| 1. |
|
|
| 2. |
- Jablonka, Lukas, Dipl.-NanoSc.
(författare)
-
Contacts and Interconnects for Germanium-based Monolithic 3D Integrated Circuits
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Three-dimensional integrated circuits have great potential for further increasing the number of transistors per area by stacking several device tiers on top of each other and without the need to continue the evermore complicated and expensive down-scaling of transistor dimensions. Among the different approaches towards the realization of such circuits, the monolithic approach, i.e. the tier-by-tier fabrication on a single substrate, is the most promising one in terms of integration density. Germanium is chosen as a substrate material instead of silicon in order to take advantage of its low fabrication temperatures as well as its high carrier mobilities. In this thesis, the work on two key components for the realization of such germanium-based three-dimensional integrated circuits is presented:the source/drain contacts to germanium the interconnects.As a potential source/drain contact material, nickel germanide is investigated.In particular, the process temperature windows for the fabrication of morphologically stable nickel germanide layers formed from initial nickel layers below 10 nm are identified and the reaction between nickel and germanium is further studied by means of in-situ x-ray diffraction. The agglomeration temperature of nickel germanide is increased by 100 °C by the addition of tantalum and tungsten interlayers and capping layers. In an effort to more thoroughly characterize the contacts, a method to reliably extract the specific contact resistivity is implemented on germanium.As a potential interconnect material cobalt is investigated. In a first step, highly conductive cobalt thin films are demonstrated by means of high-power impulse magnetron sputtering. The high conductivity of the cobalt films is owing to big grains, high density, high purity, and smooth interfaces. In a second step, the potential of high-power impulse magnetron sputtering for the metallization of nanostructures is further explored.
|
|
| 3. |
- Jablonka, Lukas, et al.
(författare)
-
Formation of nickel germanides from Ni layers with thickness below 10 nm
- 2017
-
Ingår i: Journal of Vacuum Science & Technology B. - : A V S AMER INST PHYSICS. - 1071-1023 .- 1520-8567. ; 35:2
-
Tidskriftsartikel (refereegranskat)abstract
- The authors have studied the reaction between a Ge (100) substrate and thin layers of Ni ranging from 2 to 10 nm in thickness. The formation of metal-rich Ni5Ge3 was found to precede that of the monogermanide NiGe by means of real-time in situ x-ray diffraction during ramp-annealing and ex situ x-ray pole figure analyses for phase identification. The observed sequential growth of Ni5Ge3 and NiGe with such thin Ni layers is different from the previously reported simultaneous growth with thicker Ni layers. The phase transformation from Ni5Ge3 to NiGe was found to be nucleationcontrolled for Ni thicknesses < 5 nm, which is well supported by thermodynamic considerations. Specifically, the temperature for the NiGe formation increased with decreasing Ni (rather Ni5Ge3) thickness below 5 nm. In combination with sheet resistance measurement and microscopic surface inspection of samples annealed with a standard rapid thermal processing, the temperature range for achieving morphologically stable NiGe layers was identified for this standard annealing process. As expected, it was found to be strongly dependent on the initial Ni thickness.
|
|
| 4. |
- Jablonka, Lukas, et al.
(författare)
-
Highly conductive ultrathin Co films by high-power impulse magnetron sputtering
- 2018
-
Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 112:4
-
Tidskriftsartikel (refereegranskat)abstract
- Ultrathin Co films deposited on SiO2 with conductivities exceeding that of Cu are demonstrated. Ionized deposition implemented by high-power impulse magnetron sputtering (HiPIMS) is shown to result in smooth films with large grains and low resistivities, namely, 14 mu Omega cm at a thickness of 40 nm, which is close to the bulk value of Co. Even at a thickness of only 6 nm, a resistivity of 35 mu Omega cm is obtained. The improved film quality is attributed to a higher nucleation density in the Co-ion dominated plasma in HiPIMS. In particular, the pulsed nature of the Co flux as well as shallow ion implantation of Co into SiO2 can increase the nucleation density. Adatom diffusion is further enhanced in the ionized process, resulting in a dense microstructure. These results are in contrast to Co deposited by conventional direct current magnetron sputtering where the conductivity is reduced due to smaller grains, voids, rougher interfaces, and Ar incorporation. The resistivity of the HiPIMS films is shown to be in accordance with models by Mayadas-Shatzkes and Sondheimer which consider grain-boundary and surface-scattering.
|
|
| 5. |
- Jablonka, Lukas, et al.
(författare)
-
Improving the morphological stability of nickel germanide by tantalum and tungsten additions
- 2018
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 112:10
-
Tidskriftsartikel (refereegranskat)abstract
- To enhance the morphological stability of NiGe, a material of interest as a source drain-contact in Ge-based field effect transistors, Ta or W, is added as either an interlayer or a capping layer. The efficacy of this Ta or W addition is evaluated with pure NiGe as a reference. While interlayers increase the NiGe formation temperature, capping layers do not retard the NiGe formation. Regardless of the initial position of Ta or W, the morphological stability of NiGe against agglomeration can be improved by up to 100 degrees C. The improved thermal stability can be ascribed to an inhibited surface diffusion, owing to Ta or W being located on top of NiGe after annealing, as confirmed by means of transmission electron microscopy, Rutherford backscattering spectrometry, and atom probe tomography. The latter also shows a 0.3 at. % solubility of Ta in NiGe at 450 degrees C, while no such incorporation of W is detectable.
|
|
| 6. |
- Jablonka, Lukas, Dipl.-NanoSc., et al.
(författare)
-
Metal Filling by High Power Impulse Magnetron Sputtering
- 2019
-
Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 52:36
-
Tidskriftsartikel (refereegranskat)abstract
- High power impulse magnetron sputtering (HiPIMS) is an emerging thin film deposition technology that provides a highly ionized flux of sputtered species. This makes HiPIMS attractive for metal filling of nanosized holes for highly scaled semiconductor devices. In this work, HiPIMS filling with Cu and Co is investigated. We show that the quality of the hole filling is determined mainly by the fraction of ions in the deposited flux and their energy. The discharge waveforms alone are insufficient to determine the ionization of the metal flux. The experimental results are in a good agreement with Monte-Carlo simulations using the measured flux characteristics. Based on the simulations, strategies to improve the filling are discussed.
|
|
| 7. |
|
|
| 8. |
- Kubart, Tomas, et al.
(författare)
-
Metallization of nanostructures by High Power Impulse Magnetron Sputtering
- 2015
-
Ingår i: 4 th Magnetron, Ion processing & Arc Technologies European Conference, Paris, 8-11 December 2015. - 9782918641179
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this contribution, we present the use of High Power Impulse Magnetron Sputtering (HiPIMS) for metallization of nanostructures for microelectronics. This work is motivated by meeting the increasing demands on deposition processes due to the increasing density of integration. Shrinking lateral dimensions of the structures more rapidly than vertical dimensions means increasing aspect ratios. There is also a need for deposition of new materials. Traditionally, ionized PVD (I-PVD) has been used for metallization of nanostructures. Unlike most other I-PVD techniques, HiPIMS is compatible with standard magnetron sputtering systems. It may therefore be an attractive alternative to the techniques with additional ionization of the sputtered metal flux. With two examples, we will show the great flexibility of HiPIMS in making conformal deposition vs. directed via filling.First, we show conformal formation of ultrathin Ni films in a modified self-aligned silicide process, thanks to the Ni ionization in HiPIMS. After appropriate annealing, the thickness of the resulting Ni-silicide films could be readily adjusted in the range from 4.7 to 8.6 nm by proper substrate biasing [1]. Good sidewall coverage was also achieved [2].Second, we discuss filling of via holes for vertical stacking at device level. Here, narrow (sub 100 nm) trenches and holes need to be filled with a highly conductive metal. We explore the potential of HiPIMS and determine the maximum aspect ratio that can be filled. In our experiment with Cu, the ionized metal flux fraction is estimated to be about 70% from the substrate from the substrate ion current. A significant improvement over DC sputtering has been achieved, as shown in Fig. 1, with success in filling vias of aspect ratio 1.5. We analyze the influence of ion energy and discuss approaches to further improving the filling process.
|
|
| 9. |
- Smolarczyk, Marek, et al.
(författare)
-
Self-Aligned Molding Technology (SAMT) for Fabrication of 3D Structures with a Foldable Imprint Mold
- 2019
-
Ingår i: Applied Nanoscience. - : Springer Science and Business Media LLC. - 2190-5509 .- 2190-5517. ; 9:6, s. 1255-1263
-
Tidskriftsartikel (refereegranskat)abstract
- We propose self-aligned molding technology (SAMT) as a novel nanoimprint technique with a self-aligned foldable imprint mold to control size and shape of structures and particles for a broad range of materials. SAMT is a single-step molding process for complex 3D shaped structures and particles using a reusable double-sided mold with a hinge. We present the fabrication process of SAMT molds, including electron beam lithography on a sloped surface, angular dry etching, and a template-based double inversion technique. We present fabricated SAMT molds and molding results of micro-scale 3D structures.
|
|
| 10. |
- Tran, Tuan, et al.
(författare)
-
Electronic interaction of slow hydrogen and helium ions with nickel-silicon systems
- 2019
-
Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - 2469-9926 .- 2469-9934. ; 100:3
-
Tidskriftsartikel (refereegranskat)abstract
- Electronic stopping cross sections (SCSs) of nickel, silicon, and nickel-silicon alloys for protons and helium (He) ions are studied in the regime of medium- and low-energy ion scattering, i.e., for ion energies in the range from 500 eV to 200 keV. For protons, at velocities below the Bohr velocity the deduced SCS is proportional to the ion velocity for all investigated materials. In contrast, for He ions nonlinear velocity scaling is observed in all investigated materials. Static calculations using density functional theory (DFT) available from the literature accurately predict the SCS of Ni and Ni-Si alloy in the regime with observed velocity proportionality. At higher energies, the energy dependence of the deduced SCS of Ni for protons and He ions agrees with the prediction by recent time-dependent DFT calculations. The measured SCS of the Ni-Si alloy was compared to the SCS obtained from Bragg's rule based on SCS for Ni and Si deduced in this study, yielding good agreement for protons, but systematic deviations for He projectiles, by almost 20%. Overall, the obtained data indicate the importance of nonadiabatic processes such as charge exchange for proper modeling of electronic stopping of, in particular, medium-energy ions heavier than protons in solids.
|
|
