understandingthepreferredcrystalorientationofsputtered...

Research ArticleUnderstanding the Preferred Crystal Orientation of SputteredSilver in ArN2 Atmosphere A Microstructure Investigation

YuHao Hu1 Jiajun Zhu 12 Chao Zhang 3 Wulin Yang12 Licai Fu12 Deyi Li12

and Lingping Zhou12

1College of Materials Science and Engineering Hunan University Changsha 410082 China2Hunan Province Key Laboratory for Spray Deposition Technology and Application Hunan University Changsha 410082 China3Science and Technology on Power Sources Laboratory Tianjin Institute of Power Sources Tianjin 300384 China

Correspondence should be addressed to Jiajun Zhu jiajunhnueducn and Chao Zhang zcmaster163com

Received 9 May 2019 Accepted 9 July 2019 Published 6 November 2019

Academic Editor Pramod Koshy

Copyright copy 2019 YuHao Hu et al is is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Silver thin films were prepared by direct current (DC) magnetron sputtering technique in ArN2 atmosphere with various N2volumetric ratios on Si substrates Silver thin films prepared in pure Ar atmosphere show highly (111) preferred orientationHowever as the N2 content increases Ag (111) preferred orientation evolves into (100) preferred orientation gradually When N2content is more than 125 vol silver thin films exhibit highly (100) preferred orientation Moreover the average grain sizedecreases with increasing N2 content Silver thin films with low relative density are prepared at high N2 content which results inhigher resistivity of films By analyzing the resistivity and microstructures of silver thin films the optimum range of N2 content toget compact silver thin films is found to be not more than 333 vol Finally the mechanism of N2 addition on microstructureevolution of silver thin films was proposed

1 Introduction

Noble metal silver (Ag) has excellent characteristics such aslow electrical resistivity high thermal conduction highreflectivity in visible and infrared regions and great weldableand antimicrobial properties [1ndash3] Silver and correspondingcomposites are widely used in the fields of electronicsaerospace medical instruments etc For example AgGaNmultilayer films are used as the conductor electrodes of light-emitting diodes (LEDs) the coatings of laser safety glassesand display window materials which block microwave ra-diation [4 5] AgTiN or AgTaN multilayer films are po-tential materials to be used as interconnects on integratedcircuits [6ndash8] Beyond that AgTiN multilayer films are alsoused in the photocatalytic field [9]

In the above applications the silver thin films weregenerally prepared by physical vapor deposition (PVD) in Aratmosphere while nitride thin films were prepared by PVDin ArN2 atmosphere During the preparation process of Agnitride multilayer films the sputtering gas needed to be

changed thus the preparation process of Agnitride mul-tilayer films was complicated If the Agnitride multilayerfilms can be prepared in the same ArN2 atmosphere it willsimplify the preparation process of Agnitride multilayerthin films erefore it is necessary to study the influence ofArN2 sputtering gas on microstructures of silver thin films

Compared with Ar N2 exhibits higher chemical re-activity It is difficult to obtain pure metal thin films in N2 orArN2 atmospheres Hence N2 is usually used to preparenitride thin films via PVD (physical vapor deposition)Moreover the influence of N2 content in ArN2 atmosphereon crystal orientation grain size and relative density of filmsis also demonstrated in previous research studies In 2004Kawamura et al reported that the Ni thin films were pre-pared in low N2 flow ratio however Ni3N phase was ob-served when the flow ratio of N2 arrived to 12Furthermore the crystal orientation of Ni thin films waschanged from (111) to (100) due to the introduction of N2into the sputtering atmosphere [10] Afterwards they dis-covered that the intensity of (002) peak (C-axis orientation)

HindawiAdvances in Materials Science and EngineeringVolume 2019 Article ID 3079393 8 pageshttpsdoiorg10115520193079393

of Ru thin films decreased with the increasing N2 sputteringgas proportion at a substrate temperature of 100degC and theintensity of (002) peak of Ru thin films eventually disappearedwhen the N2 content was 50 flow ratio In addition it wasobserved by Auger electron spectroscopy that the Ru filmdeposited at 50 N2 content contained nitrogen [11] Calinaset al developed the formation of nanocrystalline copper thinfilms through controlled addition of nitrogen According totheir work the average nitrogen content for the Cu-N thinfilms was found to be 15 at 35 at and 7 at for thesamples with PN2 PAr ratios of 1 60 1 30 and 1 2 re-spectively And the Cu3N phase was identified with the highestPN2 PAr ratio of 1 2 Moreover when the nitrogen content inCu thin films was low the grain size of Cu thin films rapidlydecreased with the increase of the nitrogen content [12] Basedon all above mentioned the N2 content has a significant in-fluence on the microstructures and composition of metal thinfilms however themicrostructures of silver thin films preparedat variousN2 contents inArN2 atmosphere are rarely reportedus it is meaningful to research the effect of N2 content in ArN2 atmosphere on the microstructures of silver thin films andfind a suitable range of N2 content to prepare silver thin films

In this paper a series of samples were prepared by directcurrent (DC) magnetron sputtering in ArN2 atmospherewith various N2 contents (0 vol 8 vol 125 vol 333vol 50 vol 667 vol and 100 vol) on Si substratesCrystal orientation texture coefficient and grain size ofsilver thin films were characterized as a function of N2content Furthermore surface morphology cross-sectionalmorphology and electrical properties of silver thin filmswere investigated In the end the mechanism of micro-structure evolution was also proposed

2 Experimental

Silver thin films were prepared by direct current magnetronsputtering deposition system (MIS800) (100) single crystalsilicon sheets were selected as the substrate material and cut intosquare-shaped of approximately 10mmtimes 10mmtimes 038mmese Si specimens were ultrasonically cleaned with acetoneethanol and deionized water in sequence before being driedPrior to deposition the base pressure was less than 40times10minus 4 Paen the substrates were cleaned by Ar+ beam bombardmentwith 600V50mA lasting for 10 minutes to remove surfaceimpurity e substrate holder was then rotated to be per-pendicular to the direction parallel with the Ag target (9999purity) During the deposition the distance between Ag targetand substrate was 70mmeworking pressure wasmaintainedat 1Pa and the power was 120W Finally the films were de-posited for 10 minutes at various N2 contents in ArN2 at-mospheree samples numbered on the basis of N2 content areshown in the Table 1

e phase composition and crystallographic structure ofsilver thin films were analyzed by X-ray diffraction (XRD)measurement (MiniFlex made by Rigaku) with Cu K-αradiation source Surface and cross-sectional morphologiesof silver thin films were recorded by using a scanningelectron microscope (SEM Hitachi S-4800) e surfacechemical compositions of the silver thin films were studied

by the K-ALPHA X-ray (ermo Fisher Scientific) photo-electron spectroscopy (XPS) instrument e sheet re-sistance of silver thin films on Si substrates was measured bya four-point probe (RTS-8) e resistivity was calculatedaccording the following formula

ρ Rsd (1)

where d is the thickness of the film measured by SEM and Rsis the sheet resistance of the film

3 Results and Discussion

31 Crystal Orientation of Silver in Films Figure 1 showsX-ray diffraction patterns of silver thin films on Si substratese value of ordinate was set same in order to compare the Agpeak intensity of all samples easily In Figure 1 high Ag (111)and (200) diffraction peaks are found clearly in all samplese Si substrate peak is so high that Ag (220) (311) and (222)diffraction peaks could not be observed in almost all samples

e phase of nitride is not detected by XRD which is inaccordance with the results of XPS spectra that are shown inFigure 2 Considering all the samples were exposed in airbefore XPS characterization the sample was etched 5minutes by Ar+ (2 keV) to exclude the absorptions of C Nand O elements from the air As seen from the wide-scanspectra of S0 S33 and S100 in Figure 2(a) only Ag isobserved e high-resolution spectra of Ag 3d and thecorresponding fitting curves are shown in Figure 2(b) thearea ratio of the Ag 3d32 and Ag 3d52 peaks is about 23 andthe binding energy of Ag 3d32 and Ag 3d52 is 3744 eV and3684 eV respectively which agrees with the binding energyof metallic Ag [13 14] Based on the results of XRD and XPSno nitride and oxide exist in the thin film and pure silverthin films were obtained in pure N2 atmosphere

It is clear that the relative intensities of Ag (111) and(200) diffraction peaks are different for silver thin filmsprepared at different N2 contents in Figure 1 Preferredorientation exists in all samples In order to explain thedegree of the silver thin filmsrsquo preferred orientation thetexture coefficients of (111) plane and (100) plane (P(111) andP(100)) were represented quantitatively by the Harris methodin the following formula [15 16]

P(hkl)i

I(hkl)i

I0(hkl)i

1n

1113944

n

1

I(hkl)i

I0(hkl)i

⎡⎣ ⎤⎦minus 1

(2)

where I0(hkl)i is the standard intensity of the (hkl) plane forthe ith peak from powder diffraction file (PDF) card I(hkl)i isthe detected intensity of the (hkl) plane for the ith peak andn is the total number of diffraction peaks considered in theanalysis ICSD card no 04-0783 of Ag was used in thiscalculation and other peaks were so weak that only (111)and (200) peaks were considered e values of P(111) andP(100) of silver thin films on Si substrates depending upon theN2 content are shown in Figure 3 (P(111) +P(100) 2) evalue of P(100) suddenly increases when the N2 contentchanges from 0 vol to 125 vol and slightly increaseswith the increasing N2 content ranging from 125 vol to333 vol When N2 content exceeds 333 vol P(100)

2 Advances in Materials Science and Engineering

becomes stable Overall as the N2 content increases grainsprefer to grow along (100) plane while (111) plane is re-strained Based on the above results silver thin films withhighly (111) preferred orientation were prepared in pure Aratmosphere (P(111) 166gtgt 1) and silver thin films withhighly (100) preferred orientation were prepared at 125vol N2 content (P(100) 172gtgt 1) erefore it is con-cluded that the preferred orientation of silver thin films canbe adjusted successfully in ArN2 atmosphere throughcontrolling the N2 content

32 Grain Size of Silver in Films e grain sizes of (111)plane (G(111)) and (200) plane (G(200)) were calculated basedon the Scherrer formula

G kλ

β cos θ (3)

where G is the grain size k 089 λ 0154056 nm β is thefull width at half maximum (FWHM) of the diffraction peak

and θ is the Bragg angle at corresponding diffraction peake instrument width was deducted by Si standard samplesG represents the average grain size of silver thin films whichwere estimated according to the following formula

G G(111)P(111) + G(200)P(100)

2 (4)

Grain size of silver thin films is shown in Figure 4 It isobvious that G(111) is bigger than G(200) for all samples andG(111) decreases with increasing N2 content e averagegrain size G decreases rapidly from 82 nm to 40 nm with theincreasing N2 content ranging from 0 vol to 125 voland then it decreases slightly Finally G reduces to 31 nmwhen the N2 content is 100 e results of grain sizesuggest that grain growth was suppressed in N2 atmosphereduring the deposition

33 Surface and Cross-Sectional Morphologies of Silver inFilms e SEM cross-sectional images of S0 S12 S33 S50and S100 are shown in Figure 5 e cross-sectionalstructure of silver thin films is compact as shown inFigure 5(a) Denser structure is also observed in Figure 5(b)However few holes are observed in S33 in Figure 5(c)Compared with S33 a large number of holes exist in S50 andS100 in Figures 5(d) and 5(e) and the mean diameter ofholes in S50 and S100 is bigger than that in S33 e porous-style structure indicates the low relative density of filmsthus the relative densities of S50 and S100 are extremelyworse than S33 In addition the thickness of silver thin filmsdecreases from 19 μm to 16 μmwhen the N2 content rangedfrom 0 vol to 333 vol which suggests that the de-position rate of silver thin films decreases with increasing N2content However the thickness of silver thin films preparedat 50 vol N2 content is 18 μm Compared to S33 theincrease of thickness in S50 may be caused by its loosestructure Although the structure in S100 is loose thethickness of S100 reduces to 145 μm so a very low de-position rate existed in pure N2 atmosphere In summary asN2 content increases the thickness of films decreases firstlythen increases and decreases finally

e SEM surface images of S0 S12 S33 S50 and S100are shown in Figure 5 Clean and flat surface can be observedin S0 S12 and S33 in Figures 5(a1) 5(b1) and 5(c1) eaverage surface granule size of S0 S12 and S33 decreases insequence e relative flat surface in S50 is also observed inFigure 5(d1) however many holes and a few big sphericalcrystalline granules are observed on the surface InFigure 5(e1) spherical crystalline granules are dispersed onthe surface and a lot of holes and grooves exist It is obviousthat the surface of S100 is extremely sparser and rough emorphology can indirectly reflect the relative density offilms According to the analysis of surface and cross-sec-tional morphologies the relative density of films was eval-uated e sequence of filmsrsquo relative density from high to

Table 1 ArN2 ratio and numbered messagesN2 content (volumetric ratio) 0 8 125 333 50 667 100Sample number S0 S8 S12 S33 S50 S66 S100

S100

S66

S50

S33

S12

S8

S0

Inte

nsity

(au

)

(400)clubs

30 40 70 8050 90602θ (deg)

(200)

(111)

clubs SiAg

Figure 1 X-ray diffraction patterns (XRD) of silver thin films (S0S8 S12 S33 S50 S66 and S100)

Advances in Materials Science and Engineering 3

low is as follows S0 and S12 S33 S50 and S100 whichindicates that the high N2 content in ArN2 atmosphereresulted in the low relative density of films during the de-position erefore to obtain a compact silver thin filmthrough PVD process in ArN2 atmosphere the N2 contentdoes not exceed 333 vol

34 Resistivity of Silver in Films e resistivity of silverthin films is shown in Figure 6 It can be seen from the figurethat the resistivity of silver thin films increased with increasingN2 content until the N2 content reached 667 vol and thenthe resistivity of silver thin films stabilized with increasing N2content Generally the resistivity of metal thin films is thecollaborative results of surface scattering defects and im-purity scattering and grain boundary scattering When the

thickness of metal thin films is comparable in magnitude withthe electronic mean free path of bulk material the resistivityof metal thin films increases as the thickness of films decreasesdue to the surface scattering which has been demonstrated bythe Fuchs-Sondheimer (FS) model [17 18] However thethicknesses of silver thin films in this study ranges from145 μm to 19μm and it is extremely higher than the meanfree path of electron (52 nm) [19] us the effect of filmsthickness on the resistivity can be negligible

e resistivity of silver thin films prepared in pure Aratmosphere is close to the resistivity of bulk material(16 μΩmiddotcm) As the N2 content increases from 0 vol to 333vol the resistivity of silver thin films increases slightly

S100S33S0

Inte

nsity

(au

)

1200 1000 800 600 400 200Binding energy (eV)

Ag MN1 Ag 3s Ag 3p1Ag 3p3

Ag 3d3Ag 3d5

(a)

Inte

nsity

(au

)

Binding energy (eV)

380 378 376 374 372 370 368 366 364 362 360

S100

S33

S0

3744 eV3684 eV

Ag 3d32

Ag 3d52

(b)

Figure 2 XPS spectra of S0 S33 and S100 (a) e wide-scan spectra of S100 sample (b) Ag 3d spectra

P(100)

P(111)

0002040608101214161820

P (10

0)

10 20 30 40 50 60 70 80 900 100Volumetric ratio of N2 ()

00

02

04

06

08

10

12

14

16

18

P (11

1)

Figure 3 P(111) and P(100) of silver thin films on Si substrates as afunction of the volumetric ratio of N2 content

G(111)G(200)

G

0 10 20 30 40 50 60 70 80 90 100 110ndash10Volumetric ratio of N2 ()

25303540455055

6560

707580859095

Gra

in si

zes (

nm)

Figure 4 Grain size of silver thin films as a function of the vol-umetric ratio of N2 content


while the average grain size of silver thin films decreasesfrom 82 nm to 35 nm e grain size is comparable with themean free path of electron in our works e famous

Mayadas and Shatzkes (MS) model explained the relationbetween grain boundary and resistivity and the MS model isshown as follows

Figure 5 Surface and cross-sectional morphologies of S0 S12 S33 S50 and S100 (a) (b) (c) (d) and (e) show the cross-sectional morphologiesof S0 S12 S33 S50 and S100 respectively (a1) (b1) (c1) (d1) and (e1) show the surfacemorphologies of S0 S12 S33 S50 and S100 respectively


ρ ρ0 1 +32

times1G

timesR

1 minus R1113876 1113877 (5)

where G is the grain size R is the grain boundary reflectioncoefficient ρ0 is the bulk resistivity and ρ is the measuredresistivity e amount of grain boundary per unit volumeincreases with the reduction of grain size e grainboundary prevents the electron or phonon to transportwhich leads to the increase of resistivity erefore in phaseI as shown in Figure 6 the main factor leading to the in-creasing resistivity of silver thin films is the grain boundaryscattering When the N2 content exceeds 333 vol theaverage grain size of silver thin films decreases from 40 nm to31 nm slowly so the resistivity caused by grain boundaryscattering is close When the N2 content exceeds 333 volthe relative density of films is low and loose and porousstructure can be observed from the surface and cross-sec-tional morphologies in Figure 5 e holes in films seriouslyhinder the transmission of electrons thus the defect scat-tering plays a major role in the dramatic increase in re-sistivity of films In region II the number of defects such asholes increases with increasing N2 content however thenumber of defects no longer increases while the N2 contentarrived at 667 vol Correspondingly the resistivity ofsilver thin films increases rapidly and then the resistivity ofsilver thin films stabilizes As we all know the quality ofsilver thin films can be estimated facilely by the resistivity ofsilver thin film When the N2 content ranges from 0 vol to333 vol the grain boundary scattering is the main reasonto lead to a small difference in resistivity and the effect ofdefect scattering on resistivity is similar so the relativedensity of silver thin films is close When the N2 contentexceeds 333 vol the higher resistivity indicates that silverthin films have a lower relative density

35 Mechanism of Microstructure Evolution e crystalorientation grain size morphology and relative density ofsilver thin films changed with the increasing N2 content Sothe N2 content has a significant effect on the microstructures

of silver thin films It can be speculated that the change inmicrostructures of silver thin films was related to the processof generation transport and deposition of sputtered par-ticles e schematic diagram of silver thin filmsrsquo sputteringtransport and deposition in pure Ar and pure N2 atmo-spheres is described respectively in Figure 7

During the complicated deposition process of silver thinfilms the discharge is maintained by sputtering gas In ArN2 discharge Ar+ and N2

+ are the main ions and Ar atomsN2 molecules and a small amount of N+ ion also exist in thevacuum which have been detected by plasma diagnostictechniques in some literatures [20ndash22] ere is no doubtthat Ar+ is the main ion in Ar discharge and N2

+ is the mainion in N2 discharge e electron density and ion density inAr discharge are higher than those in N2 discharge underother same parameters which have been reported in liter-atures [20 23] A higher ionization rate of gas exists in Ardischarge compared with that in N2 discharge and a largequantity of sputtered Ar+ result in high sputter yields in Ardischarge so bigger and more Ag clusters exist in Arcompared with those in N2 Moreover another role ofsputtering gas is to affect the energy distribution through thecollision process with sputtered particles in the transportprocess of sputtered particles Mean free path (λ) was es-timated according to the following formula

λ kT

2

radicπd2P

(6)

where k is the Boltzmann constant T is the absolute tem-perature (298K is adopted here) d is the molecular di-ameter and P is the working pressure (1 Pa) e moleculardiameter of Ar (34 A) is smaller than N2 (364 A) thus themean free path of N2 (λN2

is about 7mm) is lower than Ar(λAr is about 8mm) When sputtered particles are trans-ported from target to substrates the sputtered particles aredisturbed due to the collision with sputtering gas moleculese collision frequency between sputtered particles andsputtering gas molecules is more intense in N2 sputtering gasdue to the low mean free path Compared with Ar dischargethe higher collision frequency in the transport process andlower sputter yields led to a lower deposition rate in N2discharge which is directly reflected in the thickness of silverthin films Moreover the high collision frequency in N2discharge leads to severe energy loss during the transportprocess So Ag clusters have lower energy Ek in N2 dischargethan that in Ar discharge when they arrived to substrates

e carrying energy of Ag clusters is the driving force formigration and diffusion and Ag clusters have higher energyEk in Ar discharge therefore the Ag clusters are able tomove to the gap among the clusters due to higher migrationand diffusion which result in a close-packed growth modelof Ag clusters during the deposition e close-packed planeof FCC metal is (111) plane and grain growth of (111) planeis promoted Compared with Ar discharge the Ag clusters inN2 discharge have lower energy Ag clusters with lowermobility and diffusion tend to hold the initial position afterthey deposit on the substrates so a relative loose-packedgrowth model of Ag clusters exists in N2 discharge which is


I II

16

18

20

22

24

26

28

30

Resis

tivity

(microW

middotcm

)

Figure 6 Resistivity of silver thin films as a function of the vol-umetric ratio of N2 content


proved by the cross-sectional morphology in Figure 5Moreover in Ar discharge the high mobility and big size ofAg clusters lead to big initial grain size during the co-alescence stage During the grain growth the lower mobilityand diffusion leads to a higher nucleation rate in N2 dis-charge erefore the initial and final grain size in Ardischarge is bigger than that in N2 discharge In FCC metal(111) plane has the lowest surface energy and (100) plane hasthe lowest strain energy [24] e relative higher strainenergy exists in silver thin films due to the fact that a lot ofdefects exist in loose-packedmodel of Ag clustersereforethe competition between surface energy and strain energy isalso responsible for the orientation evolution which agreedwith the mobility and diffusion results of Ag clusters Inconclusion the N2 content has a significant influence on themicrostructures of silver thin films and the grain boundaryscattering and defect scattering caused by the microstruc-tures of films are mainly responsible for the change inelectrical properties

4 Conclusions

e sputtering gas N2 content plays an important role onmicrostructures of silver thin films during the deposition Asthe N2 content increases Ag (111) preferred orientation isgradually evolved into (100) preferred orientation When N2is more than 125 vol silver thin films have highly (100)preferred orientation e average grain size decreases from82 nm to 31 nm as the N2 content increases Silver thin filmsexhibit low relative density when the N2 content exceeds 333vol e mobility diffusion and energy of Ag clusters aremainly responsible for changes in the microstructures of

silver thin films e resistivity of silver thin films is alteredwith the changes of the microstructures in silver thin filmsWhen the N2 content ranges from 0 vol to 333 vol theresistivity of silver thin films increases slightly which ismainly the result of the grain boundary scattering edefects scattering is mainly responsible for high resistivity offilms prepared at high N2 content Based on the results offilmsrsquo resistivity and microstructures the optimum range ofN2 content to get compact silver thin films is below 333vol

Data Availability

All data used to support the findings of this study are in-cluded within the article

Conflicts of Interest

e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

is study was financially supported by the Foundation ofNational Key Laboratory P R China (6142808180102) andNational Natural Science Foundation of China (grant no51401080)

References

[1] E Kudo S Hibiya M Kawamura et al ldquoOptical properties ofhighly stable silver thin films using different surface metallayersrdquo in Solid Films vol 660 pp 730ndash732 2018

Ag targetAr N2

Ar+endash

N+N2+

(Different energy Ek in different colors)

Transport

Deposition

Sputtering

E k d

ecre

ases

due

to co

llisio

n

High

High

Low

Low

Ek

Close-packed Loose-packed

Top view Top view

Initial state

Final state

Hole

Ag clusters

(100)(111)

Ionization rate

Figure 7 e sputtering deposition schematic diagram of silver thin films in pure Ar and pure N2 atmospheres


[2] O Baghriche S Rtimi A Zertal C Pulgarin R Sanjines andJ Kiwi ldquoAccelerated bacterial reduction on Ag-TaN com-pared with Ag-ZrN and Ag-TiN surfacesrdquoApplied Catalysis BEnvironmental vol 174-175 pp 376ndash382 2015

[3] J Zhu Y Hu M Xu et al ldquoEnhancement of the adhesivestrength between Ag films and Mo substrate by Ag implantedvia ion beam-assisted depositionrdquo Materials vol 11 no 5p 762 2018

[4] A H Aly M Ismail and E Abdel-Rahman ldquoAgGaN onedimensional photonic crystal for many applicationsrdquo Journalof Computational and eoretical Nanoscience vol 9 no 4pp 592ndash596 2012

[5] J-O Song J Seop Kwak Y Park and T-Y Seong ldquoOhmicand degradation mechanisms of Ag contacts on p-type GaNrdquoApplied Physics Letters vol 86 no 6 Article ID 062104 2005

[6] L Gao J Gstottner R Emling et al ldquoermal stability oftitanium nitride diffusion barrier films for advanced silverinterconnectsrdquo Microelectronic Engineering vol 76 no 1ndash4pp 76ndash81 2004

[7] L Gao J Gstottner R Emling et al ldquoSilver metallization withreactively sputtered TiN diffusion barrier filmsrdquo MRS OnlineProceedings Library Archive vol 812 2004

[8] S Mardani D Primetzhofer L Liljeholm O VallinH Norstrom and J Olsson ldquoElectrical properties of AgTaand AgTaN thin-filmsrdquoMicroelectronic Engineering vol 120pp 257ndash261 2014

[9] S Rtimi O Baghriche R Sanjines et al ldquoPhotocatalysiscatalysis by innovative TiN and TiN-Ag surfaces inactivatebacteria under visible lightrdquo Applied Catalysis B Environ-mental vol 123-124 pp 306ndash315 2012

[10] M Kawamura K Iibuchi Y Abe and K Sasaki ldquoCrystalorientation change of Ni films by sputtering in Ar-N2 mixedgasesrdquo Japanese Journal of Applied Physics vol 43 no 7App 4361-4362 2004

[11] M Kawamura K Yagi Y Abe and K Sasaki ldquoEffects of theAr-N2 sputtering gas mixture on the preferential orientationof sputtered Ru filmsrdquo in Solid Films vol 494 no 1-2pp 240ndash243 2006

[12] R Calinas M T Vieira and P J Ferreira ldquoe effect ofnitrogen on the formation of nanocrystalline copper thinfilmsrdquo Journal of Nanoscience and Nanotechnology vol 9no 6 pp 3921ndash3926 2009

[13] G R Sanchez C L Castilla N B Gomez A GarcıaR Marcos and E R Carmona ldquoLeaf extract from the endemicplant Peumus boldus as an effective bioproduct for the greensynthesis of silver nanoparticlesrdquo Materials Letters vol 183pp 255ndash260 2016

[14] M S Jee H S Jeon C Kim et al ldquoEnhancement in carbondioxide activity and stability on nanostructured silver elec-trode and the role of oxygenrdquo Applied Catalysis B Envi-ronmental vol 180 pp 372ndash378 2016

[15] X Gao M Hu Y Fu L Weng W Liu and J Sun ldquoLowtemperature deposited Ag films exhibiting highly preferredorientationsrdquo Materials Letters vol 213 pp 178ndash180 2018

[16] Y Wang W Tang and L Zhang ldquoCrystalline size effects ontexture coefficient electrical and optical properties of sputter-deposited Ga-doped ZnO thin filmsrdquo Journal of MaterialsScience amp Technology vol 31 no 2 pp 175ndash181 2015

[17] E H Sondheimer ldquoe mean free path of electrons inmetalsrdquo Advances in Physics vol 1 no 1 pp 1ndash42 1952

[18] P P Wang X J Wang J L Du et al ldquoe temperature andsize effect on the electrical resistivity of CuV multilayerfilmsrdquo Acta Materialia vol 126 pp 294ndash301 2017

[19] W Zhang S H Brongersma O Richard et al ldquoInfluence ofthe electron mean free path on the resistivity of thin metalfilmsrdquo Microelectronic Engineering vol 76 no 1ndash4pp 146ndash152 2004

[20] B Fritsche T Chevolleau J Kourtev A Kolitsch andW Moller ldquoPlasma diagnostic of an RF magnetron ArN2dischargerdquo Vacuum vol 69 no 1ndash3 pp 139ndash145 2002

[21] M D Logue and M J Kushner ldquoElectron energy distribu-tions and electron impact source functions in ArN2 in-ductively coupled plasmas using pulsed powerrdquo Journal ofApplied Physics vol 117 no 4 article 043301 2015

[22] P G Reyes C Torres and H Martınez ldquoElectron temper-ature and ion density measurements in a glow discharge of anAr-N2 mixturerdquo Radiation Effects and Defects in Solidsvol 169 no 4 pp 285ndash292 2014

[23] MMMansour N M El-Sayed and O F Farag ldquoEffect of Heand Ar addition on N2 glow discharge characteristics andplasma diagnosticsrdquo Arab Journal of Nuclear Sciences andApplications vol 46 no 1 pp 116ndash125 2013

[24] J-M Zhang Y Zhang and K-W Xu ldquoDependence ofstresses and strain energies on grain orientations in FCCmetal filmsrdquo Journal of Crystal Growth vol 285 no 3pp 427ndash435 2005


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of Ru thin films decreased with the increasing N2 sputteringgas proportion at a substrate temperature of 100degC and theintensity of (002) peak of Ru thin films eventually disappearedwhen the N2 content was 50 flow ratio In addition it wasobserved by Auger electron spectroscopy that the Ru filmdeposited at 50 N2 content contained nitrogen [11] Calinaset al developed the formation of nanocrystalline copper thinfilms through controlled addition of nitrogen According totheir work the average nitrogen content for the Cu-N thinfilms was found to be 15 at 35 at and 7 at for thesamples with PN2 PAr ratios of 1 60 1 30 and 1 2 re-spectively And the Cu3N phase was identified with the highestPN2 PAr ratio of 1 2 Moreover when the nitrogen content inCu thin films was low the grain size of Cu thin films rapidlydecreased with the increase of the nitrogen content [12] Basedon all above mentioned the N2 content has a significant in-fluence on the microstructures and composition of metal thinfilms however themicrostructures of silver thin films preparedat variousN2 contents inArN2 atmosphere are rarely reportedus it is meaningful to research the effect of N2 content in ArN2 atmosphere on the microstructures of silver thin films andfind a suitable range of N2 content to prepare silver thin films

In this paper a series of samples were prepared by directcurrent (DC) magnetron sputtering in ArN2 atmospherewith various N2 contents (0 vol 8 vol 125 vol 333vol 50 vol 667 vol and 100 vol) on Si substratesCrystal orientation texture coefficient and grain size ofsilver thin films were characterized as a function of N2content Furthermore surface morphology cross-sectionalmorphology and electrical properties of silver thin filmswere investigated In the end the mechanism of micro-structure evolution was also proposed

2 Experimental

Silver thin films were prepared by direct current magnetronsputtering deposition system (MIS800) (100) single crystalsilicon sheets were selected as the substrate material and cut intosquare-shaped of approximately 10mmtimes 10mmtimes 038mmese Si specimens were ultrasonically cleaned with acetoneethanol and deionized water in sequence before being driedPrior to deposition the base pressure was less than 40times10minus 4 Paen the substrates were cleaned by Ar+ beam bombardmentwith 600V50mA lasting for 10 minutes to remove surfaceimpurity e substrate holder was then rotated to be per-pendicular to the direction parallel with the Ag target (9999purity) During the deposition the distance between Ag targetand substrate was 70mmeworking pressure wasmaintainedat 1Pa and the power was 120W Finally the films were de-posited for 10 minutes at various N2 contents in ArN2 at-mospheree samples numbered on the basis of N2 content areshown in the Table 1

e phase composition and crystallographic structure ofsilver thin films were analyzed by X-ray diffraction (XRD)measurement (MiniFlex made by Rigaku) with Cu K-αradiation source Surface and cross-sectional morphologiesof silver thin films were recorded by using a scanningelectron microscope (SEM Hitachi S-4800) e surfacechemical compositions of the silver thin films were studied

by the K-ALPHA X-ray (ermo Fisher Scientific) photo-electron spectroscopy (XPS) instrument e sheet re-sistance of silver thin films on Si substrates was measured bya four-point probe (RTS-8) e resistivity was calculatedaccording the following formula

ρ Rsd (1)

where d is the thickness of the film measured by SEM and Rsis the sheet resistance of the film

3 Results and Discussion

31 Crystal Orientation of Silver in Films Figure 1 showsX-ray diffraction patterns of silver thin films on Si substratese value of ordinate was set same in order to compare the Agpeak intensity of all samples easily In Figure 1 high Ag (111)and (200) diffraction peaks are found clearly in all samplese Si substrate peak is so high that Ag (220) (311) and (222)diffraction peaks could not be observed in almost all samples

e phase of nitride is not detected by XRD which is inaccordance with the results of XPS spectra that are shown inFigure 2 Considering all the samples were exposed in airbefore XPS characterization the sample was etched 5minutes by Ar+ (2 keV) to exclude the absorptions of C Nand O elements from the air As seen from the wide-scanspectra of S0 S33 and S100 in Figure 2(a) only Ag isobserved e high-resolution spectra of Ag 3d and thecorresponding fitting curves are shown in Figure 2(b) thearea ratio of the Ag 3d32 and Ag 3d52 peaks is about 23 andthe binding energy of Ag 3d32 and Ag 3d52 is 3744 eV and3684 eV respectively which agrees with the binding energyof metallic Ag [13 14] Based on the results of XRD and XPSno nitride and oxide exist in the thin film and pure silverthin films were obtained in pure N2 atmosphere

It is clear that the relative intensities of Ag (111) and(200) diffraction peaks are different for silver thin filmsprepared at different N2 contents in Figure 1 Preferredorientation exists in all samples In order to explain thedegree of the silver thin filmsrsquo preferred orientation thetexture coefficients of (111) plane and (100) plane (P(111) andP(100)) were represented quantitatively by the Harris methodin the following formula [15 16]

P(hkl)i

I(hkl)i

I0(hkl)i

1n

1113944

n

1

I(hkl)i

I0(hkl)i

⎡⎣ ⎤⎦minus 1

(2)

where I0(hkl)i is the standard intensity of the (hkl) plane forthe ith peak from powder diffraction file (PDF) card I(hkl)i isthe detected intensity of the (hkl) plane for the ith peak andn is the total number of diffraction peaks considered in theanalysis ICSD card no 04-0783 of Ag was used in thiscalculation and other peaks were so weak that only (111)and (200) peaks were considered e values of P(111) andP(100) of silver thin films on Si substrates depending upon theN2 content are shown in Figure 3 (P(111) +P(100) 2) evalue of P(100) suddenly increases when the N2 contentchanges from 0 vol to 125 vol and slightly increaseswith the increasing N2 content ranging from 125 vol to333 vol When N2 content exceeds 333 vol P(100)




G kλ

β cos θ (3)



G G(111)P(111) + G(200)P(100)

2 (4)





S100

S66

S50

S33

S12

S8

S0

Inte

nsity

(au

)

(400)clubs

30 40 70 8050 90602θ (deg)

(200)

(111)

clubs SiAg







S100S33S0

Inte

nsity

(au

)



Ag 3d3Ag 3d5

(a)

Inte

nsity

(au

)

Binding energy (eV)

380 378 376 374 372 370 368 366 364 362 360

S100

S33

S0

3744 eV3684 eV

Ag 3d32

Ag 3d52

(b)


P(100)

P(111)

0002040608101214161820

P (10

0)


00

02

04

06

08

10

12

14

16

18

P (11

1)


G(111)G(200)

G


25303540455055

6560

707580859095

Gra

in si

zes (

nm)







ρ ρ0 1 +32

times1G

timesR

1 minus R1113876 1113877 (5)







λ kT

2

radicπd2P

(6)





I II

16

18

20

22

24

26

28

30

Resis

tivity

(microW

middotcm

)




4 Conclusions



Data Availability




Acknowledgments


References


Ag targetAr N2

Ar+endash

N+N2+


Transport

Deposition

Sputtering

E k d

ecre

ases

due

to co

llisio

n

High

High

Low

Low

Ek


Top view Top view

Initial state

Final state

Hole

Ag clusters

(100)(111)

Ionization rate





























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls






G kλ

β cos θ (3)



G G(111)P(111) + G(200)P(100)

2 (4)





S100

S66

S50

S33

S12

S8

S0

Inte

nsity

(au

)

(400)clubs

30 40 70 8050 90602θ (deg)

(200)

(111)

clubs SiAg







S100S33S0

Inte

nsity

(au

)



Ag 3d3Ag 3d5

(a)

Inte

nsity

(au

)

Binding energy (eV)

380 378 376 374 372 370 368 366 364 362 360

S100

S33

S0

3744 eV3684 eV

Ag 3d32

Ag 3d52

(b)


P(100)

P(111)

0002040608101214161820

P (10

0)


00

02

04

06

08

10

12

14

16

18

P (11

1)


G(111)G(200)

G


25303540455055

6560

707580859095

Gra

in si

zes (

nm)







ρ ρ0 1 +32

times1G

timesR

1 minus R1113876 1113877 (5)







λ kT

2

radicπd2P

(6)





I II

16

18

20

22

24

26

28

30

Resis

tivity

(microW

middotcm

)




4 Conclusions



Data Availability




Acknowledgments


References


Ag targetAr N2

Ar+endash

N+N2+


Transport

Deposition

Sputtering

E k d

ecre

ases

due

to co

llisio

n

High

High

Low

Low

Ek


Top view Top view

Initial state

Final state

Hole

Ag clusters

(100)(111)

Ionization rate





























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls








S100S33S0

Inte

nsity

(au

)



Ag 3d3Ag 3d5

(a)

Inte

nsity

(au

)

Binding energy (eV)

380 378 376 374 372 370 368 366 364 362 360

S100

S33

S0

3744 eV3684 eV

Ag 3d32

Ag 3d52

(b)


P(100)

P(111)

0002040608101214161820

P (10

0)


00

02

04

06

08

10

12

14

16

18

P (11

1)


G(111)G(200)

G


25303540455055

6560

707580859095

Gra

in si

zes (

nm)







ρ ρ0 1 +32

times1G

timesR

1 minus R1113876 1113877 (5)







λ kT

2

radicπd2P

(6)





I II

16

18

20

22

24

26

28

30

Resis

tivity

(microW

middotcm

)




4 Conclusions



Data Availability




Acknowledgments


References


Ag targetAr N2

Ar+endash

N+N2+


Transport

Deposition

Sputtering

E k d

ecre

ases

due

to co

llisio

n

High

High

Low

Low

Ek


Top view Top view

Initial state

Final state

Hole

Ag clusters

(100)(111)

Ionization rate





























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls








ρ ρ0 1 +32

times1G

timesR

1 minus R1113876 1113877 (5)







λ kT

2

radicπd2P

(6)





I II

16

18

20

22

24

26

28

30

Resis

tivity

(microW

middotcm

)




4 Conclusions



Data Availability




Acknowledgments


References


Ag targetAr N2

Ar+endash

N+N2+


Transport

Deposition

Sputtering

E k d

ecre

ases

due

to co

llisio

n

High

High

Low

Low

Ek


Top view Top view

Initial state

Final state

Hole

Ag clusters

(100)(111)

Ionization rate





























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls





4 Conclusions



Data Availability




Acknowledgments


References


Ag targetAr N2

Ar+endash

N+N2+


Transport

Deposition

Sputtering

E k d

ecre

ases

due

to co

llisio

n

High

High

Low

Low

Ek


Top view Top view

Initial state

Final state

Hole

Ag clusters

(100)(111)

Ionization rate





























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls






























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls




understandingthepreferredcrystalorientationofsputtered...

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