Hillock Morphology Research Articles

Nanoscale effects of strontium on calcite growth: An in situ AFM study in the absence of vital effects

This experimental study presents in situ measurements of step migration rates for layer growth of calcite at various levels of superaturation and fluid Sr concentrations. Our results show that Sr has complex behavior as an impurity. At low concentrations, Sr promotes faster growth. This effect may be associated with slight shifts in calcite solubility when Sr is incorporated or may be due to as yet uncharacterized kinetic effects. At higher concentrations, Sr stops step advancement by pinning kink-sites or step edges. The threshold concentration of Sr needed to halt growth is positively correlated with supersaturation. Addition of Sr to the calcite growth system leads to significant changes in hillock morphology. Hillocks become elongate perpendicular to the projection of the c-glide plane, in contrast to the changes previously reported for Mg. Step edges also become scalloped, and the boundary between the obtuse-stepped flanks disappears and is replaced by a new step direction with edges parallel to [010]. Incorporation of Sr was measured at two supersaturation levels and identical fluid [Sr]. The results indicate a strong positive correlation between fluid supersaturation and crystal Sr content. Further, Sr is strongly fractionated between obtuse- and acute-stepped flanks by a factor of approximately two. The sensitivity of Sr uptake to supersaturation may explain apparently contradictory results in the literature regarding whether Sr uptake in the calcite produced by one-celled marine organisms is controlled by temperature. In addition, Sr contents of natural calcite samples may be good indicators of the levels of supersaturation at which the crystals grew. Results of this investigation demonstrate the importance of understanding impurity-specific interactions with calcite growth surfaces at the microscopic scale. Despite similar chemical behavior in some systems, Mg and Sr clearly have very different effects on calcite growth. If Sr and other impurities are to be used as robust indicators of growth conditions in natural calcite samples, well grounded understanding of the mechanisms of recording trace element signatures in calcite is an essential step toward correctly deciphering paleoenvironmental signals from fossil calcite compositions.

MOVPE homoepitaxial growth on vicinal GaN(0001) substrates

AbstractHomoepitaxial growth of GaN by metal organic vapor phase epitaxy (MOVPE) was systematically evaluated using nominal c‐plane and various vicinal GaN(0001) wafers: 1°, 2°, 4°, and 8° offcut in the directions of 〈10$\bar 1$0〉 and 〈11$\bar 2$0〉. It was found that a hillock morphology formed on the nominal c‐plane substrate whereas smooth epi films were formed on vicinal substrates. Silicon‐doped films showed similarly improved surface morphology with offcut angle, however Mg‐doped films exhibited a rougher microstructure. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

In situ interferometric investigation of hillock morphology of the {100} and {101} faces of KDP growing in TMS gels

AbstractThe results of an in situ interferometric study of the surface morphology of {100} and {101} faces of potassium dihydrogen phosphate (KDP) crystals growing in the tetramethoxysilane gel are described and discussed. It was observed that: (a) in the case of crystal growth in gel both slopes of hillocks and surface kinetic coefficient are smaller than in solution growth, (b) for low supersaturations face growth rate linearly depends on bulk supersaturation and the structure of growth centers depends on the supersaturation and growth rate, and (c) for high supersaturations polyhedral instability appears. Supersaturation threshold for transition to polyhedral instability was estimated and formation of gel inclusions is discussed. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

AFM investigation of step kinetics and hillock morphology of the {1 0 0} face of KDP

Step velocities and hillock slopes on the {1 0 0} face of KDP were measured over a supersaturation range of 0< σ<0.15, where σ is the supersaturation. The formation of macrosteps and their evolution with distance from the hillock top were also observed. Hillock slope depended linearly on supersaturation and hillock geometry. The two non-equivalent sectors exhibited different slopes and step velocities. AFM shows an elementary step height of 3.7 Å, or half the unit cell height, whereas previous interferometric experiments assumed the elementary step was a unit cell. Values of the step edge energy ( α), the kinetic coefficients for the slow and fast directions ( β S and β F), and the activation energies for slow and fast step motion ( E a,S and E a,F) were calculated to be 24.0 erg/cm 2, 0.071 cm/s, 0.206 cm/s, 0.26 eV/molecule, and 0.21 eV/molecule, respectively. Analysis of macrostep evolution including the dependence of step height on time and terrace width on distance were performed and compared to predictions of published models. The results do not allow us to distinguish between a shock wave model and a continuous step-doubling model. Analysis within the latter model leads to a characteristic adsorption time for impurities ( λ −1) of 0.0716 s.

Growth, structure and annealing behaviour of epitaxial ZrO 2 films on Pt(1 1 1)

For future investigations of catalytic reactions on sulfated ZrO 2 surfaces by means of scanning tunneling microscopy (STM), ZrO 2 films are prepared on Pt(1 1 1) and characterized by STM and low-energy electron diffraction (LEED). The films are prepared by vapor deposition of Zr in an O 2 atmosphere followed by annealing (also in an O 2 atmosphere). Conditions are searched where well-ordered, continuous and smooth ZrO 2 films are formed. Depositing the films according to literature data at room temperature [Surf. Sci. 237 (1990) 166] yields films with hillock morphology which decay during annealing and loose continuity. The desired film perfection is attained, however, if the films are deposited at 470 K and postannealed at 950 K. Continuous films are obtained displaying large terraces and a clear p(1 × 1) ZrO 2(1 1 1) LEED pattern. A splitting of the LEED spots reveals that the films are slightly rotated with respect to Pt(1 1 1). However, annealing the films at temperatures >1000 K again yields discontinuous films which indicates the metastable character of the ZrO 2 films on Pt(1 1 1) substrate.

Influence of carrier gas on the morphology and structure of GaN layers grown on sapphire substrate by six-wafer metal organic chemical vapor deposition system

The influence of hydrogen and nitrogen III-carrier gas mixture on the GaN layers grown at a high temperature of 1100°C by a novel six-wafer metal-organic chemical vapor deposition (MOCVD) were studied using optical microscopy, X-ray diffraction (XRD), and photoluminescence (PL). The different ratio of nitrogen and hydrogen of III-carrier gas strongly affect the growth mechanism of GaN layers. In the case of higher ratio of N 2/(N 2+H 2), the surface shows a hillock morphology. On the other hand, with decreasing the flow rate of N 2 to a smaller ratio of N 2/(N 2+H 2), the surface shows a mirror like morphology. In this case, the growth rate was also decreased. The measurement of X-ray diffraction (XRD) shows that the FWHM of XRD rocking curve of sample grown with smaller flow rate of N 2 becomes wider.

Arsenic pressure dependence of hillock morphology on GaAs ( n 1 1)A substrates grown using MBE

Surface morphology of hillocks on the surface of various orientations of a GaAs substrate was observed by an atomic force microscope (AFM). Only (1 1 1)A and (2 1 1)A substrates formed pyramidal hillocks. The surfaces were the top layers of seven-period asymmetric double quantum wells or the buffer layer, and the Ga flux and substrate temperature were kept constant at 0.76 ML/s and 520°C, respectively. With increasing As pressure from 7.6 ML/s (beam equivalent pressure, BEP; 9.0×10 −6 Torr) to 32 ML/s (BPE; 4.5×10 −5 Torr), the hillock heights and slopes on (1 1 1)A first increased and then decreased at the highest pressures. The decrease in slope was large: at an As pressure of 1.95×10 −5 Torr, the hillock slope on (1 1 1)A was about 0.8°, whereas at 2.85×10 −5 Torr, the slopes were usually less than 0.3°. This reduction of the height and slope at higher As pressure is explained by the decreasing of the super-saturation of GaAs species in a quasi-liquid layer, QLL of As due to increment of Ga desorption.

Characterization of the surface morphology and electronic properties of microwave enhanced chemical vapor deposited diamond films

The surface morphology, electronic structure and atomic bonding configurations of chemical vapor deposition (CVD) diamond films prepared at different stages of the deposition process and subjected to different postdeposition surface treatments have been studied by scanning probe microscopy (SPM), scanning tunneling spectroscopy (STS), and x-ray photoelectron spectroscopy (XPS) surface analysis techniques. SPM image observations show that (a) in the biasing nucleation process, diamond crystallites grow in a three-dimensional manner and the nucleation density reaches 109–1010/cm2; (b) both as-deposited and boron ion implanted films exhibit a hillock morphology on (100) crystal faces; (c) atomic flatness can be achieved on crystal faces by hydrogen plasma etching. STS analysis indicates that (i) the films obtained after an initial biasing nucleation process show a metallic tunneling behavior; (ii) both as-deposited and hydrogen plasma etched CVD diamond films possess typical p-type semiconductor surface electronic properties; (iii) when the as-deposited diamond films are subjected to boron implantation or argon ion etching, the surface electronic properties change from p-type semiconducting behavior to metallic behavior. XPS analysis confirmed that the surfaces for both as-deposited and hydrogen plasma etched diamond films have a tetrahedral atomic bonding configuration. However, the surfaces of boron ion implanted and argon ion etched diamond films exhibited an amorphous carbon-like feature which can be attributed to the surface damage caused by ion bombardment.

Characterisation of cubic boron nitride films at different stages of deposition

Cubic boron nitride (c-BN) films have been prepared by tuned substrate RF magnetron sputtering with different deposition times. The films have been characterised by Fourier Transform Infrared Absorption (FTIR) spectroscopy, X-ray Photoelectron Spectroscopy (XPS) and by Atomic Force Microscopy (AFM) measurements. The results show changes in composition and microstructure of the films with different deposition times that correspond to different growth stages of the BN films. By analysing the AFM images, we believe the BN layer formed at the early stages of deposition have a hillock morphology.

Scanning Probe Microscopy and Spectroscopy of CVD Diamond Films

The surface morphology and electronic properties of as-deposited CVD diamond films and the diamond films which have been subjected to boron ion implantation or hydrogen plasma etching have been systematically studied by high resolution scanning probe microscopy and spectroscopy techniques. AFM and STM image observations have shown that (a) both the as-deposited CVD diamond films and the boron ion implanted films exhibit similar hillock morphologies on (100) crystal faces and these surface features are formed during the deposition process; (b) boron ion implantation does not cause a discernible increase in surface roughness; (c) atomic flatness can be achieved on crystal faces by hydrogen plasma etching of the film surface. Scanning tunnelling spectroscopy analysis has indicated that (a) the as-deposited diamond films and the hydrogen plasma etched diamond films possess typical p-type semiconductor surface electronic properties; (b) the as-deposited diamond films subjected to boron implantation exhibit surface electronic properties which change from p-type semiconducting behaviour to metallic behaviour; (c) the damage in the boron implanted diamond films is restricted to the surface layers since the electronic properties revert to p-type on depth profiling.

Reversed calcite morphologies induced by microscopic growth kinetics: insight into biomineralization

This experimental investigation of calcite growth quantifies relationships between solution supersaturation and the rates of step advancement. Using in situ fluid cell atomic force microscopy (AFM), we show that the movement of monomolecular steps comprising growth hillocks on {1014} faces during the growth of this anisotropic material is specific to crystallographic direction. By quantifying the sensitivity of step growth kinetics to supersaturation, we can produce spiral hillocks with unique geometries. These forms are caused by a complex dependence of step migration rates, vs+ and vs−, upon small differences in solution chemistry as they grow normal to the conventional fast ([441]+ and [481]+) and slow ([441]− and [481]−) crystallographic directions. As solute activity, a, decreases, vs+ and vs− converge and growth hillocks express a pseudo-isotropic form. At still lower supersaturations where a approaches its equilibrium value, ae, an inversion in the rates of step advancement produces hillocks with unusual reversed geometries. Comparisons of the kinetic data with classical theoretical models suggest that the observed behavior may be due to minute impurities that impact the kinetics of growth through blocking and incorporation mechanisms. These findings demonstrate the control of crystallographic structure on the local-scale kinetics of growth to stabilize the formation of unusual hillock morphologies at the near-equilibrium conditions found in natural environments.

The Effect of Ti Interla Yer on the Hillock Formation of Al-0.5WT%Cu Films on the Tin/Ti/SiO2/Si Multilayer Structure

ABSTRACTThe hillock formation of Al-0.5wt%Cu films on TiN/Ti/SiO2/Si and T1N/SiO2/Si multilayer structures was investigated by the observation of FESEM. Two types of hillocks, large and small, were observed in both multilayer structures with or without Ti after annealing at 400°C for 30 minutes. A wedge-like plateau appeared next to the large hillock in the multilayer structure without Ti interlayer. The small hillock also exhibited wedge-like morphology in the same multilayer structure. Both wedge-like plateau and small wedge-like hillocks oriented toward the same direction, which disappeared in the multilayer structure with Ti interlayer. The difference in hillock morphology on these two types of multilayer has been correlated to the difference in the extent of Al(111) texture, which was characterized by the off-axis angle and orientation factors in X-ray ψ scan analysis. The wedge-like hillocks in multilayer without Ti were aligned along the tilted direction with larger off-axis angle in ψ scan. The Al(111) texture was largely improved due to the insertion of Ti into multilayer structure.

Effect of Cr implantation on the morphology of Al:Si films

Al:Si 1% films subjected to irradiation with Cr + ions are investigated for their morphology and appearance of hillocks. The oxidized silicon wafers were coated with 1 μm thick metallic layers by magnetron sputtering. Prior to sintering at 450°C for 30 min the films were implanted with chromium ions at an energy of 130 keV and to doses 4 × 10 15–9 × 10 15 cm −2. Investigations of the processed surface using SEM, alpha-step together with a procedure for digital evaluation of the surface morphology examined by an optical microscope show that chromium implantation leads to a significant reduction of the hillock population, in particular those of the largest size. The effect is observed for Al:Si and Al:Si:Cu alloys but not for pure Al. SIMS profiling gives evidence of measurable mobility of Cr atoms during the annealing. TEM analysis displays a noticeable reduction of the material grain size and reveals in Cr + implanted Al:Si layers an array of fine precipitates located within the grain volume. From the fact that the modification of grain-growth kinetics occurs only when Si is present in the film one may conclude that Cr atoms precipitate in Si-rich phases (binary or ternary). Other effects of Cr implantation into Al-based films are: reduction of the lattice constant and an increase in sheet resistance (by 10%). Formation of Cr-containing precipitates seems beneficial in suppressing overall diffusivity in the layer preventing thus the grains from excessive vertical growth.

Local Texture and Electromigration in Fine Line Microelectronic Aluminum Metallization

ABSTRACTAluminum films 1 μm thick were deposited on oxidized silicon by sputtering and partially ionized beam evaporation to vary the crystallographic texture. These films were patterned into lines and subsequently annealed at 400 °C for 1 h. A strong correlation between the electromigration behavior and the blanket film texture (X-ray diffraction (XRD) / pole figures) has been reported previously for these films. In this work, an Electron Backscatter Diffraction (EBSD) a.k.a. Backscatter Kikuchi Diffraction (BKD) technique was employed using a scanning electron microscope (SEM) to interrogate individual grain orientations. BKD pole figures were acquired for lines ≥0.3 μm wide and for blanket (pad) regions. Identical, inverse pole figures were found for blanket films measured using both XRD and BKD (pads). Furthermore, the BKD (111) fiber texture shows a line width dependency, with narrow lines having a slightly improved texture over blanket (pad) regions. Local grain orientations were investigated near and within electromigration testing sites with characteristic void and hillock morphologies. The relationship of neighboring grain orientations to electromigration damage is shown.

Observation of Crystal Growth Hillock Morphology by Using a phase Conjugation Interferometer

AbstractDetailed experimental arrangements of phase conjugation interferometer used in the studies of crystal growth hillock morphology are discussed. This method is shown very useful for the studies of crystal growth kinetics.

Isothermal annealing of hillocks in AlCu films

Vapor deposited Al-15 wt.% Cu films were formed on oxidized silicon substrates at room temperature. Subsequent heating of these samples resulted in the formation of copper-rich hillocks on the surface of the films because of compressive, substrate-induced differential thermal expansion strains. Transmission electron microscopy (TEM) showed that hillocks were also present on as-deposited films but they were much smaller and not detected by scanning electron microscopy (SEM). Isothermal annealing studies were carried out in the SEM in the 200–300°C range. The decrease in hillock density and the increase in average hillock size were measured as a function of time. Analysis showed that the activation energies for these two phenomena were 0.29 and 0.28 eV respectively, values that are typical of surface diffusion phenomena. These observations are in agreement with an Ostwald ripening mechanism. TEM of samples thinned from the silicon wafer side were also carried out to elucidate the hillock morphology.

Selective etching and photoetching of {100} gallium arsenide in CrO 3-HF aqueous solutions : II. The nature of etchFF hillocks

The morphology and formation history of hillocks formed on n-type, boat-grown, Bridgman ‘100’ GaAs after photoetching in CrO 3-HF aqueous solutions are studied in detail by in situ and ex situ microscopic observations. Two types of hillocks — with pointed and rounded tops — are found. Both are formed due to inhibition of etching as a result of attachment of gas bubbles at the crystal surfaces. The point topped hillocks are caused by bubbles which are nucleated on the GaAs surface, the rounded ones result from bubbles nucleated in the solution and attached later on, after “travelling” over the surface. During this travelling these bubbles leave traces visible by optical microscopy. The contents of the bubbles is not a reaction product but gases dissolved in the etchant which are evolved by the heat of reaction and the absorbed laser light. Intensive stirring of etchant does not prevent attachment of bubbles. However, it gives rise to underetching of the base of hillocks. Most probably, the electric field of the GaAs surface is responsible for the attachment of bubbles. The number of bubbles, i.e. the density and distribution of hillocks, depends upon the composition of etchant, illumination, temperature and pretreatment of the solution. No relation between the defects and the hillock formation has been found.