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Ion-assisted deposition of copper using an inverter plasma
Surface and Coatings Technology 136 Ž2001. 273᎐275
Ion-assisted deposition of copper using an inverter plasma Masato Kiuchi a,U , Kensuke Murai a , Katsutoshi Tanakab, Seiji Takechi b, Satoshi Sugimotob, Seiichi Goto b a
b
Osaka National Research Institute, Midorigaoka, Ikeda, Osaka 563-8577, Japan Plasma Physics Laboratory, Osaka Uni¨ ersity, Yamadaoka, Suita, Osaka 565-0871, Japan
Abstract Adhesive Cu deposition using an inverter plasma was studied. Using an inverter power supply to produce a pulse plasma, it is possible to apply high voltage in one direction and low voltage in the other, and to perform deposition by a process of sputtering alternating with ion assistance. We deposited Cu film by setting the Cu target in front of the substrate using Si wafer and glass. Deposited films were examined by a peel-off test using Scotch tape. They exhibited excellent adhesion. 䊚 2001 Elsevier Science B.V. All rights reserved. Keywords: Inverter; Pulse plasma; Copper; Ion-assisted deposition
1. Introduction An inverter plasma is a pulse plasma produced by a high-voltage power supply with an inverter circuit for alternate bipolar pulse generation. This set-up allows easy control of the voltage and pulse in both directions w1,2x, which makes a wide variety of applications possible, as demonstrated in a recent trial w3x. In the present study, we demonstrated that this inverter system is applicable to coating processes. The inverter plasma makes it possible to use the ion-assisted deposition method w4x, which produces excellent adhesion. Setting a substrate in front of a sputter target in an Ar atmosphere and applying a high-voltage pulse to the substrate results in sputter deposition of the target material on the substrate. Subsequent application of a pulse of lower voltage to the substrate results in irradiation by Ar ions, which assists deposition. In the present study, deposition of an adhesive copper film was
U
Corresponding author. Fax: q81-727-51-9535. E-mail address: [email protected] ŽM. Kiuchi..
used as an initial demonstration of the advantages of the inverter plasma method as a coating technology. Copper deposition has attracted much attention in recent years because of its application in microprocessor wiring. Much relevant research is performed using wet processes, but dry processes are also interesting from an environmental viewpoint.
2. Experimental Fig. 1 is a schematic illustration of the ion-assisted deposition process using an inverter plasma. Two copper electrodes ŽE 1 , E 2 . are set up in a vacuum chamber with a piece of Si wafer or glass as substrate ŽS. on electrode E 1. After evacuation to 10 Pa, pressure is returned to 260 Pa with Ar gas. Using the inverter power supply, a high voltage Ž V1 . of ca. 650 V is applied to electrode E 1. A glow discharge is generated between the electrodes, and the sheath around electrode E 2 accelerates the Ar ions toward electrode E 2 . The copper atoms, which make up the electrode E 2 , are sputtered in the direction of electrode E 1 , resulting in deposition of copper on substrate S. As the sput-
0257-8972r01r$ - see front matter 䊚 2001 Elsevier Science B.V. All rights reserved. PII: S 0 2 5 7 - 8 9 7 2 Ž 0 0 . 0 1 0 3 0 - 6
M. Kiuchi et al. r Surface and Coatings Technology 136 (2001) 273᎐275
274
Fig. 1. Schematic illustration of ion-assisted deposition using inverter plasma. E 1 , E 2 electrodes; S, substrate; V1 , voltage for sputtering; V2 , voltage for ion assisting.
tered copper atoms are neutral, they are not affected by the electric field. Next, using the inverter power supply, a lower voltage Ž V2 . of ca. 250 V is applied to electrode E 2 to generate a glow discharge. The Ar ions are accelerated by the sheath, and the deposited copper film is irradiated and excited. V1 must be high enough to make the target sputter and V2 low enough to not make the deposited film sputter. Ion-assisted deposition is realized by repeating this process until an adhesive copper film is formed. To demonstrate the advantages of this process, V1 and V2 were set in the range 0᎐650 V. The frequency for repetition of the process was 10 kHz. Detailed experimental parameters are shown in Table 1. The samples produced were examined by Rutherford backscattering spectroscopy ŽRBS. using a 1-MeV Heq ion beam. The thickness of the films was determined by ellipsometry.
irradiated by Arq ions. Thus, contamination with a small amount of Cu was observed on the surface of sample 1.
3. Results and discussion RBS data of samples 1᎐4 are shown in Fig. 2. In the production of sample 1, V1 was set at 0. The target did not sputter, but the sample holder made of Cu was Table 1 Experimental conditions Sample
Substrate
V1 ŽV.
V2 ŽV.
Deposition time Žmin.
1 2 3 4 5 6
Si Si Si Si Glass Glass
0 650 600 600 650 650
650 0 250 250 0 250
30 30 30 120 120 120
Fig. 2. RBS spectra of deposited specimens: Ža. sample 1; Žb. sample 2; Žc. sample 3; and Žd. sample 4.
M. Kiuchi et al. r Surface and Coatings Technology 136 (2001) 273᎐275
In the production of sample 2, the target was made to sputter by setting V1 at 650 V. The substrate received a deposition of sputtered copper in an atmosphere of Ar. However, as V2 was set at 0, the substrate had no ion assistance. In the RBS spectrum ŽFig. 2b., a very small amount of Ar contamination from the atmosphere was observed. For sample 3, V1 and V2 were 650 and 250 V, respectively. Under these conditions, ion-assisted deposition occurred. In the RBS spectrum ŽFig. 2c., implanted Ar was observed. Ion-beam mixing at the interface of the Cu film and the Si substrate was also noted. The tail of Cu at channel 340 is broader than for sample 2. This mixing effect guarantees high adhesion of the film to the substrate. The film thickness was 25 nm. Inverter conditions for sample 4 were identical to those for sample 3. Because of the longer deposition time Ž120 min., the deposited film was thicker than for no. 3, at 58 nm. In the RBS spectrum, a peak for Ar was observed, and an intermixed layer at the interface of the Si and the Cu film was also clearly seen. The Si peak at channel 260 and the Cu peak at channel 320 are broader than in sample 3. Oxygen contamination in the film was also observed at channel 150. The above results confirmed that inverter conditions with V1 higher than V2 result in deposition, and that application of an assisting voltage Ž V2 . leads to the formation of an intermixed layer. To test the strength of adhesion, we used Scotch tape to conduct a peel-off test on films deposited on glass plates. The sputter voltage for V1 was set at 650 V and the assisting voltage Ž V2 . for samples 5 and 6 at 0 and
275
250 V, respectively. Thus, sample 5 underwent sputter deposition while sample 6 underwent ion-assisted deposition. In a test using Scotch tape, the film peeled off from sample 5, but not from sample 6, demonstrating the high adhesion achieved by ion-assisted deposition using the inverter plasma.
4. Conclusion An inverter power supply was used to conduct an ion-beam deposition process, which was demonstrated to produce adhesive copper deposition. As the technique is simple, it could be used in a wide variety of manufacturing applications at low cost.
Acknowledgements We thank Dr Akio Okamoto of the Technical Research Institute of Osaka Prefecture for conducting RBS measurements. References w1x S. Sugimoto, M. Kiuchi, S. Takechi, K. Tanaka, S. Goto, in: Proceedings of PBII ’99, Surf. Coat. Technol. Žin press.. w2x S. Takechi, S. Sugimoto, M. Kiuchi, K. Tanaka, S. Goto, in: Proceedings of PBII ’99, Surf. Coat. Technol. Žin press.. w3x N. Murakami, K. Tanaka, S. Sugimoto, M. Kiuchi, S. Goto, in: Proceedings of PBII ’99, Surf. Coat. Technol. Žin press.. w4x M. Kiuchi, Nucl. Instrum. Methods Phys. Res. B 80r81 Ž1993. 1343.
Ion-assisted deposition of copper using an inverter plasma Masato Kiuchi a,U , Kensuke Murai a , Katsutoshi Tanakab, Seiji Takechi b, Satoshi Sugimotob, Seiichi Goto b a
b
Osaka National Research Institute, Midorigaoka, Ikeda, Osaka 563-8577, Japan Plasma Physics Laboratory, Osaka Uni¨ ersity, Yamadaoka, Suita, Osaka 565-0871, Japan
Abstract Adhesive Cu deposition using an inverter plasma was studied. Using an inverter power supply to produce a pulse plasma, it is possible to apply high voltage in one direction and low voltage in the other, and to perform deposition by a process of sputtering alternating with ion assistance. We deposited Cu film by setting the Cu target in front of the substrate using Si wafer and glass. Deposited films were examined by a peel-off test using Scotch tape. They exhibited excellent adhesion. 䊚 2001 Elsevier Science B.V. All rights reserved. Keywords: Inverter; Pulse plasma; Copper; Ion-assisted deposition
1. Introduction An inverter plasma is a pulse plasma produced by a high-voltage power supply with an inverter circuit for alternate bipolar pulse generation. This set-up allows easy control of the voltage and pulse in both directions w1,2x, which makes a wide variety of applications possible, as demonstrated in a recent trial w3x. In the present study, we demonstrated that this inverter system is applicable to coating processes. The inverter plasma makes it possible to use the ion-assisted deposition method w4x, which produces excellent adhesion. Setting a substrate in front of a sputter target in an Ar atmosphere and applying a high-voltage pulse to the substrate results in sputter deposition of the target material on the substrate. Subsequent application of a pulse of lower voltage to the substrate results in irradiation by Ar ions, which assists deposition. In the present study, deposition of an adhesive copper film was
U
Corresponding author. Fax: q81-727-51-9535. E-mail address: [email protected] ŽM. Kiuchi..
used as an initial demonstration of the advantages of the inverter plasma method as a coating technology. Copper deposition has attracted much attention in recent years because of its application in microprocessor wiring. Much relevant research is performed using wet processes, but dry processes are also interesting from an environmental viewpoint.
2. Experimental Fig. 1 is a schematic illustration of the ion-assisted deposition process using an inverter plasma. Two copper electrodes ŽE 1 , E 2 . are set up in a vacuum chamber with a piece of Si wafer or glass as substrate ŽS. on electrode E 1. After evacuation to 10 Pa, pressure is returned to 260 Pa with Ar gas. Using the inverter power supply, a high voltage Ž V1 . of ca. 650 V is applied to electrode E 1. A glow discharge is generated between the electrodes, and the sheath around electrode E 2 accelerates the Ar ions toward electrode E 2 . The copper atoms, which make up the electrode E 2 , are sputtered in the direction of electrode E 1 , resulting in deposition of copper on substrate S. As the sput-
0257-8972r01r$ - see front matter 䊚 2001 Elsevier Science B.V. All rights reserved. PII: S 0 2 5 7 - 8 9 7 2 Ž 0 0 . 0 1 0 3 0 - 6
M. Kiuchi et al. r Surface and Coatings Technology 136 (2001) 273᎐275
274
Fig. 1. Schematic illustration of ion-assisted deposition using inverter plasma. E 1 , E 2 electrodes; S, substrate; V1 , voltage for sputtering; V2 , voltage for ion assisting.
tered copper atoms are neutral, they are not affected by the electric field. Next, using the inverter power supply, a lower voltage Ž V2 . of ca. 250 V is applied to electrode E 2 to generate a glow discharge. The Ar ions are accelerated by the sheath, and the deposited copper film is irradiated and excited. V1 must be high enough to make the target sputter and V2 low enough to not make the deposited film sputter. Ion-assisted deposition is realized by repeating this process until an adhesive copper film is formed. To demonstrate the advantages of this process, V1 and V2 were set in the range 0᎐650 V. The frequency for repetition of the process was 10 kHz. Detailed experimental parameters are shown in Table 1. The samples produced were examined by Rutherford backscattering spectroscopy ŽRBS. using a 1-MeV Heq ion beam. The thickness of the films was determined by ellipsometry.
irradiated by Arq ions. Thus, contamination with a small amount of Cu was observed on the surface of sample 1.
3. Results and discussion RBS data of samples 1᎐4 are shown in Fig. 2. In the production of sample 1, V1 was set at 0. The target did not sputter, but the sample holder made of Cu was Table 1 Experimental conditions Sample
Substrate
V1 ŽV.
V2 ŽV.
Deposition time Žmin.
1 2 3 4 5 6
Si Si Si Si Glass Glass
0 650 600 600 650 650
650 0 250 250 0 250
30 30 30 120 120 120
Fig. 2. RBS spectra of deposited specimens: Ža. sample 1; Žb. sample 2; Žc. sample 3; and Žd. sample 4.
M. Kiuchi et al. r Surface and Coatings Technology 136 (2001) 273᎐275
In the production of sample 2, the target was made to sputter by setting V1 at 650 V. The substrate received a deposition of sputtered copper in an atmosphere of Ar. However, as V2 was set at 0, the substrate had no ion assistance. In the RBS spectrum ŽFig. 2b., a very small amount of Ar contamination from the atmosphere was observed. For sample 3, V1 and V2 were 650 and 250 V, respectively. Under these conditions, ion-assisted deposition occurred. In the RBS spectrum ŽFig. 2c., implanted Ar was observed. Ion-beam mixing at the interface of the Cu film and the Si substrate was also noted. The tail of Cu at channel 340 is broader than for sample 2. This mixing effect guarantees high adhesion of the film to the substrate. The film thickness was 25 nm. Inverter conditions for sample 4 were identical to those for sample 3. Because of the longer deposition time Ž120 min., the deposited film was thicker than for no. 3, at 58 nm. In the RBS spectrum, a peak for Ar was observed, and an intermixed layer at the interface of the Si and the Cu film was also clearly seen. The Si peak at channel 260 and the Cu peak at channel 320 are broader than in sample 3. Oxygen contamination in the film was also observed at channel 150. The above results confirmed that inverter conditions with V1 higher than V2 result in deposition, and that application of an assisting voltage Ž V2 . leads to the formation of an intermixed layer. To test the strength of adhesion, we used Scotch tape to conduct a peel-off test on films deposited on glass plates. The sputter voltage for V1 was set at 650 V and the assisting voltage Ž V2 . for samples 5 and 6 at 0 and
275
250 V, respectively. Thus, sample 5 underwent sputter deposition while sample 6 underwent ion-assisted deposition. In a test using Scotch tape, the film peeled off from sample 5, but not from sample 6, demonstrating the high adhesion achieved by ion-assisted deposition using the inverter plasma.
4. Conclusion An inverter power supply was used to conduct an ion-beam deposition process, which was demonstrated to produce adhesive copper deposition. As the technique is simple, it could be used in a wide variety of manufacturing applications at low cost.
Acknowledgements We thank Dr Akio Okamoto of the Technical Research Institute of Osaka Prefecture for conducting RBS measurements. References w1x S. Sugimoto, M. Kiuchi, S. Takechi, K. Tanaka, S. Goto, in: Proceedings of PBII ’99, Surf. Coat. Technol. Žin press.. w2x S. Takechi, S. Sugimoto, M. Kiuchi, K. Tanaka, S. Goto, in: Proceedings of PBII ’99, Surf. Coat. Technol. Žin press.. w3x N. Murakami, K. Tanaka, S. Sugimoto, M. Kiuchi, S. Goto, in: Proceedings of PBII ’99, Surf. Coat. Technol. Žin press.. w4x M. Kiuchi, Nucl. Instrum. Methods Phys. Res. B 80r81 Ž1993. 1343.