| AVS 58th Annual International Symposium and Exhibition | |
| Plasma Science and Technology Division | Thursday Sessions |
| Session PS-ThM |
| Session: | Neutral Beam and Low Damage Processing |
| Presenter: | Naoki Watanabe, Mizuho Information & Research Institute, Inc., Japan |
| Authors: | N. Watanabe, Mizuho Information & Research Institute, Inc., Japan S. Ohtsuka, Mizuho Information & Research Institute, Inc., Japan T. Iwasaki, Mizuho Information & Research Institute, Inc., Japan K. Ono, Mizuho Information & Research Institute, Inc., Japan Y. Iriye, Mizuho Information & Research Institute, Inc., Japan S. Ueki, BEANS Project 3D BEANS Center, Japan O. Nukaga, Fujikura Ltd.,Japan T. Kubota, Tohoku University, Japan M. Sugiyama, University of Tokyo, Japan S. Samukawa, Tohoku University, Japan |
| Correspondent: | Click to Email |
We have developed numerical simulation software named QuickQD[1,2] that calculates the time-evolution of wave functions of electrons based on the First pinciples Quantum Mechanics. We have applied QuickQD for analyzing neutral-beam generated by the neutral-beam etching system developed by Samukawa, et al [3]. Positive or negative ions passing through a graphite aperture of this etching system are converted to neutral atoms by exchanging their valence electrons during a collision with the aperture sidewall.
Our numerical model consists of an ion (Cl- or Cl2+) and 24 carbon atoms forming a graphite sheet. The ion has been moved to collide with the graphite sheet and then bounce back to its original position. QuickQD has simulated the time-evolution of several ten wavefunctions of both the ion and carbon electrons during the whole process of the collision. We have evaluated the distribution of electron density around the ion, and we have determined the probability of neutralization.
We have obtained some numerical results that agree well with experiment results, for example,
a negative Cl- ion transfers its valence electrons to the graphite and is converted to a neutral Cl atom with high probability, meanwhile a positive Cl2+ ion receives valence electrons from the graphite and is converted to a neutral Cl2 molecule with low probability[4].
To understand the quantum process of electron transfer and the difference of neutralization efficiencies between a negative ion and a positive ion, we have investigated the behavior of each time-evolving electron wave function. We have found that some electrons that existed in the orbital of Cl- before the collision were mainly transferred after the collision to some orbitals of graphite whose orbital energies were close, namely, resonant transitions whose transition rates are relatively high. Meanwhile, some electrons that existed in the orbitals of graphite before collision of Cl2+ were transferred after the collision to the orbital of Cl2+ whose orbital energies were not close, namely, Aujer like complicated transitions, whose transition rates are relatively low.
In this talk, we will show the time-evolution of wave functions based on the First pinciples Quantum Mechinics, which simulated the neutralization processes that occured in the neutral beam etching system.
[1] N. Watanabe and M. Tsukada, Phys. Rev. E. 65 036705 (2002).
[2] http://www.mizuho-ir.co.jp/solution/research/semiconductor/nano/meso
[3] S. Samukawa et al., Jpn. J. Appl. Phys., 40, L779 (2001).
[4] T. Kubota, N. Watanabe, et al., J. Phys. D. 44 125203 (2011)