Surface and Coatings Technology 173–174(2003) 1234–1237

0257-8972/03/$ - see front matter� 2003 Elsevier Science B.V. All rights reserved.doi:10.1016/S0257-8972Ž03.00472-9

Low temperature TiN deposition by ICP-assisted chemical vapordeposition

Dong-Kak Lee *, Jung-Joong Lee , Junghoon Jooa, b c

Research Institute of Advanced Material, Seoul National University, Seoul, South Koreaa

School of Materials Science and Engineering, Seoul National University, Seoul, South Koreab

Department of Materials Science and Engineering, Kunsan National University, Mt. 68 Miryong-dong, Kunsan, South Koreac

Abstract

TiN films were deposited by inductively coupled plasma(ICP)-assisted CVD using a gas mixture of TiCl , H , Ar and N4 2 2

with a substrate temperature of 4008C and room temperature. For ICP generation, r.f. power was applied using a dielectric-encapsulated coil antenna installed inside the deposition chamber. The ICP power was varied from 100 to 400 W. The depositionrate was as high as)1 mmyh in most deposition conditions. As the r.f. power was increased, the deposition rate decreasedirrespective of the deposition temperature. It is believed that the decrease in the deposition rate at higher ICP powers is due toresputtering of the coatings as a result of ion bombardment as well as film densification. The hardness increased with increasingr.f. power, indicating the formation of a denser film at higher power. The decrease in the resistivity at high powers is related tothe low Cl content in the film. The TiN film deposited by ICP-assisted CVD showed also a good step coverage on the trencheswith a high aspect ratio.� 2003 Elsevier Science B.V. All rights reserved.

Keywords: Inductively coupled plasma; Chemical vapor deposition; Low temperature

1. Introduction

Reducing the deposition temperature of a CVD pro-cess has been a subject that has attracted great attention,because a wide range of materials can be used as asubstrate material, including plastics as well as polycar-bonatesw1–3x. Low temperature deposition can alsoreduce the stress evolution in a film due to the differentthermal expansion coefficients between the coated filmand the substrate. In this study, TiN films were depositedat room temperature by CVD using inductively coupledplasma (ICP) as an extra energy source. For ICPgeneration, the r.f. power was applied to a dielectric-encapsulated RFI antenna which was installed inside thedeposition chamber. With conventional r.f. capacitivelycoupled plasma, the process temperature for TiN depo-sition can be lowered to 5008C using TiCl and NH4 3

gases. However, it has a problem of particulate formationcaused by homogeneous reactions in the plasmaw4x.TiN films fabricated by a conventional r.f. PECVDmethod using TiCl and N gases had a high Cl content4 2

*Corresponding author. Tel.:q82-28805511; fax:q82-28715540.E-mail address: sub91@gong.snu.ac.kr(D.-K. Lee).

and a high resistivity at deposition temperatures below620 8C w5x. To obtain high-quality TiN films at lowerdeposition temperatures, a high-density plasma is neededto dissociate the precursors more effectively than con-ventional r.f. capacitively coupled plasmaw6,7x.In this work, ICP was applied to CVD to deposit the

TiN films at 400 8C and room temperature. For ICPgeneration, the r.f. power was supplied to a dielectric-encapsulated RFI antenna which was installed inside thedeposition chamber.

2. Experimental details

TiN coatings were deposited on M2 high-speed steelsand Si wafers by internal ICP-assisted CVD using a gasmixture of TiCl , H , Ar and N . The ICP was generated4 2 2

in the region between the substrate and gas distributorby applying 13.56 MHz r.f. power through a tuningnetwork to a two-turn coil(RFI coil) of a water-cooledcopper tube. The RFI coil had a main diameter ofapproximately 10 cm. It was located inside the vacuumchamber between the substrate and the gas distributorwith an equal spacing of 1 cm, and was electricallyshielded with insulating tubes. The distances between

1235D.-K. Lee et al. / Surface and Coatings Technology 173 –174 (2003) 1234–1237

Fig. 1. Schematic illustration of the apparatus used for the ICP-assisted CVD.

Fig. 2.(a) The TiN film deposition rate as a function of the r.f. power(j, at 400 8C; d, at room temperature). (b) The effect of the r.f.power and deposition temperature on the chlorine content(j, at 4008C; d, at room temperature).

the substrate and the lower gas distributor and the twogas distributors were approximately 5 and 2 cm, respec-tively. The substrate was kept floating. Fig. 1 shows aschematic diagram of the CVD system used in thiswork.Ar was used as the carrier gas for the TiCl . The gas4

lines were heated with heating tape to avoid conden-sation of the source gases in the delivery lines. Thepurpose of the separate gas supply was to prevent theformation of solid TiClØnNH , NH Cl, which can4 3 4

clog the lines. The base pressure of the system was-1=10 Torr and the sample surface temperature wasy6

measured by attaching two chromelyalumel thermocou-ples to the surface of an identically mounted sacrificialcoupon. The deposition pressure was 200 mTorr and theICP power ranged from 100 to 400 W. The compositionsof the coatings were analyzed by Auger electron spec-troscopy. A Knoop hardness indenter with a 10-g loadwas used to measure the hardness. The resistivity of thecoating was obtained using the four-point probe method.The details of the step coverage for the contact holeswere observed by field emission scanning electronmicroscopy(FE-SEM).

3. Results and discussion

Fig. 2 shows the deposition rate and the resistivity ofthe TiN films deposited at 4008C and at room temper-ature. The deposition rate decreased with increasing r.f.power irrespective of the deposition temperature. It isbelieved that the rate decrease at higher powers isaroused by the resputtering of the coating as a result ofion bombardment. In addition to resputtering, etchingby chlorine radicals generated from TiCl dissociation4

appears to reduce the deposition rate. It was reportedthat a large quantity of Cl ions are produced from thedissociation of TiCl w8x. In addition, there is a possi-4

bility of physical sputtering by Ar ion bombardment.However, the measured plasma potential at the powerswas approximately 20–25 V, which is slightly above the

sputtering threshold. Therefore, resputtering may nothave had a large influence on the deposition rate. It issupposed that the rate decrease might also be caused by

1236 D.-K. Lee et al. / Surface and Coatings Technology 173 –174 (2003) 1234–1237

Fig. 3. (a) The resistivity of the TiN films as a function of the r.f.power(j, at 4008C; d, at room temperature). (b) The hardness ofthe TiN films as a function of the r.f. power(j, at 400 8C; d, atroom temperature).

Fig. 4. Conformity(step coverage) of the TiN films deposited at atemperature of 4008C and a pressure of 50 mTorr with an aspect ratioof 3:1.

Table 1The properties of TiN films deposited by CVD

Deposition Deposition Resistivity Cl concentration Referencetemperature(8C) rate(mmyh) (mV cm) (at.%)

450 1.5 600 – w10x220 0.3 1200 10 w11x200 – – 0.8 w12x350 0.66 350 2.5 w13x400 and 25 1.5 and 1.0 100 and 300 0.1 and 4 wthis studyx

the formation of a denser film at higher powers, sincethe deposition rate is rather lower at 4008C than atroom temperature.In Fig. 2b, the Cl content in the TiN films was

significantly lower(0.1% at 4008C) than 2–6 at.% inthe films grown by other CVD methodsw9x. The TiNfilms deposited at room temperature and at high powers()300 W) also had a relatively low Cl concentration.The effective dissociation of TiCl by the high-density4

plasma resulted in a low Cl content in the films.

Fig. 3 shows the resistivity and the hardness of TiNfilms deposited at 4008C and at room temperature. Thelower resistivity of the TiN at 4008C was mainly dueto the lower Cl content, although the film resistivity isalso under the influence of other factors, such themicrostructure, crystallinity, and preferred orientation ofthe film. The hardness of the TiN films increased withincreasing r.f. power at both temperatures, which alsoindicates the formation of a denser film at higher powers.The properties of the TiN films improved when the ICPwas applied to the CVD process(Table 1).The TiN film was deposited on a 3.0=1.0 mm2

(ARs3) trench by ICP-assisted CVD at low pressure(50 mTorr). A cross-section FE-SEM image shows agood coverage around the step edge(Fig. 4). The filmcoverage at the bottom and the edge were 69 and 57%,respectively. The TiN films obtained by the ICP-CVDprocess exhibited excellent step coverage.

4. Conclusion

TiN films were deposited by ICP-assisted CVD usinga gas mixture of TiCl , H , Ar and N at both 4008C4 2 2

1237D.-K. Lee et al. / Surface and Coatings Technology 173 –174 (2003) 1234–1237

and at room temperature. The deposition rate was ashigh as)1 mm in most deposition conditions. As ther.f. power was increased, the deposition rate decreasedirrespective of the deposition temperature. It is believedthat the decrease in the deposition rate at high ICPpowers is due to the resputtering of the coatings as aresult of ion bombardment in addition to film densifi-cation. The hardness increased with increasing r.f. power,indicating the formation of denser films at higher pow-ers. The decrease in the resistivity at higher powers isrelated to the low Cl content in the film. The TiN filmdeposited by ICP-assisted CVD also showed a good stepcoverage on the trenches with a high aspect ratio.

Acknowledgments

This work was supported by the Korea Science andEngineering Foundation through the Center forAdvanced Plasma Surface Technology at the Sung-kyunkwan University(2002).

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