An alternative method to determine the steady state nucleation rate in thermally annealed HWCVD a-Si:H films

A determination of the steady state nucleation rate r_n in thermally annealed a-Si:H has typically been performed using TEM, where the increase in grain density with isothermal sample anneal time can be directly observed for samples with small crystalline volume fractions. Using the classical model of crystallite nucleation and grain growth, this paper presents an alternative technique for determining r_n using in situ XRD measurements of the crystallization time and EBSD measurements of the final grain size, the latter in fully annealed samples. HWCVD a-Si:H samples containing different as-grown film H contents C_H have been examined by both techniques, and the agreement between these techniques is excellent. R_n is seen to decrease with increasing as-grown film C_H. Differences in the values of r_n are suggested as being due to variations in the transition rate per atom at the amorphous/crystalline interface.     

An XPS study of amorphous MoO3/SiO films deposited by co-evaporation

X-ray photoelectron spectroscopic (XPS) core-level spectra of MoO₃/SiO thin films are presented. The effects of changes in composition, substrate temperature during deposition and annealing on the binding energy of Mo(3d) and Si(2p) core lines in mixed films are compared with those of MoO₃ and SiO. Appreciable changes in Mo(3d) peak positions and slight changes in Si(2p) peak positions are observed. The change in binding energy of the Mo(3d) doublet may be attributed to the effective incorporation of silicon ions in an MoO₃ lattice which may cause the molybdenum orbital to be a little less tightly bound. This helps in the internal electron transfer from the oxygen (2p) to the molybdenum (4d) level as a result of which the molybdenum is readily changed to lower oxidation states during heat treatment. XPS spectra show that the position of the Si(2p) core state shifts monotonically with increasing oxygen concentration from the value of 101.8 to 102.6 eV.     

Optical properties of the low-energy Ge-implanted and annealed SiO2 films

Ultraviolet–visible light emissions from nanocrystalline (nc) Ge-embedded SiO₂ films fabricated by ion implantation and rapid annealing techniques are studied as a function of different fabricating conditions (implanting dose and annealing temperature). The samples exhibit seven photoluminescence (PL) peaks peaked at 1.68, 1.75, 1.84, 1.93, 2.00, 2.70, and 3.10 eV. There are also two excitation bands in the PL excitation (PLE) spectra peaked at 4.90 and 5.19 eV. Raman spectra are employed to observe and understand structural variations in SiO₂ matrix during the formation of nc-Ge and defects. Within the frame of the quantum confinement (QC) theory and Oswald ripening growth model, the origin and evolution of the seven PL peaks and two PLE bands are identified clearly demonstrated by the proposed energy-level and generated process diagrams. Our results indicate that both the implanting dose and annealing temperature play a dominant role in modulating the optical properties of the nc-Ge-embedded SiO₂ films.     

An atomic force microscope study of surface roughness of thin silicon films deposited on SiO/sub 2/

Atomic force microscope analysis, with a resolution of /spl lsim/1.1 nm, shows that peak-to-peak surface roughness (/spl Delta/h/sub p-p/) of amorphous silicon films thinner than /spl ap/50 nm on silicon dioxide can be controlled to better than 5 nm. Low-pressure, chemically-vapor-deposited silicon films on silicon dioxide initially show an approximately linear increase in the surface roughness due to growing nuclei as the deposition progresses, followed by a decrease in the surface roughness as growth nuclei coalesce. A simple model based on random nucleation and nuclei growth displays similar trends. Films deposited on rougher substrates show more surface roughness. Surface treatment during the predeposition cleaning process does not significantly affect /spl Delta/h/sub p-p/. As a means of producing smooth surfaces, films thinner than about 20 nm are first deposited more thickly than needed, and then etched back to the desired dimension; the use of a binary HNO/sub 3/ and HF etching process improves roughness control. Boron-ion implanted and subsequently crystallized 45-nm-thick Si films show significant smoothing with /spl Delta/h/sub p-p//spl ap/2.2 nm. Thin amorphous silicon films deposited by source evaporation are attractive because they can be deposited at room temperature, and have smoother surfaces (/spl Delta/h/sub p-p//spl ap/2.5 nm) than comparable films produced by chemical vapor deposition.     

Mobility activation in thermally deposited CdSe thin films

Effect of illumination on mobility has been studied from the photocurrent decay characteristics of thermally evaporated CdSe thin films deposited on suitably cleaned glass substrate held at elevated substrate temperatures. The study indicates that the mobilities of the carriers of different trap levels are activated due to the energy of incident illumination, which results in the existence of two distinct trap levels. In each trap depth the energy of the trap increases linearly. It infers that there is a linear distribution of traps of different energies below the conduction band.     

Large spontaneous nucleation rate in implanted polycrystalline silicon films on SiO2

Crystallization of a 1500 Å polycrystalline silicon film self-implanted at a dose of 2 × 10¹⁵ ions/cm² was found to be due to the nucleation of crystallites and not due to the growth of grains that survived the implant. The nucleation rate was more than three orders of magnitude faster than that for either amorphous silicon or polycrystalline silicon self-implanted at 5 × 10¹⁵ ions/cm².     

Solid-phase crystallization of amorphous SiGe films deposited by LPCVD on SiO2 and glass

The crystallization kinetics and film microstructure of poly-SiGe layers obtained by solid-phase crystallization (SPC) of amorphous SiGe with Ge fractions (x) in the 0 to 0.42 range have been studied in detail. Amorphous SiGe layers 100 nm thick were deposited by LPCVD at 450°C on thermally oxidized Si wafers and 7059 Corning glasses, using Si₂H₆ and GeH₄ as gas sources. The samples were crystallized at 550°C and low pressure (below 9 Pa). The evolution of the crystallization and the resulting film microstructure were characterized by X-ray diffractometry and transmission electron microscopy. The experimental results on growth kinetics fit the Avrami’s model. The characteristic crystallization time decreases with x, slowly for x<0.3 and more abruptly for higher values of x. The transient time depends exponentially on x in all the intervals. The crystallized films have a (111) preferred orientation for low values of x and evolve to a randomly oriented polycrystal as x increases. The grain size in the fully crystallized layers decreases with increasing x. The results are similar for the films deposited on silicon dioxide and glass.     

CAB玻璃基底不同方法制备的SiO2膜层性能研究

采用IAD、IBS、MS等三种方法在CAB玻璃上制备了SiO2膜层,通过纳米压痕和划痕仪测量了膜层的纳米硬度和摩擦系数;利用傅里叶转换红外光谱仪对薄膜光谱性能进行了测量;利用SEM,观测膜层表面和断面形貌。结果表明:不同方法制备的SiO2膜层,聚集密度、硬度和摩擦系数不相同,其中,IBS法制备膜层硬度最高,MS法所制备膜层,硬度略低,而IAD法制备的膜层硬度最低;摩擦系数上,IBS法和IAD法相当,较MS法制备的膜层摩擦系数要高。从成膜基理上,对上述结论给出了理论分析。根据试验结果,选用MS法作为CAB玻璃保护膜的制备方法。     

Silane oxidation study: Analysis of data for SiO2 films deposited by low temperature chemical vapour deposition

The purpose of this paper is to determine the rate constant k_r of the reaction and the equilibrium constants of oxygen (K_o2) and silane (K_SiH4) adsorption on the surface in the low temperature chemical vapour deposition (CVD) of SiO₂ films from the fit of the experimental dependence of the deposition rate on the CVD conditions to the theory of bimolecular surface reactions.The results obtained are discussed in terms of (i) an exponential temperature dependence of k_r with an activation energy of 7.7 kcal mol^-1 and (ii) a temperature dependence of K₀₂ and K_SiH4 which involves a transition in the adsorption process of the reactant species from physical adsorption to chemisorption as the temperature is increased over 200 °C.     

Optical properties of electrochemically deposited ZnO thin films on colloidal crystal film of SiO2 microspheres

The optical properties of electrochemically deposited ZnO thin films on colloidal crystal film of SiO2 microspheres structures were studied. Colloidal crystal film of SiO2 microspheres were self-assembled by evaporation using SiO2 in solution at a constant 0.1 wt%. ZnO in thin films was then electrochemically deposited on to colloidal crystal film of SiO2 microspheres. During electrochemical deposition, the content of Zn(NO3)2 x 6H2O in solution was 5 wt%, and the process's conditions were varied between of 2-4 V and 30-120 s at room temperature, with subsequent heat-treatment between 200 and 400 degrees C. A smooth surface and uniform thickness of 1.8 microm were obtained at 3 V for 90 s. The highest PL peak intensity was obtained in the ZnO thin film heat-treated at 400 degrees C. The double layered ZnO/SiO2 colloidal crystals showed clearly better emission properties than the SiO2/ZnO and ZnO structures.     

Structure and internal stress in ultra-thin silver films deposited on MgF2 and SiO substrates

A substantially improved bending-beam technique combined with the capacitance method was used for the continuous determination of the internal stress during vacuum deposition of ultra-thin silver films. With this method a sensitivity improvement of about two orders of magnitude was achieved compared with results reported previously. By proper experimental design all radiation interference on the stress-measuring appratus except the unavoidable direct heat radiated from the evaporators was eliminated. With this improved method it was possible to determine continuously the internal stress of silver films deposited onto fresh MgF₂ or SiO substrate films under varying experimental conditions (i.e. evaporation rate, residual gas pressure). Based on correlations between internal stress and the structure of the films observed using an electron microscope a model is proposed that explains the origin of the alternately compressive and tensile stress in such ultra-thin films.     

Influence of oxygen flow rate on photocatalytic TiO2 films deposited by rf magnetron sputtering

Titanium dioxide (TiO₂) thin films having anatase (1 0 1) crystal structure were prepared on non-alkali glass substrates by rf (13.56 MHz) magnetron sputtering using a TiO₂ ceramic target under various oxygen partial pressures. At a fixed substrate temperature of 400 °C and total gas pressure of 1 Pa after 3 h deposition. Effects of oxygen partial pressure on the structural, surface morphology, and photocatalytic activities of the TiO₂ thin films were investigated. We performed both photoinduced decomposition of methylene blue (MB) and photoinduced hydrophilicity under UV light illumination. The XRD patterns exhibited a broad-hump shape indicating the amorphous structure of TiO₂ thin films. The results showed that when the [O₂/(Ar + O₂)] flow rate increased to 50%, the photoinduced decomposition of MB and photoinduced hydrophilicity were enhanced. The water contact angle after 9 min UV illumination was approximately 4.5°, and the methylene blue (MB) solution decomposition from 12 down to 3.34 μ mol/L for 240 min UV irradiation.     

GISAXS study of Si nanocrystals formation in SiO2 thin films

We present a study on amorphous SiO/SiO₂ superlattice using grazing incidence small-angle X-ray scattering (GISAXS). Amorphous SiO/SiO₂ superlattices were prepared by high vacuum evaporation of 3 nm thin films of SiO and SiO₂ (10 layers each) on Si(100) substrate. After the evaporation, samples were annealed at 1100 °C for 1 h in vacuum, yielding Si nanocrystals formation. Using a Guinier approximation, the shape and the size of the crystals were obtained.