Diffusion Of Cu Research Articles

A Study on the Effect of Pd Layer Thickness on the Properties of Cu-Ag Intermetallic Compounds at the Bonding Interface.

This paper conducted a high-temperature storage test (HTST) on bonded samples made of Pd100 (Pd-coated Cu wire with a Pd layer thickness of 100 nm) and Pd120, and studied the growth law of Cu-Ag intermetallic compounds and the inhibitory mechanism of Pd thickness on Cu-Ag intermetallic compounds. The results show that the Kirkendall effect at the bonding interface of the Pd100-bonded sample is more obvious after the HTST, the sizes of voids and cracks are larger, and the thickness of intermetallic compounds is uneven. But, the bonding interface of the Pd120-bonded sample has almost no microcracks, the Kirkendall voids are small, and the intermetallic compound size is uniform and relatively thin. The formation sequence of intermetallic compounds is as follows: Cu atoms diffuse into the Ag layer to form Ag-rich compounds such as CuAg4 or CuAg2, and then the CuAg forms with the increase in diffused Cu elements. Pd can significantly reduce the Kirkendall effect and slow down the growth of Cu-Ag intermetallic compounds. The growth rate of intermetallic compounds is too fast when the Cu bonding wire has a thin Pd layer, which results in holes and microcracks in the bonding interface and lead to the peeling of the bonding interface. Voids and cracks will hinder the continuous diffusion of Cu and Ag atoms, resulting in the growth of intermetallic compounds being inhibited.

Investigating laser and ultrasonic welding of pouch cell multi-foil current collectors for electric vehicle battery fabrication

The escalating necessity for more efficient and defect-free joining of ‘ultra-thin foil collectors-to-tabs’ in electric vehicle (EV) Li-ion pouch cells motivates this study. The prevalent ultrasonic welding (USW) method for these joint types, faces limitations such as design constraints and access requirements, laser welding (LW) emerges as a promising alternative offering flexibility, one-side access and faster speeds with efficient heat input. This study aims to investigate the feasibility of LW as a viable alternative to USW for joining current collectors-to-tab joints. It compares the mechanical, metallurgical, electrical and thermal analysis of the joints to evaluate both welding techniques for joint defects. The comparison of solid-state material mixing during USW and the intermixing of aluminium (Al) and copper (Cu) during fusion LW using EDX analysis presents interesting observations in the study. The USW generates a thin transition layer with intermetallic compounds (IMCs) attributed to the diffusion of Cu into the Al matrix during joining, which is comparatively lower as in the case of LW with higher material mixing with brittle IMCs like Al2Cu and Al4Cu9. However, the joint strength of LW is comparatively lower than the USW joint attributed to the reduced fusion zone area. Furthermore, from the electrical contact resistance and the joint temperature analysis, it was found that the resistance and temperature vary by as much as 13% and 6%, respectively, for the 50 A and 75 A passing currents when the USW is replaced with the LW process.

Antiferromagnetic coupling in ferrimagnetic Mn4N-based bilayer structures

Mn4N/(Mn,Cu)4N epitaxial bilayer structures with (Mn,Cu)4N compositions below and above the magnetization compensation composition were prepared on SrTiO3(001) substrates by molecular beam epitaxy. The thickness of the (Mn,Cu)4N layer was fixed at approximately 20 nm, while that of the Mn4N layer was changed from 7.5 to 19.6 nm. Cross-sectional elemental mapping proved that the diffusion of Cu from the (Mn,Cu)4N layer to the Mn4N layer was negligible. The magnetization curves showed that the magnetic moments of Mn4N and (Mn,Cu)4N were antiferromagnetically coupled, independent of the Mn4N film thickness, indicating a synthetic ferrimagnetic structure. The dependence of magnetic order on Mn4N film thickness was confirmed by surface-sensitive measurements using polar magneto-optical Kerr effect and x-ray magnetic circular dichroism. This is due to the change in the layer with dominant magnetization and the strength of the antiferromagnetic coupling. The temperature dependence of the anomalous Hall effect showed that the antiferromagnetic coupling was retained in the Mn4N(7.5 nm)/(Mn,Cu)4N(22.4 nm) structure over a wide temperature range of 10–350 K.

Coadsorption mechanisms of copper and sulfamethoxazole by functionalized cellulose: A kinetic and DFT study

In order to address the issue of compound pollution from heavy metals and antibiotics in aquatic environments, multibranched functionalized cellulose materials (DACS) with abundant adsorption affinity groups (such as amino, carboxyl and imine groups) were prepared by oxidation, etherification and grafting. The maximum adsorption capacities of DACS for copper (Cu) and sulfamethoxazole (SMZ) were 42.27 and 117.92 mg/g, respectively. In addition, its excellent pH buffering capacity, resistance to coexisting interfering substances and great regeneration performance of up to 91 % after 5 cycles. In the coadsorption experiment, the multibranched structure strengthened the bridge effect during the coadsorption process, and weakened the inhibition of SMZ adsorption caused by competition. Kinetic models and error functions analysis showed that PNO model and F&S model were the most consistent with the adsorption process, and the limiting step of adsorption was the external diffusion of Cu and SMZ around the surface of DACS. Moreover, the density functional theory (DFT) was used to quantitatively calculate the adsorption binding energy of multiple sites on DACS, and clarified the adsorption tendency of DACS as electron donors for Cu and as acceptor for SMZ. In addition, the binding energy of sequential adsorption was greater than that of single and binary adsorption, and the binding stability of SMZ was significantly increased in sequential adsorption for the increasing of binding energy. The electron exchange process in the adsorption showed that SMZ played a bridging role in the binary adsorption, while Cu was the main reaction part of the complex adsorption.

Migration of copper(II) ions in humic systems—effect of incorporated calcium(II), magnesium(II), and iron(III) ions

The mobility of heavy metals in natural soil systems can be affected by the properties and compositions of those systems: the content and quality of organic matter as well as the character of inorganic constituents. In this work, the diffusion of copper(II) ions in humic hydrogels with incorporated calcium(II), magnesium(II), and iron(III) ions was investigated. The methods of instantaneous planar source and of constant source were used. Experimental data yielded the time development of the concentration in hydrogels and the values of effective diffusion coefficients. The coefficients include both the influence of the hydrogel structure and the interaction of diffusing particles with the hydrogel. Our results showed that the presence of natural metal ions such as calcium, magnesium, or iron can strongly affect the diffusivity of copper in humic systems. They indicate that the mobility of copper ions depends on their concentration. The mobility can be supported by higher contents of copper in the system. While the incorporation of Ca and Mg resulted in the decrease in the diffusivity of copper ions, the incorporation of Fe(III) into humic hydrogel resulted in an increase in the diffusivity of Cu(II) in the hydrogel in comparison with pure humic hydrogel.

Diffusion of lithium in copper current collectors of lithium metal anodes in liquid cells

Conflicting views are found in the literature on the significance of lithium diffusion into copper current collectors of lithium metal anodes. Previously published in situ Neutron Depth Profiling (NDP) measurements in a liquid cell revealed reversible Li diffusion in the current collector during electrochemical cycling, resulting in concentrations of ∼ 1 at. %. Herein, a model for these experiments is presented, in which stress in the deposit is induced by Li diffusion accompanying plating and stripping. This in turn produces stress gradients in the current collector, which together with composition gradients drive reversible grain boundary diffusion in Cu during cycling. Quantitative agreement with the NDP results is obtained for a fit diffusivity comparable to previous in situ measurements, but much larger than values from ex situ measurements using Li–Cu bilayers. Creep due to grain boundary diffusion is found to relax stress in the copper foil, resulting in low levels of stress and deformation during cycling. The results clarify the significance of Li diffusion in Cu, and also help elucidate the origin of stress in the lithium anode during cycling, which may induce interfacial instability.

Brazing of TC4 Alloy Using Ti-Zr-Ni-Cu-Sn Amorphous Braze Fillers.

In order to address the issues of excessive brittle intermetallic compounds (IMC) formation in the TC4 brazed joints, two types of novel Ti-Zr-Cu-Ni-Sn amorphous braze fillers were designed. The microstructure and shear strength of the TC4/Ti-Zr-Ni-Cu-Sn/TC4 brazed joints were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometer (XRD) and electronic universal materials testing machine. The results show that the optimized Ti35Zr25Ni15Cu20Sn5 braze filler whose chemical composition is closer to the eutectic point possesses a lower melting point compared with the equiatomic Ti23.75Zr23.75Ni23.75Cu23.75Sn5. This was beneficial to the sufficient diffusion of Cu and Ni elements with the base metal during brazing and reduces the residual (Ti,Zr)2(Ni,Cu) content in the joint, which helps to improve the joint performance. The room-temperature and high-temperature shear strength of the TC4 brazed joints using the near eutectic component Ti35Zr25Ni15Cu20Sn5 filler reached a maximum of 472 MPa and 389 MPa at 970 °C/10 min, which was 66% and 48% higher than that of the TC4 joints brazed with the equiatomic Ti23.75Zr23.75Ni23.75Cu23.75Sn5 braze filler. Microstructural evolution and the corresponding mechanical response were in-depth discussed.

Effect of solution temperature on the microstructure of 2:17 type SmCo magnets

The exceptional magnetic properties of 2:17 type SmCo magnet material is the results of its unique cellular structure. We conducted a systematic analysis of the evolution of the solid solution temperature on the microstructure of both the solid solution precursor and the final magnet, and revealed the distribution of elements affect by the magnet's properties. The findings show that a considerable number of short-range low-order microregions are observed with discontinuous alignment orientations, and overlapping zones are produced in the solid solution precursor by low-temperature solid solutions. The aging process makes these regions challenging to organize, and a lot of 2:17 R phases form close to 1:5 H cell boundary phase and grain boundary, which impedes the enhancement of magnetic characteristics. Increasing the solution temperature promotes the diffusion of Cu and Fe elements, accelerating the ordering of the 2:17 R phase and aiding in the creation of a cellular structure. The phase evolution of the 2:17 type SmCo magnet can be better understand by referring to the previously conducted research on the impact of solid solution temperature on the microstructure of the solid solution precursor and final magnet.

Investigation on interfacial compound growth kinetics in Sn-0.7Cu/Cu solder joint and mechanism analysis: Experiments and molecular dynamics simulations

Herein, the interfacial compound growth kinetics and corresponding mechanisms in Sn-0.7Cu/Cu solder joint at aging stage were investigated using both experiments and molecular dynamics simulations. The research results indicate that, the growth rates of interfacial IMCs (Cu6Sn5 IMC and Cu3Sn IMC) are affected by the aging temperature severely, the higher aging temperature leads to the larger growth kinetics for both Cu6Sn5 IMC and Cu3Sn IMC. At aging stage, Cu substrate continuously supplies Cu3Sn IMC with Cu atoms. Those Cu atoms diffuse across Cu3Sn IMC to the Cu3Sn/Cu6Sn5 interface and react with Sn atoms diffused from the Sn-based solder to form new Cu3Sn grains growing towards Cu6Sn5 IMC, and the main crystal orientations are (100), (42–1), and (3−10). As the grain boundary diffusion rate of Cu atoms in Cu3Sn IMC determines the CuSn reaction rate (new Cu3Sn grains formation rate) on Cu3Sn/Cu6Sn5 interface, the growth of Cu3Sn IMC is driven by grain boundary diffusion, which is manifested by a growth index n near to 0.3. Meanwhile, the rod-like Cu6Sn5 IMC preferentially grows into Sn-based solder attributed to the large number of Cu atoms provided by Cu3Sn IMC, which can diffuse to the top of Cu6Sn5 IMC and reacts with Sn-based solder. While when Cu6Sn5 IMC is thick enough, Cu atoms cannot reach to the top of Cu6Sn5 IMC anymore, but diffuse laterally within the Cu6Sn5 grains, resulting in the widening of scallop-like Cu6Sn5 IMCs. As the thickening of Cu6Sn5 IMC is caused by the growth of the existing Cu6Sn5 grains, the diffusion of Cu and Sn atoms in Cu6Sn5 grains plays a decisive role. Therefore, the growth of Cu6Sn5 IMC is driven by bulk diffusion, which is manifested by a growth index n near to 0.5.

Controlled Directional Cu Outflow in Cu/W Nanomultilayers

AbstractIn this study, we have investigated the feasibility of localized, focused ion beam (FIB)-stimulated Cu outflow in Cu/W nanomultilayers (NMLs) for manufacturing of heterogeneous micro-/nanojoints. Sub-micron-sized trenches were created on the nanomultilayer surface prior to heat treatment with the aim of directing the diffusion of Cu to locally defined NML surface regions. Cu outflow was triggered by annealing at 500 °C in a reducing atmosphere and lead to formation of (sub-)micron-sized Cu particles that are firmly joined to the W-terminated Cu/W NML. The results show that not only the depth of trenches (i.e., the parameters of the FIB treatment), but also the stress and the microstructure of the NMLs influence the Cu directional transport. The Cu outflow was found to be much more pronounced when the multilayer has a disordered microstructure with pores and open grain boundaries, as observed for NMLs with a tensile stress. We have thus demonstrated that FIB surface patterning enables the localized generation of (sub-)micron-sized Cu particles that can be used for manufacturing of micro-/nanojoints.

Influence of Mg and Cu on precipitation behaviors and mechanical properties of Al–Si alloys

Al–8Si-0.5 Mg, Al–8Si–2Cu, and Al–8Si–2Cu-0.5 Mg alloys have been designed in this study, aiming to reveal the influence of Mg and/or Cu additions on microstructures and mechanical properties of Al–Si alloys. Transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and the Kampman-Wagner Numerical (KWN) model have been used to investigate age-hardening behaviors as well as their relation to mechanical properties. Microstructure analysis suggest that β'', θ′ and QP precipitates have formed in peak-aged Al–8Si-0.5 Mg, Al–8Si–2Cu and Al–8Si–2Cu-0.5 Mg alloys, respectively. Notably, the Al–8Si–2Cu-0.5 Mg alloy exhibits faster precipitation kinetics, larger age-hardening response and remarkable thermal stability compared to the other two alloys. Theoretical calculations indicate that the nucleation of QP precipitates is easier than β'' and θ′ precipitates, but the slower diffusivity of Cu limits the growth rate of QP precipitates during the growth stage. Furthermore, the contribution of β'', θ′ and QP precipitates to yield strength of peak-aged Al–Si alloys has been quantified, which shows a significant variation. β'' precipitates in the Al–8Si-0.5 Mg alloy exhibit the highest strengthening effect (∼186.4 MPa), followed by QP precipitates in Al–8Si–2Cu-0.5 Mg (∼160.2 MPa) and θ′ precipitates in the Al–8Si–2Cu alloy (∼13.4 MPa). This work provides valuable insights into the influence of Mg and/or Cu additions on the aging response and mechanical properties of Al–Si alloys, offering a reference for further enhancing the performance of Al–Si alloys.

Anomalously low vacancy formation energies and migration barriers at Cu/AlN interfaces from ab initio calculations

It is well known that interfaces in nanomaterials can act as ultra-fast short-circuit diffusion paths, as originating from local structural, chemical and/or electronic modifications at the interface. For example, the interface diffusivity of Cu in Cu/AlN nanomultilayers can be up to two orders of magnitude higher as compared to the bulk, which may promote interfacial premelting of Cu. Extensive ab initio calculations of vacancy formation and migration energies in Cu/AlN nanomultilayers were performed to arrive at the fundamental understanding of such anomalously fast interface diffusion phenomena. It was found that both the metallic Al-terminated interface and the mixed-bonded N-terminated interface promote high atomic interface mobilities by lowering the vacancy formation and vacancy migration energies in the interfacial Cu planes. Moreover, the out-of-plane vacancy migration energies highlight a strong tendency of vacancy segregation toward both interfaces.

Effect of the Post‐Annealing Temperature on the Interfacial Reaction Between a High TC Superconductor and Topological Insulator

AbstractThis work reports the formation of a heterojunction composed of Tl2Ba2CaCu2O8 (Tl‐2212) and Bi2Se3 as the high critical temperature superconductor and topological insulator, respectively. The Bi2Se3 film is deposited on the Tl‐2212 by a chemical mechanical polishing process. Due to the rough surface of Tl‐2212, the treated Tl‐2212 is then subjected to post‐annealing at various temperatures. This temperature does not affect the formation of the interfacial layer at the heterojunction; however, an improved layered crystal structure of the Bi2Se3 film is observed at 500 °C. The in‐depth profile of the relative atomic concentration indicates the diffusion of Cu and Tl into the Bi2Se3 film with the Ba diffusion being closer to the interfacial layer. At 500 °C, Cu atoms are more actively diffused into the Bi2Se3 film, thus blocking Tl diffusion, and improving the layered crystal structure of the film. The density functional theory calculations reveal that the lowest formation energy of the Cu vacancy is when Bi2Se3 is in contact with Tl‐2212, which results in the diffusion of Cu atoms from Tl‐2212, thus transforming the interstitial Cu atoms into the film. These atoms have an n‐type doping effect and prefer intercalating at a vdW gap deep inside the layered Bi2Se3.

Influence behavior and mechanism of crystal orientation of Cu6Sn5 coating on interfacial intermetallic compounds growth in Sn-0.7Cu/Cu solder joint

Herein, the Cu6Sn5 coatings with principal crystal orientations were prepared on the Cu substrate using magnetron sputtering to inhibit the growth of interfacial intermetallic compounds (IMCs) in Sn-0.7Cu/Cu solder joint. The effect of sputtering parameter on the principal crystal orientation of Cu6Sn5 coating was researched firstly, followed by the investigation on the influence of Cu6Sn5 coating principal orientation on the interfacial IMCs growth kinetics. The influence mechanisms were studied using molecular dynamics simulations and first-principles calculations. The results revealed that the increasing sputtering power from 40 W to 60 W and 80 W can not only improve the bonding property between the prepared Cu6Sn5 coating and Cu substrate, but also promote the transformation of the coating principal orientation from (132) to (132)/(22-1) and (132)/(22-1)/(42-2). Moreover, the three prepared Cu6Sn5 coatings can inhibit IMC growth at SC07/Cu solder joint, and the Cu6Sn5 coatings with (132)/(22-1) and (132)/(22-1)/(42-2) principal orientations exhibit more significant inhibitory effects on IMC growth than that with (132) principal orientation. It can be proved in this work that the growth of interfacial IMCs in Sn-0.7Cu/Cu solder joint at aging stage is mainly caused by the diffusion of Cu from Cu substrate toward Cu6Sn5 phase. The difference in the growth behavior of IMCs can be attributed to the fact that when the Cu atoms diffuse across Cu6Sn5 (22-1) and Cu6Sn5 (42-2), the bonding strength between the Cu atom at the saddle point and its surrounding atoms is significantly larger than when diffusing across Cu6Sn5 (132), leading to the smaller diffusion coefficients and a slower interfacial IMCs growth rate.

Work hardening of quaternary powder metallurgy Ti alloys

The concurrent addition of Al as α stabiliser and Nb and Cu or Mn as β stabilisers was used to design new powder metallurgy quaternary Ti alloys and investigate their manufacturability and consequent performance. It is found that the powder blend's compressibility decreases with the total amount of alloying elements due to the characteristics of the powders used. Consequently, the sintered density of the quaternary Ti alloys decreases and slightly higher values are achieved if Mn instead of Cu is used, despite the higher diffusivity of Cu at the sintering temperature. The quaternary Ti alloys are characterised by a lamellar microstructure comprising α grain boundaries and α+β lamellae where the amount and type of alloying elements determine the coarseness of the microstructural features. This results in stronger and harder but less ductile quaternary Ti alloys for higher alloying elements contents and for stronger β stabilisers, although of their overall elastoplastic behaviour. Because of their lamellar microstructure, the quaternary Ti alloys show similar deformation behaviour but the actual work hardening rate is governed by the fineness of the microstructure.

The growth behavior and kinetics of intermetallic compounds in Cu–Al interface at 600°C–800 °C

Due to the low production cost and light weight, copper-clad aluminum conductors show great potential value in the field of power transmission, while the phase structure and organizational changes at the Cu–Al interface in high-temperature environments have a great impact on the electrical and mechanical properties. In this paper, Cu–Al diffusion couples are prepared to study the diffusion process, microstructure, and growth kinetics of intermetallic compounds (IMCs) in Cu–Al interface during heating from 600 °C to 800 °C, and the mechanical and electrical properties of Cu–Al diffusion couples are discussed. The results show that after heat treatment, IMC layers are formed at the Cu–Al interface and the Al-side is composed of CuAl and CuAl2, in which the CuAl phase transforms from long to thick dendrites with the increase of temperature, and finally grows into a “popcorn” form. The IMCs at the Cu–Al interface from the Cu side to the Al side are in the order of Cu3Al layer, Cu9Al4 layer, Cu3Al2 layer and CuAl layer, among which the Cu3Al2 layer is the thickest (168.42 μm at 700 °C), while the Cu3Al layer is the thinnest (37.32 μm at 700 °C). The kinetic calculations show that the diffusion layer grows up rapidly, which is caused by the generation of liquid-phase during the heating process, leading to the acceleration of the diffusion of Cu and Al. The kinetic factor of the Cu3Al2 layer is the largest (n = 0.69), causing the fastest growth rate of the Cu3Al2 layer, while the Cu3Al layer shows the largest activation energy for diffusion and the smallest diffusion rate (Q = 9.48 kJ/mol, D0 = 2.06 × 10−1 m2/s), therefore its growth rate is the slowest. Based on the thermodynamic calculations and the Cu–Al phase diagram, a growth mechanism of the Cu–Al interface is proposed, the formation sequence of IMCs at the Cu–Al interface is Cu9Al4, CuAl, Cu3Al2 and Cu3Al. The formation of IMCs layer at the Cu–Al interface leads to a significant increase in the hardness of Cu–Al samples (the hardness of the Cu3Al2 is 10 times higher than that of Cu) and an obvious decrease in electrical conductivity (the electrical resistivity of Cu–Al is 5 orders of magnitude higher than that of Cu), affecting its application in the electrical industry.

Laser butt welding of AA7075 aluminium alloy and Ti6Al4V titanium alloy using a Cu interlayer

Laser welding of AA7075 and Ti6Al4V, two very different aerospace alloys, was performed with a copper (Cu) interlayer to avoid the brittle Ti–Al intermetallics. The joint was formed owing to the diffusion of Cu into the AA7075 alloy and limited diffusion in Ti6Al4V alloy, followed by eutectic formation at the AA7075/Cu interface. Microstructural and energy dispersive spectroscopy (EDS) analyses of the joint area revealed the presence of eutectic phases at grain boundaries inside the AA7075 fusion zone (FZ). An interfacial Cu3Ti2 phase formed at the solid-state Ti6Al4V/Cu interface. A robust and sound joint was achieved through the effective utilisation of Cu as an interlayer.

Effect of bonding temperature on microstructure and properties of TLP joined Q355 steel with Cu interlayer

Abstract Q355 steel with Cu interlayer was bonded by transient liquid phase diffusion bonding (TLP-DB) at different bonding temperatures, and good bonding joints were obtained. The joints were characterized by optical microscopy, scanning electron microscopy and mechanical properties. The results show that there is a bending phenomenon caused by the difference of element diffusion at the bonding interface at the bonding temperature of 1050 °C. With the increase of the bonding temperature, the diffusion of Cu element plays a role in refining the grain, but with the increase of the bonding temperature, it will also lead to the overgrowth of the grain; At the bonding temperature of 1050 °C, there are obvious mutations in the diffusion of Cu and Fe elements, but the increase of the bonding temperature has a good effect on the interdiffusion of the elements. The mechanical properties test showed that with the increase of the bonding temperature, the hardness, shear strength, and impact toughness at the center of the joint increased first and then decreased, and all reached the maximum at 1100 °C. The electrochemical performance test showed that with the increase of temperature, the corrosion resistance of the joint also increased first and then decreased.

The effects of Ni/Cr on diffusion behavior of Cu in 304 stainless steel

The diffusion of Cu in 304 stainless steel controls the formation of Cu precipitation in the bulk of 304 stainless steel. It is influenced by the atoms such as Ni and Cr. The linear synchronous transit/quadratic synchronous transit method was employed to study the effects of alloying elements on Cu diffusion in 304, and the interactions and diffusion of Cu in fcc Fe with Cr or Ni. It is found that Cr slightly repels from vacancy, while Ni and Cu atoms attract the vacancy. The most stable configuration of the solute atom-vacancy is the Ni-vacancy. The migration barrier of Cu is larger in the vicinity of Ni atom, result from stronger Ni-vacancy binding energy. The larger diffusion barrier indicated that the rate of Cu atoms diffusion in 304 is significantly reduced by Ni atoms, while the effect of Cr atoms on diffusion of Cu in 304 is neglectable.

The preparation of polysilicon films on highly boron doped silicon substrates and their effects on Cu out-diffusion

The impurity gettering efficiency of the polysilicon film significantly hinders the out diffusion of Cu in the heavily boron-doped mono-silicon substrate. Moreover, as the thickness and layer count of the polysilicon film increase, its gettering effectiveness is further enhanced.