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Ion beam synthesis of Si3N4 amorphous buried layers
Materials Science and Engineering, B I 2 (1992) 6 1 - 6 2
61
Ion beam synthesis of Si3N4 amorphous buried layers A. I. Belogorokhov, A. B. Danilin, V. N. Mordkovich and O. I. Vyletalina Institute of Microelectronics Technologyand High Purity Materials, Russian Academy of Sciences, 142432 Chernogolovka, Moscow District (Russia)
Abstract It was demonstrated that it is possible to prevent the crystallization of buried Si3N 4 layers formed by N ÷ implantation with E - - 150 keV, • ---5.0 × 1017 N + c m 2 and TA= 1200 °C (2 h). To achieve this, preliminary implantation with E = 150 keV and • / > 5.0 x 1016 O + cm 2 has to be carried out. Radiation defects induced during O ÷ implantation stimulate the process of crystallization.
1. Introduction Buried Si3N 4 layers for silicon on insulator (SO1) structures has many advantages compared with buried SiO2 layers. The main advantages are as follows: higher SOl layer perfection, gettering of harmful impurities and diffusion barriers for most doping impurities [1, 2]. Nevertheless, the main disadvantage of SO1 structures with buried Si3N4 layers, which makes their industrial production difficult, lies in the imperfect insulating properties of the given layers. High leakage currents and unstable insulating properties of the buried layers are associated with Si3N4 crystallization during annealing. This usually starts with crystallization of silicon inclusions [3, 4]. It is known that saturation of the Si3N 4 layer with oxygen atoms prevents this layer from crystallizing [5]. This effect has been observed in surface condensed layers. There are two questions which are connected with this effect: what is the quantity of oxygen which is enough to prevent crystallization of the Si3N4 buried layer, and what is the role of radiation defects in this process.
density was about 22 p A cm-2. The wafer temperature during implantation reached 350 °C. After nitrogen implantation the samples were annealed at the temperature of SiaN 4 crystallization, 1200 °C [5] for 2 h in nitrogen ambient. IR spectroscopy measurements were made using a Bruker IFS-113v spectrometer in the range of wavenumbers 600-1200 cm. The dose 1.0x 1016 O + cm -2 is not sufficient to stabilize the amorphous state of Si3N4. This effect is independent of intermediate annealing (Fig. l(a)). The
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2. Experimental details and results O ÷ ions were implanted in n-type Si(100) wafers with energy 300 keV and doses of 1.0 x 1016 O + cm -2, 2.5 × 1016 O + c m - 2 and 5.0x 1016 O + c m -2. The average current density of the ion beam was about 2/~A cm -2. Under such conditions the temperature of the wafer, related to the radiation heating, was not higher than 250 °C. After implantation, some of the samples were annealed at 1100 °C for 1 h in nitrogen ambient: N ÷ ions were implanted with energy 150 keV and dose 5.0 × 1017 N + c m -2. The average ion current 0921-5107/92/$5.00
N.O 560
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CI WAVENUMBERSern , -4
Fig. I. IR absorption spectra for structures with buried layers, - - - with intermediate annealing, and - without intermediate annealing: (a) ~ = 1 . 0 x 1 0 1 6 O + cm-2; (b) ~ = 2.5 x 1016 O + cm-2; (c) @ = 5.0 x 1016 O + cm -2. © 1992--Elsevier Sequoia. All rights reserved
62
A. I. Beh)gorokhov et a/.
/
transmittance spectrum of Si3N 4 looks like a typical crystal phase spectrum [6]. At the dose of 2.5 × l() r~' O + cm-2, the role of radiation defects induced at the first stage of implantation is very important. After intermediate annealing the level of buried layer crystallinity is much lower (Fig. l(b)). At an oxygen dose of 5.0× l016 O + cm 2 the Si3N 4 layer remains amorphous. If the oxygen dose is this large even after intermediate annealing then the crystallization is at a very initial stage. We would like to point out the optical inactivity of oxygen in samples implanted with the largest dose of oxygen.
Ion beam synthesis (ff'Si~N4
Acknowledgments The authors are grateful to D. K. Starostin and A. F. Petrov for having carried out the ion implantation, to E. V. Nazarova for IR spectroscopy measurements, and to K. A. Drakin for constant attention to our investigations.
References 1 W. Skorupa, E Knothe and R. Grotzchel, Nucl. lnstrum. Methods B, 34 ( 1988) 523.
3. Conclusion It was shown that it is impossible to crystallize an Si3N 4 buried layer if the concentration of oxygen is more than 10% with respect to nitrogen. Radiation defects induced during oxygen implantation stimulated the process of crystallization.
2 E, Sobeslavsky and W. Skorupa, Phys. Status Solidi A, 114 (1989) 135. 3 P.L. E Hemment and K. Reeson, Phys. World, 2(1989) 39. 4 E L. Edelman, V. Z. Latuta, V. N. Zaitsev and A. A. Khoromenko, Phys. Status Solidi A, 51 (1979) 49. 5 F.L. Edelman, Phys. Status Solidi A, 51 (1979) 375. 6 P. Bourguet, J. M. Dupart, E. Le Tiran, P. Auvray, A. Guivarc'h, M. Salvi, G. Pebous and P. Henoc, J. Appl. Phys,, 51 (12)(1980)6169.
61
Ion beam synthesis of Si3N4 amorphous buried layers A. I. Belogorokhov, A. B. Danilin, V. N. Mordkovich and O. I. Vyletalina Institute of Microelectronics Technologyand High Purity Materials, Russian Academy of Sciences, 142432 Chernogolovka, Moscow District (Russia)
Abstract It was demonstrated that it is possible to prevent the crystallization of buried Si3N 4 layers formed by N ÷ implantation with E - - 150 keV, • ---5.0 × 1017 N + c m 2 and TA= 1200 °C (2 h). To achieve this, preliminary implantation with E = 150 keV and • / > 5.0 x 1016 O + cm 2 has to be carried out. Radiation defects induced during O ÷ implantation stimulate the process of crystallization.
1. Introduction Buried Si3N 4 layers for silicon on insulator (SO1) structures has many advantages compared with buried SiO2 layers. The main advantages are as follows: higher SOl layer perfection, gettering of harmful impurities and diffusion barriers for most doping impurities [1, 2]. Nevertheless, the main disadvantage of SO1 structures with buried Si3N4 layers, which makes their industrial production difficult, lies in the imperfect insulating properties of the given layers. High leakage currents and unstable insulating properties of the buried layers are associated with Si3N4 crystallization during annealing. This usually starts with crystallization of silicon inclusions [3, 4]. It is known that saturation of the Si3N 4 layer with oxygen atoms prevents this layer from crystallizing [5]. This effect has been observed in surface condensed layers. There are two questions which are connected with this effect: what is the quantity of oxygen which is enough to prevent crystallization of the Si3N4 buried layer, and what is the role of radiation defects in this process.
density was about 22 p A cm-2. The wafer temperature during implantation reached 350 °C. After nitrogen implantation the samples were annealed at the temperature of SiaN 4 crystallization, 1200 °C [5] for 2 h in nitrogen ambient. IR spectroscopy measurements were made using a Bruker IFS-113v spectrometer in the range of wavenumbers 600-1200 cm. The dose 1.0x 1016 O + cm -2 is not sufficient to stabilize the amorphous state of Si3N4. This effect is independent of intermediate annealing (Fig. l(a)). The
g20 740
20~
--..!
'
/
!
92[ 74[
'~,
,"
k-
56[ 3~0
2. Experimental details and results O ÷ ions were implanted in n-type Si(100) wafers with energy 300 keV and doses of 1.0 x 1016 O + cm -2, 2.5 × 1016 O + c m - 2 and 5.0x 1016 O + c m -2. The average current density of the ion beam was about 2/~A cm -2. Under such conditions the temperature of the wafer, related to the radiation heating, was not higher than 250 °C. After implantation, some of the samples were annealed at 1100 °C for 1 h in nitrogen ambient: N ÷ ions were implanted with energy 150 keV and dose 5.0 × 1017 N + c m -2. The average ion current 0921-5107/92/$5.00
N.O 560
3t,D
CI WAVENUMBERSern , -4
Fig. I. IR absorption spectra for structures with buried layers, - - - with intermediate annealing, and - without intermediate annealing: (a) ~ = 1 . 0 x 1 0 1 6 O + cm-2; (b) ~ = 2.5 x 1016 O + cm-2; (c) @ = 5.0 x 1016 O + cm -2. © 1992--Elsevier Sequoia. All rights reserved
62
A. I. Beh)gorokhov et a/.
/
transmittance spectrum of Si3N 4 looks like a typical crystal phase spectrum [6]. At the dose of 2.5 × l() r~' O + cm-2, the role of radiation defects induced at the first stage of implantation is very important. After intermediate annealing the level of buried layer crystallinity is much lower (Fig. l(b)). At an oxygen dose of 5.0× l016 O + cm 2 the Si3N 4 layer remains amorphous. If the oxygen dose is this large even after intermediate annealing then the crystallization is at a very initial stage. We would like to point out the optical inactivity of oxygen in samples implanted with the largest dose of oxygen.
Ion beam synthesis (ff'Si~N4
Acknowledgments The authors are grateful to D. K. Starostin and A. F. Petrov for having carried out the ion implantation, to E. V. Nazarova for IR spectroscopy measurements, and to K. A. Drakin for constant attention to our investigations.
References 1 W. Skorupa, E Knothe and R. Grotzchel, Nucl. lnstrum. Methods B, 34 ( 1988) 523.
3. Conclusion It was shown that it is impossible to crystallize an Si3N 4 buried layer if the concentration of oxygen is more than 10% with respect to nitrogen. Radiation defects induced during oxygen implantation stimulated the process of crystallization.
2 E, Sobeslavsky and W. Skorupa, Phys. Status Solidi A, 114 (1989) 135. 3 P.L. E Hemment and K. Reeson, Phys. World, 2(1989) 39. 4 E L. Edelman, V. Z. Latuta, V. N. Zaitsev and A. A. Khoromenko, Phys. Status Solidi A, 51 (1979) 49. 5 F.L. Edelman, Phys. Status Solidi A, 51 (1979) 375. 6 P. Bourguet, J. M. Dupart, E. Le Tiran, P. Auvray, A. Guivarc'h, M. Salvi, G. Pebous and P. Henoc, J. Appl. Phys,, 51 (12)(1980)6169.