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1.
In this work, we report on the structural characteristics of as-deposited and crystallized mixed-phase silicon films prepared
by thermal decomposition of silane in a low pressure chemical vapor deposition reactor. Mixed-phase films consist of crystallites
embedded in an amorphous matrix. The size of these crystallites depends upon the surface diffusion length, a parameter quantitatively
expressing the potential of adsorbed silicon atoms for surface diffusion. The density of the pre-existing crystallites can
be related to the maximum density of critical nuclei, which develops during the deposition of the film. Both variables were
quantitatively related to the deposition temperature and rate via physical models reflecting the experimental observations.
Values for the parameters associated with these models were extracted by fitting the experimental data to the theoretical
equations. Our theoretical analysis is the first to relate quantitatively the structural characteristics of as-deposited mixed-phase
films to the prevailing deposition conditions. Mixed-phase films can crystallize in a much shorter time than as-deposited
amorphous films, due to the combination of the growth of the pre-existing crystallites and the higher nucleation rate of new
crystallites within the amorphous matrix of the mixed-phase film. The crystallization time and final grain size of crystallized
mixed-phase films were found to decrease with increasing density of pre-existing crystallites. However, we showed that if
composite films are deposited, consisting of a mixed-phase layer and an amorphous layer, the grain size after crystallization
could be comparable to that of crystallized as-deposited amorphous films, with the crystallization time of such composite
films about threefold shorter. The structure of both as-deposited and crystallized single and composite mixed-phase films
was found to be identical for films deposited on both oxidized silicon and Corning Code 1735 glass substrates. 相似文献
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Jennifer L. M. Rupp Barbara Scherrer Ashley S. Harvey Ludwig J. Gauckler 《Advanced functional materials》2009,19(17):2790-2799
The introductory part reviews the impact of thin film fabrication, precipitation versus vacuum‐based methods, on the initial defect state of the material and microstructure evolution to amorphous, biphasic amorphous‐nanocrystalline, and fully nanocrystalline metal oxides. In this study, general rules for the kinetics of nucleation, crystallization, and grain growth of a pure single‐phase metal oxide thin film made by a precipitation‐based technique from a precursor with one single organic solvent are discussed. For this a complete case study on the isothermal and non‐isothermal microstructure evolution of dense amorphous ceria thin films fabricated by spray pyrolysis is conducted. A general model is established and comparison of these thin film microstructure evolution to kinetics of classical glass‐ceramics or metallic glasses is presented. Knowledge on thermal microstructure evolution of originally amorphous precipitation‐based metal oxide thin films allows for their introduction and distinctive microstructure engineering in devices‐based on microelectromechanical (MEMS) technology such as solar cells, capacitors, sensors, micro‐solid oxide fuel cells, or oxygen separation membranes on Si‐chips. 相似文献
4.
A. Brillante I. Bilotti C. Albonetti J.‐F. Moulin P. Stoliar F. Biscarini D. M. de Leeuw 《Advanced functional materials》2007,17(16):3119-3127
We report confocal micro‐Raman spectra of the organic semiconductor α‐sexithiophene (T6) on bulk crystals and on thin films grown on technologically relevant substrates and devices. We show that the two polymorphs, which are clearly identified by their lattice phonon spectra, may coexist as physical impurities of one inside the other in the same crystallite. Spatial distribution of the two phases is monitored by Raman phonon mapping of crystals grown upon different conditions. Raman microscopy has then been extended to T6 thin films grown on silicon oxide wafers. We identify the crystal phase in thin films whose thickness is just 18 nm. The most intense total‐symmetric Raman vibration is still detectable for a two‐monolayer thick film. Comparative analysis between micro‐Raman and AFM of T6 thin films grown on field effect transistors shows that electrode‐channel steps favour the nucleation and growth of T6 molecules on the substrate, at least below 50 nm. 相似文献
5.
D. G. Gromov G. P. Zhigal’skii A. V. Karev I. A. Karev I. S. Chulkov S. S. Shmelev 《Semiconductors》2011,45(13):1689-1693
Voltage fluctuations in thin nanoscale nickel films which arise during current application through a film sample upon slow
heating are studied. It is shown that positive voltage fluctuations (surges) arise due to an increase in the resistance of
local regions of the film under study, caused by its local thinnings and discontinuities which result from the film melting
onset. The temperature of the melting onset of nanoscale nickel films on oxidized silicon was experimentally determined as
740, 815, and 875 K for films 5, 20, and 40 nm thick, respectively. 相似文献
6.
Effects of oxygen in Ni films on the Ni-induced lateral crystallization (NILC) of amorphous silicon (a-Si) films at various
temperatures have been investigated. It was found that oxygen in Ni films retarded the nucleation of polycrystalline silicon
(poly-Si) from a-Si, but had little effect on the growth rate of poly-Si. This is because that needed an incubation period
to be reduced to Ni metal for the subsequent mediated crystallization of a-Si. 相似文献
7.
对离子束反应溅射沉积过程中,同时经氩离子束轰击形成的氧化锆薄膜进行了RBS,XPS,TEM及XRD的微观分析。结果表明,在本实验条件下的形成膜体部分为标准化学计量配比的ZrO_2;形成膜由非晶和微晶构成,晶化程度与薄膜沉积用的衬底材料有关;在Al衬底上沉积膜有介稳立方相和单斜相出现;所有沉积膜表面均沾污碳。 相似文献
8.
Cola B.A. Karru R. Changrui Cheng Xianfan Xu Fisher T.S. 《Components and Packaging Technologies, IEEE Transactions on》2008,31(1):46-53
This work describes an experimental study of the cross-plane thermal conductance of plasma-enhanced chemical vapor deposited (PECVD) diamond films grown as a result of bias-enhanced nucleation (BEN). The diamond films are grown on silicon wafers using a two-step process in which a nucleation layer of amorphous or diamond like (DLC) carbon is first deposited on the silicon under the influence of a voltage bias. Then, conditions are adjusted to allow for polycrystalline diamond (PD) growth. The nucleation layer is essential for seeding diamond growth on smooth substrates and for optimizing PD properties such as grain size, orientation, transparency, adhesion, and roughness. A photoacoustic (PA) technique is employed to measure the thermal conductivities of and the thermal interface resistances between the layers in the diamond film structure. The influence of nucleation layers that are 70, 240, 400, and 650 nm thick on the thermal conductance of the diamond film structure is characterized. The thermal conductivity of the nucleation layer exhibits a thickness dependence for relatively thin layers. For each sample, the thermal conductivity of the PD is higher than 500 Wldrm-1K-1 (measurement sensitivity limit). A resistive network for the diamond film structure is developed. The resistance at the silicon/nucleation interface is less than 10-9m2ldrKldrW-1 (measurement sensitivity limit), which is of the order of theoretical predictions. The minimum diamond film structure resistance occurs when the nucleation layer is thinnest. When the nucleation layer is sufficiently thick, it begins to exhibit bulk behavior, and the resistance at the nucleation/PD interface dominates the thermal resistance of the diamond film structure. 相似文献
9.
Structure and electrical properties of polycrystalline SiGe films grown by molecular beam deposition
The structural and electrical properties of polycrystalline Si0.5Ge0.5 films 150 nm thick grown by molecular beam deposition at temperatures of 200–550°C on silicon substrates coated with amorphous layers of silicon oxynitride were studied. It is shown that the films consist of a mixture of amorphous and polycrystalline phases. The amorphous phase fraction decreases from ~50% in films deposited at 200°C to zero in films grown at 550°C. Subsequent 1-h annealing at a temperature of 550°C results in complete solid-phase crystallization of all films. The electron transport of charge carriers in polycrystalline films occurs by the thermally activated mechanism associated with the energy barrier of ~0.2 eV at grain boundaries. Barrier lowering upon additional annealing of SiGe films correlates with an increase in the average grain size. 相似文献
10.
Maruf Hossain Husam H. Abu-Safe Hameed Naseem William D. Brown 《Journal of Electronic Materials》2006,35(1):113-117
The effects of hydrogen on aluminum-induced crystallization (AIC) of sputtered hydrogenated amorphous silicon (a-Si:H) were
investigated by controlling the hydrogen content of a-SiH films. Nonhydrogenated (a-Si) and hydrogenated (a-Si:H) samples
were deposited by sputtering and plasma-enhanced chemical vapor deposition (PECVD). All aluminum films were deposited by sputtering.
Hydrogen was introduced into the sputter-deposited a-Si films during the deposition. After deposition, the samples were annealed
at temperatures from 200°C to 400°C for different periods of time. X-ray diffraction (XRD) patterns were used to confirm the
presence and degree of crystallization in the a-Si:H films. For nonhydrogenated films, crystallization initiates at a temperature
of 350°C. The crystallization of sputter-deposited a-Si:H initiates at 225°C when 14% hydrogen is present in the film. As
the hydrogen content is decreased, the crystallization temperature increases. On the other hand, the crystallization initiation
temperature for PECVD a-Si:H containing 11at.%H is 200°C. Further study revealed that the crystallization initiation temperature
is a function, not only of the total atomic percent hydrogen in the film, but also a function of the way in which the hydrogen
is bonded in the film. Models are developed for crystallization initiation temperature dependence on hydrogen concentration
in a-Si:H thin films. 相似文献
11.
Pm-Si:H which has improved optical and transport properties as well as stability compared to hydrogenated amorphous silicon is studied. In order to understand the effect of the growth temperature on pm-Si:H films, hydrogen bonding and stability were analyzed in this work. Samples grown at different temperatures were compared and a change on the films morphology and structure was observed. HRTEM images evidence nanocrystals with approximate size of 9 nm. A growth surface reorganization was observed at an almost constant deposition rate. Increasing the deposition temperature leads to a more ordered, compact and smooth structure of the pm-Si:H films. Hydrogen interaction with the growing surface is related to the deposition temperature, changing the growth of the amorphous matrix due to hydrogen surface diffusion into lower energy and more stable positions. The total hydrogen in the film is reduced as temperature increases and hydrogen becomes more tightly bonded, which changes in a non monotonous way how the nanocrystals are incorporated and their environment. The optoelectronic properties of the films are directly related to the incorporation of hydrogen and whether it is weakly or tightly bonded. A diminution of the optical gap of the pm-Si:H films in the range from 1.71 to 1.65 eV was observed with the increase of the deposition temperature in the range from 175 to 275 °C. 相似文献
12.
R. Z. Bachrach K. Winer J. B. Boyce S. E. Ready R. I. Johnson G. B. Anderson 《Journal of Electronic Materials》1990,19(3):241-248
Low temperature processing is a prerequisite for compatible technologies involving combined a-Si and poly-silicon devices
or for fabricating these devices on glass substrates. This paper describes excimer-laser-induced crystallization of thin amorphous
silicon films deposited by plasma CVD (a-Si:H) and LPCVD (a-Si). The intense, pulsed UV produced by the laser is highly absorbed
by the thin amorphous material, but the average temperature is compatible with low temperature processing. The process produces
crystallites whose structure and electrical characteristics vary according to starting material and laser scan parameters.
The crystallized films have been principally characterized using x-ray diffraction, TEM, and transport measurements. The results
indicate that crystallites nucleate in the surface region and are randomly oriented. The degree of crystallization near the
surface increases as the doping level and/or deposited laser energy density is increased. The crystallite size increases with
a power law dependence on deposited energy, while the conductivity increases exponentially above threshold for unintentionally
doped PECVD films. The magnitude of the Hall mobility of the highly crystallized samples is increased by two orders of magnitude
over that of the amorphous starting material. 相似文献
13.
为了研究连续激光晶化非晶硅薄膜中激光功率密度对晶化效果的影响,利用磁控溅射法制备非晶硅薄膜,采用连续氩氪混合离子激光器对薄膜进行退火晶化,用显微喇曼光谱测试技术和场发射扫描电子显微镜研究了薄膜在5ms固定时间下不同激光功率密度对晶化效果的影响,并对比了普通玻璃片和石英玻璃两种衬底上薄膜晶化过程的差异。结果表明,在一定激光功率密度范围内(0kW/cm2~27.1kW/cm2),当激光功率密度大于15.1kW/cm2时,普通玻璃衬底沉积的非晶硅薄膜开始实现晶化;随着激光功率密度的增大,晶化效果先逐渐变好,之后变差;激光功率密度增大到24.9kW/cm2时,薄膜表面呈现大面积散落的苹果状多晶硅颗粒,晶粒截面尺寸高达478nm ;激光功率密度存在一个中间值,使得晶化效果达到最佳;石英衬底上沉积的非晶硅薄膜则呈现与前者不同的结晶生长过程,当激光功率密度为19.7kW/cm2时,薄膜表面呈现大晶粒尺寸的球形多晶硅颗粒,并且晶粒尺寸随着激光功率密度的增大而增大,在 27.1kW/cm2处晶粒尺寸达到最大5.38m。研究结果对用连续激光晶化法制备多晶硅薄膜的研究具有积极意义。 相似文献
14.
SEM and TEM investigations of the crystallization process have been performed on amorphous Ta2O5 films grown by electrochemical oxidation of Ta foils. It was found that kinetics of crystallization and final structure of
the anodic Ta2O5 film depend strongly on the thickness of the thermal oxide layer on the surface of the original Ta substrate. Two different
modes of crystallization were detected for the substrate with native surface oxide and with the thermal oxide grown at elevated
temperatures. Aborting of the crystallization was shown to be possible using short heating of the Ta2O5/Ta san dwiches which cuts crystalline inclusions grown into the amorphous matrix of the anodic Ta2O5 film from the Ta surface. 相似文献
15.
Ugo Russo Daniele Ielmini Andrea Redaelli Andrea L. Lacaita 《Electron Devices, IEEE Transactions on》2006,53(12):3032-3039
The amorphous phase of chalcogenide material in phase-change memories (PCMs) is subjected to spontaneous and thermal-activated crystallization. This represents a critical reliability issue and has to be carefully investigated and modeled for physically based projection of retention failure up to ten years. A new three-dimensional percolation model describing the statistical crystallization behavior in an intrinsic PCM cell for the amorphous state is developed. With this physical model, the authors were able to calculate the resistance evolution with time in the cell and the statistical distribution of retention failure times in a cell array. From the impact of geometrical parameters on the cell retention performance, PCM design guidelines to minimize data-loss effects can be obtained. The model allows the evaluation of nucleation and growth parameters and statistical extrapolations of intrinsic retention failure, which is shown in part 2 相似文献
16.
Phosphorus doped amorphous/nanocrystalline silicon (a-Si:H/nc-Si:H) thin films have been deposited by a filtered cathodic vacuum arc (FCVA) technique in the presence of hydrogen gas at different substrate temperatures (Ts) ranging from room temperature (RT) to 350 °C. The films have been characterized by using X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, dark conductivity (σD), activation energy (ΔE), optical band gap (Eg) and secondary ion mass spectroscopy. The XRD patterns show that RT grown film is amorphous in nature but high temperature (225 and 350 °C) deposited films exhibit nanocrystalline structure with (111) and (220) crystal orientations. The crystallite size of higher temperature grown silicon film evaluated was between 13 and 25 nm. Raman spectra reveal the amorphous nature of the film deposited at RT, whereas higher temperature deposited films show crystalline nature. The crystalline volume fraction of the silicon film deposited at higher temperatures (225 and 350 °C) was estimated to be 58 and 72%. With the increase of Ts, the bonding configuration changes from mono-hydride to di-hydride as revealed by the FTIR spectra. The values of σD, ΔE and Eg of silicon films deposited at different Ts were found to be in the range of 5.37×10−4–1.04 Ω−1 cm−1, 0.05–0.45 eV and 1.42–1.83 eV, respectively. Photoconduction of 3.5% has also been observed in n-type nc-Si:H films with the response and recovery times of 9 and 12 s, respectively. A n-type nc-Si:H/p-type c-Si heterojunction diode was fabricated which showed the diode quality factor between 1.6 and 1.8. 相似文献
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Barbara Scherrer Sebastian Heiroth Regina Hafner Julia Martynczuk Anja Bieberle‐Hütter Jennifer L. M. Rupp Ludwig J. Gauckler 《Advanced functional materials》2011,21(20):3967-3975
The crystallization and microstuctural evolution upon thermal treatment of yttria‐stabilized zirconia (YSZ, Zr0.85Y0.15O1‐δ) thin films deposited by spray pyrolysis at 370 °C are investigated. The as‐deposited YSZ films are mainly amorphous with a few crystallites of 3 nm in diameter and crystallize in the temperature range from 400 °C to 900 °C. Fully crystalline YSZ thin films are obtained after heating to 900 °C or by isothermal dwells for at least 17 h at a temperature as low as 600 °C. Three exothermic heat releasing processes with activation energies are assigned to the crystallization and the oxidation of residuals from the precursor. Microporosity develops during crystallization and mass loss. During crystallization the microstrain decreases from 4% to less than 1%. Simultaneously, the average grain size increases from 3 nm to 10 nm. The tetragonal phase content of the YSZ thin film increases with increasing temperature and isothermal dwell time. Based on these data, gentle processing conditions can be designed for zirconia based thin films, which meet the requirements for Si‐based microfabrication of miniaturized electrochemical devices such as micro‐solid oxide fuel cells or sensors. 相似文献
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Dimitrios N. Kouvatsos Apostolos T. Voutsas Miltiadis K. Hatalis 《Journal of Electronic Materials》1999,28(1):19-25
In this work, we have characterized various types of polysilicon films, crystallized upon thermal annealing from films deposited
by low pressure chemical vapor deposition in the amorphous phase and a mixed phase using silane or in the amorphous phase
using disilane. Polysilicon thin film transistors (TFTs) were fabricated, at low processing temperatures, in these three types
of films on high strain point Corning Code 1734 and 1735 glass substrates. Double layer films, with the bottom layer deposited
in a mixed phase and the top in the amorphous phase, allowed TFT fabrication at a drastically reduced thermal budget; optimum
values of thicknesses and deposition rates of the layers are reported for reducing the crystallization time and improving
film quality. Optimum deposition conditions for TFT fabrication were also obtained for films deposited using disilane. The
grain size distribution for all types of films was shown to be wider for a larger grain size. Fabricated TFTs exhibited field
effect electron mobility values in the range of 20 to 50 cm2/V·s, subthreshold swings of about 0.5–1.5 V/dec and threshold voltage values of 2–4 V. 相似文献