Large-grained Films Research Articles

Simultaneous fabrication of nanocrystalline and {100} textured large-grained diamond films

In this work, we report the simultaneous synthesis of both nanocrystalline and {100} textured large-grained diamond films in one deposition run performed in a 5-kW microwave plasma chemical vapor deposition (MPCVD) reactor. This was achieved by employing the coupled effect of nitrogen addition in the gas phase and substrate temperature on the growth of diamond films. In one deposition run, different substrate surface temperatures were obtained by a novel substrate arrangement, nanocrystalline diamond of high growth rate around 3 μm/h was formed at low temperature, while {100} textured large-grained diamond of much higher growth rate about 11 μm/h was grown at high temperature. This new method opens way for mechanical and tribological applications of both nano-diamond and {100} textured diamond in industrial level. This result indicates that distinct growth modes or growth mechanisms were involved at different substrate temperatures with a certain amount of nitrogen addition. The coupled effect of nitrogen addition and temperature on the growth of CVD diamond films and the involved growth mechanism is briefly discussed from the point of view of gas phase chemistry and surface reactions.

Large-grained poly-Si films on ZnO:Al coated glass substrates

Thin film polycrystalline silicon (poly-Si) films have been fabricated by the aluminium-induced layer exchange (ALILE) process on ZnO:Al coated glass. The formation of the poly-Si films was observed during the annealing process using an optical microscope. Poly-Si films formed on ZnO:Al coated glass consist of high-quality poly-Si material, as evidenced by Raman measurement. The average grain size of the poly-Si films slightly increases with decreasing annealing temperature. The formation of poly-Si films on ZnO:Al coated glass led to a preferential (001) orientation at all annealing temperatures (425 °C ~ 525 °C).

Recrystallization of CdTe film under conditions of high temperature and mechanical pressure

A new method, experimental device and technology for large-grained CdTe film preparation are described. This method enabled to produce CdTe films with the thickness of 1–2 µm and more. Films were recrystallized on the top of 100 µm thick Mo plate and Mo/glass substrate. Phase composition of the CdTe film remained stable up to 800 °C of heating plate temperature. Due to the temperature gradient on the recrystallization area, the CdTe film stuck on the upper, low-temperature (400 °C) surface of the substrate, and an ohmic linear contact between the Mo and CdTe was achieved. Independently, face centered cubic form and large-grained CdTe film with preferable orientation (111) was formed.

High-speed μc-Si films deposition and large-grain poly-Si films deposition by surface wave discharge

Microcrystalline silicon (μc-Si) and polycrystalline silicon (poly-Si) films are deposited by surface wave (SW) discharge at 2.45 GHz in H 2/SiH 4 gas. This high density SW plasma at relatively low pressures (4–60 Pa) enables strong dissociation of feedstock gas. The films deposited on substrate are investigated by X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). The SW discharge in 10% SiH 4 at total pressure of ∼ 30 Pa gives μc-Si films on a substrate at 250 °C, at a fairly high deposition rate of 4–20 nm/s, with a crystalline volume fraction of 0.5–0.8 and a grain size of 10–40 nm. Furthermore, poly-Si film with crystalline volume fraction of > 99% is deposited at higher substrate temperature (400 °C) in 2% SiH 4 discharge at lower pressure (4 Pa). X-ray diffraction and SEM results revealed that the grain size of poly-Si films is as large as 600 nm, which is almost 6 times larger than previously reported values.

Surface scanning probe microscopy investigation of solution deposited BiFeO3 thin films

Thin films of the multiferroic perovskite-type oxide BiFeO3 were processed via solution deposition. The annealing schedule was chosen so as to give large and fine grained thin films. Microstructure, polarization, and dielectric properties are reported. It is shown that the large grained film is characterized by poor dielectric properties. Both microstructures show, however, poor polarization characteristics. Surface scanning potential microscopy reveals areas of high and low surface potentials in both specimens with a pronounced effect in the large grained films. It is thought that these areas are indirectly responsible for the poor polarization properties of the processed BiFeO3 films.

A new high-temperature thermal sensor based on large-grain polysilicon on insulator

A new high-temperature thermal sensor based on large-grain polysilicon film formed by metal-induced lateral crystallization (MILC) is proposed. The sensor demonstrates a positive temperature coefficient (PTC) characteristic from 130 °C to high temperatures above 600 °C. Its fabrication process is more cost-effective than its silicon on insulator (SOI) counterpart, and its performance is better than the sensor based on small-grain polysilicon formed by solid-phase crystallization (SPC). Therefore, the proposed sensor is more suitable to be integrated into single-chip CMOS-MEMS gas-sensor system for monitoring the high temperature of sensing membranes.

Low Temperature Deposition and Crystallization of Large-Grained Ge Films on TiN

Germanium films were deposited by low-pressure chemical vapor deposition on TiN substrates using a Si seeding technique. By depositing a self-limiting Si film on TiN via SiH 4 decomposition at 380°C, a continuous, amorphous Ge film could subsequently be deposited by GeH 4 decomposition at 320°C. Amorphous Ge films were crystallized by thermal annealing at ≥405°C for 60 m. Polycrystalline Ge films on TiN are shown to have larger grains and fewer stacking faults when deposited amorphous and subsequently crystallized, compared to films polycrystalline as-deposited.

Copper Compatible Barium Titanate Thin Films for Embedded Passives

Barium titanate thin films have been prepared by chemical solution deposition on 18 μ m thick, industry standard copper foils in the absence of chemical barrier layers. The final embodiment exhibits randomly oriented BaTiO3 grains with diameters between 0.1 and 0.3 μ m, and an equiaxed morphology. The average film thickness is 0.6 μ m and the microstructure is free from secondary or interfacial phases. The BaTiO3 films are sintered in a high temperature reductive atmosphere such that copper oxidation is avoided. Subsequent lower-temperature, higher oxygen pressure anneals are used to minimize oxygen point defects. Permittivities of 2500 are observed at zero bias and room temperature, with permittivities greater than 3000 at the coercive field. Loss tangents under 1.5% are demonstrated at high fields. The BaTiO3 phase exhibits pronounced ferroelectric switching and coercive field values near 10 kV/cm. Temperature dependent measurements indicate a ferroelectric transition near 100∘C with very diffuse character. Combining the approaches of the multilayer capacitor industry with traditional solution processed thin films has allowed pure barium titanate to be integrated with copper. The high sintering temperature—as compared to typical film processing—provides for large grained films and properties consistent with well-prepared ceramics. Integrating BaTiO3 films on copper foil represents an important step towards high capacitance density embedded passive components and elimination of economic constraints imparted by traditional noble metallization.

Grain Growth Mechanism of Cu Thin Films

Since Cu was found to be attractive as interconnect materials for ultra-large scale integrated (ULSI) Si devices, the electrical properties of Cu films have been extensively studied to prepare low resistance films. It was found in our previous papers that reduction of the electrical resistance of the Cu films was achieved by increasing grain sizes of the Cu films and large-grained Cu films were essential for the low resistance Cu interconnects. The primary factor to increase the grain sizes was also found to be intrinsic and/or extrinsic strain (or stress) introduced into the films. The present paper addresses the driving force of the grain growth of the Cu thin films based on the strain energy criterion model.

Performance of Poly-Si TFTs Fabricated by SELAX

Selectively enlarging laser crystallization (SELAX) has been proposed as a new crystallization process for use in the fabrication of thin-film transistors (TFTs). This method is capable of producing a large-grained and flat film of poly-Si. The average grain size is 0.3/spl times/5 /spl mu/m, and the surface roughness of the poly-Si layer is less than 5 nm. The TFTs fabricated with this method have better performance and are more uniform than those produced with the conventional excimer laser crystallization (ELC) method. The average values of field-effect mobility are 440 cm/sup 2//Vs (n-type), and 130 cm/sup 2//Vs (p-type). The subthreshold slope for both types is 0.20 V/dec. Values for standard deviation of threshold voltage are 0.03 V (n-type) and 0.20 V (p-type). The delay time of the CMOS-inverter of SELAX TFTs is less than half that of ELC TFTs.

Structural Nonuniformity and Internal Stress in Chromium Films Deposited by Magnetron Sputtering

Using high-resolution transmission electron microscopy, selected area electron diffraction and X-ray diffraction methods, the microstructures and lattice parameters of different parts of Cr films deposited by magnetron sputtering under different deposition conditions have been studied. It was revealed that the microstructure and lattice parameter of the films deposited onto nonheated substrates vary in the film thickness direction. Lattice parameter a has a maximal value in the film-substrate interface region and gradually decreases towards the conventional value in the middle and upper film parts. In accordance with this, the internal tensile stress decreases, while the grain size increases in the direction from the substrate to the film surface. Elevation of the substrate temperature results in smoothing of nonuniformity of the film microstructure and stress distribution along the thickness. At a certain combination of a substrate temperature and bias voltage, unstressed large-grained films with uniform microstructure have been deposited. The model proposed for explanation of the obtained results is based on the supposition of dynamic elevation of condensation surface temperature during film growth that promotes the formation of the film with structure and stress nonuniformly distributed in the thickness direction.

Lattice-matched, large-grain HTS films for reproducible Josephson junctions

Several novel techniques are now available to dramatically increase the grain size of epitaxial Rare-earth-BCO films so they are effectively single crystals. Our motivation is to use single-crystal films for base electrodes of edge SNS junctions to improve their reproducibility. We employed the technique of tri-phase to grow films by liquid phase epitaxy in a pulsed laser deposition system and examined the surface morphology and crystal structure of the films. We tried several techniques for in-situ monitoring of a Ba-Cu liquid flux on the surface of the film during growth - including resistivity and emissivity measurements - but found that the only way to be certain that we had a liquid phase on the sample surface was from the dendritic crystal patterns that formed after cooling the samples. We observed series of small cracks in the resulting films, presumably due to stress from lattice-match and thermal expansion mismatch with the substrates so we developed a solid solution of YBa/sub 2/Cu/sub 3/O/sub 7/ and NdBa/sub 2/Cu/sub 3/O/sub 7/ to match the lattice of our substrates to better than 0.1%.

Cu-Compatible Ultra-High Permittivity Dielectrics for Embedded Passive Components

ABSTRACTBarium titanate thin films have been prepared by chemical solution deposition on 18 μm thick, industry standard copper foils in the absence of chemical barrier layers. The final embodiment exhibits randomly oriented BaTiO3 grains with diameters between 0.1 and 0.2 μm, and an equiaxed morphology. The average film thickness is 0.6 μm and high resolution cross sectional microscopy shows no indication of interfacial phases. The BaTiO3 films are sintered in a high temperature reductive atmosphere such that copper oxidation is avoided. Subsequent lower-temperature, higher oxygen pressure anneals are used to minimize oxygen point defects. Permittivities greater than 3000 are observed, with loss tangents under 2.5%. The BaTiO3 phase exhibits pronounced ferroelectric switching and coercive field values near 20 kV/cm. Temperature dependent measurements indicate a ferroelectric transition near 100 °C with very diffuse character. Combining the approaches of the multilayer capacitor industry with traditional solution processed thin films has allowed pure barium titanate to be integrated with copper. The high sintering temperature – as compared to typical film processing – provides for large grained films and properties consistent with well-prepared ceramics. Integrating BaTiO3 films on copper foil represents an important step towards high capacitance density embedded passive components.

EFFECT OF GRAIN SIZE ON THE FERROELECTRIC PROPERTIES OF Bi3.25La0.75Ti3O12 Thin Films

The Bi 3.25 La 0.75 Ti 3 O 12 (BLT) thin films were prepared by metalorganic decomposition method. The effect of grain size on the ferroelectric properties during crystallization were investigated by x-ray diffraction and field emission scanning electron microscope. The grain size and the roughness of BLT films increase with increasing of drying temperature. The leakage current densities of the BLT thin film with large grains are higher than that with small grains. The remanent polarization of BLT increase with increasing grain size. As compared BLT with small grain size, the BLT film with larger grain size shows better fatigue properties. This may be explained that small grained films shows more degradation of switching charge than large grained films.

Microstructure of Film Growth from Filtrating Mono-dispersed Particle Suspension

The deposition mechanism that determines the microstructure of colloidal films was investigated using a constant-filtration-rate procedure. In particular, we studied the dependence of the grain size on the filtration rate and the volume fraction of the particles in liquid. We correlated the surface diffusion distance to the final grain size and identified a processing window for large-grain colloidal films. The necessary conditions for homoepitaxy of colloidal crystals were successfully identified. In particular, the surface diffusion distance of deposited particles before embedment emerged as an important parameter for film microstructural control. Sufficiently long the diffusion distances correlated well with the slow deposition rates often required for crystal growth. Low deposition rates allowed more time for depositing particles to sample surface sites for low-energy configurations. This surface diffusion model for microstructure control has universal application to other film deposition methods for mono-dispersed particles.

Aluminum-induced crystallization of amorphous silicon

We investigated the aluminum-induced crystallization of amorphous silicon (a-Si) during the aluminum-induced layer exchange (ALILE) process, in which a stack of glass/Al/a-Si is transformed into a glass/polycrystalline silicon (poly-Si)/Al(Si) structure by an annealing step well below the eutectic temperature of the Al/Si system. Our experiments resulted in continuous large-grained poly-Si films on glass substrates. The nucleation and the growth of the crystalline phase during the ALILE process was observed using an optical microscope. We found an activation energy of 1.8 eV for the nucleation process and we related this energy to a large barrier at the a-Si/Al interface.

Large-Grain Polysilicon Films with Low Intragranular Defect Density by Low-Temperature Solid-Phase Crystallization

AbstractSolid phase crystallization (SPC) of a-Si: H at 600°C was investigated by transmission electron microscopy (TEM) and Raman spectroscopy in a cantilever structure, where the underlying SiO2 was removed prior to the crystallization. The absence of the underlying oxide leads to both a higher grain size and a lower intragranular defect density. The grain size increases from 0.6 μm in regions with the underlying oxide to 3.0 μm without the underlying oxide, and the intragranular defect density decreases one order of magnitude from ∼ 1011 cm-2 to ∼ 1010 cm-2. The improvements in material quality without the lower a-Si/SiO2 interface are thought to be due to a lower nucleation rate and a lower tensile stress with an easier silicon atomic rearrangement at the lower silicon interface.

The influence of filament temperature on crystallographic properties of poly-Si films prepared by the hot-wire CVD method

This paper presents the deposition and characterization of polycrystalline silicon (poly-Si) films by the hot-wire chemical vapor deposition (HWCVD) method. The filament temperature was determined to be a critical parameter for the deposition of large-grained Si films. Poly-Si films with a moderate lateral grain-size of ∼1 μm and a vertical grain size approximately the same as the film thickness (approx. 3 μm) could be deposited on a glass substrate at a substrate temperature of less than 550°C by increasing the filament temperature to 2000°C. The surface of the films has a natural textured structure, which is believed to give some positive effects on solar cell performance. Some experimental results are presented in order to elucidate these improvements in crystalline properties of the Si films deposited at high filament temperature.

Effect of composition and microstructure on temperature coefficient of resistance of polycrystalline La1−xCaxMnO3 thin films

Polycrystalline La1−xCaxMnO3 films were rf-sputtered on Si substrates coated with SiO2, and the effects of deposition parameters on the temperature coefficient of resistance (TCR) values were investigated. For the temperature higher than the metal–insulator transition temperature (Tp), the temperature dependence of resistance can be described by using the small polaron model, and the TCR value increases with the activation energy Ea for the polaron hopping. For the temperature higher than Tp, increasing the oxygen or Ca content of the film results in the decrease in resistivity, Ea, and TCR value. The resistivity and TCR value are also reduced in large-grained films. Applying a substrate bias can enhance the TCR value.

Effect of grain size of Pb(Zr 0.4Ti 0.6)O 3 sol–gel derived thin films on the ferroelectric properties

Lead zirconate titanate (PZT) (Zr/Ti=40/60) thin films on Pt/SiO 2/Si substrate with greatly different grain size were attained well with controlled atomic composition and crystalline orientation by varying the starting solution composition and annealing time. Small and large grained films with (1 1 1)-preferred orientation were obtained and their grain sizes were approximately 110 and 370 nm, respectively. Since annealing treatment induced the alternation of microstructure and stress at the interface, the effect of grain size was discussed in a standpoint of microstructural characteristic. Measurements of ferroelectric and electric properties revealed that small grained film presents more gradual polarization behavior, less degradation of polarization through switching cycles, and lower leakage current density than large grained film.