AVS 51st International Symposium
    Thin Films Friday Sessions
       Session TF-FrM

Paper TF-FrM1
Real-time and Spectroscopic Second Harmonic Generation as a Tool to Probe Surface Processes during Amorphous Silicon Film Growth

Friday, November 19, 2004, 8:20 am, Room 303C

Session: In-Situ/Ex-Situ & Real-Time Monitoring
Presenter: I.M.P. Aarts, Eindhoven University of Technology, The Netherlands
Authors: I.M.P. Aarts, Eindhoven University of Technology, The Netherlands
J.J.H. Gielis, Eindhoven University of Technology, The Netherlands
C.M. Leewis, Eindhoven University of Technology, The Netherlands
M.C.M. van de Sanden, Eindhoven University of Technology, The Netherlands
W.M.M. Kessels, Eindhoven University of Technology, The Netherlands
Correspondent: Click to Email
We have explored the capability of second harmonic generation (SHG) to probe surface and interface processes during the growth of amorphous silicon-based thin films such as hydrogenated amorphous silicon (a-Si:H). The a-Si:H thin films are deposited under ultrahigh vacuum conditions by means of a hot wire source on fused silica substrates. Real-time spectroscopic ellipsometry has been used to monitor the thickness evolution and the optical properties of the a-Si:H films. SHG has been observed during in situ experiments on as-deposited films for various input and output polarizations configurations. Although SHG is surface and interface specific for isotropic media such as a-Si:H, interpretation in the present case is complicated because not only interference effects have to be taken into account but also the macroscopic origin of the SHG is not straightforward to determine. The experimental data has therefore been analyzed with a complete optical model that takes into account interference effects of both the fundamental and the SHG radiation as well as two nonlinear polarizing sheets in which the SHG signal is generated. These sheets are positioned at the surface and at the interface between the film and the substrate. Further understanding of the SHG signal has been obtained by performing spectroscopic SHG measurements, which showed two distinct resonance peaks at photon energies of 1.2 and 1.4 eV. After exposing the a-Si:H film to oxygen the SHG signal is quenched, indicating that the corresponding resonance peaks involve transitions with dangling bond states. In addition, real-time observation of the SHG signal during film growth and dosing experiments have already revealed that SHG is sensitive to nucleation and relaxation processes at the surface and/or interface region during and after growth of these silicon-based films.