Development Of Surface Topography Research Articles

High-fluence Co implantation in Si, SiO 2/Si and Si 3N 4/Si : Part III: heavy-fluence Co bombardment induced surface topography development

The surface topography development of Si(1 0 0), Si(1 1 1), oxide/Si and nitride/Si structures under high normal fluence (1 × 10 16–2.6 × 10 18 ions cm −2) keV Co metal vapour vacuum arc (MEVVA) irradiation has been investigated by scanning electron microscopy (SEM). The results show that for normal fluences up to ∼10 17 ions cm −2, the surface topography remains flat. As the fluence increases, pores develop and grow to form a columnar structure. At even higher fluences the columns are eroded to form an acicular structure. Deposition of a silicon dioxide or nitride layer on the Si surface leads to a significant suppression of the onset fluence for the formation of a rough surface. The porous surface could not be transformed to the network of acicular structures or a flat surface by high temperature annealing.

Surface topography development and ion mixing in the study of depth profiling of multilayered structures

The depth profiling in combination with sputtering of multilayered structures is considered by the proposed models. In order to emphasize the changes in the surface composition produced by the processes of surface topography development and ion mixing during profiling two different models are proposed and considered separately. The first one includes the processes of surface roughening as a result of sputtering and smoothing of rough surface as a result of surface atom migration (no mixing in the bulk of sample). The second model includes the sequential removal of surface atoms (no surface roughening) and ion mixing in the bulk of the sample. The dependencies of the main characteristics such as the amplitude and the shape of the peaks of the oscillations of the surface concentration, surface roughness and depth resolution on sputtering time and ion beam parameters are calculated and analyzed. The influence of the ion energy, angle of incidence, ion flux and substrate temperature to the depth profile of multilayered structure are studied.

Surface structure build-up in thermosetting powder coatings during curing

A systematic attempt has been made to correlate the thermal and rheological behavior of thermosetting powder coating systems with their surface structure build-up. Epoxy-based and polyurethane-based powder coating systems, which displayed surface matting and surface wrinkling, were examined. Firstly, the evolution of the complex viscosity was correlated with the degree of conversion. Secondly, the structure build-up on the surface of the coatings was investigated with a confocal laser scanning microscope at different temperatures, and was shown to be closely related to the degree of conversion and to the evolution of the complex viscosity. The surface structure is built up just before gelation point and continues to evolve after gelation. Differences were observed in the surface structure build-up between the two systems during curing but the surface structure was not changed during the cooling process. These experimental results lead to a better understanding of the development of surface topography and morphology and provide valuable information for the development of new powder coating systems.

Surface topography development of thin polystyrene films under low energy ion irradiation

Morphological changes of spin-coated thin polystyrene (PS) films due to low energy Xe + bombardment in the energy range from 660 eV to 4 keV are investigated. These surface modifications are characterised by means of Atomic Force Microscopy (AFM). No significant topographical change between pristine and irradiated film surfaces is found for ion energy higher than 1.5 keV in the ion fluence range between 4 × 10 14 and 4 × 10 16 cm −2. An increase of surface roughness is however obtained after ion bombardment for energy lower than 2 keV at the highest ion fluence. Moreover, a strong change of the morphology is observed after an irradiation with Xe + for energy less than 1.25 keV, and ion fluences higher than 5 × 10 16 cm −2. The surface roughness increases and well-defined features appear. Their evolution is followed as a function of the fluence in the 5 × 10 16–2 × 10 17 cm −2 range for 1 keV Xe + irradiation. ToF–SIMS analyses in area bombarded in such conditions reveal deep modifications of the surface composition and structure, indicating the formation of a Carbon Black form. The energy threshold observed for the development of surface morphology features is explained on the basis of the balance between surface damage and sputtering induced by the primary ion beam.

Atomic force microscopy investigation of the O2+-induced surface topography of InP

The surface topography development of InP as a function of O2+ ion energy and incident angle was investigated using atomic force microscopy (AFM). Cone formation was found to be the dominant surface feature under various O2+ ion bombarding conditions. However, variations in the density and size of the cones at different O2+ ion bombardment conditions were observed. The variation of surface topography with O2+ ion bombardment conditions is correlated with changes in InP surface composition. The results support an intrinsic model of cone formation, which postulates that the sputtering of InP causes In enrichment at the surface due to the preferential sputtering of phosphorus from InP. Furthermore, radiation-enhanced surface diffusion results in agglomeration of indium atoms into indium clusters. These indium clusters seed the development of sputter cones due to the difference in sputter rates of InP and indium. © 1998 John Wiley & Sons, Ltd.

Surface topography development on ion-beam-sputtered surfaces: Role of surface inhomogeneity induced by ion-beam bombardment

To understand the deterioration of the interface resolution in sputter depth profiling and the surface roughness development in semiconductor and thin-film processings, the chemical states of constituents of ion-bombarded surfaces were analyzed by in situ x-ray photoelectron spectroscopy (XPS) measurement under various ion-beam bombardment conditions. The XPS results were compared with secondary-ion-mass spectrometry (SIMS) depth profiling results and surface topographic developments observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM) for a Cr/Ni multilayered thin-film structure and a GaAs/AlAs superlattice under various incidence angles and the primary ion species. SEM and AFM measurements showed that the deterioration of the interface resolution was determined mainly by surface topographic development which is very sensitive to the ion incidence angle and the primary ion species. With changing the incidence angle from the surface normal to 80° and the primary ion species between Ar+ and O+2 systematically, the effects of the ion incidence angle and the ion species on the chemical states of constituents, the depth resolution in SIMS depth profiling, and the surface topographic developments were studied by in situ XPS, SIMS, SEM, and AFM, respectively. From the systematic studies on ion-beam-bombarded surfaces of Ni, Cr, GaAs, AlAs, Si, and SrTiO3 under various ion bombardment conditions, it could be concluded that the surface inhomogeneity introduced by ion-beam bombardment is one of the most important factors that determine the surface topographic development on ion-bombarded surfaces.

An in-situ laser-light scattering study of the development of surface topography during GaAs and In xGa 1 − xAs chemical beam epitaxy

The development of surface topography during the annealing of epi-ready (001) GaAs wafers and the subsequent CBE growth of GaAs and In x Ga 1 − x As layers were investigated using laser-light scattering (LLS) from a rotating substrate. The change in scattered light intensity during the pre-growth anneal is usually attributed to oxide desorption. However, we have found that a wide range of behaviour is possible depending on the growth history of the chamber. We suggest that this is due to the desorption of previously deposited species from the cryopanel as a result of radiant heating from the substrate, leading to contamination of the wafer surface. Procedures to minimise this contamination are outlined. LLS was used to study the changes in surface topography during growth, particularly the development of elliptical islands during the growth of GaAs and the onset of the “cross-hatch” pattern during the growth of InGaAs. It has recently been established that the ridges of the cross-hatch pattern are associated with dislocations which lie parallel to the surface. The development of these ridges parallel to 〈110〉 is related to the critical thickness of the layer. Interference oscillations in scattered light intensity during the growth of multilayer structures are also shown to be observable using LLS.

Development of surface topography during cold rolling of twin-roll cast aluminium

A study of the development of surface structure during cold rolling of twin-roll cast aluminium has been carried out owing to its importance for appearance, forming properties and corrosion resistance. It is found that the as-cast surface determines the development of the surface topography during cold rolling. This is due to the large roughness associated with the groove/shingle configuration of the as-cast surface. During the first rolling pass the large grooves are deformed into gorges with flat areas between. Peaks are smeared opposite to the rolling direction forming shingles in the subsequent passes. These shingles do not completely adhere to the underlying bulk material and consequently deform heterogeneously on further rolling. Cross hatches may develop on the surface of the shingles. The cross hatches increase in size and spacing on successive rolling, and new ones are formed. Varying amounts of aluminium fines were found in the lubricant as the ends of the shingle are detached from the surface during deformation. The final rolled surface is characterized by thin shingles which overlap and make regions of lamellae in a narrow thickness range on the surface. Many cross hatches of varying size and distribution penetrate one or several of these lamellae.

Initial stages of development of the surface topography induced by ion bombardment

The development of surface topography is conducted on the basis of consideration of the stochastic sputtering process. Elemental, inhomogeneous and multilayer structures are investigated. It is shown that in the case of multilayer structures the microscopic roughness of the surface depends significantly on the ratio of sputtering yields of contacting layers and on the interface properties. It is shown that ion beams can be employed for surface roughness control.

An STM study of the development of surface features on gold under low-energy helium ion bombardment

The development of small-scale surface topography on initially atomically flat gold surfaces under irradiation with 3 keV helium ions has been investigated using a scanning tunneling microscope (STM). The study has revealed surface features that appear to result from the underlying defect morphology in the implanted metal rather than from sputter-erosion processes occurring at the surface. These features are stable at room temperature. Smaller, sub-monolayer height “bumps” have also been observed under some conditions. It is postulated that these features may be an electronic rather than an elastic effect.

Surface topography of eroded Cu and Si cathodes in a PIG ion source

The surface topography development on a Cu sheet and a Si(111) wafer was studied after being sputtered in a Penning ionization gauge (PIG) ion source using Ar gas. In the case of Cu, a high density of conical structure was developed on the surface. The most striking feature was that the individual cones, relatively large in size, were often coated with impurity layers. Some cones were decorated with concentric ring-like patterns on their surfaces. The overlying coating was thought to be responsible for the initial growth of the cones and subsequent evolution of secondary protuberances on the surfaces of the cones. In the case of Si, though a few impurity-induced conical protrusions were formed, the dominant morphology was in the form of etch pits. In addition to usual single cones, Si surface developed cones of dimeric structure and cluster of cones.

Real-time laser-light scattering studies of surface topography development during GaAs MBE growth

In-situ laser light scattering is shown to yield valuable real-time information on the development of surface micro-topography during GaAs MBE growth. In-vacuo oxide desorption results in a large increase in scattered light intensity. Ex-situ atomic force microscopy has indicated the formation of a high density (>10 9 cm -2) of surface pits, attributed to localized GaAs consumption. Subsequent GaAs homoepitaxial growth (at 600°C) results in the development of an anisotropic ridged topography (ridge axes parallel to [110] with ridge dimensions increasing with epilayer thickness (peak-valley ≤ 12 nm for a 2.0 μm thick epilayer). Post growth in-vacuo annealing generates relatively flat surfaces, dominated by misorientation steps. For a 1 μm thick epilayer, annealing has a long time constant ( > 30 min at 600°C).

Ar+-ion sputtering-induced surface topography development on aluminium

The surface topography of aluminium after bombardment with a mass-separated obliquely incident Ar+ beam while simultaneously supplying gold or tungsten “seeds”, as well as under unseeded conditions, was studied by scanning electron microscopy. The sputtered topography was characterized mainly by cones. It was noted that seeding did not necessarily always enhance the cone population, as is widely believed. The expression for the cone apex angle derived from the first-order erosion theory for normal cones was found to predict equally well that for oblique cones. The formation of tailed cones, coalescence of closely packed cones, bending of cones and disintegration of the cone apex were observed and are discussed. Finally, the corrugated terraced morphology developed on some grains was similar in nature to that observed on semiconductors rendered amorphous under ion bombardment.

Oxygen bleed-in during SIMS depth profiling: curse or blessing?

Abstract Oxygen flooding of the target during SIMS depth profiling finds widespread application foranumber of reasons. Among others it enhances the (positive) secondary ionization efficiency, helps in suppressing bombardment-induced surface topography development and reduces the transition time to steady-state erosion conditions. These attractive properties are offset by a number of artefacts that may be introduced by O2 inlet. A summary of vices and virtues, largely based on existing knowledge, is presented. Then one of the few open questions is addressed, namely to what extent O2 bleed-in ffects depth resolution. This is examined in some detail by studying ultrashallow dopant profiles of B, P, Ga or Sb in Si by SIMS with and without O2 leak.

Ion-induced topography, depth resolution, and ion yield during secondary ion mass spectrometry depth profiling of a GaAs/AlGaAs superlattice: Effects of sample rotation

Effects of sample rotation and sputtering conditions on the depth resolution and ion yield during secondary ion mass spectrometry (SIMS) sputter depth profiles have been studied on bulk GaAs and a GaAs(5 nm)/Al0.3Ga0.7As (5 nm) superlattice. Profiles without sample rotation with 1.0–7.0 keV O+2 show a rapid degradation of the depth resolution with increasing sputter depth. Profiles with Ar+ show only slight degradation. Scanning electron microscope (SEM) studies indicate that degradation is associated with development of periodic surface ripples. The wavelength of the ripples is energy dependent and increases with increasing ion impact energy. With sample rotation, no degradation of the depth resolution is observed and SEM micrographs indicate that surfaces sputtered with rotation are smooth. In addition, with 3.0 keV O+2 significant changes in the secondary ion yield of AsO+ from bulk GaAs are observed at a depth of ∼200 nm. No changes are observed with sample rotation. Our results demonstrate that sample rotation during SIMS depth profiling prevents and can reverse the development of surface topography that both degrades depth resolution and changes secondary ion yield. Thus, interpretation and quantitation of SIMS analysis is facilitated.

The effect of orientation on ion beam erosion rates in ionic crystals measured by SIMS depth profiling

AbstractThere are reports in the literature that crystal orientation is a major source of variation in sputter yields when examining biomineralized tissue material. To examine this further, single crystals of fluorapatite and calcite, both mineralogical analogues, were examined with two different SIMS machines, an Atomika 2000 and a Cameca IMSA4F. Craters were eroded on planes parallel to (0001) and (1010) of both samples for different lengths of time, at different angles and with different primary ion beams. Instruments were operated at a voltge of 10 or 15 kV for Cs+ and O2+, respectively, and a primary beam current of 200 nA. The erosion times were such that all sites were exposed to high fluences of 1018 ions cm−2. For a given experimental geometry and primary ion beam, there wee no discernible differences in erosion rates due to crystal orientation. It is believed that this is due to amorphization of the crystal surface at the target site by site by ion bombardment at high fluences. Therefore, we conclude that crystal orientation is not a significant factor in variation of sputter yield in the materials investigated, and suggest that in biomineralized tissue material the development of surface topography is due to other factors.

Analysis of the development of large area surface topography during ion etching

The model, considering the lateral displacement and collective behaviour (annihilation) of surface macrosteps together with the dependence of the local etching rate on the material properties, is proved to be able to predict the development of the surface topography at various etching parameters (incidence angle of the ion beam, static or rotating sample, sputtering gas) 1,2. The model has been applied for single crystalline (Si, Al) and polycrystalline (Ti, Cu) materials. The effect of sample rotation and rocking on the topographical development is discussed in dependence on the ion beam incidence angle. It is shown that surface polishing can be achieved for all kinds of samples using adequate parameters; however, there is a limit for the smoothness depending on the sample material and sputtering gas.

Analysis of the development of large area surface topography during ion etching : A. Barna, P. B. Barna and A. Zalar. Vacuum40(1/2), 115 (1990)

Analysis of the development of large area surface topography during ion etching : A. Barna, P. B. Barna and A. Zalar. Vacuum40(1/2), 115 (1990)

On the development of increasing surface roughness during ion sputtering

A simple statistical model has been developed to explain the development of surface topography (roughness) during ion sputtering of solid targets. The square root depth dependence of the surface roughness is explained by assuming that the roughness is caused by the differences in sputtering rates obtained on differently oriented crystallographic surfaces, and that the distribution of the sputtering rates is fully random. Deviations from the random distribution of the sputtering rate lead to different types of depth dependence of the surface roughness.

Suppression of surface topography development in ion‐milling of semiconductors

AbstractThe occurrence and growth of hummocks on semiconductor surfaces rotated during ion bombardment have been studied. A simple geometrical is proposed which explains why such topographical features may be observed at incident angles of about 65° with respect to the surface normal, whereas they disappear or do not develop at angles of about 80°. It is argued that even microscopic surface undulations with dimensions of the order of 10 nm initiate hummock formation. Finally it is shown that a smooth surface, which can be produced by ion‐milling at grazing incidence, effectively prevents surface tropography development at any angle of incidence.