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QuantumATK Case Study: Reducing Metal-Semiconductor Contact Resistance
Posted on October 4, 2017
GlobalFoundries and IBM Research at Albany NanoTech have recently published their work with QuantumATK providing atomistic-level insight into the interface between semiconducting Ge and metallic TiGe used in contacts for sub-10nm nodes. The study gives directions on how to minimize the contact resistance at the interface.
Main findings
1.The work [1] shows that the Schottky barrier heights (SBHs) of the TiGe/Ge contact depend strongly on the phase of TiGe and on the different crystallographic orientations of Ge. This indicates that SBHs are extremely sensitive to the atomic structure of the interface, which is challenging to characterize even with sophisticated experimental measurements. Atomic-scale modelling tools are therefore of paramount importance in this case. The atomic-scale modelling tools in ATK are designed to study metal-semiconductor interfaces, because they describe the interface using the physically correct boundary conditions, and account correctly for the semiconductor band gap and doping.
2. This work also shows that by increasing the doping density in the semiconductor, it is possible to reduce the contact resistance and convert the Schottky barrier into Ohmic, which is crucial for sub-10 nm nodes.
Good agreement with experiments
A number of calculated properties such as the value of Ge band gap, the SBHs, as well as the trends of the current-voltage (I-V) curves and of the contact resistance with doping are in a good agreement with the experimentally determined values as, for example, shown in Panel 4 of the Figure below.
The structure of the TiGe/Ge interface is created with the QuantumATK NanoLab graphical user interface as shown in Panel 1 of the Figure above. In the Local Density of States (LDOS) plot (Panel 2) the dark region depicts the band gap of Ge. The SBH can be extracted from the LDOS plot as a difference between the maximum value of the macroscopic average of the Hartree potential (orange line) and the chemical potential on the semiconductor side of the interface (EF, white line). At the doping concentration of 10²¹ cm⁻³ the SBH is very small, indicating that the contact is Ohmic, as also confirmed by the calculated linear I-V curve as shown in Panel 3. Panel 4 shows a good agreement between theory and experiment for the trend of the TiGe/Ge contact resistance extracted from the I-V curve at various doping concentrations (refer to the full publication [1] for details).
Relevant resources
For more details, please refer to the step-by-step case study prepared by us on the Ag-Si interface using QuantumATK [2]. It has a similar workflow as the paper presented here.
References:
[1] H. Dixit, C. Niu, M. Raymond, V. Kamineni, R. K. Pandey, Member, IEEE, A. Konar, J. Fronheiser, A. V. Carr, P. Oldiges, P. Adusumilli, N. A. Lanzillo, X. Miao, B. Sahu and F. Benistant, "First-principles Investigations of TiGe/Ge Interface and Recipes to Reduce the Contact Resistance", IEEE Transactions on Electron Devices 64, 3775 (2017).
[2] D. Stradi, U. Martinez, A. Blom, M. Brandbyge and K. Stokbro, "General atomistic approach for modeling metal–semiconductor interfaces using density functional theory and non-equilibrium Green’s function”, Phys. Rev. B 93, 155302 (2016). arXiv, pages 1601.04651, 2016. URL: arXiv:1601.04651.
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