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Hydrogen thermal stability in buried oxides of SOI structures
ELSEVIER
Microelectronic
Engineering
48 (1999) 359-362 www.elsevier.nlllocatelmee
Hydrogen Thermal Stability in Buried Oxides of SOI Structures D. Ballutaud”, A. Boutry-Forveille”, and A. Nazarovb, “Laboratoire de Physique des Solides, Centre national de la Recherche scientifique, 1 Place A&tide Briand, 92 195 Meudon cedex (France). bInstitute of Semiconductor Physics, National Academy of Science of Ukraine, Prospekt Nauki 45,25650 Kyiv (Ukraine)
The interactions of hydrogen (deuterium used as tracer) with Si-SiO,-Si buried oxide layers (BOX) prepared by thermal oxidation or by oxygen implantation (SIMOX) are investigated using Secondary Ion Mass Spectrometry (SIMS) measurements combined with effusion experiments and isothermal annealings.
1. INTRODUCTION Oxygen implantation (SIMOX, for Gseparation by implantation of oxygen ))) is one way to process buried SiO, layers in Silicon for silicon-on-insulator (SOI) technology [l]. Another way to get buried SiO, layers is the thermal oxidation of a silicon substrate followed by the deposition of an poly-Si layer recrystallized by laser zone melting (ZMR) [2]. Hydrogenation, typically using a plasma source, is used to improve the electronic properties of poly- or microcrystalline silicon for electronic devices [3]. In general, it is admitted that passivation occurs when hydrogen is trapped on dangling bonds [4], on extended defects as silicon grain boundaries or dislocations. Heterogeneous interfaces such as interfaces also presents silicon-silicon-dioxide electrically active centers able to trap hydrogen atoms [5]. The deuterium permeation through the silicon overlayer and the trapping in the oxide have been previously studied in a high range of temperature (500-1000°C) in SIMOX structures, using a deuterium gas source and nuclear-reaction analysis as characterization technique [6] and the diffision coefficient of hydrogen has been calculated in thermal SiO, by capacitance measurements [71. 0167-9317/99/$ - see front matter PII: SO167-9317(99)00405-O
0
In the present work, the interactions of hydrogen (deuterium used as a tracer) with SiO, buried layers (BOX) prepared by thermal oxidation (ZMR) or by oxygen implantation (SIMOX), were investigated Secondary Ion Mass using Spectrometry (SIMS) measurements combined experiments and isothermal with effision annealing. 2. EXPERIMENTAL The deuteration of the samples was performed in a deuterium RF plasma reactor (Deuterium plasma pressure: lmbar) at different temperatures (plasma power density lW/cm’) during 30 min. The deuterium concentration profiles were obtained by SIMS measurements with a CAMECA IMS4F apparatus, with a Cs+ primary ion beam (14 keV, 5.10-3 A/cm2). The crater depths were measured with a Tencor stylus profilometer and the absolute concentrations were determined by calibration with deuterium implanted Si standard specimen. Effusion spectra were measured by a quadrupole mass spectrometer coupled to an tube (lo-lo mbar) which evacuated quartz contained the deuterated samples, which were
1999 Elsevier Science B.V. All rights reserved.
360
D. Ballutaud et al. I Microelectronic Engineering 48 (1999) 359-362
submitted to a linear heating rate (lS”C/min) or isothermal annealing. The pumping was controlled the mass spectrometer signal was so that proportional to the deuterium gas flow outgassing from the sample, and was normalized to one square centimeter sample surface [8]. 3. RESULTS 3.1. Deuterium diffusion profiles in BOX Figure 1 shows the influence of the temperature on deuterium diffusion profiles in a SIMOX sample. Permeation through the implanted oxide layer occurs at temperatures higher than 250 “C.
coefficient of 5.5 lo-l3 cm2 s-l at 250 “C (Figure 3), although it is not generally the case in polycrystalline silicon [ 11, 121. The large deuterium peak at the poly-SiSiO, interface
rtcm-3
l.OOE+22T l.OOE+21 l.oOE+20
The deuterium diffusion profiles observed in the superficial mono-Si layer are in good agreement with the previous works of D. Mathiot et al [9, lo]. The deuterium profiles exhibit undulations showing that some deuterium is trapped on residual reactive sites in the superficial mono-Si and in the implanted oxide layers. The deuterium concentration profile in the BOX and in the silicon substrate evidences some trapping on defects (silicon inclusions or oxide protusions) The diffusion profile after deuteration at 250°C in ZMR sample is depicted in figure 2 (curve a). The deuterium diffusion profile follows accurately an erfc function in the poly-Si superficial layer with an effective diffusion
I
shows an important deuterium trapping between the thermal oxide and the polycrystalline silicon layer.
LOOE+16-I 0
0.5
l
1.5
w
Figure 1. Deuterium concentration profiles in SIMOX samples; after deuteration at 250°C (a) and at 150°C (b)( 1W/cm2 during 30 min).
at.cm 3
lE+21 I lE+20
lE+19 lE+18 lE+17
-3 lltan lE+21 -I
lE+16 0
0
0.5
1
pm
1.5
Figure 2. Deuterium concentration profiles in ZMR samples; (a) after deuteration at 25O’C; (b) sample (a) after isothermal annealing at 600°C during 2 hours (1 W/cm2 during 30 min).
0.2
0.4 P
0.6
Figure 3. Simulation of the deuterium diffusion profile in the poly-Si corresponding to curve (a) in figure 2.
3.2. Effusion results The deuterium effusion spectra obtained from SIMOX and ZMR samples after deuteration
D. Ballutaud et al. I Microelectronic Engineering 48 (1999) 359-362
( lW/cm2 at 250°C during 30 min) are reported in figure 4 (respectively curves a and b). The SIMOX sample effusion spectrum presents three large peaks at respectively 380 “C, 480 “C and 820 “C, with some shoulders at 300 “C and 650 “C. By comparison with previous results obtained on monocrystalline silicon [lo], the 300 and 380 “C effusion features may be attributed to deuterium accumulated just beneath the surface where defects and traps due to plasma damage are in a high concentration, while the breaking of isolated Si-D bonds may be responsible for the effision peak at 480 “C. Then the high temperature peaks at 630 and 820 “C would be due to the effusion of deuterium trapped in the buried oxide layer and/or at the interfaces Si-SiO,. A deuterated SIMOX sample, with the same deuteration conditions as above, was treated by potassium hydroxide in order to etch off the top silicon layer of the BOX structure, and was submitted to an effusion experiment. The results (Figure 4, curve c) show that actually the four effision peaks at 300, 380,480 and 630 “C may be attributed to deuterium coming from the top silicon layer and the top silicon / BOX interface. The peak at 820 “C (Figure 4, curve c) would be due then to the effusion of deuterium trapped in the oxide layer or at the second BOX / silicon interface. It must be pointed out that a continuous deuterium ef&sion flow is still observed between 400 “C and 630 “C for the etched sample. The deuterium effusion spectrum of the ZMR sample after deuteration at 250 “C during 30 min, presented on figure 4, curve b, shows two main effusion peaks at respectively 380 and 520 “C, with a shoulder at 620 ‘C and a small effusion feature at 820 ‘C. The important peak at 620°C could be explained by the effusion of the deuterium trapped on the poly-SilSi02 interface. After etching, only a high temperature deuterium effusion peak at about 900 “C is detected. 3.3 Thermal annealing The results of an isothermal annealing at 600°C during 2 hours performed on a deuterated SIMOX sample are presented in figure 5. It may be observed
361
that mainly deuterium contained in the silicon top layer has outdiffused after this thermal treatment, and that deuterium concentration in the BOX after isothermal annealing is of the same order as before annealing. The deuterium concentration profile in the oxide layer has become constant.
0
200
400 600 T°C
800
1000
Figure 4. Deuterium effision spectra from SIMOX sample (curve a), ZMR sample (curve b) after deuteration at 250 “C during 30 min; Deuterium effusion spectra from similar samples SIMOX (curve c) and ZMR (curve d) after etching.
l.OOEtl50
I
I
0.5
1
grn
1.5
Figure 5 . Deuterium concentration profiles in SIMOX samples; (a) After deuteration at 25O’C (1W/cm2 during 30 min) ; (b) Sample (a) after an isothermal annealing at 6OO’Cduring 2 hours.
362
D. Ballutaud et al. I Microelectronic Engineering 48 (1999) 359-362
Figure 2, curve b, shows the effects of a 600 “C isothermal annealing on a ZMR sample deuterated with a RF plasma power of 1W/cm2 at 250°C during 30 min. As for the SIMOX sample, the deuterium is stable in the oxide layer, where it can still be detected after a thermal annealing at 600°C during 2 hours. 4. CONCLUSIONS The concentration of deuterium in the buried oxide is governed by two parameters: the difiivity in the upper silicon layer, which is different in monocrystalline and polycrystalline silicon, and trapping on defects. From this point of view, deuterium diffusion profile analysis is a tool to evidence defects in the different layers. In SIMOX samples, trapping offers evidence of reactive sites probably related to silicon inclusions or oxide protusions with different compositions. However, it must be pointed out that after the isothermal annealings, the deuterium concentration profile in the implanted oxide layer becomes constant. In ZMR samples, the large deuterium peak at the poly-SilSiO, interface shows an important deuterium trapping between the thermal oxide and the polycrystalline silicon layer. Permeation through the implanted oxide layer occurs at temperatures higher than 250°C while the deuterium does not diffuse in the silicon substrate through the thermal oxide, for the studied experimental parameters range. The deuterium is stable in the oxide layers where it can still be detected after a thermal annealing at 600°C during 2 hours. Combining isothermal annealing and effusion results, it may be concluded that the detrapping of hydrogen from the BOX occurs above 800°C.
REFERENCES 1. J.-P. Colinge, Silicon-on-Znsulator Technology: materials to VLSI, Kluwer Academic Publishers, Dordrecht ( 199 1).
2. E. I. Givargizov, V. A. Loukin and A. B. Limanov in Physical and Technical Problems of SOI Structures and Devices, ed. by J.-P.
Colinge, V. S. Lysenko and A. N. Nazarov (NATO ASI series, Kluwer Academic Publishers, Dordrecht, 1994) p.27. 3. A. Chari, P. de Mierry, A. Menikh and M. Aucouturier, Rev. Phys. Appl. 22,655 (1987). 4. D. Ballutaud, M. Aucouturier and F.Babonneau, Appl. Phys. Lett. 49, 1622 (1986). 5. K. L. Brower, Appl. Phys. lett. 43, 1111 (1983). 6. S.M. Myers, G.A. Brown, A.G. Revesz and H.L. Hughes, J.Appl.Phys. 73(5) 2196 (1993). 7. I.P. Lisovskii, V.G. Litovchenko, G.P. Romanova, P.I. Didenko and E.G. Schmidt, Phys. Stat. Sol. (a) 142, 107 (1994). 8. D. Ballutaud, P. de Mien-y, J.-C. Pesant, R. Rizk, A. Boutry-Forveille and M. Aucouturier, Mat. Science Forum, vol. 83-87, pp. 45-50 (1992). 9. D. Mathiot, Phys. Rev. B 40,5867 (1989). 10. R. Rizk, P. de Mierry, D. Ballutaud and M. Aucouturier, Phys. Rev. B 44,614l (1991). 11. L. Lusson, P. Elkaim, A. Correia and D. Ballutaud, J. Phys. III (France) 5, 1173 (1995). 12. N. H. Nickel, W. B. Jackson and J. Walker, Phys. Review B 53 (12) 7750 (1996).
ACKNOWLEDGMENTS This work was supported by the CNRS (France) and the Academy of Sciences of Ukraine.
Microelectronic
Engineering
48 (1999) 359-362 www.elsevier.nlllocatelmee
Hydrogen Thermal Stability in Buried Oxides of SOI Structures D. Ballutaud”, A. Boutry-Forveille”, and A. Nazarovb, “Laboratoire de Physique des Solides, Centre national de la Recherche scientifique, 1 Place A&tide Briand, 92 195 Meudon cedex (France). bInstitute of Semiconductor Physics, National Academy of Science of Ukraine, Prospekt Nauki 45,25650 Kyiv (Ukraine)
The interactions of hydrogen (deuterium used as tracer) with Si-SiO,-Si buried oxide layers (BOX) prepared by thermal oxidation or by oxygen implantation (SIMOX) are investigated using Secondary Ion Mass Spectrometry (SIMS) measurements combined with effusion experiments and isothermal annealings.
1. INTRODUCTION Oxygen implantation (SIMOX, for Gseparation by implantation of oxygen ))) is one way to process buried SiO, layers in Silicon for silicon-on-insulator (SOI) technology [l]. Another way to get buried SiO, layers is the thermal oxidation of a silicon substrate followed by the deposition of an poly-Si layer recrystallized by laser zone melting (ZMR) [2]. Hydrogenation, typically using a plasma source, is used to improve the electronic properties of poly- or microcrystalline silicon for electronic devices [3]. In general, it is admitted that passivation occurs when hydrogen is trapped on dangling bonds [4], on extended defects as silicon grain boundaries or dislocations. Heterogeneous interfaces such as interfaces also presents silicon-silicon-dioxide electrically active centers able to trap hydrogen atoms [5]. The deuterium permeation through the silicon overlayer and the trapping in the oxide have been previously studied in a high range of temperature (500-1000°C) in SIMOX structures, using a deuterium gas source and nuclear-reaction analysis as characterization technique [6] and the diffision coefficient of hydrogen has been calculated in thermal SiO, by capacitance measurements [71. 0167-9317/99/$ - see front matter PII: SO167-9317(99)00405-O
0
In the present work, the interactions of hydrogen (deuterium used as a tracer) with SiO, buried layers (BOX) prepared by thermal oxidation (ZMR) or by oxygen implantation (SIMOX), were investigated Secondary Ion Mass using Spectrometry (SIMS) measurements combined experiments and isothermal with effision annealing. 2. EXPERIMENTAL The deuteration of the samples was performed in a deuterium RF plasma reactor (Deuterium plasma pressure: lmbar) at different temperatures (plasma power density lW/cm’) during 30 min. The deuterium concentration profiles were obtained by SIMS measurements with a CAMECA IMS4F apparatus, with a Cs+ primary ion beam (14 keV, 5.10-3 A/cm2). The crater depths were measured with a Tencor stylus profilometer and the absolute concentrations were determined by calibration with deuterium implanted Si standard specimen. Effusion spectra were measured by a quadrupole mass spectrometer coupled to an tube (lo-lo mbar) which evacuated quartz contained the deuterated samples, which were
1999 Elsevier Science B.V. All rights reserved.
360
D. Ballutaud et al. I Microelectronic Engineering 48 (1999) 359-362
submitted to a linear heating rate (lS”C/min) or isothermal annealing. The pumping was controlled the mass spectrometer signal was so that proportional to the deuterium gas flow outgassing from the sample, and was normalized to one square centimeter sample surface [8]. 3. RESULTS 3.1. Deuterium diffusion profiles in BOX Figure 1 shows the influence of the temperature on deuterium diffusion profiles in a SIMOX sample. Permeation through the implanted oxide layer occurs at temperatures higher than 250 “C.
coefficient of 5.5 lo-l3 cm2 s-l at 250 “C (Figure 3), although it is not generally the case in polycrystalline silicon [ 11, 121. The large deuterium peak at the poly-SiSiO, interface
rtcm-3
l.OOE+22T l.OOE+21 l.oOE+20
The deuterium diffusion profiles observed in the superficial mono-Si layer are in good agreement with the previous works of D. Mathiot et al [9, lo]. The deuterium profiles exhibit undulations showing that some deuterium is trapped on residual reactive sites in the superficial mono-Si and in the implanted oxide layers. The deuterium concentration profile in the BOX and in the silicon substrate evidences some trapping on defects (silicon inclusions or oxide protusions) The diffusion profile after deuteration at 250°C in ZMR sample is depicted in figure 2 (curve a). The deuterium diffusion profile follows accurately an erfc function in the poly-Si superficial layer with an effective diffusion
I
shows an important deuterium trapping between the thermal oxide and the polycrystalline silicon layer.
LOOE+16-I 0
0.5
l
1.5
w
Figure 1. Deuterium concentration profiles in SIMOX samples; after deuteration at 250°C (a) and at 150°C (b)( 1W/cm2 during 30 min).
at.cm 3
lE+21 I lE+20
lE+19 lE+18 lE+17
-3 lltan lE+21 -I
lE+16 0
0
0.5
1
pm
1.5
Figure 2. Deuterium concentration profiles in ZMR samples; (a) after deuteration at 25O’C; (b) sample (a) after isothermal annealing at 600°C during 2 hours (1 W/cm2 during 30 min).
0.2
0.4 P
0.6
Figure 3. Simulation of the deuterium diffusion profile in the poly-Si corresponding to curve (a) in figure 2.
3.2. Effusion results The deuterium effusion spectra obtained from SIMOX and ZMR samples after deuteration
D. Ballutaud et al. I Microelectronic Engineering 48 (1999) 359-362
( lW/cm2 at 250°C during 30 min) are reported in figure 4 (respectively curves a and b). The SIMOX sample effusion spectrum presents three large peaks at respectively 380 “C, 480 “C and 820 “C, with some shoulders at 300 “C and 650 “C. By comparison with previous results obtained on monocrystalline silicon [lo], the 300 and 380 “C effusion features may be attributed to deuterium accumulated just beneath the surface where defects and traps due to plasma damage are in a high concentration, while the breaking of isolated Si-D bonds may be responsible for the effision peak at 480 “C. Then the high temperature peaks at 630 and 820 “C would be due to the effusion of deuterium trapped in the buried oxide layer and/or at the interfaces Si-SiO,. A deuterated SIMOX sample, with the same deuteration conditions as above, was treated by potassium hydroxide in order to etch off the top silicon layer of the BOX structure, and was submitted to an effusion experiment. The results (Figure 4, curve c) show that actually the four effision peaks at 300, 380,480 and 630 “C may be attributed to deuterium coming from the top silicon layer and the top silicon / BOX interface. The peak at 820 “C (Figure 4, curve c) would be due then to the effusion of deuterium trapped in the oxide layer or at the second BOX / silicon interface. It must be pointed out that a continuous deuterium ef&sion flow is still observed between 400 “C and 630 “C for the etched sample. The deuterium effusion spectrum of the ZMR sample after deuteration at 250 “C during 30 min, presented on figure 4, curve b, shows two main effusion peaks at respectively 380 and 520 “C, with a shoulder at 620 ‘C and a small effusion feature at 820 ‘C. The important peak at 620°C could be explained by the effusion of the deuterium trapped on the poly-SilSi02 interface. After etching, only a high temperature deuterium effusion peak at about 900 “C is detected. 3.3 Thermal annealing The results of an isothermal annealing at 600°C during 2 hours performed on a deuterated SIMOX sample are presented in figure 5. It may be observed
361
that mainly deuterium contained in the silicon top layer has outdiffused after this thermal treatment, and that deuterium concentration in the BOX after isothermal annealing is of the same order as before annealing. The deuterium concentration profile in the oxide layer has become constant.
0
200
400 600 T°C
800
1000
Figure 4. Deuterium effision spectra from SIMOX sample (curve a), ZMR sample (curve b) after deuteration at 250 “C during 30 min; Deuterium effusion spectra from similar samples SIMOX (curve c) and ZMR (curve d) after etching.
l.OOEtl50
I
I
0.5
1
grn
1.5
Figure 5 . Deuterium concentration profiles in SIMOX samples; (a) After deuteration at 25O’C (1W/cm2 during 30 min) ; (b) Sample (a) after an isothermal annealing at 6OO’Cduring 2 hours.
362
D. Ballutaud et al. I Microelectronic Engineering 48 (1999) 359-362
Figure 2, curve b, shows the effects of a 600 “C isothermal annealing on a ZMR sample deuterated with a RF plasma power of 1W/cm2 at 250°C during 30 min. As for the SIMOX sample, the deuterium is stable in the oxide layer, where it can still be detected after a thermal annealing at 600°C during 2 hours. 4. CONCLUSIONS The concentration of deuterium in the buried oxide is governed by two parameters: the difiivity in the upper silicon layer, which is different in monocrystalline and polycrystalline silicon, and trapping on defects. From this point of view, deuterium diffusion profile analysis is a tool to evidence defects in the different layers. In SIMOX samples, trapping offers evidence of reactive sites probably related to silicon inclusions or oxide protusions with different compositions. However, it must be pointed out that after the isothermal annealings, the deuterium concentration profile in the implanted oxide layer becomes constant. In ZMR samples, the large deuterium peak at the poly-SilSiO, interface shows an important deuterium trapping between the thermal oxide and the polycrystalline silicon layer. Permeation through the implanted oxide layer occurs at temperatures higher than 250°C while the deuterium does not diffuse in the silicon substrate through the thermal oxide, for the studied experimental parameters range. The deuterium is stable in the oxide layers where it can still be detected after a thermal annealing at 600°C during 2 hours. Combining isothermal annealing and effusion results, it may be concluded that the detrapping of hydrogen from the BOX occurs above 800°C.
REFERENCES 1. J.-P. Colinge, Silicon-on-Znsulator Technology: materials to VLSI, Kluwer Academic Publishers, Dordrecht ( 199 1).
2. E. I. Givargizov, V. A. Loukin and A. B. Limanov in Physical and Technical Problems of SOI Structures and Devices, ed. by J.-P.
Colinge, V. S. Lysenko and A. N. Nazarov (NATO ASI series, Kluwer Academic Publishers, Dordrecht, 1994) p.27. 3. A. Chari, P. de Mierry, A. Menikh and M. Aucouturier, Rev. Phys. Appl. 22,655 (1987). 4. D. Ballutaud, M. Aucouturier and F.Babonneau, Appl. Phys. Lett. 49, 1622 (1986). 5. K. L. Brower, Appl. Phys. lett. 43, 1111 (1983). 6. S.M. Myers, G.A. Brown, A.G. Revesz and H.L. Hughes, J.Appl.Phys. 73(5) 2196 (1993). 7. I.P. Lisovskii, V.G. Litovchenko, G.P. Romanova, P.I. Didenko and E.G. Schmidt, Phys. Stat. Sol. (a) 142, 107 (1994). 8. D. Ballutaud, P. de Mien-y, J.-C. Pesant, R. Rizk, A. Boutry-Forveille and M. Aucouturier, Mat. Science Forum, vol. 83-87, pp. 45-50 (1992). 9. D. Mathiot, Phys. Rev. B 40,5867 (1989). 10. R. Rizk, P. de Mierry, D. Ballutaud and M. Aucouturier, Phys. Rev. B 44,614l (1991). 11. L. Lusson, P. Elkaim, A. Correia and D. Ballutaud, J. Phys. III (France) 5, 1173 (1995). 12. N. H. Nickel, W. B. Jackson and J. Walker, Phys. Review B 53 (12) 7750 (1996).
ACKNOWLEDGMENTS This work was supported by the CNRS (France) and the Academy of Sciences of Ukraine.