Photovoltaic response of Cu2O/In2S3 hetero-structure grown on Cu substrate

A thin layer of p-type Cu₂O was grown over flexible 30 μm thick copper substrates. Using Injection Chemical Vapor Deposition technique, n-type In₂S₃ thin films were grown over the Cu₂O layer. A p–n junction was thus realized. The Cu₂O/In₂S₃ hetero-structure showed photovoltaic behavior. A solar cell with the structure Cu/Cu₂O/In₂S₃/Ag could be fabricated. An acidic texturization sequence was developed which increased the photo-sensitivity of the In₂S₃ window layer. The Cu/Cu₂O/In₂S₃/Ag hetero-structure with the textured window layer had an open circuit voltage of 377 mV, short circuit current density of 0.118 mA/cm² and fill factor of 33.34%. It was found that the efficiency of the solar cell depended upon the photo-sensitivity of the In₂S₃ window layer. The work demonstrates the use of copper substrate for thin film solar cell fabrication.     

Atom probe tomography of Ni silicides: First stages of reaction and redistribution of Pt

The silicide formation and the redistribution of Pt after deposition and after a heat treatment at 290 °C of Ni_1−xPt_x films on Si have been analysed by atom probe tomography assisted by femtosecond laser pulses. Two phases with different composition were found to form during deposition at room temperature: a NiSi layer with a relatively constant thickness of approximately 2 nm and a particle of Ni₂Si. The shape of the Ni₂Si particle is in accordance with nucleation followed by lateral growth formation. After heat treatment, two silicide phases Ni₂Si and NiSi were found together with the Ni_1−xPt_x solid solution. The redistribution of Pt at the Ni_1−xPt_x/Ni₂Si interface is a clear illustration of the snowplow effect. A segregation of Pt at the Ni₂Si/NiSi interface has been observed and is attributed to interfacial segregation. The effect of the redistribution of Pt on the silicide formation is discussed.     

Diffusional creep induced stress relaxation in thin Cu films on silicon

The results of stress measurements during annealing of thin copper films deposited on 100 μm Si substrates are presented. The stress in thin films was determined by using an optical system for curvature measurements. The annealing experiments were done during thermal cycles of heating and cooling procedures from room temperature up to 400 °C with a rate 10 °C/min. The total thickness of thin films was between 20 and 100 nm. The obtained results showed that the difference between the end and the initial values of the ratio of force to width increases with the thickness of the samples. The initial linear shape of the temperature-stress plots reaches higher temperature values with an increase in film thickness. In order to explain the observations, the dependence of stress on temperature was calculated using the rate of Coble creep. It was found that the theoretical curves reveal the same features as the experimental data. It was concluded that diffusional creep mechanism dominates for thin film of thickness below 100 nm.     

Effect of Si/Ta and nitrogen ratios on the thermal stability of Ta-Si-N thin films

Ta-Si-N thin films were fabricated by using reactive magnetron cosputtering at different Si/Ta power ratios and nitrogen (N₂) to total gas (Ar + N₂) flow ratios (FN₂% = FN₂/(FAr + FN₂) × 100%). Both levels of high-vacuum furnace annealing (FA) and low vacuum rapid thermal annealing (RTA) were performed to investigate the thermal stability of films. The microstructure, morphology and electrical property of the Ta-Si-N thin films were characterized by grazing incidence X-ray diffraction, scanning electron microscope and four-point probe method, respectively. Ta-Si-N thin films at low FN₂% could endure temperature up to 900 °C for 1 h under high-vacuum FA at 6.5 × 10⁻³ Pa while their phase and morphology had changed under RTA at 750-900 °C for 1 min at 2.6 Pa. The resistivity increased with increasing both FN₂% and Si/Ta power ratios. However, the variation percentage of resistivity of Ta-Si-N films at high-temperature annealing decreased with increasing Si/Ta power ratio and inversely increased with increasing FN₂%. In brief, the thermal stability of Ta-Si-N films increased with increasing level of vacuum and Si/Ta power ratio. Increasing FN₂% and Si/Ta power ratio could enhance the thermal stability of films at RTA but also increased the resisitivity of films. Therefore, Ta-Si-N films prepared at 2 FN₂% and Si/Ta power ratio of 2/1 can be a good candidate for the application of diffusion barrier with low resistivity, low variation percentage and high stability of microstructure.     

Impact of electroplated copper thickness on copper CMP and Cu/Coral™ BEOL integration

A study was carried out to establish the impact of electrochemical plated (ECP) Cu thickness on the effect of dishing during Cu chemical mechanical planarization and the electrical and reliability performance of 0.13 μm Cu/Coral devices. The roughness of Cu films at the wafer edge was found to increase with increasing film thickness while it remained constant at the wafer centre. This resulted in different Cu grain morphology across the wafers. The reduction in sheet resistance (R_s) for the Cu film after annealing, as well as the as-deposited and post annealed film stresses were also found to be dependent on the ECP Cu thickness. As the thickness increased, the R_s reduction increased while the as-deposited and post annealed film stresses decreased. The different ECP Cu thickness did not show any significant difference in the amount of Cu dishing at the centre of the wafers. However, at the wafer edge, the Cu dishing amount was found to be significantly affected by the Cu thickness in which the amount of dishing increased as the thickness increased. The via chain, Kelvin via, M1 line and M2 line resistances also showed a strong dependence on the ECP Cu thickness. The thinnest Cu film of 0.7 μm gave the lowest results with the tightest spread for the four resistances tested. For the via chain and M1 line resistance, it was followed by the 1.0 μm Cu film and the 1.3 μm film yielded the worst data. In the case of Kelvin via and M2 line resistance, the thicker plated Cu films gave similar worse results. All the electrical results showed good coincidence with the Cu dishing data. The voltage ramp (v-ramp) data showed no significant difference in the electrical field leading to dielectric breakdown at both M1 and M2 lines for all the three types of ECP Cu thickness split.     

A low-cost copper oxide thin film memristive device based on successive ionic layer adsorption and reaction method

Metal-insulator-metal based memristive structure is a promising configuration for next generation information storage, reconfigurable circuits and neuromorphic application. In view of this, we experimentally demonstrated the simple and cost effective approach to fabricate CuO memristive device using successive ionic layer adsorption and reaction method. The developed two terminal Al/CuO/SS thin film memristive device successfully mimic the biological synapse-like properties such as analog memory, synaptic weights and bidirectional information flow. Furthermore, the bipolar resistive switching with different magnitudes of V_SET and V_RESET were observed due to stochastic nature of formation and breaking of the conductive filament. The slopes of current-voltage characteristics suggested that the Ohmic and space charge limited conduction mechanisms were dominant in developed devices. The analysis of electrical characterization suggested that the memcapacitive and meminductive properties coexisted with memristive behavior in the developed devices. The results reported herein are useful for the development of low-cost electronic synapse and nano-scaled self-resonating, reconfigurable and adaptive circuits.     

Praseodymium based high-k dielectrics grown on Si and SiC substrates

High-k polycrystalline Pr₂O₃ thin films have been deposited by metal organic chemical vapor deposition (MOCVD) technique on Si(0 0 1) and 4H–SiC(0 0 0 1) substrates. MOCVD processes have been carried out from the Pr(tmhd)₃ (H-tmhd= 2,2,6,6-tetramethyl-3,5-heptandione) precursor. Complete structural and morphological characterization of films has been carried out using several techniques (X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM)). Polycrystalline Pr₂O₃ films have been obtained and at the interface a praseodymium silicate amorphous layer has been observed on both substrates. The electrical properties of the dielectric praseodymium films have been evaluated.     

In-line control of Si loss after post ion implantation strip

Spectroscopic ellipsometry could be used as a fast and accurate method to measure Si loss resulting from post ion implantation strip. It was found that upon implantation, even at low energies (around 1 keV), the implanted layer has different optical properties from the crystalline Si. That allows ellipsometry to distinguish between Si substrate, implanted Si and SiO₂ on top. The ellipsometric measurements are confirmed by transmission electron microscopy (TEM). TEM shows that even if the Si is not amorphized at low energies, it is damaged (the lattice is strained) which is apparently enough to change the optical properties of Si. The exposure of implanted Si to an ash plasma at elevated temperatures (280 °C) results in SiO₂ growth and a decrease of the damaged Si thickness. The decrease is attributed partially to oxidation (Si loss) and partially to restoration of the strained lattice.     

Surface modification on plating-based Cu/Sn/0.7Cu lead-free copper pillars by using polishing

Thus far, no any effective countermeasure against plating-induced poor uniformity exists in the global packaging market. In this paper, we aim to develop an effective polishing process to improve the poor uniformity existing in advanced double-layer copper pillars. After polishing, the wafer and chip uniformities of copper pillars could be reduced from the original values of 6.8-3.5% and 2.9-0.9%; after reflow, the wafer and chip uniformities of copper pillars reached 3.0% and 1.7%. Excellent uniformity in copper pillars ensures accurate joints, good reliability, high yields, and flexible layouts.     

Effect of sputter deposited Zn precursor film thickness and annealing time on the properties of Cu2ZnSnS4 thin films deposited by sequential reactive sputtering of metal targets

Cu₂ZnSnS₄ (CZTS) is made of earth abundant elements and also have suitable optical properties for solar cell applications. But, in phase diagram, CZTS exists in a narrow range of temperature and composition. Therefore, optimizing the elemental composition and annealing time is very important for obtaining phase pure CZTS. In this study, the effects of elemental composition and short annealing time on the structural and optical properties of reactively sputtered CZTS thin films are reported. Thin films were deposited by reactive sputtering of Cu: Sn (60:40 wt%), Sn and Zn targets sequentially in the presence of H₂S at room temperature. Amount of Zn precursor was varied by changing the sputter time for Zn. The films were rapidly annealed in inert atmosphere for varying time. The band gap of sample changed with change in the composition as well as annealing time. Sample with higher Zn content showed better crystallinity. With increase in the annealing time the crystallinity of samples improved. Sample annealed for 12 min at 550 °C was phase pure. Obtaining good quality film even for very short anneal time is the novelty of reactive sputtering method as all the elements are already mixed and short annealing is required only for crystal growth. Through detailed experiments, the optimum composition and annealing time required for the growth of phase pure CZTS has been established.     

Stress development during evaporation of Cu and Ag on silicon

This work presents results of stress measurements during deposition of thin silver and copper films on 100 μm Si substrate. The stress in thin films has been determined by means of an optical system for the measurement of sample’s curvature. This system was applied in situ in a high vacuum deposition system. For Ag films the stress occurring during deposition goes from a low compressive value to tensile for thickness less than 30 nm and to compressive above this. For Cu films we observe tensile stress for thickness less 20 nm and above 50 nm. The same general trend of stress evolution with thickness is present in all cases at initial stage. There is the same growth mode for Cu and Ag because of the similar shapes of stress curves for thickness lower than 30 nm The behavior of stress evolution was explained by island nucleation and growth, island coalescence and continuous film growth. The difference in the stress evolution above 30 nm is caused by the fact that silver may be less sensitive than copper to adsorption of impurities. Adsorbed contamination inhibits compressive stress increase generated by grain boundary and defects remaining in the film.     

可剥网状铜箔的制作及应用

文章介绍可剥网状铜箔的制作及应用方法,目的是为实现制作出孔铜厚度大于25μm而表面铜厚度小于25μm的要求,采用的原理及流程是:在表面制作成网状铜层,这网状铜层与底铜在剥离的时候会形成差4倍以上的剥离效果,在电镀的时候起到均匀分布电流的作用,孔内的电镀铜经过烘烤之后产生原子间扩散,与孔壁铜形成牢固的结合力。     

Silicide formation and interdiffusion effects in Si-Ta,SiO2-Ta AND Si-PtSi-Ta thin film structures

The formation of TaSi₂ in the Si-PtSi-Ta and Si-Ta systems has been studied using Auger spectroscopy, x-ray diffraction and electron diffraction techniques. The reaction of tantalum with PtSi was observed by Sinha, et al.^l to take place with high temperature (800°-900°c) annealing of thin film systems consisting of Si-PtSi-Ta-W¹. In the present investigation, it is shown that tantalum reacts with PtSi at approximately 600°C to form a mixture of Ta₅Si₃ and TaSi₂ and predominantly TaSi₂ at 785°C. Platinum is displaced at the refractory metal (Ta)-PtSi interface, whereupon the more stable refractory metal-silicide is formed. The displaced platinum reacts further with the excess silicon which diffuses from the Si-PtSi interface. The Si-PtSi-Ta reaction is similar to the Si-PtSi-W reaction. However, unlike tungsten which migrates very little in the Si-PtSi-W system, tantalum appears to interdiffuse with the PtSi at temperatures as low as 600°C. In the case of the Si-Ta couple, TaSi₂ forms at approximately 750°C as determined by transmission electron microscopy (TEM) measurements. The kinetics of TaSi₂ formation at the Si-Ta interface are compared to that which takes place at the PtSi-Ta interface to determine the influence of the PtSi layer. Silicide formation was not observed in SiO₂-Ta specimens. after anneals up to 800°c. At 750°C Ta₂O₅ formed as observed by electron diffraction.     

Effect of copper seed aging on electroplating-induced defects in copper interconnects

Voids in copper thin films, observed after electroplating, have been linked to seed aging that occurs when a wafer is exposed, over time, to clean-room ambient. Oxidation of the copper seed surface prevents wetting during subsequent copper electroplating, leading to voids. Several surface treatments were employed to counteract the seed aging effect, including reduction of the copper oxide film by hydrogen, reverse plating of the copper surface, and rinsing the wafer surface with electrolyte. Each treatment was applied to wafers increasingly aged from 2 to 14 days, just prior to electroplating. Results showed a significant decrease in postelectroplating defects with all three treatments. The reduction of copper oxide by hydrogen exhibited the most marked results. An increase in surface wetting is shown by a decrease in contact angle measurements and an increase in film reflectivity for treated versus untreated copper wafers. This study shows that, although the copper surface exhibits strong aging effects over a short period of time, using proper surface treatments can eliminate such effects and voids.     

Experimental and simulation studies of resistivity in nanoscale copper films

The effect of film thickness on the resistivity of thin, evaporated copper films (approximately 10-150 nm thick) was determined from sheet resistance, film thickness, and mean grain-size measurements by using four-point probe, profilometer, and electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) methods, respectively. The resistivity of these films increased with decreasing film thickness in a manner that agreed well with the dependence given by a versatile simulation program, published earlier, using the measured values for the mean grain size and fitting parameters for surface and grain boundary scattering. Measurements of the change in sheet resistance with temperature of these films and the known change in resistivity with temperature for pure, bulk copper were used to calculate the thickness of these films electrically by using Matthiessen’s rule (this is often referred to as an “electrical thickness”). These values agreed to within 3 nm of those obtained physically with the profilometer. Hence, Matthiessen’s rule can continue to be used to measure the thickness of a copper film and, by inference, the cross-sectional area of a copper line for dimensions well below the mean free path of electrons in copper at room temperature (39 nm).     

Photochemical Formation of Au/Cu Bimetallic Nanoparticles with Different Shapes and Sizes in a Poly(vinyl alcohol) Film

Metal nanoparticle (NP)–polymer nanocomposite thin films are attractive for applications in various devices. Since bimetallic NPs provide additional opportunities for tuning the physical properties of the NP components, the development of bimetallic NP nanocomposite thin films should lead to further enhancements of various applications. Au/Cu bimetallic NPs are fabricated in a poly(vinyl alcohol) (PVA) film using a photochemical process. Interestingly, different sizes and shapes of Au/Cu bimetallic NPs are formed in the PVA film, resulting in a uniquely patterned nanocomposite structure. It is determined that the different formation and growth mechanisms of NPs inside and outside the UV‐light irradiation spot leads to the differences in size and shape.     

Antimony sulfide (Sb2S3) thin films by pulse electrodeposition: Effect of thermal treatment on structural,optical and electrical properties

Antimony sulfide films have been deposited by pulse electrodeposition on Fluorine doped SnO₂ coated glass substrates from aqueous solutions containing SbCl₃ and Na₂S₂O₃. The crystalline structure of the films was characterized by X-ray diffraction, Raman spectroscopy and TEM analysis. The deposited films were amorphous and upon annealing in nitrogen/sulfur atmosphere at 250 °C for 30 min, the films started to become crystalline with X-ray diffraction pattern matching that of stibnite, Sb₂S₃, (JCPDS 6-0474). AFM images revealed that Sb₂S₃ films have uniformly distributed grains on the surface and the grain agglomeration occurs with annealing. The optical band gap calculated from the transmittance and the reflectance studies were 2.2 and 1.65 eV for as deposited and 300 °C annealed films, respectively. The annealed films were photosensitive and exhibited photo-to-dark current ratio of two orders of magnitude at 1 kW/m² tungsten halogen radiation.     

Effects of annealing temperature on the photoluminescence of RF sputtered Barium titanate thin films

BaTiO₃ thin films were deposited onto quartz substrates by an RF magnetron sputtering method. The films deposited at room temperature and annealed at 773–1173 K were characterized using X-ray diffraction (XRD)Scanning electron microscopy (SEM), UV–vis spectroscopy and Photoluminescence spectroscopy (PL). X-ray diffraction studies revealed that the film is amorphous in nature at 773 K and that the crystallinity increases with increase in annealing temperature. The average crystallite size of the films increased from 13–18 nm and the optical band gap decreased in the range of 4.33–3.43 eV, with increase in annealing temperature. The films exhibited good adherence to the substrates and the SEM images showed smooth surface morphology. Energy dispersive X-ray (EDX) analysis confirmed the presence of barium, titanium and oxygen in the film. The red-shifts of excitonic UV emission peaks were observed in all samples which can be attributed to the stress produced due to lattice distortions. The visible PL emission intensity showed appreciable enhancement with post-deposition annealing.     

凝固条件对γ-Ni/Mo2Ni3Si合金凝固组织的影响

设计并采用激光熔炼工艺制备出镍基固溶体γ增韧的Mo_2Ni_3Si三元金属硅化物合金。差式扫描量热分析(DSC)及高温金相实验表明,该合金共晶温度约1287℃,液相线温度约1355℃。研究了该Mo_2Ni_3Si合金在炉冷、水冷及激光表面熔凝条件下的凝固组织。结果表明,在炉冷及水冷条件下,随着凝固冷却速度的提高,合金中Mo_2Ni_3Si初生枝晶体积分数降低、二次枝晶臂间距减小,但激光表面快速熔凝合金中Mo_2Ni_3Si初生枝晶体积分数急剧增加(62％)。激光表面快速熔凝γ/Mo_2Ni_3Si合金由于组织细小,且基体γ相被Mo及Si元素过饱和固溶,具有最优异的力学性能(显微硬度600HV);炉冷Mo_2Ni_3Si合金凝固组织初生枝晶上分布着许多显微裂纹,且显微组织为粗大的二相组织,力学性能较差。     

Ti and Ti/Sb ohmic contacts on n-type 6H-SiC

Ohmic contacts consisting of Ti and Ti/Sb were prepared on silicon and carbon face of 6H-SiC with different doping densities. Ni contacts were used as reference. All structures were gradually annealed at different temperatures. Specific contact resistance was measured and morphology was monitored after each annealing. It was found that the same metallization has different properties on different 6H-SiC polar faces. Sb addition to Ti contact helped to reach lower values of specific contact resistance on Si-faces of substrates. On C-faces of substrates, pure titanium contacts were comparable or better than Ti/Sb. Annealing at 960 °C and 1065 °C caused contact morphology deterioration and surface spreading of Ti and Ti/Sb contacts. Ni contacts kept good morphology at all annealing temperatures and had the best values of specific contact resistance after annealing at 960 °C and 1065 °C. Using XPS profiling only small amount of free carbon was found in Ti-based contacts.