Hardness of compositionally nano-modulated TiN films

NanoStructured Materials, Vol. 12, pp. 807-810, 1999 Elsevier Science Ltd Q 1999 Acta Metallurgica Inc. Printed in the USA. All rights reserved 09659773199lSsee front matter

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HARDNESS OF COMPOSITIONALLY NANO-MODULATED TiN FILMS E.Kusano, MXitagawa,ASatoh, T.Kobayashi,ENanto, and A.Kinbara Kanazawa Institute of Technology, AMS R&D Center Yatsukaho, Matto, Ishikawa, Japan e-mail:[email protected] Absku&-Compositionally nano-modulated f?Ims have been deposited by a reactive gas frow rate modulation sputtering using a lI target and N, gas. The explored modulation periods ranged fim 6.7nm to 8Onm. The thickness of the modulated layer was 400nm. A i’?Ofl underlapr with a thickness of IOOnm was depositedfor the entire sample jlms. By the X-ray d@action measurements, it was found that jilms consisted of polyctystalline E and l’iN mixWes for the periods longer than I Onm and of monolithic EN for the periods of 67nm and 8nm. The X-ray photoelectron spectroscopy results for the film with a modulation period of 8Onm showed that the N concentration in metallic layers was about 30% and that of the nitria’ed layers was about 45%. The maximum hardness of 11.2GPa was obtained at a modulation period of I Onmfor an indenter load of 2.94mN by nanoindentation. This value is larger than that obtainedfor a monolithic ENJlm (8.4GPa). 01999 Acta Metallurgica k.

INTRODUCTION It has been reported that the hardness of coatings can be enhanced by using nanolaminated rtmltilayer structures (l-3). The mechanisms involved in the hardness enhancement have been described by the effects based on the difference in mechanical properties of two alternatively laminated films. Since the interface seems to play an important ro1.ein an enhancement of the properties, it is expected that the films with stronger lamination, with a large number of repeated layers, provide better tribological properties. A compositionally modulated multilayer film without any abrupt interfaces is one of the films of this type. It has been reported that the hardness of the TiN/Ti nano-modulated films deposited by a reactive gas flow rate modulation sputtering yield a maximum hardness for an optimized modulation period (4). The modulation sputtering is the method to obtain ompositionally gradient multilayered film by using a combination of a metal cathode and a reactive gas (5). In this study, hardness enhancement for compositionally nano-modulated TiN multilayer coatings has been studied in conjunction with the film structures. In addition, to estimate elastic and plastic properties of the nano-laminated films, the ratio of the dissipated energy to the loaded energy during the nanoindentation process has been obtained. 807

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EXPERIMENTAL Film preparation

The sputtering apparatus used in this experiment was a batch type sputtering machine L-lOOS-FH(ANELVAcarp.). The target was a 75mm diameter Ti (99.98%). The discharge current was kept at 0.4A throughout the deposition runs. The working gases were Ar(99.9999%)and N,(99.9999%). The argon partial pressure was kept at 0.4Pa throughout the deposition runs. Nitorogen flow rate was changed to the desired values by a computercontrolled mass flow controller (‘Qpe FC-770AC, Nippon Aera) to obtain sinusoidal compositional-distribution. Total pressure was measured with a BARATRON TYPE690 capacitance manometer (MKS). The thickness of the modulated layer was 5OOmnincluding a 1OOmnTiOfi underlayer which was deposited to prevent adhesive failure that had been observed for a compositionally nano-modulated TiN multilayer film deposited directly onto the substmte in a preparatory experiment. Substratesused for the deposition were al~osilicate glass. The flow control patterns of Nz to obtain a film with a compositional modulation were determined based on the hysteresis curve in deposition rate or Ti emission intensity with the increase and decrease of the Nz gas flow rate in the range of 0 to 2sccm. The maximum flow mtc of Nz to deposit the nitride layer was lsccm. The minimum flow rate of Nz to deposit the metallic layer was 0.25sccm. Film Estimation

Film composition depth profiles were obtained by X-ray photoelectron spectroscopy (XPS) using the PHI ESCA-5600Ci. The Ar* ion beam with an incident angle of 45Owas also used for etching. The average etching rate during the XPS measurement was 1.7nmAnin for an Ar’beam with energy of 4.OkVand with a beam current of 6.5nA The film &ucture was examined by X-ray diffraction (XRD)using RlNT Ultima type dif&tmeter (Rigaku). Film hardness was measured with a nanoindentation tester ENT-1040 (Elionix Inc.). The test loads ranged from 2.94 to 4.9OmN for all measurements. Hardness values were obtained from a maximum displacement under an applied load and were an average of 5 measurement runs. The stylus used for the measurement was a Mngular diamond pyramid with the angle of 11So. The ratio of the dissipated energy to the applied energy during the indentation was also obtained from the load-displacement curve during the loading/unloading process. The difference of the energies loaded and put back during the indentation process is the energy used to cause the plastic deformation or dissipated through the sample film.

RESULTS AND DISCUSSION

Figure 1 shows XRD measurement results as a function of the modulation period. It was found that flhns consisted of polycrystalline Ti and TiN mixtures for modulation periods

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longer than 1onm and of monolithic TiN for modulation 2 periods of 6.7nm and 8nm (not ‘I shown in the figure). IllDnOlithiC Tii Figure 2 shows the XPS ’1 6.71nn $ deqth profiles obtained for the film 1Onm with a modulation period of 8Onm. EE The results showed that the film 8Omn consisted of a multilayer without IXlOIKWhiC a 2. abrupt interfaces and that the N concentration in metallic layers 40 20(& 80 was about 30% and that of the nitrided layers was about 45% for FIG.1 XRDresulti for wmpositicnallynanc-mcdulatedTiN films with modulationperiods from 6.7 to 8Onm and for the film with a modulation period monolithicTi and Tfi films of 8Omn. Figure 3 shows the film hardness as a function of modulation period for the stylus load from 2-94 to 9.8OmN.The hardness shows its maximum for the modulation period of 1Onmfor all stylus loads. The stylus load of 2.94mN yielded the maximum of 11.2GPa for the film with the period of 1Onm.This value is 1.3 times larger than that obtained for the monolithic ‘I’iNfilm. The modulation period that yields the maximum bardness is in good agreement with those reported previously (l-4). The hardness measwmen t results shows tbat the hardness of the nano-modulated film strongly depends its modulation period. The young’s modulus also showed a maximum for the films with a modulation period of 1Onm. The value was about 230GPa for a stylus load of 2.94mN. Figure 4 shows the changes in the ratio of the dissipated energy to loaded energy during the loading/unloading process of the nanoindentation, as a function ofthe modulation period for the maximum stylus load of 2.94mN. The ratio showed a minimum of 26% for the

0

100 200 300 400 500 600 Sputtaret~hing timo(min)

FIG.2 XPS depth profile for the compcsitionallynano-modulatedTii film with a mcdulationperiodof SOrun.

‘K IIN 0

I. 20 Mod&ion

I. 40

I. 60

80

pohd(mn)

FIG.3 Hardnessof compositionally nanomodulated TiN films as a function of mcdulaticnperiodand of monolithicTi and TiNfilms.

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film with a modulation period of 8mn and was about 39% for the films with modulation periods longer than 30nm. The results imply that the film with the modulation period of 8mn is most elastic, assuming that the most of the energy dissipated is used for plastic deformation. The sharp minimum shows that affects the compositionally - modulation strongly elastic and plastic behavior of the film.

Jn&ntation Load : 2.94mN 1

I,,lICl .

.

TiTiNO

20

40.60

80

Modul&n Peficd (nm)

CONCLUSION

FIG.4 Ratio of the dissipated to the loaded energy during the loadinghmloading process ..n Compositionally nauo-modulated filma of nanoindentation for compositionally naw have been deposited by a reactive gas flow rate modulated films as a fimction of the modulation period and for monolithic Ti and m~ulhm Sputtering Using a Ti target and h. gas. The maximum hardness of 11.2GPa was TIN fih~.

obtained at a modulation period of 1Omn for an indenter load of 2.94mN. This value is larger than that obtained for a monolithic TiN film (8.4GPa). The ratio of the dissipated energy to the loaded energy during the indentation showed a minimum of 26% for the fihn with a modulation period of 8mn and was about 40% for the films with modulation periods longer than 30nm. For compositionally nanomodulated TiN films, the film hardness as well as the energy dissipated during a loading/unloading process of the indentation depends on the modulation period.

ACKNOWREDGEMENTS The financial support for the Advanced Materials Science R&D Center of Kanazawa Institute of Technology from the Ministry of Education, Science aud Culture of Japan is highly appreciated.

REFERENCES 1. Helmersson, U., Todorova, S., Barnett, S.A., Sundgren, J.-E., Markett, L.C., and Greene, J.E., J.Appl.Phys., 62,481,1987 2. Shim, M., Huhman, L., aud Barnett, S.A., JMaterRes.,_l, 901, 1992 3. Chu, X., Bar&t, S.A., Wong, M.S., aud Sproul, W.D., Sur$Coat. Technol., X!, 13,1993 4. Kusano, E., Kinbara, A., Kondo, I., J.Non-Crystalline Solids, 2l.8, 58, 1997 5. Kusano, E., Kitagawa, M., Nanto, H., Kinbara, A., J. Vac.Sci.Technol. A, in presss