Nano structure formation by gas cluster ion beam irradiations at oblique incidence
- PDF / 252,364 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 13 Downloads / 189 Views
KK7.9.1
Nano structure formation by gas cluster ion beam irradiations at oblique incidence Noriaki Toyoda and Isao Yamada Laboratory of Advanced Science and Technology for Industry, University of Hyogo, 3-1-2 Kouto, Kamigori, Hyogo, 678-1205, JAPAN
ABSTRACT Nano structure formations on Au surfaces by 20 keV Ar gas cluster ion beam (GCIB) irradiation at an oblique incidence were studied. When the incident angle was close to 0o from the surface normal of Au targets, the Au surface was smoothed due to the lateral sputtering effects and there were no structure formations on the surfaces. However, ripples were formed on Au surfaces at incident angle of 60o without sample rotation. When the Au samples were irradiated with Ar-GCIB at 60o with sample rotation, cone like structures with 50nm in diameters were fabricated and the surface roughness had a maximum value. However, the surface roughness suddenly decreased over incident angle of 60o. Even though the surface roughness was the same in the cases with and without sample rotations at 85o incidence, ripple structures were formed parallel to the incoming GCIB directions when there was no rotation. The incident angle dependence of the sputtering depth decreased following cosθ dependence. Very efficient surface smoothing without removing materials were realized with oblique incidence.
INTRODUCTION Recently, ion beam induced patterning or surface polishing attracts great interests to fabricate nano-structures. Basically, the principle of ion polishing or patterning is to move the atoms located near the top of a hill. Since atoms located on a hill have smaller binding energies than those in a valley, only the atoms on the hill can be moved without inducing dislocation of the atoms in the valley if an appropriate energy is supplied. Also the kinetic energy of the projectile ions should be sufficiently low so that atoms are not induced to move perpendicularly into the target. To achieve these aims, a glancing angle of incidence is frequently used for the surface smoothing with monomer ions. However, a high-fluence ion bombardment produces a variety of surface topological features. The most interesting feature is a ripple or wavelike structures developed on metals [1], semiconductors [2], Ge [3], GaAs [4] and insulators (SiO2 [5], glass [6]). This ripple formation is problematic in many applications, including secondary ion mass spectroscopy (SIMS) [7], depth profiling of Auger electron spectroscopy [8] and ion milling [9]. In a typical SIMS apparatus, the incident angle of the primary ions is oblique to obtain high sputtering yield and to avoid ion mixing. As sputtering proceeds, ripples are formed on the surface which induces degradation of the depth resolution. Ripple formation at glancing incidence of monomer ions was first modeled by Bradley and Harper [10]. They considered it as a competition between the local curvature dependence of the sputtering yield and thermal diffusion on the surface. This theory agreed well with many experimental results with monomer ion beams. R
Data Loading...
