Film Growth Model Research Articles

Superconformal Film Growth: Mechanism and Quantification

The mechanism and modeling of superconformal film growth used in the electrochemical fabrication of 3-D Cu interconnects is briefly reviewed. The central role of electrolyte additives in controlling feature filling is fully described by the curvature enhanced adsorbate coverage (CEAC) mechanism developed at NIST. The key feature of the CEAC mechanism is redistribution of adsorbed additives through changes of local surface area as dictated by mass conservation and the relative strengths of adsorption. By examining the competition between rate suppressing, accelerating and deactivating adsorbates on planar surfaces the CEAC enables detailed prediction of shape evolution during electrodeposition on 3-D patterned surfaces that are found to be in excellent agreement with feature filling experiments.

CdTe thin film growth model under CSS conditions

A deposition rate model for CdTe via close-spaced sublimation spanning the sublimation and diffusion-limited cases is presented. The approach consists of applying governing equations for each of the two limiting cases and selecting the minimum rate. The model is validated by comparing it to two experimental datasets and adjusting two fitting parameters so that a good quantitative fit is obtained. A good quantitative fit was obtained using the fitting parameter values of α=0.36 and β=0.035 for all the datasets, spanning the sublimation and diffusion-limited cases. This gives confidence that the model is accurate and indicates that the fitting parameters represent physical phenomena. The model was validated within the temperature range from 400 to 600 °C, pressures from 10 −2 to 760 Torr, and substrate source distances from 0.87 to 1 mm but could have greater range of applicability.

Temporal Evolution of an Electron-Free Afterglow in the Pulsed Plasma Polymerisation of Acrylic Acid

By use of time and energy-resolved mass spectrometry, negative ions with masses ranging from m/z = 1-287 amu have been observed in the afterglow of a low-pressure (10 mTorr) pulsed acrylic acid polymerizing plasma. The most intense peaks, seen at m/z = 71, 143, 215, and 287, are assigned to the dehydrogenated oligomer of the form [nM-H](-) for n = 1, 2, 3, and 4, respectively. The results strongly suggest that both m/z = 71 and 143 ions are produced in the on period of the pulse cycle (0.1 ms duration), with higher masses m/z = 215 and 287 being produced by neutral ion chemistry in the off period (up to 40 ms in duration). The increase in the intensity of the [3M-H](-) and [4M-H](-) peaks in the off period is accompanied by a rapid fall in the concentration of [M-H]- ions and electrons, the latter decreasing from approximately 10(15) m(-3) to zero within 150 micros. Deep into the afterglow, Langmuir probe measurements show that the charge species only consist of positive and negative ions, present at equal concentrations in excess of approximately 10(14) m(-3) even after 10 ms that is, the plasma is wholly electron free. To describe the growth of large negative ions a number of possible ion-neutral chemical pathways have been postulated, and a calculation of the ambipolar diffusion rates to the walls suggests that, in the off period, the positive and negative ion contribution to the deposition rate is small ( approximately 1%) compared to the net total deposition rate. However, the observations do indicate that it may be necessary to update models of film growth in the pulsed plasma polymerization of acrylic acid to account for negative ions.

Cone kinetics model for two-phase film silicon deposition

We study quantitatively the morphology of nanocrystalline silicon (nc-Si:H) cones that appear during amorphous silicon (a-Si:H) film growth by chemical vapor deposition from hydrogen-diluted silane. The shapes of the nc-Si:H inclusions are found to be spherical cones, consistent with our “cone kinetics” model for silicon film growth. This model predicts cone development when growth is isotropic and there is sparse nucleation of a second material phase with a higher growth rate. Application of the cone kinetics model provides insights into the deposition of technologically important thin film materials, including protocrystalline silicon, highly P-doped nc-Si:H, silicon heterojunctions, and silicon epitaxy.

207 Kinetic Monte Carlo法によるヘテロエピタキシャル薄膜成長のモデリング(OS15.電子・原子・マルチシミュレーションに基づく材料特性評価(2),オーガナイズドセッション)

207 Kinetic Monte Carlo法によるヘテロエピタキシャル薄膜成長のモデリング(OS15.電子・原子・マルチシミュレーションに基づく材料特性評価(2),オーガナイズドセッション)

Growth of self-assembled monolayer on tetrahedral amorphous carbon film coated magnetic head

The magnetic heads overcoated by tetrahedral amorphous carbon (ta-C) films have been immersed in the 1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane (FDTS) solvent at different predetermined dipping time. The growth of FDTS self-assembled monolayer (SAM) on the ta-C surface has been confirmed by time-of-flight secondary ion mass spectrometry. Four distinct stages were observed in the growing process: (1) low coverage (nucleation), (2) growing up (3) coalescence and (4) complete monolayer, similar to the theoretical models of epitaxial film growth at low temperatures. Contact angle measurement using de-ionized water is carried out to study the time dependence of contact angle during the growth process of FDTS monolayer. The surface morphology, profiles and roughness (rms) of FDTS monolayer were determined by atomic force microscopy (AFM). Furthermore, the variation of monolayer thickness and distribution was revealed by transmission electron microscopy, which is in agreement with the AFM and contact angle results.

Solution-based synthesis of oxide thin films via a layer-by-layer deposition method: Feasibility and a phenomenological film growth model

The feasibility and kinetics of a generic layer-by-layer thin film deposition method are investigated using Y 2O 3-doped ZrO 2, pure ZrO 2, and Gd 2O 3-doped CeO 2 as model systems. Uniform nanocrystalline films have been made via dipping substrates alternately in cationic and anionic precursor solutions. The effects of several key processing parameters, including the number of deposition cycles, cationic concentration, dipping speed, and holding/immersing time, have been investigated. Growth rates of ∼ 4–12 nm per deposition cycle for as-deposited films (i.e., ∼ 2–6 nm/cycle for annealed films), tunable via varying the key deposition parameters, have been demonstrated.

Novel model for film growth based on surface temperature developing during magnetron sputtering

New physical phenomenon consisting in development of the surface temperature T surf, which being equal to the substrate temperature T s at the beginning of deposition, steeply increases and becomes several times higher than T s at the end of the process, is revealed by means of IR-camera and new calorimetric method during sputter deposition of metal films. The reason for the phenomenon is the formation of a liquid-like layer on the growth surface with extremely low (∼10 9 times lower than for metals) thermal conductivity. Variation in the film structure along thickness correlates with the variation in T surf. To explain these effects we developed a model according to which film grows by “gas → liquid → solid” rather than “gas → solid” mechanism which is realized provided that the film grows from energetic atoms.

Step coverage modeling of thin films in atomic layer deposition

A film growth model on microfeatures is proposed to evaluate step coverage depending on precursor injection time in atomic layer deposition. The proposed model is based on that the chemisorption rate of precursors at a certain position along the depth of a microfeature is determined by the total flux of precursors and the sticking probability. The total flux includes the flux coming from the entrance of a microfeature and the flux reflected from other positions inside a microfeature, and the sticking probability depends on the surface coverage of chemisorbed precursor, which is a function of precursor injection time. The proposed model was applied to the deposition of Al2O3 films on 0.3μm diameter holes with an aspect ratio of 10. It was confirmed that the experimental data for step coverage depending on precursor injection time follow the trend predicted by the proposed model.

Combined kinetic and X-ray electron probe microanalysis characterization of local porosity variation and pore shape across anodic alumina films

Porous anodic alumina films on Al were prepared by anodic oxidation of Al in H 2SO 4 electrolyte at a constant temperature and current density and different thicknesses, up to ≈ 41 μm. Their cross section was examined by EPMA for revealing the variation of local porosity across the films and shape of pores while a kinetic model for film growth was developed describing the variation of pore diameter. It was found that the pores open, and local porosity increases, towards the film surface, predicting a conical pore shape, while the results coincided with those obtained by kinetic study. The EPMA analysis combined with kinetic results emerges as a promising tool for studying structural features of these films.

Quantitative TEM analysis of 3-D grain structure in CVD-grown SiC films using double-wedge geometry

We have characterized the structure of chemical vapor deposition-grown polycrystalline cubic SiC films by quantitative transmission electron microscopy. A new double-wedge sample geometry allowed accurate statistical measurements of the grain size as a function of distance from the substrate. The data are well described by the van der Drift model of faceted film growth with a 〈1 1 1〉 texture that narrows with distance h from the substrate. It was found that the distribution of grain sizes d( h) is self-similar and the mean grain size follows a power law of the type 〈 d〉 ∝ h ν . However, the measured exponent ν = 0.68 ± 0.1 is significantly larger than that previously predicted from mean field models and computer simulations of three-dimensional film growth ( ν = 0.4). This difference may be due to the polarity of SiC, its low stacking fault energy and abundant defects, or impurities. The accuracy of the experimental observations due to the new sample geometry reported here is sufficient to enable statistical tomography or provide guidelines for improved computer modeling.

In-situ investigations of magnetron sputtering processes with laboratory X-ray equipment

An Fe–Al duplex film was prepared on a Si(111)-wafer by sputter deposition in a vacuum chamber with two integrated small magnetron sources. The chamber allows the in-situ investigation of such sputtering processes using grazing incidence X-ray reflectivity, X-ray scattering measurements and X-ray diffraction. We will present details of the new cell and present the first results obtained using reflectivity measurements of the Fe–Al thin films. Here we will focus on the detailed evaluation of the specular reflectivity data of the iron films only, which clearly indicates the presence of an iron oxide, the density and roughness of which were determined and their changes with the film thickness were discussed in the framework of thin film growth models.

Formation of (0 0 2) texture in Fe films prepared by thermal treatment

The Fe (0 0 2)-textured films are prepared by both substrate heating and post-annealing process. The (0 0 2) texture can be obtained by annealing the as-deposited films with (1 1 0) orientation. The results can be explained by the film growth model. If the island size is large and amount is small, Fe (0 0 2) texture can be obtained. Instead, the films exhibit the (1 1 0) texture. The texture of Fe films can be controlled by modifying the mobility of adatoms.

Morphology, surface topography and optical studies on electron beam evaporated MgO thin films

Electron beam evaporated thin films of MgO powder synthesized by burning of magnesium ribbon in air and sol-gel technique are studied for their microstructure (SEM), surface topography (AFM), and optical transmission behaviour (UV-visible spectroscopy). MgO thin films are shown to be either continuous or have mesh like morphology. The bar regions are believed to be of magnesium hydroxide formed due to absorption of moisture. Their AFM images exhibit columnar/pyramidal/truncated cone structure, providing support to the 3D Stranski-Krastanov model for film growth. Further, they are shown to have high transmittance (∼90%) in the wavelength range 400–600 nm, but absorb radiation below 350 nm substantially giving signature of a band transition.

Oxidation of hydrogen on oxidized platinum

Abstract The hydrogen oxidation reaction (HOR) on bare and oxidized platinum in alkaline solution was studied at temperatures from 22 °C to 220 °C. It is found that the oxide film formed on platinum has a profound impact on the HOR rate, with the oxidation current decreasing exponentially with increasing overpotential. This inverse Tafel relationship can be explained by combining quantum mechanical tunneling theory with the point defect model (PDM) for film growth and dissolution. The tunneling constant, which is determined by the potential barrier height across the film/solution interface, is found to be temperature independent, if the anodizing constant is assumed to be invariant with temperature, and to be independent of pH and H 2 concentration within the ranges of these independent variables studied. A barrier height of 0.31 eV is obtained from the derived tunneling constant. Based on the combined film growth-quantum mechanical tunneling theory, the HOR is employed as an in situ probe for characterizing the thin oxide film that forms on platinum in alkaline solution as a function of temperature. The calculated film thickness increases linearly with overpotential until the hydrogen oxidation current is too small to be differentiated from the total measured current, which comprises the passive current and the capacitive charging current when measured under potentiodynamic conditions. Compared with conventional techniques, this method has the advantage of being sensitive, convenient, and of an in situ character, although, at the current stage of development, it is limited to a maximum film thickness of 1–2 nm.

Magnetic anisotropy of (110) Fe∕Co superlattices

Magnetic anisotropy field of (110) Fe∕Co superlattices was found to be as high as 1T, with an in-plane easy axis. First principles calculations within the local spin density approximation show good agreement with the measurement. Lowering the symmetry by creating artificial superlattice structures leads to a significant increase in magnetic anisotropy energy as compared with any allotropic form of the elemental components and cubic FeCo. Large anisotropy is attributed to the cubic symmetry breaking due to the multilayer artificial atomic arrangement. Dependence of the anisotropy field on the superlattice period is supported by Monte Carlo film growth modeling.

Theoretical calculations of the AES intensity–film thickness functions for different growth models

The surface spectroscopic methods, e.g. AES and XPS, are widely used in studies of thin film growth. In experiments spectroscopic data are recorded as intensity–film thickness curves. Much theoretical effort had been devoted to calculation AES intensity–thickness functions for different growth modes. A key element of such calculations is finding coverage in each layer. Recently, we developed two models of thin film growth that allow exact determining of coverage in all layers of a growing film. In island growth model the lateral islands growth occurs via capture of migrating adatoms whereas their vertical growth-owing to direct impingement of deposited atoms. Analysis of arising film morphology yields coverage in each layer in analytic form. In layer growth model based on rate equation approach combined with a feeding zone accounting for interlayer mass transport coverage in successive layers are calculated in a straightforward manner. Thus the AES intensity–film thickness functions were derived analytically for island growth and computed numerically for layer growth in various growth regimes (complete/incomplete condensation) and modes (smooth/rough), enabling experimental data to be examined quantitatively and in greater detail than has previously been reported.

A flow model of porous anodic film growth on aluminium

The development of pores in a classical porous anodic film formed on aluminium in phosphoric acid solution is investigated. The study employs a tungsten tracer layer that is incorporated into the anodic film from the aluminium substrate, followed by detection of the tracer by transmission electron microscopy and Rutherford backscattering spectroscopy. Distortions of the tungsten layer on entry into the film and retention of tungsten species in the film are compatible with porosity arising mainly from flow of anodic oxide beneath the pore bases towards the cell walls. The behaviour is contrary to expectations of a dissolution model of pore formation.

Translation-related domain boundaries form to relieve strain in a thin alumina film on NiAl (110)

We examine how translation-related domains form in thin alumina films synthesized by oxidizing a NiAl (110) surface. Low-energy electron microscopy observations reveal that translation-related domains (sometimes called antiphase domains in the literature) are created within isolated alumina islands as they grow or are annealed. Thus, the domains do not originate when islands with displaced lattices impinge, as frequently assumed in models of film growth. Even though the planar defects that bound the translation-related domains cost energy, the misfit dislocations that terminate the domain boundaries lower the film’s strain energy.

Curvature Enhanced Adsorbate Coverage Model for Electrodeposition

The influence of a catalyst deactivating leveling additive in electrodeposition is explored in the context of the previously developed curvature enhanced accelerator coverage model of superconformal film growth. Competitive adsorption between a rapidly adsorbed suppressor, rate accelerating catalyst, and catalyst-deactivating leveler is examined. Rate equations are formulated where the leveling agent is capable of deactivating the adsorbed catalyst by either direct adsorption from the electrolyte or by deactivation/displacement during surface area reduction that accompanies advancing concave surfaces. The influence of a prototypical cationic surfactant leveler on electrochemical kinetics and feature filling is examined for copper electrodeposition from an electrolyte containing polyethylene glycol-chloride-bis(3-sulfopropyl)disulfide (PEG-Cl-SPS).