Open Access

Heteroepitaxial growth of TiN film on MgO (100) by reactive magnetron sputtering

Nanoscale Research Letters20149:551

https://doi.org/10.1186/1556-276X-9-551

Received: 25 June 2014

Accepted: 10 September 2014

Published: 3 October 2014

Abstract

TiN thin films were deposited on MgO (100) substrates at different substrate temperatures using rf sputtering with Ar/N2 ratio of about 10. At 700°C, the growth rate of TiN was approximately 0.05 μm/h. The structural and electrical properties of TiN thin films were characterized with x-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Hall measurements. For all deposition conditions, XRD results show that the TiN films can be in an epitaxy with MgO with cube-on-cube orientation relationship of (001)TiN // (001)MgO and [100]TiN // [100]MgO. TEM with selected-area electron diffraction pattern verifies the epitaxial growth of the TiN films on MgO. SEM and AFM show that the surface of the TiN film is very smooth with roughness approximately 0.26 nm. The minimum resistivity of the films can be as low as 45 μΩ cm.

Keywords

Heteroepitaxial TiNMgO (100)High qualityrf sputtering

Background

Titanium nitride (TiN) thin films have been extensively used in a wide range of applications as wear-protective coatings on mechanical components, cutting tools, decorations, as well as diffusion barriers and metal gates in integrated circuits [1, 2], owing to its remarkable physical and chemical properties such as high hardness, high thermal stability, low electrical resistivity, and high wear excellent corrosion resistance [3, 4]. Also, Pure TiN films are highly reflective and gold in color and have found applications in jewelery and optics [5]. Studies on TiN properties have solved significant problems, such as the reduction of the usefulness of TiN films for corrosion-resistant coatings and for diffusion barriers in the films [6]. Grigorov et al. reported that TiN has uses in microelectronics due to its efficiency in preventing aluminum diffusion into silicon in Al-TiN-Si trilayers at up to 550°C [7].

In order to deposit thin films of TiN on various substrates, it is common to use processes such as physical vapor deposition (PVD) [8], chemical vapor deposition (CVD) [9], atomic layer deposition (ALD) [10], and hallow cathode ionic plating (HCIP). Among those processes, the PVD process is known to be easy and to present a good adhesion between the film and the substrates of metals and ceramics [11]. Among various PVD processes, dc reactive sputtering is commonly used for deposition of polycrystalline and single-crystalline films. For epitaxial growth, TiN films have been often grown on an MgO substrate based on a consideration of the same rock salt structure and small lattice mismatch (<1% at room temperature) between their lattice parameters [12]. Previous studies of TiN deposition on the MgO (100) substrate showed that high-quality epitaxial TiN films can be obtained using ultrahigh vacuum dc reactive magnetron sputtering of pure Ti [1316]. Reactive radio-frequency (rf) magnetron sputtering of a Ti target has been demonstrated for deposition of TiN polycrystalline films with preferred orientation dependence on argon/nitrogen ratio and substrate temperature [17]. In addition, Ingason et al. indicated that a minimum substrate temperature of 200°C is required for a good epitaxy. Also, substrate temperatures of 100°C and below yield low density, polycrystalline films with in-plane texture of ±12° around the main crystal axis of the MgO substrate [18].

In this article, we report heteroepitaxial growth of TiN deposited on MgO (100) using rf reactive magnetron sputtering in high vacuum at 600°C and 700°C. The crystallinity, surface morphologies, and microstructure of deposited films were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM).

Methods

In our previous study of rf reactive sputtering of a Ti target for TiN polycrystalline films on Si (100), we found an optimum condition for growth of <100 > preferentially oriented TiN films [19] which was used for the present study for epitaxial growth of TiN films on MgO (100). TiN epilayers were deposited on the MgO (100) substrate using a 13.56 MHz rf sputtering apparatus without a bias voltage. MgO (100) of 2-in size was chosen as a substrate. The vacuum chamber was equipped with a cryopump to reduce the pressure to about approximately 1 × 10-6 Torr. An elemental Ti target (99.99% purity) was reactively sputtered in a mixture of Ar (99.999%) and pure N2 (99.9999%) with a ratio of 10:1, and the total gas pressure during the growth was 1 mTorr. The distance between the substrate holder and the target was 20 cm. The rf power was 200 W. MgO substrates were ultrasonically cleaned in acetone and ethanol and dried with dry N2 and immediately inserted into the vacuum chamber. Prior to TiN growth, the MgO (100) substrate was heat-treated in a vacuum of 5 × 10-6 torr at 700°C for 2 h, and the target was sputtered to clean the surface for 10 min with a shutter covering the substrate. Final, TiN epilayers were prepared on the MgO substrate at 600°C and 700°C. The epitaxial nature of the TiN (200) layer was examined using x-ray diffraction in ω-2θ, rocking curve (Siemens D5000, Siemens, Shinagawa-ku, Japan), and ø-scan mode with CuKα radiation (Bruker D8, Bruker Optik GmbH, Ettlingen, Germany). Surface morphology and microstrucure of deposited TiN in a cross section were analyzed in a field emission SEM (FE-SEM; Hitachi S-4300, Hitachi, Ltd, Chiyoda-ku, Japan) and TEM (Philips Tecnai 20, Philips, Amsterdam, The Netherlands). The cross-sectional TEM specimens were prepared by focused ion beam technique. The morphology of the film with surface roughness was investigated by AFM. Room-temperature electrical resistivities were determined with a four-point probe (Keithley 237, Keithley Instruments, Inc., Minato-ku, Japan).

Results and discussion

Figure 1a shows a ω-2θ x-ray diffraction pattern of TiN films grown on the MgO (100) substrate at 500°C to 700°C by reactive magnetron sputtering. It can be seen that the TiN peaks in the pattern exhibit only (200) and (400) reflections at 42.17° and 92.48° in the scanned 2θ range from 20° to 120°, suggesting the film is purely <100 > orientated in the direction normal to the substrate. The peaks of TiN and MgO (400) are separated in 0.9°, indicating the small lattice mismatch between them. While growth temperature is below 700°C, the TiN exhibit worse crystallinity. Specially, the TiN film grown on the MgO (100) substrate shows preferred orientation at 500°C. At 700°C, and from the peak positions of MgO, the lattice parameter of TiN in <100 > is deduced to be about 4.246 Å close to a stoichiometric value, implying that the strain of TiN film has been relaxed at the growth temperature [20]. The mismatch at room temperature between the TiN film and MgO substrate is estimated to be 0.8%. In order to better delineate the crystallinity of the TiN layer, an x-ray rocking curve was measured as shown in Figure 1b. The out-of-plane rocking curve of the TiN (200) peak shows the full width at half maximum (FWHM) of 220 arcsec, which is comparable to that of the MgO in 100 arcsec. Figure 2 shows the results of XRD phi-scans for the 220 peaks of MgO and TiN at a tilt angle of 45° with respect to the normal surface. Clearly, it is seen that both MgO and TiN have four 90°-distanced 220 peaks, showing the epitaxy of TiN on MgO with a cube-on-cube relationship of TiN (100) // MgO (100) and TiN [100] // MgO [100]. The results suggest that the TiN film on MgO (100) can be epitaxially grown with high quality, in comparison with our previous studies of TiN deposition on Si (100) studies in the same deposition condition [19].
Figure 1

XRD analysis of TiN films. (a) XRD ω-2θ diffraction pattern and (b) (200) rocking curve of epi-TiN grown on MgO (100) at 700°C.

Figure 2

Phi-scan patterns of XRD (220). (a) MgO and (b) TiN film.

The surface morphology of the TiN film is shown in SEM and AFM images (Figure 3). The SEM image in Figure 3a from a tilted view shows that the TiN surface is smooth, and the cross-sectional SEM in the inset illustrates that the uniform thickness of the TiN thin film on the MgO substrate is about 100 nm, giving the growth rate of 50 nm/h. Also, the surface roughness of TiN measured by AFM in Figure 3b of 3 × 3 μm2 area is about 0.26 nm in a root-mean-square value slightly greater than that of MgO in 0.13 nm after 700°C heat treatment in vacuum.
Figure 3

Surface morphology of the TiN film. (a) SEM in a tilted view with inset in a cross section and (b) AFM images.

Figure 4 shows a cross-sectional bright-field TEM image of the TiN/MgO (100) interface. The image also shows the smoothness of the TiN film at the surface and the interface with MgO. The dislocation density is roughly estimated in the order of magnitude of 1011 cm-2. Between MgO and TiN, a sharp interface can be seen. It should be noted that the layer-like image contrast around the interface region is due to artifacts from FIB milling in a number of steps as HRTEM and diffraction data show no evidence for the existence of other phases. The epitaxial growth of the TiN film on the MgO substrate is further confirmed with the result of the corresponding selected-area diffraction (SAD) pattern from the interfacial region as shown in Figure 4b. The SAD pattern illustrates that both of {002}-type spots of TiN and MgO are nearly coincidental due to the small lattice mismatch, while some of {004} spots are slightly split in a detailed examination. Also, no diffraction spots from extra phases have been observed, suggesting that no interlayer reaction occurs between TiN and MgO. Further, the coherency of TiN with MgO can be observed in Figure 4c of an HRTEM image from the interfacial region. As the misfit dislocations can be separated in about 26 nm, the image reveals most of the good coherent regions along the interface. Also, it is noticed that more defects appear at the region above 2-nm thickness from the interface, suggesting that the crystallinity may decrease with film growth. Further improvement may require varying the Ar/N ratio and the deposition rate.
Figure 4

TEM images of the cross section of the TiN/MgO. (a) Cross-sectional bright-field TEM micrograph. The discontinuous features at the middle region of TiN and at the TiN/NgO interface were artifacts due to FIB milling. (b) a corresponding SAED pattern from an epitaxial TiN film grown on the MgO (100) substrate. (c) High-resolution TEM showing the TiN/MgO interfacial region.

Resistivity measurements can be used to qualitatively determine the defect concentration in a metal film. Also, the resistivity of TiN films depends on microstructure, preferred orientation, and stoichiometry. TiN films exhibit resistivity of 45 μΩ cm in average at room temperature higher than the bulk crystal value of 13 μΩ cm. The result is in agreement with the reports of Yokota et al. [21] and Biunno et al. [22]. In contrast, polycrystalline TiN films deposited on Si (100) in the same sputtering condition have the resistivities in the range of 200 μΩ cm, implying that grain boundaries have strong effects on electron scattering.

Compared to other studies on electrical resistivity of TiN, the value is very close to present accepted values. Therefore, the result implies that the film quality is reasonably good.

Conclusions

In summary, high-quality epitaxial TiN (100) films can be deposited on a 2-in MgO (100) substrate at 700°C by rf reactive sputtering process in a high vacuum. Structural characterization shows that epitaxial TiN films exhibit a smooth surface and a coherent good interface with MgO. Also, TiN films of 100-nm thickness are close to stoichiometry and strain-relaxed.

Declarations

Acknowledgements

This work was supported by the National Science Council (NSC) of Taiwan under contract no. NSC 103-2622-E-492-010-CC3.

Authors’ Affiliations

(1)
Instrument Technology Research Center, National Applied Research Laboratories
(2)
Department of Materials Science and Engineering, National Chiao Tung University

References

  1. Sundgren JE: Structure and properties of TiN coatings. Thin Solid Films 1985, 128: 21–44. 10.1016/0040-6090(85)90333-5View ArticleGoogle Scholar
  2. Kothari DC, Scardi P, Gialanella S, Guzman L: Structural analysis of TiNx films prepared by reactive-ion-beam-enhanced deposition. Philos Mag B 1990, 61: 627–637. 10.1080/13642819008219298View ArticleGoogle Scholar
  3. Hogmark S, Jacobson S, Larsson M: Design and evaluation of tribological coatings. Wear 2000, 246: 20–33. 10.1016/S0043-1648(00)00505-6View ArticleGoogle Scholar
  4. Cunha L, Ansritschky M, Rebouta L, Pischow K: Corrosion of CrN and TiAlN coatings in chloride-containing atmospheres. Surf Coat Technol 1999, 116–119: 1152–1160.View ArticleGoogle Scholar
  5. Perry AJ, Georgson M, Sproul WD: Variations in the reflectance of TiN, ZrN and HfN. Thin Solid Films 1988, 157: 255–265. 10.1016/0040-6090(88)90007-7View ArticleGoogle Scholar
  6. Hinode K, Homma Y, Horiuchi M, Takahashi T: Morphology-dependent oxidation behavior of reactively sputtered titanium–nitride films. J Vac Sci Technol A 1997, 15: 2017–2022. 10.1116/1.580673View ArticleGoogle Scholar
  7. Grigorov GI, Grigorov KG, Stayanova M, Vignes JL, Langeron JP, Denjean P: Aluminium diffusion in titanium nitride films. Efficiency of TiN barrier layers. Appl Phys A 1993, 57: 195–197. 10.1007/BF00331444View ArticleGoogle Scholar
  8. Jun K, Shimogaki Y: Effect of partial pressure of TiCl4 and NH3 on chemical vapor deposition titanium nitride (CVD-TiN) film Cl content and electrical resistivity. Jpn J Appl Phys 2004, 43: L519-L521. 10.1143/JJAP.43.L519View ArticleGoogle Scholar
  9. Paranjpe A, IslamRaja M: Chemical vapor deposition TiN process for contact/via barrier applications. J Vac Sci Technol B 1995, 13: 2105–2114.View ArticleGoogle Scholar
  10. Kim J, Hong H, Ghosh S, Oh KY, Lee C: Physical properties of highly conformal TiN thin films grown by atomic layer deposition. Jpn J Appl Phys 2003, 42: 1375–1379. 10.1143/JJAP.42.1375View ArticleGoogle Scholar
  11. Li Y, Qui L, Wang F: The electrochemical corrosion behavior of TiN and (Ti, Al) N coatings in acid and salt solution. Corros Sci 2003, 45: 1367–1381. 10.1016/S0010-938X(02)00223-8View ArticleGoogle Scholar
  12. Karr BW, Petrov I, Cahill DG, Greene JE: Morphology of epitaxial TiN (001) grown by magnetron sputtering. Appl Phys Lett 1997, 70: 1703–1705. 10.1063/1.118675View ArticleGoogle Scholar
  13. Kawakubo T, Sano K, Oose M: Heteroepitaxial TiN films grown by reactive ion beam epitaxy at room temperature. Jpn J Appl Phys 1993, 32: L1692-L1694. 10.1143/JJAP.32.L1692View ArticleGoogle Scholar
  14. Lawanda NS, Frencha PJ, Briaireb JJ, Frijns JHM: Thin Titanium Nitride films deposited using DC magnetron sputtering used for neural stimulation and sensing purposes. Procedia Eng 2012, 47: 726–729.View ArticleGoogle Scholar
  15. Ljungcrantz H, Odén M, Hultman L, Greene JE, Sundgren JE: Nanoindentation studies of single‒crystal (001)‒, (011)‒, and (111)‒oriented TiN layers on MgO. J Appl Phys 1996, 80: 6725–6733. 10.1063/1.363799View ArticleGoogle Scholar
  16. Shin CS, Rudenja S, Gall D, Hellgren N, Lee TY, Petrov I, Greene JE: Growth, surface morphology, and electrical resistivity of fully strained substoichiometric epitaxial layers on MgO (001). J Appl Phys 2004, 95: 356–362. 10.1063/1.1629155View ArticleGoogle Scholar
  17. Li TQ, Noda S, Tsuji Y, Ohsawa T, Komiyama H: Initial growth and texture formation during reactive magnetron sputtering of TiN on Si (111). J Vac Sci Technol A 2002, 20: 583–588. 10.1116/1.1458944View ArticleGoogle Scholar
  18. Ingason AS, Magnus F, Olafsson S, Gudmundsson JT: Morphology of TiN thin films grown on MgO (001) by reactive dc magnetron sputtering. J Vac Sci Technol A 2010, 28: 912–915.View ArticleGoogle Scholar
  19. Chen WC, Wang WL, Tiwari RN, Chang L: Growth and characterization of diamond films on TiN/Si (100) by microwave plasma chemical vapor deposition. Diamond Relat Mater 2009, 18: 124–127. 10.1016/j.diamond.2008.10.018View ArticleGoogle Scholar
  20. Pryds N, Cockburn D, Rodrigo K, Rasmussen IL, Knudesn J, Schou J: Growth of thin films of TiN on MgO (100) monitored by high-pressure RHEED. Appl Phys A 2008, 93: 705–710. 10.1007/s00339-008-4700-2View ArticleGoogle Scholar
  21. Yokota K, Nakamura K, Kasuya T, Mukai K, Ohnishi M: Resistivities of titanium nitride films prepared onto silicon by an ion beam assisted deposition method. J Phys D Appl Phys 2004, 37: 1095–1101. 10.1088/0022-3727/37/7/023View ArticleGoogle Scholar
  22. Biunno N, Narayan J, Srivatsa AR, Holland OW: Laser deposition of epitaxial titanium nitride films on (100) MgO. Appl Phys Lett 1989, 55: 405–407. 10.1063/1.101881View ArticleGoogle Scholar

Copyright

© Chen et al.; licensee Springer. 2014

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.