AVS 50th International Symposium
    Surface Science Monday Sessions
       Session SS1-MoA

Paper SS1-MoA10
Femtosecond Photo-generated Carrier and Reaction Dynamics on a Chlorinated Silicon Surface: Reaction Yield Calculation by Rate Equation of Adsorbed Chlorine

Monday, November 3, 2003, 5:00 pm, Room 326

Session: Stimulated Processes at Surfaces
Presenter: S. Haraichi, National Institute of Advanced Industrial Science and Technology, Japan
Authors: S. Haraichi, National Institute of Advanced Industrial Science and Technology, Japan
F. Sasaki, National Institute of Advanced Industrial Science and Technology, Japan
Correspondent: Click to Email
We have studied the mechanism of a photo-induced reaction of Si/Cl system especially in the low fluence region, which is a promising candidate for an extremely low-damage etching. The following procedures were employed in the femtosecond pump probe experiment to obtain the photo-generated carrier dynamics during the reaction. First, the variation of surface second-harmonic (SH) intensities generated by probe light, which directly reflects surface chlorine coverage, has been measured during a photo-induced reaction. Here both incident lights respectively produces two reaction factors of carrier generation and instantaneous surface vibration. However the pump beam of 3.1 eV photon energy mainly produces carrier generation, and the probe light of 0.95 eV photon energy mainly produces instantaneous surface vibration. In addition, the pump power is set just under the reaction threshold, so the reaction must be induced only when the carrier generation by pump beam and the surface vibration by probe light simultaneously occur on the surface. After obtaining the variation of surface chlorine coverage during a photo-induced reaction, the reaction yield is calculated by using a first and second-order rate equation of the surface chlorine atoms. Second, the reaction yield is calculated for several delays between two beams, and the obtained reaction yield dependence on the delay time reflects the femtosecond photo-generated carrier dynamics. The dynamics can be described by first and second-order kinetics, and both results show no significant difference but the almost equal excitation peak at around 0.4 ps. Here the excitation time constant in the obtained carrier dynamics is 0.1-0.2 ps and tends to decrease with increasing the power of each excitation lights. On the other hand, we have found two relaxation time constants of 0.2-1.0 ps and 1.5-10.0 ps, and both short and long relaxation time constants tend to increase with increasing the excitation power.