Dauchot, J.P.

Del Re, M.

Gouttebaron, R.

Hecq, M.

Leclere, P.

Terwagne, Guy

Zirconium nitride films are deposited onto borosilicate wafers by reactive magnetron sputtering. The films are analysed in situ by X-ray photoelectron spectroscopy (XPS). We have studied by XPS the effects of the nitrogen partial pressure (1'100%), the subtract temperature (ambient to 450 °C), and biasing (0'80 W) on the stoichiometry of ZrN films. The N1s peak is composed of three components at 397.2, 396.4 and 395.8 eV in binding energy. These components are correlated with the three existing phases of zirconium nitride (ZrN, Zr3N4 and ZrN2). With an increase of the nitrogen partial pressure, a shift of the Zr3d line to the high binding energy and the increase of the N1s component at 395.8 eV are observed. These observations are explained by the charge transfer between Zr to N which increases with P(N2) as previously described for the Ti'N2 system [1]. The bulk stoichiometry is calculated by Rutherford backscattering and nuclear reaction measurements. The resistivity of the films is measured by the four-point probes technique. The reflectivity of the films are recorded by a spectrophotometer in the IR'Vis range. A correlation between the reflectivity and the resistivity is observed. The roughness of the films is measured by atomic force microscopy. The bias voltage has a great influence on the surface roughness and on the reflectivity of the films. The dependence of the ZrNx films structure and morphology with the discharge parameters is established

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RESEARCH OUTPUTS / RÉSULTATS DE RECHERCHEAuthor(s) - Auteur(s) :Publication date - Date de publication :Permanent link - Permalien :Rights / License - Licence de droit d’auteur :Bibliothèque Universitaire Moretus PlantinInstitutional Repository - Research PortalDépôt Institutionnel - Portail de la Rechercheresearchportal.unamur.beStudy of ZrN layers deposited by reactive magnetron sputteringDel Re, M.; Gouttebaron, R.; Dauchot, J.P.; Leclere, P.; Terwagne, Guy; Hecq, M.Published in:Surface and Coatings TechnologyPublication date:2003Document VersionPeer reviewed versionLink to publicationCitation for pulished version (HARVARD):Del Re, M, Gouttebaron, R, Dauchot, JP, Leclere, P, Terwagne, G & Hecq, M 2003, 'Study of ZrN layersdeposited by reactive magnetron sputtering', Surface and Coatings Technology, vol. 174-175, pp. 240-245.General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.            • Users may download and print one copy of any publication from the public portal for the purpose of private study or research.            • You may not further distribute the material or use it for any profit-making activity or commercial gain            • You may freely distribute the URL identifying the publication in the public portal ?Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Download date: 13. Nov. 2019Surface and Coatings Technology 174–175 (2003) 240–2450257-8972/03/$ - see front matter  2003 Elsevier Science B.V. All rights reserved.doi:10.1016/S0257-8972Ž03.00679-0Study of ZrN layers deposited by reactive magnetron sputteringM. Del Re *, R. Gouttebaron , J.-P. Dauchot , P. Leclere , G. Terwagne , M. Hecqa, a a b c a`Laboratoire de Chimie Inorganique et Analytique, Universite de Mons-Hainaut, Parc Initialis, Av. Copernic 7000 Mons, Belgiuma ´Service de Chimie des Materiaux Nouveaux, Universite de Mons-Hainaut, Parc Initialis, Av. Copernic 7000 Mons, Belgiumb ´ ´Laboratoire d’Analyse par Reactions Nucleaires, FUNDP, Rue de Bruxelles, 61 5000 Namur, Belgiumc ´ ´AbstractZirconium nitride films are deposited onto borosilicate wafers by reactive magnetron sputtering. The films are analysed in situby X-ray photoelectron spectroscopy (XPS). We have studied by XPS the effects of the nitrogen partial pressure (1–100%), thesubtract temperature (ambient to 450 8C), and biasing (0–80 W) on the stoichiometry of ZrN films. The N1s peak is composedof three components at 397.2, 396.4 and 395.8 eV in binding energy. These components are correlated with the three existingphases of zirconium nitride (ZrN, Zr N and ZrN ). With an increase of the nitrogen partial pressure, a shift of the Zr3d line to3 4 2the high binding energy and the increase of the N1s component at 395.8 eV are observed. These observations are explained bythe charge transfer between Zr to N which increases with P(N ) as previously described for the Ti–N system w1x. The bulk2 2stoichiometry is calculated by Rutherford backscattering and nuclear reaction measurements. The resistivity of the films ismeasured by the four-point probes technique. The reflectivity of the films are recorded by a spectrophotometer in the IR–Visrange. A correlation between the reflectivity and the resistivity is observed. The roughness of the films is measured by atomicforce microscopy. The bias voltage has a great influence on the surface roughness and on the reflectivity of the films. Thedependence of the ZrN films structure and morphology with the discharge parameters is established.x 2003 Elsevier Science B.V. All rights reserved.Keywords: XPS; RBS; Reactive magnetron sputtering; ZrN1. IntroductionThe thermal insulation techniques of windows havebeen enhanced due to the development of thin filmssputter deposition. ZrN is known to be a good reflectivematerial in the IR wavelength range w2x. It is due to themetallic structure of the stoichiometric ZrN. This prop-erty is interesting for applications in thermal insulationcoatings. Thin films are deposited by various methods:evaporation, spray pyrolysis, chemical vapour depositionand sputtering. In the present work, we study thesputtering of a zirconium target in a mixture of AryN2direct current magnetron discharges. X-ray photoelectronspectroscopy (XPS), Rutherford backscattering (RBS)and NRA are used to characterize the composition ofthe films. The resistivity is given by the four pointsprobe technique. The reflectivity of the films are record-ed in the IR–Vis range. The roughness of the films ismeasured by atomic force microscopy (AFM). We have*Corresponding author. Tel.: q32-65-37-38-51; fax: q32-65-37-38-41.E-mail address: michael.delre@umh.ac.be (M. Del Re).correlated the shapes and positions of the XPS peakswith the stoichiometries of the ZrN films.x2. Experimental detailsThe ZrN films are deposited by d.c. reactive magne-tron sputtering. The target–substrate distance is 15 cm.The substrate is a borosilicate glass of 1 cm cleaned2with a Balzers substrate cleaner 1 and 2. The experi-mental system is described elsewhere w3x. The lowpressure is obtained by means of a turbomolecular–diaphragm pump combination. The ultimate vacuumpressure is approximately 10 Torr. The sputtering gasy7is an argonynitrogen mixture and the pressure is regu-lated with a throttlevalve. The gas inlet is situated infront of the substrate holder. Two gas flow controllersmaintain the argon and nitrogen flows in the chamber.A continuously variable power supply MDX 500 is usedas the power source. The target current is set at 200mA. The target voltage is fluctuating (f250 V) withthe nitrogen partial flow. Zirconium disk (99.2% purity)of 1.3 inch in diameter is used as target. The deposition241M. Del Re et al. / Surface and Coatings Technology 174 –175 (2003) 240–245Fig. 1. Stoichiometry vs. P N .2Fig. 2. (a) ZrN without bias, profile, after air contamination; (b) ZrN with bias, profile, after air contamination.rate is measured using a quartz microbalance. All theexperiments have been performed under UHV, there isno air contamination of film surfaces before XPS anal-ysis. The samples are transferred under UHV into anESCA analysis chamber. XPS was performed on a VG-ESCALAB 220iXL spectrometer. The pressure in theanalysis chamber was typically 8=10 Torr. Atomicy11composition were derived from peak areas by usingphotoionisation cross section calculated by Scofield w4x,corrected for the dependence of the escape depth on thekinetic energy (KE) of the electrons (assumed to havethe form lsKE ) and corrected for the analyser0.6transmission function of our spectrometer. The diameterof the Al Ka X-ray beam is 250 mm. The scan numberfor each XPS area corresponding to all the film elementsvaries from 10 to 15. RBS and NRA measurementswere performed on the Tandetron 2 MV (ALTAIS) at¨´the LARN. For RBS measurements, the energy of theincident particles ( He ) is 2.0 MeV. This technique is4 2qsuitable for the quantification of heavy atoms like Zr.Otherwise, for the NRA measurement, the energy of theincident particles is raised to 4.8 MeV. This techniqueis preferred for the quantification of light atoms like Nor O. Simulated curves are compared to the experimentalones to quantify the atomic composition of the films.AFM measurements were performed on a NanoscopeIIIa microscope in the tapping mode. The root meansquare (RMS) deviation are calculated from severalpictures taken on each sample w10x. This measure isassimilated to the roughness of the film surface. Theanalysed surface is varied from 25 to 1 mm .23. Results and discussion3.1. StoichiometryWe have studied ZrN coatings deposited at roomtemperature under different nitrogen partial pressure (1–100%). The total pressure is fixed at 8 mTorr. The ZrNfilms are synthesized with and without bias voltage ofy200 V and analysed by XPS. Whatever the experi-mental conditions may be, oxygen traces are detectedon the films surfaces (f4% at.) and on the bulk films(f2% at.). This low oxygen contamination of the filmscan be explained by the extreme reactivity of Zr inrelation to H O still present as traces in the residual gas2phase of the preparation and transfer chambers (10y7Torr). The results are shown on Fig. 1. Without bias,the ratio NyZr is under 1 until 15% of nitrogen andgoes to 1.07 at 100%. The addition of a bias of 200 Vinduces a decrease of the ratio. It stays under 1 for allthe nitrogen partial pressure. It is due to the preferentialsputtering of the nitrogen in the growing film. We haverealized an XPS depth profile of ZrN films synthesizedwith and without bias voltage and after air contamination(Fig. 2a and b). We can observe that the films synthe-sized without any bias are oxidised through all the bulk.The final stoichiometry reaches ZrN O . On the other0.5 0.5hand, the films synthesized with bias contents only 6%of oxygen in the bulk. It is due to the porosity decreaseof the films when bias is added during deposition. Theoxygen diffusion in the bulk film is decreased.The N1s XPS spectrum shows three components at397.1 eV (1) in binding energy, 396.4 eV (2) and 395.8242 M. Del Re et al. / Surface and Coatings Technology 174 –175 (2003) 240–245Fig. 3. N1s peak fit.Table 1Bulk stoichiometries of the ZrN films obtained by RBS and NRAEch. PN2 (%) Bias (V) Zr (%) N (%) O (%) Stiochio princ1 1 250 46 46 7 ZrN2 3 250 50 47 2 ZrN3 50 250 43 51 4 ZrN1,24 100 250 30 57 13 ZrN25 1 0 36 34 30 ZrNO6 3 0 36 32 32 ZrNO7 50 0 36 60 4 ZrN28 100 0 35 60 5 ZrN2Fig. 4. (a) Quantification of the N1s XPS peak, film synthesized with bias; (b) quantification of the N1s XPS peak, film synthesized withoutbias.eV (3) (Fig. 3: at 4% N2, y200 V bias). In somepapers w1,2x, the component (1) is attributed to the ZrNstoichiometry while the component (2) is attributed tozirconium oxynitride w5x. But in an other paper w6x, thecomponent (2) corresponds to the Zr N stoichiometry.3 4The component (3) could be attributed to an over-stoichiometry like ZrN . We have followed the evolution2of these three components areas with the increase of thenitrogen partial pressure in films synthesized with biasand without bias (Fig. 4a and b, respectively). Theseevolutions are quite different depending on whether thedeposition is done with or without bias voltage. In bothcases, the area of the component (1) is higher than theothers until a nitrogen partial pressure of 40%. On theother hand, the area of the component (2) increasesonly with bias voltage. At 100% of nitrogen, the ratiobetween area (3) and (1) is almost 3 with bias while itis under 2 without bias. The components (2) and (3)correspond to phases which appear when the sputteredatoms arriving on the film surface receive an energysupply thanks to the bombardment of the growing filmby positive ions (Ar , N ). These two componentsq q2could correspond to the over-stoichiometric metastablephases of the ZrN (Zr N and ZrN ). A chemical shiftx 3 4 2to the high binding energy of the Zr3d XPS peak withthe nitrogen partial pressure increases has been observed(Fig. 5). The Zr3d peak goes from 179.6 eV at 1% ofnitrogen partial pressure to 180.6 eV at 100%. Thesekind of shift has already been observed for TiN filmssputtered by N ions w1x. The absence of the oxydeq2components in the Zr3d peaks (located at 182.2 eV and184.6 eV in binding energy) turns down the oxynitridehypothesis. From the XPS results, zirconium nitridefilms synthesized with bias voltage are made of overstoichiometric metastable phases (Zr N , ZrN ). But the3 4 2atomic composition derived from peak areas (calculatedby the method describes at point 2) shows that nitrogenyzirconium ratio is always lower than 1. In order tounderstand this result, the stoichiometry of the films hasbeen measured using another techniques, RBS and NRAw7x. The combination of these techniques gives thestoichiometry of the films which varies from ZrN toZrN when the N percentage increases from 1 to 100%2 2(Table 1).The under-estimated stoichiometry results obtained byXPS can be explained by the approximation of theelectron mean free path to KE from the universal0.6curve (at 1 KE, strong variations of l depending on thenature of the analysed components), the sensitivityfactor used (Scofield rather than Wagner). This pointhas still to be improved.243M. Del Re et al. / Surface and Coatings Technology 174 –175 (2003) 240–245Fig. 5. Chemical shift of the Zr3d XPS peak with nitrogen.Fig. 6. Isoresistivity curves obtained by DESIGN-EXPERT .Fig. 7. Reflectivity of ZrN films.A correlation between the bulk stoichiometries of thefilms and the Zr3d and N1s XPS peaks shapes andpositions has been observed. We can also conclude thatthe component (1) of the N1s peak is correlated to aZrN stoichiometry. The component (3) is correlated toa ZrN stoichiometry. Otherwise, the component (2) is2not yet well defined.3.2. ResistivityWe have studied the influence of the bias voltage andthe substrate temperature on the films resistivity. Thenitrogen partial pressure is fixed at 3.5% to stay in theZrN stoichiometry. The total pressure is 8 mTorr andthe target current is fixed at 200 mA. The DESIGN-EXPERT software has been used to reduce the experi-ments number w8x. It is a statistical tool that allows usto calculate the dependence of the resistivity on differentparameters (temperature, bias voltage). The ranges ofstudied temperatures and bias are (80–450 8C) and(y50 to y450 V). The isoresistivity curves are shownon Fig. 6. This statistical tool pointed the strong influ-ence of the bias on the resistivity. A theoretical minimumof 70 mV cm has been located at y350 V and 380 8C.3.3. ReflectivityThe relative reflectivity (the reference sample is asilver film of 50 nm deposited onto borosilicate) of ZrNfilms has been measured on the same samples used forthe resistivity measurements. We have investigated theinfluence of the bias voltage and substrate temperatureon the film reflectivity. The wavelength range is (300–2000 nm). Fig. 7 shows an example of the results. Thesample 13 has been synthesized at y350 V and 3508C, the sample 1 at y200 V and 80 8C and the sample5 at y90 V and 260 8C. Afterwards, we have measuredthe reflectivity of the films at 1500 nm. The results havebeen analysed by the DESIGN-EXPERT software. Theo-retical isoreflectivity curves has been calculated by thesoftware. A maximum of reflectivity at 1500 nm hasbeen located at approximately y370 V and 390 8C. Itcorresponds approximately to the minimum of resistivity.It confirms the relation of Hagen–Rubens for the reflec-tivity and resistivity of metals w9x.3.4. RoughnessFinally, the samples have been analysed by AFM. Allthe pictures are quite similar (Fig. 8). The RMS devia-tion are calculated from several pictures taken on eachsample w10x. Here again, the results are treated by theDESIGN-EXPERT software. With the theoretical iso-roughness curves (Fig. 9), we can observe that the biasvoltage has a great influence on the roughness. Anoptimal bias appears at approximately y360 V. On theopposite, the roughness seems to be quite indifferent tothe substrate temperature. The fact that the roughness isincreasing after a critical value of bias voltage isexplained as follows. The negative bias voltage of the244 M. Del Re et al. / Surface and Coatings Technology 174 –175 (2003) 240–245Fig. 8. AFM picture of ZrN film.Fig. 9. Isoroughness curves obtained by DESIGN-EXPERT .substrate induces a bombardment of the growing filmby the positive ions of the plasma. The collisions smooththe film surface and the roughness decreases. However,when the ions energy is too high, the film surface startsto be sputtered and the roughness increases again.4. ConclusionsWe have correlated the shapes and the positions ofthe XPS peaks with the stoichiometries of the ZrNxfilms thanks to the combination of XPS, RBS and NRAtechniques. The positions of the N1s and Zr3d peakscorresponding to the ZrN and ZrN stoichiometries have2been defined.The measurements of the roughness, resistivity andreflectivity of the ZrN films have pointed a substratetemperature and bias voltage limits. Over these limits,these three parameters deteriorate. We have observedthat a substrate temperature of approximately 350 8Cand a bias voltage of y350 V allows us to obtain aZrN film with optimum features.For industrial applications of these results, the opti-mum conditions in bias voltage and substrate tempera-ture must be adjusted to the real coating equipment andall coating conditions.AcknowledgmentsM. Del Re thanks the Fonds pour la Recherche dansl’Industrie et l’Agriculture (FRIA, Brussels) for finan-cial support.Referencesw1x I. Bertoti, S.O. Saied, Surf. Interface Anal. 21 (1994) 467–473.w2x L. Pichon, T. Girardeau, A. Straboni, F. Lignou, P. Guerin, J.´Perriere, Appl. Surf. Sci. 150 (1999) 115–124.`w3x V. Vancoppenolle, P.-Y. Juan, M. Wautelet, M. Hecq, J. Vac.Sci. Technol. A 17 (6) (1999) 3317–3321.w4x A. Tarniowy, R. Mania, M. Rekas, Thin Solid Films 311(1997) 93–100.w5x P. Prieto, L. Galan, J.M. Sanz, Surf. Interface Anal. 21 (1994)395–399.w6x J.M. Sanz, L. Soriano, P. Prieto, G. Tyuliev, C. Morant, E.Elizalde, Thin Solid Films 332 (1998) 209–214.245M. Del Re et al. / Surface and Coatings Technology 174 –175 (2003) 240–245w7x G. Terwagne, J. Colaux, G.A. Collins, F. Bodart, Thin SolidFilms 377–378 (2000) 441–446.w8x Optimisation des conditions operatoires de la spectrometrie de´ ´masse des decharges electriques magnetrons par la methodol-´ ´ ´ ´ogie des plans d’experiences Sabine Springael, Memoire de´ ´Licence en Sciences Chimiques, 1994.w9x Charles Kittel, Physique de l’etat solide, Editions DUNOD,´301.w10x Pascal Viville, Analyse par Microscopie a force atomique de`biomateriaux polymeres a surface heterogene Ph.D. Thesis,´ ` ` ´ ´ `UMH, 1997.

Study of ZrN layers deposited by reactive magnetron sputtering

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Study of ZrN layers deposited by reactive magnetron sputtering

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