Ge/Si薄膜材料生长的偏压效应研究

利用超高真空磁控浅射系统生长了不同偏压下Ge／Si薄膜材料,所生长的材料采用了不加偏压和加偏压的生长环境。通过X射线小角衍射分析表明,加一定偏压的Ge／Si薄膜材料的层状远比不加偏压的材料好,并且加偏压可有效降低材料的生长温度。在加15－25V偏压明,获得了300℃的生长温度下,层状优良,粗糙度小的薄膜材料。     

Low temperature interdiffusion in Au/In thin film couples

Interdiffusion in Au/In thin film couples was studied by in situ backscattering spectrometry. The substrate temperature was varied in the range from -170 to +50 °C. It was found that a uniform layer of AuIn₂ grows at the same rate as that at which gold condenses onto an indium film for substrate temperatures down to -50 °C. This is the fastest formation of intermetallic phases that has been reported. By lowering the substrate temperature the formation of an AuIn₂ layer during evaporation is suppressed. In this case the temperature of the thin film couple has to be raised considerably (to about 20 °C) to obtain interdiffusion within a reasonable time, and the final state of the thin film couple is different from that obtained when the phase formation is completed during evaporation. A possible explanation for this behaviour is discussed. The formation and growth of AuIn₂ after evaporation may be characterized by an activation energy of 0.23 eV.     

Grain boundary interdiffusion in Cd/Te thin film couples

Interdiffusion in Cd/Te thin film couples was studied experimentally through optical measurements and surface analysis. A grain boundary diffusion model was used and the corresponding activation energy was measured and found to be 0.12 ± 0.02 eV.     

Room temperature interactions in Ni/metal thin film couples

Interactions in Ni/metal thin film couples at room temperature were studied. It was found that nickel reacts with gallium, indium and tin to form NiGa₄, Ni₂In₃, Ni₁₀In₂₇ and NiSn, but no reaction was observed with bismuth, cadmium, germanium, magnesium, manganese, antimony, samarium and zinc under the conditions employed.     

Polycrystalline Si1-x Ge x thin film deposition by rapid thermal chemical vapor deposition

Polycrystalline silicon germanium (poly-Si_1−xGe_x) thin films on a-Si film have been deposited by rapid thermal chemical vapor deposition (RTCVD) with SiH₄–GeH₄–H₂. Effect of GeH₄/SiH₄ and deposition temperature on stoichiometry (x), Si-Ge binding character, composition, hydrogen configuration, crystallinity, preferred orientation, grain size, and surface roughness of poly-Si_1−xGe_x films has been investigated. Poly-Si_1−xGe_x deposited on the substrate with amorphous silicon buffer layer on oxide shows better crystallinity and contains the less amount of oxygen than the one deposited directly on the oxide surface. At low temperature region, the Ge–H bond with the small amount of Si–H₂ bond is dominant but all hydrogen bonds are desorbed at high temperature. All films have polycrystalline phase and the grain size and (111) orientation increased with increasing deposition temperature in which Ge content also increases at the fixed gas flow rate of GeH₄ to total source gas. Poly-Si_1−xGe_x/Si thin film transistors (TFT) are fabricated and hydrogen during post-hydrogenation process preferentially is attached to Ge dangling bond and the TFT characteristics could be improved.     

Room temperature interactions in Ag-metals thin film couples

The results of room temperature interactions of silver and various metals in thin films are presented. It has been found that aluminium, gold, bismuth, chromium, copper, antimony and samarium do not react with silver under the conditions given, but cadmium, gallium, indium, tin, tellurium and zinc do, and the reactions lead to the formation of corresponding intermetallic compounds. In the AgGa system only one compound is formed, which has been identified as Ag₃Ga. In the AgIn system, with less than 50 wt.% In, one compound is formed and this has been identified as Ag₂In. A compound formed with over 50 wt.% In has been identified as AgIn₂ LT (low temperature phase). Between 60 and 120°C this compound transforms into AgIn₂ MT (medium temperature phase). In the AgSn system the compound Ag₃Sn is formed and in the AgTe system the compounds Ag₂Te and Ag₅Te₃ are formed.     

Interface transformations in thin film aluminum-gold diffusion couples

Interface phase transformations in 1 μm aluminum + 1 μm gold thin film couples upon 24-h isothermal annealing at 125, 150 and 175 °C were studied. It is shown that temperature change does not affect the type of phases formed but only alters their growth rates. The layered structures consisting of multiple intermetallics were identified by X-ray diffraction and electron microscopy. Interface tracking using secondary ion mass spectroscopy depth profiling showed that Au is the predominant diffusant in this system. Intermetallic thickness growth measurements were made and the activation energy calculated to be 33.602 kJ/mol.     

Interdiffusion in PbIn thin film couples

Interdiffusion in PbIn thin film couples has been examined by an X-ray diffraction technique. Initial results indicate that the interdiffusion in such couples is significantly faster than that expected from reported bulk data.     

Interfacial reactions in bimetallic Ag-Sn thin film couples

Interfacial reactions in bimetallic Ag-Sn thin film couples have been investigated by measurement of electrical resistance and contact resistance as a function of time and temperature in order to understand kinetic behaviour in the above system where the intermetallic phase γ-Ag₃Sn is formed. Since the reaction is found to start at room temperature, the conventional vacuum coating unit has been modified for preparing such films and conducting subsequent measurements without breaking the vacuum. The results from the above different methods of resistance measurement indicate that interfacial reactions are characterized by a mean diffusion coefficient of 10^-13 cm² s^-1 at room temperature. X-ray diffraction indicates growth of the γ-Ag₃Sn phase immediately after deposition. Scanning electron microscopy confirms the diffusion of tin into silver by grain boundary diffusion rather than by bulk diffusion. The results from transmission electron microscopy confirm the presence of a γ-Ag₃Sn phase.     

Mechanisms of interdiffusion in Pd-Cu thin film diffusion couples

Interdiffusion in sputter-deposited polycrystalline Pd-Cu bilayers (thickness of each sublayer: 50 nm) was studied in the temperature range 175 °C-250 °C by sputter-depth profiling in combination with Auger electron spectroscopy. X-ray diffraction and transmission electron microscopy investigations revealed that the layers are polycrystalline, consisting of columnar grains separated by grain boundaries oriented more or less perpendicularly to the film surface. Considerable diffusional intermixing occurred in the studied temperature range, which was accompanied by the sequential formation of (ordered) phases Cu₃Pd and CuPd. Volume interdiffusion coefficients were determined using the so-called ‘centre-gradient’ and ‘plateau-rise’ methods. Grain-boundary diffusion coefficients of Pd through Cu grain boundaries were determined by the Whipple-Le Claire method and grain-boundary diffusion coefficients of Cu through Pd grain boundaries were determined by the Hwang-Balluffi method. It was found that both volume and grain-boundary diffusion coefficients decreased roughly exponentially with annealing time. Activation energies were determined which pertain to the same (defect) microstructure at each temperature. The differences with literature results for macroscopic diffusion couples were discussed.     

Real time spectroscopic ellipsometry of Ag/ZnO and Al/ZnO interfaces for back-reflectors in thin film Si:H photovoltaics

Real time spectroscopic ellipsometry (RTSE) has been applied to analyze the optical characteristics of Ag/ZnO and Al/ZnO interfaces used in back-reflector (BR) structures for thin film silicon photovoltaics. The structures explored here are relevant to the substrate/BR/Si:H(n-i-p) solar cell configuration and consist of opaque Ag or Al films having controllable thicknesses of microscopic surface roughness, followed by a ZnO layer up to ~ 3000 Å thick. The thicknesses of the final surface roughness layers on both Ag and Al have been varied by adjusting magnetron sputtering conditions in order to study the effects of metal film roughness on interface formation and interface optical properties. The primary interface loss mechanisms in reflection are found to be dissipation via absorption through localized plasmon modes for Ag/ZnO and through intraband and interband transitions intrinsic to metallic Al for Al/ZnO.     

Interpretation of dielectric properties of thin film Al/Al2O3/Au structures

On the basis of experimental data previously presented, the dielectric properties of thin film Al/Al₂O₃/Au structures were investigated in the frequency range 10^-2−10⁺⁵Hz. The results of the measurements suggested the existence of two laws of dispersion of the complex dielectric susceptibility, each obeying the empirical relation χ′(ω)∝χ≈(ω)∝ωⁿ⁻¹, with n = 0.14 in the low frequency range and n = 0.88 at higher frequencies. In this paper, an equivalent circuit is proposed; it takes into account, firstly, the two laws of dispersion which coexist over the whole temperature (393–505 K) and frequency ranges studied and, secondly, the existence of a thin interfacial zone at the electrode(s), which is less conducting than the bulk of the dielectric.     

5. VCNR type characteristic in thin film amorphous TeGeAsSi films

In the hope of further understanding the memory and switching effects of amorphous evaporated semi-conductor films, the current-voltage curve of the quarternary system TeGeAsSi was experimentally examined and our findings are discussed below.     

Numerical modeling of SiH4 discharge for Si thin film deposition for thin film transistor and solar cells

Amorphous and microcrystalline silicon thin films are used in solar cells as a multi-junction photovoltaic device. Plasma enhanced chemical vapor deposition is used and high deposition rate of a few nm/s is required while keeping film quality. SiH₄ is used as a precursor diluted with H₂. Electron impact processes give complex interdependent plasma chemical reactions. Many researchers suggest keeping high H/SiH_x ratio is important. Numerical modeling of this process for capacitively coupled plasma and inductively coupled plasma is done to investigate which process parameters are playing key roles in determining it. A full set of 67 volume reactions and reduced set are used. Under most of conditions, CCP shows 100 times higher H/SiH₃ ratio over ICP case due to its spatially localized two electron temperature distribution. Multi hollow cathode type CCP is also modeled as a 2 × 2 hole array. For Ar, the discharge is well localized at the neck of the hole at a few Torr of gas pressure. H₂ and SiH₄ + H₂ needed higher gas pressure and power density to get a multi hole localized density profile. H/SiH₃ was calculated to be about 1/10.     

Low temperature interdiffusion in the Au-Pd and Au-Rh thin film couples

Interdiffusion profiles in thin polycrystalline multilayer films of Pd-Au and Ti-Rh-Au at temperatures up to 490°C have been measured by Rutherford backscattering. Room temperature grain boundary diffusion of Au into Rh was observed and analyzed to give D_B = 3.5 × 10^-17 cm² sec^-1. The Whipple analysis is applied to our data for the diffusion of Au in Pd; using the lattice diffusivity of Neukam, an activation energy for grain boundary diffusion of 0.9 eV is found. The diffusion of Pd in Au has also been analyzed using the Whipple model, which gives a grain boundary activation energy of 0.6 eV.     

Quenched aging of thin film deposits by chopping

We studied the aging of thin films of MgF₂, of cryolite and of mixtures of these compounds prepared by codeposition with and without chopping of the incident beams. Ellipsometric measurements indicated that chopping of the films during deposition reduces the aging of the films. Spectrophotometric data showed that the transmittances of the single films change owing to aging much more than those of mixed films.     

Interdiffusion and compound formation in the Mo/Pd/Si thin film metallization system

The process of interdiffusion and compound formation in Mo/Pd/Si thin films was studied between 250 and 750°C via sheet resistance measurements, X-ray diffraction, Rutherford backscattering spectrometry and Auger electron spectroscopy. The results indicate that thermal annealing of the Mo/Pd/Si thin film couples between 250 and 475°C lead to PdSi interaction, Pd₂Si compound formation and consequently a small increase in the sheet resistance. In contrast, exposure of the Mo/Pd/Si thin films to temperatures higher than 475°C lead to MoPd₂Si interaction in addition to PdSi interaction, MoSi₂ compound formation and a dramatic increase in the sheet resistance. The influence of interdiffusion and compound formation on the interface morphology in the Mo/Pd/Si system was studied, and the implications of these observations to a very-large-scale integration contact metallization utilizing an Mo/Pd₂Si/Si system are discussed.     

Investigation of Si and Ge growth on Si3N4/Si

The growth of Si and Ge on silicon nitride surfaces has been investigated using scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and Auger electron spectrometer (AES). In the early stages, Si or Ge nanoclusters appeared irrespective of the different substrates. When annealed, the Si clusters were more stable against coalescence than those of Ge. As these clusters continued to grow, crystalline facets started to form. Both Si and Ge islands grew predominantly with (111)-oriented top facets on the crystalline Si₃N₄(0001)/Si(111). By contrast, they both grew in random orientation on the amorphous Si₃N₄ surface. Low-index facets such as (111) and (001) coexisted with high-index facets such as (113).