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Crystal orientation and microstructure of nickel film deposited at liquid nitrogen temperature by sputtering
Electrochimica Acta 44 (1999) 3933±3944
Crystal orientation and microstructure of nickel ®lm deposited at liquid nitrogen temperature by sputtering H. Shimizu a, E. Suzuki b, Y. Hoshi b,* a Niigata University, Ikarashi 2-8050, Niigata, 950-2181, Japan Tokyo Institute of Polytechnics, 1583 Iiyama, Atsugi, Kanagawa, 243-0213, Japan
b
Received 10 September 1998
Abstract Sputter deposition of nickel ®lms at liquid nitrogen temperature was performed to clarify the eects of the surface migration of the deposited atoms. The ®lm deposited at liquid nitrogen temperature and low Ar gas pressure had excellent (111) orientation and good crystallinity. Therefore, deposition at a low-temperature and low Ar gas pressure is a useful technique for obtaining ®lm with excellent crystal orientation of the closest packing plane. Ion bombardment of the ®lm surface during deposition at liquid nitrogen temperature led to a large degradation of the ®lm crystallinity, but it had quite the opposite eect at room temperature, i.e., it promoted the (111) orientation of the ®lm and improved the crystallinity of the ®lm. These results indicate that the ion bombardment produced defects in the crystallites at a low temperature where migration of the deposited atoms was limited. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Deposition at liquid nitrogen temperature; Ni ®lm; Magnetron sputtering; Bias sputtering; Surface migration
1. Introduction To obtain a thin ®lm with desired properties (the size and orientation of the crystallites in ®lm) in sputter deposition, one must control the eects of sputterdeposition parameters (sputtering gas pressure, substrate temperature, and high-energy particle bombardment of the ®lm surface) [1±4]. One of the key factors aecting the ®lm structure in sputter deposition is surface migration. In this study, we deposited nickel ®lms at liquid nitrogen temperature by dc magnetron sputtering to investigate the eect of low-temperature de-
* Corresponding author. Tel.: +81-462-429560; fax: +81462-423000. E-mail address: [email protected] (Y. Hoshi)
position on ®lm structure. Bias sputtering was also performed, to clarify the eect of high-energy particle bombardment on the microstructure of the ®lm at liquid nitrogen temperature.
2. Experiments Nickel ®lms were deposited on glass slide substrates at both room temperature and liquid nitrogen temperature with various substrate bias voltages using a dc magnetron sputtering apparatus. The base pressure was less than 6 10ÿ7 Torr and the sputtering argon gas pressure was varied from 1±10 mTorr. The substrate bias voltage was varied from 0±150 V. Typical ®lm preparation conditions are listed in Table 1.
0013-4686/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 0 1 3 - 4 6 8 6 ( 9 9 ) 0 0 1 0 1 - 2
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Table 1 Film preparation conditions Ar gas pressure Substrates temperature Substrate bias voltage Target voltage Discharge current Deposition time Deposition rate Thickness of ®lm
The crystal structure and orientation of the crystallites in the ®lms were investigated by X-ray diraction (XRD), and their surface morphology was examined by atomic force microscopy (AFM). The resistivity was measured by the four-point-probe method.
3. Results and discussion Fig. 1 shows changes in XRD diagrams of ®lms prepared at room temperature and liquid nitrogen temperature with Ar gas pressure. All of the ®lms deposited at room temperature had poor (111) orientation, although the (111) orientation was promoted by an increase in gas pressure. This promotion of (111) orientation may be due to a decrease in kinetic energy of the depositing particles caused by the increase in
1±10 mTorr Room temperature and liquid nitrogen temperature 0±150 V 220±360 V 130±240 mA About 5 min About 20 nm/min About 100 nm
gas pressure. On the other hand, all of the ®lms deposited at liquid nitrogen temperature had (111) texture and the intensity of the (111) diraction peak decreased signi®cantly as the Ar gas pressure increased. These results can be explained as follows: the (111) plane has the lowest surface energy in the nickel crystal, so the growth of crystallites with (100) orientation was suppressed at such a low temperature. We think the decrease in (111) diraction peak intensity with increasing Ar gas pressure was caused by the self-shadowing eect of depositing atoms and by the suppression of surface migration, since the kinetic energy of depositing atoms on the substrate was decreased and number of depositing atoms on the substrate having a large incident angle increased as the Ar gas pressure increased. These results indicate that deposition at a low substrate temperature and low Ar gas pressure is
Fig. 1. Changes in X-ray diraction diagrams of ®lms prepared at room temperature and liquid nitrogen temperature with Ar gas pressure.
H. Shimizu et al. / Electrochimica Acta 44 (1999) 3933±3944
Fig. 2. Changes in AFM surface images of ®lms deposited at room temperature with Ar gas pressure.
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Fig. 2 (continued)
useful for obtaining ®lm with excellent crystal orientation of the closest packing plane. Figs. 2 and 3 show typical AFM surface topographies of these ®lms. No clear dierences were observed in the AFM images of the ®lms deposited at liquid nitrogen temperature and room temperature, although both their surface roughnesses increased with increasing Ar gas pressure. This was probably caused by suppression of the surface migration of the deposited atoms at higher Ar gas pressure and by the selfshadowing eect being more prominent. Next, we investigated the eect of ion bombardment on the structure of the ®lm at liquid nitrogen temperature. Fig. 4 shows changes in XRD diagrams of the ®lms deposited at room temperature and liquid nitrogen temperature with substrate bias voltage. The Ar gas pressure was ®xed at 1 mTorr. Fig. 5 shows full width at half-maximum (FWHM) values of the (111) rocking curves of these ®lms. The (111) diraction peak of the ®lm deposited at room temperature increased as the substrate bias voltage increased, whereas that of the ®lm deposited at liquid nitrogen temperature decreased as the substrate bias voltage increased. On the other hand, the FWHM of the ®lm deposited at room tem-
perature decreased as the substrate bias voltage increased, whereas that of the ®lm deposited at liquid nitrogen temperature increased as the substrate bias voltage increased. These results suggest that the growth of crystallites with (111) orientation in the ®lm deposited at room temperature was promoted by Ar ion bombardment of the ®lm surface during deposition, whereas it was suppressed by ion bombardment of the ®lm surface at liquid nitrogen temperature. Fig. 6 shows the mean crystallite size estimated from the Ni (111) diraction peak of these ®lms. The crystallite size of the ®lm deposited at room temperature increased as the substrate bias voltage increased, whereas that of the ®lm deposited at liquid nitrogen temperature decreased as the substrate bias voltage increased. This result indicates that the growth of crystallite was suppressed as the bombarding energy of Ar ions increased at liquid nitrogen temperature. Figs. 7 and 8 show typical AFM surface images of these ®lms. Fig. 9 shows changes in surface roughness (Ra) of these ®lms with bias voltage. It is clear from the ®gure that the surface roughness of the ®lms deposited at room temperature and liquid nitrogen temperature increased when the substrate bias voltage increased from 0 to 100 V. Further increase in the bias
H. Shimizu et al. / Electrochimica Acta 44 (1999) 3933±3944
Fig. 3. Changes in AFM surface images of ®lms deposited at liquid nitrogen temperature with Ar gas pressure.
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Fig. 3 (continued)
voltage, however, led to a decrease in the surface roughness of the ®lm, which may be due to the promotion of resputtering by the increase in the bombarding ion energy. Fig. 10 shows changes in resistivity of ®lms deposited at liquid nitrogen temperature and room temperature with bias voltage. Clear changes in resistivity were not observed in the ®lms deposited at either liquid nitrogen temperature or room temperature; the resistivity was about 20 m O cm. Figs. 11 and 12 show changes in lattice spacing of the (111) plane and the stress in ®lms deposited at liquid nitrogen temperature and room temperature with bias voltage, respectively. It is evident from Fig. 11 that when the substrate bias voltage was increased, the lattice spacing of the (111) plane of the ®lm deposited at room temperature increased, while that of the ®lm deposited at liquid nitrogen temperature decreased. The reason for this dierence is not clear. On the other hand, the stress in both these ®lms decreased as the substrate bias voltage increased and we did not observe any clear dierences in stress caused by substrate temperature.
4. Conclusions Nickel ®lms were deposited on glass slide substrates at both room temperature and liquid nitrogen temperature under various Ar gas pressures and substrate bias voltages using a dc magnetron sputtering apparatus. The ®lm deposited at liquid nitrogen temperature and low Ar gas pressure had excellent (111) orientation and good crystallinity. The growth of crystallites with (111) orientation in the ®lm was promoted by Ar ion bombardment of the ®lm surface during deposition at room temperature, while it was suppressed at liquid nitrogen temperature. The surface roughnesses of ®lms deposited at room temperature and liquid nitrogen temperature both increased as the substrate bias voltage increased from 0 to 100 V. Further increase in the bias voltage above 100 V led to a reduction in the roughness. The resistivities of the ®lms deposited at liquid nitrogen temperature and room temperature depended little on substrate bias. Film stress depended little on substance temperature and compressive stress increased monotonically as the substrate bias voltage increased.
H. Shimizu et al. / Electrochimica Acta 44 (1999) 3933±3944
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Fig. 4. Changes in XRD diagrams of the ®lms deposited at room temperature and liquid nitrogen temperature with substrate bias voltage (Ar gas pressure: 1 mTorr).
Fig. 5. Changes in FWHM of (111) rocking curves of the ®lms deposited at room temperature (closed circles) and liquid nitrogen temperature (open circles) with substrate bias voltage.
Fig. 6. Changes in crystallite size for Ni (111) diraction peak of ®lms deposited at room temperature (closed circles) and liquid nitrogen temperature (open circles) with substrate bias voltage.
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Fig. 7. Changes in AFM surface images of ®lms deposited at room temperature with substrate bias voltage.
H. Shimizu et al. / Electrochimica Acta 44 (1999) 3933±3944
Fig. 7 (continued)
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Fig. 8. Changes in AFM surface images of ®lms deposited at liquid nitrogen temperature with substrate bias voltage.
H. Shimizu et al. / Electrochimica Acta 44 (1999) 3933±3944
Fig. 8 (continued)
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Fig. 9. Changes in surface roughness (Ra) of the ®lms deposited at room temperature (closed circles) and liquid nitrogen temperature (open circles) with bias voltage.
Fig. 10. Changes in resistivity of the ®lms deposited at liquid nitrogen temperature (open circles) and room temperature (closed circles) with bias voltage.
References [1] J.A. Floro, S.M. Rossnagel, R.S. Robinson, J. Vac. Sci. Technol. A1 (3) (1983) 1398. [2] Y. Hoshi, E. Suzuki, T. Osaka, J. Mag. Mag. Mat. 176 (1997) 51.
Fig. 11. Changes in lattice spacing of (111) plane of the ®lms deposited at liquid nitrogen temperature (open circles) and
Fig. 12. Changes in stress of ®lms deposited at liquid nitrogen temperature (open circles) and room temperature (closed circles) with bias voltage.
[3] E. Suzuki, Y. Hoshi, J. Mag. Soc. Jpn. 21 (S2) (1997) 43. [4] Y. Hoshi, E. Suzuki, T. Osaka, J. Mag. Soc. Jpn. 19 (S2) (1995) 104.
Crystal orientation and microstructure of nickel ®lm deposited at liquid nitrogen temperature by sputtering H. Shimizu a, E. Suzuki b, Y. Hoshi b,* a Niigata University, Ikarashi 2-8050, Niigata, 950-2181, Japan Tokyo Institute of Polytechnics, 1583 Iiyama, Atsugi, Kanagawa, 243-0213, Japan
b
Received 10 September 1998
Abstract Sputter deposition of nickel ®lms at liquid nitrogen temperature was performed to clarify the eects of the surface migration of the deposited atoms. The ®lm deposited at liquid nitrogen temperature and low Ar gas pressure had excellent (111) orientation and good crystallinity. Therefore, deposition at a low-temperature and low Ar gas pressure is a useful technique for obtaining ®lm with excellent crystal orientation of the closest packing plane. Ion bombardment of the ®lm surface during deposition at liquid nitrogen temperature led to a large degradation of the ®lm crystallinity, but it had quite the opposite eect at room temperature, i.e., it promoted the (111) orientation of the ®lm and improved the crystallinity of the ®lm. These results indicate that the ion bombardment produced defects in the crystallites at a low temperature where migration of the deposited atoms was limited. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Deposition at liquid nitrogen temperature; Ni ®lm; Magnetron sputtering; Bias sputtering; Surface migration
1. Introduction To obtain a thin ®lm with desired properties (the size and orientation of the crystallites in ®lm) in sputter deposition, one must control the eects of sputterdeposition parameters (sputtering gas pressure, substrate temperature, and high-energy particle bombardment of the ®lm surface) [1±4]. One of the key factors aecting the ®lm structure in sputter deposition is surface migration. In this study, we deposited nickel ®lms at liquid nitrogen temperature by dc magnetron sputtering to investigate the eect of low-temperature de-
* Corresponding author. Tel.: +81-462-429560; fax: +81462-423000. E-mail address: [email protected] (Y. Hoshi)
position on ®lm structure. Bias sputtering was also performed, to clarify the eect of high-energy particle bombardment on the microstructure of the ®lm at liquid nitrogen temperature.
2. Experiments Nickel ®lms were deposited on glass slide substrates at both room temperature and liquid nitrogen temperature with various substrate bias voltages using a dc magnetron sputtering apparatus. The base pressure was less than 6 10ÿ7 Torr and the sputtering argon gas pressure was varied from 1±10 mTorr. The substrate bias voltage was varied from 0±150 V. Typical ®lm preparation conditions are listed in Table 1.
0013-4686/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 0 1 3 - 4 6 8 6 ( 9 9 ) 0 0 1 0 1 - 2
3934
H. Shimizu et al. / Electrochimica Acta 44 (1999) 3933±3944
Table 1 Film preparation conditions Ar gas pressure Substrates temperature Substrate bias voltage Target voltage Discharge current Deposition time Deposition rate Thickness of ®lm
The crystal structure and orientation of the crystallites in the ®lms were investigated by X-ray diraction (XRD), and their surface morphology was examined by atomic force microscopy (AFM). The resistivity was measured by the four-point-probe method.
3. Results and discussion Fig. 1 shows changes in XRD diagrams of ®lms prepared at room temperature and liquid nitrogen temperature with Ar gas pressure. All of the ®lms deposited at room temperature had poor (111) orientation, although the (111) orientation was promoted by an increase in gas pressure. This promotion of (111) orientation may be due to a decrease in kinetic energy of the depositing particles caused by the increase in
1±10 mTorr Room temperature and liquid nitrogen temperature 0±150 V 220±360 V 130±240 mA About 5 min About 20 nm/min About 100 nm
gas pressure. On the other hand, all of the ®lms deposited at liquid nitrogen temperature had (111) texture and the intensity of the (111) diraction peak decreased signi®cantly as the Ar gas pressure increased. These results can be explained as follows: the (111) plane has the lowest surface energy in the nickel crystal, so the growth of crystallites with (100) orientation was suppressed at such a low temperature. We think the decrease in (111) diraction peak intensity with increasing Ar gas pressure was caused by the self-shadowing eect of depositing atoms and by the suppression of surface migration, since the kinetic energy of depositing atoms on the substrate was decreased and number of depositing atoms on the substrate having a large incident angle increased as the Ar gas pressure increased. These results indicate that deposition at a low substrate temperature and low Ar gas pressure is
Fig. 1. Changes in X-ray diraction diagrams of ®lms prepared at room temperature and liquid nitrogen temperature with Ar gas pressure.
H. Shimizu et al. / Electrochimica Acta 44 (1999) 3933±3944
Fig. 2. Changes in AFM surface images of ®lms deposited at room temperature with Ar gas pressure.
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Fig. 2 (continued)
useful for obtaining ®lm with excellent crystal orientation of the closest packing plane. Figs. 2 and 3 show typical AFM surface topographies of these ®lms. No clear dierences were observed in the AFM images of the ®lms deposited at liquid nitrogen temperature and room temperature, although both their surface roughnesses increased with increasing Ar gas pressure. This was probably caused by suppression of the surface migration of the deposited atoms at higher Ar gas pressure and by the selfshadowing eect being more prominent. Next, we investigated the eect of ion bombardment on the structure of the ®lm at liquid nitrogen temperature. Fig. 4 shows changes in XRD diagrams of the ®lms deposited at room temperature and liquid nitrogen temperature with substrate bias voltage. The Ar gas pressure was ®xed at 1 mTorr. Fig. 5 shows full width at half-maximum (FWHM) values of the (111) rocking curves of these ®lms. The (111) diraction peak of the ®lm deposited at room temperature increased as the substrate bias voltage increased, whereas that of the ®lm deposited at liquid nitrogen temperature decreased as the substrate bias voltage increased. On the other hand, the FWHM of the ®lm deposited at room tem-
perature decreased as the substrate bias voltage increased, whereas that of the ®lm deposited at liquid nitrogen temperature increased as the substrate bias voltage increased. These results suggest that the growth of crystallites with (111) orientation in the ®lm deposited at room temperature was promoted by Ar ion bombardment of the ®lm surface during deposition, whereas it was suppressed by ion bombardment of the ®lm surface at liquid nitrogen temperature. Fig. 6 shows the mean crystallite size estimated from the Ni (111) diraction peak of these ®lms. The crystallite size of the ®lm deposited at room temperature increased as the substrate bias voltage increased, whereas that of the ®lm deposited at liquid nitrogen temperature decreased as the substrate bias voltage increased. This result indicates that the growth of crystallite was suppressed as the bombarding energy of Ar ions increased at liquid nitrogen temperature. Figs. 7 and 8 show typical AFM surface images of these ®lms. Fig. 9 shows changes in surface roughness (Ra) of these ®lms with bias voltage. It is clear from the ®gure that the surface roughness of the ®lms deposited at room temperature and liquid nitrogen temperature increased when the substrate bias voltage increased from 0 to 100 V. Further increase in the bias
H. Shimizu et al. / Electrochimica Acta 44 (1999) 3933±3944
Fig. 3. Changes in AFM surface images of ®lms deposited at liquid nitrogen temperature with Ar gas pressure.
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Fig. 3 (continued)
voltage, however, led to a decrease in the surface roughness of the ®lm, which may be due to the promotion of resputtering by the increase in the bombarding ion energy. Fig. 10 shows changes in resistivity of ®lms deposited at liquid nitrogen temperature and room temperature with bias voltage. Clear changes in resistivity were not observed in the ®lms deposited at either liquid nitrogen temperature or room temperature; the resistivity was about 20 m O cm. Figs. 11 and 12 show changes in lattice spacing of the (111) plane and the stress in ®lms deposited at liquid nitrogen temperature and room temperature with bias voltage, respectively. It is evident from Fig. 11 that when the substrate bias voltage was increased, the lattice spacing of the (111) plane of the ®lm deposited at room temperature increased, while that of the ®lm deposited at liquid nitrogen temperature decreased. The reason for this dierence is not clear. On the other hand, the stress in both these ®lms decreased as the substrate bias voltage increased and we did not observe any clear dierences in stress caused by substrate temperature.
4. Conclusions Nickel ®lms were deposited on glass slide substrates at both room temperature and liquid nitrogen temperature under various Ar gas pressures and substrate bias voltages using a dc magnetron sputtering apparatus. The ®lm deposited at liquid nitrogen temperature and low Ar gas pressure had excellent (111) orientation and good crystallinity. The growth of crystallites with (111) orientation in the ®lm was promoted by Ar ion bombardment of the ®lm surface during deposition at room temperature, while it was suppressed at liquid nitrogen temperature. The surface roughnesses of ®lms deposited at room temperature and liquid nitrogen temperature both increased as the substrate bias voltage increased from 0 to 100 V. Further increase in the bias voltage above 100 V led to a reduction in the roughness. The resistivities of the ®lms deposited at liquid nitrogen temperature and room temperature depended little on substrate bias. Film stress depended little on substance temperature and compressive stress increased monotonically as the substrate bias voltage increased.
H. Shimizu et al. / Electrochimica Acta 44 (1999) 3933±3944
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Fig. 4. Changes in XRD diagrams of the ®lms deposited at room temperature and liquid nitrogen temperature with substrate bias voltage (Ar gas pressure: 1 mTorr).
Fig. 5. Changes in FWHM of (111) rocking curves of the ®lms deposited at room temperature (closed circles) and liquid nitrogen temperature (open circles) with substrate bias voltage.
Fig. 6. Changes in crystallite size for Ni (111) diraction peak of ®lms deposited at room temperature (closed circles) and liquid nitrogen temperature (open circles) with substrate bias voltage.
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Fig. 7. Changes in AFM surface images of ®lms deposited at room temperature with substrate bias voltage.
H. Shimizu et al. / Electrochimica Acta 44 (1999) 3933±3944
Fig. 7 (continued)
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Fig. 8. Changes in AFM surface images of ®lms deposited at liquid nitrogen temperature with substrate bias voltage.
H. Shimizu et al. / Electrochimica Acta 44 (1999) 3933±3944
Fig. 8 (continued)
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Fig. 9. Changes in surface roughness (Ra) of the ®lms deposited at room temperature (closed circles) and liquid nitrogen temperature (open circles) with bias voltage.
Fig. 10. Changes in resistivity of the ®lms deposited at liquid nitrogen temperature (open circles) and room temperature (closed circles) with bias voltage.
References [1] J.A. Floro, S.M. Rossnagel, R.S. Robinson, J. Vac. Sci. Technol. A1 (3) (1983) 1398. [2] Y. Hoshi, E. Suzuki, T. Osaka, J. Mag. Mag. Mat. 176 (1997) 51.
Fig. 11. Changes in lattice spacing of (111) plane of the ®lms deposited at liquid nitrogen temperature (open circles) and
Fig. 12. Changes in stress of ®lms deposited at liquid nitrogen temperature (open circles) and room temperature (closed circles) with bias voltage.
[3] E. Suzuki, Y. Hoshi, J. Mag. Soc. Jpn. 21 (S2) (1997) 43. [4] Y. Hoshi, E. Suzuki, T. Osaka, J. Mag. Soc. Jpn. 19 (S2) (1995) 104.