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Chemical vapor deposition of ruthenium oxide thin films from Ru(tmhd)3 using direct liquid injection
Thin Solid Films 413 (2002) 237–242
Chemical vapor deposition of ruthenium oxide thin films from Ru(tmhd)3 using direct liquid injection Dong-Jin Lee, Sang-Woo Kang, Shi-Woo Rhee* Electrical and Computer Engineering Division, Department of Chemical Engineering, Pohang University of Science and Technology (POSTECH), Pohang 790-784, South Korea Received 23 August 2001; received in revised form 11 February 2002; accepted 7 May 2002
Abstract Direct liquid injection (DLI) of Ru(tmhd)3 (tmhds2,2,6,6-tetramethylheptane-3,5-dione) in n-butylacetate solvent was used to deposit ruthenium oxide and ruthenium thin films in the temperature range of 250–450 8C. Arrhenius plot showed that the mass transfer of the reactant determined the deposition rate at high temperature and it was determined by the surface reaction at lower temperature. Depending on the operating conditions, oxide phase, metal phase or mixed phase was obtained. At low O2 flow rate and high injection rate of the precursor solution, the formation of ruthenium was preferred. For example, at the condition of the injection rate of 0.07 mlymin and O2 flow rate of 300 sccm, ruthenium metal phase was deposited over 350 8C. At lower injection rate, ruthenium oxide films with low resistivity of approximately 45–60 mV cm were formed which showed dense and smooth surface morphology. At high deposition temperature, the resistivity of the film was increased due to the carbon incorporation. 䊚 2002 Elsevier Science B.V. All rights reserved. Keywords: DLI-MOCVD; Ruthenium oxide; Ruthenium; Ru(tmhd)3; Electrode
1. Introduction Recently, there has been a considerable interest in the deposition of high dielectric material such as (Ba,Sr)TiO3 and (Pb,Zr)TiO3 for the integration of DRAM (dynamic random access memory) w1x. For the successful application of these materials, the selection of a suitable electrode material is important. The deposition of high dielectric material is performed in the oxygen environment at high temperatures and a suitable electrode material that can endure and prevent oxygen migration is needed. For this reason, noble metals (e.g. Pt, Pd) and conducting oxide (e.g. RuO2, IrO2, etc.) have been chosen as suitable electrode materials w2x. Among these materials, ruthenium dioxide (RuO2), a transition metal oxide with a rutile structure, has drawn attention as a capacitor electrode material since it shows low electrical resistivity (46 mV cm), w3x good etching *Corresponding author. Tel.: q82-54-279-2265; fax: q82-54-2795388. E-mail address: [email protected] (S.-W. Rhee).
w4x and barrier properties against oxygen diffusion w5x. However, RuO2 thin films have been deposited mostly by a sputtering process w1,4x and in this case, it is difficult to obtain conformal step coverage and low stress level films. To overcome these problems, the development of a chemical vapor deposition (CVD) process is required. Especially, the direct liquid injection (DLI)-metal organic chemical vapor deposition (MOCVD) employed in this study is an attractive method to use solid precursors. CVD process has characteristic features including good step coverage, ability to deposit high quality films, good control of composition, and uniformity over a large area. There have been several studies to develop a CVD process for RuO2 w3,6–8x. For example, Green et al. w3x reported the CVD of RuO2 thin films using Ru(C5H7O2)3, Ru3(CO)12 and Ru(C5H5)2. They indicated that a high substrate temperature ()575 8C) is needed to deposit RuO2. In contrast, Park et al. w6x recently reported that RuO2 and Ru films could be deposited at very low substrate temperatures (225–500
0040-6090/02/$ - see front matter 䊚 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 4 0 - 6 0 9 0 Ž 0 2 . 0 0 4 3 9 - X
D.-J. Lee et al. / Thin Solid Films 413 (2002) 237–242
238 Table 1 Deposition conditions of RuO2 thin films Substrate Source Solvent Oxidizer Carrier gas
TiN Ru(tmhd)3 n-butylacetate O2 flow rate Ar flow rate
0–300 sccm 100 sccm
Injection speed Substrate temperature Vaporizer temperature Reactor pressure
0.04 and 0.075 mlymin 250–450 8C 240 8C 1 Torr
0.1 M
8C). Vetrone et al. w7x have also reported depositions of RuO2 films using Ru(tmhd)3 by bubbler method and the deposited RuO2 films had resistivity comparable to that of bulk RuO2 and Bai et al. w12x have studied texture of the RuO2 films depending on the growth temperature and growth rate. Lee et al. w8x recently reported Ru(OD)3 (OD: 2,4-octanedionate)3 as a new liquid source. Ru(tmhd)3 is most promising due to its high vapor pressure and low decomposition temperature but since it is a solid, reproducible delivery into the reactor has been a problem. In this study, we dissolved Ru(tmhd)3 in a solvent to make a liquid solution and deposited RuO2 thin films by using DLI system with a flash evaporator. We studied the deposition characteristics and the film properties such as a composition, resistivity, texture, and morphology. 2. Experimental
Fig. 2. TGAyDSC analysis of Ru(tmhd)3 under (a) Ar atmosphere and (b) O2 atmosphere.
To investigate the thermal properties of the precursor, thermogravimetric analysis (TGA) and differential scan-
ning calorimetry (DSC) were used in N2 atmosphere at a heating rate of 10 8Cymin. RuO2 thin films were deposited with a solution of Ru(tmhd)3 in n-butylacetate. Operating conditions for the deposition are summarized in Table 1. A precise amount of the solution was introduced into the flash evaporator with a syringe pump. A schematic diagram of the experimental setup
Fig. 1. Schematic diagram of the DLI–MOCVD system.
Fig. 3. Arrhenius plot of the growth rate of RuO2 thin films.
D.-J. Lee et al. / Thin Solid Films 413 (2002) 237–242
Fig. 4. XRD pattern of Ru oxide films as a function of the deposition temperature and injection speed. (a) Injection speed: 0.04 mlymin; ˚ (b) Injection speed: 0.075 mlymin (film thickness: 900 A).
was shown in Fig. 1. Vaporizer temperature was held at 240 8C. The reactor pressure was held at 1 Torr by using the throttle valve between the pump and the reaction chamber. The wafers used were TiN on Si. The modified RCA method was used for the pre-deposition cleaning. The temperature of the substrate was between 250 and 450 8C. The phase of the as-deposited film was identified using X-ray diffractometry (XRD) with Cu Ka radiation. Composition of the film was analyzed using X-ray photoelectron spectroscopy (XPS, PHI 5400 ESCA) with Al Ka radiation. The thickness and resistivity were measured using a scanning electron microscopy (SEM) and four-point probe, respectively. Both the surface morphology and the grain size of the film were investigated using SEM. 3. Results and discussion To investigate the thermal behavior of the precursor, DSC and TGA were used under Ar and O2 atmosphere. The results are shown in Fig. 2. In N2 atmosphere, we identified the melting point of Ru(tmhd)3, which was 218 8C. In Fig. 2a, the evaporation of Ru(tmhd)3 was
239
observed without any dissociation of the precursor. Also, the residue left after the evaporation of Ru(tmhd)3 above 250 8C was approximately 5%. It is believed that Ru(tmhd)3 is stable in Ar atmosphere. In O2 atmosphere, other properties were similar to Ar atmosphere but a exothermic peak and rapid weight loss were detected at approximately 250 8C where Ru(tmhd)3 was decomposed and oxidized. Deposition rate was measured as a function of the deposition temperature and the injection speed of a precursor solution. Arrhenius plot of the deposition rate is shown in Fig. 3. For a TiN surface, the deposition rate of RuO2 film was divided into surface reaction and mass transport controlled regimes, as is typically the case in CVD. The surface reaction controlled regime appears below 275 and 300 8C, respectively at the injection speed of 0.04 and 0.075 mlymin, respectively. The value of the activation energy of this regime is 13.5 kcalymol at all injection speed. In the mass transport controlled regime, the value of the apparent activation energy is less than 1.5 kcalymol. As the injection speed is increased, the deposition rate increases in the mass transport controlled regime. These results are in agreement with the general CVD process scheme. The growth rate of mass transport limited region was approximately ˚ 90–120 Aymin. This growth rate by a DLI system was faster than that by a bubbler system w7,9x. However, at the injection speed of 0.075 mlymin, the deposition rate was decreased above 350 8C. In fact, above this temperature, the formation of Ru metal phase was confirmed in the XRD measurement. It is believed that the sudden decrease in the deposition rate is related to the formation of the Ru metal phase. Ru incorporation in the film is directly related to the decrease in the volume or thickness of the film due to the difference of the density of Ru (rRus12.30 gycm3) and RuO2 (rRuO2s6.97 gy cm3). From the X-ray diffraction analysis of the film shown in Fig. 4, we could detect the formation of RuO2, Ru or mixed phase of both. We investigated the effect of the injection speed of the precursor solution and a deposition temperature. O2 flow rate and reactor pressure were fixed at 300 sccm (standard cubic centers per minute) and 1 Torr, respectively. At the injection speed of 0.04 mlymin, the peak of RuO2 phase in XRD was only observed as shown in Fig. 4a. However, at 0.075 mlymin, the peak of RuO2 phase abruptly decreased over 350 8C and the peak of Ru metal phase was observed as shown in Fig. 4b. It is believed that the formation of the Ru metal phase in the as-deposited film is dependent on the ratio of oxygen flow rate and the injection rate of the precursor solution. To investigate the effect of the ratio of oxygen flow rate and the injection rate of the precursor solution on the deposited film phase, the oxygen flow rate was varied from 0 to 300 sccm while other parameters such as Ar flow rate, substrate temperature, and the injection
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Fig. 5. XRD pattern of the film as a function of the oxygen flow rate. Injection speed: 0.075 mlymin and deposition temperature: 300 8C (film ˚ thickness: 900 A).
speed were fixed at 100 sccm, 300 8C, and 0.075 mly min, respectively. Fig. 5 shows the changes in the XRD pattern as a function of the oxygen flow rate. This figure clearly shows that the Ru phase is deposited below 200 sccm of oxygen flow rate, while the intensity of RuO2 peaks increases as the oxygen flow rate is increased from 100 to 300 sccm. This result shows that both phases (Ru and RuO2) can be deposited and the phase composition of the as-deposited film changes from Ru to RuO2 with the increase of oxygen flow rate. Fig. 6 summarizes the operating window of deposition temperature and oxygenyprecursor mole ratio where metal, oxide or mixed phase was formed. It is seen that at lower deposition temperature and higher oxygeny precursor ratio, oxide formation is preferred. Fig. 7 shows the Ru 3d region of the XPS spectra of films grown at 300 and 400 8C. The binding energies at 280.0 and 284.1 eV correspond to Ru 3d5y2 and Ru 3d3y2, respectively w10x. C 1s and Ru 3d3y2 peak appear at the same energy level and carbon content in the film was measured indirectly by comparing Ru 3d3y2 and Ru 3d5y2 peak intensity w11x. For pure metallic Ru, Ru 3d3y2 and Ru 3d5y2 peak intensity ratio is 2:3 and when carbon is incorporated, the ratio becomes higher. In Fig. 7a the intensity ratio of Ru 3d3y2 and Ru 3d5y2 peak is 2.02:3. It means that carbon was not contained in the film. In the case of the film deposited at 400 8C (Fig. 7b), the intensity ratio is 2.51:3. From this result, we believe that carbon is incorporated at higher deposition temperature and in this case, the resistivity is increased.
Fig. 8a shows the resistivity of the film as a function of the deposition temperature. The injection speed of the precursor solution used were at 0.04 and 0.075 mly min and the deposition temperature was varied from 250 to 450 8C at each injection speed. At the injection speed of 0.04 mlymin, only RuO2 is deposited at all
Fig. 6. The region of Ru, RuO2 and mixed phase formation as a function of the deposition temperature and the mole ratio of O2yprecursor.
D.-J. Lee et al. / Thin Solid Films 413 (2002) 237–242
241
Fig. 8. XPS analysis of the RuO2 thin film deposited at (a) 300 8C and (b) 400 8C. (O2: 300 sccm, injection speed: 0.04 mlymin).
Fig. 7. Resistivity of the film as a function of the deposition temperature. (a) Injection speed: 0.04 mlymin; (b) Injection speed: 0.075 ˚ mlymin (film thickness: 900 A).
deposition temperatures and the resistivity was increased as the deposition temperature was increased due to the incorporation of the carbon impurities. At the injection speed of 0.075 mlymin, Fig. 8b shows that above 350 8C, the resistivity suddenly decreased. This occurs because of the formation of Ru metal in the RuO2 film. This result was confirmed by the XRD measurement. Over 400 8C, the resistivity was increased with increasing deposition temperature due to the impurity incorporation. Fig. 9a and b show the surface morphology of RuO2 films deposited at 275 and 400 8C respectively. All RuO2 films were crack-free and well adhered on the TiN substrates. The RuO2 films deposited at 275 8C had
a clean, specular dark blue and dense surface and the film deposited at 400 8C had a rough surface and large ˚ grains. The grain size is approximately 300 and 900 A at the deposition temperature of 275 and 400 8C, respectively. The grain size was increased as a function of the deposition temperature. 4. Conclusion The thermal properties of Ru(tmhd)3 were investigated by thermal analysis and RuO2 films were deposited by DLI-MOCVD system using the liquid solution prepared by dissolving Ru(tmhd)3, a solid phase, in nbutylacetate. The effect of process parameters (e.g. O2 flow rate, the injection rate of precursor solution, and deposition temperature) on deposition behavior was investigated. Depending on the operating conditions, RuO2 oxide phase, Ru metal phase or mixed phase was obtained. At lower injection rate, RuO2 films were formed which showed dense and smooth surface mor-
242
D.-J. Lee et al. / Thin Solid Films 413 (2002) 237–242
phology with resistivity of approximately 45–60 mV cm. At high deposition temperature, the resistivity of the film was increased due to the carbon incorporation. Acknowledgments This work is partly financed by the Censortium of Semiconductor Advanced Research (Project no. 00-B6CO-00-09-00-01). References
Fig. 9. Surface morphology of RuO2 thin films deposited on TiN at (a) 275 8C and (b) 400 8C (O2: 300 sccm, injection speed: 0.04 ˚ mlymin, film thickness: 900 A).
w1x T. Kawahara, M. Yamamura, A. Yuuki, K. Ono, Jpn J. Appl. Phys. 35 (1996) 4880. w2x R. Ramesh, Thin Film Ferroelectric Materials and Device, Kluwer Academic Press, Amsterdam, 1997, p. 24. w3x M.L. Green, M.E. Gross, L.E. Papa, K.J. Schnoes, D. Brasen, J. Electrochem. Soc. 132 (1985) 2677. w4x S. Saito, K. Kuramasu, Jpn J. Appl. Phys. 31 (1992) 135. w5x L. Krusin-Elbaum, M. Wittmer, J. Electrochem. Soc. 135 (1988) 2610. w6x S.-E. Park, H.-M. Kim, K.-B. Kim, S.-H. Min, J. Electrochem. Soc. 147 (2000) 203. w7x J. Vetrone, C.M. Foster, G.R. Bai, A. Wang, J. Mater. Res. 13 (1998) 2281. w8x J.-H. Lee, J.-Y. Kim, S.-W. Rhee, Electochem. Solid-State Lett. 2 (1999) 622. w9x J.M. Lee, J.C. Shin, C.S. Hwang, H.J. Kim, J. Vac. Sci. Tech. A 16 (1998) 2768. w10x K.S. Kim, N. Winograd, J. Catalysis 35 (1974) 66. w11x Y. Senzaki, W.L. Gladfelter, F.B. McCormick, Chem. Mater. 5 (1993) 1715. w12x G.R. Bai, A. Wang, C.M. Foster, J. Vetrone, Thin Solid films 310 (1997) 75.
Chemical vapor deposition of ruthenium oxide thin films from Ru(tmhd)3 using direct liquid injection Dong-Jin Lee, Sang-Woo Kang, Shi-Woo Rhee* Electrical and Computer Engineering Division, Department of Chemical Engineering, Pohang University of Science and Technology (POSTECH), Pohang 790-784, South Korea Received 23 August 2001; received in revised form 11 February 2002; accepted 7 May 2002
Abstract Direct liquid injection (DLI) of Ru(tmhd)3 (tmhds2,2,6,6-tetramethylheptane-3,5-dione) in n-butylacetate solvent was used to deposit ruthenium oxide and ruthenium thin films in the temperature range of 250–450 8C. Arrhenius plot showed that the mass transfer of the reactant determined the deposition rate at high temperature and it was determined by the surface reaction at lower temperature. Depending on the operating conditions, oxide phase, metal phase or mixed phase was obtained. At low O2 flow rate and high injection rate of the precursor solution, the formation of ruthenium was preferred. For example, at the condition of the injection rate of 0.07 mlymin and O2 flow rate of 300 sccm, ruthenium metal phase was deposited over 350 8C. At lower injection rate, ruthenium oxide films with low resistivity of approximately 45–60 mV cm were formed which showed dense and smooth surface morphology. At high deposition temperature, the resistivity of the film was increased due to the carbon incorporation. 䊚 2002 Elsevier Science B.V. All rights reserved. Keywords: DLI-MOCVD; Ruthenium oxide; Ruthenium; Ru(tmhd)3; Electrode
1. Introduction Recently, there has been a considerable interest in the deposition of high dielectric material such as (Ba,Sr)TiO3 and (Pb,Zr)TiO3 for the integration of DRAM (dynamic random access memory) w1x. For the successful application of these materials, the selection of a suitable electrode material is important. The deposition of high dielectric material is performed in the oxygen environment at high temperatures and a suitable electrode material that can endure and prevent oxygen migration is needed. For this reason, noble metals (e.g. Pt, Pd) and conducting oxide (e.g. RuO2, IrO2, etc.) have been chosen as suitable electrode materials w2x. Among these materials, ruthenium dioxide (RuO2), a transition metal oxide with a rutile structure, has drawn attention as a capacitor electrode material since it shows low electrical resistivity (46 mV cm), w3x good etching *Corresponding author. Tel.: q82-54-279-2265; fax: q82-54-2795388. E-mail address: [email protected] (S.-W. Rhee).
w4x and barrier properties against oxygen diffusion w5x. However, RuO2 thin films have been deposited mostly by a sputtering process w1,4x and in this case, it is difficult to obtain conformal step coverage and low stress level films. To overcome these problems, the development of a chemical vapor deposition (CVD) process is required. Especially, the direct liquid injection (DLI)-metal organic chemical vapor deposition (MOCVD) employed in this study is an attractive method to use solid precursors. CVD process has characteristic features including good step coverage, ability to deposit high quality films, good control of composition, and uniformity over a large area. There have been several studies to develop a CVD process for RuO2 w3,6–8x. For example, Green et al. w3x reported the CVD of RuO2 thin films using Ru(C5H7O2)3, Ru3(CO)12 and Ru(C5H5)2. They indicated that a high substrate temperature ()575 8C) is needed to deposit RuO2. In contrast, Park et al. w6x recently reported that RuO2 and Ru films could be deposited at very low substrate temperatures (225–500
0040-6090/02/$ - see front matter 䊚 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 4 0 - 6 0 9 0 Ž 0 2 . 0 0 4 3 9 - X
D.-J. Lee et al. / Thin Solid Films 413 (2002) 237–242
238 Table 1 Deposition conditions of RuO2 thin films Substrate Source Solvent Oxidizer Carrier gas
TiN Ru(tmhd)3 n-butylacetate O2 flow rate Ar flow rate
0–300 sccm 100 sccm
Injection speed Substrate temperature Vaporizer temperature Reactor pressure
0.04 and 0.075 mlymin 250–450 8C 240 8C 1 Torr
0.1 M
8C). Vetrone et al. w7x have also reported depositions of RuO2 films using Ru(tmhd)3 by bubbler method and the deposited RuO2 films had resistivity comparable to that of bulk RuO2 and Bai et al. w12x have studied texture of the RuO2 films depending on the growth temperature and growth rate. Lee et al. w8x recently reported Ru(OD)3 (OD: 2,4-octanedionate)3 as a new liquid source. Ru(tmhd)3 is most promising due to its high vapor pressure and low decomposition temperature but since it is a solid, reproducible delivery into the reactor has been a problem. In this study, we dissolved Ru(tmhd)3 in a solvent to make a liquid solution and deposited RuO2 thin films by using DLI system with a flash evaporator. We studied the deposition characteristics and the film properties such as a composition, resistivity, texture, and morphology. 2. Experimental
Fig. 2. TGAyDSC analysis of Ru(tmhd)3 under (a) Ar atmosphere and (b) O2 atmosphere.
To investigate the thermal properties of the precursor, thermogravimetric analysis (TGA) and differential scan-
ning calorimetry (DSC) were used in N2 atmosphere at a heating rate of 10 8Cymin. RuO2 thin films were deposited with a solution of Ru(tmhd)3 in n-butylacetate. Operating conditions for the deposition are summarized in Table 1. A precise amount of the solution was introduced into the flash evaporator with a syringe pump. A schematic diagram of the experimental setup
Fig. 1. Schematic diagram of the DLI–MOCVD system.
Fig. 3. Arrhenius plot of the growth rate of RuO2 thin films.
D.-J. Lee et al. / Thin Solid Films 413 (2002) 237–242
Fig. 4. XRD pattern of Ru oxide films as a function of the deposition temperature and injection speed. (a) Injection speed: 0.04 mlymin; ˚ (b) Injection speed: 0.075 mlymin (film thickness: 900 A).
was shown in Fig. 1. Vaporizer temperature was held at 240 8C. The reactor pressure was held at 1 Torr by using the throttle valve between the pump and the reaction chamber. The wafers used were TiN on Si. The modified RCA method was used for the pre-deposition cleaning. The temperature of the substrate was between 250 and 450 8C. The phase of the as-deposited film was identified using X-ray diffractometry (XRD) with Cu Ka radiation. Composition of the film was analyzed using X-ray photoelectron spectroscopy (XPS, PHI 5400 ESCA) with Al Ka radiation. The thickness and resistivity were measured using a scanning electron microscopy (SEM) and four-point probe, respectively. Both the surface morphology and the grain size of the film were investigated using SEM. 3. Results and discussion To investigate the thermal behavior of the precursor, DSC and TGA were used under Ar and O2 atmosphere. The results are shown in Fig. 2. In N2 atmosphere, we identified the melting point of Ru(tmhd)3, which was 218 8C. In Fig. 2a, the evaporation of Ru(tmhd)3 was
239
observed without any dissociation of the precursor. Also, the residue left after the evaporation of Ru(tmhd)3 above 250 8C was approximately 5%. It is believed that Ru(tmhd)3 is stable in Ar atmosphere. In O2 atmosphere, other properties were similar to Ar atmosphere but a exothermic peak and rapid weight loss were detected at approximately 250 8C where Ru(tmhd)3 was decomposed and oxidized. Deposition rate was measured as a function of the deposition temperature and the injection speed of a precursor solution. Arrhenius plot of the deposition rate is shown in Fig. 3. For a TiN surface, the deposition rate of RuO2 film was divided into surface reaction and mass transport controlled regimes, as is typically the case in CVD. The surface reaction controlled regime appears below 275 and 300 8C, respectively at the injection speed of 0.04 and 0.075 mlymin, respectively. The value of the activation energy of this regime is 13.5 kcalymol at all injection speed. In the mass transport controlled regime, the value of the apparent activation energy is less than 1.5 kcalymol. As the injection speed is increased, the deposition rate increases in the mass transport controlled regime. These results are in agreement with the general CVD process scheme. The growth rate of mass transport limited region was approximately ˚ 90–120 Aymin. This growth rate by a DLI system was faster than that by a bubbler system w7,9x. However, at the injection speed of 0.075 mlymin, the deposition rate was decreased above 350 8C. In fact, above this temperature, the formation of Ru metal phase was confirmed in the XRD measurement. It is believed that the sudden decrease in the deposition rate is related to the formation of the Ru metal phase. Ru incorporation in the film is directly related to the decrease in the volume or thickness of the film due to the difference of the density of Ru (rRus12.30 gycm3) and RuO2 (rRuO2s6.97 gy cm3). From the X-ray diffraction analysis of the film shown in Fig. 4, we could detect the formation of RuO2, Ru or mixed phase of both. We investigated the effect of the injection speed of the precursor solution and a deposition temperature. O2 flow rate and reactor pressure were fixed at 300 sccm (standard cubic centers per minute) and 1 Torr, respectively. At the injection speed of 0.04 mlymin, the peak of RuO2 phase in XRD was only observed as shown in Fig. 4a. However, at 0.075 mlymin, the peak of RuO2 phase abruptly decreased over 350 8C and the peak of Ru metal phase was observed as shown in Fig. 4b. It is believed that the formation of the Ru metal phase in the as-deposited film is dependent on the ratio of oxygen flow rate and the injection rate of the precursor solution. To investigate the effect of the ratio of oxygen flow rate and the injection rate of the precursor solution on the deposited film phase, the oxygen flow rate was varied from 0 to 300 sccm while other parameters such as Ar flow rate, substrate temperature, and the injection
240
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Fig. 5. XRD pattern of the film as a function of the oxygen flow rate. Injection speed: 0.075 mlymin and deposition temperature: 300 8C (film ˚ thickness: 900 A).
speed were fixed at 100 sccm, 300 8C, and 0.075 mly min, respectively. Fig. 5 shows the changes in the XRD pattern as a function of the oxygen flow rate. This figure clearly shows that the Ru phase is deposited below 200 sccm of oxygen flow rate, while the intensity of RuO2 peaks increases as the oxygen flow rate is increased from 100 to 300 sccm. This result shows that both phases (Ru and RuO2) can be deposited and the phase composition of the as-deposited film changes from Ru to RuO2 with the increase of oxygen flow rate. Fig. 6 summarizes the operating window of deposition temperature and oxygenyprecursor mole ratio where metal, oxide or mixed phase was formed. It is seen that at lower deposition temperature and higher oxygeny precursor ratio, oxide formation is preferred. Fig. 7 shows the Ru 3d region of the XPS spectra of films grown at 300 and 400 8C. The binding energies at 280.0 and 284.1 eV correspond to Ru 3d5y2 and Ru 3d3y2, respectively w10x. C 1s and Ru 3d3y2 peak appear at the same energy level and carbon content in the film was measured indirectly by comparing Ru 3d3y2 and Ru 3d5y2 peak intensity w11x. For pure metallic Ru, Ru 3d3y2 and Ru 3d5y2 peak intensity ratio is 2:3 and when carbon is incorporated, the ratio becomes higher. In Fig. 7a the intensity ratio of Ru 3d3y2 and Ru 3d5y2 peak is 2.02:3. It means that carbon was not contained in the film. In the case of the film deposited at 400 8C (Fig. 7b), the intensity ratio is 2.51:3. From this result, we believe that carbon is incorporated at higher deposition temperature and in this case, the resistivity is increased.
Fig. 8a shows the resistivity of the film as a function of the deposition temperature. The injection speed of the precursor solution used were at 0.04 and 0.075 mly min and the deposition temperature was varied from 250 to 450 8C at each injection speed. At the injection speed of 0.04 mlymin, only RuO2 is deposited at all
Fig. 6. The region of Ru, RuO2 and mixed phase formation as a function of the deposition temperature and the mole ratio of O2yprecursor.
D.-J. Lee et al. / Thin Solid Films 413 (2002) 237–242
241
Fig. 8. XPS analysis of the RuO2 thin film deposited at (a) 300 8C and (b) 400 8C. (O2: 300 sccm, injection speed: 0.04 mlymin).
Fig. 7. Resistivity of the film as a function of the deposition temperature. (a) Injection speed: 0.04 mlymin; (b) Injection speed: 0.075 ˚ mlymin (film thickness: 900 A).
deposition temperatures and the resistivity was increased as the deposition temperature was increased due to the incorporation of the carbon impurities. At the injection speed of 0.075 mlymin, Fig. 8b shows that above 350 8C, the resistivity suddenly decreased. This occurs because of the formation of Ru metal in the RuO2 film. This result was confirmed by the XRD measurement. Over 400 8C, the resistivity was increased with increasing deposition temperature due to the impurity incorporation. Fig. 9a and b show the surface morphology of RuO2 films deposited at 275 and 400 8C respectively. All RuO2 films were crack-free and well adhered on the TiN substrates. The RuO2 films deposited at 275 8C had
a clean, specular dark blue and dense surface and the film deposited at 400 8C had a rough surface and large ˚ grains. The grain size is approximately 300 and 900 A at the deposition temperature of 275 and 400 8C, respectively. The grain size was increased as a function of the deposition temperature. 4. Conclusion The thermal properties of Ru(tmhd)3 were investigated by thermal analysis and RuO2 films were deposited by DLI-MOCVD system using the liquid solution prepared by dissolving Ru(tmhd)3, a solid phase, in nbutylacetate. The effect of process parameters (e.g. O2 flow rate, the injection rate of precursor solution, and deposition temperature) on deposition behavior was investigated. Depending on the operating conditions, RuO2 oxide phase, Ru metal phase or mixed phase was obtained. At lower injection rate, RuO2 films were formed which showed dense and smooth surface mor-
242
D.-J. Lee et al. / Thin Solid Films 413 (2002) 237–242
phology with resistivity of approximately 45–60 mV cm. At high deposition temperature, the resistivity of the film was increased due to the carbon incorporation. Acknowledgments This work is partly financed by the Censortium of Semiconductor Advanced Research (Project no. 00-B6CO-00-09-00-01). References
Fig. 9. Surface morphology of RuO2 thin films deposited on TiN at (a) 275 8C and (b) 400 8C (O2: 300 sccm, injection speed: 0.04 ˚ mlymin, film thickness: 900 A).
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