Diffusion barrier performance of chemically vapor deposited TiN films prepared usingtetrakisdimethylamino titanium in the Cu/TiN/Si structureDoHeyoung Kim, SungLae Cho, KiBum Kim, Jung Ju Kim, Jin Won Park, and Jae Jung Kim Citation: Applied Physics Letters 69, 4182 (1996); doi: 10.1063/1.116979 View online: http://dx.doi.org/10.1063/1.116979 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/69/27?ver=pdfcov Published by the AIP Publishing Articles you may be interested in The effect of density and microstructure on the performance of TiN barrier films in Cu metallization J. Appl. Phys. 80, 5674 (1996); 10.1063/1.363620 TiN barrier layer formation by the twostep rapid thermal conversion process J. Vac. Sci. Technol. A 14, 3245 (1996); 10.1116/1.580220 Growth behavior of copper metalorganic chemical vapor deposition using the (hfac)Cu(VTMOS) precursor ontitanium nitride substrates J. Vac. Sci. Technol. A 14, 3214 (1996); 10.1116/1.580215 Efficiency of TiN diffusion barrier between Al and Si prepared by reactive evaporation and rapid thermalannealing J. Appl. Phys. 79, 7612 (1996); 10.1063/1.362418 Comparison of the diffusion barrier properties of chemicalvapordeposited TaN and sputtered TaN between Cuand Si J. Appl. Phys. 79, 6932 (1996); 10.1063/1.361518

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:

129.171.233.72 On: Tue, 25 Nov 2014 01:04:35

Diffusion barrier performance of chemically vapor deposited TiN filmsprepared using tetrakis-dimethyl-amino titanium in the Cu/TiN/Si structure

Do-Heyoung KimProcess Group, Advanced Technology Laboratory, LG Semicon Co., Ltd., 50 Hayangjeong-Dong,Cheongju-Si 360-480, Korea

Sung-Lae Cho and Ki-Bum KimSeoul National University, Seoul, Korea

Jung Ju Kim, Jin Won Park, and Jae Jung KimProcess Group, Advanced Technology Laboratory, LG Semicon Co., Ltd., 50 Hayangjeong-Dong,Cheongju-Si 360-480, Korea

~Received 24 June 1996; accepted for publication 28 October 1996!

We investigated diffusion barrier performance of chemical vapor deposition~CVD! TiN filmsprepared using tetrakis-dimethyl-amino titanium, Ti@N~CH3!2#4, to copper in the Cu/TiN/Sistructure. Thein situ treatment of the TiN films using N2/H2 plasma was found to significantlyimprove barrier performance against copper diffusion. The plasma-treated TiN films were stable upto 650 °C but as-deposited TiN films showed an evidence of copper diffusion into silicon even afterannealing at 550 °C. The causes of the different effectiveness as a copper diffusion barrier of thetwo types of the CVD TiN films were discussed. ©1996 American Institute of Physics.@S0003-6951~96!02653-8#

Copper is expected to be used as a major interconnectmaterial in subquarter micron devices due to its lower resis-tivity and higher electromigration resistance compared toaluminum or aluminum alloys. However, there are severalproblems to be overcome for the use of copper in on-chipinterconnection. The major obstacle being considered is itsfast diffusion into Si. TiN is most commonly used as a majorbarrier at present in integrated circuit~IC! metallizationschemes due to its excellent diffusion barrier properties, highstability, and good electrical conductivity. It is also thoughtto be a promising barrier to the diffusion of copper. Althoughthere are many reports on the applicability of TiN films as acopper diffusion barrier, almost all barrier performance stud-ies were conducted using sputtered-TiN films, so far.1–5

However, conformal chemical vapor deposition~CVD! pro-cess for TiN is being expected to be used for subquartermicron IC devices. Therefore, evaluation of diffusion barrierperformance of CVD TiN films is emerging.

One of the most widely investigated precursors in TiNCVD is tetrakis-dimethyl-amino titanium ~TDMAT,Ti@N~CH3!2#4. TDMAT-based TiN offers low depositiontemperature and is free of chlorine contamination in the filmwith moderate step coverage compared to TiCl4-based CVDTiN. However, TiN CVD of the TDMAT precursor sufferssignificant carbon impurity in the deposits, causing high re-sistivity. Therefore, improvement of film quality usingN2/H2 plasma or rapid thermal nitration~RTN! of themetalorganic-precursor-based TiN films is becoming of greatinterest. In this work, we compared diffusion barrier perfor-mance of two kinds of TDMAT-based TiN films with theCu/TiN/Si structure for copper metallization; one wasin situ plasma treated and the other one was as-deposited~no plasma treated!.

Two kinds of CVD TiN films were prepared on the~100!p-type Si substrates using TDMAT. The plasma-treated onewas made using a cyclic process; deposition of TiN films and

plasma treatment was conducted cyclically. Plasma treatmentwas carried out for 20 s at 350 W plasma power withN2/H2 gas mixture~1000 sccm! after growing of every;40Å of TiN. Temperature and pressure for the deposition andplasma treatment were 350 °C and 1 Torr, respectively. Thenumber of cycles~deposition/plasma treatment! required togrow about 500-Å-thick TiN were 12~a total of 686 selapsed time!. To stabilize pressure and flow, there were pe-riodic interruptions for 10 s after every step of plasma treat-ment and deposition. The other one was made convention-ally, i.e., no plasma treatment during TiN deposition, at thesame temperature. For comparison, physical vapor deposi-tion ~PVD! TiN film was also prepared at 400 °C in a mix-ture of N2/Ar with a total pressure of 5 mTorr. The thicknessof the tested TiN films was 500 Å.

To prepare the test structure, Cu/TiN/Si, about 3000 Åof copper was deposited by CVD using hexafluoroacetylac-etonate copperI vinyltrimethylsilane,@~hfac!Cu~vtms!#, ontothe TiN samples. Deposition of copper was conducted at180 °C substrate temperature and 0.5 Torr total pressure. Ef-fectiveness of the diffusion barrier was evaluated by sheetresistance measurements and etch-pit test after annealing at550–750 °C in hydrogen ambient for 1 h. For the observa-tion of etch pits, copper was stripped at first in 1:20HNO3H2O solution, followed by a TiN layer removal in1:2:6 NH4OH:H2O2H2O solution, and then finally etching ofthe Si surface using Secco etching solution6 for 5 s. Previ-ously, usefulness of the etch-pit test was reported for theevaluation of diffusion barrier effectiveness in a copper met-allization schemes;5 the temperature where the etch pits ap-pear was always lower than the temperature where the for-mation of the Cu3Si was identified by x-ray diffraction~XRD!, and also etch pits are observed. Even the Auger elec-tron spectroscopy~AES! depth profile reveals no noticeablediffusion of copper into silicon through the TiN barrier.

Plasma treatment is known to be enhancing the stability

4182 Appl. Phys. Lett. 69 (27), 30 December 1996 0003-6951/96/69(27)/4182/3/$10.00 © 1996 American Institute of Physics This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:

129.171.233.72 On: Tue, 25 Nov 2014 01:04:35

of the TiN films in air and also reducing the level of carbonimpurity due to the increased film density.7 Figure 1 showsthe film stability of the tested CVD TiN films. In the case ofthe no-plasma treated TiN films, the sheet resistance wascontinuously increased as it was exposed to air. However,plasma-treated TiN shows good stability in air. No-plasmatreated films were Ti-rich TiN~N/Ti50.9! according to Ru-therford backscattering~RBS! analysis. Also AES resultsshowed an increased N/Ti ratio in the plasma-treated TiNcompared to that of no-plasma treated TiN~not shown in thiswork!. Therefore, it might be inferred that the activated ni-trogen react with the Ti in the films, resulting in more sto-ichemetric TiN formation. In addition, greatly reduced car-bon impurity level was observed in the films deposited byplasma treatment process. Carbon content in the no-plasmatreated TiN and in the plasma-treated TiN films was 30%and 10%, respectively~Fig. 2!. This indicates that activatedhydrogen species react somehow with CHx (x,4) in thefilms to form a volatile CH4 gas, providing a much lowerlevel of carbon incorporation. Plasma treatment was alsofound to affect the film crystallinity, enhancing crystallinityof the films after plasma treatment.7

Figure 3 shows the sheet resistance of copper depositedon the TiN films as a function of annealing temperature. Thesheet resistance of the copper deposited on the TiN was sub-stantially decreased with annealing to 550 °C, and then in-creased after further increment of the annealing temperature.The decrease in sheet resistance seems to be caused by thedensification of the films during annealing. A great increasein the sheet resistance was observed with the sample of theno-plasma treated and plasma-treated TiN after annealing to

650 °C and 750 °C, respectively. This indicates that diffusionbarrier effectiveness of TDMAT-based TiN can be improvedby plasma treatment along with improving film propertiessuch as stability in air, resistivity, and impurity level. Thedetailed cause of improvement in diffusion barrier effective-ness is not clear at present, but it seems to be related to themicrostructure of the TiN film, particularly porosity. Previ-ously, it was reported that high density~or low porosity! ofthe TiN film is of primary importance in achieving a gooddiffusion barrier performance between copper and Si. Asshown in Fig. 2, plasma-treated TiN contains much loweroxygen content compared to no-plasma treated TiN after airexposure. Because oxygen content in the TiN film can beconsidered as an indicator for the density of the film, wemight be able to conclude that TiN films deposited by cyclicprocess have a higher density than that of no-plasma treatedTiN. Therefore, an increased film density~reduced film po-rosity! by plasma treatment is believed to be the main reasonfor the improved barrier performance of the TiN films.

The results of the etch-pit test are shown in Fig. 4. Theseresults clearly confirmed the results in the above. The etchpits usually appeared to be a distinctive crystallographic ori-entation and some of these took the form of the invertedsquare pyramids which is similar to what was observed inprevious work.5 As the anneal temperature increased, thesize of etch pits became larger. It is worth noting that the

FIG. 1. AES depth profile of the CVD TiN film deposited at 350 °C.~a!No-plasma treated TiN,~b! plasma-treated TiN.

FIG. 2. The sheet resistance of the TiN films as a function of air exposuretime ~film thickness5500 Å!.

FIG. 3. The sheet resistance of Cu/TiN/Si structure as a function of anneal-ing temperature.

4183Appl. Phys. Lett., Vol. 69, No. 27, 30 December 1996 Kim et al. This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:

129.171.233.72 On: Tue, 25 Nov 2014 01:04:35

etch pits first appear even after annealing at 550 °C, althoughno significant change in sheet resistance was observed in theCu/TiN ~no-plasma!/Si systems. This suggests that sheet re-sistance measurement is not very useful for evaluation of thediffusion barrier effectiveness. In the Cu/TiN~plasma-

treated!/Si and Cu/TiN~PVD!/Si systems, no noticeable etchpits could be seen even after annealing at 650 °C. However,many etch pits can be seen in the samples annealed at750 °C. Relatively smaller size of pits and changes of thesheet resistance with Cu/TiN~plasma-treated!/Si structurecompared to those with Cu/TiN~PVD!/Si structure appeared.These results show that plasma-treated TiN has a comparablebarrier effectiveness to the PVD TiN against copper diffu-sion, i.e., stable up to 650 °C.

In summary, barrier performance of TDMAT-basedCVD TiN films to copper diffusion in the Cu/TiN/Si struc-ture was evaluated. The etch-pit test was used to examine theeffectiveness of the diffusion barrier for copper after anneal-ing at temperatures of 550–750 °C. No-plasma treated TiNfails after annealing at 550 °C. Plasma-treated CVD TiNfilms using N2/H2 plasma showed better diffusion barrierproperty compared to the no-plasma treated CVD TiN, com-parable to the tested PVD TiN films~stable up to 650 °C!.Detailed structural studies for CVD TiN deposited by cyclicprocess using plasma treatment are on the way.

1J. O. Olowolafe, C. J. Mogab, R. B. Gregory, and M. Kottke, J. Appl.Phys.72, 4099~1992!.

2D.-Y. Shih, C.-A. Chang, J. Paraszczak, S. Nunes, and J. Cataldo, J. Appl.Phys.70, 3052~1991!.

3T.-S. Chang, W.-C. Wang, L.-P. Wang, J.-C. Hwang, and F.-S. Huang, J.Appl. Phys.75, 7847~1994!.

4K.-C. Park, K.-B. Kim, I. Raaijmakers, and K. Ngan, J. Appl. Phys.~sub-mitted!.

5K.-C. Park and K.-B. Kim, J. Electrochem.142, 3109~1995!.6S. Wolf and R. N. Tauger,Silicon processing for the VLSI era~Lattice,Sunset Beach, CA, 1987!, Vol. 1, p. 533.

7D.-H. Kim, J. J. Kim, J.-W. Park, and J.-J. Kim, J. Electrochem.143,L188 ~1996!.

FIG. 4. Scanning electron microscopy~SEM! micrographs of the etch pitsobtained from the Cu/TiN/Si samples:~a! and ~b! with no-plasma treatedTiN films after annealing at 550 and 650 °C, respectively.~c! and ~d! withsputtered TiN films after annealing at 650 °C and 750 °C, respectively, and~e! and ~f! with plasma-treated TiN after annealing at 650 and 750 °C,respectively.

4184 Appl. Phys. Lett., Vol. 69, No. 27, 30 December 1996 Kim et al. This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:

129.171.233.72 On: Tue, 25 Nov 2014 01:04:35