Synergetic effect between ion energy and sample temperature in the formation of distinct dot pattern on Si(1 1 0) by ion-sputter erosion

We observed a synergetic effect between ion energy and sample temperature in the formation of distinct dot pattern on Si(1 1 0) by Ar⁺ ion sputtering. The ion flux was 20 μA/cm², a value smaller than those used in preceding reports by one or two orders of magnitude. In experiments, the ion energy was from 1 to 5 keV, and the temperature from room temperature to 800 °C. A phase diagram indicating the ranges of ion energy and temperature within which distinct dot patterns can be achieved has been obtained. Data analyses and simulation results reveal that the synergetic effect is consistent with the effect of the Ehrlich-Schwoebel step-edge barrier, rather than the Bradley-Harper model.     

An electrostatic force microscope study of Si nanostructures on Si(1 0 0) as a function of post-annealing temperature and time

The evolution of Si nanostructures induced by Ar⁺ ion sputtering on Si(1 0 0) was studied with electrostatic force microscopy (EFM) as a function of post-annealing temperature (T = room temperature-800 °C) and time (t = 0-160 min). The post-annealing of the nanostructure was conducted in vacuum. It was found that with T increasing, the EFM contrast degraded steadily and became nearly undetectable at T = 800 °C; with t increasing at T = 800 °C, the EFM contrast fell down steadily as well. However, the surface morphology and roughness were much less affected after annealing. The results suggest that the as-formed Si nanostructures may not be epitaxially grown on Si(1 0 0) substrate as claimed before. A plane capacitance model supported this conclusion.     

Flattening of micro-structured Si surfaces by hydrogen annealing

We report atomic scale flattening of surfaces of microstructures formed on Si wafers by furnace annealing. To avoid thermal deformation of the fabricated structures, advantage was taken of hydrogen annealing, which enables us to decrease the relaxation rate of Si surfaces due to surface hydrogenation. We examined cross-sectional shape and sidewall morphology of 3 μm deep trenches on Si(0 0 1) substrates after annealing at 1000 °C under various H₂ pressures of 40-760 Torr. We successfully formed Si trenches with flat surfaces composed of terraces and steps while preserving the designed trench profile by increasing H₂ pressure to 760 Torr.     

The effect of Ehrlich-Schwoebel step-edge barrier on the formation of self-organized Si nanodots by ion-sputter erosion

The ion flux dependence of the self-organized Si nanodots induced by 1.5 keV Ar⁺ ion sputter erosion has been studied. It shows that for the regime with ion flux >∼280 μA/cm², the currently adopted Bradley-Harper (BH) model, which is incorporated in a dynamic continuum equation holds valid. However, for ion flux <∼280 μA/cm², the measured dot size and surface roughness deviate drastically from the BH model. To interpret the data for this lower ion flux regime, the effect of the Ehrlich-Schwoebel (ES) step-edge barrier was introduced into the continuum equation. A consistency between the calculated and the experimental results was reached, furthermore, a reasonable trend was found, that is, the effective ES diffusion decreases steadily with the increasing ion flux, and at ∼280 μA/cm², it became negligibly small.     

Characteristics of surface nano-structural modifications in nitrogen ion implanted W as a function of temperature

The surface modifications of tungsten massive samples (0.5 mm foils) made by nitrogen ion (30 keV; 1 × 10¹⁸ N⁺ cm⁻²) implantation are studied by XRD, AFM, and SIMS. XRD patterns clearly showed WN₂ (0 1 8) (rhombohedral) very close to W (2 0 0) line. Crystallite sizes obtained from WN₂ (0 1 8) line, showed an increase with substrate temperature. AFM images showed the formation of grains on W samples, which grew in size with temperature. These morphological changes are similar to those observed for thin films by increasing substrate temperature (i.e. structure zone model (SZM)). Surface roughness variation with temperature, showed a decrease with increasing temperature. The density of implanted nitrogen ions, and the depth of nitrogen ion implantation in W are studied by SIMS. The results show a minimum for N⁺ density at a certain temperature consistent with XRD results (i.e. I_W (2 0 0)/I_W (2 1 1)). This minimum in XRD results is again similar to that obtained for different thin films by Savaloni et al. [Physica B, 349 (2004) 44; Vacuum, 77 (2005) 245] and Shi and Player [Vacuum, 49 (1998) 257].     

Nano- and micro-scale patterning of Si (1 0 0) under keV ion irradiation

Evolution of Si (1 0 0) surface under 100 keV Ar⁺ ion irradiation at oblique incidence has been studied. The dynamics of surface erosion by ion beam is investigated using detailed analysis of atomic force microscopy (AFM) measurements. During an early stage of sputtering, formation of almost uniformly distributed nano-dots occurs on Si surface. However, the late stage morphology is characterized by self-organization of surface into a regular ripple pattern. Existing theories of ripple formation have been invoked to provide an insight into surface rippling.     

Dependence of surface nano-structural modifications of Ti implanted by N ions on temperature

The surface modification of titanium thin foil/sheet samples (0.5 mm) implanted by nitrogen ions of 30 keV energy and a fluence of 1 × 10¹⁸ N⁺ cm⁻² at different temperatures is studied using XRD, AFM, SEM, and SIMS. XRD patterns showed the development of titanium nitride with different compositions in the implanted samples, while the presence of different titanium compositions such as titanium oxides was also observed. AFM images at 654 K showed the formation of grains, that after initial sputtering of the grain boundary at 728 K temperature, the morphology of the surface changed from small grains to a bimodal distribution of grains at 793 K which consisted of larger grains with bright hillocks within them. This was considered to be due to phase transformation/compositional changes, explained by correlating XRD and SIMS results. The SIMS results showed a maximum at about 730 K and a minimum at about 790 K for both N⁺ density and depth of N⁺ penetration in the Ti sample. The variation of these results with temperature was explained on the basis of the residual gas, substrate temperature, dissociation of water in the chamber and the gettering property of titanium.     

On the influence of the surface roughness onto the ultrathin SiO2/Si structure properties

The surface roughness of the semiconductor substrate substantially influences properties of the whole semiconductor/oxide structure. SiO₂/Si structures were prepared by using low temperature nitric acid oxidation of silicon (NAOS) method and then the whole structure was passivated by the cyanidization procedure. The influence of the surface morphology of the silicon substrate onto the electrical properties of ultrathin NAOS SiO₂ layer was investigated. Surface height function properties were studied by the AFM method and electrical properties were studied by the STM method. The complexity of analyzed surface structure was sensitive to the oxidation and passivation steps. For describing changes in the oxide layer structure, several fractal measures in an analysis of the STM images were used. This fractal geometry approach enables quantifying the fine spatial changes in the tunneling current spectra.     

Surface nano-structural modifications and characteristics in nitrogen ion implanted W as a function of temperature and N energy

The surface modifications of tungsten massive samples (0.5 mm foils) made by nitrogen ion implantation are studied by SEM, XRD, AFM, and SIMS. Nitrogen ions in the energy range of 16-30 keV with a fluence of 1 × 10¹⁸ N⁺ cm⁻² were implanted in tungsten samples for 1600 s at different temperatures. XRD patterns clearly showed WN₂ (0 1 8) (rhombohedral) very close to W (2 0 0) line. Crystallite sizes (coherently diffracting domains) obtained from WN₂ (0 1 8) line, showed an increase with substrate temperature. AFM images showed the formation of grains on W samples, which grew in size with temperature. Similar morphological changes to that has been observed for thin films by increasing substrate temperature (i.e., structure zone model (SZM)), is obtained. The surface roughness variation with temperature generally showed a decrease with increasing temperature. The density of implanted nitrogen ions and the depth of nitrogen ion implantation in W studied by SIMS showed a minimum for N⁺ density as well as a minimum for penetration depth of N⁺ ions in W at certain temperatures, which are both consistent with XRD results (i.e., I_{W (2 0 0)}/I_{W (2 1 1)}) for W (bcc). Hence, showing a correlation between XRD and SIMS results.     

Quasi-one-dimensional structures on the Si(1 1 1) surface induced by Ba adsorption

Ba-induced quasi-one-dimensional reconstructions of the Si(1 1 1) surface have been investigated by low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). While the 3 × ‘2’ surface shows double-periodicity along the stripes in STM images consistent with half-order streaks observed in LEED patterns, no sign of the double-periodicity along the chain direction was detected for the 5 × 1 surface. The 5× stripes in STM images show internal structures with multiple rows. The two rows comprising the boundaries of a 5× stripe in the filled-state STM image are found to have 3a × √3/2 spacing across the stripe. The observation of the successive 3× and 2× spacings between the boundary rows supports a structural model proposed for the Ba-induced 5 × 1 Si reconstruction composed of honeycomb chains and Seiwatz chains. The highest coverage 2 × 8 surface does not reveal a quasi-1D row structure in STM images.     

Surface structure investigations using noncontact atomic force microscopy

Surfaces of several A_IIIB_V compound semiconductors (InSb, GaAs, InP, InAs) of the (0 0 1) orientation have been studied with noncontact atomic force microscopy (NC-AFM). Obtained atomically resolved patterns have been compared with structural models available in the literature. It is shown that NC-AFM is an efficient tool for imaging complex surface structures in real space. It is also demonstrated that the recent structural models of III-V compound surfaces provide a sound base for interpretation of majority of features present in recorded patterns. However, there are also many new findings revealed by the NC-AFM method that is still new experimental technique in the context of surface structure determination.     

AFM lateral force imagining of modified polychloroprene: A study based on roughness analysis

Films of a binary polymer blends comprising polychloroprene (PCP) and piperylene-styrene copolymer (PSC) have been prepared by solution casting. The dependence of the surface morphology of the free blend films on PSC content was studied with both roughness and correlation analysis of lateral force microscopy (LFM) images. Significant changes in roughness and lateral parameter values of different blend film sides have been observed depending on the blend composition. It was shown that up to 15 wt.% PSC is distributed continuously in PCP bulk. The increase of roughness and lateral parameter values at the air/film surface shows the enrichment of PCP in the blends containing 25 wt.% or more PSC. The enrichment of PCP on the air/film surface favours the increase of PSC concentration at the backing/film surface. The films underside morphology becomes similar to that of PSC, when its content reaches 40 wt.%.     

Atomic structure of the carbon induced Si(0 0 1)-c(4 × 4) surface

The atomic and electronic structures of the Si(0 0 1)-c(4 × 4) surface have been studied by scanning tunneling microscopy (STM) and density functional theory (DFT). To explain the experimental bias dependent STM observations, a modified mixed ad-dimer reconstruction model is introduced. The model involves three tilted Si dimers and a carbon atom incorporated into the third subsurface layer per c(4 × 4) unit cell. The calculated STM images show a close resemblance to the experimental ones.     

Self-organized nanostructures in Si1-xGex films on Si(001)

Received: 30 July 1998/Accepted: 23 October 1998     

Stable reconstruction and adsorbates of InAs(1 1 1)A surface

We investigated the surface properties of InAs(1 1 1)A by low-temperature scanning tunneling microscopy (LT-STM) with atomic resolution and first-principles calculation. Very clear atom image was observed, showing that the surface reconstruction is an In-vacancy structure. We also observed two kinds of adsorbates on the surface. The first-principles calculations indicate that the In-vacancy structure is the most stable surface reconstruction under any experimental conditions, which is consistent with the LT-STM observation. Investigations of adsorption properties of an In atom, an As atom, and an As₂ molecule by the first-principles calculations imply that the observed adsorbates are an In atom and an As₂ molecule.     

Interaction of atomic hydrogen with the Si(100)2×1 surface

The interaction of atomic hydrogen with the Si(100)2×1 surface has been investigated in detail by a field ion-scanning tunneling microscope (FI-STM). At low exposure, hydrogen atoms reside singly on top of the dimerised Si atoms, and are imaged brightly. The hydrogen chemisorption induces the buckling of dimers, indicating the strong bonding between Si and hydrogen atoms. The adsorption geometry changed from the (2×1) monohydride phase to the (1×1) dihydride phase with increasing exposure of hydrogen. The former is imaged dark compared with the unreacted Si dimers due to the reduction of the density of electronic states near the Fermi level. Surface etching was also observed during the formation of the dihydride phase. The behavior of hydrogen desorption from the H-saturated Si(100) surface was investigated as a function of annealing temperatures. Our STM results suggest that the desorbing H₂ molecules are formed by two hydrogen atoms on the same dihydride species.     

Ni thin films vacuum-evaporated on polyethylene naphthalate substrates with and without the application of magnetic field

We study the structural properties of the surface roughness, the surface mound size and the interfacial structure in Ni thin films vacuum-deposited on polyethylene naphthalate (PEN) organic substrates with and without the application of magnetic field and discuss its feasibility of fabricating quantum cross (QC) devices. For Ni/PEN evaporated without the magnetic field, the surface roughness decreases from 1.3 nm to 0.69 nm and the surface mound size increases from 32 nm to 80 nm with the thickness increased to 41 nm. In contrast, for Ni/PEN evaporated in the magnetic field of 360 Oe, the surface roughness tends to slightly decrease from 1.3 nm to 1.1 nm and the surface mound size shows the almost constant value of 28-30 nm with the thickness increased to 35 nm. It can be also confirmed for each sample that there is no diffusion of Ni into the PEN layer, resulting in clear Ni/PEN interface and smooth Ni surface. Therefore, these experimental results indicate that Ni/PEN films can be expected as metal/insulator hybrid materials in QC devices, leading to novel high-density memory devices.     

Investigation into defects occurring on the polymer surface during the photolithography process

With a view to improving the realisation of polymer optical waveguide some features relevant to the photolithography process are analysed. This paper focuses on defects that occur on the surface of polymer layers involved in the process. For example, depending on the heat treatment or the deposited material, some worm-like defects appear on the polymer surface. When they occur, the waveguide surface roughness becomes too high (about one hundred nm and more). This means that the optical performance of the waveguides is too poor. In this document, we show the changes in temperature on polymer film surfaces which are coated with a thin inorganic layer and the occurrence of these defects is observed. This work confirms that the defect occurrence is clearly linked to the glass transition temperature. The paper reports that, in some cases, the adjustment of thermal properties by annealing can advantageously shift the glass transition, without changing the target optical properties.     

Structure and morphology of Cu/Ni film grown by electrodeposition method: A study of neutron reflectivity and AFM

We present detailed study of structure and interface morphology of an electrodeposited Cu/Ni film using X-ray diffraction, X-ray reflectivity, neutron reflectivity and atomic force microscopy (AFM) techniques. The crystalline structure of the film has been determined by X-ray diffraction, which suggest polycrystalline growth of the film. The depth profile of density in the sample has been obtained from specular X-ray and neutron reflectivity measurements. AFM image of the air-film interface shows that the surface is covered by globular islands of different sizes. The AFM height distribution of the surface clearly shows two peaks and the relief structure (islands) on the surface in the film, which can be treated as a quasi-two-level random rough surface structure. We have demonstrated that the detailed morphology of air-film interfaces, the quasi-two-level surface structure as well as morphology of the buried interfaces can be obtained from off-specular neutron reflectivity data. AFM and off-specular neutron reflectivity measurements also show that the morphologies of electrodeposited surface is distinctively different as compared to that of sputter-deposited surfaces in the sample.     

Hydrogen on Si: Ubiquitous surface termination after wet-chemical processing

The manufacture of microelectronic devices based on silicon technology is largely dominated by wet chemical processes. By ultraclean sample preparation in air and a fast transfer into UltraHigh Vacuum (UHV) we open up a way for the atomic-scale structural and chemical characterization of silicon surfaces immediately after wet-chemical processing. Using Scanning Tunneling Microscopy (STM), ThermoDesorption (TDS) and InfraRed Spectroscopy (IRS), we find that a surface termination predominantly by hydrogen results from all the different wet-chemical treatments investigated (etching with hydrofluoric acid, rinsing with hot water, chemomechanical polishing)-despite the different chemical ambients and process parameters involved. Microscopically, a crystallographically preferential attack of the silicon is observed in all these processes which results, to a different extent, in anisotropic defect structures on the surfaces. This is explained by an interplay of aqueous reaction kinetics and sterical hindrance on the silicon surface. It is pointed out how a UHV surface analysis of the micromorphology of wet-chemically treated silicon surfaces, so far carried out mostly on Si(111) due to its easier preparation and experimental accessability, may help to provide the in-depth understanding of the atomic-scale mechanisms during wet-chemical processing demanded by the progressing miniaturization of microelectronic devices. The atomically smoother and chemically more homogeneous Si(111) obtained after preferential etching with NH₄F suggests that in future applications Si(111) may gain importance over Si(100), which still dominates in today's semiconductor technology, since future devices increasingly rely on tailor-made and ideal properties on an atomic scale. Due to their structural and chemical simplicity and well-controlable characteristics, H-teminated surfaces after wet-chemical preparation also form ideal substrates for conventional UHV surface studies such as absorption and MBE-growth experiments.