The performance improvement at every new technology node increasingly encounters constraints in access resistances and overall conductivity within various components of the device. For that purpose, various solutions to improve dopant activation and/or more specifically layer conductivity are investigated. These encompass alternative technologies (laser anneal, co-doping) leading to improved dopant activation, stress engineering for enhancing activation as well as higher carrier mobility and exploiting new high-mobility materials (Ge, SiGe, III-V) again for improving mobility and thus conductivity. The reduced dimensionality of future devices creates additional difficulties due to the dramatically different surface/volume ratio’s (changing the relative concentrations of dopant atoms versus interstitials and vacancies which impacts on diffusion and activation), the ubiquitous presence of the surface (causing loss of dopants by surface migration), non-uniform strains and reduced dimensions (impacting on bandgap and thus activation etc.). From a theoretical point of view, such effects can be studied using atomistic modeling approaches but the dimensions of the model to be used to account for these contributions require the development of innovative approaches. Vice versa, since all these devices moved from planar to three-dimensional architectures with very limited volumes, the metrology approaches used to determine dopant activation and incorporation as well as strain are severely challenged as well.
This project aims at tackling these critical issues by a global approach whereby the necessary modelling tools are developed and exploited concurrently with the exploitation and optimization of advanced 3D-metrology.
On the modelling side emphasis will be set on the development of realistic atomistic models whose dimensions are compatible with the ones probed with APT and on the improvement of methodologies to:
- Evaluate the dopant solubility & activation in confined dimensions (impact of surface effects)
- Establish the role of stress/strain relaxation @ the atomic level on the doping profile
This requires developing innovative multi-physics approaches to capture the complexity of the atomic structure of the devices investigated, whose dimensions typically span beyond the current state-of-the-art capabilities of atomistic modeling techniques.
Experimentally, the project targets investigating the use of Atomprobe tomography to probe the dopants in confined volume with near atomic scale resolution. The latter may require further improvements of the APT technique itself as well in order to meet the required precision, spatial accuracy. Moreover, advanced data algorithms (cluster analysis) may be required to extract the dopant clustering as a source of dopant deactivation. These studies are to be complemented by metrology probing the electrical activation and carrier density using for instance sheet resistance on single fins or nanowires using micro-four point probes, and 3D-carrier distributions using Scanning Probe Microscopy 9SSRM, C-AFM, KPFM). As SPM is inherently 2D, the exploration of 3D-devices (nanowires, nanosheets,..) requires the use of the Scalpel technique whereby SPM-tips are also used to remove (on the atomic scale) material thus essentially creating a three-dimensional probing concept. For the Strain metrology into confined volumes you will collaborate with experts in Raman Spectroscopy and Transmission Electron Microscopy. Ultimately the correlation between modelling and metrology will be used to explain the electrical behavior of various technologies implement into dedicated test structures such that their electrical properties can be determined relative to a complete device to understand the impact of the contact geometry and of the confinement on the free carriers and currents inside the investigated structures. This work will be done in the characterization group of imec in conjunction with activities within the modelling group. The results are of relevance for multiple projects at Imec and of high relevance for many of its industrial partners.
Required background: engineering technology, engineering science, computer science or equivalent
Type of work: 20% literature, 30% modelling, 30% metrology, 20% device analysis and technology
Supervisors: Wilfried Vandervorst and Geoffrey Pourtois
Daily advisor: Claudia Fleischmann
The reference code for this PhD position is STS1804-01. Mention this reference code on your application form.