Electroless deposition of Co(W) thin films

Thin films of cobalt that contain small amounts of tungsten [Co(W)] were deposited by the electroless process. Those films do not contain either phosphorus or boron which are included in most electroless cobalt films processes. The deposition bath for Co(W) thin films include Co ions, tungstate ions as a source for tungsten, di-methyl-amine-borane (DMAB) complex as a reducing agent, ammonium hydrate as a complexing agent, acetic acid for buffering and surfactants. Co(W) layers were deposited on two types of seed layers: (a) thin sputtered cobalt or copper films on 100 nm SiO₂/Si and (b) bare silicon wafers activated by an aqueous Pd/PdCl₂ solution. The deposited layer thickness range was 40–1000 nm with deposition rate at 90 °C and pH 9 of 7 nm/s for both Pd activated Si and sputtered Co seed, and 5 nm/s for the sputtered Cu seed. Lowering the temperature to 70 °C lowered the deposition rate to 0.7 nm/s for the Pd activated Si. The deposited layers were bright coloured, uniform, and with low defect density under visual inspection. The thin films composition was found to be Cobalt with 3–4 at.% tungsten for all types of seed layers. The Co(W) thin films specific resistivity was in the range of 60–90 μΩ cm. Finally we present the thin film morphology as it was characterized using atomic force microscopy and scanning electron microscopy.     

Electrical resistivity of thin electroless Ag–W films for metallization

It is shown that optimization of the electroless deposition and the use of vacuum annealing yield dramatic decrease in the resistivity and its scatter in 100- and 50-nm silver–tungsten (Ag–W) films. Physical processes, which control the resistivity drop during low-temperature annealing and the residue resistivity in the annealed films are discussed.     

Characteristics of W and Cu/W gate MOS diodes fabricated by a process utilizing LPCVD of W and Cu lift-off

MOS diodes having double layer Cu/W, W, or Al gates were fabricated using tungsten chemical vapor deposition, copper evaporation and lift-off and were characterized before and after thermal anneals. The breakdown field statistics were determined for all kinds of devices, while the high field conduction and charge trapping in the oxide were investigated. The W gate devices exhibited high performance and very low degradation even after annealing at 650 °C. In Cu/W gate diodes good barrier action of our LPCVD tungsten films against copper penetration after annealing at 510 °C was observed, while reduced breakdown integrity and degradation due to copper diffusion occurred after annealing at 650 °C.     

CdS薄膜的结构特性及其对Cu(In,Ga)Se2(CIGS)薄膜太阳电池的影响

报道了CdS薄膜的CBD法沉积及其结构特性,其中的水浴溶液包括硫脲、乙酸镉、乙酸铵和氨水溶液.研究了水浴溶液的pH值、温度、各反应物溶液的浓度和滴定硫脲与倾倒硫脲等基本工艺参数对CdS薄膜结构特性的影响.其中,溶液的pH值对CdS薄膜的特性起着关键的作用.XRD图显示了随着溶液pH值的变化,薄膜的晶相由六方相向立方相转变.CdS薄膜的这两种晶相对CIGS薄膜太阳电池性能的影响不相同.c-CdS(立方相的CdS)与CIGS之间的晶格失配和界面态密度分别为1.419%和8.507×1012cm-2,而h-CdS(六方相的CdS)与CIGS之间的晶格失配和界面态密度则分别为32.297%和2.792×1012cm-2.高效CIGS薄膜太阳电池需要的是立方相CdS薄膜.     

High temperature ohmic contacts to 3C–silicon carbide films

Currently, large-area 3C–SiC films are available from a number of sources and it is imperative that stable high temperature contacts be developed for high power devices on these films. By comparing the existing data in the literature, we demonstrate that the contact behavior on each of the different polytypes of SiC will vary significantly. In particular, we demonstrate this for 6H–SiC and 3C–SiC. The interface slope parameter, S, which is a measure of the Fermi-level pinning in each system varies between 0.4–0.5 on 6H–SiC, while it is 0.6 on 3C–SiC. This implies that the barrier heights of contacts to 3C–SiC will vary more significantly with the choice of metal than for 6H–SiC. Aluminum, nickel and tungsten were deposited on 3C–SiC films and their specific contact resistance measured using the circular TLM method. High temperature measurements (up to 400°C) were performed to determine the behavior of these contacts at operational temperatures. Aluminum was used primarily as a baseline for comparison since it melts at 660°C and cannot be used for very high temperature contacts. The specific contact resistance (ρ_c) for nickel at room temperature was 5×10⁻⁴ Ω cm², but increased with temperature to a value of 1.5×10⁻³ Ω cm² at 400°C. Tungsten had a higher room temperature ρ_c of 2×10⁻³ Ω cm², which remained relatively constant with increasing temperature up to 400°C. This is related to the fact that there is hardly any reaction between tungsten and silicon carbide even up to 900°C, whereas nickel almost completely reacts with SiC by that temperature. Contact resistance measurements were also performed on samples that were annealed at 500°C.     

C49 defect influence on the C49–C54 transition

The C49–C54 transformation has been studied in TiSi₂ thin films having different concentration of defects. The defect concentration in the C49 phase has been varied using different thermal processes in the 460–540 °C temperature range; in fact, the defect concentration decreases with increasing the temperature and/or the duration of the thermal process as attested by the large variation of the silicide residual resistivity at 4 K. The kinetics of the transformation at 650 °C has been followed by in situ resistivity measurements and, for each sample, the transition time decreases as the defect concentration in the metastable phase decreases.     

Acetone-assisted deposition of silver films in supercritical carbon dioxide

Growth of silver films was studied by supercritical fluid deposition (SCFD) using H₂ and acetone as reducing agents for (1,5-cyclooctadiene)(hexafluoroacetylacetonato)silver(I) in supercritical CO₂ (scCO₂). H₂ reduction did not yield continuous Ag films, whereas continuous films were deposited on Ru substrates by acetone-assisted reduction of 0.006–0.03 mol% precursor in the temperature range of 150–250 °C. Surface qualities of the Ag films were effectively improved by decreasing water content in acetone reagent, as well as reducing acetone and precursor concentrations in scCO₂. Ultimately, a 50 nm-thick film with shiny surface was obtained in optimized conditions. A possible mechanism for acetone reduction of Ag precursor on Ru surface was also proposed.     

Filament-activated chemical vapour deposition of nitride thin films

We have applied the novel method of hot filament-activated chemical vapour deposition (HFCVD) for low-temperature deposition of a variety of nitride thin films. In this paper the results from our recent work on aluminium, silicon and titanium nitride have been reviewed. In the HFCVD method a hot tungsten filament (1500–1850°C) was utilised to decompose ammonia in order to deposit nitride films at low substrate temperatures and high rates. The substrate temperatures ranged from 245 to 600°C. The film properties were characterised by a number of analytical and optical methods. The effect of various deposition conditions on film properties was studied. All the films obtained were of high chemical purity and had very low or no detectable tungsten contamination from the filament metal.     

Optimization of Al/a-SiC:H optical sensor device by means of thermal annealing

The optimization of optoelectronic properties of Al/a-SiC:H Schottky diodes grown as Al/a-SiC:H/c-Si(n) structures is studied by means of thermal annealing of a-SiC:H thin films. According to the spectral response of the Schottky diodes the measured quantum efficiency, η_measured, increases with increasing annealing temperature (400–600 °C), whereas η_measured decreases for T_a>600 °C. For T_a=600 °C, optimum material quality of a-SiC:H films is achieved and the spectral response of the Al/a-SiC:H/c-S(n) structures present very high and almost constant values (η_measured80%) for the whole range of wavelengths from 500 up to 850 nm. These results show that our Al/a-SiC:H/c-S(n) structures can be very attractive as optical sensors. Diffusion length calculations as well as the mobility by lifetime product (μτ)_p of the minority carriers (holes) of a-SiC:H films present a dependence on T_a similar to that of the measured quantum efficiency. Finally, the quantum efficiency of films processed with T_a=675 °C is found to increase when the Al/a-SiC:H/c-S(n) structures are exposed to hydrogen, a result that could be promising for the construction of a hydrogen detection sensor.     

Characterization of sputtered tungsten nitride film and its application to Cu electroless plating

In this study, W and tungsten nitride films were fabricated by reactive sputtering in a N₂/Ar atmosphere, the native oxide growth on the surface of the tungsten nitride films was investigated by X-ray photoelectron spectroscopy (XPS). It was found that tungsten nitride films were the mixture of W and W₂N sputtered in atmospheres of 3 mTorr argon and at the N₂ partial pressure from 0.1 to 2.0 mTorr. The ratio of W and W₂N in films was changed with the nitrogen partial pressure in sputtered chamber. Surface oxidations of the W film and tungsten nitride films advanced with time. Electrochemical measurement shows that all reduction-oxidation (redox) potentials of tungsten and tungsten nitrides were lower than that of copper film in electroless copper solution. And so, electroless-plated copper could be deposited on the surface of tungsten nitride films when the substrates were immersed into electroless copper plating solution without any pretreatment. Tungsten nitride films are appropriate for ULSI Cu interconnections using electroless Cu deposition.     

Thickness dependent physical properties of chemically deposited nanocrystalline MgSe thin films deposited at room temperature by solution growth method

Chemical bath deposition method has been employed to deposit nanocrystalline magnesium selenide thin films of thickness 104–292 nm onto glass substrates at room temperature. The deposition bath consists of magnesium chloride, triethanolamine (TEA) and selenium dioxide. The as deposited films were characterized by X-ray diffraction, scanning electron microscopy (SEM), atomic force microscopy (AFM), optical absorption, electrical resistivity and thermo-emf measurements. The X-ray diffraction (XRD) studies revealed that the crystallinity of the magnesium selenide thin film increases with thickness. SEM studies reveal that MgSe films exhibit uniform distribution of round shaped grains over the entire substrate surface.The optical band-gap and electrical resistivity of MgSe film decrease as the film thickness increases. Such type of dependence is attributed to the quantum size effect that is observed in nanocrystalline semiconductors.The thermo-emf measurement confirms its p-type conductivity.     

Size dependence of hall mobility and dislocation density in Ge heteroepitaxial layers grown by MBE on a SiO2 patterned Si template

We have investigated the size dependent properties of the Hall mobility and etch pit dislocations (EPDs) in germanium (Ge) heteroepitaxial layers. Pure Ge thin films were grown by molecular beam epitaxy (MBE) using pattern guided growth at 650 °C and compared with homoepitaxially grown films. The results show enhanced Hall mobility and lower dislocation density as the pattern size decreases. The number of EPDs was decreased by one order of magnitude and the Hall mobility measured with different sizes of van der Pauw patterns was enhanced by two times as the pattern size was decreased from 200×200 μm² to 3×3 μm². Raman spectroscopy was also employed to characterize residual strain and crystalline quality of the epitaxial films with respect to the pattern size. We conclude that nano-scale pattern guided heteroepitaxial growth of Ge may be a plausible method for monolithic integration of Ge optoelectronic or electronic devices onto a Si substrate.     

Reliability of ultra thin ZrO2 films on strained-Si

Ultra thin high-k zirconium oxide (equivalent oxide thickness 1.57 nm) films have been deposited on strained-Si/relaxed-Si_0.8Ge_0.2 heterolayers using zirconium tetra-tert-butoxide (ZTB) as an organometallic source at low temperature (<200 °C) by plasma enhanced chemical vapour deposition (PECVD) technique in a microwave (700 W, 2.45 GHz) plasma cavity discharge system at a pressure of 66.67 Pa. The trapping/detrapping behavior of charge carriers in ultra thin ZrO₂ gate dielectric during constant current (CCS) and voltage stressing (CVS) has been investigated. Stress induced leakage current (SILC) through ZrO₂ is modeled by taking into account the inelastic trap-assisted tunneling (ITAT) mechanism via traps located below the conduction band of ZrO₂ layer. Trap generation rate and trap cross-section are extracted. A capture cross-section in the range of 10⁻¹⁹ cm² as compared to 10⁻¹⁶ cm² in SiO₂ has been observed. The trapping charge density, Q_ot and charge centroid, X_t are also empirically modeled. The time dependence of defect density variation is calculated within the dispersive transport model, assuming that these defects are produced during random hopping transport of positively charge species in the insulating layer. Dielectric breakdown and reliability of the dielectric films have been studied using constant voltage stressing. A high time-dependent dielectric breakdown (TDDB, t_bd > 1500 s) is observed under high constant voltage stress.     

Study of Ta–Si–N thin films for use as barrier layer in copper metallizations

This work focuses on the deposition process, microanalytical characterization and barrier behaviour of 10–100-nm thick sputtered Ta–Si and Ta–Si–N films. Pure Ta–Si films were found to be already nanocrystalline. The addition of N₂ leads to a further grain fining resulting in amorphous films with excellent thermal stability. According to microanalytical investigations, Ta–Si barriers between Cu and Si with a thickness of only 10 nm are not stable at 600°C. Copper silicides are formed due to intensive Cu diffusion throughout the barrier. In contrast, 10-nm thick nitrogen-rich Ta–Si–N barriers remain thermally stable during annealing at 600°C and protect the Si wafer from Cu indiffusion.     

Electrical properties of high permittivity ZrO2 gate dielectrics on strained-Si

Deposition and electrical properties of high dielectric constant (high-k) ultrathin ZrO₂ films on tensilely strained silicon (strained-Si) substrate are reported. ZrO₂ thin films have been deposited using a microwave plasma enhanced chemical vapor deposition technique at a low temperature (150 °C). Metal insulator semiconductor (MIS) structures are used for high frequency capacitance–voltage (C–V), current–voltage (I–V), and conductance–voltage (G–V) characterization. Using MIS capacitor structures, the reliability and the leakage current characteristics have been studied both at room and high temperature. Schottky conduction mechanism is found to dominate the current conduction at a high temperature. Observed good electrical and reliability properties suggest the suitability of deposited ZrO₂ thin films as an alternative as gate dielectrics. Compatibility of ZrO₂ as a gate dielectric on strained-Si is shown.     

Single-step selective metallization of Mg/NH3 pretreated Teflon by copper chemical vapor deposition

The surface of Teflon^®, which can be made hydrophilic by chemical treatment in a solution of solvated electrons in the presence of magnesium, can be restored by UV photochemical oxidation under oxygen. The Mg/NH₃ treated Teflon surfaces are easily metallized in a single-step process by copper CVD when (MHY)Cu(hfac) is used as precursor (hfac, hexafluoroacetylacetonate; MHY, 2-methyl-1-hexene-3-yne). The growth rate of the copper film (thickness 200–500 nm) is in the range 30–50 nm/min. The Cu films, with a resistivity of 1.9±0.2 μΩ cm, are pure, as determined by X-ray photoelectron spectroscopy. Patterned UV irradiation of the treated Teflon resulted in an identical copper pattern after CVD and, hence, selective copper deposition could be achieved on Teflon.     

Growth mechanism and optical properties of semiconducting Mg2Si thin films

Reactive deposition of magnesium onto a hot silicon substrate (200–500°C) does not result in any accumulation of magnesium or its silicide — the condensation coefficient of magnesium being zero. On the other hand, codeposition of magnesium with silicon at 200°C, using a magnesium-rich flux ratio, gives a stoichiometric Mg₂Si film. The number of magnesium atoms which condense is equal to twice the number of silicon atoms which were deposited. The Mg₂Si layers are polycrystalline with a (111) texture. These stoichiometric silicide films still show a tendency to sublimate; whereas capping with an oxide results in extensive intermixing during annealing. The Mg₂Si films thus obtained exhibit optical transparency at sufficiently long wavelength, and an absorption edge. Extraction of the absorption coefficient from the data, and analysis of its energy dependence suggest an indirect bandgap of 0.74 eV, plus direct transitions at 0.83 and 0.99 eV.     

Temperature-controlled self-organized InP nanostructures grown on GaAs(1 0 0) substrate by MOCVD

The self-organized InP nanostructures grown on GaAs(0 0 1) substrates by metalorganic vapor deposition were examined in detail using atomic force microscopy. By properly selecting growth temperature, three kinds of nanostructure, islands, pits and ripples were formed. For growth temperature of 400–450 °C, the surface morphologies were governed by islands; but, for the growth temperature of 500 °C, the formation of surface ripples instead of islands was presumably due to the combination effect of temperature-controlled surface kinetics and strain effect. On the other hand, the observation of enhanced growth of pits upon a high-temperature annealing (at 685 °C for 90 s) indicated that the strained InP epitaxial film would be morphologically stabilized by taking the form of pits formation.     

不同方法及衬底类型对CdS多晶薄膜性能的影响

采用化学水浴法和磁控溅射法分别在AZO、FTO、ITO透明导电玻璃衬底上制备了CdS薄膜,利用扫描电镜、XRD以及透射光谱等测试手段,研究了两种制备方法对不同衬底生长CdS薄膜形貌、结构和光学性能的影响.研究结果表明,不同方法制备的CdS薄膜表面形貌均依赖于衬底的类型,水浴法制备的CdS薄膜晶粒度较大,表面相对粗糙.不同方法制备的CdS薄膜均为立方相和六角相的混相结构,溅射法制备的多晶薄膜衍射峰清晰、尖锐,结晶性较好.水浴法制备的CdS薄膜透过率整体低于溅射法,但在短波处优势明显.     

Formation kinetics and structure of Pd2Si films on Si

Backscattering and X-ray techniques have been used to study properties of palladium silicide (Pd₂Si) formed by evaporating thin Pd layers on Si followed by heat treatment. The rate of formation of Pd₂Si in the temperature range of 200–275°C has been measured by 2-MeV ⁴He⁺ ion backscattering. The Pd₂Si layer is found to grow at a rate proportional to the square root of time for thicknesses ranging from approximately 200–4000 Å. The rate of growth is found to be independent of Si substrate orientation or doping type and the rate constant is found to fit a single activation energy of E_a = 1·5±0·1 eV over the temperature range measured. X-ray diffraction indicates the structure to be Pd₂Si with the basal plane roughly parallel to the substrate surface for films formed on 111, 110, 100 and evaporated (amorphous) silicon substrates. The degree of preferred orientation is markedly stronger on [111] Si. Ion channeling measurements confirm that in this case the c-direction of the Pd₂Si is parallel with the [111] direction in the underlying Si.