Browsing by Author "Rosseel, Erik"

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On the Evolution of Strain and Electrical Properties in As-Grown and Annealed Si: P Epitaxial Films for Source-Drain Stressor Applications
(2018) Dhayalan, Sathish Kumar; Kujala, Jiri; Slotte, Jonatan; Pourtois, Geoffrey; Simoen, Eddy; Rosseel, Erik; Hikavyy, Andriy; Shimura, Yosuke; Loo, Roger; Vandervorst, Wilfried
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Heavily P doped Si:P epitaxial layers have gained interest in recent times as a promising source-drain stressor material for n type FinFETs (Fin Field Effect Transistors). They are touted to provide excellent conductivity as well as tensile strain. Although the as-grown layers do provide tensile strain, their conductivity exhibits an unfavorable behavior. It reduces with increasing P concentration (P > 1E21 at/cm(3)), accompanied by a saturation in the active carrier concentration. Subjecting the layers to laser annealing increases the conductivity and activates a fraction of P atoms. However, there is also a concurrent reduction in tensile strain (
On the manifestation of phosphorus-vacancy complexes in epitaxial Si:P films
(2016-02-22) Dhayalan, Sathish Kumar; Kujala, Jiri; Slotte, Jonatan; Pourtois, Geoffrey; Simoen, Eddy; Rosseel, Erik; Hikavyy, Andriy; Shimura, Yosuke; Iacovo, Serena; Stesmans, Andre; Loo, Roger; Vandervorst, Wilfried
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
In situ doped epitaxial Si:P films with P concentrations >1 × 1021 at./cm3 are suitable for source-drain stressors of n-FinFETs. These films combine the advantages of high conductivity derived from the high P doping with the creation of tensile strain in the Si channel. It has been suggested that the tensile strain developed in the Si:P films is due to the presence of local Si3P4 clusters, which however do not contribute to the electrical conductivity. During laser annealing, the Si3P4 clusters are expected to disperse resulting in an increased conductivity while the strain reduces slightly. However, the existence of Si3P4 is not proven. Based on first-principles simulations, we demonstrate that the formation of vacancy centered Si3P4 clusters, in the form of four P atoms bonded to a Si vacancy, is thermodynamically favorable at such high P concentrations. We suggest that during post epi-growth annealing, a fraction of the P atoms from these clusters are activated, while the remaining part goes into interstitial sites, thereby reducing strain. We corroborate our conjecture experimentally using positron annihilation spectroscopy, electron spin resonance, and Rutherford backscattering ion channeling studies.
Source/Drain Materials for Ge nMOS Devices: Phosphorus Activation in Epitaxial Si, Ge, Ge1-xSnx and SiyGe1-x-ySnx
(2020-05-07) Vohra, Anurag; Makkonen, Ilja; Pourtois, Geoffrey; Slotte, Jonatan; Porret, Clement; Rosseel, Erik; Khanam, Afrina; Tirrito, Matteo; Douhard, Bastien; Loo, Roger; Vandervorst, Wilfried
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
This paper benchmarks various epitaxial growth schemes based on n-type group-IV materials as viable source/drain candidates for Ge nMOS devices. Si:P grown at low temperature on Ge, gives an active carrier concentration as high as 3.5 × 1020 cm−3 and a contact resistivity down to 7.5 × 10−9 Ω.cm2. However, Si:P growth is highly defective due to large lattice mismatch between Si and Ge. Within the material stacks assessed, one option for Ge nMOS source/drain stressors would be to stack Si:P, deposited at contact level, on top of a selectively grown n-Si y Ge1−x−y Sn x at source/drain level, in line with the concept of Si passivation of n-Ge surfaces to achieve low contact resistivities as reported in literature (Martens et al. 2011 Appl. Phys. Lett., 98, 013 504). The saturation in active carrier concentration with increasing P (or As)-doping is the major bottleneck in achieving low contact resistivities for as-grown Ge or Si y Ge1−x−y Sn x . We focus on understanding various dopant deactivation mechanisms in P-doped Ge and Ge1−x Sn x alloys. First principles simulation results suggest that P deactivation in Ge and Ge1−x Sn x can be explained both by P-clustering and donor-vacancy complexes. Positron annihilation spectroscopy analysis, suggests that dopant deactivation in P-doped Ge and Ge1−x Sn x is primarily due to the formation of P n -V and Sn m P n -V clusters.