Electronically induced defect creation at semiconductor/oxide interface revealed by time-dependent density functional theory

Carrier induced defect creation at the semiconductor-oxide interface has been known as the origin of electronic device degradation for a long time, but how exactly the interface lattice can be damaged by carriers (especially low-energy ones) remains unclear. Here we carry out real-time time-dependent density functional theory simulations on concrete $\mathrm{Si}/\mathrm{Si}{\mathrm{O}}_2$ interfaces to study the interaction between excited electrons and interface bonds. We show that the normal interface Si-H bonds are generally resistant to electrons due to the delocalized nature and high energy level of the Si-H antibonding states, and due to the high-energy barrier to break the Si-H bond. However, if an additional hydrogen atom exists by attaching to a nearby oxygen atom (forming a “Si-H···H-O” complex), the Si-H bond will be greatly weakened, including the reduction of energy barrier for bond breaking, and the lowering of the antibonding state energy level which favors electron injection. Together with the multiple vibrational excitation process, the corresponding Si-H bond can be broken much more easily. Thus we propose that the Si-H···H-O complex will be the center for defect creation and device degradation. We also explain why such a center might be relatively easy to form during the hydrogen annealing process.

Figure 1

(a) The partial DOS of the top H atom in a ${\mathrm{Si}}_4{\mathrm{H}}_{10}$ molecule, and the wave function of each Si-H state. (b) The vibration of the Si-H bond at ground state (black), after electron injection (blue), and after electron excitation (red). The inset shows the large force caused by electron excitation.

Figure 2

(a) The PDOS of the H atom at the $\mathrm{Si}/\mathrm{Si}{\mathrm{O}}_2$ interface. (b), (c) The wave function of the two Si-H states that correspond to the PDOS peaks. (d), (e) The decoupled Si-H states obtained by superposition of the eigenstates within range 1 and range 2.

Figure 3

The evolution of the localized nonadiabatic Si-H state after electron injection.

Figure 4

The Si-H bond dynamics at the $\mathrm{Si}/\mathrm{Si}{\mathrm{O}}_2$ interface. Electrons are injected to the Si-H states at (a) 35 fs, when the Si-H bond is at its minimum length, and (b) 58fs, when the bond is at maximum length. The left inset in each subfigure is the force change caused by electrons, and the right inset is a schematic explanation for the phase-coherent and phase-incoherent interaction.

Figure 5

(a) The precursors that could facilitate Si-H bond breaking. (b) The reaction barrier of the precursor with the “Si-H···H-O” complex. (c) Energy decrease of the Si-H states when the two H atoms approach each other.

Figure 6

The carrier induced Si-H bond breaking and ${\mathrm{H}}_2$ formation in two different Si-H···H-O configurations. The additional H atom bonds with an O atom (a) at the exact $\mathrm{Si}\text{−}\mathrm{Si}{\mathrm{O}}_2$ interface and (b) inside the amorphous oxide.

Figure 7

The Si-O bond breaking caused by the H atom and low-energy electron. (a), (b) The H atom induced Si-O antibonding state. (c) The electron induced repulsive force and bond breaking. (d) The resulted interface defect.

Figure 8

(a)–(e) The structural relaxation of the $a_5$ structure after rotating the attached H atom to the other side of the O atom. (f), (g) The Si-O bond detail in the two kinds of Si-H···H-O configurations.

Figure 9

The extrapolated forming process of the Si-H···H-O complex during hydrogen annealing.

Figure 10

(a), (b) The retention time of the electrons injected to Si-H antibonding states at different time points (corresponds to Fig. 4). (c), (d) The retention time of the single electron injected to different configurations.

Figure 11

The simulation on a Si(100) interface structure. (a) The delocalized Si-H states. (b) The small effect of single electron excitation on the bond vibration.