60keV Ar+-ion induced pattern formation on Si surface: Roles of sputter erosion and atomic redistribution (original) (raw)
2003
Using cross-section transmission electron microscopy ͑XTEM͒ we have studied the surface and subsurface structure of individual ripples having submicron scale wavelength and nanometer scale amplitude, generated by obliquely incident ͑50-120 keV͒ Ar ion bombardment of Si. The XTEM results reveal that the front slopes of ion-induced ripples have amorphous layers containing bubbles with sizes ranging from about 3 to 15 nm facing the ion beam direction. A thinner amorphous layer without bubbles, on the other hand, persists on the rear slope of ripples. We also observe an irregular interface between a-Si and c-Si, which is due to the direct impact amorphization mechanism prevalent near the end-of-range during heavy ion irradiation.
Morphology change of teh silicon surface by Ar+ ion beam sputtering
Two-level modeling for nanoscale pattern formation on silicon target by Ar + ion sputtering is presented. Phase diagram illustrating possible nanosize surface patterns is discussed. Scaling characteristics for the structure wavelength dependence versus incoming ion energy are defined. Growth and roughness exponents in different domains of the phase diagram are obtained.
Formation of ripple pattern on silicon surface by grazing incidence ion beam sputtering
2009
Off-normal low energy ion beam sputtering of solid surfaces often leads to morphological instabilities resulting in the spontaneous formation of ripple structures in nanometer length scales. In the case of Si surfaces at ambient temperature, ripple formation is found to take place normally at lower incident angles with the wave vector parallel to the ion beam direction. The absence of ripple pattern on Si surface at larger angles is due to the dominance of ion beam polishing effect. We have shown that a gentle chemical roughening of the starting surface morphology can initiate ripple pattern under grazing incidence ion beam sputtering, where the ripple wave vector is perpendicular to the ion beam direction. The characteristics of the perpendicular mode ripples are studied as a function of pristine surface roughness and ion fluence. The quality of the morphological structure is assessed from the analysis of ion induced topological defects.
Nanotechnology, 2002
We report on the production of nanoscale patterning on Si substrates by low-energy ion-beam sputtering. The surface morphology and structure of the irradiated surface were studied by atomic force microscopy (AFM) and high-resolution transmission electron microscopy (HRTEM). Under ion irradiation at off-normal incidence angle (∼50 • ), AFM images show the formation of both nanoripple and sawtooth-like structures for sputtering times longer than 20 min. The latter feature coarsens appreciably after 60 min of sputtering, inducing a large increase in the surface roughness. This behaviour is attributed to the preferential direction determined on the substrate by the ion beam for this incidence angle, leading to shadowing effects among surface features in the sputtering process. Under irradiation at normal incidence, the formation of an hexagonal array of nanodots is induced for irradiation times longer than 2 min. The shape and crystallinity of the nanodots were determined by HRTEM. At this incidence angle, the surface roughness is very low and remains largely unchanged even after 16 h of sputtering. For the two angle conditions studied, the formation of the corresponding surface structures can be understood as the interplay between an instability due to the sputtering yield dependence on the local surface curvature and surface smoothing processes such as surface diffusion.
Topographical characterization of Ar-bombarded Si(111) surfaces by atomic force microscopy
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2002
We used atomic force microscopy to study the topographical changes induced on Si(1 1 1) surfaces by 10-22 keV Ar + bombardment. The irradiation was carried on normal to the surface with doses in the 1-60×10 16 ions/cm 2 range. We observed a first generation of blisters at a critical dose around 3×10 16 ions/cm 2, which flakes off at 19×10 16 ions/cm 2, and a second generation of smaller blisters between 35 and 45×10 16 ions/cm 2. Measurements of the mean surface height show that at low irradiation doses the surface inflates because of voids produced by Ar + implantation. For doses greater than 20×10 16 Ar +/cm 2 the height decreases linearly because of sputtering, with a slope corresponding to a sputtering yield of 1.4. Finally, we present electron spectra produced during grazing proton bombardment of samples whose topography has been modified by Ar irradiation.
The temporal evolution of a periodic ripple pattern on a silicon surface undergoing erosion by 30 keV argon ion bombardment has been studied for two angles of ion incidence of 60°and 70°using ex situ atomic force microscopy ͑AFM͒ in ambient condition. The roughness amplitude ͑w͒ grows exponentially with sputtering time for both the angle of ion incidence followed by a slow growth process that saturates eventually with almost constant amplitude. Within the exponential growth regime of amplitude, however, ripple wavelength ͑l͒ remains constant initially and increases subsequently as a power law fashion l ϰ t n , where n = 0.47± 0.02 for a 60°angle of ion incidence followed by a saturation. Wavelength coarsening was also observed for 70°but ordering in the periodic ripple pattern is destroyed quickly for 70°as compared to 60°. The ripple orientation, average ripple wavelength at the initial stage of ripple evolution, and the exponential growth of ripple amplitude can be described by a linear continuum model. While the wavelength coarsening could possibly be explained in the light of recent hydrodynamic model based continuum theory, the subsequent saturation of wavelength and amplitude was attributed to the effect of geometrical shadowing. This is an experimental result that probably gives a hint about the upper limit of the energy of ion beam rippling for applying the recently developed type of nonlinear continuum model.
Thin Solid Films, 2004
Ion beam sputtering i.e. the removal of material from a surface due to the impact of energetic ions or atoms, is an inherent part of numerous surface processing techniques. Due to self-organization caused by the process of low-energy ion beam erosion, nanostructures with different shape and high order arrangement can be evolved. In this work, results for Ar ion beam erosion q of silicon and IIIyV semiconductor surfaces under oblique ion incidence with simultaneous sample rotation are presented. The evolution of the surface topography and patterns are analyzed by scanning force microscopy (AFM). Especially, the influence of different settings of the used Kaufman-type broad beam ion source on nanostructures is discussed. The ion beam is extracted and formed by a multiaperture two-grid system. Beside the ion energy, the divergence of the ion beam as well as the angular distribution of the ions within the ion beam can influence the pattern formation. By a careful adjustment of the individual ion source settings regular nanopatterns on various surfaces can be achieved. Examples are given for InP, GaSb, InAs, and Si. ᮊ
The formation of a self-organized nanoscale ripple pattern after off-normally incident ion bombardment on the surface of amorphous materials, or on semiconductors like silicon that are easily amorphized by ion bombardment, has attracted much attention in recent years from the point of view of both theory and applications. As the energy of the impinging ions increases from low to medium, i.e. several hundred eV to a few tens of keV, the ratio of amplitude to wavelength of the generated ripple pattern becomes so large that inter-peak shadowing of the incident ion flux takes place. Morphologically, the sinusoidal surface profile starts to become distorted after prolonged ion bombardment under such conditions. Structural and compositional modifications of the ripple morphology generated under shadowing conditions include the formation of a thicker amorphous layer with high incorporation of argon atoms in the form of nanometer sized bubbles around the middle part of the front slope of the ripple facing the ion beam, as compared to the rear slope. The present paper reviews recent developments in the experimental study of morphological, structural and compositional aspects of ripple patterns generated on a silicon surface after medium keV (30-120 keV) argon bombardment mainly at an angle of ion incidence of 60 • .
Impurity in low energy Ar+ ion beam is the cause of pattern formation on Si
2018
We report the decisive role of reactive ion impurities in low energy Ar+ ion beam on surface nanopattern formation. The source of experimental inconsistency in pattern formation by low energy (few keV to 10's of KeV) Ar+ ion beam has been identified by irradiating Si surface at an oblique angle with pure and impure Ar+ ion beam of energy 3-10 keV. No well-defined patterns are observed for mass selected pure Ar+ ion bombardment, whereas well defined periodic ripple pattern is formed by the same experimental condition with impure mass unanalyzed Ar+ ion irradiation. The contaminants in mass unanalyzed beam specifically reactive nitrogen, oxygen and carbon play the main role of pattern formation by introducing chemical instability on the Si surface. The surface morphology of the irradiated Si surfaces is examined by Atomic Force Microscopy (AFM). The surface contamination and corresponding chemical compound formation are investigated by X-ray photoelectron spectroscopy (XPS).