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Copper film prepared with ArF excimer laser
Applied Surface Science 169±170 (2001) 493±495
Copper ®lm prepared with ArF excimer laser A. Yoshidaa,*, H. Satoa, M. Uchidaa, A. Wakaharaa, A. Hoshinob, H. Machidab a
Department of Electricity and Electronic Engineering, Toyohashi University of Technology, Tenpaku, Toyohashi 441-8580, Japan b TRI Chemical Laboratory Inc., Kitatsurugun, Yamanashi 409-0112, Japan Received 11 August 1999; accepted 9 November 1999
Abstract In the future large-scale integrated circuits, Al metal connection should be replaced because of the large electromigration and the lower electrical conductivity. In this study, Cu metal ®lms were deposited at room temperature on glass substrates by using ArF excimer laser, and the ®lm properties have been investigated. The source material was Cu(hfac)(TMVS). In XPS analyses, the peaks of C, F and O were not found in the ®lms. The resistivity of the samples was decreased sharply after the post-annealing in nitrogen atmosphere. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Cu ®lms; Photo-CVD; Excimer laser
1. Introduction In the future advanced IC technology, the dimension of metal interconnects become smaller and smaller, and the increase in the resistance of metal interconnects induces the signal propagation delay and degrades remarkably the operating characteristics. The higher current density results in the large electromigration in Al interconnects. Copper is one of the promising candidates for replacing Al metal, because the resistivity is lower and highly electromigrationresistant. Copper bulk resistivity is signi®cantly lower than that of Al and Al-alloy, and Cu shows less electromigration. There have been several kinds of deposition techniques of copper metal [1±5]. Since the vapor pressure of Cu halides is substantially low, however,
*
Corresponding author. Tel.: 81-532-44-6738; fax: 81-532-44-6557. E-mail address: [email protected] (A. Yoshida).
the reactive ion etching (RIE) at low temperatures is not easy [6]. At higher substrate temperatures, the conventional photomask cannot be applied, and the patterning with submicron resolution is dif®cult. Hosoi and Ohshita [7] were successful in the photoassisted RIE of Cu ®lms with chlorine gas plasma at low temperatures. Laser-induced CVD is another method for the deposition in a selective manner [8,9], where the desired interconnects can be patterned on the samples with the appropriate mask or by direct writing [10]. In this study, we deposited Cu metal ®lms on glass substrates from Cu(hfac)(TMVS) by using ArF excimer laser, and we have investigated the ®lm properties. 2. Experiments The experimental set-up is shown in Fig. 1. The source material was copper(hexa¯uoroacetylacetonate)(trimethylvinylsilane), Cu(hfac)(TMVS), and was
0169-4332/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 9 - 4 3 3 2 ( 0 0 ) 0 0 7 4 4 - 3
494
A. Yoshida et al. / Applied Surface Science 169±170 (2001) 493±495
Fig. 1. Experimental set-up.
Fig. 3. Film thickness vs. number of laser pulses.
supplied from the container directly connected to the reaction chamber. ArF excimer laser beam (193 nm) was incident through a quartz window and perpendicular to the substrates in the chamber. The window was blown off with nitrogen gas in order to prevent the deposition of ®lms on the inside surface of the window. The repetition rate of the laser beam was 10 Hz and the beam energy was adjusted at 100 and 180 mJ per pulse. The Corning 7059 glass substrates were ultrasonically cleaned in organic solvent, and afterwards in deionized water. During the deposition of the ®lms, the substrates were kept at room temperature without any heating from the outside. The total pressure in the chamber was kept at 0.1 Torr during the deposition.
with the beam energy of 180 mJ per pulse for the number of 60,000 pulses. The two peaks were correspondent to Cu(1 1 1) and Cu(2 0 0) planes. This means that the thin ®lm was composed of polycrystalline copper metal. In scanning electron microscope (SEM) observations, the surface of the deposited ®lms was shiny and smooth. The thickness of the deposited ®lms was increased with increasing the number of the laser pulses, as shown in Fig. 3. For each irradiation dose with 100 and 180 mJ per pulse, the deposition rate was constant, yielding 0.007 and 0.013 nm per pulse, respectively. The deposition rate is proportional to the laser beam power. XPS spectra were measured and the composition of the deposited ®lms was analyzed. As shown in Fig. 4, the peaks related to Cu pure metal were observed. Before the sputter-cleaning of the sample surface with Ar ions, we observed C, F and O peaks. These atoms were highly contained in the source material.
3. Results and discussion The deposited ®lms were characterized with X-ray diffraction (XRD) method. In Fig. 2, the X-ray diffraction pattern is shown on the samples deposited
Fig. 2. X-ray diffraction (XRD) pattern on deposited ®lms.
Fig. 4. XPS spectra before and after sputter cleaning with Ar ions.
A. Yoshida et al. / Applied Surface Science 169±170 (2001) 493±495
However, after the sputter-cleaning of the ®lm surface with 4 kV Ar ions for 3 min, C and F peaks were completely removed, and the very small trace of O peak was only observed, indicating that the ®lms were composed of only Cu metal. Complete reduction of the source material was performed in the deposition process. The resistivity of the ®lms was measured with fourpoint method, giving 41.8 mO cm. This value is much larger than that of pure Cu metal. After the postannealing process at 5008C for one hour in nitrogen atmosphere, the measured resistivity was decreased sharply down to 9.2 mO cm. This is due to the densi®ed structure and the grain growth in the annealed Cu ®lms. This post-annealing process is effective to reduce the resistivity even if the deposition is due to pyrolytic decomposition. But the further improvement for the electrical characteristics of the Cu ®lms is required in this process, because the resistivity is still larger than that of Cu pure metal. 4. Summary We deposited Cu metal ®lms on glass substrates at room temperature from Cu(hfac)(TMVS) by using ArF excimer laser. The deposition of Cu ®lms was con®rmed from XRD and XPS analyses. The deposi-
495
tion rate was constant with increasing the number of irradiating laser pulses, and was proportional to the laser beam energy. The resistivity of the deposited ®lms is signi®cantly higher than that of pure Cu metal. However, after the post-annealing of the ®lms in nitrogen atmosphere, the resistivity of the deposited ®lms was decreased sharply. Although the quality of the ®lms should be improved, this depositing method yields Cu ®lms without impurities from the complete decomposition of the source material. References [1] J. Rober, C. Kaufman, T. Gessner, Appl. Surf. Sci. 91 (1995) 134. [2] A. Jain, K.M. Chi, T.T. Kodas, M.J. Hampden-Smith, J. Electrochem. Soc. 140 (1993) 1434. [3] A.V. Gelatos, R. Marsh, M. Kottke, C.J. Mogab, Appl. Phys. Lett. 63 (1993) 2842. [4] A. Jain, J. Farkas, T.T. Kodas, K.M. Chi, M.J. HampdenSmith, Appl. Phys. Lett. 61 (1992) 2662. [5] F.A. Houle, R.J. Wilson, T.H. Baum, J. Vac. Sci. Technol. A4 (1986) 2452. [6] G.C. Schwartz, P.M. Schaible, J. Electrochem. Soc. 130 (1983) 1777. [7] N. Hosoi, Y. Ohshita, Appl. Phys. Lett. 63 (1993) 2703. [8] R. Izquierdo, J. Bertomeu, M. Suys, E. Sacher, M. Meunier, Appl. Surf. Sci. 86 (1995) 509. [9] J. Han, K.F. Jensen, J. Appl. Phys. 75 (1994) 2240. [10] F. Foulon, M. Stuke, Appl. Phys. Lett. 62 (1993) 2173.
Copper ®lm prepared with ArF excimer laser A. Yoshidaa,*, H. Satoa, M. Uchidaa, A. Wakaharaa, A. Hoshinob, H. Machidab a
Department of Electricity and Electronic Engineering, Toyohashi University of Technology, Tenpaku, Toyohashi 441-8580, Japan b TRI Chemical Laboratory Inc., Kitatsurugun, Yamanashi 409-0112, Japan Received 11 August 1999; accepted 9 November 1999
Abstract In the future large-scale integrated circuits, Al metal connection should be replaced because of the large electromigration and the lower electrical conductivity. In this study, Cu metal ®lms were deposited at room temperature on glass substrates by using ArF excimer laser, and the ®lm properties have been investigated. The source material was Cu(hfac)(TMVS). In XPS analyses, the peaks of C, F and O were not found in the ®lms. The resistivity of the samples was decreased sharply after the post-annealing in nitrogen atmosphere. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Cu ®lms; Photo-CVD; Excimer laser
1. Introduction In the future advanced IC technology, the dimension of metal interconnects become smaller and smaller, and the increase in the resistance of metal interconnects induces the signal propagation delay and degrades remarkably the operating characteristics. The higher current density results in the large electromigration in Al interconnects. Copper is one of the promising candidates for replacing Al metal, because the resistivity is lower and highly electromigrationresistant. Copper bulk resistivity is signi®cantly lower than that of Al and Al-alloy, and Cu shows less electromigration. There have been several kinds of deposition techniques of copper metal [1±5]. Since the vapor pressure of Cu halides is substantially low, however,
*
Corresponding author. Tel.: 81-532-44-6738; fax: 81-532-44-6557. E-mail address: [email protected] (A. Yoshida).
the reactive ion etching (RIE) at low temperatures is not easy [6]. At higher substrate temperatures, the conventional photomask cannot be applied, and the patterning with submicron resolution is dif®cult. Hosoi and Ohshita [7] were successful in the photoassisted RIE of Cu ®lms with chlorine gas plasma at low temperatures. Laser-induced CVD is another method for the deposition in a selective manner [8,9], where the desired interconnects can be patterned on the samples with the appropriate mask or by direct writing [10]. In this study, we deposited Cu metal ®lms on glass substrates from Cu(hfac)(TMVS) by using ArF excimer laser, and we have investigated the ®lm properties. 2. Experiments The experimental set-up is shown in Fig. 1. The source material was copper(hexa¯uoroacetylacetonate)(trimethylvinylsilane), Cu(hfac)(TMVS), and was
0169-4332/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 9 - 4 3 3 2 ( 0 0 ) 0 0 7 4 4 - 3
494
A. Yoshida et al. / Applied Surface Science 169±170 (2001) 493±495
Fig. 1. Experimental set-up.
Fig. 3. Film thickness vs. number of laser pulses.
supplied from the container directly connected to the reaction chamber. ArF excimer laser beam (193 nm) was incident through a quartz window and perpendicular to the substrates in the chamber. The window was blown off with nitrogen gas in order to prevent the deposition of ®lms on the inside surface of the window. The repetition rate of the laser beam was 10 Hz and the beam energy was adjusted at 100 and 180 mJ per pulse. The Corning 7059 glass substrates were ultrasonically cleaned in organic solvent, and afterwards in deionized water. During the deposition of the ®lms, the substrates were kept at room temperature without any heating from the outside. The total pressure in the chamber was kept at 0.1 Torr during the deposition.
with the beam energy of 180 mJ per pulse for the number of 60,000 pulses. The two peaks were correspondent to Cu(1 1 1) and Cu(2 0 0) planes. This means that the thin ®lm was composed of polycrystalline copper metal. In scanning electron microscope (SEM) observations, the surface of the deposited ®lms was shiny and smooth. The thickness of the deposited ®lms was increased with increasing the number of the laser pulses, as shown in Fig. 3. For each irradiation dose with 100 and 180 mJ per pulse, the deposition rate was constant, yielding 0.007 and 0.013 nm per pulse, respectively. The deposition rate is proportional to the laser beam power. XPS spectra were measured and the composition of the deposited ®lms was analyzed. As shown in Fig. 4, the peaks related to Cu pure metal were observed. Before the sputter-cleaning of the sample surface with Ar ions, we observed C, F and O peaks. These atoms were highly contained in the source material.
3. Results and discussion The deposited ®lms were characterized with X-ray diffraction (XRD) method. In Fig. 2, the X-ray diffraction pattern is shown on the samples deposited
Fig. 2. X-ray diffraction (XRD) pattern on deposited ®lms.
Fig. 4. XPS spectra before and after sputter cleaning with Ar ions.
A. Yoshida et al. / Applied Surface Science 169±170 (2001) 493±495
However, after the sputter-cleaning of the ®lm surface with 4 kV Ar ions for 3 min, C and F peaks were completely removed, and the very small trace of O peak was only observed, indicating that the ®lms were composed of only Cu metal. Complete reduction of the source material was performed in the deposition process. The resistivity of the ®lms was measured with fourpoint method, giving 41.8 mO cm. This value is much larger than that of pure Cu metal. After the postannealing process at 5008C for one hour in nitrogen atmosphere, the measured resistivity was decreased sharply down to 9.2 mO cm. This is due to the densi®ed structure and the grain growth in the annealed Cu ®lms. This post-annealing process is effective to reduce the resistivity even if the deposition is due to pyrolytic decomposition. But the further improvement for the electrical characteristics of the Cu ®lms is required in this process, because the resistivity is still larger than that of Cu pure metal. 4. Summary We deposited Cu metal ®lms on glass substrates at room temperature from Cu(hfac)(TMVS) by using ArF excimer laser. The deposition of Cu ®lms was con®rmed from XRD and XPS analyses. The deposi-
495
tion rate was constant with increasing the number of irradiating laser pulses, and was proportional to the laser beam energy. The resistivity of the deposited ®lms is signi®cantly higher than that of pure Cu metal. However, after the post-annealing of the ®lms in nitrogen atmosphere, the resistivity of the deposited ®lms was decreased sharply. Although the quality of the ®lms should be improved, this depositing method yields Cu ®lms without impurities from the complete decomposition of the source material. References [1] J. Rober, C. Kaufman, T. Gessner, Appl. Surf. Sci. 91 (1995) 134. [2] A. Jain, K.M. Chi, T.T. Kodas, M.J. Hampden-Smith, J. Electrochem. Soc. 140 (1993) 1434. [3] A.V. Gelatos, R. Marsh, M. Kottke, C.J. Mogab, Appl. Phys. Lett. 63 (1993) 2842. [4] A. Jain, J. Farkas, T.T. Kodas, K.M. Chi, M.J. HampdenSmith, Appl. Phys. Lett. 61 (1992) 2662. [5] F.A. Houle, R.J. Wilson, T.H. Baum, J. Vac. Sci. Technol. A4 (1986) 2452. [6] G.C. Schwartz, P.M. Schaible, J. Electrochem. Soc. 130 (1983) 1777. [7] N. Hosoi, Y. Ohshita, Appl. Phys. Lett. 63 (1993) 2703. [8] R. Izquierdo, J. Bertomeu, M. Suys, E. Sacher, M. Meunier, Appl. Surf. Sci. 86 (1995) 509. [9] J. Han, K.F. Jensen, J. Appl. Phys. 75 (1994) 2240. [10] F. Foulon, M. Stuke, Appl. Phys. Lett. 62 (1993) 2173.