Nanoindentation Methodologies for Characterizing Thin (Porous) Low Dielectric Constant Materials and Copper Pads

The continuous scaling of integrated circuits and miniaturization of microelectronic devices with higher device densities to increase the performance, have led to the introduction of highly porous low dielectric constant (low-k) materials and miniature cu nails and pads. A factor that plays an increasing role in the development of these new technologies is mechanical stress. The processing, assembly and packaging of chips introduce stresses and all the building blocks should be designed and selected such that they can withstand these stresses. It is not known in detail what the strength and mechanical properties are of these small films and structures, which stresses they can survive and which parameters affect their mechanical response. Therefore, it is important to assess the mechanical properties of porous materials and Cu pads in a reliable and reproducible way. To date, nanoindentation is the most commonly used technique in the semiconductor industry to assess the mechanical properties (elastic modulus, hardness, fracture toughness and adhesion etc.) of such materials. However, special care is required when nanoindentation is performed on ultra-thin porous materials or small Cu nails or pillars since the response will be affected by the thickness, tip geometry, porosity and material/probe interactions. The focus of this PhD is to use the nanoindentation technique at its limits to understand and assess the elastic and plastic properties of porous and confined-micro size materials. Finite-element analysis is used to help getting deeper insight and fundamental understanding.status: publishe

Extraction of elastic modulus of porous ultra-thin low-k films by two-dimensional finite-element simulations of nanoindentation

Continuous scaling of integrated circuits has led to the introduction of highly porous low dielectric constant (low-k) materials, whose inferior mechanical properties raise concerns regarding the reliability of integrated circuits. Nanoindentation is proven to be a straightforward method to study mechanical properties of films. However, in the case of low-k, the measurement and analysis are complex due to the porous nature of the films and reduced film thicknesses which give rise to substrate effects. A methodology that combines nanoindentation experiments with finite-element simulations is proposed and validated in this study to extract the substrate-free elastic modulus of porous ultra-thin low-k films. Furthermore, it is shown that imperfections of the nanoindentation probe significantly affect the finite-element results. An effective analytical method that captures the actual nanoindenter behavior upon indentation is proposed by taking both tip radius and conical imperfections into account. Using this method combined with finite element modeling, the elastic modulus of sub-100 nm thick low-k films is successfully extracted. Standard indentation tests clearly overestimated the actual modulus for such thin films, which emphasizes the importance of the proposed methodology.status: publishe

Tuning the properties of periodic mesoporous organosilica films for low-k application by Gemini surfactants

Periodic mesoporous organosilica (PMO) thin films were synthesized by evaporation-induced self-assembly of 1,2-bis(triethoxysilyl)ethane and an ionic Gemini 16-12-16 surfactant under acidic conditions. The films were characterized by Fourier-transform infrared spectroscopy, grazing-incidence small-angle X-ray scattering, ellipsometric porosimetry, impedance measurements, and nanoindentation. The ease of control of the packing parameter in Gemini surfactants makes the PMO film templated by a Gemini an exciting first step towards small pore size PMO films with engineered mesostructures

Vapor-deposited zeolitic imidazolate frameworks as gap-filling ultra-low-k dielectrics

The performance of modern chips is strongly related to the multi-layer interconnect structure that interfaces the semiconductor layer with the outside world. The resulting demand to continuously reduce the k-value of the dielectric in these interconnects creates multiple integration challenges and encourages the search for novel materials. Here we report a strategy for the integration of metal-organic frameworks (MOFs) as gap-filling low-k dielectrics in advanced on-chip interconnects. The method relies on the selective conversion of purpose-grown or native metal-oxide films on the metal interconnect lines into MOFs by exposure to organic linker vapor. The proposed strategy is validated for thin films of the zeolitic imidazolate frameworks ZIF-8 and ZIF-67, formed in 2-methylimidazole vapor from ALD ZnO and native CoOx, respectively. Both materials show a Young's modulus and dielectric constant comparable to state-of-the-art porous organosilica dielectrics. Moreover, the fast nucleation and volume expansion accompanying the oxide-to-MOF conversion enable uniform growth and gap-filling of narrow trenches, as demonstrated for 45 nm half-pitch fork-fork capacitors.status: Published onlin