Function Of Film Depth Research Articles

Surface Stoichiometry and Depth Profile of Tix-CuyNz Thin Films Deposited by Magnetron Sputtering.

We report the surface stoichiometry of Ti-CuN thin film as a function of film depth. Films are deposited by high power impulse (HiPIMS) and DC magnetron sputtering (DCMS). The composition of Ti, Cu, and N in the deposited film is investigated by X-ray photoelectron spectroscopy (XPS). At a larger depth, the relative composition of Cu and Ti in the film is increased compared to the surface. The amount of adventitious carbon which is present on the film surface strongly decreases with film depth. Deposited films also contain a significant amount of oxygen whose origin is not fully clear. Grazing incidence X-ray diffraction (GIXD) shows a CuN phase on the surface, while transmission electron microscopy (TEM) indicates a polycrystalline structure and the presence of a TiCuN phase.

Crosslinking gradients of a photopolymerized multifunctional acrylate film control mechanical properties

Photopolymerization of thin monomer films can be used to manufacture parts rapidly, but can lead to gradients of elastic modulus, particularly when the film is illuminated from only one side. In order to better understand the relationship between film curing (expressed in terms of carbon–carbon double bonds, C=C) and mechanical properties, a model was developed and tested against experimental results. The example system used in this work was a thin film microfluidics chip made from a multifunctional acrylate monomer. An 800-micron monomer film containing a photoinitiator was illuminated from the top surface, producing a solid chip. The C=C content and mechanical properties of the chip were measured at multiple positions over the cross sections. Raman spectroscopy was used to measure local C=C concentrations, and nanoindentation was used to measure local Young’s modulus and hardness. Spatial gradients in monomer conversion, Young’s modulus, and hardness were measured on a series of chips manufactured at different light doses. A photopolymerization model was used to fit the Raman data, providing quantitative predictions of the monomer conversion as a function of film depth and light dose. These data were then correlated with the values of Young’s modulus and hardness. The correlation between the photopolymerization and the mechanical properties can be used to optimize the mechanical properties of thin films within the manufacturing and energy constraints and should be scalable to other multifunctional monomer systems.

Growth evolution of SiGe graded buffers during LPE cooling process

Low-Ge-content (up to 6.4%) SiGe compositionally graded buffers were grown on Si (0 0 1) by liquid phase epitaxy. All growths were grown with the same initial temperature and solution composition but cooled to different final temperatures. The growth transitions from two-dimensional crosshatch morphology into a three-dimensional-type morphology. The composition and strain state as a function of film depth was determined by combining results from the reciprocal space maps and scanning electron microscopy thickness measurements. This study revealed that, at first, the initial film growth is fully strained and during a longer growth process this initial film becomes fully relaxed. As the growth continued with further temperature reductions, the films increase in both Ge content and strain. The threading dislocation density (∼106 cm−2) of the buffers is low and remains roughly constant with increasing thickness for the SiGe buffers studied here.

Quadratic nonlinear optics to assess the morphology of riboflavin doped chitosan for eco-friendly lithography

We report the use of the Second Harmonic Generation response from a riboflavin doped chitosan film as a characterization method of the film morphology. This film is of particular interest in the development of new and bio-sourced material for eco-friendly UV lithography. The method allows us to determine how riboflavin is distributed as a function of film depth in the sample. This possibility is of importance in order to have a better understanding of the riboflavin influence in chitosan films during the lithography process. On the contrary, linear optical techniques provide no information beyond the mere confirmation of the riboflavin presence.

A physiochemical processing kinetics model for the vapor phase infiltration of polymers: measuring the energetics of precursor-polymer sorption, diffusion, and reaction.

Vapor phase infiltration (VPI) is a new approach for transforming polymers into organic-inorganic hybrid materials with unique properties. Here, we combine experimental measurements with phenomenological theory to develop a universal strategy for measuring, modeling, and predicting the processing kinetics of VPI. We apply our approach to the well-studied VPI system of trimethylaluminum (TMA) infiltrating poly(methyl methacrylate) (PMMA) because the system undergoes both precursor-polymer diffusion and reaction. By experimentally measuring aluminum concentration profiles as a function of film depth with secondary ion mass spectrometry (SIMS) and film swelling with ellipsometry, we have extracted equilibrium solubility and effective diffusivity as a function of process temperature. Fitting these values to appropriate Van't Hoff and Arrhenius relationships, we can then extract enthalpies for precursor sorption and diffusion. We observe an abrupt mechanistic change in both the sorption and diffusion processes around 95 °C, where greater chain mobility at higher processing temperatures lead to greater reactivity between TMA and PMMA. With new understanding of this VPI process, we demonstrate precise control of inorganic infiltration depth and loading fraction into PMMA.

Thermal Transitions in Dry and Hydrated Layer-by-Layer Assemblies Exhibiting Linear and Exponential Growth

Layer-by-layer (LbL) assemblies are remarkable materials, known for their tunable mechanical, optical, and surface properties in nanoscale films. However, questions related to their thermal properties still remain unclear. Here, the thermal properties of a model LbL assembly of strong polyelectrolytes, poly(diallyldimethylammonium chloride)/poly(styrene sulfonate) (PDAC/PSS), assembled from solutions of varying ionic strength (0-1.25 M NaCl) are investigated using quartz crystal microbalance with dissipation (QCM-D) and modulated differential scanning calorimetry. Hydrated exponentially growing films (assembled from 0.25 to 1.25 M NaCl) exhibited distinct thermal transitions akin to a glass transition at 49-56 °C; linearly growing films (assembled without added salt) did not exhibit a transition in the temperature range investigated and were glassy. Results support the idea that exponentially growing films have greater segmental mobility than that of linearly growing films. On the other hand, all dry LbL assemblies investigated were glassy at room temperature and did not exhibit a T(g) up to 250 °C, independent of ionic strength. For the first time, thermal transitions such as T(g) values can be measured for LbL assemblies using QCM-D by monitoring fluctuations in changes in dissipation, allowing us to probe the film's internal structure as a function of film depth.

Using a new approach to analyze a depth profile of double bond conversion in model formulations

A new approach of analyzing the depth profile of double bond conversion as a function of film depth has been studied. By using a combination of statistical calculation and traditional FTIR, a new approach to analyze the depth profile of conversion “layer by layer” in the characterization of photopolymerization was explored. Utilizing a formula ( X 1 + X 2 + ⋯ + X n )/ n = average conversion, n = 1, 2, 3, ⋯ n is a number of layers (μm), an average conversion of any 5 μm depth could be calculated from the prior 5 μm conversion and the total average conversion. More detailed information of photopolymerization, such as the depth profile of conversion and a difference in conversion between the top 5 μm and the bottom 5 μm in a 25 μm film as a function of film depth, was obtained. This investigation was accomplished using a variation of film depth, non-photo bleaching photo initiator [PhI] as well as the concentration of PhIs in the presence of air and in the absence of air. Results of analyzing double bond conversion between traditional FTIR and the new approach (statistical calculation/FTIR) were compared.

Chemical Analysis of Spray Pyrolysis Gadolinia-Doped Ceria Electrolyte Thin Films for Solid Oxide Fuel Cells

Current solid oxide fuel cell research aims for the reduction of operating temperatures while maintaining power output to reduce the cost of operation. A promising strategy for achieving this goal is to replace common microcrystalline yttria-stabilized zirconia (YSZ) electrolytes of 10−200 μm thickness with nanocrystalline gadolinia-doped ceria electrolytes (CGO) of 100−500 nm thickness deposited by spray pyrolysis. While decreasing the electrolyte thickness, we expect ohmic losses of the fuel cell to decrease linearly and can realize lower operation temperatures at equal efficiency. In this study, the chemical homogeneity of as-deposited and annealed Ce0.8Gd0.2O1.9-x thin films deposited by spray pyrolysis at 350 °C and annealed at 1000 °C were investigated. The chemical composition of the gadolinia-doped ceria films was studied by X-ray photoelectron spectroscopy and Ar+ sputtering as a function of film depth. After the topmost layer was removed by Ar+ sputtering, the thin films showed a surprisingly homogeneous dopant concentration of 23.4 ± 0.6 at % gadolinia in ceria, independent of the film depth. However, spray-pyrolysis-related residues of the precursors (i.e., chlorine from the precursor salt, carbon from the pyrolysis solvents, and water) could be found at unexpected depths in the film and even after annealing at temperatures as high as 1000 °C. The pyrolytic decomposition of the spray pyrolysis thin films is not completely finished after deposition. Changes in the chemical composition may be present during solid oxide fuel cell operation of CGO electrolytes at 600−1000 °C.

Complexity of the microstructure evolution for optimization cBN growth in a four-step ion-assisted deposition process

The changes in microstructure of a specially prepared boron nitride (BN) film as a function of film depth were studied by high resolution transmission electron microscopy (HRTEM) and other materials analysis tools. These changes were then correlated to the changes in processing parameters during film growth. The analyzed film was fabricated by the four-step ion-assisted deposition procedure known to be effective in film-stress engineering for the formation and retention of a thick cubic BN (cBN) layer with a three-step buffer-layer deposition. In this deposition, the energy of the ions assisting cBN formation was increased stepwise from 200 to 280, and then to 360 eV [ S.F. Wong, C. W. Ong, G.K.H. Pang, K.Z. Baba-Kishi, W. M. Lau, J. Vac. Sci. Technol. A 22 (2004) 676]. The nominal thickness of the cBN layer was 650 nm and that for each of the three buffer layers was about 160 nm. Both the HRTEM and electron diffraction results confirmed that the top cBN layer, with a thickness of 643 nm, consisted of cBN grains with a preferred orientation of their c-axis along the film growth direction. In comparison, the three-step buffer layer deposition yielded complex and intriguing microstructures. In the first buffer layer adjacent to the substrate, grains containing sp 2 planes with a preferred orientation of their basal planes parallel to the film growth direction were the main constituents. The increase of ion energy from 200 to 280 eV for the formation of the second buffer layer first led to an enrichment of the concentration of these sp 2 grains with the preferred orientation. Then, bending of some of the sp 2 planes into curved microstructures was evident. The microstructure became very complex and displayed multiple phases including some amorphous structures. The presence of a cBN-like phase was indeed detected by electron energy loss spectroscopy. This complex microstructure persisted until it was replaced by the cBN structure, without abrupt change when the ion energy was increased from 280 to 360 eV for the deposition of the third buffer layer. It is proposed that small grains with cBN-like sp 3 bonding configurations are present in the 2nd and 3rd buffer layers, probably with crystalline domains less than 5 nm and thus difficult for direct detection even by HRTEM. A sufficient accumulation of these cBN nuclei transformed the buffer layer to the cBN layer.

Non-uniform composition profiles in thin film polymeric nanofoams

Neutron reflectivity (NR) and dynamic secondary ion mass spectroscopy (DSIMS) were used to study compositional variations as a function of film depth in thin polymeric nanofoam films formed from triblock copolymers containing 15 wt%, 13 kg/mol polypropylene oxide end blocks with a fluorinated polyimide center block. The triblock copolymer films were spun cast and imidized on silicon substrates and showed an excess amount of polyimide present at both the air/film and film/substrate interfaces. Upon foaming the films showed a slight densification, and the formation of a 50–150 Å thick polyimide skin at the air interface. The final nanofoam materials had a calculated porosity of roughly 20 vol.% in the center portion of the film.

Doppler broadening positron annihilation spectroscopy: A technique for measuring open-volume defects in silsesquioxane spin-on glass films

Doppler broadening positron annihilation spectroscopy is used to measure the concentration, spatial distribution, and size of open-volume defects in low dielectric constant (low-k) hydrogen- and methyl-silsesquioxane thin films. A simple correlation between the number of open-volume defects and the dielectric constant is obtained. In addition, the depth-resolving capability enables profiling of the local electronic environment of open-volume defects as a function of depth. The potential for using this technique for measuring k as a function of film depth is also discussed.

Using Surface Active Random Copolymers To Control the Domain Orientation in Diblock Copolymer Thin Films

The structure of thin films of a symmetric diblock copolymer, P(dS-b-MMA) (dS = perdeuterated styrene, MMA = methyl methacrylate), was investigated near preferential and nonpreferential (neutral) surfaces. Neutral surfaces were achieved at the substrate and air interfaces by localizing random copolymer, P(S-r-MMA), having a styrene fraction of 0.60, to each of these interfaces. This was performed by chemically grafting the random copolymer to the substrate and anchoring a surface active random copolymer having a perfluorinated end group to the air interface, respectively. Neutron reflectivity and small-angle neutron scattering were used to determine the orientation of the lamellar microdomains for films having various boundary conditions. Successive steps of CF4 reactive ion etching followed by field emission scanning electron microscopy were used to ascertain the orientation of the microdomains as a function of film depth. For films confined between two continuous neutral surfaces, the orientation of the...

Improving the resistance of PECVD silicon nitride to dry etching using an oxygen plasma

The resistance of PECVD SiN films to dry etching is increased by more than three orders of magnitude by exposure to an oxygen plasma. In this paper we describe the oxygen treatment. Both the film thickness and the refractive index are modified by the oxygen treatment suggesting a homogenous densification of the SiN network to depths greater than 500 nm. The etch rate of these films was measured during SF6 RIE using in-situ reflectometry as a function of the oxygen treatment time and the SF6 pressure. The SF6 RIE of the untreated films was limited by the reactive ion flux density impinging on the etching surface. The oxygen treatment reduced the SiN etch rate by more than three orders of magnitude and modified the etch mechanism resulting in an ion energy limited etch. The in-situ reflectometry indicated that the SiN etch rate as a function of film depth was essentially constant for any given sample, again suggesting a homogenous modification of the film properties throughout the entire film depth (> 500 nm). We demonstrate and discuss this masking technology for reactive ion etching of deep (> 100 μm) anisotropic via holes in GaAs using SiCl4HBr RIE.

High-efficiency CuInxGa1−xSe2 solar cells made from (Inx,Ga1−x)2Se3 precursor films

In, Ga, and Se were coevaporated to form precursor films of (Inx,Ga1−x)2Se3. The precursors were then converted to CuInxGa1−xSe2 by exposure to a flux of Cu and Se. The final films were smooth, with tightly packed grains, and had a graded Ga content as a function of film depth. Photovoltaic devices made from these films showed good tolerance in device efficiency to variations in film composition. A device made from these films resulted in the highest total-area efficiency measured for any non-single-crystal, thin-film solar cell, at 15.9%.

Depth Profiling of Molybdenum Thin Films Using Grazing Incidence X-Ray Scattering

ABSTRACTIt is important that inherent strains (or stresses) be controlled during thin film processing. This study used grazing incidence x-ray scattering (G1XS) to determine the strain gradient present in a ∼1700 Å sputtered molybdenum thin film. In particular, the gradient in the hydrostatic strain was Measured. This observation corresponded to assessing the average change in the lattice parameter as a function of depth throughout the thickness of the film. In addition, the strain ellipsoids, which represent the state of strain in three dimensions, were calculated as a function of film depth. It was shown that the strain varied throughout the ∼1700 Å Mo film thickness and that the principal strains were anisotropic, with one principal strain much larger than the others in Magnitude.

Spectroscopic Ellipsometry Characterisation of Thin Film Polysilicon

AbstractPhase modulated Spectroscopic Ellipsometry (SE), in the spectral range from 1.5eV to 4.6eV, was employed to characterise thin film polysilicon (poly-Si) deposited by Low Pressure Chemical Vapour Deposition (LPCVD) on SiO2/Si(100) substrates as a function of process parameters. The LPCVD deposition temperature was varied from 550°C to 620°C for silane pressures ranging from 100mTorr to 230mTorr. A variation in poly-Si microstructure was observed as a function of film depth. The influence of deposition conditions on poly-Si surface morphology was quantified using both atomic force microscopy (AFM) and SE. An increase in the measured Raman TO phonon amplitude was observed for the 620°C sample set as a function of increasing LPCVD process pressure.

X-ray study of substrate-induced alignment of a smectic A liquid crystal

Abstract We have performed a structural study of the liquid crystal (LC) octylcyanobiphenyl (8CB), deposited on gratings and flat surfaces, using high resolution X-ray scattering as a function of film thickness. 8CB is a room temperature smectic A2, with a layer spacing of 31·6 Å. Glass was used as substrate and treated with either one of the organic surfactants MAP or DMOAP. Surface tension forces cause the liquid crystal molecules to align perpendicularly with respect to the plane of the substrate at the air interface. Competing with the LC-air interface, which is a strong aligner, a grating at the LC-substrate interface produces distortions in the smectic layering with an excess of elastic energy, which favours alignment parallel to the substrate and the grooves. Our purpose was to detect the onset and evolution of parallel alignment as a function of film thickness. The studies used 9 keV (1·403 Å) X-rays focused to a spot size of 2 mm2 at the sample position. In-plane scans, which detect the smectic layers perpendicular to the plane of the substrate, were done at angles φ = 0° and 90° with respect to the gratings to ascertain the molecular orientation, at a nominal X-ray incidence angle of α = 0°. In order to observe regions of varying smectic layer orientation within the film, we performed a series of scans where the out-of-plane tilt angle χ changed from 0°, corresponding to scattering in the plane of the film, to 90°, which corresponds to scattering normal to the surface of the film. The results from these scans were fitted to a multilayer model where the orientation of the smectic layers varies as a function of film depth. The analysis confirmed our earlier observations that surface tension at the air interface plays a dominant role in the alignment of the LC molecules.

Ion beam analysis of the imidization kinetics of polyamic ethyl ester

The extent of imidization was determined as a function of depth in films of the deuterated version of a model polyimide precursor, polyamic ethyl ester ( d-PAE), using a novel ion beam analysis technique. Monitoring the loss of the deuterated ethyl moiety provided a precise means of evaluating the extent of imidization f as a function of the temperature of imidization and time at the imidization temperature. The imidization reaction was found to proceed uniformly as a function of depth down to 700 nm below the surface. The imidization kinetics followed a two-stage sequence in which the initial rate of imidization was rapid, up to f values of ca. 0.6, whereupon the reaction rate diminished sharply.

Low-temperature processing of titanium nitride films by laser physical vapor deposition

We have investigated the formation of polycrystalline TiN films on (100) Si substrates using a low-temperature laser processing method. The films were deposited by laser ablation of a TiN hot-pressed pellet in the presence of neutral or ionized nitrogen using a XeCl excimer laser (wavelength 308 nm, pulse duration 45×10−9 s, and energy density of 4–5 J cm−2). The substrate temperature ranged from 25 to 550 °C. Plan-view and cross-section transmission electron microscopy studies show that the films are polycrystalline (average grain size ∼100 Å) with face-centered-cubic structure and lattice constant of 4.25 Å. It is interesting to note that the average grain size remained approximately constant with substrate temperature up to 550 °C. Chemical composition was analyzed by Rutherford backscattering and Auger electron spectroscopy as a function of film depth. The results show that the films reproduced closely the chemical composition of the TiN target which contained some oxygen, and that the oxygen content decreased with increased substrate temperature. Four-point probe measurements and I-V characteristics show that the films are metallic with a typical resistivity of ∼150 μΩ cm. The microhardness values of these films were found to be as high as 17 GPa.

MOLECULAR SPUTTERING AND DAMAGE INDUCED BY keV IONS IN MULTILAYERED LANGMUIR-BLODGETT FILMS

The irradiation effects (sputtering and damage) induced by keV ion in LangmuirBlodgett f i lms of different thickness a r e studied for different incidence angles and fo r doses up t o 3 x 1013 ions.cm-2. The fi lms composed of different superposed monolayers allow to study, in SIMS, t h e evolution of t h e molecular ion intensity as a function of film depth. The volume excited by the primary ion is characterized a t small incidence angle by a small radial extension with respect t o i t s depth extension.