Influence of microwave annealing on optical and electrical properties of plasma-induced defect structures in Si substrate.

The authors investigate the effects of microwave annealing (MWA) on the recovery of plasma process-induced ion-bombardment damage in Si substrates. For damage creation, Ar discharges by a capacitively coupled plasma etcher are used. For damage repairing, the MWA or a rapid thermal annealing (RTA) are conducted. The authors employ spectroscopic ellipsometry (SE), photoreflectance spectroscopy (PRS), and capacitance-voltage (C-V) measurement to analyze the damaged structures. Recovery of the damage is discussed by comparing the obtained parameters before and after the annealing processes. In the SE analysis, the change in the real part of dielectric constant (Δεr) is investigated. The Δεr spectral peak around 3.4 eV decreases with an increase in the annealing temperature (Ta) for both MWA and RTA, indicating the decrease in the density of defects created in the Si substrate. In the PRS analysis, the spectral peak intensity is found to decrease by the plasma exposure, and then to increase with Ta, which implies the recovery of the Si crystalline structure by MWA as well as by RTA. In the C-V measurement, the voltage shift (ΔVb) in the respective C-V curves is used as a measure of the number of defects present in the surface and interface damaged regions. The ΔVb in the negative bias direction is observed after the plasma exposure for all damaged structures, while after annealing the ΔVb in the positive bias direction is confirmed, suggesting the recovery of the damage in the surface and interface regions. Moreover, it is experimentally found that MWA induces larger |ΔVb| than RTA. These findings indicate the decrease in carrier trap sites in the surface and interface regions of damaged structures, and that MWA is more effective in repairing such damage than RTA. The authors propose a model explaining these mechanisms where defect-induced dipole moments that interact with the incident microwave are considered. The present results draw a new damage-recovery picture by MWA, in particular, for plasma-induced damage in surface and interface regions of Si substrates.