AVS 47th International Symposium
    Thin Films Wednesday Sessions
       Session TF-WeM

Paper TF-WeM4
Molecular Dynamics Simulation of Ion Bombardment on Hydrogen-terminated Si(001)-(2X1) Surfaces

Wednesday, October 4, 2000, 9:20 am, Room 203

Session: Modeling of Thin Film Growth
Presenter: K. Satake, Mitsubishi Heavy Industries, Ltd., Japan
Authors: K. Satake, Mitsubishi Heavy Industries, Ltd., Japan
D.B. Graves, University of California, Berkeley
Correspondent: Click to Email
In crystalline Si growth using low-temperature plasma enhanced chemical vapor deposition (PECVD), it is important to clarify the role of ions in the surface reactions. We present here the interaction between an H-terminated Si(001)-(2X1) surface and normal incident SiH@sub 3@ @super +@ and H@sub 2@ @super +@ ions as a function of the incident energy (10 eV, 20 eV, and 40 eV) using molecular dynamics (MD) simulations. SiH@sub 3@ @super +@ was observed to penetrate less than 3-4 Å at 10 eV and 20 eV, increasing to about 5 Å at 40 eV. H@sub 2@ @super +@ penetrated the surface only slightly at 10 eV, but the penetration depth increased rapidly with increasing energy. At 40 eV, H@sub 2@ @super +@ was observed to penetrate up to 20 Å, or even farther. Per trajectory, SiH@sub 3@ @super +@ was observed to displace about 4 Si atoms in the lattice, an average distance of about 2-3 Å, at 40 eV. H@sub 2@ @super +@, by contrast, displaced on average, only 0.7 Si atoms per trajectory, and the displacement distance was about 1.5 Å, at 40 eV. It is suspected that ion impact creates sites which react more readily with neutral species. The generation rate of dangling bonds (DB) at the surface due to H@sub 2@ @super +@ ion impact is about twice that of SiH@sub 3@ @super +@ ions for the energies studied. In the DB generation by H@sub 2@ @super +@ ions, the primary process is direct surface H atom sputtering. In addition, we also observed the DB generation with dihydride and monohydride formation by H insertion into the Si dimer and H exchange. In the case of SiH@sub 3@ @super +@ ions, the probability of DB generation by direct sputtering is almost the same as that of insertion; however, in addition, the near-surface crystallinity is disrupted in most of the trajectories. The H@sub 2@ @super +@ ion bombardment under 20 eV, by contrast, can enhance the surface reactivity by creating defects only in the top surface layer without damaging the crstallinity of the underlying silicon.