Effect of chlorine on gold-titanium thin films

In this study the effect of a small concentration of chlorine on gold-titanium metallization was investigated. Samples were prepared by deposition of gold and titanium layers on a glass substrate. Samples were exposed at 75, 135 and 175° C for 53 days to an argon atmosphere and to an argon atmosphere containing 50 ppm chlorine. In all cases the electrical resistance of the exposed samples decreased and the addition of chlorine made this decrease even larger. Depending on the conditions, migration of the titanium atoms and formation of preferred oriented structure took place. At 135 and 175° C in the argon atmosphere containing 50 ppm chlorine, a very active migration of titanium atoms from the gold layer to the external surface of the samples was observed. Migration of titanium was not observed in the samples exposed to the pure argon atmosphere. This strongly suggests that chlorine acts as an agent bringing titanium from the gold layer to the external surface by a process known as chemisorption-induced segregation; on the surface titanium forms an oxide. When samples were exposed for 53 days at 175° C, preferred oriented structure in the gold layer was developed. Formation of the preferred oriented structure was neither conditioned nor related to the presence of chlorine in the atmosphere.     

Investigation of interfacial reactions in thin film couples of aluminum and copper by measurement of low temperature contact resistance

Interfacial reactions in bimetallic thin film couples of aluminum and copper were investigated by measurement of contact resistance between 4.2 and 300 K. Results for as-deposited couples indicate that electrical properties, such as resistance and temperature coefficient of resistance, correspond closely to those computed from a simple model involving current flow parallel to the interface. These properties change appreciably after step annealing at elevated temperatures. Results in this case indicate that interfacial reactions commence by nucleation and growth of Al₂Cu along grain boundaries at 145°C, whereas significant solid solution alloying precedes nucleation and growth of intermetallic compounds at 250°C. Homogenization of these couples proceeds, sequentially, by (1) rapid diffusion of aluminum along grain boundaries in copper, (2) rapid diffusion of copper along grain boundaries in aluminum and (3) slower diffusion of each species into grain interiors of the other until a uniform composition, controlled by relative thickness of the constituent films, is achieved. This interpretation of the evolution of contact resistance is entirely consistent with complementary microstructural characterization by optical and transmission electron microscopy and chemical characterization by Auger electron spectroscopy.     

电子束与电阻复合蒸发法制备Zr-Cu非晶薄膜及性能表征

主要采用电子束蒸发与电阻蒸发复合镀膜系统制备Zr-Cu二元非晶薄膜,衬底基板无冷却装置。通过X射线衍射仪(XRD)、场发射透射电子显微镜(FE-TEM)、场发射扫描电子显微镜(FE-SEM)、微控四探针测量仪等仪器,系统地研究了样品沉积时间对薄膜厚度、微观结构、表面形貌以及电学性能的影响,另外还分析了与磁控溅射制备的Zr-Cu非晶样品的区别。结果显示,该复合镀膜技术制备的ZrxCu100-x非晶薄膜玻璃形成成分范围为x=30~85;薄膜的结构与性能对沉积时间比较敏感。样品随沉积时间的延长从非晶结构逐渐向非晶纳米晶复合结构转变;相比磁控溅射制备的薄膜样品,复合蒸发法制备的薄膜表面呈现较大尺寸的"团簇"形貌;样品的电阻率和方块电阻随沉积时间的延长逐渐减小。     

Effects of scandium addition on electrical resistivity and formation of thermal hillocks in aluminum thin films

This study investigates the effects of doping aluminum (Al) films with minor amounts of scandium (Sc) on the electrical resistivity and the formation of thermal hillocks. The pure Al and Al-Sc films, prepared via sputtering deposition, before and after isochronal annealing are examined using a scanning electron microscope and a transmission electron microscope. In-situ thermal stress analyses of the films are also carried out. The grain size of the as-deposited films is reduced by addition of Sc. Moreover, the Sc can immobilize the grain boundaries, retarding grain growth and re-crystallization of the films during annealing. Although the as-deposited Al-Sc films show higher resistivity than that of a pure Al film, the former is significantly decreased after annealing at 300 °C. The hillock density dramatically reduces with increasing the Sc concentration in the films. Average size of the hillocks in Al-Sc films clearly increases when the temperature is elevated.     

Effects of deposition and annealing conditions on the structure and electrical properties of LPCVD silicon thin films

Deposition temperature and annealing conditions have pronounced effects on the structure and electrical properties of LPCVD silicon thin films. Films grown at 580°C are amorphous whereas those grown at 620°C are microcrystalline. All thin films are subjected to phosphorous diffusion followed by different annealing treatments. Annealing of amorphous films at 1000°C results in large grains with no favoured orientation and with a relatively high mobility value. Annealing treatment at 1000°C of the microcrystalline sample results in moderate grain growth with a relatively low mobility which presumably is due to some favoured grain orientation.     

Titanium nitride diffusion barrier for copper metallization on gallium arsenide

The diffusion properties of Cu, Cu/titanium nitride (TiN) and Cu/TiN/Ti metallization on GaAs, including as-deposited film and others annealed at 350-550 °C, were investigated and compared. Data obtained from X-ray diffractometry, resistivity measurements, scanning electron microscopy, energy dispersive spectrometer and Auger electron spectroscopy indicated that in the as-deposited Cu/GaAs structure, copper diffused into GaAs substrate, and a diffusion barrier was required to block the fast diffusion. For the Cu/TiN/GaAs structure, the columnar grain structure of TiN films provided paths for diffusion at higher temperatures above 450 °C. The Cu/TiN/Ti films on GaAs substrate were very stable up to 550 °C without any interfacial interaction. These results show that a TiN/Ti composite film forms a good diffusion barrier for copper metallization with GaAs.     

Preparation of aluminum doped zinc oxide films and the study of their microstructure, electrical and optical properties

Aluminum doped zinc oxide (AZO) polycrystalline thin films were prepared by sol-gel dip-coating process on optical glass substrates. Zinc acetate solutions of 0.5 M in isopropanol stabilized by diethanolamine and doped with a concentrated solution of aluminum nitrate in ethanol were used. The content of aluminum in the sol was varied from 1 to 3 at.%. Crystalline ZnO thin films were obtained following an annealing process at temperatures between 300 °C and 500 °C for 1 h. The coatings have been characterized by X-ray diffraction, UV-Visible spectrophotometry, scanning electron microscopy, and electrical resistance measurement. The ZnO:Al thin films are transparent (∼ 90%) in near ultraviolet and visible regions. With the annealing temperature increasing from 300 °C to 500 °C, the film was oriented more preferentially along the (0 0 2) direction, the grain size of the film increased, the transmittance also became higher and the electrical resistivity decreased. The X-ray diffraction analysis revealed single-phase ZnO hexagonal wurtzite structure. The best conductors were obtained for the AZO films containing 1 at.% of Al, annealed at 500 °C, 780 nm film thickness.     

Ion back-scattering analysis of interdiffusion in Cu-Au thin films

Helium ion back-scattering has been used to examine the interdiffusion behavior of the thin film copper-gold system. Techniques for distinguishing bulk diffusion and grain boundary diffusion using back-scattering are presented. At temperatures in the range 200°–500°C, the grain boundary diffusion mechanism is shown to predominate in Cu-Au thin films. The back-scattering results suggest a model in which interdiffusion takes place by very rapid saturation of the grain boundaries in the gold film by copper and a slower filling of the copper grain boundaries by gold. The atoms in the grain boundaries then diffuse into the grains by bulk diffusion. In the parent gold film, we suggest that the amount of Cu Au ₃ formed near the grain boundaries is uniform in depth. In the parent copper film, more Cu₃Au forms near the original Cu-Au interface than further into the copper film. No evidence was found to suggest the formation of a pure layer of CuAu₃ or Cu₃Au. The interdiffusion and compound formation process is found to be characterized by an activation energy of 1.35-1.5 eV.     

Effect of sulfur-doped graphene quantum dots incorporation on morphological,optical and electron transport properties of CH3NH3PbBr3 perovskite thin films

Organic–inorganic hybrid perovskite materials have recently attracted extensive interest to develop next-generation high efficiency optoelectronic devices. However, in many of these devices, perovskite thin films are the key source of photogenerated electron and hole pairs. Therefore, a strategy for the preparation of high-quality perovskite thin films with a fewer number of traps at surfaces and grain boundaries is highly desired. In this work, sulfur-doped graphene quantum dots (S-GQDs) were synthesized and incorporated in the CH₃NH₃PbBr₃ perovskite precursor to prepare S-GQDs incorporated perovskite thin films. The as-prepared thin films were systematically characterized using X-ray diffractometer, field emission scanning electron microscope, UV–Vis and fluorescence spectrophotometer to investigate the effect of different amounts of S-GQDs on their morphology, optical absorbance and electron transfer properties. The experimental findings revealed that multiple surface functional groups, quantum confinement and desirable electronic conductivity in S-GQDs help passivate the perovskite surface by reducing the surface and grain boundary traps. Interestingly, the incorporation of S-GQDs increased the light absorption of CH₃NH₃PbBr₃ along with faster electron transfer across their interfaces. Hence, this strategy of S-GQDs incorporation presents a versatile and novel way to prepare highly efficient perovskite thin films for developing next-generation solar cells, light emitting diodes and other optoelectronic devices.

     

Electron scattering mechanisms in indium-tin-oxide thin films: grain boundary and ionized impurity scattering

Carrier concentrations and mobilities of indium-tin-oxide (ITO) thin films by DC magnetron sputtering at the various process temperatures were measured using the Hall Technique. The relationship between the carrier concentrations and mobilities had two distinct regions: (i) roughly up to the process temperatures of 300°C with carrier concentrations of 9.0×10²⁰/cm³, both carrier concentrations and mobilities increased together with the process temperatures; (ii) above the process temperature of 300°C with carrier concentrations over 9.0×10²⁰/cm³, the carrier mobilities decreased as the carrier concentrations increased with the process temperatures. These distinct relationship between carrier concentrations and mobilities were due to the transition of the dominant electron scattering mechanisms in ITO thin films with the process temperatures. At low process temperatures, the crystallinities were low and the grain boundary scattering was dominant. However, at high process temperatures, ITO thin films were highly crystallized and the ionized impurity scattering was dominant. The overall characterizations related to the carrier concentrations and mobilities were also performed using an X-ray diffractometer and a scanning electron microscope.     

Effects of temperature,thickness and atmosphere on mixing in Au-Ti bilayer thin films

The interdiffusion and intermetallic compound formation of Au-Ti bilayer thin films annealed at 125 to 350 °C have been investigated. The bilayer thin films were prepared through electron beam deposition at comparatively low temperature. The interdiffusion of annealed specimens was examined by measuring electrical resistance and the depth-composition profile, and by observation using a transmission electron microscope. Interdiffusion between the thin films was detected at temperature above 175°C in a vacuum of 10^–4 Pa. The starting temperature at which interdiffusion occurred decreases with lowering annealing vacuum. The intermetallic compounds AuTi, Au₄Ti, Au₂Ti and Ti₃Au form during annealing at over 250 °C. The activation energies of Au in Ti and Ti in Au obtained by the penetration depth are approximately 0.45 and 0.41 eV, respectively. These measurements indicate that the diffusion is controlled by a short-circuit mechanism. The diffusion of Ti species in Au depends on the annealing vacuum and Au thickness.     

Spray pyrolyzed β-In2S3 thin films: Effect of postdeposition annealing

Indium sulfide thin films prepared using spray pyrolysis, with In/S ratio 2/3 in the solution, were annealed in vacuum at 300 and 400 °C. The effect of this treatment on properties of the films was studied using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, optical absorption, transmission and electrical measurements. Optical constants of the films were calculated using the envelope method. Annealing did not affect the optical properties of the film much, but the resistivity of the films showed a drastic decrease and the grain size increased. In₂S₃ thin films have potential use as buffer layer in photovoltaic heterojunction devices.     

Void growth in thin silver films

A high density of small voids was observed in thin films of silver on examination with a high resolution transmission electron microscope. Void growth was studied in these films by annealing them in a vacuum as well as in the electron microscope using a specimen heating stage. Heating of the films to 700°C led to thermal grooving at the grain boundaries and finally to grain separation. It appears that the void growth occurs essentially as a result of annihilation of excess vacancies trapped in the film. The observed phenomena of thermal grooving and grain separation can be explained in terms of surface diffusion of silver atoms.     

Microtexture of chloride treated CdTe thin films deposited by CSS technique

This work investigates the microstructural changes—especially in grain boundary structure and grain orientation distribution—in CdTe thin films deposited by close spaced sublimation at low (LT) and high temperatures (HT) and submitted to a CdCl₂ heat treatment. These changes are quantitatively described by microtexture analysis, a spatial distribution of the orientation of the grains. The analysis is performed in a scanning electron microscope by means of identification of the electron back-scattered diffraction patterns from individual grains. The texture of each grain, the misorientation between grains, and coincident site lattice boundary maps are obtained. The results show that the CdCl₂ treatment did not promote significant microstructural changes in HT-CdTe films, which grow with large and randomly oriented grains, and with a predominance of high-angle boundaries. On the other hand, for LT-CdTe films, this treatment promotes a substantial increase in grain size, a decreasing of preferential orientation, and an increase in the number of CSL and high-angle boundaries. These changes are considered to be a strong evidence for recrystallization.     

On the role of indium underlays in the prevention of thermal grooving in thin gold films

Thin gold films are potentially important for metallizations in microelectronic devices because of the high activation energy of gold for electrotransport. A high activation energy ensures a longer lifetime of microelectronic devices compared with those in which aluminum metallizations are used. When electromigration is no longer the principal failure mechanism, other failure mechanisms, caused by d.c. stressing, might become important. One possibility is grain boundary grooving. Preliminary studies have shown that grain boundary grooving in thin gold films is prevented by inserting an indium underlay between the gold film and the substrate. The objective of this work was to investigate the mechanisms for the prevention of grain boundary grooving in In/Au composite films by comparing the microstructural evolution of pure gold films with In/Au composite films during isothermal annealing. Microstructures were characterized in terms of grain size, grain size distribution, preferred orientation and surface morphology utilizing transmission electron microscopy (TEM), cross-sectional TEM, scanning electron microscopy and X-ray diffraction. The chemical reactions and the distributions of the phases were monitored by selected area diffraction in TEM, and by Auger electron spectroscopy sputter profiling.It was found that the principal mechanisms that inhibit grain boundary grooving in IN/Au composite films area as follows.

• 1.(1) Indium underlays modify the microstructure of gold films by randomizing the orientation of the grains, refining the grain size, narrowing the grain size distribution and roughening the surface of the gold films.
• 2.(2) Indium is redistributed on gold films and forms In₂O₃ on the free surface and within the film during air annealing.
• 3.(3) The In₂O₃ on the surface “caps” the surface of gold films and limits mass transport during annealing.
• 4.(4) The In₂O₃ within the gold film, presumably residing at grain boundaries, impedes grain growth by pinning the grain boundary migration.

     

Role of the crystallinity of ZnO films in the electrical properties of bottom-gate thin film transistors

The strong correlation between the microstructural characteristics of ZnO channel layers grown at various temperatures by radio-frequency magnetron sputtering and the electrical performances of resulting bottom-gate thin film transistors (TFTs) was reported. Transmission electron microscopy revealed that increasing growth temperature enhanced degree of c-axis preferred orientation and enlarged width of columns in the ZnO films. The ZnO channel layers grown at 250 and 350 °C exhibited TFT saturation behavior. However, growing them at ≥ 350 °C produced small grains in the junctions of ZnO/SiO₂ interface and grain boundaries, which led to hump behavior in TFT transfer curve caused by formation of additional boundaries.     

Structural and electrical characteristics of chemical solution derived (Bi3.2La0.4Nd0.4)Ti3O12 thin films

(Bi_3.2La_0.4Nd_0.4)Ti₃O₁₂ (BLNT) thin films were prepared on Pt/Ti/SiO₂/Si substrates by using chemical solution deposition technique, and the effects of annealing temperatures in the range of 550-750 °C on structure and electrical properties of the thin films were investigated. X-ray diffraction analysis shows that the thin films have a bismuth-layered perovskite structure with preferred (117) orientation. The surface morphology observation by field-emission scanning electron microscopy confirms that films are dense and smooth with uniformly distributed grains. The grain size of the thin films increases with increasing annealing temperature; meanwhile, the structural distortion of the thin films also increases. It was demonstrated that the thin films show good electrical properties. The dielectric constant and dielectric loss are 191 and 0.028, respectively, at 10 kHz for the thin film annealed at 600 °C, and the 2Pr value of the thin film annealed at 700 °C is 20.5 μC/cm² at an electric field of 500 kV/cm.     

Structural properties of indium tin oxide thin films prepared for application in solar cells

Indium tin oxide (ITO) thin films prepared by rf sputtering were annealed in several temperatures. The electrical, optical and structural properties of these films are systematically investigated. The post annealing of the samples lead to considerably higher electrical conductivity, better optical transparency and larger grain size for the films. In an optimum annealing temperature of 400 °C, we have found that a maximized conductivity of films is achieved without a remarkable loss in their transparency. The sheet resistance of 2.3 Ω/□ and average grain size of 30 nm, are the results of the optimized post processing of films. The investigation for microstructure of films investigated by X-ray diffraction measurement (XRD) shows that a preferential crystal growth toward the (2 2 2) orientation takes place when the annealing temperature increases to 400 °C.     

Diffusion barrier performance of amorphous W-Ti-N films in Cu metallization

W-Ti-N films were prepared on a Si wafer by reactive sputter-deposition, followed by a deposition of a Cu thin film by DC magnetron sputtering. The Cu/W-Ti-N/Si samples prepared were annealed at different temperatures under vacuum and then characterized using X-ray diffraction, scanning electron microscopy and auger electron microscopy. The sheet resistivity was determined by four point probe analysis. The results show that the amorphous W-Ti-N film is mainly composed of TiN and W and the crystallization temperature is above 800 °C. W-Ti-N thin films prepared have good thermal stability at 700 °C, but the Cu film tends to agglomerate when the temperature is above 700 °C. A failure mechanism of the diffusion barrier is proposed based on the thermal stress and interface reaction.