Cu3O2 and CuO, depending on the oxidation conditions. These oxides were analysed ex situ using X-ray Photoelectron Spectroscopy (XPS) combined with depth profiling, Linear Sweep Voltammetry (LSV) and Galvanostatic Reduction (GR). In this work it will be shown that Raman Spectroscopy can be used to follow the formation of the different copper oxides in situ. The experiments were performed using a Raman Microscope with a sample heating extension, which enables in situ copper oxidation in air between room temperature and 300 Δ. Raman spectra were acquired in the range between 3000 Δcm-1 to 150 cm-1. From these spectra one can see that Cu20 is formed between 70 Δ and 130 Δ, Cu302 is formed between 150 Δ and 250 Δ and CuO starts to form at temperatures higher than 250 Δ.
Thin films of HfO2 high-κ dielectric have been prepared by pulsed-laser deposition (PLD) at various deposition conditions. X-ray diffraction (XRD), atomic force microscopy (AFM), and secondary ion mass spectroscopy (SIMS) were used to characterize the deposited films. Experimental results show that substrate temperature has little effect on the stoichiometry, while deposition pressure plays an important role in determining the ratio of Hf and O. The electrical properties of HfO2 Metal-Insulator-Metal (MIM) capacitors were investigated at various deposition temperatures. It is shown that the HfO2 (56 nm) MIM capacitor fabricated at 200 oC shows an overall high performance, such as a high capacitance density of ∼3.0 fF/νm2, a low leakage current of 2x10-9 A/cm2 at 3 V, etc. All these indicate that the HfO2 MIM capacitors are very suitable for use in Si analog circuit applications.
Adhesion property of Cu film on a low-k material was investigated. The low-k films deposited using a mixture of hexamethyldisilane(HMDS) and para-xylene had a dielectric constant as low as 2.7 and thermal stability up to 400°C. In this work, Ti glue layer, boron dopant, and N2 plasma treatment were applied to improve adhesion between Cu and the low-k films. Adhesion property was significantly enhanced by N2 plasma-treatment on the low-k film and boron dopant in Cu film. This enhanced adhesion was attributed to the formation of new binding states between Ti and the plasma-treated surface of the low-k film and to the diffusion of B from Cu to Ti and low-k films. Cu(B)/Ti/low-k film annealed at 350°C withstood an applied load of about 23 N during the scratch test.
The effect of different plasma pre-treatments of chemical vapor deposited (CVD) tungsten nitride (W2N) surfaces on the dewetting behavior of subsequently grown CVD Cu films was investigated by annealing the resulting film stacks in high purity argon. It was found that a hydrogen plasma pre-treatment significantly improved the resistance to Cu dewetting from the W2N surfaces while ammonia and nitrogen plasma pretreatment slightly accelerated the dewetting process. The proposed mechanisms and ramifications of these findings were discussed.
Porous low dielectric films containing nano pores (∼20Å) with low dielectric constant (<2.2), have been prepared by using various kinds of cyclodextrin derivatives as porogenic materials. The pore structure such as pore size and interconnectivity can be controlled by changing functional groups of the cyclodextrin derivatives. We found that mechanical properties of porous low-k thin film prepared with mCSSQ (modified cyclic silsesquioxane) precursor and cyclodextrin derivatives were correlated with the pore interconnection length. The longer the interconnection length of nanopores in the thin film, the worse the mechanical properties of the thin film (such as hardness and modulus) even though the pore diameter of the films were microporous (∼2nm).
Various Cu films were fabricated using sputtering and electroplating with and without additive, and their surface damages after annealing were investigated. After annealing at 435°C, the difference between damage morphologies of the films was observed. In some films stressinduced grooves along the grain boundaries were observed, while in the others voids at the grain boundary triple junctions were observed. It was also observed that the stress-induced groove was formed along the high energy grain boundaries. To explain the morphological difference of surface damages, a simple parameter considering the contributions of grain structures and grain boundary characteristics to surface and grain boundary diffusions is suggested. The effective grain boundary area, which is a function of grain size, film thickness and the fraction of high energy grain boundaries, played a key role in the morphological difference.
The reliability of Cu dual-damascene interconnect trees with 3-terminal (dotted-I), 4-terminal (‘T’) and 5-terminal (‘+’) configurations has been investigated. The lifetime of multiterminal interconnect trees with the same current density through the common middle via was determined to be independent of the number of segments connected at the common junction. Furthermore, our experimental results on dotted-I test structures showed an increase in the reliability of the interconnect tree when the distribution of a same current was not equal in the two connected segments, especially for the cases where one of the segments was acting as a passive reservoir or active source of Cu atoms for the adjoining segment. Due to the low barrier for void nucleation at the Cu/Si3N4 interface, the presence of any small atomic source in neighboring segments will enhance the reliability of a connected segment in which Cu atoms are being drained away. As a consequence, failure can occur in a tree segment which is stressed at significantly lower current densities than more highly stressed adjoining segments.
Back-end interconnect structures (BEIS) of micro-electronic devices are susceptible to several deformation phenomena during thermal excursions, because of large differences in thermal expansion coefficients (CTE) between Si, interlayer dielectric (ILD) and metal lines. Here we use atomic force microscopy (AFM) to study plastic deformation and interfacial sliding of Cu interconnect lines on embedded in a low K dielectric (LKD). Following thermal cycling, changes were observed in both inplane Cu line dimensions, as well as out-of plane step height between Cu and LKD in single layer structures. The results of AFM measurements following both ex-situ and in-situ thermal cycling presented. A shear-lag based model is utilized to simulate the thermal cycling response, and rationalize the observed interfacial sliding behavior. Results of in-situ AFM experiments to observe the deformation of Cu-low K interconnect structures under far-field (i.e., package-level) stresses are also presented.
Using a new multi-dimensional contact mechanics system, it was recently shown that the experimentally measured tangential to normal stiffness ratio of a contact can be described as a function of the bulk Poisson's ratio of the material as predicted by Mindlin [1-3]. This system has been utilized to measure the normal and tangential elastic contact stiffness of a series of porous low-k films, with increasing starting porogen content. These results indicate a transition from a material-controlled elastic behavior to a structure-controlled elastic behavior as the porosity of the film is increased. These structural effects and their potential influence on the mechanical response to forces imposed on integrated circuits are discussed. The experimental details and apparatus are introduced and described.
Metal organic chemical vapor deposition (MOCVD) TixCyNz films were deposited by using tetrakis-dimethylamino-titanium (TDMAT) and NH3 as a reaction gas at temperatures from 325 to 400°C with multi-layer Ar/NH3 plasma treatment. Effects of annealing and Ar/NH3 plasma treatment on the microstructure, composition, and electrical properties of TixCyNz films were studied. By multi-layers plasma treatment, the resistivity of TixCyNz barriers decreased from 960 to 548 νΔ–cm and the concentration of oxygen in barrier films are also decreased. The integration of the TixCyNz with low-k methylsilsesquiazane (MSZ) was investigated through Cu/CVD-TixCyNz/SiO2 and Cu/CVD-TixCyNz /MSZ capacitors after being annealed in furnace at temperatures from 500 to 800°C. With thermal annealing in N2 ambient for 30 min, Cu/CVD-TixCyNz/ MSZ structure remains metallurgically stable up to 700°C.
Porous materials are being investigated as low dielectric constant (low-k) materials. While porosity decreases the k-value of a material by decreasing its density, it simultaneously allows unwanted adsorption and diffusion of chemicals inside the porous matrix. To investigate this, different porous low-k materials, specifically silicon oxycarbide (SiOCH), methylsilsesquioxane (MSQ), and a polymer, were exposed to polar (ethanol) and non-polar (toluene) solvents. A difference in diffusion of polar and non-polar solvents would be an indication of the density of polar centers which attract polar molecules (such as water) and increase the dielectric constant of a film. The diffusion coefficient for toluene at room temperature was found to be approximately 2×10-5 cm2/sec for MSQ (40% porosity), 10-7 cm2/sec for SiOCH (7% porosity), 2×10-8 cm2/sec for the polymer. The observed diffusion can be described by a model of a viscous flow in a porous medium. The toluene/ethanol diffusion coefficient ratios were 4.4, 1.3, 1 for MSQ, SiOCH, and the polymer, respectively. The difference in toluene/ethanol diffusion can potentially be used to screen a material's affinity for water adsorption.
The influence of surfactant-based liner post-treatment on the wetting and nucleation characteristics of ultra-thin copper (Cu) films has been examined, employing ultra-thin atomic layer deposited (ALD) tantalum nitride (TaNx) as liner material. This surfactant-based posttreatment consists of in-situ exposure of the liner to a metal-organic source containing a low surface free energy metal (Sn) surfactant, which is a potential candidate for enhancing the wetting of Cu on liner surfaces and subsequently suppressing island-type growth of Cu, due to both the high atomic volume and low surface free energy of the surfactant relative to Cu. A methodology involving thermally-enhanced de-wetting of Cu, promoted by annealing Cu/liner stacks in a forming gas (95% Ar, 5% H2) ambient under several applied thermal budgets (annealing at 350°C for 30 minutes, and at 600°C for 4, 12, and 48 hrs, respectively), was utilized to both elucidate and quantify the wetting properties of Cu on liners, via detailed analyses of the surface morphology of annealed stacks by atomic force microscopy (AFM) and scanning electron microscopy (SEM). By comparing stacks containing ALD TaNx liners to those that contain post-treated ALD TaNx liners, this method allowed an evaluation of the effectiveness of surfactant-based liner surface post-treatments in inhibiting Cu de-wetting.
In this study, nanoporous silica films were prepared from the poly(hydrogen silsesquioxane)(HSSQ) and a templating agent. Three different kinds of the HSSQ with different molecular weight and Si-OH end group content were prepared through the variation of the water/triethoxysilane ratio or pH. The templaing agent for generating nanopore was triphenylsilanol (TPS). The experimental results of refractive index, dielectric constant, and FE-SEM supported the formation of the nano-size pores in the prepared silica films. The dielectric constant of the prepared nanoporous thin films could be reduced form 2.89 (porosity: 12%) to 1.85 (porosity: 58%) by increasing the added TPS. The surface roughness of the prepared nanoporous silica film in comparison with the film thickness was less than 1%. For successful generating small and uniform nanopore in the film, low molecular weight or high Si-OH content of the prepared HSSQ would be required. The current approach is useful for preparing new kinds of low dielectric constant materials.
Future interlayer dielectric (ILD) requirements necessitate reductions in dielectric constant to 2.1 within four years. Due to gaseous-like transport properties and near liquid-like densities, supercritical methods have been developed to dry and strip resist from these highly porous materials. Although a non-polar molecule, the solvating capability of supercritical CO2 (SCCO2) can be tailored by varying pressure, temperature, and co-solvents. This flexibility has been employed to remove photoresist and moisture from porous low-k films. The results of these experiments have been characterized using FTIR, ellipsometry, and SEM.
Small angle neutron and x-ray scattering (SANS, SAXS) are powerful tools in determination of the pore size and content of nano-porous materials with low dielectric constants (low-k) that are being developed as interlevel dielectrics. Several models have been previously applied to fit the scattering data in order to extract information on the average pore and/or matrix size. A new method has been developed to provide information on the size distributions of the pore and matrix phases based on the “chord length distribution” introduced by Tchoubar and Mering. Examples are given of scattering from samples that have size distributions that are narrower and broader than the random distribution typical of scattering described by Debye, Anderson, and Brumberger. An example of fitting SANS data to a phase size distribution is given.
The microelectronic industry's transition to low dielectric constant insulators in the wiring levels of integrated circuits has proven to be more difficult than expected. Materials properties are an integral part of the problem, as much for yield as for reliability. Unfortunately, many properties which are important for manufacturing robustness tend to degrade as the dielectric constant is lowered. Although materials properties are a useful guide to low-K manufacturability, inflexibility with regard to specifications could ultimately limit future progress. Application of basic principles of materials science to the integration of low-K dielectrics can give critical insight into the nature of the difficulties. Several examples of problems in low-K integration which benefit from such analysis are given.
Subcritical delamination of dielectric and metal films from organosilicate glass (OSG) thin films was studied in controlled ambient with different levels of relative humidity and in aqueous environments of varying pH. The material systems studied include OSG/SiO2, OSG/TaN and OSG/SiNx. For both sets of experiments, subcritical crack growth in OSG is found to be described by a model originally developed for soda-lime silicate glass. The threshold energy release rate for water molecule-assisted cracking varies linearly with the natural logarithm of water partial pressure. In aqueous environments, the threshold value decreases linearly with increasing pH in accordance with a simple model. The slope of crack growth rate curve also decreases with increasing pH.
The effects of various integration processes on the adhesion of SiLKTM to the Ta barrier layer were studied. We have found that the H2/He reactive plasma clean treatment (RPC) causes poor adhesion between these two layers. The results obtained from TOF-SIMS showed that hydrogen plasma had caused damage to the SiLK surface causing molecular fragmentation. Hydrogen had also been chemically incorporated into SiLK to form a hydrogen-saturated surface. To improve adhesion, an argon sputtering process was employed to remove this altered SiLK surface layer. Adhesion was found to have been improved and no delamination was observed even up to integration of 7 metal layers.
We have shown previously the results from out-of-plane and in-plane X-ray scattering /diffraction measurements together with transmission electron microscope and X-ray reflectance measurements and shown that they are effective in characterization of a periodic porous silica low-k film . In the present work, we report the results on pore-size distribution, pore-diameter anisotropy, and size and macroscopic isotropy of domain structure.