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FTIR and RBS study of ion-beam synthesized buried silicon oxide layers
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NIM B Beam Interactions with Materials & Atoms
Nuclear Instruments and Methods in Physics Research B 266 (2008) 1443–1446 www.elsevier.com/locate/nimb
FTIR and RBS study of ion-beam synthesized buried silicon oxide layers A.P. Patel a, A.D. Yadav a,*, S.K. Dubey a, B.K. Panigrahi b, K.G.M. Nair b a
Department of Physics, University of Mumbai, Vidyanagari campus, Santacruz (E), Mumbai 400098, India b Materials Science Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, India Received 21 September 2007; received in revised form 3 December 2007 Available online 23 December 2007
Abstract Single crystal silicon samples were implanted at 140 keV by oxygen (16O+) ion beam to fluence levels of 1.0 1017, 2.5 1017 and 5.0 1017 cm2 to synthesize buried silicon oxide insulating layers by SIMOX (separation by implanted oxygen) process at room temperature and at high temperature (325 °C). The structure and composition of the ion-beam synthesized buried silicon oxide layers were investigated by Fourier transform infrared (FTIR) and Rutherford backscattering spectroscopy (RBS) techniques. The FTIR spectra of implanted samples reveal absorption in the wavenumber range 1250–750 cm1 corresponding to the stretching vibration of Si–O bonds indicating the formation of silicon oxide. The integrated absorption band intensity is found to increase with increase in the ion fluence. The absorption peak was rather board for 325 °C implanted sample. The FTIR studies show that the structures of ion-beam synthesized buried oxide layers are strongly dependent on total ion fluence. The RBS measurements show that the thickness of the buried oxide layer increases with increase in the oxygen fluence. However, the thickness of the top silicon layer was found to decrease with increase in the ion fluence. The total oxygen fluence estimated from the RBS data is found to be in good agreement with the implanted oxygen fluence. The high temperature implantation leads to increase in the concentration of the oxide formation compared to room temperature implantation. Ó 2007 Elsevier B.V. All rights reserved. PACS: 61.72.Tt; 61.80.Jh; 61.82.Ms; 78.30.j; 82.80.Yc Keywords: Silicon; Ion implantation; SIMOX; Buried oxide layer; FTIR; RBS; Structure; Composition
1. Introduction The fabrication of devices on a thin layer of silicon separated from the bulk silicon substrate by a buried insulator layer, i.e. silicon-on-insulator (SOI) technology is useful to increase the circuit speed, device density and radiation hardness. The synthesis of buried insulating layers with high quality top silicon and good interfaces to produce SOI structures by SIMOX (separation by implanted oxygen) process using P1016 cm2 oxygen ion implantation * Corresponding author. Tel.: +91 22 26526250/26528835; fax: +91 22 26529780. E-mail addresses: [email protected], drad_yadav@yahoo. com (A.D. Yadav).
0168-583X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2007.12.048
into silicon has scope of potential applications in semiconductor devices technology. Ogura and Ono [1] have reported infrared studies of buried oxide layer formation in 2.0–4.0 1017 cm2 implanted silicon wafer held at temperature of 550–600 °C at 180 keV and annealed in an O2/ Ar atmosphere. Ono et al. [2] have reported infrared studies of silicon oxide formation in silicon wafers implanted with oxygen at 180 keV in fluence range 0.5–7.0 1017 cm2 and annealed at 400–1300 °C in Ar with 0.5% O2. Hayashi et al. [3] have reported SIMS and RBS studies of SIMOX wafer prepared at 180 keV at 600 °C substrate temperature with fluence 4.0 1017 cm2 followed by non-oxidizing anneal at 1300 °C in 0.5% O2–Ar. The results reported in the literature depend considerably on implantation and post implantation annealing treatments.
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A.P. Patel et al. / Nucl. Instr. and Meth. in Phys. Res. B 266 (2008) 1443–1446
In the present work we have studied the effect of fluence and the substrate temperature on the SIMOX structure synthesized by implantation of oxygen (16O+) ion beam at 140 keV to fluence levels ranging from 1.0 1017 to 5.0 1017 cm2 into silicon substrates held at room temperature and 325 °C. The structural and compositional analysis of ion-beam synthesized SIMOX structures were carried out by Fourier transform infrared (FTIR) and Rutherford backscattering spectroscopy (RBS) techniques.
Table 1 Range of the FTIR absorption band and peak position at different ion fluences Fluence (cm2)
1.0 1017 2.5 1017 5.0 1017
Room temperature implanted sample
High temperature (325 °C) implanted sample
Absorption band range (cm1)
Peak position (cm1)
Absorption band range (cm1)
Peak position (cm1)
1076–763 1122–765 1142–768
949.7 963.6 983.7
1136–788 1220–809 1242–812
997.0 1000.8 1010.5
2. Experimental details
3. Results and discussion 3.1. Fourier transform infrared (FTIR) studies The absorption bands observed in the FTIR spectra of the silicon samples implanted with 140 keV (16O+) at room temperature to different fluences are given in Table 1. The observed absorption band is associated with the stretching vibration of the Si–O bond and shows the formation of silicon oxide [2]. The FTIR results showed an increase in the integrated absorption band intensity and sharpening of the
band with increasing ion fluence indicating transformation of implanted layer towards stoichiometric SiO2. The FTIR spectra of the silicon samples implanted with 140 keV (16O+) at high temperature (325 °C) to different fluences are shown in Fig. 1. The absorption band range and the peak position for different fluences are shown in Table 1. It is observed that the sample implanted to fluence of 1.0 1017 cm2 shows absorption band in the wavenumber range 1136–788 cm1 centered at 997 cm1. On increasing the oxygen fluence, the range of the IR absorption band increases and the peak position shifts towards higher wavenumber. The intensity of the band increases with increasing the ion fluence. At low fluence level, the absorption band is relatively weak and rather broad. This is due to random distribution of Si–O stretching bonds and/ formation of suboxide of silicon. The observed band shift towards higher frequencies with increasing ion fluence indicates transformation of oxygen-implanted layer towards the formation of SiO2. Fig. 2 shows a comparison of the FTIR spectra of room temperature and high temperature implanted silicon samples for fluence of 2.5 1017 cm2. The room temperature implanted sample indicates partial oxidation of silicon and high temperature implanted sample shows higher degree
Transmittance (arb. unit)
Single crystal p-type silicon wafers with h1 1 1i orientation and 10–15 X cm resistivity were selected as substrate material. The silicon wafers were thoroughly cleaned adopting standard RCA-I and RCA-II cleaning procedures using electronic grade chemicals and distilled deionized (DI) water. The cleaned wafers were then cut into 1 cm 1 cm size samples for loading onto the sample holder of the implanter. Implantation was carried out with 140 keV oxygen (16O+) ion beam at beam current density of 1–2 lA cm2 using 150 kV ion accelerator at Materials Science Division, IGCAR, Kalpakkam. For implantation, the collimation of the scanned beam was further done through a collimator of diameter 12.5 mm. During implantation, a vacuum of 1.0 106 mbar was maintained in the target chamber. To study the effect of implantation temperature and fluence, samples were implanted at room temperature (RT) and at high temperature 325 °C with fluence levels 1.0 1017, 2.5 1017 and 5.0 1017 cm2. The identification of structure of ion-beam synthesized buried silicon oxide layers was carried out by FTIR spectroscopy studies. The FTIR spectra were recorded in the wavenumber range 6000–400 cm1 on a JASCO-610 FTIR spectrometer at the Department of Physics, University of Mumbai. A matched reference silicon sample was used for background correction for the FTIR spectra. The composition and thickness measurements of the samples were carried out by RBS technique using 1.7 MV Tandetron Accelerator at Materials Science Division, IGCAR, Kalpakkam. 4He++ ion beam at 3.644 MeV energy and 165° scattering angle was used to analyze the implanted silicon layer. The RBS data was simulated using RUMP software to obtain the concentration versus depth profiles of the implanted samples.
1400
3 2 1
1300
1200
1100
1000
900
800
700
600
Wavenumber (cm-1) Fig. 1. FTIR spectra of the silicon samples implanted with 140 keV (16O+) at high temperature (325 °C) to fluence levels; (1) 1.0 1017, (2) 2.5 1017 and (3) 5.0 1017 cm2.
A.P. Patel et al. / Nucl. Instr. and Meth. in Phys. Res. B 266 (2008) 1443–1446
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Table 2 Total oxygen fluence estimated from RBS data for implanted samples
Transmittance (arb. unit)
RBS measurement
2
1300
1200
1100
1000
Room temperature implanted sample (atoms cm2)
High temperature implanted sample (atoms cm2)
1.0 1017 2.5 1017 5.0 1017
1.25 1017 2.44 1017 5.67 1017
1.16 1017 2.42 1017 5.20 1017
Table 3 Buried oxide and top silicon layer thickness determined from RBS ˚) Thickness (A
1
1400
Implanted fluence (atoms cm2)
900
800
700
Fluence (cm2)
600
Wavenumber (cm-1) 16
+
Fig. 2. FTIR spectra of the silicon samples implanted with 140 keV ( O ) at (1) room temperature and (2) high temperature (325 °C) to fluence 2.5 1017 cm2.
oxidation of silicon. The absorption peak intensity of high temperature implanted sample is observed to be more than the room temperature implanted sample. These results show that enhanced reactivity of oxygen with silicon at higher temperature implantation results in the formation of more Si–O bonds. 3.2. Rutherford backscattering spectroscopy (RBS) studies Fig. 3 shows the RBS spectra of silicon samples implanted with 140 keV oxygen (16O+) at RT and 325 °C to fluence of 2.5 1017 cm2. The decreasing scattering yield between the channels 600 to 670 with smooth falling
1.0 1017 2.5 1017 5.0 1017
Room temperature implanted sample
High temperature implanted sample
Top surface silicon layer
Buried oxide layer
Top surface silicon layer
Buried oxide layer
1651 1167 740
3145 3355 3591
1736 1582 1308
3224 3434 3984
edge shows reduction in the volume concentration of the silicon due to the presence of implanted oxygen in the region and represents silicon in the buried oxide layer [4]. It shows that the oxygen has distributed to form a buried silicon oxide layer with well-defined boundaries between silicon and oxide. The total oxygen fluence estimated from the RBS data [5] is found to be in good agreement with the implanted oxygen fluence (Table 2). These thickness of the top surface silicon layer and the buried oxide layer (as given in Table 3) were determined from the RBS measurements. The thickness calculations are based on the stopping cross section for the Helium ion and Bragg’s additivity rules in SiO2 [6]. It is observed that with increase
E=3.644 MeV 4He++ O in SiO2
110
Si in SiO2
Yield (arb. unit)
1
RT
100
Top Si
325ºC
90
Concentration (%)
80
2
Silicon
70 60 50 40 30
Oxygen
20
200
250
300
350
400
450
500
550
600
650
10
700
Channel Number
0 16
+
Fig. 3. RBS spectra of the silicon samples implanted with 140 keV ( O ) at (1) room temperature and (2) high temperature (325 °C) to fluence 2.5 1017 cm2. Solid line represents the RUMP simulation and h and D symbols represent the experimental data.
0
1000
2000
3000
4000
5000
6000
7000
Thickness (Å)
Fig. 4. RBS concentration profile of the silicon and oxygen for the silicon sample implanted with 2.5 1017 cm2 at 140 keV.
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A.P. Patel et al. / Nucl. Instr. and Meth. in Phys. Res. B 266 (2008) 1443–1446
in ion fluence the thickness of the buried silicon oxide layer increases whereas the thickness of the top surface silicon layer decreases. The thickness of the buried oxide layer in high temperature implanted sample is found to be more than the room temperature implanted sample. The RBS data were simulated using the RUMP software in terms of percentage concentration of silicon and oxygen in the implanted sample. The simulation results of the sample implanted with 2.5 1017 cm2 at RT and 325 °C are shown in Fig. 4. The concentration ratio of oxygen and silicon at projected range (Rp) are found to be different for room temperature and high temperature implanted samples. High temperature implanted sample reveals more oxide formation compared to room temperature implanted sample. It is seen that the oxygen distribution is maximum ˚ . This depth matches very at the depth of around 3200 A ˚ ) calculated for closely to the theoretical depth (3187 A + 140 keV O in silicon using SRIM code [7].
of buried silicon oxide layers. The thickness of the buried oxide layer was found to increase with increase in the oxygen fluence. However, the thickness of the top silicon layer decreases with increase in ion fluence.
4. Conclusion
References
The buried silicon oxide (SiO2) layers were synthesized using SIMOX process by implantation of 140 keV oxygen (16O+) ions at different fluence levels into silicon substrates held at room temperature and at high temperature (325 °C). The FTIR studies show that the absorption band associated with the stretching vibration of the Si–O bonds indicates the formation of silicon oxide. The absorption peak intensity of high temperature implanted sample is found to be more than the room temperature implanted sample. The RBS depth profile studies show the formation
[1] A. Ogura, H. Ono, Appl. Surf. Sci. 159–160 (2000) 104. [2] H. Ono, T. Ikarashi, A. Ogura, Appl. Phys. Lett. 72 (22) (1998) 2853. [3] S. Hayashi, T. Sasaki, K. Kawamura, A. Matsumura, K. Yanagihara, K. Tanaka, Appl. Surf. Sci. 203–204 (2003) 504. [4] A.D. Yadav, A.P. Patel, S.K. Dubey, B.K. Panigrahi, K.G.M. Nair, in: Proc. DAE Solid State Physics Symposium 50 (2005) 793. [5] W.K. Chu, J.W. Mayer, M.A. Nicolet, Backscattering Spectrometry, Academic press, New York, 1978. [6] J.W. Mayer, E. Rimini, Ion beam handbook for Material Analysis, Academic press, New York, 1977. [7] J.F. Ziegler, J.P. Biersack, Stopping and Range of Ions in Matter, in: SRIM 2003.
Acknowledgements We would like to thank UGC-DAE Consortium for Scientific Research, Kolkata Centre for financial support to the IUC-IGCAR collaborative research Project No: IUCDAEF CFS-IG-09/ UM/ ADY/6230 dated 12th May 2004 for carrying out this work. One of the authors (APP) is grateful for the award of research fellowship under the project. We are grateful to Indira Gandhi Centre for Atomic Research, Kalpakkam for extending the facilities of heavy ion accelerator to carry out ion implantation and RBS experiments.
NIM B Beam Interactions with Materials & Atoms
Nuclear Instruments and Methods in Physics Research B 266 (2008) 1443–1446 www.elsevier.com/locate/nimb
FTIR and RBS study of ion-beam synthesized buried silicon oxide layers A.P. Patel a, A.D. Yadav a,*, S.K. Dubey a, B.K. Panigrahi b, K.G.M. Nair b a
Department of Physics, University of Mumbai, Vidyanagari campus, Santacruz (E), Mumbai 400098, India b Materials Science Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, India Received 21 September 2007; received in revised form 3 December 2007 Available online 23 December 2007
Abstract Single crystal silicon samples were implanted at 140 keV by oxygen (16O+) ion beam to fluence levels of 1.0 1017, 2.5 1017 and 5.0 1017 cm2 to synthesize buried silicon oxide insulating layers by SIMOX (separation by implanted oxygen) process at room temperature and at high temperature (325 °C). The structure and composition of the ion-beam synthesized buried silicon oxide layers were investigated by Fourier transform infrared (FTIR) and Rutherford backscattering spectroscopy (RBS) techniques. The FTIR spectra of implanted samples reveal absorption in the wavenumber range 1250–750 cm1 corresponding to the stretching vibration of Si–O bonds indicating the formation of silicon oxide. The integrated absorption band intensity is found to increase with increase in the ion fluence. The absorption peak was rather board for 325 °C implanted sample. The FTIR studies show that the structures of ion-beam synthesized buried oxide layers are strongly dependent on total ion fluence. The RBS measurements show that the thickness of the buried oxide layer increases with increase in the oxygen fluence. However, the thickness of the top silicon layer was found to decrease with increase in the ion fluence. The total oxygen fluence estimated from the RBS data is found to be in good agreement with the implanted oxygen fluence. The high temperature implantation leads to increase in the concentration of the oxide formation compared to room temperature implantation. Ó 2007 Elsevier B.V. All rights reserved. PACS: 61.72.Tt; 61.80.Jh; 61.82.Ms; 78.30.j; 82.80.Yc Keywords: Silicon; Ion implantation; SIMOX; Buried oxide layer; FTIR; RBS; Structure; Composition
1. Introduction The fabrication of devices on a thin layer of silicon separated from the bulk silicon substrate by a buried insulator layer, i.e. silicon-on-insulator (SOI) technology is useful to increase the circuit speed, device density and radiation hardness. The synthesis of buried insulating layers with high quality top silicon and good interfaces to produce SOI structures by SIMOX (separation by implanted oxygen) process using P1016 cm2 oxygen ion implantation * Corresponding author. Tel.: +91 22 26526250/26528835; fax: +91 22 26529780. E-mail addresses: [email protected], drad_yadav@yahoo. com (A.D. Yadav).
0168-583X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2007.12.048
into silicon has scope of potential applications in semiconductor devices technology. Ogura and Ono [1] have reported infrared studies of buried oxide layer formation in 2.0–4.0 1017 cm2 implanted silicon wafer held at temperature of 550–600 °C at 180 keV and annealed in an O2/ Ar atmosphere. Ono et al. [2] have reported infrared studies of silicon oxide formation in silicon wafers implanted with oxygen at 180 keV in fluence range 0.5–7.0 1017 cm2 and annealed at 400–1300 °C in Ar with 0.5% O2. Hayashi et al. [3] have reported SIMS and RBS studies of SIMOX wafer prepared at 180 keV at 600 °C substrate temperature with fluence 4.0 1017 cm2 followed by non-oxidizing anneal at 1300 °C in 0.5% O2–Ar. The results reported in the literature depend considerably on implantation and post implantation annealing treatments.
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A.P. Patel et al. / Nucl. Instr. and Meth. in Phys. Res. B 266 (2008) 1443–1446
In the present work we have studied the effect of fluence and the substrate temperature on the SIMOX structure synthesized by implantation of oxygen (16O+) ion beam at 140 keV to fluence levels ranging from 1.0 1017 to 5.0 1017 cm2 into silicon substrates held at room temperature and 325 °C. The structural and compositional analysis of ion-beam synthesized SIMOX structures were carried out by Fourier transform infrared (FTIR) and Rutherford backscattering spectroscopy (RBS) techniques.
Table 1 Range of the FTIR absorption band and peak position at different ion fluences Fluence (cm2)
1.0 1017 2.5 1017 5.0 1017
Room temperature implanted sample
High temperature (325 °C) implanted sample
Absorption band range (cm1)
Peak position (cm1)
Absorption band range (cm1)
Peak position (cm1)
1076–763 1122–765 1142–768
949.7 963.6 983.7
1136–788 1220–809 1242–812
997.0 1000.8 1010.5
2. Experimental details
3. Results and discussion 3.1. Fourier transform infrared (FTIR) studies The absorption bands observed in the FTIR spectra of the silicon samples implanted with 140 keV (16O+) at room temperature to different fluences are given in Table 1. The observed absorption band is associated with the stretching vibration of the Si–O bond and shows the formation of silicon oxide [2]. The FTIR results showed an increase in the integrated absorption band intensity and sharpening of the
band with increasing ion fluence indicating transformation of implanted layer towards stoichiometric SiO2. The FTIR spectra of the silicon samples implanted with 140 keV (16O+) at high temperature (325 °C) to different fluences are shown in Fig. 1. The absorption band range and the peak position for different fluences are shown in Table 1. It is observed that the sample implanted to fluence of 1.0 1017 cm2 shows absorption band in the wavenumber range 1136–788 cm1 centered at 997 cm1. On increasing the oxygen fluence, the range of the IR absorption band increases and the peak position shifts towards higher wavenumber. The intensity of the band increases with increasing the ion fluence. At low fluence level, the absorption band is relatively weak and rather broad. This is due to random distribution of Si–O stretching bonds and/ formation of suboxide of silicon. The observed band shift towards higher frequencies with increasing ion fluence indicates transformation of oxygen-implanted layer towards the formation of SiO2. Fig. 2 shows a comparison of the FTIR spectra of room temperature and high temperature implanted silicon samples for fluence of 2.5 1017 cm2. The room temperature implanted sample indicates partial oxidation of silicon and high temperature implanted sample shows higher degree
Transmittance (arb. unit)
Single crystal p-type silicon wafers with h1 1 1i orientation and 10–15 X cm resistivity were selected as substrate material. The silicon wafers were thoroughly cleaned adopting standard RCA-I and RCA-II cleaning procedures using electronic grade chemicals and distilled deionized (DI) water. The cleaned wafers were then cut into 1 cm 1 cm size samples for loading onto the sample holder of the implanter. Implantation was carried out with 140 keV oxygen (16O+) ion beam at beam current density of 1–2 lA cm2 using 150 kV ion accelerator at Materials Science Division, IGCAR, Kalpakkam. For implantation, the collimation of the scanned beam was further done through a collimator of diameter 12.5 mm. During implantation, a vacuum of 1.0 106 mbar was maintained in the target chamber. To study the effect of implantation temperature and fluence, samples were implanted at room temperature (RT) and at high temperature 325 °C with fluence levels 1.0 1017, 2.5 1017 and 5.0 1017 cm2. The identification of structure of ion-beam synthesized buried silicon oxide layers was carried out by FTIR spectroscopy studies. The FTIR spectra were recorded in the wavenumber range 6000–400 cm1 on a JASCO-610 FTIR spectrometer at the Department of Physics, University of Mumbai. A matched reference silicon sample was used for background correction for the FTIR spectra. The composition and thickness measurements of the samples were carried out by RBS technique using 1.7 MV Tandetron Accelerator at Materials Science Division, IGCAR, Kalpakkam. 4He++ ion beam at 3.644 MeV energy and 165° scattering angle was used to analyze the implanted silicon layer. The RBS data was simulated using RUMP software to obtain the concentration versus depth profiles of the implanted samples.
1400
3 2 1
1300
1200
1100
1000
900
800
700
600
Wavenumber (cm-1) Fig. 1. FTIR spectra of the silicon samples implanted with 140 keV (16O+) at high temperature (325 °C) to fluence levels; (1) 1.0 1017, (2) 2.5 1017 and (3) 5.0 1017 cm2.
A.P. Patel et al. / Nucl. Instr. and Meth. in Phys. Res. B 266 (2008) 1443–1446
1445
Table 2 Total oxygen fluence estimated from RBS data for implanted samples
Transmittance (arb. unit)
RBS measurement
2
1300
1200
1100
1000
Room temperature implanted sample (atoms cm2)
High temperature implanted sample (atoms cm2)
1.0 1017 2.5 1017 5.0 1017
1.25 1017 2.44 1017 5.67 1017
1.16 1017 2.42 1017 5.20 1017
Table 3 Buried oxide and top silicon layer thickness determined from RBS ˚) Thickness (A
1
1400
Implanted fluence (atoms cm2)
900
800
700
Fluence (cm2)
600
Wavenumber (cm-1) 16
+
Fig. 2. FTIR spectra of the silicon samples implanted with 140 keV ( O ) at (1) room temperature and (2) high temperature (325 °C) to fluence 2.5 1017 cm2.
oxidation of silicon. The absorption peak intensity of high temperature implanted sample is observed to be more than the room temperature implanted sample. These results show that enhanced reactivity of oxygen with silicon at higher temperature implantation results in the formation of more Si–O bonds. 3.2. Rutherford backscattering spectroscopy (RBS) studies Fig. 3 shows the RBS spectra of silicon samples implanted with 140 keV oxygen (16O+) at RT and 325 °C to fluence of 2.5 1017 cm2. The decreasing scattering yield between the channels 600 to 670 with smooth falling
1.0 1017 2.5 1017 5.0 1017
Room temperature implanted sample
High temperature implanted sample
Top surface silicon layer
Buried oxide layer
Top surface silicon layer
Buried oxide layer
1651 1167 740
3145 3355 3591
1736 1582 1308
3224 3434 3984
edge shows reduction in the volume concentration of the silicon due to the presence of implanted oxygen in the region and represents silicon in the buried oxide layer [4]. It shows that the oxygen has distributed to form a buried silicon oxide layer with well-defined boundaries between silicon and oxide. The total oxygen fluence estimated from the RBS data [5] is found to be in good agreement with the implanted oxygen fluence (Table 2). These thickness of the top surface silicon layer and the buried oxide layer (as given in Table 3) were determined from the RBS measurements. The thickness calculations are based on the stopping cross section for the Helium ion and Bragg’s additivity rules in SiO2 [6]. It is observed that with increase
E=3.644 MeV 4He++ O in SiO2
110
Si in SiO2
Yield (arb. unit)
1
RT
100
Top Si
325ºC
90
Concentration (%)
80
2
Silicon
70 60 50 40 30
Oxygen
20
200
250
300
350
400
450
500
550
600
650
10
700
Channel Number
0 16
+
Fig. 3. RBS spectra of the silicon samples implanted with 140 keV ( O ) at (1) room temperature and (2) high temperature (325 °C) to fluence 2.5 1017 cm2. Solid line represents the RUMP simulation and h and D symbols represent the experimental data.
0
1000
2000
3000
4000
5000
6000
7000
Thickness (Å)
Fig. 4. RBS concentration profile of the silicon and oxygen for the silicon sample implanted with 2.5 1017 cm2 at 140 keV.
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A.P. Patel et al. / Nucl. Instr. and Meth. in Phys. Res. B 266 (2008) 1443–1446
in ion fluence the thickness of the buried silicon oxide layer increases whereas the thickness of the top surface silicon layer decreases. The thickness of the buried oxide layer in high temperature implanted sample is found to be more than the room temperature implanted sample. The RBS data were simulated using the RUMP software in terms of percentage concentration of silicon and oxygen in the implanted sample. The simulation results of the sample implanted with 2.5 1017 cm2 at RT and 325 °C are shown in Fig. 4. The concentration ratio of oxygen and silicon at projected range (Rp) are found to be different for room temperature and high temperature implanted samples. High temperature implanted sample reveals more oxide formation compared to room temperature implanted sample. It is seen that the oxygen distribution is maximum ˚ . This depth matches very at the depth of around 3200 A ˚ ) calculated for closely to the theoretical depth (3187 A + 140 keV O in silicon using SRIM code [7].
of buried silicon oxide layers. The thickness of the buried oxide layer was found to increase with increase in the oxygen fluence. However, the thickness of the top silicon layer decreases with increase in ion fluence.
4. Conclusion
References
The buried silicon oxide (SiO2) layers were synthesized using SIMOX process by implantation of 140 keV oxygen (16O+) ions at different fluence levels into silicon substrates held at room temperature and at high temperature (325 °C). The FTIR studies show that the absorption band associated with the stretching vibration of the Si–O bonds indicates the formation of silicon oxide. The absorption peak intensity of high temperature implanted sample is found to be more than the room temperature implanted sample. The RBS depth profile studies show the formation
[1] A. Ogura, H. Ono, Appl. Surf. Sci. 159–160 (2000) 104. [2] H. Ono, T. Ikarashi, A. Ogura, Appl. Phys. Lett. 72 (22) (1998) 2853. [3] S. Hayashi, T. Sasaki, K. Kawamura, A. Matsumura, K. Yanagihara, K. Tanaka, Appl. Surf. Sci. 203–204 (2003) 504. [4] A.D. Yadav, A.P. Patel, S.K. Dubey, B.K. Panigrahi, K.G.M. Nair, in: Proc. DAE Solid State Physics Symposium 50 (2005) 793. [5] W.K. Chu, J.W. Mayer, M.A. Nicolet, Backscattering Spectrometry, Academic press, New York, 1978. [6] J.W. Mayer, E. Rimini, Ion beam handbook for Material Analysis, Academic press, New York, 1977. [7] J.F. Ziegler, J.P. Biersack, Stopping and Range of Ions in Matter, in: SRIM 2003.
Acknowledgements We would like to thank UGC-DAE Consortium for Scientific Research, Kolkata Centre for financial support to the IUC-IGCAR collaborative research Project No: IUCDAEF CFS-IG-09/ UM/ ADY/6230 dated 12th May 2004 for carrying out this work. One of the authors (APP) is grateful for the award of research fellowship under the project. We are grateful to Indira Gandhi Centre for Atomic Research, Kalpakkam for extending the facilities of heavy ion accelerator to carry out ion implantation and RBS experiments.