Thick Copper Films Research Articles

Fluorophore-Induced Plasmonic Current Generation from Copper Nanoparticle Films.

We describe the process of generating a fluorophore-induced plasmonic current (FIPC) from copper nanoparticle films. Previous work and the literature have shown that excited near-field fluorophores are able to plasmonically couple with metal nanoparticle films (MNFs), inducing surface plasmons in the films. These induced surface plasmons are then in turn able to generate a directly measurable electrical current across the film. These generated currents have been quantified and detected in noble metal films, such as those made from Ag and Au, but due to the cost of such films, there has been a push to use lower cost materials for FIPC. Previous work has detailed the use of gold, silver, and aluminum films for these purposes, and in this paper, we will subsequently examine the ability of thermally deposited copper films to generate FIPC when in close proximity to excited near-field fluorophores. We report the effects of copper film thickness, the effects of light polarization and solution conductance, and the effects of metal-enhanced fluorescence (MEF) emission on the generation of plasmonic current.

Effect of Cu Film Thickness on Cu Bonding Quality and Bonding Mechanism.

In the hybrid bonding process, the final stage of chemical mechanical polishing plays a critical role. It is essential to ensure that the copper surface is recessed slightly from the oxide surface. However, this recess can lead to the occurrence of interfacial voids between the bonded copper interfaces. To examine the effects of copper film thickness on bonding quality and bonding mechanisms in this study, artificial voids were intentionally introduced at the bonded interfaces at temperatures of 250 °C and 300 °C. The results revealed that as the thickness of the copper film increases, there is an increase in the bonding fraction and a decrease in the void fraction. The variations in void height with different copper film thicknesses were influenced by the bonding mechanism and bonding fraction.

Influences of parameters of film on acoustical absorption performance of copper film-copper fiber composite structure

Fiber porous materials excel at sound absorption, but their effectiveness suffers at thin thicknesses. This study proposed a novel copper film-copper fiber porous material (FFM) structure to overcome this limitation. We designed a composite material with improved sound absorption, by coating a thin copper film onto an existing copper fiber matrix. This innovative approach enables effective sound absorption when the sample thickness is small. Our analysis revealed that FFM structures are better than the individual copper film and fiber porous material regarding sound absorption, particularly near their resonance frequency. Notably, a 2 mm-thick FFM structure boasts an average sound absorption coefficient of 0.35, a remarkable fourfold increase compared to the individual copper fiber matrix (0.08). The further investigation explores the influence of copper film thickness and bond area percentage on acoustic performance. We successfully validate our simulation model against experimental data, enabling us to calculate energy consumption ratios for various design parameters. This provides research ideas for optimizing FFM structures for specific noise reduction applications.

AUTOMATED CONTROL OFTHE THIN FILMS ELECTRICALCONDUCTIVITY BY THE EDDY CURRENT METHOD

The article considers the possibility of using the eddy current method of non-destructive testing for the problems of measuring the electrical conductivity of thin metal films. As the object of measurement, we used copper films of various thicknesses obtained by vacuum vapor deposition. A review of current trends in the use of copper films in modern industry and science is presented, and an analysis is made of current methods of non-destructive testing suitable for studying thin copper films. A brief description of the deposition method and the hardware-software complex for measuring the electrical conductivity of the film is presented. A calibration curve is presented, which makes it possible to restore the values of the electrical conductivity of the film from the value of the signal of the eddy current transducer. GaAs samples were selected to construct a calibration curve. The decision is explained by the proximity of the values of the electrical conductivity of this chemical compound to the calculated indicators of the obtained thin films. The results of testing films with different characteristics are presented and the distribution of the electrical conductivity of the films depending on the batch is shown. A series of practical measurements of thin films demonstrated the existence of a relationship between the mass of the initial substance that was subjected to deposition and the characteristics of the resulting films. According to different values of electrical conductivity within the same batch, it was concluded that there is a difference in the quality of deposition of different films.

Testing of Electromigration Resistance of Copper and Silver Thick Films

This paper is focused on the electromigration resistance of copper and silver thick films. Electromigration was tested by water drop test. Four common conductive thick film pastes were used for testing – silver paste with low platinum content, and two silver pastes with different content of palladium and copper paste. Electromigration was tested under voltage of 6 and 12 V and time to shortcut was measured. Results of testing including the comparison of electromigration resistance depending on thick film paste type and different electrode spacing are described in this paper.

Random crystal orientation and tensile strength of nanocrystalline dumbbell-shaped copper thick films electrodeposited from acidic aqueous solutions containing polyethylene glycol

Nanocrystalline thick copper films with the thickness of ∼250 μm were electrochemically synthesized from an acidic aqueous solution containing polyethylene glycol (PEG) with the average molecular weight of 3,000 to investigate the preferential crystal orientation and mechanical properties such as microhardness and tensile strength. By addition of PEG to the electrolytic bath, the cathode potential was shifted to a less noble direction during the electrodeposition and the average crystallite size of electrodeposited copper thick films was decreased. The copper thick films electrodeposited from the solution without PEG exhibited a preferentially orientation in (220) texture while that obtained from the solution containing PEG was composed of nanocrystals with random crystal orientation that containing (111) and (200) textures. The micro-Vickers hardness, tensile strength, and elongation of the electrodeposited copper thick films reached up to 133 HV, 234 MPa, and 13.1%, respectively. These improvements in mechanical properties can be explained by the grain refinement effect and the random crystal orientation effect.

The effect of electrical parameters of eddy current sensor on metal film thickness measurement performance and the optimization method.

Eddy current sensors have been widely used in the field of micro- and nano-measurements. The detection circuit is a key part of eddy current sensors. In particular, the electrical parameters in the signal conversion circuit have an important effect on the measurement performance. It is necessary to study the effect of the electrical parameters on the measurement performance and propose an optimization method. In this study, a simulation model of the eddy current sensor is established by coupling a magnetic field and a circuit field. The circuits include the LC parallel resonance, the AC bridge, and three combination circuits of the LC resonant and AC bridge. The output voltage variation with the thickness of copper film is calculated, and the effect of the electrical parameters on sensitivity Ki is obtained. In the LC parallel resonant circuit, it' is revealed that K1 is maximum when the parallel capacitance CP is equal to the resonant capacitance C0. An optimization method of adjusting resistance RS in different thickness intervals is proposed. In the AC bridge circuit, it' is revealed that there exists an optimal RS, which makes K2 maximum. In three combination circuits, K3, K4, and K5 are the maximum when the capacitances (C1, C2, and C3) reach the resonant capacitance C0. In addition, the sensitivity of each combination circuit is improved compared with that of the AC bridge. The relevant analysis results are further verified by a series of experiments. According to the calculation results and the experimental analysis, the optimization method for electrical parameters is further proposed.

On regularities of the formation of fractal structure on the surface of metal films of different thickness

The surface morphology of nanosized copper and nickel films on mica is studied using a scanning tunneling microscope. Altitude parameters and fractal dimension are determined for copper and nickel films of different thicknesses. The characteristic sizes of structural agglomerates for copper and nickel films are indicated depending on the thickness. The choice of the film thickness and the conditions for its production makes it possible to formulate recommendations for the development of the technology of “growing” structures with a given surface morphology.

Control of Cu Film Stress Deposited by Magnetron Sputtering Using Graphene Flake Layers

Residual stress of a 10 μm thick copper (Cu) film deposited using direct current (DC) magnetron sputtering system was analyzed. Graphene flake, having high toughness and strength properties, was inserted in Cu film for decreasing residual stress. Compared with the Graphene sheet transfer method, a Cu film sample with Graphene flake inserted using a simple brush deposition method could be fabricated. By using a graphene flake layer, the Cu residual stress was decreased from 25.4 MPa to 14.6 MPa. As decreasing the Graphene flake area ratios from 100% to 40%, the residual stress was reduced to 2.8 MPa. A 50×50 mm size heat sink was fabricated to confirm the thermal diffusion of Graphene flake, and the LED device was mounted on it. As a result, graphene flake was obtained the result that improved thermal diffusion of the heat sink.

Photonic sintering of copper for rapid processing of thick film conducting circuits on FTO coated glass

Copper potentially provides a cost-effective replacement for silver in printed electronic circuitry with diverse applications in healthcare, solar energy, IOT devices and automotive applications. The primary challenge facing copper is that it readily oxidizes to its non-conductive state during the sintering process. Photonic sintering offers a means of overcoming the oxidation by which rapid conversion from discrete nano-micro particles to fully or partially sintered products occurs. An experimental study of flash lamp sintering of mixed nano copper and mixed nano/ micro copper thick film screen printed structures on FTO coated glass was carried out. It shows that there may be multiple energy windows which can successfully sinter the thick film copper print preventing detrimental copper oxidation. Under optimum conditions, the conductivities achieved in under 1 s was (3.11–4.3 × 10–7 Ω m) matched those achieved in 90 min at 250 °C under reducing gas conditions, offering a significant improvement in productivity and reduced energy demand. Also present a good film stability of a 14% increase in line resistance of 100 N material, around 10% for the 50N50M ink and only around 2% for the 20N80M.

Hardness Determination of Thin Film Structural Materials Using Laser-Induced Breakdown Spectroscopy

The hardness of a thin film structural material is a direct reflection of its comprehensive mechanical properties, which are dependent on the film thickness. In recent years, laser-induced breakdown spectroscopy (LIBS) has been gradually applied to the determination of the hardness of materials; however, there is no relevant studies have been conducted on thin film structural materials. In this study, Q235 steels with different copper plating thicknesses on the surface were used to determine the correlation between the hardness and spectroscopic parameters. Nanoindentation was used for the hardness analysis. First, a linear relationship was obtained between the sample hardness and copper film thickness and the goodness-of-fit value was 0.9961. Second, we calibrated the plasma temperature and Cu ionic-to-atomic line intensity ratio of the surface spectra to the hardness and found that the spectroscopic parameters of the surface spectra of the samples were not sufficient to characterize their hardness. Finally, the number of shots reaching the Cu-substrate interface is determined by the similarity between the spectra obtained from two adjacent shots, 2, 5, 21, and 96, respectively. We determined a more accurate linear relationship between the plasma temperature, ionic-to-atomic line intensity ratio of the spectra at the film-substrate interface, and sample hardness. The goodness-of-fit values were 0.9923 and 0.9973. This demonstrates that the spectra at the film-substrate interface are more suitable for sample hardness analysis and LIBS is a potential method for the estimation of the hardness of thin film structural materials.

Laser-machined thin copper films on silicon as physical unclonable functions.

Physical unclonable functions (PUFs) are receiving significant attention with the rise of cryptography and the drive towards creating unique structures for security applications and anti-counterfeiting. Specifically, nanoparticle based PUFs can produce a high degree of randomness through their size, shape, spatial distribution, chemistry, and optical properties, rendering them very difficult to replicate. However, nanoparticle PUFs typically rely on complex preparation procedures involving chemical synthesis in solution, therefore requiring dispersion, and embedding within a host medium for application. We propose laser machining of surfaces as a one-step process for the creation of complex nanoparticle based PUFs by machining 600 nm thick copper films on a silicon substrate to yield a complex spatial and chemical distribution of redeposited copper, silicon, and oxide species. The approaches and material system investigated have potential applications in silicon chip authentication.

Study on Controlling Residual Stress in Thick Copper Film for Heat Sink Using Graphene

Nowadays, high-density electronic devices and component mounting have gained popularity. Because of the heat generated from these devices, efficiency of the electronic parts is significantly lowered and life time of these devices is considerably shortened. Therefore, it is very important to efficiently dissipate the heat generated from the device to extend product. In this study, a copper thick film was deposited using a sputtering technique using plasma. In addition, graphene, a two-dimensional nanomaterial, was inserted in the form of a sandwich structure between the deposited copper (Cu) layers of various thicknesses. Through this, a study was conducted to control the residual stress of thick copper foil deposited by sputtering. In this study, the residual stress was measured according to the location where graphene was inserted, the treatment method, and the transfer area. As a result, the highest residual stress reduction effect was observed when the transfer area of graphene was about 70%. Reduction of residual stress was observed by inserting graphene into the deposited copper thick film of various thicknesses. In addition, by increasing the number of layers of graphene inserted, changes in residual stress were observed.

Additive Nanosecond Laser-Induced Forward Transfer of High Antibacterial Metal Nanoparticle Dose onto Foodborne Bacterial Biofilms.

Additive laser-induced forward transfer (LIFT) of metal bactericidal nanoparticles from a polymer substrate directly onto food bacterial biofilms has demonstrated its unprecedented efficiency in combating pathogenic microorganisms. Here, a comprehensive study of laser fluence, metal (gold, silver and copper) film thickness, and the transfer distance effects on the antibacterial activity regarding biofilms of Gram-negative and Gram-positive food bacteria (Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Listeria monocytogenes, Salmonella spp.) indicated the optimal operation regimes of the versatile modality. LIFT-induced nanoparticle penetration into a biofilm was studied by energy-dispersion X-ray spectroscopy, which demonstrated that nanoparticles remained predominantly on the surface of the biofilm.

High-Precision Thickness Measurement of Cu Film on Si-Based Wafer Using Erasable Printed Eddy Current Coil and High-Sensitivity Associated Circuit Techniques

The eddy current coil is widely adopted to measure the thickness of copper (Cu) film on the silicon (Si) based wafer. However, the lift-off distance (LOD) variation between the coil and Cu film has a strong negative effect on the accuracy and repetitiveness of the thickness measurement. Therefore, it is necessary to eliminate the impact of LOD variation. In this article, a high-precision thickness measurement method is proposed to determine the thickness of Cu film on the Si-based wafer by using the techniques of the erasable printed eddy current coil (EPECC) and the high-sensitivity associated circuit. The theoretical feasibility and sensitivity improvement of the conceptual design are analyzed in detail. As a proof of concept, a prototype of the proposed method is fabricated. The EPECC is prepared on the back surface of the wafer, and the LOD is unvaried during the measurement. Experimental results show that comparing with the traditional eddy current coil, the measurement stability, precision, and accuracy of the Cu film thickness by the proposed method are significantly improved even under severe vibration conditions. The relative error is 2% in repeated measurements.

Numerical simulation of fatigue behavior of flexible metal films in multiphysics fields

AbstractThe operating ambient of flexible electronics interconnects is a complex environment that includes mechanical deformation, electric current, and temperature. It is a potential threat to the long‐term service reliability of flexible electronic devices. This paper aims to develop a multiphysics fatigue model for flexible metal films. The effect of multiphysics fields is considered in the Coffin–Manson relationship based on reasonable simplification. The fatigue behavior of copper films of various thicknesses on a flexible substrate was investigated when electrical current and mechanical displacement loads were applied simultaneously. The developed model is validated to compare with experimental results. The numerical results show that it can analyze the effect of multiphysics fields and predict the fatigue life of copper films. Therefore, it could be a means to assess the fatigue performance of metal films on flexible substrates in multiphysics fields.

Experimental study of the copper-coated hollow fiber surface plasmon resonance sensor

A novel optical fiber surface plasmon resonance (SPR) sensor based on the copper-coated hollow fiber structure was proposed. The simple chemical liquid phase deposition method was developed to coat the thin copper film on the inner surface of the hollow fiber to fabricate the proposed sensor. The performance of the hollow fiber SPR sensors with different copper film thickness were investigated experimentally by measuring the transmission spectra of the sensors filled by sensed liquid media with different refractive indices. Theoretical analysis based on the ray transmission model was also carried out for comparison. The experimental and theoretical results agree well with each other. The factors which affect the sensor performance are discussed. The sensor achieves a maximum sensitivity of 7111 nm/RIU, which is relatively high in the copper film based optical fiber SPR sensors and comparable to the silver-coated hollow fiber sensors. Moreover, the fabrication process of the proposed sensor is much simpler than other copper based optical fiber SPR sensors, which make it more practical. The copper film deposition method presented in this paper is also applicable to the fabrication of some microstructured optical fiber or photonic crystal fiber based sensors with copper film.

Superminiature Eddy Current Probe for Measuring the Electrical Conductivity of Copper Thin Films

The article considers the possibility of applying the eddy current method of non-destructive testing for measuring the electrical conductivity of new material - thin metal films. Copper films of various thickness obtained by physical vapour deposition were used as the measurement object. The deposition method and the hardware and software complex for measuring the electrical conductivity of the film were briefly described. A calibration curve that makes it possible to restore the values of the electrical conductivity of the material by the signal value of the eddy current probe was presented. The test results of films with different characteristics were given, and the distribution of the electrical conductivity of the films depending on the batch was shown. Based on different values of the electrical conductivity in a batch, the difference in deposition quality of various films was found.

Edge Effects of an Eddy-Current Thickness Sensor During Chemical Mechanical Polishing

Accurate and in-situ thickness measurements of copper films on Si-based wafers are employed to improve global planarization, adjust polishing pressure, and avoid over-polishing and under-polishing during chemical mechanical polishing (CMP). However, edge effects cause inaccurate thickness measurements at the wafer edge, and greatly decrease the effective area of integrated circuit (IC) manufacturing. In this study, edge effects were studied using both a trans-dimensional simulation model of electromagnetic fields and circuit coupling in eddy-current thickness measurement and an experimental nanoscale thickness-measurement sensor system with a resolution of 2.07 Å /mV. The simulation and experimental results were in close agreement when the sensor coil was located at different edge positions. The influence of different factors such as copper film thickness, edge positions, calibrated thickness, lift-off distance, and excitation voltages on thickness-measurement performance in the edge region were also examined. Copper film surface current density was calculated to clearly evaluate eddy-current distortion at different edge positions. The determined influences of these parameters on edge effects could be used to improve the edge-measurement performance of sensor systems by adjusting coil and circuit parameters or propose an edge signal compensation algorithm during CMP.

Flexible ABS hollow waveguides with an inner copper coating for terahertz transmission

We fabricated flexible hollow fibres with an inner copper coating. A liquid-phase chemical deposition process was used to coat copper thin films inside an acrylonitrile butadiene styrene (ABS) plastic tube. The attenuation characteristics of terahertz(THz)radiation in ABS plastic tubes with bore diameters of 2, 3, and 5 mm were determined at 0.32, 0.65, and 0.98 THz. The lowest loss of 0.85 dB/m at 0.98 THz was obtained for hybrid TE mode propagation in a waveguide consisting of a 0.7-µm- thick copper film layer deposited inside a 97.5-cm-long ABS plastic tube with a 5-mm bore.