MD-Simulations Wafer Bonding


MD simulations of wafer bonded interfaces using BOP

K. Scheerschmidt and V. Kuhlmann


Molecular dynamics simulations using empirical potentials have been performed to describe atomic interactions during the relaxation of nanostructures. To include the quantum mechanical nature of atomic bonding a tight-binding based bond order potential is developed applying analytically the most important momenta up to 6th order. The applicability of the bond order potential and resulting enhancements in structural predictions are analyzed recalculating interface defects arising during bonding of two wafers with twist rotation misalignment.



Fig. 1 shows the resulting minimum structures gained for higher annealing temperatures (900K) of a wafer bonded interface with a twist rotation of 2.8o in [001]-projection, and both the Tersoff and the BOP4+ simulation projected by different colors into the same [110]-view. One reveals the more located imperfectly bonded regions around the screw dislocations for the Tersoff potential, whereas the relaxation with BOP4+ yield more stability due to the higher potential stiffness according to the 6th moment hopping terms.
In Fig. 2 the pair-, bond angle-, and torsion angle distributions are shown for the 2.8o twist bonded interface, only 3 lattice planes around the interface are considered in distance and angle counting. The Tersoff potential yields the characteristic first and second neighbor distances as well as the bond angle of $109^\circ$. The calculation with the BOP4+ demonstrates the characteristic deviations due to the better description of the electronic bond structure. So, for instance, the Tersoff potential is defined without torsion, thus the corresponding distribution has no relevant peaks. However, the angular distribution shows remarkable maxima at 95o and 125o.

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