Chiang Mai J. Sci. 2013; 40(5) 857

Chiang Mai J. Sci. 2013; 40(5) : 857-864http://it.science.cmu.ac.th/ejournal/Contributed Paper

Reactive Gas Feeding Technique in Deposition ofTitanium Nitride Film by Magnetron SputteringWitthawat Wongpisan*, Kanin Ruthairung, Autcharaporn Srion, Suphakan Kijamnajsukand Panadda SheppardNational Metal and Materials Technology Center, National Science and Technology Development Agency,Pathumthani, Thailand.*Author for correspondence; e-mail: witthaww@mtec.or.th

Received: 18 July 2012Accepted: 18 February 2013

ABSTRACTThe paper discusses the effect of the reactive gas feeding parameters in a magnetron

sputtering unit on the microstructural development of Titanium Nitride thin film. Inthis work, TiN films were deposited using DC reactive magnetron sputtering at substratetemperatures of 400oC, 200oC and at room temperature. The film fabrication employedfour feeding configurations for the N2 reactive gas. The nitrogen gas was fed through adistribution ring positioned above the Ti target into the plasma flux at 4 different distancesfrom the target resulting in different gas distribution patterns and also different levels ofgas warming prior to it entering the sputtering chamber. The effect of the plasma warmingof the reactive gas caused the sputtering reaction, and hence the phase formation of theTiN, to alter. XRD and SEM were utilized in the microstructural study of the TiNfilms. It was found that for type D N2 feeding configuration, where N2 enters thedeposition chamber at the middle of chamber, the lattice parameter of TiN film is notaffected by the substrate temperature ranging from RT to 400oC. In practice, this meansthat altering the gas feeding technique can help to reduce the variation in the film structurecaused by an uneven distribution in the substrate temperature.

Keywords: titanium nitride, reactive sputtering, gas feeding technique

1. INTRODUCTIONTitanium nitride (TiN) films deposited

using PVD (physical vapor deposition)techniques are useful material for surfaceengineering because of properties such ashigh hardness, good corrosion resistanceat room temperature and elevatedtemperatures, good thermal stability, lowfriction coefficient, good appearance andhigh electrical conductivity [1-5]. They have

been successfully employed as hardcoatings, diffusion barriers, optical coatingsand anti-oxidation coatings.

Three main sputtering parametersaffect the film structure, and consequentlythe properties of titanium nitride thinfilms. These are substrate temperature,range of nitrogen partial pressure and biasvoltage.

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The formation of TiN film dependson the supply of reactant N atoms fromthe plasma. N2 gas consists of diatomicmolecules. These molecules need todissociate into N atoms before reactingwith Ti atoms. This dissociation of N2

molecules and the subsequent reaction toform TiN requires plasma energy.However, the diatomic N2 molecules haveinternal rotational and vibrationalelectronic states that consume energy fromthe plasma [6].

In this paper, titanium nitride filmsprepared by DC pulse reactive magnetronsputtering using different nitrogen feedingconfigurations were investigated usingX-ray diffractometry (XRD) and scanningelectron microscopy (SEM). The workfocused on the effect of nitrogen feedingconfigurations on the microstructuralproperties of the TiN films.

2. EXPERIMENTAL METHODSTiN thin films were deposited on

silicon (100) substrates using differentnitrogen feeding configurations andsubstrate temperatures (RT, 200oC and400oC ) using pulsed direct current (DC)magnetron sputtering. Recently, pulsedsputtering has been developed for thedeposition of highly adherent, uniform anddense coatings of nitrides and oxides.Si (100) is the substrate. The schematicdiagram of a custom built magnetronsputtering system used in the present studyis given in Figure 1.

The sputtering was carried out in astainless steel chamber of 40 cm diameterand 60 cm depth. A 99.995% Ti disc of 50.8mm. (2") diameter and 3mm. thickness wasused as a sputtering target. The depositionchamber was evacuated to a base pressureof 5×10-6 mbar using a pumping systemconsisting of rotary and turbomolecular

pumps. Silicon substrates (size of20mm×15mm×0.5mm) were first cleanedusing soap solution and then ultrasonicallycleaned in acetone for 10 min and driedbefore being placed in the depositionchamber. The flow rates of Ar (99.99%)and N2 (99.999%) were controlled by MKSflow controllers. A Pinnacle Plus bipolarpulsed DC power supply (AE, USA) wasused as the electrical power source for thethin film deposition. The substratetemperature was set at RT, 200oC and400oC using two halogen lamp (1,000W)heaters with a digital programmabletemperature controller. The substrateholder temperature was monitored usinga chromel–alumel thermocouple. Thethermocouple is placed in the rear side ofsubstrate holder to avoid its contact withthe plasma. The substrates were kept ateach desired temperature for 30 minute toestablish a homogeneous temperaturedistribution before each deposition.Substrate bias at -70 V was found to be bestperforming in a scratch adhesion test.Therefore a substrate bias of -70V wasapplied to the substrates during thedeposition. Pre-sputtering of the Ti target

Figure 1. Magnetron sputtering setup.

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was performed for 5 min before eachdeposition. The deposition conditions aregiven in Table 1.

There are 4 types of N2 feedingconfiguration used in this work. They areexplained using diagram Figure 2.

The crystallographic structure of thedeposited films was analyzed by XRD inθ–2θ configuration. The diffractometerused the Cu Kα line at 1.5406 nm as theX-ray source. Scans were made in grazingangle mode with the incident radiationimpinging the sample with an angle ofapproximately 3o with respect to thespecimen surface. The average latticeparameter is analyzed with MDI Jade 6.0software.

3. RESULTS AND DISCUSSION3.1 Crystal Structure

TiN films deposited by various PVDmethods generally have three kinds ofpreferred orientation, i.e. (111), (200) and(220) [6]. Figure 3-6 shown XRD patternsof the films in this work prepared atsubstrate temperature of roomtemperature, 200oC and 400oC by N2

gas-feeding type A, B, C and D respectively.All of the diffraction peaks correspond toFCC TiN (JCPDS card no: 38-1420).

Figure 3 shows the XRD patterns ofthe films prepared at different substrate

Figure 2. Nitrogen feeding configurations.

Table 1. Deposition Parameters for TiN. Objects Specification

Figure 3. XRD pattern of the filmsprepared by N2 gas-feeding type A at roomtemperature, 200oC and 400oC.

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temperatures by using N2 gas-feeding typeA. The TiN (111) and (220) peak intensitiesincrease with increasing substratetemperature. The TiN (200) appears in thefilm formed at the substrate temperatureof 400oC.

temperature. The relative intensity of the(111) peak increases whilst that of the (200)peak is decreased. The TiN (200) peakappears at a substrate temperature of400oC

Figure 4. XRD pattern of the filmsprepared by N2 gas-feeding type B at roomtemperature, 200oC and 400oC.

Figure 5. XRD pattern of the filmsprepared by N2 gas-feeding type C at roomtemperature, 200oC and 400oC.

Figure 6. XRD pattern of the filmsprepared by N2 gas-feeding type D at roomtemperature, 200oC and 400oC.

Figure 4 and 5 show the XRD patternsof the films prepared at different substratetemperatures using N2 gas-feeding type Band C. This configuration of gas feedingfed N2 into the plasma above the surfaceof the target. The intensity of the (220) peakis higher than that of the (111) peak atroom temperature. The (220) peak and(111) peak change with increase in substrate

In N2 gas-feeding type D, the TiNthree strong peaks, (111), (200) and (220),appear at room temperature. Intensitiesof each peak increased with increasingsubstrate temperature.

The preference in the orientation of afilm is due to its lowest overall energy,which depends on competition between thesurface energy, the strain energy and thebombardment energy of different latticeplanes. The (200) plane has the lowestsurface energy, the (111) plane has thelowest strain energy and the (220) has thelowest bombardment energy [7,8].

Each gas flow configuration affects thepreferred orientation of titanium nitridethin film differently especially at roomtemperature. Figure 7 shows the XRDpattern of the films prepared at roomtemperature by the four types of N2 gas-feeding configuration.

At room temperature, the (220) peakachieved using the gas feeding configurationstype B and C dominates due to the effectof bombardment energy. At the N2

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distributor outlet in the plasma, N2

dissociate into N atoms. High energy ofN moves near the substrate and some Nacts as bombardment atoms. This XRDpattern is similar to a TiNx thin filmprepared using high bias voltage reportedin other literature [9].

3.2 Microstructural StudiesThe cross-sectional observations from

Figure 8,9 and 11 indicate that the filmshave columnar structures. However, thecolumnar structures exhibited somedifferences in thickness and latticeparameter as shown in Table 2 and Table 3,respectively.

Figure 7. XRD pattern of the filmsprepared by the different N2 gas-feedingmethods at room temperature.

Figure 8. SEM micrographs of TiN crosssections prepared using N2 gas-feedingconfiguration type A at 400oC.

Figure 9. SEM micrographs of TiN crosssections prepared using N2 gas-feedingconfiguration type B at 400oC.

Figure 10. SEM micrographs of TiN crosssections prepared using N2 gas-feedingconfiguration type C at 400oC.

Table 2. The film thickness and depositionrate in samples prepared using different N2

feeding configurations.

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Figure 11. SEM micrographs of TiN crosssections prepared using N2 gas-feedingconfiguration type D at 400oC.

Table 3. The average lattice parameter insamples prepared using different N2

feeding configurations.

The microstructure of film shown inFigure 10 is very fine, dense and well-bonded to the substrate. This indicates thatat suitable plasma energy conditions anddeposition rate coatings may be produced

free of open pores or pin-holes, whichoften appear in TiN film produced byPVD techniques.

The factors that reduce sputtering yieldof the target are: (i) TiN compoundformation on the target surface and (ii)lower effective bombardment ion in plasmaor lower relative concentration of Ar. Themain reason for lowest deposition rate intype A sample is the forming a compoundof TiN. Compound formation will alsotake place at the surface of the sputteringtarget and the sputtering yield of the TiNis substantially lower than the sputteringyield of the Ti target material. The causeof the highest deposition rate in type D isdue to the lowest amount of compoundformation on the target and the highestrelative concentration of Ar in thesputtering zone.

For this experiment, the lattice para-meters calculated for each specimen areshown in Figure 12. The lattice parameterschange with a change in the substratetemperature especially in type A and BN2 feeding configurations, respective. Butfor type D feeding configuration, the latticeparameter does not alter significantly.

Figure 12. Lattice parameter of titaniumnitride in different type N2 feedingconfigurations.

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The reasons that explain the fluctuationof lattice parameter are:

(i) The effect of different nitrogenfeeding positions on the plasma energy,especially for a small size sputteringtarget. Different plasma energy can be anadditional source of substrate heating, andthis can make a difference to the effects ofthe substrate temperature.

(ii) Different nitrogen feeding posi-tions affect N/Ti ratio since sputtering rateof the titanium atom is changed and thenitrogen has different time to incorporateinto the film, respectively. In addition,some nitrogen feeding positions couldenhance the mobility of nitrogen atoms onthe growing film surface. Previousliterature has also shown that the latticeparameter increases with increasing (N/Ti)ratio in the deposition of TiN film usingsputtering techniques [7,10].

In large-scale production using a largechamber and many small sputtering targets,an even temperature distribution of thesubstrates is a factor that can be difficultto control. In this case, the type D N2

feeding configuration can be used in orderto minimize the effect of the temperaturefluctuation, thus reducing the changing oflattice parameter of TiN related to stressin the thin film.

4. CONCLUSIONS

1. N2 gas feeding configuration affectsthe preferred orientation and the latticeparameter of TiN thin film deposited atlow temperature.

2. For type A, B and C N2 gas feedingconfigurations, the change in the tem-perature of the substrate affects the latticeparameter of the deposited TiN film.

3. For type D N2 gas feeding con-figuration, the lattice parameter is notaffected by the substrate temperatureranging from RT to 400oC.

5. REFERENCES

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[2] Makinoa Y., Moria, Miyakea S.,Saitob K. and Asami K., Characteriza-tion of Zr–Al–N films synthesized bya magnetron sputtering method, Surf.Coat. Tech., 2005; 193: 219-222.

[3] Carrascoa C.A. and Vergara V., Therelationship between residual stressand process parameters in TiNcoatings on copper alloy substrates,Mater. Charact., 2002; 48: 81-88.

[4] Kraft O., Rattunde O., Rusu A., andHaberland H., Thin films from fastclusters: golden TiN layers on a roomtemperature substrate, Surf. Coat.Tech., 2002; 158-159: 131-135.

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[8] Zhao J.P., Wang X., Chen Z.Y., YangS.Q., Shi T.S. and Liu X.H., Evolutionof the texture of TiN films preparedby filtered arc deposition, J. Phys. D:Appl. Phys. 1997; 30: 5-12.

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