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Synchrotron topography of high temperature–pressure treated silicon implanted with helium
Nuclear Instruments and Methods in Physics Research B 200 (2003) 358–362 www.elsevier.com/locate/nimb
Synchrotron topography of high temperature–pressure treated silicon implanted with helium a,*
, W. Wierzchowski b, K. Wieteska c, L. Bryja d, W. Graeff
A. Misiuk
e
a Institute of Electron Technology, Al. Lotnikow 32/46, 02-668 Warsaw, Poland Institute of Electronic Materials Technology, Wolczynska 133, 01-919 Warsaw, Poland c Institute of Atomic Energy, 05-400 Otwock-Swierk, Poland d Wroclaw University of Technology, Wyb. Wyspianskiego 27, 50-370 Wroclaw, Poland e HASYLAB at DESY, Notkestrasse 85, D-22603 Hamburg, Germany
b
Abstract Silicon implanted with Heþ at 150 keV to a dose 5 1016 cm2 (Si:He) and treated at high temperature (up to 1270 K) and pressure (up to 1.2 GPa) was investigated using synchrotron X-ray topography, rocking curve and photoluminescence measurements. Rocking curves of as-implanted Si:He exhibit interference maxima related to strain resulting from the presence of He. Annealing at 720 K under 105 Pa for 1 h reduces the strain by about 1.5 while the treatment at 720 K–1.2 GPa affects it to a less degree. The pressure-moderated decrease of strain was observed also for the treatment at 870 K but not at 1270 K. The HP induced effects depend on retarded He diffusion and creation of specific defects at HP. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 61.10.)i; 62.50.þp; 66.30.)h; 71.20.Mg Keywords: Helium implanted Si; High temperature-pressure; Strain; Synchrotron
1. Introduction Helium implanted silicon (Si:He) has become a topic of remarkable interest, mostly because the bubbles and cavities created in Si:He during annealing are active in respect of gettering of metallic impurities [1]. Implanted helium atoms are also known to assist in the important effect of silicon surface splitting in Si implanted with hydrogen or
*
Corresponding author. Tel.: +48-22-548-7792; fax: +48-22847-0631. E-mail address: [email protected] (A. Misiuk).
hydrogen and helium, known as the smart-cut process [2]. During annealing at 105 Pa (atmospheric pressure), the trapped He atoms diffuse and segregate near the implantation peak region creating helium filled bubbles and microcavities. More prolonged annealing can result in complete outdiffusion of He. Enhanced hydrostatic pressure of ambient atmosphere at annealing (HT–HP treatment) of Si:He results in decreased dimension of postimplantation defects, retardation of He outdiffusion and strongly stimulated creation of thermal donors [3] as well as in gettering of oxygen in the
0168-583X/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 0 2 ) 0 1 7 0 1 - 9
A. Misiuk et al. / Nucl. Instr. and Meth. in Phys. Res. B 200 (2003) 358–362
case of He implantation in oxygen containing Czochralski silicon [4]. In the present work we report on the HT–HP treatment effect on Si:He. In order to study this effect we performed a number of experiments, such as Bragg-case section topography, rocking curve and photoluminescence (PL) measurements.
2. Experimental Floating zone single crystalline silicon (Fz-Si) with low interstitial oxygen concentration (co 6 2 1016 cm3 ) was implanted with Heþ ions (dose, D ¼ 5 1016 cm2 , energy E ¼ 150 keV). The Si:He samples were subjected to the HT–HP treatment in Ar atmosphere at temperatures equal to 720, 870 and 1270 K for up to 6 h. The Si:He samples were examined with a number of X-ray methods using both white and monochromatic radiation from DORIS III at HASYLAB. The white beam experiments were realised at the experimental station F1 by means of projection and section back-reflection topography. In both cases a relatively low glancing angle 4–5° was used. In the case of section topographs the beam was limited with a 5 lm narrow slit. The monochromatic beam experiments were realised at the experimental station E2 using a beam with k ¼ 0:11 nm selected by piezoelectronically stabilised monochromator with two Si crystals. The rocking curves were recorded in the symmetrical 0 0 4 reflection with a probe beam limited to a size of about 50 50 lm2 . The beam of a very small size enables significant reduction of the effects caused by sample bending. We performed also low temperature (10 K) PL studies. An Ar-ion laser (k ¼ 488 nm) was used as an excitation source. The spectra were analysed in 0.55 m Jobin-Yvone monochromator (Triax 550) with nitrogen cooled germanium detector.
3. Results and discussion All investigated Si:He samples were elastically bent by the strain coming from the implanted layer and, in some cases, also from the damaged back-
359
side. Due to the sample bending, the Bragg-case section topographs usually revealed a characteristic pattern [5] of the Chukhovski–Zaumseil fringes (Fig. 1). The formation of these fringes is assisted with reflection of the redirected wavefields from backside of the implanted layer. In the case of relatively perfect Si:He samples with the Chukhovski–Zaumseil fringes, it is also possible to see small irregularities of the deformed layer far behind the place illuminated by the narrow incident X-ray beam. The Chukhovski–Zaumseil fringes are not formed, however, in the samples with a high concentration of defects. In that case only the defects intersected by the narrow X-ray beam inside the crystal are visualised. The interference fringes were observed in the section topographs for the Si:He samples annealed/HT–HP treated at 720 K (Fig. 1) and even at 870 K. Only the samples annealed/treated at 1270 K did not exhibit the presence of interference fringes (compare Fig. 2 and Fig. 3). In the as-implanted Si:He sample the rocking curve exhibits characteristic interference maxima (Fig. 2) with the periodicity increasing toward the lower angles. These maxima are connected with the strain profile maximum located at some depth under a shot-through layer. One can assume that the distance to the furthest recognisable maximum is proportional to the maximal strain value while their number and width are dependent on the steepness of the maximum: the interference maxima are usually wider in the case of a steeper maximum of the strain profile. The formation of He filled inclusions results generally in decreased recognizability of the interference maxima and in an increased diffusion background in the lower angle part of the diffraction peak. The formation of gaseous inclusions in Si:He can be visualised by their effect on the interference fringes and visibility of resolved inclusions. In Si implanted with hydrogen (Si:H) and in the Si:He samples the HT–HP treatment results in an increased concentration of smaller gas-filled microcavities, as compared to the same annealing under 105 Pa [3]. In the case of the HT–HP treated Si:H, hydrogen agglomeration into hydrogen-filled bubbles resulted in fast vanishing of the interference
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A. Misiuk et al. / Nucl. Instr. and Meth. in Phys. Res. B 200 (2003) 358–362
Fig. 1. Synchrotron white beam Bragg-case projection (A, left) and section topographs (B, right) of Si:He (D ¼ 5 1016 cm2 , 150 keV): annealed at 720 K–105 Pa for 1 h, HT–HP treated at 720 K–1.1 GPa for 6 h and at 1270 K–1.2 GPa for 1 h. Image width equals to about 7 mm.
maxima of rocking curves, even for the treatments at 720 K [6]. Contrary to the case of HT–HP treated Si:H, the Si:He samples indicate the presence of interference maxima even after the treatment at 870 K– 105 Pa or 1.2 GPa for 1 h; the interference maxima disappeared only after processing the samples at 1270 K. Even in the last case some features of rocking curve may be interpreted, however, as the traces of the interference maxima (Fig. 3). From the number and angular distance covered by the interference fringes one may conclude that the treatment at 720 K for 1 h reduces the amplitude of strain by 25–40% (the evaluated maximal strain in as-implanted sample is about 1:8 103 ). This effect was most pronounced for the sample annealed at 720 K under atmospheric pressure (105 Pa) for 1 h and much less – for Si:He treated at
720 K–1.1 GPa for 1 h. The strain decreases with increasing treatment time both for the samples annealed at 720 K–105 Pa and treated at 720 K–1.1 GPa but this decrease is moderated by the HP–HT treatment (Figs. 1 and 2). Similar effect was observed for Si:He processed at 870 K (Fig. 3). The Si:He samples processed 1270 K–105 Pa/1.2 GPa indicate no interference maxima while the diffusion background was distinctly enhanced (Fig. 3). This effect is similar both for the sample annealed at 1270 K–105 Pa and for that treated at 1270 K–1.2 GPa. That last sample indicates the presence of distinctly recognisable individual defects, probably dislocations loops (Fig. 1B, the presence of dislocations was confirmed by transmission electron microscopy [7]). After the HT–HP treatments at 720/870 K–1.1/ 1.2 GPa in PL spectra of Si:He we observed a few
A. Misiuk et al. / Nucl. Instr. and Meth. in Phys. Res. B 200 (2003) 358–362
361
Fig. 2. Rocking curves (symmetrical 0 0 4 reflection) of Si:He samples: as-implanted and annealed/treated at 720 K under–105 Pa for 1 h, under 1.1 GPa for 1 h and under 1.1 GPa for 6 h.
Fig. 3. Rocking curves (symmetrical 0 0 4 reflection) of Si:He samples: annealed under 105 Pa and HT–HP treated under 1.2 GPa at 870 K and at 1270 K for 1 h.
lines (Fig. 4): D2 dislocation related line at energy position 0.87 eV, D3 at 0.935 eV and a line at energy equal to about 1.1 eV (originating from radiative recombination of the exciton bound to boron). Very low intensity of the PL peak at about 1.1 eV (the highest intensity for the non implanted Si samples) confirms strongly worsened structural perfection of all investigated Si:He samples. The type and concentration of defects in annealed Si:He are dependent on the implantation
(D, E) and HT–HP treatment parameters. Temperature (HT) of the HT–HP treatment is the most important factor in that respect while enhanced pressure (HP) during processing of Si:He results in retarded helium outdiffusion [3] and so in creation of more numerous but smaller He filled microcavities. Other defects in the implanted areas are dislocations as evidenced by the presence of the D2 and D3 peaks at 0.87 eV and 0.93 eV in processed
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A. Misiuk et al. / Nucl. Instr. and Meth. in Phys. Res. B 200 (2003) 358–362
Acknowledgements The authors thank Prof. V. Raineri from CNRIMETEM, Catania, Italy for supply of some Si:He samples and Mr. M. Prujszczyk from the Institute of Electron Technology for performing of the HT– HP treatments. This work was supported partially by the Polish Committee for Scientific Research, grants no. 8T11B 072 19 and 4 T08A 034 23. References Fig. 4. PL of Si:He samples: treated at 720 K–1.1 GPa for 1 h and 6 h, annealed at 870 K–105 Pa for 1 h and treated at 870 K– 1.1 GPa for 1 h.
Si:He. The presence of point-like defects in such samples has been reported previously, especially for the case of helium implanted oxygen containing Czochralski silicon [3,4]. The use of synchrotron methods (topography and rocking curve measurements) gives valuable information on the evolution of strain as well as on creation and annihilation of the He filled cavities and of other defects in Si:He in condition of enhanced hydrostatic pressure of ambient atmosphere.
[1] V. Raineri, Mater. Sci. Eng. B 73 (2000) 47. [2] X. Duo, W. Liu, M. Zhang, L. Wang, C. Lin, M. Okuyama, M. Noda, W.-Y. Cheung, S.P. Wong, P.K. Chu, P. Hu, S.X. Wang, L.M. Wang, J. Appl. Phys. 90 (2001) 3780. [3] A. Misiuk, J. Bak-Misiuk, I.V. Antonova, V. Raineri, A. Romano-Rodriguez, A. Bachrouri, H.B. Surma, J. Ratajczak, J. Katcki, J. Adamczewska, E.P. Neustroev, Comput. Mater. Sci. 21 (2001) 515. [4] A. Misiuk, A. Barcz, V. Raineri, J. Ratajczak, J. BakMisiuk, I.V. Antonova, W. Wierzchowski, K. Wieteska, Physica B 308–310 (2001) 371. [5] F.N. Chukhovski, P.V. Petrashen, Acta Cryst. A 44 (1988) 8. [6] W. Wieteska, W. Wierzchowski, W. Graeff, A. Misiuk, A. Barcz, L. Bryja, V.P. Popov, Acta Phys. Polon. A 102 (2002) 239. [7] V. Raineri, private communication.
Synchrotron topography of high temperature–pressure treated silicon implanted with helium a,*
, W. Wierzchowski b, K. Wieteska c, L. Bryja d, W. Graeff
A. Misiuk
e
a Institute of Electron Technology, Al. Lotnikow 32/46, 02-668 Warsaw, Poland Institute of Electronic Materials Technology, Wolczynska 133, 01-919 Warsaw, Poland c Institute of Atomic Energy, 05-400 Otwock-Swierk, Poland d Wroclaw University of Technology, Wyb. Wyspianskiego 27, 50-370 Wroclaw, Poland e HASYLAB at DESY, Notkestrasse 85, D-22603 Hamburg, Germany
b
Abstract Silicon implanted with Heþ at 150 keV to a dose 5 1016 cm2 (Si:He) and treated at high temperature (up to 1270 K) and pressure (up to 1.2 GPa) was investigated using synchrotron X-ray topography, rocking curve and photoluminescence measurements. Rocking curves of as-implanted Si:He exhibit interference maxima related to strain resulting from the presence of He. Annealing at 720 K under 105 Pa for 1 h reduces the strain by about 1.5 while the treatment at 720 K–1.2 GPa affects it to a less degree. The pressure-moderated decrease of strain was observed also for the treatment at 870 K but not at 1270 K. The HP induced effects depend on retarded He diffusion and creation of specific defects at HP. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 61.10.)i; 62.50.þp; 66.30.)h; 71.20.Mg Keywords: Helium implanted Si; High temperature-pressure; Strain; Synchrotron
1. Introduction Helium implanted silicon (Si:He) has become a topic of remarkable interest, mostly because the bubbles and cavities created in Si:He during annealing are active in respect of gettering of metallic impurities [1]. Implanted helium atoms are also known to assist in the important effect of silicon surface splitting in Si implanted with hydrogen or
*
Corresponding author. Tel.: +48-22-548-7792; fax: +48-22847-0631. E-mail address: [email protected] (A. Misiuk).
hydrogen and helium, known as the smart-cut process [2]. During annealing at 105 Pa (atmospheric pressure), the trapped He atoms diffuse and segregate near the implantation peak region creating helium filled bubbles and microcavities. More prolonged annealing can result in complete outdiffusion of He. Enhanced hydrostatic pressure of ambient atmosphere at annealing (HT–HP treatment) of Si:He results in decreased dimension of postimplantation defects, retardation of He outdiffusion and strongly stimulated creation of thermal donors [3] as well as in gettering of oxygen in the
0168-583X/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 0 2 ) 0 1 7 0 1 - 9
A. Misiuk et al. / Nucl. Instr. and Meth. in Phys. Res. B 200 (2003) 358–362
case of He implantation in oxygen containing Czochralski silicon [4]. In the present work we report on the HT–HP treatment effect on Si:He. In order to study this effect we performed a number of experiments, such as Bragg-case section topography, rocking curve and photoluminescence (PL) measurements.
2. Experimental Floating zone single crystalline silicon (Fz-Si) with low interstitial oxygen concentration (co 6 2 1016 cm3 ) was implanted with Heþ ions (dose, D ¼ 5 1016 cm2 , energy E ¼ 150 keV). The Si:He samples were subjected to the HT–HP treatment in Ar atmosphere at temperatures equal to 720, 870 and 1270 K for up to 6 h. The Si:He samples were examined with a number of X-ray methods using both white and monochromatic radiation from DORIS III at HASYLAB. The white beam experiments were realised at the experimental station F1 by means of projection and section back-reflection topography. In both cases a relatively low glancing angle 4–5° was used. In the case of section topographs the beam was limited with a 5 lm narrow slit. The monochromatic beam experiments were realised at the experimental station E2 using a beam with k ¼ 0:11 nm selected by piezoelectronically stabilised monochromator with two Si crystals. The rocking curves were recorded in the symmetrical 0 0 4 reflection with a probe beam limited to a size of about 50 50 lm2 . The beam of a very small size enables significant reduction of the effects caused by sample bending. We performed also low temperature (10 K) PL studies. An Ar-ion laser (k ¼ 488 nm) was used as an excitation source. The spectra were analysed in 0.55 m Jobin-Yvone monochromator (Triax 550) with nitrogen cooled germanium detector.
3. Results and discussion All investigated Si:He samples were elastically bent by the strain coming from the implanted layer and, in some cases, also from the damaged back-
359
side. Due to the sample bending, the Bragg-case section topographs usually revealed a characteristic pattern [5] of the Chukhovski–Zaumseil fringes (Fig. 1). The formation of these fringes is assisted with reflection of the redirected wavefields from backside of the implanted layer. In the case of relatively perfect Si:He samples with the Chukhovski–Zaumseil fringes, it is also possible to see small irregularities of the deformed layer far behind the place illuminated by the narrow incident X-ray beam. The Chukhovski–Zaumseil fringes are not formed, however, in the samples with a high concentration of defects. In that case only the defects intersected by the narrow X-ray beam inside the crystal are visualised. The interference fringes were observed in the section topographs for the Si:He samples annealed/HT–HP treated at 720 K (Fig. 1) and even at 870 K. Only the samples annealed/treated at 1270 K did not exhibit the presence of interference fringes (compare Fig. 2 and Fig. 3). In the as-implanted Si:He sample the rocking curve exhibits characteristic interference maxima (Fig. 2) with the periodicity increasing toward the lower angles. These maxima are connected with the strain profile maximum located at some depth under a shot-through layer. One can assume that the distance to the furthest recognisable maximum is proportional to the maximal strain value while their number and width are dependent on the steepness of the maximum: the interference maxima are usually wider in the case of a steeper maximum of the strain profile. The formation of He filled inclusions results generally in decreased recognizability of the interference maxima and in an increased diffusion background in the lower angle part of the diffraction peak. The formation of gaseous inclusions in Si:He can be visualised by their effect on the interference fringes and visibility of resolved inclusions. In Si implanted with hydrogen (Si:H) and in the Si:He samples the HT–HP treatment results in an increased concentration of smaller gas-filled microcavities, as compared to the same annealing under 105 Pa [3]. In the case of the HT–HP treated Si:H, hydrogen agglomeration into hydrogen-filled bubbles resulted in fast vanishing of the interference
360
A. Misiuk et al. / Nucl. Instr. and Meth. in Phys. Res. B 200 (2003) 358–362
Fig. 1. Synchrotron white beam Bragg-case projection (A, left) and section topographs (B, right) of Si:He (D ¼ 5 1016 cm2 , 150 keV): annealed at 720 K–105 Pa for 1 h, HT–HP treated at 720 K–1.1 GPa for 6 h and at 1270 K–1.2 GPa for 1 h. Image width equals to about 7 mm.
maxima of rocking curves, even for the treatments at 720 K [6]. Contrary to the case of HT–HP treated Si:H, the Si:He samples indicate the presence of interference maxima even after the treatment at 870 K– 105 Pa or 1.2 GPa for 1 h; the interference maxima disappeared only after processing the samples at 1270 K. Even in the last case some features of rocking curve may be interpreted, however, as the traces of the interference maxima (Fig. 3). From the number and angular distance covered by the interference fringes one may conclude that the treatment at 720 K for 1 h reduces the amplitude of strain by 25–40% (the evaluated maximal strain in as-implanted sample is about 1:8 103 ). This effect was most pronounced for the sample annealed at 720 K under atmospheric pressure (105 Pa) for 1 h and much less – for Si:He treated at
720 K–1.1 GPa for 1 h. The strain decreases with increasing treatment time both for the samples annealed at 720 K–105 Pa and treated at 720 K–1.1 GPa but this decrease is moderated by the HP–HT treatment (Figs. 1 and 2). Similar effect was observed for Si:He processed at 870 K (Fig. 3). The Si:He samples processed 1270 K–105 Pa/1.2 GPa indicate no interference maxima while the diffusion background was distinctly enhanced (Fig. 3). This effect is similar both for the sample annealed at 1270 K–105 Pa and for that treated at 1270 K–1.2 GPa. That last sample indicates the presence of distinctly recognisable individual defects, probably dislocations loops (Fig. 1B, the presence of dislocations was confirmed by transmission electron microscopy [7]). After the HT–HP treatments at 720/870 K–1.1/ 1.2 GPa in PL spectra of Si:He we observed a few
A. Misiuk et al. / Nucl. Instr. and Meth. in Phys. Res. B 200 (2003) 358–362
361
Fig. 2. Rocking curves (symmetrical 0 0 4 reflection) of Si:He samples: as-implanted and annealed/treated at 720 K under–105 Pa for 1 h, under 1.1 GPa for 1 h and under 1.1 GPa for 6 h.
Fig. 3. Rocking curves (symmetrical 0 0 4 reflection) of Si:He samples: annealed under 105 Pa and HT–HP treated under 1.2 GPa at 870 K and at 1270 K for 1 h.
lines (Fig. 4): D2 dislocation related line at energy position 0.87 eV, D3 at 0.935 eV and a line at energy equal to about 1.1 eV (originating from radiative recombination of the exciton bound to boron). Very low intensity of the PL peak at about 1.1 eV (the highest intensity for the non implanted Si samples) confirms strongly worsened structural perfection of all investigated Si:He samples. The type and concentration of defects in annealed Si:He are dependent on the implantation
(D, E) and HT–HP treatment parameters. Temperature (HT) of the HT–HP treatment is the most important factor in that respect while enhanced pressure (HP) during processing of Si:He results in retarded helium outdiffusion [3] and so in creation of more numerous but smaller He filled microcavities. Other defects in the implanted areas are dislocations as evidenced by the presence of the D2 and D3 peaks at 0.87 eV and 0.93 eV in processed
362
A. Misiuk et al. / Nucl. Instr. and Meth. in Phys. Res. B 200 (2003) 358–362
Acknowledgements The authors thank Prof. V. Raineri from CNRIMETEM, Catania, Italy for supply of some Si:He samples and Mr. M. Prujszczyk from the Institute of Electron Technology for performing of the HT– HP treatments. This work was supported partially by the Polish Committee for Scientific Research, grants no. 8T11B 072 19 and 4 T08A 034 23. References Fig. 4. PL of Si:He samples: treated at 720 K–1.1 GPa for 1 h and 6 h, annealed at 870 K–105 Pa for 1 h and treated at 870 K– 1.1 GPa for 1 h.
Si:He. The presence of point-like defects in such samples has been reported previously, especially for the case of helium implanted oxygen containing Czochralski silicon [3,4]. The use of synchrotron methods (topography and rocking curve measurements) gives valuable information on the evolution of strain as well as on creation and annihilation of the He filled cavities and of other defects in Si:He in condition of enhanced hydrostatic pressure of ambient atmosphere.
[1] V. Raineri, Mater. Sci. Eng. B 73 (2000) 47. [2] X. Duo, W. Liu, M. Zhang, L. Wang, C. Lin, M. Okuyama, M. Noda, W.-Y. Cheung, S.P. Wong, P.K. Chu, P. Hu, S.X. Wang, L.M. Wang, J. Appl. Phys. 90 (2001) 3780. [3] A. Misiuk, J. Bak-Misiuk, I.V. Antonova, V. Raineri, A. Romano-Rodriguez, A. Bachrouri, H.B. Surma, J. Ratajczak, J. Katcki, J. Adamczewska, E.P. Neustroev, Comput. Mater. Sci. 21 (2001) 515. [4] A. Misiuk, A. Barcz, V. Raineri, J. Ratajczak, J. BakMisiuk, I.V. Antonova, W. Wierzchowski, K. Wieteska, Physica B 308–310 (2001) 371. [5] F.N. Chukhovski, P.V. Petrashen, Acta Cryst. A 44 (1988) 8. [6] W. Wieteska, W. Wierzchowski, W. Graeff, A. Misiuk, A. Barcz, L. Bryja, V.P. Popov, Acta Phys. Polon. A 102 (2002) 239. [7] V. Raineri, private communication.