Dmytro Chumakov

Imaging and strain analysis of nano-scale SiGe structures by tip-enhanced Raman spectroscopy.

The spatial resolution and high sensitivity of tip-enhanced Raman spectroscopy allows the characterization of surface features on a nano-scale. This technique is used to visualize silicon-based structures, which are similar in width to the transistor channels in present leading-edge CMOS devices. The reduction of the intensive far-field background signal is crucial for detecting the weak near-field contributions and requires beside a careful alignment of laser polarization and tip axis also the consideration of the crystalline sample orientation. Despite the chemical identity of the investigated sample surface, the structures can be visualized by the shift of the Raman peak positions due to the patterning induced change of the stress distribution within lines and substrate layer. From the measured peak positions the intrinsic stress within the lines is calculated and compared with results obtained by finite element modeling. The results demonstrate the capability of the tip-enhanced Raman technique for strain analysis on a sub-50nm scale.

Depth dependence of ultraviolet curing of organosilicate low-k thin films

UV radiation curing has emerged as a promising postdeposition curing treatment to strengthen organosilicate interlayer dielectric thin films. We provide the evidence of film depth dependent UV curing which has important effects on through thickness mechanical and fracture properties. Force modulation atomic force microscopy measurements of the elastic modulus through the thickness of the films revealed evidence of periodic modulations of the glass stiffness which increased in magnitude with UV curing time. Furthermore, while significant increases in fracture energy were observed with UV curing time at the top of the organosilicate film, much lower increases were observed at the bottom. The increase in fracture energy with UV curing was film thickness dependent. The cohesive fracture resistance was less sensitive to UV curing. Possible explanations for the stiffness modulations through the film thickness involving UV light interference or phase separation by spinodal decomposition during the cure process a...

Tuning depth profiles of organosilicate films with ultraviolet curing

This study demonstrates that ultraviolet (UV) radiation curing can control depth profiles of organosilicate films. Striking differences between the effects of monochromatic and broadband UV irradiation were observed. For the same as-deposited organosilicate film and cure duration, monochromatic radiation has a greater impact on film structure, elastic modulus, and fracture resistance, but also results in a greater degree of depth dependent properties. Oscillating elastic modulus through the film thickness was observed with force modulation atomic force microscopy. We present a new standing wave model that accurately predicts the resulting depth dependent stiffness variations considering changes in film shrinkage and refractive index in terms of curing time, and can further be used to account for initial film thickness dependence of UV curing and film absorption. Promising applications of the depth dependent UV curing to produce multifunctional ultralow-k layers with a single postdeposition curing process ...

Stress-induced phenomena in nanosized copper interconnect structures studied by x-ray and electron microscopy

We present the first dynamic study of damage mechanisms in nanosized on-chip Cu interconnects caused by stress-induced voiding in advanced integrated circuits. Synchrotron-based transmission x-ray microscopy is applied to visualize the void evolution and conical dark-field analysis in the transmission electron microscopy to characterize the Cu microstructure. Our x-ray microscopy measurements showed, in contradiction to electromigration studies, no void movement over large dimensions during the stress-induced void evolution. We observed in via/line Cu interconnect structures that voids are formed directly beneath the via, i.e., in the Cu wide line at the edge of the via bottom. It is concluded that voids are originally formed at the site where eventually the catastrophic failure occurs. During stress migration tests, Cu atoms migrate from regions of low stress to regions of high tensile stress, and simultaneously, vacancies migrate along the stress gradient (within a limited range of some microns) in the ...

Novel Carbon-Cage-Based Ultralow-

A new class of materials is presented that is supposed to be a potential candidate for isolating ultra low-k thin films between metal on-chip interconnects in future CMOS technology nodes. The ideal structure of the novel carbon-cage-based materials is described by a model that assumes an ordered network (mosaic structure) with fullerenes (C60) as the nodes and linker molecules along the edges of the mosaic cells. The interior of the network represents a nanopore of a 1-nm scale. According to the molecular design-based model, structures with simple cubic and diamond-like topology of the network are considered promising candidates. A dielectric constant (k value) of 1.7 and an elastic bulk modulus of about 20 GPa are predicted of ideal combinations of network topology and linker molecules. First experimental results, based on electron energy loss spectroscopy, X-ray absorption spectroscopy, nanoindentation, and atomic force microscopy are presented. A more controlled film fabrication process is needed to get more homogeneous thin films with characteristic material parameters as predicted by the model.

k

Dual cantilever beam (DCB) mechanical testing is applied to two kinds of chips, manufactured in the 45 nm technology node. Both chips consist of different numbers of ultra low-k (ULK) dielectric layers, however, they have similarly designed crack-stop structures. It is shown that in all cases, cohesive cracking occurred in the upper ULK layers. The crack-stops hamper the crack propagation, and cracks are deflected outside the interconnect stack. The paths of the deflected crack fronts are FIB-sectioned and imaged in SEM. The increasing number of ULK layers leads to decrease in effective Gc of the stack.

Materials: Modeling and First Experiments

The adhesive and cohesive properties of organosilicate thin films are remarkably insensitive to UV curing. We demonstrate how to maximize these properties with UV standing waves together with an optical spacer underlying layer. Using a simulation of the UV cure profile through the film thickness, we demonstrate how a UV transparent SiN optical spacer layer can be selected to maximize curing at both sides of the organosilicate film with marked increases in interfacial fracture energy. On the contrary, a UV absorbing SiCN underlying layer resulted in significantly reduced UV intensities and small improvements of the interfacial fracture energies.

Fracture Toughness Assessment of Patterned Cu-Interconnect Stacks by Dual-Cantilever-Beam (DCB) Technique

High‐resolution x‐ray imaging with a spatial resolution in the 20 nm range offers unique capabilities for process development in semiconductor industry. Buried copper on‐chip interconnect structures can be studied with excellent element specific contrast. In addition, it is possible to obtain 3‐D views of fully embedded copper interconnect lines and vias. Moreover, transmission x‐ray microscopy (TXM) is a very suitable technique to study dynamical, reliability‐limiting processes like electromigration (EM) or stress‐induced voiding (SIV). Stress‐induced void formation is investigated in dual damascene Cu/SiOx and Cu/low‐k interconnect stacks. The initial pre‐stressing of the about 1.5 μm thick focused ion beam(FIB)‐prepared cross‐sections was performed by heating at a temperature of 175° C for 50 hours. Subsequently, a series of x‐ray images was recorded using images after every five hours of heating at the same temperature. The dynamical SIV experiments show for the first time directly that voids are form...

Tailoring UV cure depth profiles for optimal mechanical properties of organosilicate thin films

For successfully developing and controlling BEoL structures of the 32 nm CMOS technology node and beyond, advanced analytical techniques are needed for process development and control, for physical failure localization and analysis as well as for the investigation of reliability-limiting degradation mechanisms. These challenges are discussed from the point of view of a high volume leading-edge manufacturing.

Dynamical X‐ray Microscopy Study of Stress‐Induced Voiding in Cu Interconnects

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.