PhD

Process Technology

• Ge and III-V CMOS scaling
• Post-CMOS nano
• Reliability research at imec
• Memories
• Power devices
• GaN Power Converters
• Nanoscale properties of new materials for emerging memory de
• Ion-solid interactions
• Probing semiconductor devices on the atomic scale
• Packaging and interconnection
• SiGe-based MEMS
• RF-MEMS
• Advanced lithography
• Simulation of wafer plating uniformity
• Superfilling of 3D via structures with alternative metals
• Diamond bit cutting for metal bonding

Ion-solid interactions

One of the major challenges for process development is the engineering of the gate stack and source/drain profiles as the down scaling calls for layers which are only a few nm thick and doping profiles extending less than 10-20 nm deep. Compositional characterization of these layers is almost exclusively done with Secondary Ion Mass Spectrometry (SIMS) in view of its unchallenged sensitivity and depth resolution. SIMS is based on the interaction of a primary ion beam with the target causing particles to be sputtered from which the ionized fraction can be analyzed in a mass Spectrometer. The main problems encountered in this method are the interaction mechanisms induced by the primary ion (collision cascade, radiation enjanced diffusion, primary ion incorporation, compound formation) as well as the secondary processes (sputtering, particle ionization, cluster formation of emitted particles) and practical issues (charging, crater edge effects, roughnening, collection efficiencies, isotopic fractionation effects) which all lead to potential distortions of the recorded profile. In view of the objective to arrive at a fully quantified profile with sub-nm depth resolution, fundamental studies addressing all these aspects are required. Within Imec several Ph.D-studies have already addressed some of these problems. At present a further effort is required with an emphasis on :

• the interaction (incorporation, workfunction variation, Cs-migration, collision cascade, transients in sputter yields) of a (very) low energy Cs-beam with a semiconductor target and its influence on profile distortions (surface transients, depth resolution, tailing,..),
•  theoretical and experimental investigation of surface roughness development (ripple formation) under ion erosion and its impact on depth resolution.,
• comprehensive study of ionization mechanisms of sputtered particles. The latter is an extremely complex and challenging problem (requiring detailed physical insight) as the ionization mechanism occurs within a perturbed lattice (validity of concepts such as band structure) and depends on many parameters (workfunction of the surface, degree of oxidation of the surface, valence band structure, heat of oxide formation of individual elements, polarity of the secondary ion, …) and
• fundamental and practical aspects of quantitative analysis of multilayer systems such a Si/SiGe, Si/SiO2, high-k (Hf, Zr, Al based) dielectrica/Si whereby one is confronted with changing ionization and sputter yields and sometimes unstable materials (relaxation of strained SiGe, oxygen migration in Zr-oxides, ..)

Within this work extensive use is made of complimentary methods such as Rutherford Backscattering (1-2 MeV He-beams) to probe dynamically primary ion incorporation, ion beam mixing and X-ray Photoelectron Spectroscopy to probe chemical compositions and valence band structure. Besides the fundamental aspects the work is driven by the technological developments (and interactions with process engineers) requiring an extremely precise analysis with very near-atomic depth resolution.

Responsible scientist: Wilfried Vandervorst