Advanced nanoscale characterization concepts for copper interconnection technologies /
- Autores: Tobias Berthold
- Directores de la Tesis: Günther Benstetter (codir. tes.), Rosana Rodríguez Martínez (codir. tes.)
- Lectura: En la Universitat Autònoma de Barcelona ( España ) en 2017
- Idioma: español
- Tribunal Calificador de la Tesis: Sergi Claramunt Ruiz (presid.), Vanessa Iglesias Santiso (secret.), Franz Daiminger (voc.)
- Programa de doctorado: Programa de Doctorado en Ingeniería Electrónica y de Telecomunicación por la Universidad Autónoma de Barcelona
- Materias:
- Enlaces
- Resumen
For the implementation of a direct copper-copper interconnection technology, the different properties of copper (Cu), especially the oxidation behavior, impede the easy transition to Cu compared to standard materials such as aluminum or gold. Since Cu is subject to oxidation, even at room temperature, the characterization of the Cu surface is an important aspect for the process development.
A novel method to research the oxidation behavior of the Cu surface in the nanoscale was developed by using combined characterization techniques. Characteristic values of the Contact Potential Difference (CPD) were obtained for the copper oxide states. By this means, Peakforce Kelvin Probe Force Microscopy (PF-KPFM) enabled to distinguish between the different types of Cu oxide with nanometer resolution and to correlate the oxidation states to local topography features.
Beside the nanoscale characterization of the Cu surface, novel passivation layer in the nanometer range were introduced to achieve reliable and stable surface conditions without limiting the ability for interconnection processes.
For advanced atomic force microscopy (AFM) investigations of chemical surface modifications or very soft organic protective coatings, the AFM probe tip needs to be operated in a liquid environment. The presented numerical model is able to provide accurate predictions of the drag forces present in AFM fluid imaging applications. It could be shown that triangular cantilevers provide significant lower drag forces. The influence of different liquids such as ultrapure water or an ethanol-water mixture as well as the temperature induced variation of the drag force could be demonstrated.
Studies showed that thin organic Self-Assembled Monolayer (SAM) act as effective barrier to protect Cu from corrosion. The numerical model improved the AFM fluid measurements and enabled the nanoscale characterization of the CH3-terminated SAM film protecting the Cu surface. Torsional Resonance Tunneling AFM (TR-TUNA) and dynamic Chemical Force Microscopy (dCFM) enabled the correlation of high hydrophobicity and low tunneling current on nanometer scale with intact film integrity and vice versa. Compared with additional analyses, high current and low hydrophobicity could be assigned to local SAM film disintegration and local oxidation of the Cu surface at 100 °C. 150 °C finally leads to a complete decomposition of the SAM film.
In addition to SAM films, the protective effect of platinum (Pt) and carbon (C) based films deposited onto Cu surfaces was reported by combined non-destructive Scanning Electron Microscopy (SEM) techniques and PF-KPFM. A C film provides a much better protective effect than a Pt layer. Besides very local sporadically distributed Cu oxide grains, a gradual degradation of the C film was not observable for a temperature up to 200 °C and layer thicknesses down to 3 nm. In contrast, the 10 nm Pt protected Cu surface exhibits already at a temperature of 150 °C locally grown Cu oxide grains. The C film passivated Cu surface has the potential of being a key technique for a reliable Cu-Cu wire bonding.
Beside the research of the Cu pad surface, the Cu free air ball (FAB) formation in the ambient environment was investigated by using SEM based characterization techniques. Topographic changes of FABs with various diameters could be assigned to different oxidation layers which were well below a thickness of 55 nm. Element mappings of cross sectioned FABs showed that the oxidation occurs only on the surface. A finer grain structure and a lower grain size could be achieved by lower discharge voltages. In contrast, a lower dislocation density at the borders could be detected for higher EFO voltages. The heat transfer up to the wire and the convective cooling by the surrounding air could explain the introduced conclusions regarding the oxidation and the dislocation density.
