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Structural changes of Si surfaces by nitrogen implantation using plasma based ion implantation
Nuclear Instruments and Methods in Physics Research B 267 (2009) 1303–1306
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Structural changes of Si surfaces by nitrogen implantation using plasma based ion implantation Setsuo Nakao * Materials Research Institute for Sustainable Development, National Institute of Advanced Industrial Science and Technology (AIST) – Chubu, 2266-98 Anagahora, Moriyama, Nagoya 463-8560, Japan
a r t i c l e
i n f o
Article history: Available online 31 January 2009 PACS: 52.77.Dq 78.30.j 81.65.Lp 61.43.j 68.47.Fg Keywords: Plasma based ion implantation Surface modification EDX Raman spectroscopy FT-IR SiNx
a b s t r a c t Nitrogen ion implantation to Si wafers is carried out by a plasma based ion implantation (PBII) and the compositional and structural changes of the Si surfaces are examined as a function of implantation time by energy dispersive X-ray spectrometer (EDX), Raman and Fourier Transform Infrared (FT-IR) spectroscopy. The implantation time is varied from 10 min to 7 h. From the results of EDX measurements, the N concentration is increased with increasing implantation time up to 1 h, but it is not significantly increased at further increase of implantation time. In the Raman spectra, the sharp peak from Si crystal is decreased in intensity and the small peaks from a-Si and/or a-SiNx appear after N ion implantation. On the other hand, in the FT-IR spectra, a broad peak assigned to Si–N bonds appears after N ion implantation. The result of RBS measurement indicates that the N/Si ratio is approximately 1.3. Judging from these results, it is suggested that a-SiN1.3 is formed as a surface layer on Si wafer by N ion implantation using PBII system. Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction Ion implantation is a useful technique for the surface modification of materials. Recently, plasma based ion implantation (PBII) technique has attracted much interest because of the capability of ion implantation on 3 dimensional workpieces [1]. Moreover, in the PBII technique, the sample also can be covered with proper films by coating process. Therefore, with this technique, ion implantation process is sometimes employed before coating to modify surface for getting high adhesion strength. Walter et al. [2] reported that carbon implantation caused adherent diamond-like carbon films on various materials. It is also expected that the surface modification can be done by implantation with not only carbon but also various other gases, such as nitrogen, oxygen and hydrogen. Especially, many studies on nitrogen (N) implantation by PBII technique have been carried out for surface nitridation of metals, such as aluminum [3], steel [4] and titanium alloys [5] and for modification of surface properties of polymer, such as polyethylene [6]. However, it is not always clarified on the time dependence of N implantation. In this study, Si
* Tel.: +81 52 736 7286; fax: +81 52 736 7406. E-mail address: [email protected] 0168-583X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2009.01.117
wafer is used as a target and N implantation is carried out with a PBII system. The relative concentration of N is examined as a function of implantation time and the bonding structure of Si surface is also examined after N implantation. 2. Experimental Nitrogen implantation was carried out by the PBII system [7]. The detail of system illustration was reported in a previous paper [8]. The Si(1 0 0) wafers (10 20 mm) were held on the center of the cylindrical vacuum chamber. The chamber was evacuated to less than 103 Pa by a turbomolecular pump. RF power was 150 W at a frequency of 13.56 MHz. Negative pulse voltage (Vn) was applied to the substrate through a high-voltage feed-through and kept 20 kV. N2 gas was inlet to the chamber at a flow rate of 10 sccm. The working pressure during implantation was kept at 0.05 Pa. Implantation time was changed in the range of 10 min to 7 h. Depth profile of the implanted N in Si was calculated by the simulation program of the transport of ions in matter (TRIM ver. 95.06) code [9]. Relative concentration of N was examined by energy dispersive X-ray spectrometer (EDX) as a function of implantation time. The acceleration voltage was 20 kV and the analyzed area was approximately 2 2 lm2. The projected range of 20 keV
S. Nakao / Nuclear Instruments and Methods in Physics Research B 267 (2009) 1303–1306
electrons into Si was calculated to 4.6 lm by the equation reported by Kanaya and Okayama [10]. Although the signal information depth is not always clear, it may generally be around 1 lm. Raman spectra of nitrogen implanted Si surfaces were measured on microRaman spectrometer (Renishaw inVia) with 514.5 nm line of an Ar ion laser. The penetration depth of Ar ion laser into Si is estimated to around 0.5 lm. The power of the laser was 10 mW. The laser was focused to about 1 lm in diameter on the sample surface through a confocal optical microscope. Typical acquisition time was 10 s. The Si–N bonding after implantation was examined by Fourier Transform Infrared (FT-IR) spectroscopy. Rutherford backscattering spectrometry (RBS) was performed using 1.8 MeV He+ ions with a 1.7 MV tandem-type ion accelerator (NEC 5SDH-II pelletron accelerator). Quantitative analysis of the RBS spectrum was carried out by the simulation program of the Rutherford universal manipulation program code [11,12] for the Windows XP (XRUMP).
400 N 7h 300 4h
Intensity (a.u.)
1304
1h 200 30m 20m 100 10m
0 0
0.2 0
0.4 0
0.6 0
0.8 0
Energy (keV) Fig. 2. EDX spectra of the N implanted Si samples. The implantation time is varied from 10 min to 7 h.
3. Results and discussion Fig. 1 shows depth profile of implanted N in Si target calculated by TRIM code [9]. Calculation is performed on 20 keV N+ and Nþ 2 (10 keV per N) ions. The projected range (Rp) and straggling for N+ are 54.2 nm and 21.5 nm, respectively. On the other hand, the Rp and straggling for Nþ 2 are 29.0 nm and 12.8 nm, respectively. In the case of PBII, however, the ratio of N+ to Nþ 2 ions is varied depending on the plasma density (RF power). In a previous paper [7,13], the plasma density, electron temperature and substrate temperature were approximately 4 1010/cm3, around 1 eV and less than 200 °C, respectively, under the typical experimental conditions for our PBII system. Although the conditions are slightly different in this experiment, these plasma parameters may be similar values. The RF power of 150 W (the plasma density) is relatively low so that Nþ 2 ion is considered to be main ion species, as reported by Qi et al. [14]. In fact, it was reported by Tang et al. [15] that 70– 80% molecular ions of Nþ 2 were observed in their measurement system. Therefore, it is expected that the distribution of implanted N in Si is close to that for Nþ 2 implantation case. However, the distribution should shift toward the surface as a consequence of target compositional change and sputtering during N implantation, as reported in the previous paper [7]. The measurement of depth profile of implanted N and the comparison with the simulation are necessary and now in progress. Fig. 2 shows the EDX spectra of the N implanted Si samples at various implantation time ranging from 10 min to 7 h. Signal from
N appears at 0.4 keV for implanted sample for 10 min. The intensity of N signal is increased with increasing implantation time up to 1 h. However, further increase of implantation time does not cause a significant increase of the intensity. Fig. 3 indicates the change of relative N/Si ratio as a function of implantation time. It is noted that the projected range and the signal information depth should be deeper than N implanted range so that the N concentration is not true because the signal from Si comes from over the thickness of N implanted layer. However, the behavior of N concentration against implantation time is figured out. N concentration is increased with increasing implantation time up to 1 h and tends to be saturated at further implantation time. Fig. 4 shows Raman spectra of Si surface before and after N implanted for 7 h. The strong peak is observed at 520 cm1 for beforeimplanted sample due to TO band of crystalline silicon. The intensity is decreased and the weak shoulder peak appears at 480 cm1 for after-implanted sample. The shoulder peak corresponds to the TO band of amorphous Si and/or amorphous SiNx [16]. In addition, the small broad peak appears at 150 cm1. This peak also corresponds to the TA band of amorphous SiNx [16]. These results suggest that the amorphization of Si and the formation of Si–N bonding have taken place on the surface of the Si target by N implantation. Similar tendency is also reported by Sadiq et al. [17]. Fig. 5 shows FT-IR spectrum of N implanted Si for 7 h. The
30
Relative N/Si ratio (%)
N atoms/nm/ions
N2 +
N+
20
10
0 0
20
40
60
80
100
120
140
Depth (nm) Fig. 1. Depth profile of the implanted N ions in the Si substrate calculated by TRIM code (ver. 95.06).
0
2
4
6
8
Time (hours) Fig. 3. The changes in relative N/Si ratio obtained from EDX measurements as a function of the implantation time.
1305
S. Nakao / Nuclear Instruments and Methods in Physics Research B 267 (2009) 1303–1306
200
Energy (MeV) Si
50
0.6
0.8
1.8 MeV He+
a-Si or a-SiNx
1.0
1.2
N implanted Si for 7h
40
Normalized Yield
Intensity (a.u.)
150
0.4
100 a-SiNx
50
N
30
Si 20
10
0 100
200
300
400
500
600
700
Raman shift (cm-1) Fig. 4. Raman spectra of the Si samples before and after N implantation for 7 h.
broad peak centered around 830 cm1 is observed. This peak is assigned to Si–N bond vibration [18]. Therefore, it is confirmed that Si–N bonding is formed in the Si target. To make clear the N/Si ratio, RBS measurement is carried out. Fig. 6 shows RBS spectrum of N implanted Si for 7 h. Open circles and solid line indicate the measured signals and the fitting result by XRUMP code, respectively. It is noticed that the gradient of Si surface signals is subtly changed on N concentration. Then, the simulation was carried out by fitting to the gradient of Si surface signals. The error in determining the N concentration is believed to be minimized by this procedure, although the intensity of N signals is very low. The simulation result shows that the N/Si ratio is approximately 1.3, assuming the layer thickness of 3 1017/cm2. This value is close to the saturated concentration (1.33) of N in Si. From these results, it is suggested that amorphous SiN1.3 layer is formed by N implantation using PBII system. The results of EDX analysis show that the N concentration tends to be saturated at longer implantation time, as shown in Figs. 2 and 3. Miyagawa et al. [19] reported that the implanted N into metal follows the binary collision model until the concentration reaches the saturated concentration of the saturated nitride phase and excess N diffuses towards the surface and releases from there. In addition, in the case of thin Si layer (80 nm) on glassy carbon, the implanted N spreads towards the upper Si layer when the implanted dose increased over the saturated concentration in C [20]. These results suggest that the implanted N may diffuse towards the surface and release from the surface after the N concentration reaches the saturated concentration of silicon nitride phase (Si3N4: 0.2 7h
30
40
50
60
70
80
90
Channel Fig. 6. RBS spectrum of the N implanted Si sample for 7 h.
N/Si = 1.33) if the thickness is very thin, although the implanted N is not always easy to move in Si as compared with metals. It is + noted that the Rp 29.0 nm for Nþ 2 case (54 nm for N case), as shown in Fig. 1, is enough thin as compared with the thickness in [20]. Moreover, the N/Si ratio estimated to 1.3 from RBS measurement, as shown in Fig. 6, is close to the saturated concentration of silicon nitride phase. In addition, surface sputtering should be occurred during N implantation. It is expected that the N concentration is reduced by sputtering of nitride surface, leading to the compensation for the increase of N concentration in Si. Therefore, it might be said that the observed saturation tendency of the N concentration in Si is caused by the diffusion and release of excess N from the surface and sputtering of the nitride surface at longer implantation time. 4. Summary N implantation into Si is carried out by the PBII system, and the compositional and structural changes of the surface of Si are examined as a function of implantation time in the range of 0.17–7 h. It is found that the N/Si ratio is increased up to 1 h, but tends to be saturated at further increase of implantation time. The result of RBS measurement indicates that the N/Si ratio is about 1.3 which is close to the saturated concentration of 1.33 of N in Si. The result of FT-IR measurement shows that Si–N bonding is certainly formed by N implantation into Si. The result of Raman measurement indicates that amorphous SiNx is presumably formed after N implantation. These results suggest that amorphous SiN1.3 layer is formed by N implantation.
Si-N
0.15
Absorbance
0 20
References
0.1
0.05
0 400
600
800
1000 -1
Wavenumber (cm ) Fig. 5. FT-IR spectrum of the N implanted Si sample for 7 h.
1200
[1] A. Anders, Handbook of Plasma Immersion Ion Implantation and Deposition, Wiley, New York, 2000. [2] K.C. Walter, M. Nastasi, C. Munson, Surf. Coat. Technol. 93 (1997) 287. [3] T. Yamanishi, Y. Hara, R. Morita, K. Azuma, E. Fujiwara, M. Yatsuzuka, Surf. Coat. Technol. 136 (2001) 223. [4] S. Xu, X. Ma, M. Sun, Y. Sun, K. Yukimura, Nucl. Instr. and Meth. B 242 (2006) 374. [5] V. Fouquet, E. Le Bourhis, L. Pichon, M. Drouet, A. Straboni, Scripta Mater. 51 (2004) 899. [6] I. Bertoti, M. Mohai, A. Toth, T. Ujvari, Surf. Coat. Technol. 201 (2007) 6839. [7] S. Miyagawa, S. Nakao, M. Ikeyama, Y. Miyagawa, Surf. Coat. Technol. 156 (2002) 322. [8] J. Choi, S. Nakao, M. Ikeyama, T. Kato, Phys. Status Solidi C 5 (2008) 956. [9] J.B. Biersack, L.G. Haffmark, Nucl. Instr. and Meth. 174 (1980) 257. [10] K. Kanaya, S. Okayama, J. Phys. D. Appl. Phys. 5 (1972) 43.
1306
S. Nakao / Nuclear Instruments and Methods in Physics Research B 267 (2009) 1303–1306
[11] L.R. Doolittle, Nucl. Instr. and Meth. B 9 (1985) 344. [12] L.R. Doolittle, Nucl. Instr. and Meth. B 15 (1986) 227. [13] S. Miyagawa, Y. Miyagawa, Mater. Res. Soc. Symp. Proc. 647 (2001) O11.7.1. [14] S. Qi, X. Lifang, M. Xinxin, S. Mingren, Appl. Surf. Sci. 206 (2003) 53. [15] B.Y. Tang, R.P. Fetherston, M. Shamim, R.A. Breun, A. Chen, J.R. Conrad, J. Appl. Phys. 73 (1993) 4176. [16] Y. Wang, R. Yue, H. Han, X. Liao, J. Non-Cryst. Solids 291 (2001) 107.
[17] M. Sadiq, S. Ahmad, M. Shafiq, M. Zakaullah, Nucl. Instr. and Meth. B 252 (2006) 219. [18] S.B. Patil, A. Kumbhar, P. Waghmare, V.R. Rao, R.O. Dusane, Thin Solid Films 395 (2001) 270. [19] Y. Miyagawa, S. Nakao, K. Baba, M. Ikeyama, K. Saitoh, S. Miyagawa, Mater. Sci. Eng. A 253 (1998) 135. [20] Y. Miyagawa, M. Ikeyama, S. Nakao, S. Miyagawa, Nucl. Instr. and Meth. B 153 (1999) 422.
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Structural changes of Si surfaces by nitrogen implantation using plasma based ion implantation Setsuo Nakao * Materials Research Institute for Sustainable Development, National Institute of Advanced Industrial Science and Technology (AIST) – Chubu, 2266-98 Anagahora, Moriyama, Nagoya 463-8560, Japan
a r t i c l e
i n f o
Article history: Available online 31 January 2009 PACS: 52.77.Dq 78.30.j 81.65.Lp 61.43.j 68.47.Fg Keywords: Plasma based ion implantation Surface modification EDX Raman spectroscopy FT-IR SiNx
a b s t r a c t Nitrogen ion implantation to Si wafers is carried out by a plasma based ion implantation (PBII) and the compositional and structural changes of the Si surfaces are examined as a function of implantation time by energy dispersive X-ray spectrometer (EDX), Raman and Fourier Transform Infrared (FT-IR) spectroscopy. The implantation time is varied from 10 min to 7 h. From the results of EDX measurements, the N concentration is increased with increasing implantation time up to 1 h, but it is not significantly increased at further increase of implantation time. In the Raman spectra, the sharp peak from Si crystal is decreased in intensity and the small peaks from a-Si and/or a-SiNx appear after N ion implantation. On the other hand, in the FT-IR spectra, a broad peak assigned to Si–N bonds appears after N ion implantation. The result of RBS measurement indicates that the N/Si ratio is approximately 1.3. Judging from these results, it is suggested that a-SiN1.3 is formed as a surface layer on Si wafer by N ion implantation using PBII system. Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction Ion implantation is a useful technique for the surface modification of materials. Recently, plasma based ion implantation (PBII) technique has attracted much interest because of the capability of ion implantation on 3 dimensional workpieces [1]. Moreover, in the PBII technique, the sample also can be covered with proper films by coating process. Therefore, with this technique, ion implantation process is sometimes employed before coating to modify surface for getting high adhesion strength. Walter et al. [2] reported that carbon implantation caused adherent diamond-like carbon films on various materials. It is also expected that the surface modification can be done by implantation with not only carbon but also various other gases, such as nitrogen, oxygen and hydrogen. Especially, many studies on nitrogen (N) implantation by PBII technique have been carried out for surface nitridation of metals, such as aluminum [3], steel [4] and titanium alloys [5] and for modification of surface properties of polymer, such as polyethylene [6]. However, it is not always clarified on the time dependence of N implantation. In this study, Si
* Tel.: +81 52 736 7286; fax: +81 52 736 7406. E-mail address: [email protected] 0168-583X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2009.01.117
wafer is used as a target and N implantation is carried out with a PBII system. The relative concentration of N is examined as a function of implantation time and the bonding structure of Si surface is also examined after N implantation. 2. Experimental Nitrogen implantation was carried out by the PBII system [7]. The detail of system illustration was reported in a previous paper [8]. The Si(1 0 0) wafers (10 20 mm) were held on the center of the cylindrical vacuum chamber. The chamber was evacuated to less than 103 Pa by a turbomolecular pump. RF power was 150 W at a frequency of 13.56 MHz. Negative pulse voltage (Vn) was applied to the substrate through a high-voltage feed-through and kept 20 kV. N2 gas was inlet to the chamber at a flow rate of 10 sccm. The working pressure during implantation was kept at 0.05 Pa. Implantation time was changed in the range of 10 min to 7 h. Depth profile of the implanted N in Si was calculated by the simulation program of the transport of ions in matter (TRIM ver. 95.06) code [9]. Relative concentration of N was examined by energy dispersive X-ray spectrometer (EDX) as a function of implantation time. The acceleration voltage was 20 kV and the analyzed area was approximately 2 2 lm2. The projected range of 20 keV
S. Nakao / Nuclear Instruments and Methods in Physics Research B 267 (2009) 1303–1306
electrons into Si was calculated to 4.6 lm by the equation reported by Kanaya and Okayama [10]. Although the signal information depth is not always clear, it may generally be around 1 lm. Raman spectra of nitrogen implanted Si surfaces were measured on microRaman spectrometer (Renishaw inVia) with 514.5 nm line of an Ar ion laser. The penetration depth of Ar ion laser into Si is estimated to around 0.5 lm. The power of the laser was 10 mW. The laser was focused to about 1 lm in diameter on the sample surface through a confocal optical microscope. Typical acquisition time was 10 s. The Si–N bonding after implantation was examined by Fourier Transform Infrared (FT-IR) spectroscopy. Rutherford backscattering spectrometry (RBS) was performed using 1.8 MeV He+ ions with a 1.7 MV tandem-type ion accelerator (NEC 5SDH-II pelletron accelerator). Quantitative analysis of the RBS spectrum was carried out by the simulation program of the Rutherford universal manipulation program code [11,12] for the Windows XP (XRUMP).
400 N 7h 300 4h
Intensity (a.u.)
1304
1h 200 30m 20m 100 10m
0 0
0.2 0
0.4 0
0.6 0
0.8 0
Energy (keV) Fig. 2. EDX spectra of the N implanted Si samples. The implantation time is varied from 10 min to 7 h.
3. Results and discussion Fig. 1 shows depth profile of implanted N in Si target calculated by TRIM code [9]. Calculation is performed on 20 keV N+ and Nþ 2 (10 keV per N) ions. The projected range (Rp) and straggling for N+ are 54.2 nm and 21.5 nm, respectively. On the other hand, the Rp and straggling for Nþ 2 are 29.0 nm and 12.8 nm, respectively. In the case of PBII, however, the ratio of N+ to Nþ 2 ions is varied depending on the plasma density (RF power). In a previous paper [7,13], the plasma density, electron temperature and substrate temperature were approximately 4 1010/cm3, around 1 eV and less than 200 °C, respectively, under the typical experimental conditions for our PBII system. Although the conditions are slightly different in this experiment, these plasma parameters may be similar values. The RF power of 150 W (the plasma density) is relatively low so that Nþ 2 ion is considered to be main ion species, as reported by Qi et al. [14]. In fact, it was reported by Tang et al. [15] that 70– 80% molecular ions of Nþ 2 were observed in their measurement system. Therefore, it is expected that the distribution of implanted N in Si is close to that for Nþ 2 implantation case. However, the distribution should shift toward the surface as a consequence of target compositional change and sputtering during N implantation, as reported in the previous paper [7]. The measurement of depth profile of implanted N and the comparison with the simulation are necessary and now in progress. Fig. 2 shows the EDX spectra of the N implanted Si samples at various implantation time ranging from 10 min to 7 h. Signal from
N appears at 0.4 keV for implanted sample for 10 min. The intensity of N signal is increased with increasing implantation time up to 1 h. However, further increase of implantation time does not cause a significant increase of the intensity. Fig. 3 indicates the change of relative N/Si ratio as a function of implantation time. It is noted that the projected range and the signal information depth should be deeper than N implanted range so that the N concentration is not true because the signal from Si comes from over the thickness of N implanted layer. However, the behavior of N concentration against implantation time is figured out. N concentration is increased with increasing implantation time up to 1 h and tends to be saturated at further implantation time. Fig. 4 shows Raman spectra of Si surface before and after N implanted for 7 h. The strong peak is observed at 520 cm1 for beforeimplanted sample due to TO band of crystalline silicon. The intensity is decreased and the weak shoulder peak appears at 480 cm1 for after-implanted sample. The shoulder peak corresponds to the TO band of amorphous Si and/or amorphous SiNx [16]. In addition, the small broad peak appears at 150 cm1. This peak also corresponds to the TA band of amorphous SiNx [16]. These results suggest that the amorphization of Si and the formation of Si–N bonding have taken place on the surface of the Si target by N implantation. Similar tendency is also reported by Sadiq et al. [17]. Fig. 5 shows FT-IR spectrum of N implanted Si for 7 h. The
30
Relative N/Si ratio (%)
N atoms/nm/ions
N2 +
N+
20
10
0 0
20
40
60
80
100
120
140
Depth (nm) Fig. 1. Depth profile of the implanted N ions in the Si substrate calculated by TRIM code (ver. 95.06).
0
2
4
6
8
Time (hours) Fig. 3. The changes in relative N/Si ratio obtained from EDX measurements as a function of the implantation time.
1305
S. Nakao / Nuclear Instruments and Methods in Physics Research B 267 (2009) 1303–1306
200
Energy (MeV) Si
50
0.6
0.8
1.8 MeV He+
a-Si or a-SiNx
1.0
1.2
N implanted Si for 7h
40
Normalized Yield
Intensity (a.u.)
150
0.4
100 a-SiNx
50
N
30
Si 20
10
0 100
200
300
400
500
600
700
Raman shift (cm-1) Fig. 4. Raman spectra of the Si samples before and after N implantation for 7 h.
broad peak centered around 830 cm1 is observed. This peak is assigned to Si–N bond vibration [18]. Therefore, it is confirmed that Si–N bonding is formed in the Si target. To make clear the N/Si ratio, RBS measurement is carried out. Fig. 6 shows RBS spectrum of N implanted Si for 7 h. Open circles and solid line indicate the measured signals and the fitting result by XRUMP code, respectively. It is noticed that the gradient of Si surface signals is subtly changed on N concentration. Then, the simulation was carried out by fitting to the gradient of Si surface signals. The error in determining the N concentration is believed to be minimized by this procedure, although the intensity of N signals is very low. The simulation result shows that the N/Si ratio is approximately 1.3, assuming the layer thickness of 3 1017/cm2. This value is close to the saturated concentration (1.33) of N in Si. From these results, it is suggested that amorphous SiN1.3 layer is formed by N implantation using PBII system. The results of EDX analysis show that the N concentration tends to be saturated at longer implantation time, as shown in Figs. 2 and 3. Miyagawa et al. [19] reported that the implanted N into metal follows the binary collision model until the concentration reaches the saturated concentration of the saturated nitride phase and excess N diffuses towards the surface and releases from there. In addition, in the case of thin Si layer (80 nm) on glassy carbon, the implanted N spreads towards the upper Si layer when the implanted dose increased over the saturated concentration in C [20]. These results suggest that the implanted N may diffuse towards the surface and release from the surface after the N concentration reaches the saturated concentration of silicon nitride phase (Si3N4: 0.2 7h
30
40
50
60
70
80
90
Channel Fig. 6. RBS spectrum of the N implanted Si sample for 7 h.
N/Si = 1.33) if the thickness is very thin, although the implanted N is not always easy to move in Si as compared with metals. It is + noted that the Rp 29.0 nm for Nþ 2 case (54 nm for N case), as shown in Fig. 1, is enough thin as compared with the thickness in [20]. Moreover, the N/Si ratio estimated to 1.3 from RBS measurement, as shown in Fig. 6, is close to the saturated concentration of silicon nitride phase. In addition, surface sputtering should be occurred during N implantation. It is expected that the N concentration is reduced by sputtering of nitride surface, leading to the compensation for the increase of N concentration in Si. Therefore, it might be said that the observed saturation tendency of the N concentration in Si is caused by the diffusion and release of excess N from the surface and sputtering of the nitride surface at longer implantation time. 4. Summary N implantation into Si is carried out by the PBII system, and the compositional and structural changes of the surface of Si are examined as a function of implantation time in the range of 0.17–7 h. It is found that the N/Si ratio is increased up to 1 h, but tends to be saturated at further increase of implantation time. The result of RBS measurement indicates that the N/Si ratio is about 1.3 which is close to the saturated concentration of 1.33 of N in Si. The result of FT-IR measurement shows that Si–N bonding is certainly formed by N implantation into Si. The result of Raman measurement indicates that amorphous SiNx is presumably formed after N implantation. These results suggest that amorphous SiN1.3 layer is formed by N implantation.
Si-N
0.15
Absorbance
0 20
References
0.1
0.05
0 400
600
800
1000 -1
Wavenumber (cm ) Fig. 5. FT-IR spectrum of the N implanted Si sample for 7 h.
1200
[1] A. Anders, Handbook of Plasma Immersion Ion Implantation and Deposition, Wiley, New York, 2000. [2] K.C. Walter, M. Nastasi, C. Munson, Surf. Coat. Technol. 93 (1997) 287. [3] T. Yamanishi, Y. Hara, R. Morita, K. Azuma, E. Fujiwara, M. Yatsuzuka, Surf. Coat. Technol. 136 (2001) 223. [4] S. Xu, X. Ma, M. Sun, Y. Sun, K. Yukimura, Nucl. Instr. and Meth. B 242 (2006) 374. [5] V. Fouquet, E. Le Bourhis, L. Pichon, M. Drouet, A. Straboni, Scripta Mater. 51 (2004) 899. [6] I. Bertoti, M. Mohai, A. Toth, T. Ujvari, Surf. Coat. Technol. 201 (2007) 6839. [7] S. Miyagawa, S. Nakao, M. Ikeyama, Y. Miyagawa, Surf. Coat. Technol. 156 (2002) 322. [8] J. Choi, S. Nakao, M. Ikeyama, T. Kato, Phys. Status Solidi C 5 (2008) 956. [9] J.B. Biersack, L.G. Haffmark, Nucl. Instr. and Meth. 174 (1980) 257. [10] K. Kanaya, S. Okayama, J. Phys. D. Appl. Phys. 5 (1972) 43.
1306
S. Nakao / Nuclear Instruments and Methods in Physics Research B 267 (2009) 1303–1306
[11] L.R. Doolittle, Nucl. Instr. and Meth. B 9 (1985) 344. [12] L.R. Doolittle, Nucl. Instr. and Meth. B 15 (1986) 227. [13] S. Miyagawa, Y. Miyagawa, Mater. Res. Soc. Symp. Proc. 647 (2001) O11.7.1. [14] S. Qi, X. Lifang, M. Xinxin, S. Mingren, Appl. Surf. Sci. 206 (2003) 53. [15] B.Y. Tang, R.P. Fetherston, M. Shamim, R.A. Breun, A. Chen, J.R. Conrad, J. Appl. Phys. 73 (1993) 4176. [16] Y. Wang, R. Yue, H. Han, X. Liao, J. Non-Cryst. Solids 291 (2001) 107.
[17] M. Sadiq, S. Ahmad, M. Shafiq, M. Zakaullah, Nucl. Instr. and Meth. B 252 (2006) 219. [18] S.B. Patil, A. Kumbhar, P. Waghmare, V.R. Rao, R.O. Dusane, Thin Solid Films 395 (2001) 270. [19] Y. Miyagawa, S. Nakao, K. Baba, M. Ikeyama, K. Saitoh, S. Miyagawa, Mater. Sci. Eng. A 253 (1998) 135. [20] Y. Miyagawa, M. Ikeyama, S. Nakao, S. Miyagawa, Nucl. Instr. and Meth. B 153 (1999) 422.