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Hydrogen gettering at buried defect layers in ion-implanted silicon by plasma hydrogenation and annealing
NIM B Beam Interactions with Materials & Atoms
Nuclear Instruments and Methods in Physics Research B 253 (2006) 126–129 www.elsevier.com/locate/nimb
Hydrogen gettering at buried defect layers in ion-implanted silicon by plasma hydrogenation and annealing A.G. Ulyashin a
a,*
, J.S. Christensen a, B.G. Svensson a, R. Ko¨gler b, W. Skorupa
b
University of Oslo, Center for Materials Science and Nanotechnology, Sem Saelands vei 24, P.O. Box 1048 Blindern, NO-0316 Oslo, Norway b Institut fu¨r Ionenstrahlphysik und Materialforschung, Forschungszentrum Rossendorfe, PF 510119, D-01314 Dresden, Germany Available online 7 November 2006
Abstract In this study gettering of atomic hydrogen in-diffused from a plasma hydrogenated surface into self ion implanted and annealed Si is investigated. Cz Si p-type samples were implanted with 3.5 MeV Si+ ions to a fluence 5 · 1015 cm 2 and then annealed at 900 C. The hydrogenation of the samples was performed by exposure to the direct RF hydrogen plasma in a plasma enhanced chemical vapour deposition (PECVD) reactor. A remote deuterium plasma treatment was used as well. Secondary ion mass spectrometry (SIMS) was employed for analysis of the hydrogen/deuterium distributions. It is demonstrated for the first time that accumulation of diffused hydrogen occurs both at the projected range of the silicon ions, Rp, and at Rp/2. It is shown that hydrogen accumulation by vacancy-type defects at Rp/2 is as efficient as for trapping by dislocations at Rp. 2006 Elsevier B.V. All rights reserved. PACS: 61.72.Tt; 61.72.Yx Keywords: Silicon; Hydrogen; Deuterium; Gettering; SIMS
1. Introduction It is well established recently that a strong impurity gettering effect appears in Si after high-energy Si implantation and subsequent annealing [1–3]. In particular, this effect has been observed for the diffusing Cu impurities, which are trapped in two zones: (i) at the projected range of the silicon ions (Rp) and in a region at about Rp/2 [1–3]. It is necessary to note that the origin of the defects at Rp/2 has been a subject of intensive investigations and discussion during last years and it has been shown that implantation induces an excess of vacancies in this region, which getter impurities (Cu for instance), whereas at the Rp region an excess of interstitials occurs. Thus, Cu atoms
*
Corresponding author. Tel.: +47 22852828; fax: +47 22852860. E-mail address: [email protected] (A.G. Ulyashin).
0168-583X/$ - see front matter 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2006.10.048
being intentionally introduced in ion-implanted Si decorate the implantation damage, which remain after post-implantation annealing [3]. A very important issue is that the Cu contamination process and the Cu distribution are often performed by ion implantation and subsequent annealing at temperatures around 700 C [1–3] for few minutes. It is evident that such treatments may modify the vacancy/ interstitial defect structure in addition to previous treatments and the final Cu decoration of the defect regions may reflect this modification especially if the previous thermal treatment was performed at relatively low temperatures. Thus, a lower temperature decoration process of ion induced damages would be interesting to study in order to minimize partial defect annealing. It is necessary to note with this regard that accumulation of hydrogen by defect layers is a well known phenomenon [4–8], which can be used to decorate defects formed by ion implantation. Decoration of ion-induced defects by hydrogen has the advantage that the decoration process can be realized at
A.G. Ulyashin et al. / Nucl. Instr. and Meth. in Phys. Res. B 253 (2006) 126–129
low temperatures if atomic hydrogen is used (from a plasma, for instance), since the atomic hydrogen exhibits a high mobility in silicon even at low temperatures [9]. In this study it is shown for the first time that, corresponding to Cu gettering, atomic hydrogen can be in-diffused into self ion implanted and annealed Si from a plasma hydrogenated surface also at low temperatures such as 260 C. Moreover, the initial stage of hydrogen accumulation at the buried defect layers and the stability of such accumulation at temperatures up to 500 C are demonstrated.
127
2. Experimental Cz Si n-type samples were implanted with 3.5 MeV Si+ ions to a fluence 5 · 1015 cm 2 and then annealed at 900 C for 30 s. The hydrogenation of the samples was performed by exposure to the direct RF hydrogen plasma in a plasma enhanced chemical vapour deposition (PECVD) reactor. The plasma frequency/power was 110 MHz/50 W, with a hydrogen flux of 200 sccm. During the plasma treatment the substrate temperature was about 260 C. The post-hydrogenation annealing was carried out
Fig. 1. AFM image of ion implanted and then 900 C for 30 s annealed Si sample, hydrogenated at: (a) 260 C for 2 h by a direct plasma and (b) 260 C for 2 h by a remote plasma.
A.G. Ulyashin et al. / Nucl. Instr. and Meth. in Phys. Res. B 253 (2006) 126–129
3. Results and discussion Fig. 1(a) shows the surface morphology (3D image) of the Si+ implanted, then annealed and hydrogenated (260 C) Si sample. The morphology of the Si surface layer changes dramatically after the hydrogenation and initially flat surface of the polished Si sample becomes textured Rq = 8.90 nm, Ra = 7.1 nm, hmax = 63.40 nm,. This implies that exposure by a direct hydrogen plasma creates a heavily damaged layer near the surface. In case of a remote plasma treatment the Si surface (Fig. 1(b)) remains as flat as for the initial polished un-implanted wafer (Rq = 0.39 nm, Ra = 0.32 nm, hmax = 3.15 nm), which shows that the remote plasma hydrogenation is a less destructive process compared to the direct plasma treatment. Transmission electron microscopy (TEM) confirmed a similar heavily damaged sub-surface layer after direct plasma hydrogenation and different structural defects such as platelets, dislocation loops and voids were revealed [11]. In other words, the direct plasma hydrogenation not only gives rise to a high concentration of hydrogen but also leads to a texturing of the Si surface and introduces structural defects in the sub-surface area. The latter process can influence the hydrogen distribution in heavily hydroge-
10
Concentration H/cm3
in the temperature interval 300–500 C for 20 min in flowing nitrogen. For comparison a deuterium plasma treatment was also applied using a remote plasma OXFORD Plasmalab microwave system. In this case deuterium plasma at temperature 260 C for 2 h with a molecular deuterium flux of 200 sccm was used. Secondary ion mass spectrometry (SIMS) was used for analysis of the hydrogen/deuterium distributions (CAMECA ims 7f instrument) in negative secondary ion mode with a 15 keV Cs+ primary beam. The raw SIMS profiles are given as sputter time versus secondary ion intensity. The sputter time is related to depth and the conversion factor is determined by measuring the SIMS craters with a Dektak 8 surface stylus profilometer assuming a linear dependence. The concentration calibrations for hydrogen and deuterium have been done using 5 · 1015 cm 2 150 keV H+ and 2.22 · 1014 cm 2 100 keV D+ ion implanted Si reference samples. The surface morphology of the samples was analyzed by the atomic force microscopy (AFM) method using a Digital Instrument’s Nanoscope Dim 3100 microscope. The following characteristic parameters for the analysis of the AFM measurements were used: (i) the root mean square (RMS) roughness (Rq), which gives the standard deviation within a given area; (ii) the Mean Roughness (Ra), which represents the arithmetic average of the deviations from the centre plane; (iii) the difference in height between the highest and lowest points on the surface relative to the mean plane (hmax) [10]. The AFM measurements were performed in tapping mode using commercial silicon tips MikroMasch NSC35/AlBS with a typical tip curvature radius less than 10 nm.
10 10 10 10 10
22
21
non implanted hydrogenated Si 20
19
18
17
ion implanted hydrogenated Si
0
1
2
3
4
5
Depth, μm
Fig. 2. SIMS profiles of hydrogen in hydrogenated ion implanted and hydrogenated non-implanted (reference) Si samples.
nated Si material, since during the etching/texturing of the Si surface an injection of point defects into the subsurface region may occur. Fig. 2 shows the SIMS profile of hydrogen after self-ion implantation, annealing and hydrogenation at 260 C of a n-type Si sample. The hydrogen distribution for a nonimplanted n-type sample is shown for comparison. Fig. 2 demonstrate trapping of hydrogen in two zones: (i) at Rp and (ii) in a region at about Rp/2, similar to Cu decoration in these regions [1,2]. In addition, a strong hydrogen trapping occurs in the sub-surface region too, presumably because of the structural defects formed during the direct plasma treatments [11]. Interestingly, the hydrogen accumulation at Rp/2 is even more pronounced than at Rp. This shows that in general both regions, Rp/2 and Rp, have a comparable capacity to getter the hydrogen, which is diffusing from the surface towards the bulk. One may assume that the hydrogen is trapped preferentially by the gettering centres at Rp/2, (and after saturation of these gettering centres hydrogen is trapped deeper at the dislocations in the Rp region). Indeed, such a behavior can be seen in Fig. 3, which shows a deuterium accumulation in the Rp/2 region after remote deuterium plasma treatment. Since the remote plasma is much softer the accumulation
10 Concentration D/cm3
128
10 10 10 10 10
20
19
18
17
16
15
0
1
2 Depth, μm
3
4
Fig. 3. SIMS profile of deuterium in ion implanted Si sample annealed at 900 C for 30 s and then treated by deuterium plasma at 260 C for 2 h.
A.G. Ulyashin et al. / Nucl. Instr. and Meth. in Phys. Res. B 253 (2006) 126–129
Concentration H/cm3
10 10
region around Rp, i.e. more stable hydrogen-defect complexes are found at Rp/2.
21
20
4. Conclusions o
300 C
10 10
19
o
400 C
Our main results can be summarized as follows:
o
450 C 18
o
10
129
500 C
17
0
1
2 3 Depth, μm
4
5
Fig. 4. SIMS profiles of hydrogen in hydrogenated ion implanted Si upon annealing at different temperatures for 20 min.
of deuterium in the sub-surface region takes not place. The deuterium concentration in the Rp/2 region in this case is much lower than that for hydrogen in the case of the direct plasma hydrogenation (see Figs. 2 and 3). All in-diffused deuterium is accumulated inside the Rp/2 region. Thus, this region, where the pre-deposited defects are nanocavities, can be regarded as the preferential gettering site for deuterium/hydrogen penetrating into the bulk of the sample. Hence, it is basically possible to decorate the Rp/2 region by deuterium separately from the Rp region at low temperatures. This effect can lead to blistering in Rp/2 region [6], if concentration of the accumulated hydrogen/deuterium is high enough. It should be noted that deuterium is regarded as an element which exhibits a behavior identical to hydrogen from chemical point of view. Therefore D can be used instead of H to clarify peculiarities of the defect distribution at low concentrations of this element, since SIMS has better sensitivity (about 2 order magnitude) for D than for H. In our case it was difficult to demonstrate that H can be accumulated only at Rp/2, since only quite high concentrations of hydrogen are detectable, at which H can already penetrate to Rp. It has to be noted that all conclusions, which are made regarding the behavior of D in ion implanted Si are valid also for hydrogen. Fig. 4 shows the evolution of the hydrogen concentration upon heat treatments at different temperatures for ion-implanted/annealed samples subjected to direct plasma hydrogenation. The hydrogen profiles are rather stable up to about 400 C, while at 450 C the total hydrogen concentration starts to decrease. Interestingly, the decrease has different rates for the different regions and is most pronounced in the region around Rp. This suggests that the vacancy-rich region around Rp/2 preserves hydrogen more effectively upon heat treatments than the interstitial-rich
• For the first time it is demonstrated that accumulation of hydrogen diffused from a plasma hydrogenated surface, occurs at both Rp and at Rp/2 in self-ion implanted and annealed silicon samples. • It is shown that hydrogen accumulation at Rp/2 is at least as efficient as at Rp for the investigated regimes of ion implantation and post-implantation/hydrogenation treatments. • It is demonstrated that at low hydrogen/deuterium concentrations exclusively the vacancy-related defects at Rp/2 trap the hydrogen/deuterium and gettering at Rp proceeds only for higher concentrations. • The vacancy-rich region around Rp/2 preserves hydrogen more effectively upon heat treatments than the interstitial-rich region around Rp.
Acknowledgement Financial support by the Norwegian Research Council (Nanomat program and Strategic University Project on ‘‘Advanced sensors’’) is gratefully acknowledged. References [1] R. Krause-Rehberg, F. Borner, F. Redmann, J. Gebauer, R. Ko¨gler, R. Kliemann, W. Skorupa, W. Egger, G. Kogel, W. Triftshauser, Physica B 308–310 (2001) 442. [2] R. Ko¨gler, A. Peeva, J. Ky, W. Skorupa, H. Hutter, Nucl. Instr. and Meth. B 186 (2002) 298. [3] R. Ko¨gler, A. Peeva, A. Lebedev, M. Posselt, W. Skorupa, G. Ozelt, H. Hutter, M. Behar, J. Appl. Phys. 94 (2003) 3834. [4] T. Hochbauer, A. Misra, N. Nastasi, J.W. Mayer, J. Appl. Phys. 92 (2002) 2335. [5] P. Chen, P.K. Chu, T. Ho¨rchbauer, J.-K. Lee, M. Nastasi, D. Buca, S. Manti, R. Loo, M. Caymax, T. Alford, J.W. Mayer, N.D. Theodore, M. Cai, B. Schmidt, S.S. Lau, Appl. Phys. Lett. 86 (2005) 031904. [6] A.Y. Usenko, A.G. Ulyashin, Jpn. J. Appl. Phys. 41 (2002) 5021. [7] R. Job, A.G. Ulyashin, W.R. Fahrner, A.I. Ivanov, L. Palmetshofer, Appl. Phys. A 72 (2001) 325. [8] A.G. Ulyashin, A.I. Ivanov, R. Job, W.R. Fahrner, F.F. Komarov, A.V. Frantskevich, Mater. Sci. Eng. B 73 (2000) 64. [9] S.J. Pearton, J.W. Corbett, M. Stavola, Hydrogen in Crystalline Semiconductors, Springer-Verlag, Heidelberg, 1992, p. 220. [10] NanoScope Command Reference Manual, DI/Veeco Metrology Group Inc., 2001. [11] A. Ulyashin, R. Job, W. Fahrner, O. Richard, H. Bender, C. Claeys, E. Simoen, D. Grambole, J. Phys.: Condens. Mat. 14 (2002) 13037.
Nuclear Instruments and Methods in Physics Research B 253 (2006) 126–129 www.elsevier.com/locate/nimb
Hydrogen gettering at buried defect layers in ion-implanted silicon by plasma hydrogenation and annealing A.G. Ulyashin a
a,*
, J.S. Christensen a, B.G. Svensson a, R. Ko¨gler b, W. Skorupa
b
University of Oslo, Center for Materials Science and Nanotechnology, Sem Saelands vei 24, P.O. Box 1048 Blindern, NO-0316 Oslo, Norway b Institut fu¨r Ionenstrahlphysik und Materialforschung, Forschungszentrum Rossendorfe, PF 510119, D-01314 Dresden, Germany Available online 7 November 2006
Abstract In this study gettering of atomic hydrogen in-diffused from a plasma hydrogenated surface into self ion implanted and annealed Si is investigated. Cz Si p-type samples were implanted with 3.5 MeV Si+ ions to a fluence 5 · 1015 cm 2 and then annealed at 900 C. The hydrogenation of the samples was performed by exposure to the direct RF hydrogen plasma in a plasma enhanced chemical vapour deposition (PECVD) reactor. A remote deuterium plasma treatment was used as well. Secondary ion mass spectrometry (SIMS) was employed for analysis of the hydrogen/deuterium distributions. It is demonstrated for the first time that accumulation of diffused hydrogen occurs both at the projected range of the silicon ions, Rp, and at Rp/2. It is shown that hydrogen accumulation by vacancy-type defects at Rp/2 is as efficient as for trapping by dislocations at Rp. 2006 Elsevier B.V. All rights reserved. PACS: 61.72.Tt; 61.72.Yx Keywords: Silicon; Hydrogen; Deuterium; Gettering; SIMS
1. Introduction It is well established recently that a strong impurity gettering effect appears in Si after high-energy Si implantation and subsequent annealing [1–3]. In particular, this effect has been observed for the diffusing Cu impurities, which are trapped in two zones: (i) at the projected range of the silicon ions (Rp) and in a region at about Rp/2 [1–3]. It is necessary to note that the origin of the defects at Rp/2 has been a subject of intensive investigations and discussion during last years and it has been shown that implantation induces an excess of vacancies in this region, which getter impurities (Cu for instance), whereas at the Rp region an excess of interstitials occurs. Thus, Cu atoms
*
Corresponding author. Tel.: +47 22852828; fax: +47 22852860. E-mail address: [email protected] (A.G. Ulyashin).
0168-583X/$ - see front matter 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2006.10.048
being intentionally introduced in ion-implanted Si decorate the implantation damage, which remain after post-implantation annealing [3]. A very important issue is that the Cu contamination process and the Cu distribution are often performed by ion implantation and subsequent annealing at temperatures around 700 C [1–3] for few minutes. It is evident that such treatments may modify the vacancy/ interstitial defect structure in addition to previous treatments and the final Cu decoration of the defect regions may reflect this modification especially if the previous thermal treatment was performed at relatively low temperatures. Thus, a lower temperature decoration process of ion induced damages would be interesting to study in order to minimize partial defect annealing. It is necessary to note with this regard that accumulation of hydrogen by defect layers is a well known phenomenon [4–8], which can be used to decorate defects formed by ion implantation. Decoration of ion-induced defects by hydrogen has the advantage that the decoration process can be realized at
A.G. Ulyashin et al. / Nucl. Instr. and Meth. in Phys. Res. B 253 (2006) 126–129
low temperatures if atomic hydrogen is used (from a plasma, for instance), since the atomic hydrogen exhibits a high mobility in silicon even at low temperatures [9]. In this study it is shown for the first time that, corresponding to Cu gettering, atomic hydrogen can be in-diffused into self ion implanted and annealed Si from a plasma hydrogenated surface also at low temperatures such as 260 C. Moreover, the initial stage of hydrogen accumulation at the buried defect layers and the stability of such accumulation at temperatures up to 500 C are demonstrated.
127
2. Experimental Cz Si n-type samples were implanted with 3.5 MeV Si+ ions to a fluence 5 · 1015 cm 2 and then annealed at 900 C for 30 s. The hydrogenation of the samples was performed by exposure to the direct RF hydrogen plasma in a plasma enhanced chemical vapour deposition (PECVD) reactor. The plasma frequency/power was 110 MHz/50 W, with a hydrogen flux of 200 sccm. During the plasma treatment the substrate temperature was about 260 C. The post-hydrogenation annealing was carried out
Fig. 1. AFM image of ion implanted and then 900 C for 30 s annealed Si sample, hydrogenated at: (a) 260 C for 2 h by a direct plasma and (b) 260 C for 2 h by a remote plasma.
A.G. Ulyashin et al. / Nucl. Instr. and Meth. in Phys. Res. B 253 (2006) 126–129
3. Results and discussion Fig. 1(a) shows the surface morphology (3D image) of the Si+ implanted, then annealed and hydrogenated (260 C) Si sample. The morphology of the Si surface layer changes dramatically after the hydrogenation and initially flat surface of the polished Si sample becomes textured Rq = 8.90 nm, Ra = 7.1 nm, hmax = 63.40 nm,. This implies that exposure by a direct hydrogen plasma creates a heavily damaged layer near the surface. In case of a remote plasma treatment the Si surface (Fig. 1(b)) remains as flat as for the initial polished un-implanted wafer (Rq = 0.39 nm, Ra = 0.32 nm, hmax = 3.15 nm), which shows that the remote plasma hydrogenation is a less destructive process compared to the direct plasma treatment. Transmission electron microscopy (TEM) confirmed a similar heavily damaged sub-surface layer after direct plasma hydrogenation and different structural defects such as platelets, dislocation loops and voids were revealed [11]. In other words, the direct plasma hydrogenation not only gives rise to a high concentration of hydrogen but also leads to a texturing of the Si surface and introduces structural defects in the sub-surface area. The latter process can influence the hydrogen distribution in heavily hydroge-
10
Concentration H/cm3
in the temperature interval 300–500 C for 20 min in flowing nitrogen. For comparison a deuterium plasma treatment was also applied using a remote plasma OXFORD Plasmalab microwave system. In this case deuterium plasma at temperature 260 C for 2 h with a molecular deuterium flux of 200 sccm was used. Secondary ion mass spectrometry (SIMS) was used for analysis of the hydrogen/deuterium distributions (CAMECA ims 7f instrument) in negative secondary ion mode with a 15 keV Cs+ primary beam. The raw SIMS profiles are given as sputter time versus secondary ion intensity. The sputter time is related to depth and the conversion factor is determined by measuring the SIMS craters with a Dektak 8 surface stylus profilometer assuming a linear dependence. The concentration calibrations for hydrogen and deuterium have been done using 5 · 1015 cm 2 150 keV H+ and 2.22 · 1014 cm 2 100 keV D+ ion implanted Si reference samples. The surface morphology of the samples was analyzed by the atomic force microscopy (AFM) method using a Digital Instrument’s Nanoscope Dim 3100 microscope. The following characteristic parameters for the analysis of the AFM measurements were used: (i) the root mean square (RMS) roughness (Rq), which gives the standard deviation within a given area; (ii) the Mean Roughness (Ra), which represents the arithmetic average of the deviations from the centre plane; (iii) the difference in height between the highest and lowest points on the surface relative to the mean plane (hmax) [10]. The AFM measurements were performed in tapping mode using commercial silicon tips MikroMasch NSC35/AlBS with a typical tip curvature radius less than 10 nm.
10 10 10 10 10
22
21
non implanted hydrogenated Si 20
19
18
17
ion implanted hydrogenated Si
0
1
2
3
4
5
Depth, μm
Fig. 2. SIMS profiles of hydrogen in hydrogenated ion implanted and hydrogenated non-implanted (reference) Si samples.
nated Si material, since during the etching/texturing of the Si surface an injection of point defects into the subsurface region may occur. Fig. 2 shows the SIMS profile of hydrogen after self-ion implantation, annealing and hydrogenation at 260 C of a n-type Si sample. The hydrogen distribution for a nonimplanted n-type sample is shown for comparison. Fig. 2 demonstrate trapping of hydrogen in two zones: (i) at Rp and (ii) in a region at about Rp/2, similar to Cu decoration in these regions [1,2]. In addition, a strong hydrogen trapping occurs in the sub-surface region too, presumably because of the structural defects formed during the direct plasma treatments [11]. Interestingly, the hydrogen accumulation at Rp/2 is even more pronounced than at Rp. This shows that in general both regions, Rp/2 and Rp, have a comparable capacity to getter the hydrogen, which is diffusing from the surface towards the bulk. One may assume that the hydrogen is trapped preferentially by the gettering centres at Rp/2, (and after saturation of these gettering centres hydrogen is trapped deeper at the dislocations in the Rp region). Indeed, such a behavior can be seen in Fig. 3, which shows a deuterium accumulation in the Rp/2 region after remote deuterium plasma treatment. Since the remote plasma is much softer the accumulation
10 Concentration D/cm3
128
10 10 10 10 10
20
19
18
17
16
15
0
1
2 Depth, μm
3
4
Fig. 3. SIMS profile of deuterium in ion implanted Si sample annealed at 900 C for 30 s and then treated by deuterium plasma at 260 C for 2 h.
A.G. Ulyashin et al. / Nucl. Instr. and Meth. in Phys. Res. B 253 (2006) 126–129
Concentration H/cm3
10 10
region around Rp, i.e. more stable hydrogen-defect complexes are found at Rp/2.
21
20
4. Conclusions o
300 C
10 10
19
o
400 C
Our main results can be summarized as follows:
o
450 C 18
o
10
129
500 C
17
0
1
2 3 Depth, μm
4
5
Fig. 4. SIMS profiles of hydrogen in hydrogenated ion implanted Si upon annealing at different temperatures for 20 min.
of deuterium in the sub-surface region takes not place. The deuterium concentration in the Rp/2 region in this case is much lower than that for hydrogen in the case of the direct plasma hydrogenation (see Figs. 2 and 3). All in-diffused deuterium is accumulated inside the Rp/2 region. Thus, this region, where the pre-deposited defects are nanocavities, can be regarded as the preferential gettering site for deuterium/hydrogen penetrating into the bulk of the sample. Hence, it is basically possible to decorate the Rp/2 region by deuterium separately from the Rp region at low temperatures. This effect can lead to blistering in Rp/2 region [6], if concentration of the accumulated hydrogen/deuterium is high enough. It should be noted that deuterium is regarded as an element which exhibits a behavior identical to hydrogen from chemical point of view. Therefore D can be used instead of H to clarify peculiarities of the defect distribution at low concentrations of this element, since SIMS has better sensitivity (about 2 order magnitude) for D than for H. In our case it was difficult to demonstrate that H can be accumulated only at Rp/2, since only quite high concentrations of hydrogen are detectable, at which H can already penetrate to Rp. It has to be noted that all conclusions, which are made regarding the behavior of D in ion implanted Si are valid also for hydrogen. Fig. 4 shows the evolution of the hydrogen concentration upon heat treatments at different temperatures for ion-implanted/annealed samples subjected to direct plasma hydrogenation. The hydrogen profiles are rather stable up to about 400 C, while at 450 C the total hydrogen concentration starts to decrease. Interestingly, the decrease has different rates for the different regions and is most pronounced in the region around Rp. This suggests that the vacancy-rich region around Rp/2 preserves hydrogen more effectively upon heat treatments than the interstitial-rich
• For the first time it is demonstrated that accumulation of hydrogen diffused from a plasma hydrogenated surface, occurs at both Rp and at Rp/2 in self-ion implanted and annealed silicon samples. • It is shown that hydrogen accumulation at Rp/2 is at least as efficient as at Rp for the investigated regimes of ion implantation and post-implantation/hydrogenation treatments. • It is demonstrated that at low hydrogen/deuterium concentrations exclusively the vacancy-related defects at Rp/2 trap the hydrogen/deuterium and gettering at Rp proceeds only for higher concentrations. • The vacancy-rich region around Rp/2 preserves hydrogen more effectively upon heat treatments than the interstitial-rich region around Rp.
Acknowledgement Financial support by the Norwegian Research Council (Nanomat program and Strategic University Project on ‘‘Advanced sensors’’) is gratefully acknowledged. References [1] R. Krause-Rehberg, F. Borner, F. Redmann, J. Gebauer, R. Ko¨gler, R. Kliemann, W. Skorupa, W. Egger, G. Kogel, W. Triftshauser, Physica B 308–310 (2001) 442. [2] R. Ko¨gler, A. Peeva, J. Ky, W. Skorupa, H. Hutter, Nucl. Instr. and Meth. B 186 (2002) 298. [3] R. Ko¨gler, A. Peeva, A. Lebedev, M. Posselt, W. Skorupa, G. Ozelt, H. Hutter, M. Behar, J. Appl. Phys. 94 (2003) 3834. [4] T. Hochbauer, A. Misra, N. Nastasi, J.W. Mayer, J. Appl. Phys. 92 (2002) 2335. [5] P. Chen, P.K. Chu, T. Ho¨rchbauer, J.-K. Lee, M. Nastasi, D. Buca, S. Manti, R. Loo, M. Caymax, T. Alford, J.W. Mayer, N.D. Theodore, M. Cai, B. Schmidt, S.S. Lau, Appl. Phys. Lett. 86 (2005) 031904. [6] A.Y. Usenko, A.G. Ulyashin, Jpn. J. Appl. Phys. 41 (2002) 5021. [7] R. Job, A.G. Ulyashin, W.R. Fahrner, A.I. Ivanov, L. Palmetshofer, Appl. Phys. A 72 (2001) 325. [8] A.G. Ulyashin, A.I. Ivanov, R. Job, W.R. Fahrner, F.F. Komarov, A.V. Frantskevich, Mater. Sci. Eng. B 73 (2000) 64. [9] S.J. Pearton, J.W. Corbett, M. Stavola, Hydrogen in Crystalline Semiconductors, Springer-Verlag, Heidelberg, 1992, p. 220. [10] NanoScope Command Reference Manual, DI/Veeco Metrology Group Inc., 2001. [11] A. Ulyashin, R. Job, W. Fahrner, O. Richard, H. Bender, C. Claeys, E. Simoen, D. Grambole, J. Phys.: Condens. Mat. 14 (2002) 13037.