- Email: [email protected]
Backside and frontside depth profiling of B delta doping, at low energy, using new and previous magnetic SIMS instruments
Applied Surface Science 231–232 (2004) 668–672
Backside and frontside depth profiling of B delta doping, at low energy, using new and previous magnetic SIMS instruments F. Laugiera,*, J.M. Hartmanna, H. Moriceaua, P. Holligera, R. Truchea, J.C. Dupuyb a CEA-DRT-LETI/DTS-CEA/GRE, 17 av. des Martyrs, 38054 Grenoble Cedex 9, France Laboratoire de Physique de la Matie`re, UMR CNRS 5511, INSA-Lyon, 20 av. Albert Einstein, F-69621 Villeurbanne Cedex, France
b
Available online 25 May 2004
Abstract A sample, composed of inverted boron deltas/SiO2/boron deltas/silicon on an insulator substrate (SOI), was analyzed using a Cameca IMS 5f and a Cameca IMS Wf, with 500 eV O2þ, oxygen flooding, and an electron gun. To synthesize this ‘‘double delta doping’’ sample, two identical boron multi-deltas were grown on SOI wafers and molecularly bonded upside down, then one SOI substrate was removed. The quality of this sample was checked by TEM and AFM. From the boron deltas’ SIMS depth profiles, a comparative study of the two SIMS instruments was carried out by looking in detail at the depth resolution parameters. It was found that depth profiles acquired with both tools are very similar to those measured by TEM. Both tools separate B deltas 2 nm apart. However, the primary beam density is higher with the IMS Wf, allowing a two times faster analysis time than with the IMS 5f. This sample structure also allowed us to acquire in one measurement both the backside and the conventional front side depth profiles, therefore allowing the contribution from both the epitaxial growth and the contribution from the instrumental SIMS profiling conditions to be separated. # 2004 Elsevier B.V. All rights reserved. Keywords: SIMS; Low energy; Depth resolution; Boron; SOI; TEM
1. Introduction Boron deltas in silicon are the material of choice for the study of depth resolution in secondary ion mass spectrometry (SIMS). Indeed, this type of sample has been shown to be of excellent quality, i.e. very thin heavily B doped Si layers. However, the depth resolution contribution from the epitaxial growth is difficult *
Corresponding author. Tel.: þ33-4-3878-5544; fax: þ33-4-3878-9485. E-mail address: [email protected] (F. Laugier).
to separate from the instrumental SIMS contribution using standard B delta depth profiles. To overcome this limitation, we propose to use a new type of B multideltas, with a ‘‘double delta doping’’. This specific sample consists of two identical B multi-deltas bonded upside down. This specimen allows one, by acquisition of a single SIMS depth profile to obtain information from both directions of the delta’s growth. Both the latest generation Cameca IMS Wf and IMS 5f magnetic sector SIMS instruments have been used for this study. The Full width at half maximum (FWHM), down slope decay lengths (ld) and Gaussian broad-
0169-4332/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2004.03.143
F. Laugier et al. / Applied Surface Science 231–232 (2004) 668–672
ening parameter are calculated [1]. A comparative study of both tools is also carried out. In addition, this ‘‘double delta doping’’ sample was imaged by transmission electron microscopy (TEM).
2. Double boron delta doping sample To fabricate this special sample, several operations were needed. First, two boron multi-delta samples were epitaxially grown on silicon-on-insulator (SOI) substrates by RP-CVD [2]. The SOI wafers are 200 mm in diameter, with a 400 nm thick buried silicon dioxide layer and a 50 nm Si over-layer. On top of those SOI wafers five pairs of B deltas were epitaxially grown, each pair being separated from the other by 15 nm of Si. The dose of each B delta is 1014 atoms/cm2. The target spacing between two B peaks was: 1, 2, 3, 5, and 8 nm. The Si growth was capped with a 15 nm Si cap. Next a high temperature thermal SiO2 layer was deposited on top and the two processed wafers were molecularly bonded face to face. Mechanical grinding was used to remove most of the bulk Si from one of the two SOI samples. A thin Si layer was left in order to avoid any grinding damage being transferred to the Si over-layer underneath [3]. This residual Si layer was subsequently removed by chemical etching. Finally, the SiO2 layer was etched in a dilute (50%) hydrofluoric acid bath, resulting in the following final structure: inverted B deltas/SiO2/B deltas/SOI substrate.
669
3. Experimental SIMS analyses were performed on a Cameca IMS 5f and on a Cameca IMS Wf, with O2þ at 500 eV and oxygen flooding at 448 incidence angle. Electron flooding was used to neutralize charging effects due to the two buried oxide layers. In order to enhance secondary ion intensity, an electron multiplier with a post accelerating voltage was used. The primary beam was rastered over a 200 by 200 mm2 area; gating was used. Concentrations were calculated using RSF’s deduced from implanted samples. In order to get a precise depth scale, cross-sectional transmission electron microscopy imaging was performed on the sample. High-resolution images were obtained on an Akashi EM-002B, equipped with an ultra-high resolution pole piece not only to determine the individual thickness of the Si:B and SiO2 layers, but also to know the distance between boron deltas. The sample surface roughness was measured using a Digital Instruments Nanoscope D3100 atomic force microscope. Despite SOI removal, a very smooth and flat surface was found (the root-mean-square roughness is 0.12 nm for 1 mm 1 mm scan sizes). Finally, using a depth resolution function, the FWHM, ld and s are extracted [4].
4. Results and discussion Fig. 1 presents a boron depth profile of the sample, acquired with the Wf machine. Peaks corresponding to
B concentration (at/cm3)
1021 1020 1019 1018
B delta
Inverted B delta
1017 SiO2
Si
1016
0
50
100
150
200
Si
250
300
Depth (nm) Fig. 1. B depth profile acquired with the IMS Wf.
350
400
670
F. Laugier et al. / Applied Surface Science 231–232 (2004) 668–672
the boron deltas are clearly visible in the silicon layers. The total SIMS profile shows a succession of the backside and conventional front side depth profiles. The first Si layer, containing the ‘‘inverted B deltas’’, ends at the position of the medium height single B peak that comes from some boron contamination. In the middle of the SiO2 layer, another smaller B peak is observed. It corresponds to the molecular bonding of the two SOI samples. The third medium height B peak points to the end of the SiO2 layer. The thickness of this SiO2 layer has been evaluated by TEM to be 54 nm. The second Si layer, containing the normal B deltas ends with a small B contamination single peak, locating the SOI oxide interface. TEM images give as thickness 174.5 and 183 nm for the ‘‘inverted’’ and ‘‘normal’’ multi-B deltas-doped Si layers. From these TEM measurements, it is easy to scale the SIMS depth profile correctly. Distances between each pair of boron peaks were targeted to be 15 nm. However, SIMS measurements reveal a not constant spacing of 16 2 nm. This discrepancy of 10% is supposed to come from the deposition tool. The background at 8 1018 atoms/ cm3 that limits the dynamic range is due to a slight mass flow controller dysfunction during the growth process. Fig. 2 shows the SIMS analyses performed using both instruments of the inverted B doped Si layer. It is important to note that the primary beam density is higher with the IMS Wf, halving the analysis time compared with the IMS 5f. From this figure, IMS 5f
and IMS Wf give the same B depth profiles. Peaks positions are identical and peak heights are similar. The closest peaks are not distinct but the SIMS resolution is adequate to differentiate B deltas 2 nm apart. The other peaks are easily separable with Si spacing ranging in SIMS from 3.5 up to 7.5 nm. Boron layer positions were independently determined by TEM. The distances between two B peaks of the same pair are measured at 0.8, 2.05, 3.4, 4.8 and 7.37 nm, which is close to the SIMS results and the targeted values: 1, 2, 3, 5 and 8 nm. In Fig. 3, a detailed comparison between IMS 5f and IMS Wf is carried out by means of the B peaks separated by 8 nm of Si. These peaks are located in the B double delta structure at 76.1, 83.6, 318 and 325.5 nm. The extracted FWHM and ld are summarized in Table 1. For the same machine, peaks at 76.1 and 83.6 nm are similar. However, IMS 5f results are about 10% better than the IMS Wf ones. For peaks at 318 and 326 nm, values are very close to each other (differences below 3%) for a given equipment. IMS 5f is also better than Wf, especially as far as ld is concerned. By comparing the evolution of these parameters as a function of the depth, a broadening occurs for deep peaks. The FWHM increases with both equipments, but the increase is lower for the IMS Wf (20%) than for the IMS 5f (33%). However, ld is stable for the IMS 5f while there is a 30% increase with the IMS Wf. Evolution of the IMS Wf can be judged as normal considering the depth, the charge
B concentration (at/cm3)
1021
1020
1019
Ims 5f
Ims Wf 10
18
70
90
110
130
150
170
Depth (nm) Fig. 2. Boron depth profiles in the ‘‘inverted’’ B doped Si layer obtained with both equipments.
F. Laugier et al. / Applied Surface Science 231–232 (2004) 668–672
Backside 30
671
Frontside 30
30
30
25
25
25
Fit 25
Data
20
20
20
15
15
15
15
10
10
10
10
5
5
5
5
B concentration (at/cm3) x 1019
20
0
0 74
76
nm
78
81
80
83
nm
85
87
0 316
318
nm
320
322
0 324
30
30
30
30
25
25
25
25
20
20
20
20
15
15
15
15
10
10
10
10
5
5
5
5
0
0 74
76
nm
78
80
81
83
nm
85
87
0 316
318
nm
320
322
0 324
Ims 5f
326
nm
328
330
Ims Wf
326
nm
328
330
Fig. 3. Comparison between the front side (right) and back side (left) depth profiles for the IMS 5f (up) and IMS Wf (down).
Table 1 FWHM and ld calculated from the IMS 5f and IMS Wf depth profiles on the B peaks separated by 8 nm of Si Peak position (nm)
FWHM IMS 5f (nm)
FWHM IMS Wf (nm)
ld IMS 5f (nm)
ld IMS Wf (nm)
76.1 83.6 318 325.5
1.75 1.79 2.43 2.36
2.03 2.06 2.48 2.46
0.88 0.90 0.86 0.89
1 1.02 1.29 1.29
compensation required and the particular structure of the sample with the bonding. The degradation of the FWHM and the slight reduction of dynamic range without any variation for the ld value is more problematic for the IMS 5f. The acquisition time could be a new parameter to take into account. At 500 eV, the primary current density is low for the IMS 5f. This implies a low sputtering rate for the IMS 5f (1 nm/ min) compared to the IMS Wf (2.2 nm/min). Analysis time is too long. As a consequence, the sample surface roughness in the crater may increase. An other possibility is a difference between the incidence angles. By matching the Gaussian broadening parameter s of the Wf peak profiles for the backside and the front side B deltas, it is possible to check the quality,
especially the sharpness, of boron deltas. We can also, for the first time, separate the contributions coming from the actual boron delta growth process and from the SIMS profiling. s is found to be 0:6 0:03 nm in the backside and 0:65 0:03 nm in the front side. This indicates a 10% dissymmetry in boron concentration slopes, which are nevertheless very sharp. In addition, s results, when compared to ld, prove that the trailing edges are only due to the SIMS tool.
5. Conclusion The IMS Wf SIMS apparatus has been compared at low energy with the IMS 5f for boron depth profiling.
672
F. Laugier et al. / Applied Surface Science 231–232 (2004) 668–672
Depth resolution parameters are very close to each other, but the highest primary beam density of Wf, that reduces by a factor of two the analysis time, is a real advantage. We have analyzed in sequence B multideltas in Si in the growth direction as well as in the opposite direction instead of classical measure in the opposite direction to the growth only. From this complementary B depth profiling, it has been possible to check the quality of boron delta layers and to separate the SIMS contribution from the boron growth conditions.
Acknowledgements This work has been carried out in the frame of CCMC consortium between CEA-LETI, ST Micro-
electronics and FRANCE TELECOM-R&D. The authors would like to thank Franc¸ois Desse (Cameca) for his helpful advice in tuning the Wf electron gun and Geoffroy Auvert (STMicroelectronics) for valuable discussions. References [1] M.G. Dowsett, G. Rowlands, P.N. Allen, R.D. Barlow, Surf. Interf. Anal. 21 (1994) 310. [2] N. Baboux, J.C. Dupuy, G. Prudon, P. Holliger, F. Laugier, A.M. Papon, J.M. Hartmann, J. Cryst. Growth 245 (2002) 1–8. [3] H. Moriceau, B. Aspar, M. Bruel, A.M. Cartier, C. Morales, A. Sousbie, in: P.L. Hemment (Ed.), Proceedings of the Silicon on Insulator: Technology and Devices IX, Electro-Chemical Society, 1999, pp. 173–178. [4] B. Gautier, G. Prudon, J.C. Dupuy, Surf. Interf. Anal. 26 (1998) 974.
Backside and frontside depth profiling of B delta doping, at low energy, using new and previous magnetic SIMS instruments F. Laugiera,*, J.M. Hartmanna, H. Moriceaua, P. Holligera, R. Truchea, J.C. Dupuyb a CEA-DRT-LETI/DTS-CEA/GRE, 17 av. des Martyrs, 38054 Grenoble Cedex 9, France Laboratoire de Physique de la Matie`re, UMR CNRS 5511, INSA-Lyon, 20 av. Albert Einstein, F-69621 Villeurbanne Cedex, France
b
Available online 25 May 2004
Abstract A sample, composed of inverted boron deltas/SiO2/boron deltas/silicon on an insulator substrate (SOI), was analyzed using a Cameca IMS 5f and a Cameca IMS Wf, with 500 eV O2þ, oxygen flooding, and an electron gun. To synthesize this ‘‘double delta doping’’ sample, two identical boron multi-deltas were grown on SOI wafers and molecularly bonded upside down, then one SOI substrate was removed. The quality of this sample was checked by TEM and AFM. From the boron deltas’ SIMS depth profiles, a comparative study of the two SIMS instruments was carried out by looking in detail at the depth resolution parameters. It was found that depth profiles acquired with both tools are very similar to those measured by TEM. Both tools separate B deltas 2 nm apart. However, the primary beam density is higher with the IMS Wf, allowing a two times faster analysis time than with the IMS 5f. This sample structure also allowed us to acquire in one measurement both the backside and the conventional front side depth profiles, therefore allowing the contribution from both the epitaxial growth and the contribution from the instrumental SIMS profiling conditions to be separated. # 2004 Elsevier B.V. All rights reserved. Keywords: SIMS; Low energy; Depth resolution; Boron; SOI; TEM
1. Introduction Boron deltas in silicon are the material of choice for the study of depth resolution in secondary ion mass spectrometry (SIMS). Indeed, this type of sample has been shown to be of excellent quality, i.e. very thin heavily B doped Si layers. However, the depth resolution contribution from the epitaxial growth is difficult *
Corresponding author. Tel.: þ33-4-3878-5544; fax: þ33-4-3878-9485. E-mail address: [email protected] (F. Laugier).
to separate from the instrumental SIMS contribution using standard B delta depth profiles. To overcome this limitation, we propose to use a new type of B multideltas, with a ‘‘double delta doping’’. This specific sample consists of two identical B multi-deltas bonded upside down. This specimen allows one, by acquisition of a single SIMS depth profile to obtain information from both directions of the delta’s growth. Both the latest generation Cameca IMS Wf and IMS 5f magnetic sector SIMS instruments have been used for this study. The Full width at half maximum (FWHM), down slope decay lengths (ld) and Gaussian broad-
0169-4332/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2004.03.143
F. Laugier et al. / Applied Surface Science 231–232 (2004) 668–672
ening parameter are calculated [1]. A comparative study of both tools is also carried out. In addition, this ‘‘double delta doping’’ sample was imaged by transmission electron microscopy (TEM).
2. Double boron delta doping sample To fabricate this special sample, several operations were needed. First, two boron multi-delta samples were epitaxially grown on silicon-on-insulator (SOI) substrates by RP-CVD [2]. The SOI wafers are 200 mm in diameter, with a 400 nm thick buried silicon dioxide layer and a 50 nm Si over-layer. On top of those SOI wafers five pairs of B deltas were epitaxially grown, each pair being separated from the other by 15 nm of Si. The dose of each B delta is 1014 atoms/cm2. The target spacing between two B peaks was: 1, 2, 3, 5, and 8 nm. The Si growth was capped with a 15 nm Si cap. Next a high temperature thermal SiO2 layer was deposited on top and the two processed wafers were molecularly bonded face to face. Mechanical grinding was used to remove most of the bulk Si from one of the two SOI samples. A thin Si layer was left in order to avoid any grinding damage being transferred to the Si over-layer underneath [3]. This residual Si layer was subsequently removed by chemical etching. Finally, the SiO2 layer was etched in a dilute (50%) hydrofluoric acid bath, resulting in the following final structure: inverted B deltas/SiO2/B deltas/SOI substrate.
669
3. Experimental SIMS analyses were performed on a Cameca IMS 5f and on a Cameca IMS Wf, with O2þ at 500 eV and oxygen flooding at 448 incidence angle. Electron flooding was used to neutralize charging effects due to the two buried oxide layers. In order to enhance secondary ion intensity, an electron multiplier with a post accelerating voltage was used. The primary beam was rastered over a 200 by 200 mm2 area; gating was used. Concentrations were calculated using RSF’s deduced from implanted samples. In order to get a precise depth scale, cross-sectional transmission electron microscopy imaging was performed on the sample. High-resolution images were obtained on an Akashi EM-002B, equipped with an ultra-high resolution pole piece not only to determine the individual thickness of the Si:B and SiO2 layers, but also to know the distance between boron deltas. The sample surface roughness was measured using a Digital Instruments Nanoscope D3100 atomic force microscope. Despite SOI removal, a very smooth and flat surface was found (the root-mean-square roughness is 0.12 nm for 1 mm 1 mm scan sizes). Finally, using a depth resolution function, the FWHM, ld and s are extracted [4].
4. Results and discussion Fig. 1 presents a boron depth profile of the sample, acquired with the Wf machine. Peaks corresponding to
B concentration (at/cm3)
1021 1020 1019 1018
B delta
Inverted B delta
1017 SiO2
Si
1016
0
50
100
150
200
Si
250
300
Depth (nm) Fig. 1. B depth profile acquired with the IMS Wf.
350
400
670
F. Laugier et al. / Applied Surface Science 231–232 (2004) 668–672
the boron deltas are clearly visible in the silicon layers. The total SIMS profile shows a succession of the backside and conventional front side depth profiles. The first Si layer, containing the ‘‘inverted B deltas’’, ends at the position of the medium height single B peak that comes from some boron contamination. In the middle of the SiO2 layer, another smaller B peak is observed. It corresponds to the molecular bonding of the two SOI samples. The third medium height B peak points to the end of the SiO2 layer. The thickness of this SiO2 layer has been evaluated by TEM to be 54 nm. The second Si layer, containing the normal B deltas ends with a small B contamination single peak, locating the SOI oxide interface. TEM images give as thickness 174.5 and 183 nm for the ‘‘inverted’’ and ‘‘normal’’ multi-B deltas-doped Si layers. From these TEM measurements, it is easy to scale the SIMS depth profile correctly. Distances between each pair of boron peaks were targeted to be 15 nm. However, SIMS measurements reveal a not constant spacing of 16 2 nm. This discrepancy of 10% is supposed to come from the deposition tool. The background at 8 1018 atoms/ cm3 that limits the dynamic range is due to a slight mass flow controller dysfunction during the growth process. Fig. 2 shows the SIMS analyses performed using both instruments of the inverted B doped Si layer. It is important to note that the primary beam density is higher with the IMS Wf, halving the analysis time compared with the IMS 5f. From this figure, IMS 5f
and IMS Wf give the same B depth profiles. Peaks positions are identical and peak heights are similar. The closest peaks are not distinct but the SIMS resolution is adequate to differentiate B deltas 2 nm apart. The other peaks are easily separable with Si spacing ranging in SIMS from 3.5 up to 7.5 nm. Boron layer positions were independently determined by TEM. The distances between two B peaks of the same pair are measured at 0.8, 2.05, 3.4, 4.8 and 7.37 nm, which is close to the SIMS results and the targeted values: 1, 2, 3, 5 and 8 nm. In Fig. 3, a detailed comparison between IMS 5f and IMS Wf is carried out by means of the B peaks separated by 8 nm of Si. These peaks are located in the B double delta structure at 76.1, 83.6, 318 and 325.5 nm. The extracted FWHM and ld are summarized in Table 1. For the same machine, peaks at 76.1 and 83.6 nm are similar. However, IMS 5f results are about 10% better than the IMS Wf ones. For peaks at 318 and 326 nm, values are very close to each other (differences below 3%) for a given equipment. IMS 5f is also better than Wf, especially as far as ld is concerned. By comparing the evolution of these parameters as a function of the depth, a broadening occurs for deep peaks. The FWHM increases with both equipments, but the increase is lower for the IMS Wf (20%) than for the IMS 5f (33%). However, ld is stable for the IMS 5f while there is a 30% increase with the IMS Wf. Evolution of the IMS Wf can be judged as normal considering the depth, the charge
B concentration (at/cm3)
1021
1020
1019
Ims 5f
Ims Wf 10
18
70
90
110
130
150
170
Depth (nm) Fig. 2. Boron depth profiles in the ‘‘inverted’’ B doped Si layer obtained with both equipments.
F. Laugier et al. / Applied Surface Science 231–232 (2004) 668–672
Backside 30
671
Frontside 30
30
30
25
25
25
Fit 25
Data
20
20
20
15
15
15
15
10
10
10
10
5
5
5
5
B concentration (at/cm3) x 1019
20
0
0 74
76
nm
78
81
80
83
nm
85
87
0 316
318
nm
320
322
0 324
30
30
30
30
25
25
25
25
20
20
20
20
15
15
15
15
10
10
10
10
5
5
5
5
0
0 74
76
nm
78
80
81
83
nm
85
87
0 316
318
nm
320
322
0 324
Ims 5f
326
nm
328
330
Ims Wf
326
nm
328
330
Fig. 3. Comparison between the front side (right) and back side (left) depth profiles for the IMS 5f (up) and IMS Wf (down).
Table 1 FWHM and ld calculated from the IMS 5f and IMS Wf depth profiles on the B peaks separated by 8 nm of Si Peak position (nm)
FWHM IMS 5f (nm)
FWHM IMS Wf (nm)
ld IMS 5f (nm)
ld IMS Wf (nm)
76.1 83.6 318 325.5
1.75 1.79 2.43 2.36
2.03 2.06 2.48 2.46
0.88 0.90 0.86 0.89
1 1.02 1.29 1.29
compensation required and the particular structure of the sample with the bonding. The degradation of the FWHM and the slight reduction of dynamic range without any variation for the ld value is more problematic for the IMS 5f. The acquisition time could be a new parameter to take into account. At 500 eV, the primary current density is low for the IMS 5f. This implies a low sputtering rate for the IMS 5f (1 nm/ min) compared to the IMS Wf (2.2 nm/min). Analysis time is too long. As a consequence, the sample surface roughness in the crater may increase. An other possibility is a difference between the incidence angles. By matching the Gaussian broadening parameter s of the Wf peak profiles for the backside and the front side B deltas, it is possible to check the quality,
especially the sharpness, of boron deltas. We can also, for the first time, separate the contributions coming from the actual boron delta growth process and from the SIMS profiling. s is found to be 0:6 0:03 nm in the backside and 0:65 0:03 nm in the front side. This indicates a 10% dissymmetry in boron concentration slopes, which are nevertheless very sharp. In addition, s results, when compared to ld, prove that the trailing edges are only due to the SIMS tool.
5. Conclusion The IMS Wf SIMS apparatus has been compared at low energy with the IMS 5f for boron depth profiling.
672
F. Laugier et al. / Applied Surface Science 231–232 (2004) 668–672
Depth resolution parameters are very close to each other, but the highest primary beam density of Wf, that reduces by a factor of two the analysis time, is a real advantage. We have analyzed in sequence B multideltas in Si in the growth direction as well as in the opposite direction instead of classical measure in the opposite direction to the growth only. From this complementary B depth profiling, it has been possible to check the quality of boron delta layers and to separate the SIMS contribution from the boron growth conditions.
Acknowledgements This work has been carried out in the frame of CCMC consortium between CEA-LETI, ST Micro-
electronics and FRANCE TELECOM-R&D. The authors would like to thank Franc¸ois Desse (Cameca) for his helpful advice in tuning the Wf electron gun and Geoffroy Auvert (STMicroelectronics) for valuable discussions. References [1] M.G. Dowsett, G. Rowlands, P.N. Allen, R.D. Barlow, Surf. Interf. Anal. 21 (1994) 310. [2] N. Baboux, J.C. Dupuy, G. Prudon, P. Holliger, F. Laugier, A.M. Papon, J.M. Hartmann, J. Cryst. Growth 245 (2002) 1–8. [3] H. Moriceau, B. Aspar, M. Bruel, A.M. Cartier, C. Morales, A. Sousbie, in: P.L. Hemment (Ed.), Proceedings of the Silicon on Insulator: Technology and Devices IX, Electro-Chemical Society, 1999, pp. 173–178. [4] B. Gautier, G. Prudon, J.C. Dupuy, Surf. Interf. Anal. 26 (1998) 974.