Spectroscopic second-harmonic generation during Ar+-ion bombardment of Si(100)

Spectroscopic and real time optical second-harmonic generation (SHG) has been applied to gain insight into the surface and interface processes during low-energy (70-1000 eV) Ar+-ion bombardment of H terminated Si(100). The Ar+-ion bombardment of the crystalline silicon (c-Si), which creates a layer of amorphous silicon (a-Si), has been studied in the SH photon energy range of 2.7-3.5 eV. The time-resolved SHG signal has been observed to increase with an order of magnitude upon ion bombardment. Spectroscopic SHG during ion bombardment and after subsequent XeF2 dosing indicates that the SHG signal has both a contribution generated at the buried interface between the a-Si and the c-Si and an additional contribution originating from the a-Si surface. By separating these contributions using a critical point model it has been shown that the SHG spectra consist of a sharp resonance at 3.36 eV with a linewidth of 0.1 eV at the buried a-Si/c-Si interface and a much broader resonance at a resonance energy of 3.2 eV with a linewidth of 0.5 eV at the a-Si surface. The former resonance is identified to originate from E-0(')/E-1 transitions between bulk electronic states in the c-Si that are modified due to the vicinity of the interface, while the latter resonance is caused by transitions related to Si-Si bonds in the surface region of the a-Si. The time-resolved dynamics of the SHG signal can help in understanding the mechanism of ion-beam and plasma etching of silicon.