Erik Rosseel

Shapiro steps in a superconducting film with an antidot lattice

Shapiro voltage steps at voltages V_n=nV_0 (n integer) have been observed in the voltage-current characteristics of a superconducting film with a square lattice of perforating microholes (antidots)in the presence of radiofrequent radiation. These equidistant steps appear at the second matching field H_2 when the flow of the interstitial vortex lattice in the periodic potential created by the antidots and the vortices trapped by them, is in phase with the applied rf frequency. Therefore, the observation of Shapiro steps clearly reveals the presence of mobile intersitial vortices in superconducting films with regular pinning arrays. The interstitial vortices, moved by the driving current, coexist with immobile vortices strongly pinned at the antidots.

Surface and grain boundary scattering studied in beveled polycrystalline thin copper films

The inverse relationship between film thickness and electrical resistivity of metallic films is usually studied by depositing a series of films with different thickness and measuring their sheet resistance with a four-point probe. However, the structure and uniformity of polycrystalline thin films typically depend on thickness, rendering it difficult to establish the dominant electron scattering mechanism. In order to circumvent the uniformity issue we now use beveled films to establish the thickness dependent resistivity of thin copper films. Here the resistivity of films down to a few nm’s can be studied without, e.g., a percolation effect. Additionally, the comparison of data obtained on samples where beveling took place either before or after anneal is used to study the impact of grain size on resistivity. It is shown that the normally observed strong increase in resistivity is dominated by grain boundary scattering. However, the influence of surface scattering can be clearly observed when thick films...

Comparative study of size dependent four-point probe sheet resistance measurement on laser annealed ultra-shallow junctions

In this comparative study, the authors demonstrate the relationship∕correlation between macroscopic and microscopic four-point sheet resistance measurements on laser annealed ultra-shallow junctions (USJs). Microfabricated cantilever four-point probes with probe pitch ranging from 1.5to500μm have been used to characterize the sheet resistance uniformity of millisecond laser annealed USJs. They verify, both experimentally and theoretically, that the probe pitch of a four-point probe can strongly affect the measured sheet resistance. Such effect arises from the sensitivity (or “spot size”) of an in-line four-point probe. Their study shows the benefit of the spatial resolution of the micro four-point probe technique to characterize stitching effects resulting from the laser annealing process.

High quality Ge epitaxial layers in narrow channels on Si (001) substrates

We demonstrate the selective growth of high quality Ge epitaxial layers in channels as narrow as 10 nm on patterned Si (001) substrates by a combination of low temperature growth and selective recrystallization using Ge melt and regrowth during a millisecond laser anneal. Filling narrow trenches at high growth temperature as required for obtaining high quality layers was shown to be prohibited by Ge outdiffusion due to the high Ge chemical potential in such narrow channels. At low temperature, a hydride-terminated surface is maintained which counteracts the outdiffusion of the Ge adatoms and provides excellent trench filling. The resulting low crystalline quality can be restored by a selective Ge melt and epitaxial regrowth using a millisecond laser anneal.

Ultra Shallow Arsenic Junctions in Germanium Formed by Millisecond Laser Annealing

DTU Orbit (15/03/2019) Ultra Shallow Arsenic Junctions in Germanium Formed by Millisecond Laser Annealing Millisecond laser annealing is used to fabricate ultra shallow arsenic junctions in preamorphized and crystalline germanium, with peak temperatures up to 900 degrees C. At this temperature, As indiffusion is observed while yielding an electrically active concentration up to 5.0 x 10(19) cm(-3) for a junction depth of 31 nm. Ge preamorphization and the consecutive solid phase epitaxial regrowth are shown to result in less diffusion and increased electrical activation. The recrystallization of the amorphized Ge layer during laser annealing is studied using transmission electron microscopy and spectroscopic ellipsometry.

VORTEX CONFIGURATIONS IN A PB/CU MICRODOT WITH A 2 X 2 ANTIDOT CLUSTER

We present a detailed study of the transport properties of a superconducting Pb/Cu microdot with a 2x2 antidot cluster. The superconducting-normal (S/N) phase boundary, critical currents and current-voltage characteristics of this structure have been measured. The S/N phase boundary as a function of field B (T_c(B)) reveals an oscillatory structure caused by the limited number of possible vortex configurations which can be realized in these small clusters of pinning centres (antidots). We have analyzed the stability of these configurations and discussed the possible dissipation mechanisms using the critical current (J_c(B)) and voltage-current (V(I)) characteristics data. A comparison of the experimental data of T_c(B) and J_c(B) with calculations in the London limit of the Ginzburg-Landau theory confirms that vortices can indeed be pinned by the antidots forming a cluster and that the ground-state configurations of the vortices are noticeably modified by sending current through the structure. The possibility of generating phase-slips as well as motion of the vortices in the 2x2 antidot cluster has also been discussed.

Study of ohmic contacts to n-type Ge: Snowplow and laser activation

Typical contacts to n-Ge result in high specific contact resistivity (ρC) or rectifying behaviour due to Fermi level pinning (resulting in high barrier heights) and low dopant activation generally observed for n-Ge. In this work, we fabricated and studied ohmic contacts to n-type Ge prepared by Ni germanidation of samples with As ion implantation for two different approaches: (1) dopant activation by sub-melt laser anneal (LA) prior to germanidation and (2) Snowplow, i.e., dopant segregation during Ni germanidation without previous thermal activation. Low resistivity ohmic contacts of 8 × 10−7 Ω cm2 for LA and 2 × 10−5 Ω cm2 for Snowplow were obtained using circular transfer length method to determine ρC. We show contacts to be thermally stable to 350 °C. Furthermore, by studying the temperature dependence of ρC, we clarify that the underlying cause of the low contact resistivity for both approaches is the high active dopant concentration obtained. We find the results in both cases to be consistent with t...

Atomic Layer Deposition of Gd-Doped HfO2 Thin Films

Gd x Hf 1-x O y thin films were deposited by atomic layer deposition (ALD) using tris(isopropyl-cyclopentadienyl) gadolinium [Gd( i PrCp) 3 ] and HfCl 4 in combination with H 2 0 as an oxidizer. Growth curves showed a nearly ideal ALD behavior. The growth per individual Gd( i PrCp) 3 /H 2 O or HfCl 4 /H 2 O cycle was 0.55 A, independent of the Gd/(Gd + Hf) composition x in the studied range. This indicates that the amount of HfO 2 deposited during a HfCl 4 /H 2 O cycle was essentially identical to the amount of Gd 2 O 3 deposited during a Gd( i PrCp) 3 /H 2 O cycle, assuming identical atomic densities of the films independent of composition. The crystallization of Gd x Hf 1-x O y , with Gd/(Gd + Hf) contents x between 7 and 30% was studied. Films with x ≳ 10% crystallized into a cubic/tetragonal HfO 2 -like phase during spike or laser annealing up to 1300°C, demonstrating that the cubic/tetragonal phase is thermally stable in this temperature range. A maximum dielectric constant of K ~ 36 was found for a Gd/(Gd + Hf) concentration of x ~ 11%.

Silicide yield improvement with NiPtSi formation by laser anneal for advanced low power platform CMOS technology

A novel silicide formation technique using milli-second anneal is reported for the first time, delivering superior silicide film morphology that translates electrically into significant yield improvement over a conventional soak anneal, without any degradation of transistor performances. In addition, we demonstrate how this new technique enables the integration of thin silicides required for further junction scaling, and demonstrate up to 6nm gate length reduction and more than 1 decade junction leakage imporvement.

Analysis of Dopant Diffusion and Defect Evolution during sub-millisecond Non-melt Laser Annealing based on an Atomistic Kinetic Monte Carlo Approach

n-type dopant diffusion during sub-millisecond (ms) non-melt laser annealing (NLA) is investigated through the experiments and atomistic KMC modeling. Laser-only annealing can improve the n-type dopant activation and achieve shallow junctions. KMC model with vacancy complexes indicates that laser-only annealing for nFET can achieve highly activated junctions and reduce dopant fluctuations in the channel region and that P is an attractive replacement for the As extension with laser-only anneal.Sub-millisecond (ms) non-melt laser annealing (NLA) is investigated through experiments and atomistic KMC modeling. NLA can improve the dopant activation dramatically and achieve shallow junctions. B diffusivity during sub-ms annealing is discussed for the first time. The KMC model with FnVm complexes indicates that the thermal budget of sub-ms annealing is too small for full defect evolution and one possible solution for defect stabilization is F co-implant