Controllable Crystallographic Texture in Copper Foils Exhibiting

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Controllable Crystallographic Texture in Copper Foils Exhibiting Enhanced Mechanical and Electrical Properties by Pulse Reverse Electrodeposition Pavithra Leela Chokkakula, Sarada V Bulusu, Koteswararao v Rajulapati, Ramakrishna Mantripragada, Ravi Chandra Gundakaram, Tata N. Rao, and Govindan Sundararajan Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.5b00748 • Publication Date (Web): 10 Aug 2015 Downloaded from http://pubs.acs.org on August 13, 2015

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Crystal Growth & Design

Controllable Crystallographic Texture in Copper Foils Exhibiting Enhanced Mechanical and Electrical Properties by Pulse Reverse Electrodeposition AUTHOR NAMES Chokkakula L. P. Pavithraa, b, BulusuV.Saradaa#, Koteswararao V. Rajulapatib, M. Ramakrishna a, Ravi C. Gundakarama, Tata N. Raoa, G. Sundararajana AUTHOR ADDRESS a

International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur (P.O), Hyderabad-500005, INDIA

#

Corresponding Author:

Bulusu V. Sarada International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur (PO), Hyderabad-500005, INDIA E-mail:[email protected],Ph: +91-40-24452448; Fax: +91-40-24442699

ACS Paragon Plus Environment

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b

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School of Engineering Sciences and Technology (SEST), University of Hyderabad (UoH), Gachibowli, Hyderabad-500046,INDIA

KEYWORDS Texture; Pulse reverse electrodeposition; Mechanical properties, Electron Backscatter diffraction; Grain boundaries; Nanoindentation

ABSTRACT

The texture evolution in copper foils prepared by a rapid pulse reverse electrodeposition (PRED) technique using an ‘additive-free’ electrolyte and the subsequent correlation with the mechanical and electrical properties is investigated in the present study. Control over (111), (100) and (101) crystallographic textures in copper foils has been achieved by optimization of the pulse parameters and current density. Hardness as high as 2.0-2.7 GPa, while maintaining the electrical conductivity in the same range as that of bulk copper was exhibited by these foils. The complete study of controlling the (111), (100) and (101) textures, CSL Σ3 coherent twin boundaries, grain refinement and their effect on the mechanical and electrical properties is performed in detail by characterizing the foils with electron backscatter diffraction (EBSD), X-ray diffraction (XRD), nanoindentation and electrical resistivity measurements. PRED technique with short and high energy pulses enabled the (111) texture while increasing the forward off-time with optimized current density resulted in the formation of (100) and (101) textures. The reverse/anodic pulse applied after every forward pulse aided the minimization of residual stresses with no additives in the electrolyte, stability of texture in the foils, grain refinement and formation of growth-twins. Among the three highly textured copper foils, those with dominant (111) texture exhibited a


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lower electrical resistivity of ~1.65×10-6 Ω-cm and better mechanical strength compared to those with (100) and (101) textures.

1. Introduction: Advancement of materials technology and development in the electronic industry has led to the miniaturization of electronic products including interconnects etc. It also demands the usage of environment-friendly materials with high performance, exhibiting superior mechanical and electrical properties

1-3

. Copper is proven to be a promising metal compared to conventionally

used aluminum in terms of mechanical, electrical, thermal properties and electromigration resistance 4. In addition, due to the lower resistivity, resistive-capacitive (RC) delays in interconnects are much lesser in copper compared to aluminum4, 5. However, strength of this material becomes a major issue during the miniaturization of electronic circuits 6. Efforts have been made to strengthen copper by cold rolling, alloying, reinforcement of nanoparticles etc. 7-11. Yet these methods have turned out to be obligatory while sustaining electrical conductivity. Therefore, it is necessary to maintain the electrical properties of copper during strengthening processes. It is well known that the electrical properties are mainly influenced by grain size, type of grain boundaries (GBs) and the texture in any metal 3. Grain refinement plays a major role in enhancing the mechanical properties

12-14

, while preferred crystallographic orientation (texture)

influences the resistance to electromigration15, oxidation, thermal stresses and voids etc.

16, 17

.

Moreover, special grain boundaries including low energy high angle grain boundaries also known as coherent twin boundaries (CSL Σ3 boundaries)

18

act as key strengthening agents and

help in attaining hardness and electrical conductivity simultaneously by hindering the dislocation


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motion as well as reducing the scattering of electrons at the twin boundaries

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3, 19

. The nanoscale

twin boundaries can be introduced into copper by plastic deformation, electrodepositionand sputter deposition etc. By introducing these twin boundaries, a high tensile strength of about ~1GPa has been reported 20-25. Therefore, it is necessary to control the microstructural features in pure copper for achieving the required properties. Electrodeposition has gathered widespread attention for the synthesis of copper foils for their use in electronic applications, due to its industrial feasibility and cost effectiveness

26-29

. Numerous

research efforts have been devoted towards the preparation of copper foils with high hardness and electrical conductivity. As part of these studies, highly textured and twinned copper foils with enhanced mechanical and electrical properties were synthesized by electrodepositionusing DC and PED techniques

23, 30-37

(various reports on usage of DC and PED to deposit copper in

various forms with varied microstructure and texture are summarized in supporting information). However, literature suggests the use of organic additives in the electrolyte in order to achieve grain refinement, formation of twin boundaries/to control the texture and surface modifications 30, 33, 38-42

. Also, use of additives has been shown to manipulate the texture and the mechanical

properties

33

. However, stresses introduced by additives result in reducing the deposit ductility

and increase the scattering of electrons leading to decrease in the electrical conductivity. Further, the impurities cause grain growth resulting in deteriorated mechanical properties posing environmental concerns

31

43

, while also

. Therefore achieving the required properties can be

conceivable by pulse reverse electrodeposition (PRED), where, the cathodic and reverse/anodic pulse parameters influence the texture, grain size, and type of grain boundaries facilitates several advantages

46-48

44, 45

.PRED

where it (1) reduces the usage of additives (2) refines grain

size (3) improves properties due to lower residual stress (4) minimizes impurities in the deposit


4

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and (5) reduces adsorption of hydrogen species and results in lesser surface roughness over the foils prepared by DC and PED44,

45

. Therefore, PRED can be a viable option to control the

texture, refine grain size and type of grain boundaries, which is the main focus of the present study. However, very limited work has been done on the use of PRED for controlling crystallographic orientations in copper suggesting that no correlation has been made so far on the processing parameters with the properties of as deposited copper. To the best of our knowledge; no reports have appeared on PRED technique for controlling the three textures simultaneously in copper with high hardness while maintaining electrical conductivity by variation of current and pulse parameters and avoiding the additives in the electrolyte. Lu et al., and Chen et al., reported about 10 times increase in the strength compared to that of bulk copper, while an electrical resistivity of 1.75±0.02×10-6Ω-cm was achieved by pulse electrodeposition (PED) with (101) texture

1, 49

. Preparation of highly (111) textured copper foils with high hardness and electrical

conductivity by PRED has been reported by us previously

31

. In the present paper, for the first

time we report a novel approach involving a rapid PRED technique in order to manipulate the (111), (100) and (101) textures, CSLΣ3 coherent twin boundaries and the grain size in order to obtain enhanced hardness and required electrical properties in copper using an additive-free electrolyte. Apart from the scientific interest, highly textured foils with high hardness play an important role in electronic applications where dimensions of interconnects are reducing rapidly. 2. Experimental details: Copper foils were synthesized by PRED technique in an ‘additive- free’ electrolyte using DPR series Pulse Power Supply (Dynatronix, USA). The electrolytic bath contained 250gm/L copper sulphate in de-ionized water with pH maintained between 1.0- 0.5 by adding sulphuric acid to the electrolyte. The temperature was maintained between 15-20°C during the deposition.


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Titanium plate and electrolytic copper (99.9 % purity) were used as cathode and anode, respectively.Titanium is used as cathode because it is an inert metal, highly resistant to corrosion in acidic and alkaline media, in addition to high deposition temperature stability. Further it also facilitates in peeling of the deposited foil easily after the deposition compared to that of steel substrate. The cathode was polished as scratch-free to avoid the replication of the scratches arising from the substrate which may influence the texture formation in the electrodeposited copper foils. This step was followed by cleaning in acetone, ultrasonication and dipping in boiling water, prior to deposition in order to remove the impurities and residual stresses on the surface that might have been induced during mechanical polishing. Electrodeposition was performed in constant current density mode. Pulse parameters and current densities for the forward pulse were varied while the reverse pulse parameters were kept constant. Electrolyte composition, pH and temperature of the electrolytic bath during the deposition were maintained constant for all depositions. PRED technique facilitated rapid deposition and a coating of about 40-70 µm thick was feasible in about 1hr of deposition. The as-deposited foils were peeled off from the substrate to make them free standing prior to characterization. The surface of the copper foils was electropolished to determine the texture by Electron backscatter diffraction (EBSD). The step size during the EBSD scanning was about 40nm. The diffraction patterns from EBSD data were analyzed using Orientation Imaging Microscopy (OIM™ V6.1) analysis software from EDAX-TSL to determine the crystal orientations in each grain, grain boundary misorientations such as low angle grain boundaries (LAGBs), high angle grain boundaries (HAGBs) and other grain boundary statistics. Confirmation of the texture in large areas of the copper foils was also done conventionally by Xray diffraction (BRUKER D8 ADVANCE) with Cu Kα radiation (λ=1.5406Å). Hardness and


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elastic modulus of copper foils were measured using an MTS XP Nanoindenter; the indentations were performed in the continuous stiffness measurement (CSM) mode using a Berkovich indenter at a constant maximum indentation depth of 2µm. The electrical resistivity measurements were carried out by four point probe technique and electrical conductivity was measured by eddy current electrical conductivity gauge (Sigma test 2.069, FOERSTER, USA).

3. Results and discussion: 3.1. Texture validation by EBSD and XRD: The crystallographic orientations of the highly (111), (101) and (100) textured foils in the present study have been obtained by adjusting the pulse parameters as well as the current density. The range of pulse parameters and current densities used during the deposition process are given in Table 1 below. Table 1 Pulse parameters and current densities used in PRED for the preparation of different highly textured copper foils

(111)

Pulse Duration (ms) TF on TF off TR on 5-15 20-50 2

(100)

10-20

100-200

2

2

0.25-0.5

0.1

(101)

15-20

1000-2000

2

2

0.4-1

0.1

Texture

TR off 2

Forward current density (amp/cm2) 0.5

Reverse current density (amp/cm2) 0.1

Fig. 1 shows the representative crystallographic orientation maps/OIM mapsand corresponding color coded inverse pole figure (IPF)taken from several scans for the copper foils.Pole figures with color scale indicate the crystallographic orientations of each grain and their pole densities, respectively from the pole figures for a selected area of the foils at the microscopic level. In the


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present study, the orientation maps were processed from the normal direction (ND) of the sample, indicated as crystallographic plane normal, which is parallel to the normal direction. It can be seen from Fig. 1(b) that the pole in pole figure of the sample with (100) texture is shifted by 8° with respect to (-1, 3, 23). A similar shift has been reported where, authors have further mentioned that a shift of 12° is acceptable 50. From the EBSD orientation maps, it is evident that the copper foils are highly textured with a pole density of 12.59, 10.84 and 7.31 calculated from the orientation distribution function (ODF) indicating the preferred orientation for ơ ND, ơND andơ ND textured foils, respectively. EBSD data shown in this study have been cleaned up using OIMTM data analysis software. After grain confidence index (CI) standardization and neighbor CI correlation, a partition was created for each scan consisting of only those data points with CI ≥ 0.1. Thus it was ensured that the data used for the analysis is of high quality. In order to confirm the texture of the copper foils at the macroscopic level, XRD patterns were obtained and the texture coefficients were calculated to confirm the preferred orientations. From X-ray diffractograms (Fig. 2), it is clear that the foils are preferentially oriented along (111), (220) and (200), respectively. The reflections from the crystallographic planes of (111), (220) and (200) from XRD correspond to (111), (101) and (100) from EBSD51.The texture coefficient (Tc) 52 was calculated from the XRD patterns by using equation 1. ( ) ⁄ ( )

() = ⁄ ∑

( ) ⁄ ( )

(1)

Where Tcis the texture coefficient of (hkl) plane, I (hkl) and I0 (hkl) are the measured and relative intensities of the corresponding planes, respectively and ‘n’ is the number of reflections. It has been reported that Tc>1 indicates a preferred crystallographic orientation 53 and Tc~1 indicates a


8

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random orientation

52

. From the XRD patterns (Fig. 2), for the (111), (100) and (101) textured

copper foils, the texture coefficients (Tc) were calculated as 2.39, 3.38 and 3.78, respectively. These larger values of Tc show a strong texture in these foils (Fig. 3). The texture coefficients calculated for various crystallographic directions in all these foils are shown in Fig. 3(a). Fig. 3(b) shows the coefficients of (111), (100) and (101) foils. According to the texture formation studies in FCC metals, at initial stages of the deposition, the crystallographic orientation is dominated by substrate texture at the interface due to its large interfacial energy in conventional DC and PED processes

54

. During the

electrodeposition process, surface energy, strain energy or a combination of both and the energy arising out of various interfaces may control the texture formation55. In addition, texture of the films is also influenced by several aspects such as pH of the electrolyte, applied current densities, pulse parameters, additives, impurities, thickness of deposit, stress/strain formation in the deposit56 and their relaxation etc. In most of the cases the crystallographic orientation changes from (111) to either(100) or to (101), depending on the changes that occur during the deposition process

57, 58

. Apart from these, the stability of the surface plane of the metal also has a

significant role

59, 60

. However, the stability of the individual surface plane of the FCC metals

during the texture formation follows the order as (111)> (100)> (101)

61

as minimization of

surface energies in these metals follow the order of γ(101)>γ (100)>γ (111) 62. Therefore initially copper growth is generally is expected to be inclined towards the (111) direction irrespective of the deposition technique used. It is mainly driven by several reasons like low surface energy of the (111) plane which in turn depends on the coordination number compared to the other (100) and (101) planes

57, 64-66

63

and atomic density when

. During the deposition, development of

(111) texture is also favored at large current densities applied at low temperatures due to


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minimization of the surface/interfacial energy during growth process. Our previous study has also revealed that (111) texture is favorable at high current densities with short forward pulses and short reverse pulses

31

. In addition, low deposition temperatures are suggested in order to

minimize the surface and interfacial energies, for twin boundary formation, good surface properties and to reduce the usage of additives 67. Although (100) and (101) textures are known to be dominated by the strain energies

68

due to the anisotropy in elastic constants of copper 51,

(100) and (101) grains nucleate at (111) boundaries at initial stages of electrodeposition69 and gradually change completely to either (101) or (100) depending on the stresses, which usually occurs at higher current densities and low temperatures during conventional deposition process51. Specially for thicker and free standing films, lowest strain energy density in the elastic regime favors the (100) direction and is considered as free growth mode formed due to H2 co-deposition 70, 71

. However, during deposition, (100) growth is favored slightly at larger off-times

72

and

(101) is known to be favored at very large off-times 1. This happens by consuming the (111) grains resulting from the stress driven recrystallization during PED due to lower strain energies favored at high current densities 73. High current densities result in high initial stresses, causing defects within the grains, which are associated to the strains leading to the formation of texture. Increase in (101) with the extent of self-annealing and at very low deposition rates was reported to be because of higher off-times

33

. Further due to lesser atomic density in the plane and high

broken bonds, (101) is known to be dissolved more easily compared to (111) and (100) textures. Therefore, (101) growth appears to be highly favorable during PED technique with longer offtimes 74.

Accordingly, moderate changes in the pulse parameters have been made in our PREDtechnique to deposit copper foils with various orientations namely (111), (100) and (101) textures during


10

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deposition (Table 1). In the present study, very short pulses and higher current densities favored (111) texture in the copper foils. As theforward-on and forward-off times increased, at lower current densities, the texture gradually shifted from (111) to (100). Dominant (101) texture was observed for the pulse parameters mentioned in the table. With further increase in the off-time as well as current densities, predominant (101) texture was observed. In PRED several processes occur at the cathode 31 as well as at the anode during each cycle 75. During the cathodic pulse or forward pulse, copper ions get reduced at the cathode and deposit as copper metal, while forward off-time aids in relieving of stresses and rearrangement of crystals, leading to texture development

76, 77

. In addition, uniform diffusion of Cu ions occurs from the bulk of the

electrolyte towards the cathode, improving the deposition process 78. Short anodic/reverse pulse, during which current isapplied in the negative direction, removes the deposited copper partially, resulting in the availability of fresh active nucleation sites during each cycle. This will lead to grain refinement and equi-axed grain formation throughout the thickness (~100microns). Anodic pulse also aids in the formation of twin boundaries due to the strains formed77, 79. In addition to the dissolution of loosely bonded atoms, removal of entrapped hydrogen and impurities, etc. also happens during the anodic pulse. Hence, with the applied cathodic and anodic pulses with optimum on and off-times, a number of microstructural changes take place that could influence the texture. However, the stabilization of texture is taken care by the applied anodic pulse immediately after forward pulse in every cycle by relieving all the induced stresses, which alter the texture during room temperature annealing after the conventional deposition. In the present case, for (111) textured foils, high forward current densities with shorter forward and reverse pulses with low reverse current densities were applied. High current densities are employed in order to increase the nucleation sites which aid in grain refinement and also to have


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low impurity levels

67

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. For achieving the (100) and (101) textured foils, slightly large forward

off-times were employed in comparison to (111) with same anodic pulse. Pulse parameters employed in the present work play the major role in controlling the textures and limit the use of additives in the electrolyte since additives stay as impurities in the deposited foils and disturb the texture during room temperature annealing. The mechanism for formation of texture during each cycle during the process is not understood as of today. However in the current study, formation of highly stable (111) texture is probably due to the rapid pulses which are leading to the preferred orientation 61, whereas, formation of (100) texture is possibly by self-annealing during the forward off-time due to the high induced stresses leading to the high strain energies at high current densities

76, 80

. While, very long forward off durations might allow the formation and

growth of (101) because (101) growth occurs at grain boundaries of (111). In addition, the PRED foils have also exhibited high compactness, high surface smoothness and less porosity 44, 67. Here the deposition rates are quite fast compared to PED due to the high current densities with application of reverse pulse. In case of PED, longer pulse off-times are required for the rearrangement of the deposited grains for minimization of energy, removal of the residual stresses and adsorbed hydrogen along with the impurities from the surface. In the case of PRED, the applied reverse pulse also takes care of the processes happening during off-time of PED, wherein it removes impurities quickly and also acts as an internal stress reliever after each cycle and porosity reducer by introducing the new nucleation sites. This leads to grain refinement

81

and twin formation due to the stress/ strain development during the deposition while reducing the deposition times rapidly. In addition, anodic pulse increasesthe stability of texture with equi-axed grain growth throughout the thickness of the foils,whichcan be observed from focused ion beam (FIB) milled image (Fig.S1) with the usage of moderate to high current densities, which is not


12

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the case in DC and PED. The EBSD orientation maps with IPF figures in the supporting information (Fig. S2 and S3) is an observation that confirms the influence of reverse pulse in controlling the texture formation, stability of texture andequi-axed grain growth.

In addition to texture evolution, the copper foils have been further characterized to study the grain size, type of grain boundaries etc. It is known that grain size and grain boundaries play a significant role in controlling the mechanical and electrical properties besides texture 1. Analysis of the copper foils by EBSD yields the information regarding grain misorientations, grain boundary distributions including sub-grain boundaries, LAGBs (5-15°), HAGBs (>15°) and special grain boundaries

82

. The special grain boundaries including low-energy coincident site

lattice boundaries (CSL) and coherent twin boundaries in all the textured foils are distinguished by different colored plots. In addition to all these, the grain size distribution and grain boundary fractions are also estimated from EBSD. 3.2 Grain size and grain boundaries distribution: Fig. 4 shows the grain size distribution in copper foils with (a) (111), (b) (100) and (c) (101), respectively. The corresponding statistics and grain size distribution histograms are also shown. It is seen that the foil with (111) texture had an average grain size of 0.57±0.2 µm with majority of the grains in the submicron size. The (100) and (101) foils had an average grain size of 0.72±0.3µm and 0.97±0.5 µm, respectively.

From the EBSD data, the fraction of LAGBs and HAGBs is calculated. The low angle boundaries are 6.2%, 2.8% and 2.9% among the total number of grain boundaries, respectively (Fig. 5) whereas HAGBs are 66.6%, 78.8% and 85.5% for foils with (111), (100) and (101) textures, respectively. HAGBs were indicated in blue color and Σ3 boundaries were indicated in


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red color (Fig. 5). It can be observed that a large fraction of HAGBs are with a misorientation angle of ~ 60°. LAGBs generally have very less energy due to the minimum misfit at GBs between the adjacent grains which leads to increase in the hardness 76. These LAGBs were found in larger fraction in foils with (111) texture as compared to other textured foils. HAGBs have high energy with large misfit at the GBs that may have no significant influence on the mechanical and electrical properties. According to Randle

83

, special grain boundaries called

CSL Σ3 coherent twin boundaries, categorized under the HAGBs, lead to increase in the mechanical strength as well as maintaining theelectrical conductivity. These are essential for improving the properties due to the mirror-like arrangement of atoms at the GBs with the misorientation of 60° . Consequently, in order to measure the fraction of coherent twin boundaries (CSL Σ3) among the HAGBs, the analysis was carried out. From the grain-boundary statistics, the most important feature of all the textured copper foils is that among the total length of grain boundaries, the large fraction of grain boundaries is accounted for CSL Σ3 (60° to ) boundaries (Fig. 5). It was observed that highly (111) textured copper has 40.4%, (100) has 30.6% and (101) has 47.8% Σ3 boundaries among total boundaries. However, among the fraction of HAGBs (111) has 60.6%, (100) has 38.8% and (101) has 55.9% Σ3 boundaries. From the analysis, though (100) and (101) textures have large fraction of HAGBs, fraction of Σ3 boundaries is higher in (111) and (101) compared to that of (100). This is because, Σ3 boundaries are more common in (101) texture and boundaries with Σ < 27 and LAGBs are more common in (100) texture compared to (111) texture

84, 85

. This could be the probable reason that (100) has

less fraction of LAGBs and slightly large fraction of Σ < 27 boundaries such as Σ9 etc., in addition to the Σ3 boundaries (Fig 5). These boundaries lead to a decrease in the fraction of Σ3boundaries among HAGBs(30.6% of total length of GBs and 38.8% among HAGBs). Here


14

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the length of HAGBs accounts to 78.8% of total length of GBs.Also, Σ boundaries < 27 are resistant to intergranular corrosion. As a result, in the (111) and (101) textured foils, the fraction of CSL Σ3 boundaries were 40.4% and 47.8% among the total length of GBs and 60.6% and 55.9% among HAGBs,respectively. This is in agreement with literature that (100) and (101) favors the Σ boundaries other than Σ3 boundaries compared to (111) 85. Though all the textured foils have significant fraction of CSL Σ3 boundaries, coherent twin boundaries contribute better for maintaining theelectrical conductivity. The boundaries with a deviation of only a few degrees from the ideal Σ3 boundary condition (60°) can be considered as coherent twin boundaries which are essential for enhancing the electrical conductivity and ductility along with other mechanical properties

18

. According to the Brandon criterion

86, 87

, for CSL Σ3 boundaries

including coherent and incoherent twin boundaries, the allowable deviation can be up to 8°. Also Randle 18 has reported that the deviation must be in between 1°- 3° for coherent twin boundaries, with low energy compared to conventional CSL and HAGBs. Coherent twin boundaries are the only boundaries which can reduce the scattering of electrons at GBs leading to enhancement in the electrical conductivity which is not the case with incoherent twin boundaries 88. In the present study, it is found that in (111), (100) and (101) textured copper foils, majority of these CSL Σ3 boundaries are very close to the ideal Σ3 condition from the GB statistics (Fig. 6).

An angular deviation of 1° from the reference condition is considered to calculate the percentage of coherent twin boundaries (CSL Σ3) which is found to be ~ 80% (Fig. 6). The twins formed in the present deposition process are growth-in twins and the formation of these twins reduces the total interfacial energy of the system. As mentioned earlier, these twins are formed due to the induced stresses and strains during the PRED. In all the textured foils, the presence of twin boundaries is confirmed after a detailed analysis of EBSD data. Mechanical and electrical


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properties were measured for the copper foils prepared by PRED with good control over the texture.

3.3 Mechanical and electrical properties of the highly textured copper foils:

Nanoindentation has been used to evaluate the mechanical properties of these foils. Hardness and modulus are measured performing indentation at different locations in the foils of 1 cm2 area, which shows overlapping curves indicating high structural homogeneity of the foils (Fig. 7a). Fig. 7b shows the representative load-displacement curves indicating the variation of hardness and modulus with variation in the copper foils with varied textures. Copper foils with dominant (111) texture have shown excellent hardness in the range of ~2.2-2.7 GPa and elastic modulus in the range of ~110-130 GPa. The hardness value of these copper foils is superior to that of bulk copper and modulus is comparable to that of bulk copper. Since there is a slight difference in the average grain size obtained for various foils in this study, Fig.7c was made by incorporating both hardness and grain size values of various textured foils. It is clear from Fig.7b that the hardness is high for the (111) textured foils(2.45±0.15GPa) while slightly lower values are observed for (101) (1.85±0.15GPa) and (100) (2.1±0.20 GPa). Similarly, (111) textured foils exhibited highest modulus (117 ± 7.5 GPa), in comparison to (101) (102 ± 12.5 GPa) and (100) (90 ± 10 GPa) foils. It has already been shown experimentally that the Young’s modulus for Cu (111) is 193GPa, which is 2.9, times higher than Cu (100) with 69GPa55. Generally for all FCC metals, elastic modulus follows a trend with E (111) >E (101) >E (100)55, 89. A similar trend has been observed for the elastic modulus of the highly textured foils in this study. High energy due to low atomic density and coordination number of (100) and (101) planes leads to slightly lower modulus. In order to correlate the texture dependent mechanical properties, the critical resolved shear stress


16

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(CRSS) values for Cu single crystalhave been taken into consideration for comparison, as CRSS is an indirect measure of hardness

90

. Similar studies have been reported by Chan et al.33 for

nanotwinned copper where hardness of (111) and (110) oriented Cu films have been correlated with the CRSS values. The present study deals with the highly textured copper foils, which are expected to exhibit mechanical properties similar to those of single crystal copper. The trend observed in the hardness values for different crystallographic orientations of the highly textured copper foils is in line with that reported CRSS values 91, 92. Dub et.al 92have reported a CRSS of 4.56 GPa and 3.8 GPa for (111) and (100) planes, respectively for copper single crystal. The ratio (1.2) in the CRSS for (111) and (100) is in agreement with the observed ratio (1.19) of the average hardness value in the present study for these two textures.

Electrical conductivity was found to be 56-66 MS/m for all the foils in this study (Electrical conductivity for bulk copper the value is 58-62 MS/m). In addition, resistivity measurement made using 4-probes have shown that all the copper foils including (111), (100) and (101) exhibited a low electrical resistivity in the range from ~1.65-2.0×10-6 Ω-cm, which is 85-104 % of that of bulk copper. Usually, when the grain size is reduced, the volume fraction of grain boundaries increases, leading to the scattering of electrons at the grain boundaries resulting in reduced electrical conductivity. In contrast to that, the electrical conductivity of the copper foils in the present study has not deteriorated with the grain refinement as well as texture development (Fig.8). This could be attributed to several aspects such as preferred crystallographic orientations (texture), low impurities and the presence of CSL Σ3 coherent twin boundaries, which reduce the scattering leading to enhancement in the electrical conductivity.


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In addition to the mechanical and electrical properties, the structural stability is also important while adapting these copper foils for various electronic applications. In order to evaluate this, the copper foils are stored at room temperature for six months. Subsequently hardness of these foils was measured and it was found that the hardness has decreased by only 5% in comparison to its as-deposited value

31

. This constancy of hardness at room temperature is probably due to the

absence of grain growth

68

. Further, the very slight deviation from the preferred orientation

(texture) to random orientation was observed in the representative orientation map and IPF are shown in Fig. S2 (b-c).An additional feature observed is that density of all the textured foils was found to be 8.92 ± 0.05 g/cm3 i.e., about 99.6% of that of the bulk copper, using Archimedes principle method.

Hence, it has been mainly observed during the present study that in PRED the usage of additive free electrolyte reduces the impurities in the deposited material, resulting in minimal stresses giving stability to mechanical and electrical properties with texture in addition to the minimization of hydrogen embrittlement.Among the copper foils which were deposited using different pulse parameters in order to control the texture, high hardness in (111) is probably due to the high atomic density in (111) resulting in compact structure with low energy

93

. The

enhancement of properties (mechanical, electrical) also results from low residual stresses and large number of coherent twin boundaries, which behave similar to conventional grain boundaries in blocking the dislocation motion while reducing the scattering of electrons. Similarly, in spite of large number of grain boundaries, the electrical conductivity of the foils is high due to LAGBs in (111), about 6.2% among the total number of grain boundaries with low energy and low mobility contributing to lower resistivity of the foils. The highly uniform orientation of the grains in (111) textured foils (texture coefficient) results in the reduction in


18

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scattering of electrons leading to lower values of electrical resistivity

80

. (111) is harder

compared to the other planes because of the difficulty in activating the {111} slip systems 94

. Further, predominant advantage with highly (111) textured copper is that, it improves the

electromigration resistance compared to all other textures

15

. In the present study, among all

textured copper foils, the highly (111) textured foil has prominent properties compared to the rest due to its standalone features. Thus, the enhancement of hardness in (111) is probably due to the grain refinement, texture and presence of CSL Σ3 coherent twin boundaries compared to the other (100) and (101) textured foils. 4. Conclusions: The copper foils with highly (111), (100) and (101) crystallographic textures with the alignment of ƠƠND, ƠƠND, ƠƠND were synthesized using an ‘additive-free’ electrolyte by PRED technique. The crystallographic structure, CSL boundaries, twin-boundaries and mechanical properties can be controlled exclusively by optimizing the pulse parameters and cathodic/anodic current densities. Copper foils have shown a substantial improvement in mechanical properties while maintaining electrical conductivity with an average grain size of 0.57±0.2 µm for (111), 0.72±0.3µm and 0.97±0.5 for (100) and (101) foils, respectively with majority of the grains in the submicron size. The hardness, modulus and electrical resistivity were in the range of ~2 - 2.7 GPa, ~90-130 GPa and ~1.65 - 2.0×10-6Ω-cm, respectively for all the copper foils with dominant (111), (100) and (101) textures. For synthesizing these foils, current densities between 0.4-1.0 amp/cm2 were used to enable the texture formation in addition to the optimized pulse parameters. Increment in forward off (Toff) duration controls the textures where, shorter forward pulses lead to form (111), slightly higher off-times form (100) and at very larger off-times formation of (101) occurs due to the self-annealing. Further, reverse pulse


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resulted in equi-axed grains with high stability in maintaining texture with negligible stresses. Additive-free electrolyte facilitated the minimization of impurities during deposition process. The room temperature stability of the copper foils was tested for their use in electronic applications. The process is scalable for mass production using this rapid, economic and environment-friendly PRED method. The enhancement in the mechanical and maintaining electrical conductivity is probably due to a cumulative effect of smaller grain size, texture and the presence of coherent twin boundaries with absence of impurities in the foils.


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FIGURES Figure 1

Figure 1. (a), (b) and (c) indicate the representative crystallographic orientation maps for copper foils highly oriented towards (111), (100) and (101) textures as indicated by the color codes allocated in the inverse pole figure (crystal direction with respect to the sample normal) and pole figures with pole densities given to the right of the respective image


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Figure 2

Figure 2. X-ray diffractograms of various copper foils deposited byPRED representing strong (a) (111), (b) (200) and (c) (220) textures, respectively

Figure 3

Figure 3. Texture coefficients of (a) each plane and (b) Total Tc of the copper foils with (111), (100) and (101) textures


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Figure 4

Figure 4. Grain size distribution of copper foils with highly (a) (111), (b) (100), (c) (101) textures, respectively Figure 5


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 ACS Paragon Plus Environment

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Figure 5. Representative EBSD maps for HAGBs, Σ 3 boundaries and respective grain boundary misorientation distribution in copper foils highly oriented towards (a) (111), (b) (100) and (c) (101), respectively

Figure 6

Figure 6. Deviation from the CSL boundary in copper foils with (a) (111) (b) (100) and (c) (101) textures

Figure 7


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Figure7. (a) Load-displacement curves for copper foils highly textured towards (111), (100) and (101) (b) hardness and modulus vs. texture (c) grain size, hardness vs. texture Figure 8

Figure 8. Electrical resistivity vs. texture and grain size of foils with highly oriented towards (111), (100) and (101)


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TABLES. Table 1: Pulse parameters and current densities used in PRED for the preparation of different highly textured copper foils

(111)

Pulse duration (ms) TF on TF off TR on 5-15 20-50 2

(100)

10-20

100-200

2

2

0.25-0.5

0.1

(101)

15-20

1000-2000

2

2

0.4-1

0.1

Texture

TR off 2

Forward current density (amp/cm2) 0.5

Reverse current density (amp/cm2) 0.1


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Author Contributions Chokkakula . L. P. Pavithra, Bulusu. V. Sarada: design and study of experiments and research. K.V. Rajulapati.contribulted to the interpretation of mechanical properties, M.Ramakrishna and Ravi C Gundakaram contributed to the EBSD analysis and nanoindentation, Tata.N. Rao and G. Sundarajan contributed to the discussions of the data. All authors contributed equally to the interpretation of the data and provided significant effort to the final manuscript. All authors reviewed the manuscript. ACKNOWLEDGMENTS Authors would like to acknowledge Mr. K. Ramesh Reddy, Centre for materials characterization and testing, ARCI for assisting in characterization with XRD.


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REFERENCES (1)

Lu, L.; Shen, Y.; Chen, X.; Qian, L.; Lu, K., Ultrahigh strength and high electrical

Conductivity in Copper. Science 2004, 304, 422-426. (2)

Lu, L.; Chen, X.; Huang, X.; Lu, K., Revealing the maximum strength in nanotwinned

copper. Science 2009, 323, 607. (3)

Lu, K.; Lu, L.; Suresh, S., Strengthening materials by engineering coherent internal

boundaries at the nanoscale. Science 2009, 324, 349-352. (4)

Lloyd, J. R.; Clement, J. J., Electromigration in copper conductors. Thin Solid Films

1995, 262, 135-141. (5)

Havemann, R. H.; Hutchby, J. A. In High-Performance Interconnects: An Integration

Overview, proceedings of the IEEE, 2001; IEEE: 2001; pp 586-601. (6)

Peercy, P. S., The drive to miniaturization. Nature 2000, 406, 1023-1026.

(7)

Sakai, Y.; Inoue, K.; Asano, T.; Wada, H.; Maeda, H., Development of highstrength,

highconductivity Cu–Ag alloys for highfield pulsed magnet use. Appl. Phys. Lett.1991, 2965. (8)

Hu, Y.; Shenderova, O. A.; Hu, Z.; Padgett, C. W.; Brenner, D. W., Carbon

nanostructures for advanced composites. Rep. Prog. Phys. 2006, 69, 1847-1895. (9)

Chrysanthou, A.; Erbaccio, G., Production of copper-matrix composites by in situ

processing. J. Mater.Sci.1995, 30, 6339-6344. (10) Upadhyaya, A.; G.S.Upadhyaya, Sintering of copper-alumina composites through blending and mechanical alloying powder metallurgy routes.Mater. Des. 1995, 16, 41-45.


29


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 41

(11) Hwang, J.; Yoon, T.; Jin, S. H.; Lee, J.; Kim, T.-S.; Hong, S. H.; Jeon, S., Enhanced mechanical properties of graphene/copper nanocomposites using a molecular-level mixing process. Adv. Mater. 2013,25, 6724–6729. (12) Hall, EO.,The deformation and ageing of mild steel: II characteristics of the Lüders deformation.Proc. Phys. Soc. B 1951, 64, 747. (13) Petch, NJ., The cleavage strength of polycrystals. Int. J. Iron and Stee Res.1653, 174, 25. (14) Hansen, N., Hall–Petch relation and boundary strengthening. Scripta Mater.2004, 51 801–806. (15) Ryu, C.; Loke, A. L. S.; Nogami, T.; Wong, S. S. In Effect of Texture on the Electromigration of CVD Copper, Proceedings of

IEEE International Reliability Physics

Symposium, 1997; 1997; pp 201-205. (16) Baker, S. P.; Kretschmann, A.; Arzt, E., Thermomechanical behavior of different texture components in Cu thin films. Acta Mater.2001, 49, 2145. (17) Toyoda, H.; Kawanoue, T.; Ito, S.; Hasunuma, M.; Kaneko, H., Effects of aluminum texture on electromigration lifetime. AIP Conference Proceedings 1996, 373, 169-184. (18) Randle, V., Twinning-related grain boundary engineering. Acta Mater.2004, 52, 40674081. (19) Zhu, Y.; Liao, X.; Wu, X., Deformation twinning in nanocrystalline materials. Prog. Mater. Sci.2012, 57, 1-62.


30

Page 31 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(20) Wang, K.; Tao, N. R.; Liu, G.; J.Lu; K.Lu, Plastic strain-induced grain refinement at the nanometer scale in copper. Acta Mater.2006, 54, 5281-5291. (21) Ma, E.; Wang, Y. M.; Lu, Q. H.; Sui, M. L.; Lu, L.; Lu, K., Strain hardening and large tensile elongation in ultrahigh-strength nano-twinned copper. Appl. Phys. Lett.2004, 85, 49324934. (22) Lui, G.-T.; Chen, D.; Kuo, J.-C., EBSD characterization of twinned copper using pulsed electrodeposition. J. Phys. D: Appl. Phys.2009, 42, 215410. (23) Zhong, S.; Koch, T.; Wang, M.; Scherer, T.; Walheim, S.; Hahn, H.; Schimmel, T., Nanoscale twinned copper nanowire formation by direct electrodeposition. Small 2009, 5, 22652270. (24) Zhang, X.; Wang, H.; Chen, X. H.; Lu, L.; Lu, K.; Hoagland, R. G.; Misra, A., Highstrength sputter-deposited Cu foils with preferred orientation of nanoscale growth twins. Appl. Phys. Lett.2006, 88, 173116. (25) Shen, Y. F.; Lu, L.; Lu, Q. H.; Jin, Z. H.; Lu, K., Tensile properties of copper with nanoscale twins. Scripta Mater.2005, 52, 989-994. (26) Gurrappa, I.; Binder, L., Electrodeposition of nanostructured coatings and their characterization—a review. Sci. Tech. Adv. Mater.2008, 9, 043001. (27) Ibanez, A.; Fatas, E., Mechanical and structural properties of electrodeposited copper and their relation with the electrodeposition parameters. Surf. Coat. Tech.2005, 191, 7–16.


31


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 41

(28) Zhang, X.; K.N.Tu; Chen, Z.; Y.K.Tan; C.C.Wong; Mhaisalkar, S. G.; X.M.Li; C.H.Tung; Cheng, C. K., Pulse electroplating of copper film: A study of process and microstructure. J. Nanosci. Nanotech.2008, 8, 2568-2574. (29) Balasubramanian, A.; Srikumar, D. S.; Raja, G.; Saravanan, G.; Mohan, S., Effect of pulse parameter on pulsed electrodeposition of copper on stainless steel. Surf. Eng.2009, 25, 389392. (30) West, A. C.; Cheng, C. C.; Baker, B. C., Pulse reverse copper electrodeposition in high aspect ratio trenches and vias. J. Electrochem. Soc.1998, 145, 3070-3074. (31) Sarada, B. V.; Pavithra, C. L. P.; Ramakrishna, M.; Rao, T. N.; Sundararajan, G., Highly (111) textured copper foils with high hardness and high electrical conductivity by pulse reverse electrodeposition. Electrochem. Solid-State Lett. 2010, 13, D40-D42. (32) Cui, B. Z.; Han, K.; Xin, Y.; Waryoba, D. R.; Mbaruku, A. L., Highly textured and twinned Cu films fabricated by pulsed electrodeposition. Acta Mater.2007, 55, 4429-4438. (33) Chan, T.-C.; Chueh, Y.-L.; Liao, C.-N., Manipulating the crystallographic texture of nanotwinned Cu films by electrodeposition. Cryst. Growth Des.2011, 11, 4970-4974. (34) Liu, T.-C.; Liu, C.-M.; Hsiao, H.-Y.; Lu, J.-L.; Huang, Y.-S.; Chen, C., Fabrication and characterization of (111)-oriented and nanotwinned Cu by DCelectrodeposition. Cryst. Growth Des.2012, 12, 5012-5016. (35) Hsiao, H.-Y.; Liu, C.-M.; Lin, H.-w.; Liu, T.-C.; Lu, C.-L.; Huang, Y.-S.; Chen, C.; Tu, K. N., Unidirectional growth of microbumps on (111)-oriented and nanotwinned copper. Science 2012, 336, 1007.


32

Page 33 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(36) Liao, C.-N.; Lu, Y.-C.; Xu, D., Modulation of crystallographic texture and twinning structure of Cu nanowires by electrodeposition. J. Electrochem. Soc.2013, 160, D207-D211. (37) Xu, L.; Xu, D.; Tu, K. N.; Cai, Y.; Wang, N.; Dixit, P.; Pang, J. H. L.; Miao, J., Structure and migration of (112) step on (111) twin boundaries in nanocrystalline copper. J. Appl. Phys.2008, 104, 113717. (38) Quemper, J.-M.; Dufour-Gergam, E.; Frantz-Rodriguez, N. e.; Gilles, J.-P.; Grandchamp, J.-P.; Bosseboeuf, A., Effects of direct and pulse current on copper electrodeposition through photoresist molds. J. Micromech. Microeng.2000, 10, 116-119. (39) Hu, C.-C.; Wu, C.-M., Effects of deposition modes on the microstructure of copper deposits from an acidic sulfate bath. Surf. Coat. Tech.2003, 176, 75-83. (40) Pearson, T.; Dennis, J. K., Effect of pulsed reverse current on the structure and hardness of copper deposits obtained from acidic electrolytes containing organic additives. Surf. Coat. Tech.1990, 42, 69-79. (41) Gu, C.; Xu, H.; Zhang, T.-Y.,Fabrication of high aspect ratio through-wafer copper interconnects by reverse pulse electroplating.J. Micromech. Microeng.2009, 19, 0655011. (42) Oniciu, L.; Muresan, L., Some fundamental aspects of levelling and brightening in metal electrodeposition J. Appl. Electrochem.1991, 21, 565. (43) Stangl, M.; Acker, J.; Dittel, V.; Gruner, W.; Hoffmann, V.; Wetzig, K.,Characterization of

electroplated

copper

self-annealing

with

investigations

focused

on

incorporated

impurities.Microelectro. Eng.2005, 82, 189.


33


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 41

(44) Chandrasekar, M. S.; Pushpavanam, M., Pulse and pulse reverse plating — Conceptual , advantages and applications. Electrochim. Acta 2008, 53, 3313-322. (45) Mandich, N., Pulse and pulse-reverse electroplating. Metal Finishing 2000, 98,375-380. (46) Yeh, Y.-M.; Chen, C.-S.; Tsai, M.-H.; Shyng, Y.-C.; Lee, S.-Y.; Ou, K.-L.,Effect of pulse-reverse current on microstructure and properties of electroformed nickel–iron mold insert.Jpn. J. Appl. Phys. Part 1 2005, 44 1086. (47) Kim, M. J.; Lim, T.; Park, K. J.; Kim, S.-K.; Kim, J. J., Pulse-reverse electrodeposition of Cu for the fabrication of metal interconnection: II. Enhancement of Cu superfilling and leveling. J. Electrochem. Soc. 2013, 160, D3088-D3092. (48) Kim, M. J.; Lim, T.; Park, K. J.; Cho, S. K.; Kim, S.-K.; Kim, J. J., Characteristics of pulse-reverse electrodeposited Cu thin films: I. effects of the anodic step in the absence of an organic additive. J. Electrochem. Soc. 2012, 159, D538-D543. (49) Chen, X. H.; Lu, L.; Lu, K., Electrical resistivity of ultrafine-grained copper with nanoscale growth twins. J. Appl. Phys.2007, 102, 083708. (50) Chmiela, B.; Sozańska, M., Analysis of high angle boundaries in directionally solidified turbine blade made of CMSX-4® superalloy. IOP Conference Series: Materials Science and Engineering 2011, 22, 012008. (51) Huang, H.; Wei, H. L.; Woo, C. H.; Zhang, X. X., Copper thin film of alternating textures. Appl. Phys. Lett.2003, 82, 4265-4267. (52) Muresan,

L.;

Oniciu,

L.;

Froment,

M.;

Maurin,

G.,

Inhibition

of

lead

electrocrystallization by organic additives. Electrochim. Acta 1992, 37, 2249-2254.


34

Page 35 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(53) Kim, S. H.; Sohn, H. J.; Joo, Y. C.; Kim, Y. W.; Yim, T. H.; Lee, H. Y.; Kang, T., Effect of saccharin addition on the microstructure of electrodeposited Fe–36 wt.% Ni alloy. Surf. Coat. Tech.2005, 199, 43-48. (54) Reddy, A. K. N., Preferred orientations in nickel electro-deposits: I. The mechanism of development of textures in nickel electro-deposits. J. Electroanal. Chem. (1959) 1963, 6, 141152. (55) Field,

D.

P.,

Textured

Structures.

In ASM Handbook: Metallography and

microstructures, Voort, G. F. V., Ed. ASM International: 2004; Vol. 9, pp 215-226. (56) Hong, B.; Jiang, C.-h.; Wang, X.-j., Texture of electroplated copper film under biaxial stress. Mater.Trans.2006, 47, 2299-2301. (57) Thompson, C. V., Coarsening of particles on a planar substrate: Interface energy anisotropy and application to grain growth in thin films Acta Metall.1988, 36, 2929-2934. (58) McLean, M.; Gale, B., Surface energy anisotropy by an improved thermal grooving technique. Phil. Mag.1969, 20, 1033-1045. (59) Kozlov, V. M.; Peraldo Bicelli, L., Texture formation of electrodeposited fcc metals. Mater. Chem. Phys.2003, 77, 289-293. (60) Nielsen, C. B.; Horsewell, A.; Østergard, M., On texture formation of nickel electrodeposits. J. Appl. Electrochem.1997, 27, 839-845. (61) Wang, S. G.; Tian, E. K.; Lung, C. W., Surface energy of arbitrary crystal plane of bcc and fcc metals. J. Phys. Chem. Solids 2000, 61, 1295-1300.


35


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 41

(62) Stokes, R. J.; Evans, D. F., Fundamentals of interfacial engineering. ed.; John Wiley & Sons: 1997. (63) Zielinski, E. M.; Vinci, R. P.; Bravman, J. C., The influence of strain energy minimization on abnormal grain growth in copper thin films. MRS Proceedings 1995, 391, 103. (64) Thompson, C. V., Texture evolution during grain growth in polycrystalline films. Scripta Metall. Mater.1993, 28, 167-172. (65) Dubin, V. M.; Lopatin, S.; Chen, S.; Cheung, R.; Ryu, C.; Wong, S. S., Copper electroplating for damascene ULSI interconnects. MRS Online Proceedings Library 1998, 514, null-null. (66) Schlesinger, M.; Paunovic, M., Modern electroplating. ed.; John Wiley & Sons: 2011; Vol. 55. (67) Lee, H.; Wong, S. S., Correlation of stress and texture evolution during self- and thermal annealing of electroplated Cu films. J. Appl. Phys.2003, 93, 3796. (68) Wei, H. L.; Huang, H.; Woo, C. H.; Zheng, R. K.; Wen, G. H.; Zhang, X. X., Development oftexture in copper thin films. Appl. Phys. Lett.2002, 80, 2290-2292. (69) Brongersma, S. H.; Kerr, E.; Vervoort, I.; Saerens, A.; Maex, K., Grain growth, stress, and impurities in electroplated copper. J. Mater. Res.2002, 17, 582-589. (70) Liu, J.; Liu, C.; Conway, P. P., Crystallographic features of copper column growth by reversible pulse current electrodeposition. In Electronic Components and Technology Conference, ed.; IEEE: 2007.


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Page 37 of 41

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(71) Schu¨ler, K.; Philippi, B.; Weinmann, M.; Marx, V. M.; Vehoff, H., Effects of processing on texture, internal stresses and mechanical properties during the pulsed electrodeposition of nanocrystalline and ultrafine-grained nickel. Acta Mater.2013, 61, 3945-3955. (72) Lin, Y.-W.; Kuo, J.-C.; Lui, K.-T.; Chen, D., Effect of plating current density and frequency on the crystallographic texture of electrodeposited copper. Mater. Sci. Forum 2010, 638-642, 2841-2845. (73) Maurer, F.; Brotz, J.; Karim, S.; Molares, M. E. T.; Trautmann, C.; Fuess, H., Preferred growth orientation of metallic fcc nanowires under direct and alternating electrodeposition conditions. Nanotechnology 2007, 18, 135709. (74) Georgiadou, M.; Veyret, D., Modeling of transient electrochemical systems involving moving boundaries parametric study of pulse and pulse-reverse plating of copper in trenches. J. Electrochem. Soc.2002, 149, (6), C324-C330. (75) Chung, C.-J.; Field, D. P.; Park, N.-J.; Johnson, R. G., Simulation of structure evolution in Cu films. Thin Solid Films 2009, 517, 1977-1982. (76) Xu, D.; Kwan, W. L.; Chen, K.; Zhang, X.; Vidvuds Ozoliņš; Tu, K. N., Nanotwin formation in copper thin films by stress/strain relaxation in pulse electrodeposition. Appl. Phys. Lett. 2007, 91, 254105. (77) Seah, C. H.; Mridha, S.; Chan, L. H., DC/pulse plating of copper for trench/via filling. J. Mater. Process. Technol. 2001, 114, 233-239.


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Page 38 of 41

(78) Xu, D.; Sriram, V.; Ozolins, V.; Yang, J.-M.; Tu, K. N.; Stafford, G. R.; Beauchamp, C., In situ measurements of stress evolution for nanotwin formation during pulse electrodeposition of copper. J. Appl. Phys.2009, 105, 023521. (79) Kim, M. J.; Cho, S. K.; Koo, H.-C.; Lim, T.; Park, K. J.; Kim, J. J., pulse electrodeposition for improving electrical properties of Cu thin film. J. Electrochem. Soc. 2010, 157, D564-D569. (80) Aroyo, M.; Tzonev, N., Pulse periodic reverse plating: Possibilities for electrodeposition of metal coatings with improved properties: Part 2. Plat. Surf.Finish.2003, 90, 50-54. (81) Dieter, G. E.; Bacon, D., Mechanical metallurgy. ed.; McGraw-Hill New York: 1986; Vol. 3. (82) Randle, V., Grain boundary engineering: an overview after 25 years. Mater. Sci. Technol.2010, 26, 253-261. (83) J.Koike; A.Sekiguchi; M.Wada; K.Maruyama, A Relationship between film texture and stress-voiding tendency in copper thin films. In Stress-Induced Phenomena in Metallization : Sixth Int'l. Workshop, ed.; et.al, S. P. B., Ed. AIP: 2002; Vol. CP612. (84) Ebrahimi, F.; Liscano, A. J.; Kong, D.; Krishnamoorthy, V., Evolution of texture in electrodeposited Ni/Cu layered nanostructures. Phil. Mag.2003, 83, 457-476. (85) Brandon, D. G.; Ralph, B.; Ranganathan, S.; Wald, M. S., A field ion microscope study of atomic configuration at grain boundaries. Acta Metall.1964, 12, 813-821. (86) Brandon, D. G., The structure of high-angle grain boundaries. Acta Metall.1966, 14, 1479-1484.


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Page 39 of 41

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(87) Porter, D. A.; Easterling, K. E., Phase Transformations in Metals and Alloys, Third Edition (Revised Reprint). ed.; Taylor & Francis: 1992. (88) Liang, H.; Woo, C. H.; Huang, H.; Ngan, A. H. W.; Yu, T. X., Crystalline plasticity on copper (001), (110), and (111) surfaces during nanoindentation. Comput. Model. Eng. Sci.2004, 6, 105-114. (89) Sirdeshmukh, D.; Sirdeshmukh, L.; Subhadra, K. G., Micro-and Macro-Properties of Solids: Thermal, Mechanical and Dielectric Properties. ed.; Springer Berlin Heidelberg: 2006. (90) Tschopp, M. A.; Spearot, D. E.; McDowell, D. L., Atomistic simulations of homogeneous dislocation nucleation in single crystal copper. Modell. Simul. Mater. Sci. Eng. 2007, 15, 693. (91) Dub, S. N.; Lim, Y. Y.; Chaudhri, M. M., Nanohardness of high purity Cu (111) single crystals: The effect of indenter load and prior plastic sample strain. J. Appl. Phys. 2010, 107, 043510. (92) Surface Structure of fcc Metals. http://www.chem.qmul.ac.uk/surfaces/scc/scat1_2.htm (93) D.Y.Li; Q.Chen; X.Y.Wang, Will crystallographic faces of a crystal keep their order in strength and friction coefficient when the contact force is reduced to nano/micro-Newton level. J. Appl. Phys.2006, 99, 044305.


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For Table of Contents Use Only Controllable Crystallographic Texture in Copper Foils Exhibiting Enhanced Mechanical and Electrical Properties by Pulse Reverse Electrodeposition Chokkakula L. P. Pavithraa, b, BulusuV.Saradaa, Koteswararao V. Rajulapatib, M. Ramakrishna a, Ravi C. Gundakarama, Tata N. Raoa, G. Sundararajana a

International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur (P.O), Hyderabad-500005, INDIA b

School of Engineering Sciences and Technology (SEST), University of Hyderabad (UoH), Gachibowli, Hyderabad-500046,INDIA

Table of Contents Graphic


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Synopsis: •

Application of pulse reverse electrodeposition (PRED) technique in an ‘additive-free’ electrolyte for preparation of copper foils

•

Control over preferred crystallographic orientations and introducing special CSLΣ3 coherent twin boundaries in copper foils

•

Enhanced mechanical properties simultaneously with electrical properties

•

High stability of texture and properties in PRED copper foils


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Controllable Crystallographic Texture in Copper Foils Exhibiting

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