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Behavior of hydrogen implanted into Si-implanted SiO2
Nuclear Instruments and Methods in Physics Research B 209 (2003) 154–158 www.elsevier.com/locate/nimb
Behavior of hydrogen implanted into Si-implanted SiO2 Mitsuharu Ikeda a, Ryuta Mitsusue a, Masaharu Nakagawa a, Satoshi Kondo a, Makoto Imai a, Nobutsugu Imanishi a,b,* a
Department of Nuclear Engineering, Kyoto University, Yoshida-Honmachi, Sakyo-ku, Kyoto 606-8501, Japan b Quantum Science and Engineering Center, Kyoto University, Uji, Kyoto 611-0011, Japan
Abstract We applied the elastic recoil detection method to the in situ measurement of the hydrogen behavior in Si-implanted SiO2 samples, where annealing in hydrogen environment increases photoluminescence efficiency. Dominant hydrogen trap sites changed depending on implantation conditions. In samples annealed at room temperature, hydrogen seems to be trapped forming vacancy–H (V–H) and Si–H bonds. The thermal annealing of the high-dose Si-implanted SiO2 samples up to a temperature of 1173 K changes defects into tight hydrogen trapping of Si–H bond in conflict with results obtained at a low dose implantation. Annealing at 1343 K grows Si nanocrystals, and hydrogen seems to be trapped at the interface of Si nanocrystal/SiO2 matrix. However, a result of high-dose implantation of Si up to 6 1017 cm2 showed that a large part of hydrogen is trapped as self-induced V–H complexes formed inside the crystals instead of the trap at interface. Ó 2002 Elsevier B.V. All rights reserved. PACS: 61.46.þw; 61.80.)x; 66.30.)h Keywords: Hydrogen-trapping; Thermal behavior; Implantation; Si nanocrystal; Si/SiO2
1. Introduction The formation of Si nanocrystals buried in SiO2 through ion implantation is now one of very attractive topics for the fabrication of silicon-based photo devices [1–5]. It has been reported that annealing the Si-implanted SiO2 sample in hydrogen environment increases its photoluminescence efficiency [5]. That is, hydrogen is expected to passi* Corresponding author. Address: Department of Nuclear Engineering, Kyoto University, Yoshida-Honmachi, Sakyo-ku, Kyoto 606-8501, Japan. Tel./fax: +81-75-7535821. E-mail address: [email protected] (N. Imanishi).
vate dangling bonds on the surface of the nanocrystal. The aim of the present study is to understand the hydrogen behavior in SiO2 with high-density defects produced by the high-dose implantation of Si ions and with locally concentrated Si. Trapping of hydrogen by irradiation damages caused by ion implantation has been a great concern of many groups for several decades [6–9]. It was also pointed out that even a small amount of an additive element drastically affects the hydrogen trapping [10–13]. That is, hydrogen is trapped by vacancies, by dangling bonds of both implanted and matrix elements and at grain boundaries if the implanted elements segregate in the matrix [7,14]. Therefore, we applied the elastic
0168-583X/$ - see front matter Ó 2002 Elsevier B.V. All rights reserved. doi:10.1016/S0168-583X(02)02008-6
M. Ikeda et al. / Nucl. Instr. and Meth. in Phys. Res. B 209 (2003) 154–158
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recoil detection (ERD) method in order to understand the behavior of hydrogen and search a condition of the hydrogen trapping on the nanocrystal surface for the Si-implanted SiO2 samples. The measurement was done at several conditions of dose and annealing temperature for the Si implantation. The H trap sites were identified and the observed facts are explained well by taking into account the vacancies, the dangling bonds, and the boundaries of grains and nanocrystals formed by the Si implantation.
2. Experimental procedures Experimental procedures were previously described in detail [12,13,15] and are shown briefly. Samples used were 300-nm thick SiO2 layers thermally grown on Si wafers. After appropriate chemical treatments, 120 keV Si ions were implanted into the samples to doses of 1 1017 , 3 1017 and 6 1017 cm2 . After the respective implantations the samples were kept at room temperature (RT), or annealed at 1173 and 1343 K. Irradiation damages produced by the Si implantation were eliminated by keeping the samples at 1173 K. The implanted Si ions coagulated and formed small crystals of nm size by a procedure of 1-h annealing at 1343 K [5]. Hydrogen ions with an energy of 10 keV per atom were then implanted into these samples to a dose of 1 1017 cm2 at RT. Typical depth profiles of implanted silicon and hydrogen were calculated with the TRIM code [16], and are shown in Fig. 1 along with their damage populations. After the hydrogen implantation, the depth profiles of hydrogen were measured by the ERD method using a 2-MeV 4 Heþ ion beam [17,18]. The hydrogen energy spectra were taken with a surface barrier detector set at an angle of 30° using a 4 Heabsorbing film. The spectra were recorded every 10 min during an isochronal temperature-ramp measurement from 300 to 870 K at a rate of 3 K/min. The depth profiles of hydrogen were deduced from the energy spectra using the TRIM simulation code [16]. The amount of hydrogen decreased without varying the shape of profile during the isochronal temperature-ramp measurements.
Fig. 1. Simulated depth profiles of 120 keV Si (the solid line) and 10 keV H (the dashed line) in SiO2 . Distributions of vacancies produced by silicon (the dotted-dash line) and hydrogen (the double-dotted-dash line) implantation are also shown. Respective doses of Si and H ions are both 1 1017 Si cm2 [16].
3. Results and discussion Examples of the depth profile and of the thermal release of hydrogen during the temperatureramp measurement are shown in Figs. 2 and 3, for the three different Si doses of 1 1017 , 3 1017 and 6 1017 cm2 , as a function of the temperature of the sample annealing done before the hydrogen implantation. Hydrogen trapped by the surface formed the peak around 0 nm in depth [10]. The retention of hydrogen was very low in a SiO2 sample not implanted with Si. As shown in Fig. 2, however, a large part of implanted hydrogen was trapped in the Si-implanted samples. According to the observation done by Myers et al., dominant silicon-related trap sites of hydrogen are vacancy–hydrogen (V–H) complexes (with a binding energy of 1.3–1.7 eV), Si–H bonds (2.5 eV) and hydrogen trapping (2.56 eV) on grain boundary [6]. In SiO2 , an O–H bond is another candidate. The samples kept at RT before the hydrogen implantation contained lots of vacancies and Si dangling bonds induced by the Si implantation, and, therefore, the implanted hydrogen diffused toward the surface through the damage after
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M. Ikeda et al. / Nucl. Instr. and Meth. in Phys. Res. B 209 (2003) 154–158
Fig. 2. Depth profiles of hydrogen in Si-implanted SiO2 as a function of the sample annealing temperature before the hydrogen implantation. The doses of Si are (a) 1 1017 cm2 , (b) 3 1017 cm2 and (c) 6 1017 cm2 . The solid, dashed and dotted-dash lines denote the data for annealing at RT, 1173 and 1343 K, respectively.
stopping at the projected range, and was trapped by vacancies and silicon [19]. In this case, the hydrogen profile corresponds to the damage region and the implanted silicon layers. When one increased the Si dose up to and higher than 3 1017 cm2 , the profile moved to a shallow region caused by the enhancement of radiation induced diffusion of the high-dose implantation. That is, as measured by the Rutherford backscattering spectroscopy (RBS), the implanted Si moved this side of the projected range of 120 keV Si and trapped in
Fig. 3. Thermal release of hydrogen during temperature-ramp measurement as a function of the sample annealing temperature before the hydrogen implantation. The doses of Si are (a) 1 1017 cm2 , (b) 3 1017 cm2 and (c) 6 1017 cm2 . The solid, dashed and dotted-dash lines denote the data for annealing at RT, 1173 and 1343 K, respectively.
the damage region produced by themselves. The movement of the hydrogen profile is not expected in the case of the O–H bond. Therefore, the contribution of the O–H bond can be safely omitted from the further consideration. In the case of the RT annealing, the increase in the Si dose induced two additional phenomena. One is that, as shown in Fig. 2, the width of the hydrogen depth profile decreased with increasing Si dose, and the other is that, as shown in Fig. 3, the temperature of the hydrogen thermal release increased with increasing dose. The width and the release temperature at high doses are almost the same as those for the 1173 K annealing, in which
M. Ikeda et al. / Nucl. Instr. and Meth. in Phys. Res. B 209 (2003) 154–158
the Si–H bond is the dominant hydrogen trap site. These observations show that for the high-dose implantation, the contribution of the Si–H bond becomes important compared with the V–H complex. The 1173 K annealing eliminated the vacancies caused by the Si implantation, and supersaturated silicon probably segregated and formed grains leaving lots of dangling bonds. In this case hydrogen was trapped forming the Si–H bond in the layer of segregated Si (Fig. 2(b)). The vacancy elimination resulted in the decrease of hydrogen retention factor and the narrow width of the profile. The resultant tight bonding compared with the RT annealing was unambiguously observed irrespective of the Si dose, as shown in Fig. 3(b) of the hydrogen thermal release dependence. The feature is in conflict with the observed facts at a low dose implantation with techniques such as electron spin resonance and positron annihilation spectroscopy [20,21]. The obtained results show that the 1173 K annealing changes defects into tight hydrogen trapping sites in stead of making them disappear in the case of the highdose implantation. The 1343 K annealing crystallized the Si grains and, therefore, eliminated the dangling bonds. The expected trap sites are the Si/SiO2 interface and the V–H complexes formed in the Si nanocrystals by hydrogen itself. Trapped hydrogen was distributed tracing the TRIM profile of Si at the 1 1017 cm2 Si dose. On the other hand, at the doses of 3 1017 and 6 1017 Si cm2 hydrogen was trapped around the overlapped region of the TRIM vacancy regions of Si and hydrogen. This movement was caused by the enhancement of radiation induced diffusion of Si at high doses. When compared in detail the peak positions of the hydrogen profiles, the position for 1343 K locates a little deeper than that for the 1173 K annealing. The width of the hydrogen profile is narrower for the 1343 K annealing than for 1173 K. These facts are consistent with the expectation that the 1343 K profile reflects the overlap of the Si-segregated layer with the hydrogen-produced vacancy region. The V–H complexes (1.3–1.7 eV) have a low binding energy compared with the Si–H bonding (2.5 eV) and the Si/SiO2 interface (2.56 eV). The
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thermal release for the high-dose implantation at 6 1017 Si cm2 started at a low temperature compared with those for the 1 1017 and 3 1017 cm2 Si doses. That is, the increase in the Si dose increased the average size of the nanocrystals and decreased the contribution of the surface against the volume. That is, the increase in the Si dose decreases the contribution of the trapping at the Si/SiO2 interface compared with the trapping by monovacancies produced in the Si nanocrystals by hydrogen itself.
4. Summary We have studied the hydrogen behavior in the Si-implanted SiO2 sample at several conditions of dose and annealing temperature for the Si implantation. The dominant hydrogen trap sites changed depending on the implantation condition. In the case of the RT annealing the samples contained lots of vacancies and Si dangling bonds induced by the Si implantation, and, therefore, the implanted hydrogen diffused toward the surface through the damage after stopping at the projected range, and was trapped by vacancies and silicon. The contribution of the Si–H bond became important compared with the V–H complex with increasing Si dose. The thermal annealing of the Si-implanted SiO2 sample up to a temperature of 1173 K increased the binding energy of hydrogen irrespective of the Si-implantation dose. The obtained results show that the 1173 K annealing changed defects into tight hydrogen trapping as a Si–H bond in conflict with the result obtained at a low dose implantation. Annealing at 1343 K produced Si nanocrystals and the hydrogen trap site changed from the Si–H bond to the interface of Si nanocrystal/SiO2 matrix. However, at the implantation of Si up to the dose of 6 1017 cm2 the nanocrystals grew up and a large part of hydrogen was trapped as selfinduced V–H complexes formed inside the crystals instead of the trap at interface. As a conclusion, in order to trap the implanted hydrogen on the interface of the crystals, the implantation Si dose should be less than about 3 1017 cm2 .
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Acknowledgements This work was done with a 250-keV Cockcroft– Walton Accelerator, a 30-kV Ion Implanter and a 4-MV Van de Graaff Accelerator at Kyoto University. We thank Prof. A. Itoh, Mr. K. Yoshida and Mr. K. Norizawa for their useful advice and technical support during the experiments. It has been supported in part by a Grant-in-Aid for Scientific Research from JSPS.
References [1] H. Atwater, K.V. Shcheglov, S.S. Wong, K.J. Vahala, R.C. Flagan, M.L. Brongersma, A. Polman, Mater. Res. Soc. Symp. Proc. 316 (1994) 409. [2] T. Shimizu-Iwayama, K. Fujita, S. Nakao, K. Saitoh, T. Fujita, N. Itoh, J. Appl. Phys. 75 (1994) 7779. [3] S. Guha, M.D. Pace, D.N. Dunn, I.L. Singer, Appl. Phys. Lett. 70 (1997) 1207. [4] K.S. Min, K.V. Shcheglov, C.M. Tang, H.A. Atwater, M.L. Brongersma, A. Polman, Appl. Phys. Lett. 69 (1996) 2033. [5] C.W. White, J.D. Budai, S.P. Withrow, J.G. Zhu, E. Sonder, R.A. Zuhr, A. Meldrum, D.M. Hembree Jr., D.O. Henderson, S. Prawer, Nucl. Instr. and Meth. B 141 (1998) 228. [6] S.M. Myers, P.M. Richards, W.R. Wampler, J. Nucl. Mater. 165 (1989) 9, and references cited therein.
[7] S.M. Myers et al., Rev. Mod. Phys. 64 (1992) 559, and references cited therein. [8] J.P. Bugeat, A.C. Chami, E. Ligeon, Phys. Lett. 58A (1976) 127. [9] S.M. Myers, F. Besenbacher, J.K. Nørskov, J. Appl. Phys. 58 (1985) 1841. [10] M. Ogura, N. Nakatani, N. Yamaji, M. Imai, A. Itoh, N. Imanishi, Radiat. Phys. Chem. 49 (1997) 645. [11] M. Ogura, N. Yamaji, M. Imai, A. Itoh, N. Imanishi, Nucl. Instr. and Meth. B 121 (1997) 470. [12] M. Ogura, T. Higuchi, M. Imai, A. Itoh, N. Imanishi, Nucl. Instr. and Meth. B 136–138 (1998) 478. [13] M. Ogura, T. Higuchi, M. Ikeda, A. Itoh, N. Imanishi, in: Proceedings of the 12th International Conference on Ion Implantation Technology, Kyoto, Japan, 1999, p. 606. [14] S.M. Myers, D.M. Follstaedt, H.J. Stein, W.R. Wampler, Phys. Rev. B 47 (1993) 13380. [15] N. Imanishi, M. Ogura, M. Ikeda, R. Mitsusue, A. Itoh, Nucl. Instr. and Meth. B 161–163 (2000) 401. [16] J.F. Ziegler, J.P. Biersack, U. Littmark, The Stopping and Range of Ions in Solids, Pergamon Press, New York, 1985. [17] S. Nagata, S. Yamaguchi, Y. Fujino, Y. Hori, N. Sugiyama, K. Kamada, Nucl. Instr. and Meth. B 6 (1985) 53. [18] W. Hong, Z.G. Qing, Nucl. Instr. and Meth. B 34 (1988) 145. [19] M. Ogura, N. Yamaji, M. Imai, A. Itoh, N. Imanishi, in: Proceedings of International Conference on Accelerator Application in Research and Industry, Denton, 1997, p. 953. [20] M. Fujinami, N.B. Chilton, Appl. Phys. Lett. 62 (1993) 1131. [21] P. Asoka-Kumar, K.G. Lynn, D.O. Welch, J. Appl. Phys. 76 (1994) 4935.
Behavior of hydrogen implanted into Si-implanted SiO2 Mitsuharu Ikeda a, Ryuta Mitsusue a, Masaharu Nakagawa a, Satoshi Kondo a, Makoto Imai a, Nobutsugu Imanishi a,b,* a
Department of Nuclear Engineering, Kyoto University, Yoshida-Honmachi, Sakyo-ku, Kyoto 606-8501, Japan b Quantum Science and Engineering Center, Kyoto University, Uji, Kyoto 611-0011, Japan
Abstract We applied the elastic recoil detection method to the in situ measurement of the hydrogen behavior in Si-implanted SiO2 samples, where annealing in hydrogen environment increases photoluminescence efficiency. Dominant hydrogen trap sites changed depending on implantation conditions. In samples annealed at room temperature, hydrogen seems to be trapped forming vacancy–H (V–H) and Si–H bonds. The thermal annealing of the high-dose Si-implanted SiO2 samples up to a temperature of 1173 K changes defects into tight hydrogen trapping of Si–H bond in conflict with results obtained at a low dose implantation. Annealing at 1343 K grows Si nanocrystals, and hydrogen seems to be trapped at the interface of Si nanocrystal/SiO2 matrix. However, a result of high-dose implantation of Si up to 6 1017 cm2 showed that a large part of hydrogen is trapped as self-induced V–H complexes formed inside the crystals instead of the trap at interface. Ó 2002 Elsevier B.V. All rights reserved. PACS: 61.46.þw; 61.80.)x; 66.30.)h Keywords: Hydrogen-trapping; Thermal behavior; Implantation; Si nanocrystal; Si/SiO2
1. Introduction The formation of Si nanocrystals buried in SiO2 through ion implantation is now one of very attractive topics for the fabrication of silicon-based photo devices [1–5]. It has been reported that annealing the Si-implanted SiO2 sample in hydrogen environment increases its photoluminescence efficiency [5]. That is, hydrogen is expected to passi* Corresponding author. Address: Department of Nuclear Engineering, Kyoto University, Yoshida-Honmachi, Sakyo-ku, Kyoto 606-8501, Japan. Tel./fax: +81-75-7535821. E-mail address: [email protected] (N. Imanishi).
vate dangling bonds on the surface of the nanocrystal. The aim of the present study is to understand the hydrogen behavior in SiO2 with high-density defects produced by the high-dose implantation of Si ions and with locally concentrated Si. Trapping of hydrogen by irradiation damages caused by ion implantation has been a great concern of many groups for several decades [6–9]. It was also pointed out that even a small amount of an additive element drastically affects the hydrogen trapping [10–13]. That is, hydrogen is trapped by vacancies, by dangling bonds of both implanted and matrix elements and at grain boundaries if the implanted elements segregate in the matrix [7,14]. Therefore, we applied the elastic
0168-583X/$ - see front matter Ó 2002 Elsevier B.V. All rights reserved. doi:10.1016/S0168-583X(02)02008-6
M. Ikeda et al. / Nucl. Instr. and Meth. in Phys. Res. B 209 (2003) 154–158
155
recoil detection (ERD) method in order to understand the behavior of hydrogen and search a condition of the hydrogen trapping on the nanocrystal surface for the Si-implanted SiO2 samples. The measurement was done at several conditions of dose and annealing temperature for the Si implantation. The H trap sites were identified and the observed facts are explained well by taking into account the vacancies, the dangling bonds, and the boundaries of grains and nanocrystals formed by the Si implantation.
2. Experimental procedures Experimental procedures were previously described in detail [12,13,15] and are shown briefly. Samples used were 300-nm thick SiO2 layers thermally grown on Si wafers. After appropriate chemical treatments, 120 keV Si ions were implanted into the samples to doses of 1 1017 , 3 1017 and 6 1017 cm2 . After the respective implantations the samples were kept at room temperature (RT), or annealed at 1173 and 1343 K. Irradiation damages produced by the Si implantation were eliminated by keeping the samples at 1173 K. The implanted Si ions coagulated and formed small crystals of nm size by a procedure of 1-h annealing at 1343 K [5]. Hydrogen ions with an energy of 10 keV per atom were then implanted into these samples to a dose of 1 1017 cm2 at RT. Typical depth profiles of implanted silicon and hydrogen were calculated with the TRIM code [16], and are shown in Fig. 1 along with their damage populations. After the hydrogen implantation, the depth profiles of hydrogen were measured by the ERD method using a 2-MeV 4 Heþ ion beam [17,18]. The hydrogen energy spectra were taken with a surface barrier detector set at an angle of 30° using a 4 Heabsorbing film. The spectra were recorded every 10 min during an isochronal temperature-ramp measurement from 300 to 870 K at a rate of 3 K/min. The depth profiles of hydrogen were deduced from the energy spectra using the TRIM simulation code [16]. The amount of hydrogen decreased without varying the shape of profile during the isochronal temperature-ramp measurements.
Fig. 1. Simulated depth profiles of 120 keV Si (the solid line) and 10 keV H (the dashed line) in SiO2 . Distributions of vacancies produced by silicon (the dotted-dash line) and hydrogen (the double-dotted-dash line) implantation are also shown. Respective doses of Si and H ions are both 1 1017 Si cm2 [16].
3. Results and discussion Examples of the depth profile and of the thermal release of hydrogen during the temperatureramp measurement are shown in Figs. 2 and 3, for the three different Si doses of 1 1017 , 3 1017 and 6 1017 cm2 , as a function of the temperature of the sample annealing done before the hydrogen implantation. Hydrogen trapped by the surface formed the peak around 0 nm in depth [10]. The retention of hydrogen was very low in a SiO2 sample not implanted with Si. As shown in Fig. 2, however, a large part of implanted hydrogen was trapped in the Si-implanted samples. According to the observation done by Myers et al., dominant silicon-related trap sites of hydrogen are vacancy–hydrogen (V–H) complexes (with a binding energy of 1.3–1.7 eV), Si–H bonds (2.5 eV) and hydrogen trapping (2.56 eV) on grain boundary [6]. In SiO2 , an O–H bond is another candidate. The samples kept at RT before the hydrogen implantation contained lots of vacancies and Si dangling bonds induced by the Si implantation, and, therefore, the implanted hydrogen diffused toward the surface through the damage after
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Fig. 2. Depth profiles of hydrogen in Si-implanted SiO2 as a function of the sample annealing temperature before the hydrogen implantation. The doses of Si are (a) 1 1017 cm2 , (b) 3 1017 cm2 and (c) 6 1017 cm2 . The solid, dashed and dotted-dash lines denote the data for annealing at RT, 1173 and 1343 K, respectively.
stopping at the projected range, and was trapped by vacancies and silicon [19]. In this case, the hydrogen profile corresponds to the damage region and the implanted silicon layers. When one increased the Si dose up to and higher than 3 1017 cm2 , the profile moved to a shallow region caused by the enhancement of radiation induced diffusion of the high-dose implantation. That is, as measured by the Rutherford backscattering spectroscopy (RBS), the implanted Si moved this side of the projected range of 120 keV Si and trapped in
Fig. 3. Thermal release of hydrogen during temperature-ramp measurement as a function of the sample annealing temperature before the hydrogen implantation. The doses of Si are (a) 1 1017 cm2 , (b) 3 1017 cm2 and (c) 6 1017 cm2 . The solid, dashed and dotted-dash lines denote the data for annealing at RT, 1173 and 1343 K, respectively.
the damage region produced by themselves. The movement of the hydrogen profile is not expected in the case of the O–H bond. Therefore, the contribution of the O–H bond can be safely omitted from the further consideration. In the case of the RT annealing, the increase in the Si dose induced two additional phenomena. One is that, as shown in Fig. 2, the width of the hydrogen depth profile decreased with increasing Si dose, and the other is that, as shown in Fig. 3, the temperature of the hydrogen thermal release increased with increasing dose. The width and the release temperature at high doses are almost the same as those for the 1173 K annealing, in which
M. Ikeda et al. / Nucl. Instr. and Meth. in Phys. Res. B 209 (2003) 154–158
the Si–H bond is the dominant hydrogen trap site. These observations show that for the high-dose implantation, the contribution of the Si–H bond becomes important compared with the V–H complex. The 1173 K annealing eliminated the vacancies caused by the Si implantation, and supersaturated silicon probably segregated and formed grains leaving lots of dangling bonds. In this case hydrogen was trapped forming the Si–H bond in the layer of segregated Si (Fig. 2(b)). The vacancy elimination resulted in the decrease of hydrogen retention factor and the narrow width of the profile. The resultant tight bonding compared with the RT annealing was unambiguously observed irrespective of the Si dose, as shown in Fig. 3(b) of the hydrogen thermal release dependence. The feature is in conflict with the observed facts at a low dose implantation with techniques such as electron spin resonance and positron annihilation spectroscopy [20,21]. The obtained results show that the 1173 K annealing changes defects into tight hydrogen trapping sites in stead of making them disappear in the case of the highdose implantation. The 1343 K annealing crystallized the Si grains and, therefore, eliminated the dangling bonds. The expected trap sites are the Si/SiO2 interface and the V–H complexes formed in the Si nanocrystals by hydrogen itself. Trapped hydrogen was distributed tracing the TRIM profile of Si at the 1 1017 cm2 Si dose. On the other hand, at the doses of 3 1017 and 6 1017 Si cm2 hydrogen was trapped around the overlapped region of the TRIM vacancy regions of Si and hydrogen. This movement was caused by the enhancement of radiation induced diffusion of Si at high doses. When compared in detail the peak positions of the hydrogen profiles, the position for 1343 K locates a little deeper than that for the 1173 K annealing. The width of the hydrogen profile is narrower for the 1343 K annealing than for 1173 K. These facts are consistent with the expectation that the 1343 K profile reflects the overlap of the Si-segregated layer with the hydrogen-produced vacancy region. The V–H complexes (1.3–1.7 eV) have a low binding energy compared with the Si–H bonding (2.5 eV) and the Si/SiO2 interface (2.56 eV). The
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thermal release for the high-dose implantation at 6 1017 Si cm2 started at a low temperature compared with those for the 1 1017 and 3 1017 cm2 Si doses. That is, the increase in the Si dose increased the average size of the nanocrystals and decreased the contribution of the surface against the volume. That is, the increase in the Si dose decreases the contribution of the trapping at the Si/SiO2 interface compared with the trapping by monovacancies produced in the Si nanocrystals by hydrogen itself.
4. Summary We have studied the hydrogen behavior in the Si-implanted SiO2 sample at several conditions of dose and annealing temperature for the Si implantation. The dominant hydrogen trap sites changed depending on the implantation condition. In the case of the RT annealing the samples contained lots of vacancies and Si dangling bonds induced by the Si implantation, and, therefore, the implanted hydrogen diffused toward the surface through the damage after stopping at the projected range, and was trapped by vacancies and silicon. The contribution of the Si–H bond became important compared with the V–H complex with increasing Si dose. The thermal annealing of the Si-implanted SiO2 sample up to a temperature of 1173 K increased the binding energy of hydrogen irrespective of the Si-implantation dose. The obtained results show that the 1173 K annealing changed defects into tight hydrogen trapping as a Si–H bond in conflict with the result obtained at a low dose implantation. Annealing at 1343 K produced Si nanocrystals and the hydrogen trap site changed from the Si–H bond to the interface of Si nanocrystal/SiO2 matrix. However, at the implantation of Si up to the dose of 6 1017 cm2 the nanocrystals grew up and a large part of hydrogen was trapped as selfinduced V–H complexes formed inside the crystals instead of the trap at interface. As a conclusion, in order to trap the implanted hydrogen on the interface of the crystals, the implantation Si dose should be less than about 3 1017 cm2 .
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M. Ikeda et al. / Nucl. Instr. and Meth. in Phys. Res. B 209 (2003) 154–158
Acknowledgements This work was done with a 250-keV Cockcroft– Walton Accelerator, a 30-kV Ion Implanter and a 4-MV Van de Graaff Accelerator at Kyoto University. We thank Prof. A. Itoh, Mr. K. Yoshida and Mr. K. Norizawa for their useful advice and technical support during the experiments. It has been supported in part by a Grant-in-Aid for Scientific Research from JSPS.
References [1] H. Atwater, K.V. Shcheglov, S.S. Wong, K.J. Vahala, R.C. Flagan, M.L. Brongersma, A. Polman, Mater. Res. Soc. Symp. Proc. 316 (1994) 409. [2] T. Shimizu-Iwayama, K. Fujita, S. Nakao, K. Saitoh, T. Fujita, N. Itoh, J. Appl. Phys. 75 (1994) 7779. [3] S. Guha, M.D. Pace, D.N. Dunn, I.L. Singer, Appl. Phys. Lett. 70 (1997) 1207. [4] K.S. Min, K.V. Shcheglov, C.M. Tang, H.A. Atwater, M.L. Brongersma, A. Polman, Appl. Phys. Lett. 69 (1996) 2033. [5] C.W. White, J.D. Budai, S.P. Withrow, J.G. Zhu, E. Sonder, R.A. Zuhr, A. Meldrum, D.M. Hembree Jr., D.O. Henderson, S. Prawer, Nucl. Instr. and Meth. B 141 (1998) 228. [6] S.M. Myers, P.M. Richards, W.R. Wampler, J. Nucl. Mater. 165 (1989) 9, and references cited therein.
[7] S.M. Myers et al., Rev. Mod. Phys. 64 (1992) 559, and references cited therein. [8] J.P. Bugeat, A.C. Chami, E. Ligeon, Phys. Lett. 58A (1976) 127. [9] S.M. Myers, F. Besenbacher, J.K. Nørskov, J. Appl. Phys. 58 (1985) 1841. [10] M. Ogura, N. Nakatani, N. Yamaji, M. Imai, A. Itoh, N. Imanishi, Radiat. Phys. Chem. 49 (1997) 645. [11] M. Ogura, N. Yamaji, M. Imai, A. Itoh, N. Imanishi, Nucl. Instr. and Meth. B 121 (1997) 470. [12] M. Ogura, T. Higuchi, M. Imai, A. Itoh, N. Imanishi, Nucl. Instr. and Meth. B 136–138 (1998) 478. [13] M. Ogura, T. Higuchi, M. Ikeda, A. Itoh, N. Imanishi, in: Proceedings of the 12th International Conference on Ion Implantation Technology, Kyoto, Japan, 1999, p. 606. [14] S.M. Myers, D.M. Follstaedt, H.J. Stein, W.R. Wampler, Phys. Rev. B 47 (1993) 13380. [15] N. Imanishi, M. Ogura, M. Ikeda, R. Mitsusue, A. Itoh, Nucl. Instr. and Meth. B 161–163 (2000) 401. [16] J.F. Ziegler, J.P. Biersack, U. Littmark, The Stopping and Range of Ions in Solids, Pergamon Press, New York, 1985. [17] S. Nagata, S. Yamaguchi, Y. Fujino, Y. Hori, N. Sugiyama, K. Kamada, Nucl. Instr. and Meth. B 6 (1985) 53. [18] W. Hong, Z.G. Qing, Nucl. Instr. and Meth. B 34 (1988) 145. [19] M. Ogura, N. Yamaji, M. Imai, A. Itoh, N. Imanishi, in: Proceedings of International Conference on Accelerator Application in Research and Industry, Denton, 1997, p. 953. [20] M. Fujinami, N.B. Chilton, Appl. Phys. Lett. 62 (1993) 1131. [21] P. Asoka-Kumar, K.G. Lynn, D.O. Welch, J. Appl. Phys. 76 (1994) 4935.