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Energy-dispersive X-ray spectrometry (EDXS) in the transmission electron microscope (TEM) is applied for accurate spatially resolved quantitative chemical analysis of SiGe structures implemented into high-performance complementary metal oxide semiconductor (CMOS) transistors. For fast and high-quality TEM target specimen preparation, an advanced focused ion beam (FIB)-based lift-out technique employing Be half ring grids is developed to significantly minimize post-specimen scatter artifacts during EDXS data recording. Based on systematic variation of acquisition parameters (dwell time, sampling area) at fixed beam current, the influence of electron irradiation on microstructure and composition of SiGe alloys is studied, and a critical electron fluence for beam-induced damage is identified. While chemical analysis is unaffected for smaller values, higher electron fluences cause atom displacement by surface sputtering. Applying optimal acquisition parameters for accurate composition analysis at standard TEM settings, spatially confined graded embedded SiGe cavities, introduced into the CMOS process flow to transfer compressive stress into the pMOS transistor channel, are characterized.

Nanolithography based on local anodic oxidation (LAO) by atomic force microscopy is a promising technique for patterning strained film nanostructures on the silicon substrates. Due to its versatility and precise control, LAO is suited for preparing well defined calibration structures for local strain measurements. We investigated silicon–germanium patterns prepared by LAO and subsequent selective anisotropic wet etching. By combining the nanolithography and etching, dedicated strain test structures with a line width of 65 nm were achieved and utilized for calibration of tip - enhanced Raman measurements.

A modulus mapping technique is described which provides quantitative information about the elastic properties of the near-surface region of both unpatterned and patterned silica-based low dielectric constant (low-k) thin films. The extent of oxygen plasma-induced damage has been studied using this method. Compared with quasi-static nanoindentation, the modulus mapping technique is more surface sensitive. This is first demonstrated for thin Ta layers on top of low-k films, where the effective modulus systematically increases with the Ta film thickness. Correspondingly, the effective modulus of the near-surface region of a plasma-treated low-k film is significantly higher than that measured on the same type of low-k film without treatment. Modulus mapping performed on integrated Cu/low-k structures showed that a sub-micrometer spatial resolution is clearly achievable. Furthermore, the effective modulus of patterned low-k material between inlaid copper interconnects was found to be considerably higher than the modulus measured on a blanked low-k film of the same type.

Electromigration (EM) in sub-micron metal interconnects depends on interface bonding and metal microstructure. The process of EM-induced degradation in on-chip interconnects as observed from both in-situ scanning electron microscopy (SEM) experiments at embedded inlaid copper interconnect structures and numerical simulations based on a physical model is explained based on transmission electron microscopy (TEM) brightfield images. Interface strengthening results in completely changed degradation and failure mechanisms. The changed void evolution for interconnects with strengthened interfaces, e.g. caused by additional metal coating like CoWP or self-assembled monolayers (SAMs) on top of the polished copper lines, is explained with increased atomic order and stronger bonding compared to standard Cu/SiN x interfaces.

The effect of the nitrogen content on the thermal stability and degradation mechanisms of Ta–Si–N diffusion barriers was studied using methods that prove Cu interdiffusion. On the one hand, glancing angle X-ray diffraction was applied to detect Cu 3 Si formation after annealing of Cu/Ta–Si–N/Si layer stacks. On the other hand, a combined secondary ion mass spectroscopy and transmission electron microscopy analysis of Ta–Si–N/Cu/Ta–Si–N/SiO 2 /Si samples was performed. For a detailed investigation of the microstructure evolution, the crystallization behavior of both Cu-capped and uncapped Ta–Si–N/Si samples was analyzed using X-ray diffraction. In the case of an uncapped Ta 73 Si 27 film, Si interdiffusion from the substrate precedes the layer crystallization. The substrate influence on the crystallization process decreases with increasing N content x N of the Ta–Si–N layer. Using Cu/Ta–Si–N/Si samples, a critical temperature for Cu silicide formation was determined. This temperature increases with increasing N content of the Ta–Si–N barrier. In the case of Ta–Si–N films with x N > 25 at.%, Cu interdiffusion into the substrate occurs before a significant barrier crystallization is observed. For Ta–Si–N layers with x N ≤ 25 at.%, no indications for Cu diffusion before crystalline phase formation were detected.

The influence of N content on the crystallization behavior of initially amorphous Ta–Si–N diffusion barriers deposited with a thickness of 10 nm between Cu and SiO 2 was investigated by means of glancing angle X-ray diffraction (XRD), glow discharge optical emission spectroscopy (GD-OES), transmission electron microscopy (TEM), and graphite furnace atomic absorption spectrometry (GF-AAS) after annealing for various times at a temperature of T an =600 °C. For a Ta 73 Si 27 film, only Ta silicide phases (Ta 5 Si 3 , Ta 2 Si) are formed, whereas all barriers containing nitrogen crystallize primarily into a Ta nitride. Si is not incorporated into this phase but diffuses mostly into the Cu film. Although the crystalline Ta nitride grows mainly within the original barrier region, it does not form a continuous layer. For barriers with a N content x N ≥25 at.%, the annealing time necessary to start the crystallization increases and the formed Ta nitride phases become N-richer (Ta 2 N→Ta 5 N 6 ). A Ta 30 Si 18 N 52 layer maintains its amorphous structure even after annealing for t an =100 h. With increasing N content in the barrier, the thermal stability against Cu diffusion is improved.

The degradation mechanisms of 10 nm thick Ta and Ta 73 Si 27 diffusion barriers deposited between Cu and SiO 2 are compared by means of X-ray reflectometry, glancing angle X-ray diffraction, glow discharge optical emission spectroscopy depth profiling and transmission electron microscopy analysis. Annealing the samples at T an =600 °C for t an =1 h results in a diffusion of Ta atoms through the Cu capping layer to the sample surface, particularly in the case of the pure Ta barrier. During longer heat treatment ( t an >1 h), microstructural changes occur within both barrier types. Whereas the amorphous Ta–Si layer starts to crystallize into Ta 5 Si 3 , the initially grown metastable β-Ta of the pure Ta film transforms into the equilibrium α-Ta phase. Analyzing the diffusion rate of Cu atoms into the substrate, the Ta 73 Si 27 barrier shows an enhanced thermal stability compared to the pure Ta film.

Sputter deposited Ta and TaN single layers of 10 nm thickness as well as graded TaN/Ta and Ta/TaN/Ta layer stacks that act as diffusion barriers for Cu metallization were investigated after annealing at temperatures between T an =300 and 700 °C. By means of glancing angle X-ray diffraction, glow discharge optical emission spectroscopy and transmission electron microscopy, results of microstructure and phase characterization were correlated with diffusion phenomena. For the pure Ta barrier, Ta diffusion through the Cu cap layer to the sample surface is observed at T an =500 °C, and the transformation of initially grown metastable β-Ta into the equilibrium α-Ta phase occurs at T an =600 °C. In contrast, a fcc TaN layer remains stable at least up to T an =700 °C. In the case of the graded layer stacks, first signs of N diffusion out of the TaN film into the adjacent Ta layers are observed after annealing at T an =300 °C, and formation of hexagonal Ta 2 N starts at T an =500 °C. Whereas in the course of thermal treatments for the threefold graded Ta/TaN/Ta barrier all TaN reacts with Ta to form Ta 2 N, some fcc TaN remains in the twofold graded TaN/Ta barrier.

Structural properties of thin Ta and Ta–N films acting as diffusion barriers were investigated. Blanket Ta-based films of 10 nm thickness were deposited by conventional sputtering techniques onto (100)-Si and covered with a Cu cap layer. X-ray diffraction, depth profile analysis and electron microscopy were used to correlate results of microstructure and phase characterization with diffusion phenomena. Different barrier failure mechanisms were observed after annealing at temperatures between 450 and 800 °C. Ta and Cu silicides were formed suddenly in layer stacks with pure Ta and Ta–20 at.% N barrier films at 550 °C. The application of the stoichiometric TaN as a diffusion barrier prevents the formation of Ta silicides and does not lead to significant Cu silicide formation up to 800 °C. However, trace Cu diffusion into the substrate was also detected at lower temperatures. The barrier stability against Cu diffusion is improving with increasing N content.

The ongoing scaling-down of semiconductor device structures requires new techniques for cross-sectional thin film characterization. Energy filtering transmission electron microscopy was used for both elemental mapping and electron energy-loss near edge structure (ELNES) mapping of Si compounds. Si, Si 3 N 4 and SiO 2 layers could be clearly differentiated by elemental mapping as well as by ELNES mapping. A clear differentiation of the two phases in CoSi/CoSi 2 layer stacks was only possible by ELNES mapping. It is shown that specific energy filter settings allows distinction between all the Si compounds using only the Si–L 2,3 electron energy-loss edge and the respective electron energy-loss near edge structures.