Self-organized Ion Beam Pattern Formation on Si(001)

Self-organized ion beam pattern formation of Si(001) by 2 keV Kr+ ion bombardment was investigated in-situ with scanning tunnelling microscopy, and low energy electron diffraction and ex-situ with atomic force microscopy, scanning electron microscopy, transmission electron microscopy, and Rutherford backscattering spectrometry. It is known that metal impurities can induce pattern formation. The effect of co-depositing Pd, Ir, Fe, Ag, and Pb on ion beam pattern formation was analyzed. For the condition analyzed here, the ability of the metal to form a silicide is necessary for inducing pattern formation. However this is not sufficient. Comparing the effects of metals with similar nuclear charge and mass, but with different ability to form silicides, shows that collision kinetics are not decisive for pattern formation. To understand the observed phenomena one has to consider that the morphology and the composition of the surface are bidirectionally coupled. Due to this coupling the metal concentration depends on the surface history and it does not determine the resulting morphology. For ion incidence angles from 58° to 79° patterns develop on Si during 2 keV Kr+ ion bombardment at room temperature even without co-deposition of impurities. The evolution of the surface morphology was studied using in-situ scanning tunnelling microscopy for the ion incidence angles 63° and 75°. The fluence was varied by a factor of 1000. Two fluence regimes can be distiguished. While a similar ripple pattern evolves in the low fluence regime for both incidence angles, the evolution differs for both incidence angles in the high fluence regime. In the high fluence regime perpendicular mode ripples and a roof-tile morphology develop for 63° and 75° respectively. The observations will be compared to experimental data of ion beam patterning of Si and Ge from literature to identify universal phenomena. Comparing the results with theoretical models allows to asses their applicability to ion beam pattern formation of Si. Si(001) amorphizes under ion bombardment below a critical temperature and is crystalline above the critical temperature. For 2 keV Kr+ ions the critical temperature is (674 ± 10) K. In a limited temperature range of 674 K to 720 K the surface develops a pit and mound morphology with the step edges parallel to the ⟨110⟩ directions. The pattern formation is driven by the Ehrlich-Schwoebel barrier inducing an effective uphill diffusion current. The surface roughness is maximum at T ≈ 700 K. At this temperature the fluence dependence of the surface morphology was studied. For high fluences the pattern changes into a ridge and valley morphology where the directions of the ridges and valley is ≈ 45° rotated to the ⟨110⟩ directions