IEAE CRP F1.20.16. Ion Beam Modification of Insulators 3rd RCM, Chiang Mai, Thailand, 10-14 Dec 2007 Ion Beam Modification of Sputtered Metal-Nitride Thin Films - a Study of the Induced Microstructural Changes VINČA Institute of Nuclear Sciences, Belgrade, Serbia - project started in May 2006 - researchers: Momir Milosavljević (Dr) Davor Peruško (PhD student) Maja Popović (MSc student) Mirjana Novaković (MSc student) other co-workers in the group: Velimir Milinović (Dr – Goett) Bane Timotijević (Dr-Surrey)

Investigations on this Project - started in May 2006 - Ion beam modification of Cr-N and TiN thin films on Si reactively sputtered, ~ 250 nm, implanted with 120 keV Ar Deposition of TiN coatings on pre-implanted stainless steel, 40 KeV nitrogen, 1.3 mm TiN coatings subsequently deposited Ion beam modification of Al/Ti and AlN/TiN multilayers on Si, with 200 keV Ar or N2 ions

VINČA Institute of Nuclear Sciences

Lab for Atomic Physics - research facilities used for this Project -

Balzers SPUTTRON II thin film deposition system d. c. and r. f Balzers SPUTTRON II thin film deposition system d.c. and r.f. sputtering, four target, rective deposition

Ion implanter – HV terminal 500 kV, Nielsen or RF ion sources for gases and solids, beam current 1-100 mA, scanned target area up to 5 cm diameter

2MV Van de Graaff ion accelerator RBS – beam line in preparation

TEM – Philips EM400T 120 keV

Multimode NanoScope 3D, STM, AFM, MFM… VEECO NANOINDENTER

Results to be presented - from the start of this project - Ion beam modification of Cr-N and TiN thin films on Si reactively sputtered, ~ 250 nm, RT or 150oC, different N2 pressure, implanted with argon at 120 keV, to 1x1015 and 1x1016 ions/cm2 Deposition of TiN coatings on pre-implanted stainless steel – AISI C1045 steel substrates implanted with 40 KeV nitrogen, to 5x1016 – 5x1017 ions/cm2, 1.3 mm TiN coatings subsequently deposited Ion beam modification of Al/Ti and AlN/TiN multilayers on Si, with 200 keV Ar or N2 ions, to 5x1016 – 2x1017 /cm2

Ion beam modification of Cr-N films on Si RBS spectra of as-deposited films as a function of N2 pressure (Goettingen)

RBS analysis of as-deposited and implanted Cr-N/Si Ar

XRD analysis => for PN2 = 2 and 3.5x10-4 mbar, Cr2N is formed for PN2 = 5x10-4 mbar, CrN phase forms as-deposited 1x1015 Ar/cm2 1x1016 Ar/cm2 analysis of samples deposited at 150oC, PN2 = 5x10-4 mbar, implanted to 1x1015 and 1x1016 Ar/cm2

X-TEM analysis of Cr-N deposited at 150oC, PN2 = 5x10-4 mbar as-deposited 1x1015 Ar/cm2 1x1016 Ar/cm2

Sheet resistance measurements of Cr-N films Samples deposited at 150oC RT 1500C

Ion beam modification of TiN films on Si RBS analysis of as-deposited films (Goettingen)

TEM analysis of TiN deposited at RT implanted 1x1016Ar/cm2 as-deposited

XRD analysis of TiN deposited at 150o C Sheet resistance measurements

Conclusions for Cr-N and TiN films Ion irradiation induces local rearrangements in the layer structure, the polycrystalline structure being retained Original columns become disconnected, nano-particles of the same phase are formed The resulting structures contain more crystalline defects (point defects in larger grains, nano-particles) which induce higher electrical resistivity No measurable changes in surface roughness were found Sheet resistance measurements can be useful to interpret the results of structural analysis

Nitrogen pre-implantation of steel substrates shallow implants at 40 keV unimplanted standard XRD of TiN coating 2x1017 5x1017 GXRD of implanted substrate

Microhardness measurements

Conclusions for substrate pre-implantation Low energy, high fluence nitrogen implants induce formation of Fe-nitrides in the near surface region of the substrates Substrate pre-implantation influences preferred orientation of the grown TiN crystal grains The layers deposited on pre-implanted substrate exhibit a higher microhardness Total increase of the substrate microhardness after nitrogen pre-implantation and TiN deposition is up to more than eight times

Ion beam modification of multilayered thin film structures nano-scaled multilayered structures TiN/Ti, TiN/AlN, etc, offer numerous advantages over single layer components higher performance at much lower thickness, higher strength and hardness due to multiple interfaces, can form super lattices, graded structures, etc ion beams can be useful for preparation and modification in the processes such as IBAD, plasma immersion, or ion implantation – homogenization, more dense and less porous structures

High fluence nitrogen implantation in Al/Ti multilayers on Si 10 alternative Al and Ti layers, deposited by ion sputtering in a single vacuum run, total thickness ~ 270 nm 200 keV N2+ ions, to 1x1017 and 2x1017 at/cm2, Rp ~ mid depth aim – to study interface mixing and formation of metal-nitrides N2+ ions Al/Ti multilayers Si

Experimental work Thin film deposition, ion implantation and TEM analysis – Vinča Inst RBS analysis, 1.5 MeV He+ beam, two detectors, 148.2o scatt in ibm and172.8o in cornel geometry, Data Furnace – University of Surrey AES primary electron energy 3 keV, two Ar ion guns for sputtering off 5x5 mm2 of the sample area – Jožef Stefan Inst, Ljubljana

RBS experimental spectra (Surrey)

as-deposited sample

sample implanted to 2x1017 N/cm2

1x1017 N/cm2 RBS depth profiles as deposited 2x1017 N/cm2

1x1017 N/cm2 AES depth profiles JS Institute as deposited 2x1017 N/cm2

x-TEM analysis as-deposited samples implanted to 2x1017 N/cm2

Conclusions for high fluence N implantation in Al/Ti multilayers Nitrogen implantation can be used to form (Al,Ti)N multilayered structures from Al/Ti layers The layers are intermixed => tightly bound at the interfaces, have graded composition, but the multilayered structure is preserved Ion irradiation induces larger grains and formation of lamellar grains stretching over a number of layers XPS studies are in progress to analyze chemical composition Microhardness results – shown below

Comparative analysis of ion irradiation stability of Al/Ti versus AlN/TiN multilayers Similar structures as described before, total thickness ~ 270 nm irradiated with 200 keV Ar+, from 5x1015 to 4x1016 ions/cm2 deposition of AlN/TiN done by reactive sputtering

RBS spectra of Al/Ti structures on Si (Surrey) as a function of Ar+ fluence

RBS analysis of Al/Ti sample irradiated with 200 keV Ar+, to 1x1016 ions/cm2

RBS analysis of AlN/TiN structures on Si (Surrey)

as-deposited sample

Titanium point by point depth profiles AlN/TiN structure Al/Ti structure

Interface mixing in Al/Ti system

TEM analysis of Al/Ti multilayers implanted to 2x1016 ions/cm2 as-deposited

TEM analysis of AlN/TiN multilayers as-deposited implanted to 4x1016 ions/cm2 implanted to 2x1016 ions/cm2

Other TEM images of AlN/TiN multilayers as-deposited implanted to 4x1016 ions/cm2 implanted to 2x1016 ions/cm2

Ion Beam Mixing models fo diffusio profiles: k = Δσ2 /Φ ξ = [4mM/(mM)2]1/2 – kinematic factor m, M – masses of the ion and target atom Γo = 0.608 – dimensionless constant N – atomic density of the target Rd  1nm – minimum separation distance for the production of a stable Frenkel pair FD – deposited energy per ion per unit length - Ballistic mixing: - Global spike mixing: k1=0.35 nm; k2=27.4 – constants ΔHr – reaction enthalpy ΔHcoh – cohesive energy of the reaction products - Local spike mixing: k1’ and k2’ – constants Zt – atomic number of the target

Microhardness measurements indentation depth ~ 200 nm AlN/TiN and Al/Ti implanted with Ar Al/Ti Implanted with N

A. Misra, M. J. Demkowicz, X. Zhang, and R. G A.Misra, M.J.Demkowicz, X.Zhang, and R.G.Hoagland, JOM, Sep 2007, 62-65 T. Höchbauer, A. Misra,a K. Hattar, and R. G. Hoagland, JAP, 98, (2005) 123516 Los Alamos National Laboratory Cu/Nb irradiated with high fluence He+, (33-150 keV helium, 1 × 10^17/cm^2)

Effects of swift heavy ion irradiation and thermal annealing on nearly immiscible W/Ni multilayer structure Sharmistha Bagchi , Satish Potdar, F. Singh, N. P. Lallaa (India) JAP, 102, (2007) 074310 W/Ni with 120 MeV Au9+, as-deposited and 5x1013 ions/cm 2

Conclusions for ion irradiation stability of Al/Ti versus AlN/TiN multilayers Both systems preserve multilayered structure Al and Ti are chemically reactive => the layers become progressively intermixed with increasing the ion fluence, formation of Al-Ti phases is detected; ion irradiation induces larger grains and formation of lamellar columns stretching over a number of layers In AlN/TiN system the components are immiscible => no detectable intermixing is observed, it is lower compared even to ballistic mixing, only a small increase of the mean grain size in individual layers can be seen Non-mixing, or de-mixing published so far only for immiscible metal layers Cu/Nb with He+, W/Ni with Au9+,

Presentations and publications: two at IBMM-2006, five at YUKOMAT 2006 and 2007, two at ECAART-9 2007, one at IBA 2007 three journal papers and three accepted for NIM B two papers submitted 2 Msci and 1 PhD thesis Joint UniS – Vinča Workshop on Ion Beam Applications for Materials Modification and Analysis – held in Vinča, Belgrade, 2nd September 2006, with 6 lecturers from Surrey, 2 from Germany, 1 from Hungary and 3 from Serbia, and a wide audience of local potential users Further work will be on investigations of multilayered structures prepared AlN/Al, TiN/Ti and Ta/Ti for further studies