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New MOCVD precursor for iridium thin films deposition
Materials Letters 61 (2007) 216 – 218 www.elsevier.com/locate/matlet
New MOCVD precursor for iridium thin films deposition Xin Yan ⁎, Qiuyu Zhang, Xiaodong Fan Department of Chemical Engineering, Northwestern Polytechnical University, Xi'an 710072, PR China Received 31 October 2005; accepted 6 April 2006 Available online 5 May 2006
Abstract Thin films of metallic iridium were grown by metal organic chemical vapor deposition in a vertical hot-wall reactor. The new solid compound Ir (thd)3 (thd = 2,2,6,6-tetramethyl-3,5-heptadione) was used as the iridium source. The iridium precursor was analyzed by elemental analysis, infrared spectroscopy, 1H NMR spectroscopy and thermogravimetry (TG). The results of TG showed that the iridium β-diketonate was found to vary with the nature of the β-diketonate group and the use of the thd led to a precursor with higher volatilities than the Ir(acac)3 (acac = acetylacetonate) source. Deposited iridium films were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM) in order to determine crystallinity and surface morphology. © 2006 Elsevier B.V. All rights reserved. Keywords: MOCVD; Thin films; Iridium; Precursor
1. Introduction Depositions of noble metal thin films, including Pt, Pd, Rh, or Ir, are of particular interest because of their unique physical and chemical properties. Generally, these metals have high melting temperature, high resistance towards oxidation and good electrical conductivity; therefore, they are considered as ideal electrode and barrier materials for future microelectronic devices. Iridium, due to the absence of a carbide state and the excellent electrical properties of its oxide, is of great interest to the scientific and technical communities [1,2]. Various physical and chemical processes have been employed to prepare iridium thin films, including chemical vapor deposition (CVD), electrochemical vapor deposition (EVD), sputtering, and other wet chemical processes [3–6]. These vapor deposition methods are generally more expensive because they involved the use of sophisticated reactors and vacuum systems and they are not viable for mass production. Wet processes are cost-effective but rather poor in reproducibility. MOCVD, the precursor based on metal-organic precursors, is a suitable method for the fabrication of many noble thin films [7–9]. It possessed several advantages: simple equipment, high deposition rate, easy control of film composition and availability for conformal coverage. ⁎ Corresponding author. Tel.: +86 29 88495304; fax: +86 29 88491000. E-mail address: [email protected] (X. Yan). 0167-577X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2006.04.034
In a previous report [10], MOCVD technology was used to prepare iridium thin films on a glass substrate with an Ir(acac)3 (acac = acetylacetonate) precursor. Thus resultant iridium films were dense, smooth and homogeneous, with an average grain size of 10–40 nm. However its high melting point and low volatility limited its possible application field. In our work, we report the synthesis of Ir(thd)3 (thd = 2,2,6,6-tetramethyl-3,5heptanedionate), in which two (CH3)3C substituents are introduced onto the acac ligand to improve the volatility of the final
Fig. 1. TG curves of Ir(thd)3 and Ir(acac)3 in N2 with a heating rate of 10 °C/min.
X. Yan et al. / Materials Letters 61 (2007) 216–218
217
Fig. 4. The AFM plane images of the iridium films.
Fig. 2. The XRD pattern of the iridium film deposits at 400 °C on glass substrates.
metal complexes. Iridium thin films were prepared by MOCVD on glass substrates. The structure and morphology of the iridium thin films were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). 2. Experimental The precursor, Ir(thd)3 was synthesized from the H2IrCl6 reaction from aqueous ammonia and Hthd in ethanol/aqueous solution followed by recrystallization from benzene–hexane. The metal complex has been characterized by elemental analysis, infrared spectroscopy, 1H NMR spectroscopy, and thermogravimetry (TG) analysis. Ir(thd)3 was studied by thermogravimetric analysis to get information about volatility and thermal stability. The MOCVD experiments were performed in a vertical hot-wall reactor. The deposition temperature used was at 350– 500 °C. The iridium films were deposited on glass substrates. 3. Results and discussion Fig. 1 shows the TG curves of the samples in N2 which show the sublimation features of Ir(thd)3. The Ir(thd)3 maintains its initial weight
up to about 195 °C in N2 corresponding to its sublimation temperature, then starts to lose weight significantly above 230 °C, and no further weight loss appears up to 290 °C. The residue amount is about 1.76% of the initial weight. The Ir(acac)3 maintains its initial weight up to about 220 °C in N2 corresponding to its sublimation temperature, then starts to lose weight significantly above 260 °C, and no further weight loss appears up to 300 °C. The residue amount is about 1.74% of the initial weight. The TG results show that the Ir(thd)3 is highly volatile than Ir (acac)3, which may serve as a precursor in MOCVD of iridium films. Fig. 2 displays the XRD patterns of the Ir films on glass substrates at the growth temperature of 400 °C. The θ–2θ scan data of the films exhibited strong 2θ peaks at 40.8616°, 47.4554°, and 69.3365°, 83.6825°, 88.1406° respectively, corresponding to the (111), (200), (220), (311) and (222) peaks of Ir, revealing that the Ir films were fully polycrystalline and no evidence for a preferential orientation was found. The EDS data of the iridium films is shown in Fig. 3. The spectra reveal the presence of the Si, Au, Ca, Cu, Ir elements in the films. Among these elements, Si, Ca, and Cu are from the glass substrates and the equipment itself, and Au was deposited by sputtering in order to improve the films conductivity. Thus, the presence of Ir in the films is further confirmed by the EDS data whereby the Ir peak is detected in the EDS spectra. The AFM plane and 3-D images of the iridium films were showed in Figs. 4 and 5. The surface had a roughness of about 1.006 nm. The AFM images show that the Ir films consist of closely spaced particles with various shapes and sizes. The average particle size in the films is 40 nm. We speculate that growth starts probably with the isolated iridium clusters, which grow three dimensionally. Thus the growth mechanism
Fig. 3. The EDS analysis of the iridium film deposits at 400 °C on glass substrates.
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X. Yan et al. / Materials Letters 61 (2007) 216–218
reasoned that the sterically hindered iridium β-diketonate Ir (thd)3 has increased volatility with respect to the Ir(acac)3. The iridium thin films were successfully synthesized on glass substrates at 400 °C by the MOCVD method. Deposited films were found to consist of islands grown on the glass substrate. The growth mechanism follows the Volmer–Weber model. Acknowledgements This work was supported by the National Defence Aviation Foundation of China under contract no 00G53066. Fig. 5. The AFM stereo images of the iridium films.
follows the Volmer–Weber model. Up to now it has not been possible to realize atomic resolution. More detailed investigations will be presented elsewhere.
4. Conclusions The new solid compound Ir(thd)3 (thd = 2,2,6,6-tetramethyl3,5-heptadione) was used as the iridium source. The properties of the iridium β-diketonate were found to vary with the nature of the β-diketonate group and the use of the thd led to a precursor with higher volatilities than the Ir(acac)3 source. We
References [1] Yoon J. Song, H.H. Kim, Sung Y. Lee, D.J. Jung, B.J. Koo, J.K. Lee, Y.S. Park, H.J. Cho, S.O. Park, Kinam Kim, Appl. Phys. Lett. 76 (2000) 451. [2] Ju Cheol Shin, Cheol Seong Hwang, Hyeong Joon Kim, Appl. Phys. Lett. 76 (2000) 1609. [3] J.S. Cohan, Haojie Yuan, R.S. Williams, Appl. Phys. Lett. 60 (1992) 1402. [4] K. Nishio, T. Toshio, Sol. Energy Mater. 68 (2001) 279. [5] T. Pauporte, R. Durand, J. Appl. Electrochem. 30 (2000) 35. [6] K. Mumtaz, J. Echigoya, T. Hirai, J. Mater. Sci. Lett. 12 (1993) 1411. [7] J.P. Endle, Y.-M. Sun, N. Nguyen, Thin Solid Films 388 (2001) 126. [8] Philippe Serp, Roselyne Feurer, Philippe Kalck, Helder Gomes, Joaquin Luis Faria, Jose Luis Figueiredo, Chem. Vap. Depos. 7 (2001) 59. [9] J.P. Endle, Y.-M. Sun, N. Nguyen, Thin Solid Films 388 (2001) 126. [10] Y.-M. Sun, J.P. Endle, K. Smith, Thin Solid Films 346 (1999) 100.
New MOCVD precursor for iridium thin films deposition Xin Yan ⁎, Qiuyu Zhang, Xiaodong Fan Department of Chemical Engineering, Northwestern Polytechnical University, Xi'an 710072, PR China Received 31 October 2005; accepted 6 April 2006 Available online 5 May 2006
Abstract Thin films of metallic iridium were grown by metal organic chemical vapor deposition in a vertical hot-wall reactor. The new solid compound Ir (thd)3 (thd = 2,2,6,6-tetramethyl-3,5-heptadione) was used as the iridium source. The iridium precursor was analyzed by elemental analysis, infrared spectroscopy, 1H NMR spectroscopy and thermogravimetry (TG). The results of TG showed that the iridium β-diketonate was found to vary with the nature of the β-diketonate group and the use of the thd led to a precursor with higher volatilities than the Ir(acac)3 (acac = acetylacetonate) source. Deposited iridium films were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM) in order to determine crystallinity and surface morphology. © 2006 Elsevier B.V. All rights reserved. Keywords: MOCVD; Thin films; Iridium; Precursor
1. Introduction Depositions of noble metal thin films, including Pt, Pd, Rh, or Ir, are of particular interest because of their unique physical and chemical properties. Generally, these metals have high melting temperature, high resistance towards oxidation and good electrical conductivity; therefore, they are considered as ideal electrode and barrier materials for future microelectronic devices. Iridium, due to the absence of a carbide state and the excellent electrical properties of its oxide, is of great interest to the scientific and technical communities [1,2]. Various physical and chemical processes have been employed to prepare iridium thin films, including chemical vapor deposition (CVD), electrochemical vapor deposition (EVD), sputtering, and other wet chemical processes [3–6]. These vapor deposition methods are generally more expensive because they involved the use of sophisticated reactors and vacuum systems and they are not viable for mass production. Wet processes are cost-effective but rather poor in reproducibility. MOCVD, the precursor based on metal-organic precursors, is a suitable method for the fabrication of many noble thin films [7–9]. It possessed several advantages: simple equipment, high deposition rate, easy control of film composition and availability for conformal coverage. ⁎ Corresponding author. Tel.: +86 29 88495304; fax: +86 29 88491000. E-mail address: [email protected] (X. Yan). 0167-577X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2006.04.034
In a previous report [10], MOCVD technology was used to prepare iridium thin films on a glass substrate with an Ir(acac)3 (acac = acetylacetonate) precursor. Thus resultant iridium films were dense, smooth and homogeneous, with an average grain size of 10–40 nm. However its high melting point and low volatility limited its possible application field. In our work, we report the synthesis of Ir(thd)3 (thd = 2,2,6,6-tetramethyl-3,5heptanedionate), in which two (CH3)3C substituents are introduced onto the acac ligand to improve the volatility of the final
Fig. 1. TG curves of Ir(thd)3 and Ir(acac)3 in N2 with a heating rate of 10 °C/min.
X. Yan et al. / Materials Letters 61 (2007) 216–218
217
Fig. 4. The AFM plane images of the iridium films.
Fig. 2. The XRD pattern of the iridium film deposits at 400 °C on glass substrates.
metal complexes. Iridium thin films were prepared by MOCVD on glass substrates. The structure and morphology of the iridium thin films were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). 2. Experimental The precursor, Ir(thd)3 was synthesized from the H2IrCl6 reaction from aqueous ammonia and Hthd in ethanol/aqueous solution followed by recrystallization from benzene–hexane. The metal complex has been characterized by elemental analysis, infrared spectroscopy, 1H NMR spectroscopy, and thermogravimetry (TG) analysis. Ir(thd)3 was studied by thermogravimetric analysis to get information about volatility and thermal stability. The MOCVD experiments were performed in a vertical hot-wall reactor. The deposition temperature used was at 350– 500 °C. The iridium films were deposited on glass substrates. 3. Results and discussion Fig. 1 shows the TG curves of the samples in N2 which show the sublimation features of Ir(thd)3. The Ir(thd)3 maintains its initial weight
up to about 195 °C in N2 corresponding to its sublimation temperature, then starts to lose weight significantly above 230 °C, and no further weight loss appears up to 290 °C. The residue amount is about 1.76% of the initial weight. The Ir(acac)3 maintains its initial weight up to about 220 °C in N2 corresponding to its sublimation temperature, then starts to lose weight significantly above 260 °C, and no further weight loss appears up to 300 °C. The residue amount is about 1.74% of the initial weight. The TG results show that the Ir(thd)3 is highly volatile than Ir (acac)3, which may serve as a precursor in MOCVD of iridium films. Fig. 2 displays the XRD patterns of the Ir films on glass substrates at the growth temperature of 400 °C. The θ–2θ scan data of the films exhibited strong 2θ peaks at 40.8616°, 47.4554°, and 69.3365°, 83.6825°, 88.1406° respectively, corresponding to the (111), (200), (220), (311) and (222) peaks of Ir, revealing that the Ir films were fully polycrystalline and no evidence for a preferential orientation was found. The EDS data of the iridium films is shown in Fig. 3. The spectra reveal the presence of the Si, Au, Ca, Cu, Ir elements in the films. Among these elements, Si, Ca, and Cu are from the glass substrates and the equipment itself, and Au was deposited by sputtering in order to improve the films conductivity. Thus, the presence of Ir in the films is further confirmed by the EDS data whereby the Ir peak is detected in the EDS spectra. The AFM plane and 3-D images of the iridium films were showed in Figs. 4 and 5. The surface had a roughness of about 1.006 nm. The AFM images show that the Ir films consist of closely spaced particles with various shapes and sizes. The average particle size in the films is 40 nm. We speculate that growth starts probably with the isolated iridium clusters, which grow three dimensionally. Thus the growth mechanism
Fig. 3. The EDS analysis of the iridium film deposits at 400 °C on glass substrates.
218
X. Yan et al. / Materials Letters 61 (2007) 216–218
reasoned that the sterically hindered iridium β-diketonate Ir (thd)3 has increased volatility with respect to the Ir(acac)3. The iridium thin films were successfully synthesized on glass substrates at 400 °C by the MOCVD method. Deposited films were found to consist of islands grown on the glass substrate. The growth mechanism follows the Volmer–Weber model. Acknowledgements This work was supported by the National Defence Aviation Foundation of China under contract no 00G53066. Fig. 5. The AFM stereo images of the iridium films.
follows the Volmer–Weber model. Up to now it has not been possible to realize atomic resolution. More detailed investigations will be presented elsewhere.
4. Conclusions The new solid compound Ir(thd)3 (thd = 2,2,6,6-tetramethyl3,5-heptadione) was used as the iridium source. The properties of the iridium β-diketonate were found to vary with the nature of the β-diketonate group and the use of the thd led to a precursor with higher volatilities than the Ir(acac)3 source. We
References [1] Yoon J. Song, H.H. Kim, Sung Y. Lee, D.J. Jung, B.J. Koo, J.K. Lee, Y.S. Park, H.J. Cho, S.O. Park, Kinam Kim, Appl. Phys. Lett. 76 (2000) 451. [2] Ju Cheol Shin, Cheol Seong Hwang, Hyeong Joon Kim, Appl. Phys. Lett. 76 (2000) 1609. [3] J.S. Cohan, Haojie Yuan, R.S. Williams, Appl. Phys. Lett. 60 (1992) 1402. [4] K. Nishio, T. Toshio, Sol. Energy Mater. 68 (2001) 279. [5] T. Pauporte, R. Durand, J. Appl. Electrochem. 30 (2000) 35. [6] K. Mumtaz, J. Echigoya, T. Hirai, J. Mater. Sci. Lett. 12 (1993) 1411. [7] J.P. Endle, Y.-M. Sun, N. Nguyen, Thin Solid Films 388 (2001) 126. [8] Philippe Serp, Roselyne Feurer, Philippe Kalck, Helder Gomes, Joaquin Luis Faria, Jose Luis Figueiredo, Chem. Vap. Depos. 7 (2001) 59. [9] J.P. Endle, Y.-M. Sun, N. Nguyen, Thin Solid Films 388 (2001) 126. [10] Y.-M. Sun, J.P. Endle, K. Smith, Thin Solid Films 346 (1999) 100.