- Email: [email protected]
Ion channeling study of cavities in silicon formed by He implantation
Nuclear Instruments and Methods in Physics Research B 127/128 (1997) 379-382
W,W EISEVIER
Ion channeling study of cavities in silicon formed by He implantation R. Moons
*,
W. Deweerd ‘, H. Pattyn, A. Vantomme *, G. Lmgouche
Instituut voor Kern- en Stralingsfysica, K.U. Lewen, Celestijnenlaan 200 D, B-3001 Leuuen, Belgium
Abstract Cavities formed by desorption of He implantation in Si are studied by Rutherford backscattering and channeling spectrometry. Whereas axial channeling is better to determine the depth profile of the defects, planar channeling is more suited to locate the position of the cavities. Measurements as a function of scattering angle show that a large scattering angle is more sensitive to reveal the lattice disorder. Energy-dependent dechanneling measurements indicate an energy-independent behavior in the depth region where only cavities are present. At larger depths, the dechanneling cross section is inversely proportional to the analysing energy.
1. Introduction Metallic impurities, more than extended defects, greatly degrade the performance of semiconductor devices [l]. In particular, the transition metals and their silicides can be extremely detrimental, even at very dilute concentrations. Highly controlled and efficient get&ring therefore becomes crucial for sub-micron ULSI processing. In this context, nanosized voids in c-Si have been demonstrated to be a powerful and promising technique for the proximity gettering of transition metal impurities [2-51. The most important advantage of this gettering process is that it can be controllably induced in a well-defined region of the wafer and at the same time provide highly efficient gettering. Rutherford backscattering and channeling spectrometry (RBS-C) have been used to analyse and depth-profile these cavities [6,7] and to determine the amount of impurities present in the gettering sites [8]. Recently, an RBS-C study was performed on the influence of nanosized voids on the formation of a buried CoSi, layer [7]. The aim of the present work is to highlight the specific features of the RBS-C analysis and the characteristics of cavities as defects in silicon.
2. Experimental The substrates consist of float zone n-type (111) oriented Si with p = 4000 Q cm and a thickness of 380 pm.
* Correspondingauthor. Tel.: +32 16 32 75 14, fax: f32 16 e-mail: [email protected]. ’ Research Assistant NFWO (National Fund for Scientific Re-
32 79 85,
search, Belgium). * Postdoctoral Researcher NFWO (National Fund for Scientific Research, Belgium).
All He implantations were performed at room temperature under an angle of 7” off axis to minimize channeling effects. Subsequently, the samples were annealed in a UHV furnace at 973 K for 30 min, the pressure being kept below 5 X 10m9 Tot-r, resulting in desorption of the He [9]. By monitoring the desorption of the implanted He and by observing the nanosized voids with TEM, we ascertain that empty cavities are left in the silicon. RBS-C experiments were performed on all studied samples, using a 1.7 MV SSDH-2 pelletron producing a He beam collimated within 0.05”. To facilitate comparison of the spectra to projected range values as calculated with the TRIM simulation code [lo] and to facilitate comparison of spectra using various experimental conditions (beam energy, scattering angle, . . . ), the energy axis of all backscattering spectra was converted to a depth axis. The modification of the Si density, due to the presence of cavities, was taken into account when calculating the depth scale.
3. Results and discussion 3.1. Density correction In order to produce a relatively thick (= 400 nm) and homogeneous void layer, He was implanted in four steps as illustrated in Table 1. Fig. 1 shows the depth-profiled RBS-C spectrum after desorption, where the backscattered yield was normalized to random. The channeled spectrum clearly indicates a gradual increase of the dechanneling as a function of depth, with small, localized, direct scattering peaks at depths corresponding to the TRIM calculated mean projected ranges from Table 1. This direct scattering contribution is attributed to point defects, resulting from the implantation and the concurrent bubble formation. On the other hand, extended defects such as cavities give rise
0168-583X/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved. PII SO1 68-583X(96)00961 -5
IIIa. PROCESSING ELECTRONIC MATERIALS
380
R. Moons et al./Nucl.
Instr. and Meth. in Phys. Res. B 127/ 128 (1997) 379-382
Table 1 He implantation parameters for a (111) oriented float zone Si
sample. The local He concentration lies between 6 and 8 at.% over a range of more than 400 nm Fluence [He/cm* I Energy [IreV] Mean projectedrange [nm] a 5x 5x 5x 8x
10’6 10’6 10’6 lOI
16 30 50 80
169f90 278* 110 4O9f 130 560* 145
aAccording to TRIM calculations [ 101.
0.0 0
50
109
150
200
250
300
350
400
Depth (nm)
to lattice distortions which have the effect of increasing the dechanneling rate [ 111. Ion channeling studies [7] show that the direct scattering peak disappears while the dechanneling contribution of the dechanneling yield remains when all point damage is annealed out. The dechanneled fraction is a monotonically increasing function of penetration depth because ions, once dechanneled, remain so. Hence, the dechanneled fraction at a given depth is related to the total number of defects encountered in reaching that depth. The conversion from energy to depth scale was realized using a reduced atomic density, due to the presence of the cavities. Using this density, obtained by decreasing the bulk density with a factor equal to the cavity concentration (e.g. 7% at d = 300 nm) at the corresponding depth, the direct scattering peaks correspond to ranges as calculated by TRIM. If the energy-to-depth conversion would be realized with the normal silicon density of 5 X 10” atoms/cm3, one would locate the direct scattering peaks too close to the sample’s surface. 3.2. Planar versus axial channeling Both axial and planar channeling were performed on a Si sample implanted with 1 X 10” He/cm2 at 30 keV, for
Fig. 2. (+) Random, (X) (110) planar channeled and (0) (11 I> axial channeled spectra after depth-profiling an RBS-C experiment recorded with a 1.97 MeV He++ beam and a detector at 8 = 172”.
which a mean projected range of (278 + 110) nm is obtained with TRIM. As can be derived from Fig. 2, the cavities produce a broad band of defects giving rise to an increase in the (110) planar channeling backscattering yield starting from a depth of 12.5 nm and saturating around 175 nm. The ( 111) axial channeled spectrum shows, originating at 150 nm, an increasing dechanneling yield after which a direct scattering peak is observed at 275 nm. These values are consistent with TRIM calculations. We note that (110) planar channeling is much more sensitive to the presence of the cavities, which makes it more suited to locate rather low defect concentrations. The reason for this is that the critical angle for planar channeling is 2.7 times smaller than for axial channeling, resulting in a higher dechanneling probability for He ions propagating in a defect zone. On the other hand, the axial channeling spectrum does not show a saturation after the direct scattering peak, which makes it more suited for depth-profiling the lattice disorder. Axial channeling reveals an asymmetric distribution of the dechanneling yield, indicating an asymmetric distribution of the formed cavities around a depth equal to the mean projected range value. While cavities are already present at a depth of 125 nm, they are not formed at 370 nm. These observations are in good agreement with XTBM studies [4] on samples implanted and annealed under similar conditions. 3.3. Dependence on scattering angle
Depth (nm)
Fig. I. 1.97 MeV He+’ depth-profiled backscattering spectra with (+) random and (0) (I1 1) aligned beam incidence. The scattering angle of the detected particles is 0 = 172”. The arrows indicate the mean projected range of the implantation, as cakelated by TRIM.
To study the influence of the dechanneling on the scattering angle a silicon sample was implanted with a fluence of 1.5 x 10” He/cm* at 95 keV. The calculated mean projected range of the He was (614 + 142) nm [ 101. After desorption ( 111) axial channeling measurements were performed by collecting the backscattered He particles simultaneously with two detectors with a solid angle fl = 0.8”. Scattering angles of 8 - 172” and 6 = 110” re-
381
R. Moons et al./Nucl. Instr. and Meth. in Phys. Res. B 127/ 128 (1997) 379-382
$
0.3
> P z!! 0.2 g z
0.1
0.0
0
loo
200
300
400
ml
600
709
800
0
50
100
Fig. 3. ( 6) Random and ( 111)axial channeling spectra measured with a 1.97 MeV He++ beam with a detector located at (X) 0 = 172” and (0) 0 = 110”. The distinct peaks (in 0 = 110 geometry) at 320 and 5 15 nm respectively, correspond to 0 and C surface contaminations which due to their low kinematic factor ate detected on top of the Si signal.
spectively, were chosen to exclude double alignment effects. As Fig. 3 indicates, a striking difference between spectra taken at large and small scattering angle is observed: the former scattering geometry reveals far better the increased dechanneling due to the presence of the cavities. Indeed, in the spectrum recorded at 0 = 172”, one notices a drastically increased dechanneling yield starting around 400 nm and saturating around 620 nm. On the other hand, the spectrum recorded with the detector located at B = 110” does not reveal any dechanneling but it shows some discrete peaks on the aligned Si signal. These peaks can be attributed to 0 and C surface contaminations, which find their origin in the He implantation. These implantation-related artifacts are not observed in the large-angle scattering geometry due to a smaller path length and an inferior effective scattering cross section. The reason for the strikingly different cavity-related dechanneling behavior is unclear up to now. 3.4. Energy-dependent
200
250
300
Fig. 4. (1 II) axial channeling spectra on the self-implanted Si sample measured with a (0) I.02 MeV He+ and a (X) 1.97 MeV He++ beam. The detector was positioned at 8 = 125”.
planting 1 X 10” He/cm* at 30 keV and subsequent desorption. Channeling measurements were performed using a 1.02 MeV He+ and a 1.97 MeV He++ collimated beam. From Fig. 4 it is clear that decreasing the energy of the analysing He beam, results in an increase of the dechanneling yield. This relationship is characteristic for randomly displaced atoms (cza E-‘) [15] or interstitials (aa,!?‘/*) [15] which both can be introduced by the self-implantation. This energy dependence is different from the sample containing cavities, as shown in Fig. 5. The presence of cavities results in a gradually increasing dechanneling yield starting from 150 to 270 nm after which a direct scattering peak is observed. The energy-independent dechanneling behavior is characteristic for cavity-like defects [ 151, which make us conclude that between 150 and 270 nm cavities are the main defect. At and after the direct scattering peak the dechanneling cross section becomes inversely proportional to the analysing energy, which indicates the presence of similar defects as observed in the self-implanted sample. Note that, at these deeper
dechanneling
It has been generally acknowledged that it is possible to deduce information about the nature of defects from the energy dependence of the dechanneling cross section [ 121. However, the superposition of direct scattering and dechanneling components is difficult to separate, making it hard to retrieve quantitative analysis. Nevertheless, this technique can be used to identify qualitatively defects which exhibit dechanneling cross sections (a) with different energy dependences [ 13,141. In order to distinguish between cavities and other defects, both a self-implanted sample and a He-implanted sample was investigated. The former sample was self-implanted with a dose of 5 X 1Or4 Si/cm*, well below the amorphisation dose, at 60 keV, which results in a mean projected range of (67 f 22) nm [lo]. In the latter sample, cavities were produced by im-
150
Depth (nm)
Depth (nm)
0.6
p $
0.4
p
0.3
I
I
0
100
,
,
I
g g
0.2
z 0.1
0.0
2ml
3w
400
Depth (nm)
Fig. 5. (Ill> axial channeling spectra on the sample containing cavities. Spectra were measured with a detector at 8 = 125” and an analysing beam of (0) 1.02 MeV He+ and (X) I .97 MeV
He++. IIIa. PROCESSINGELECTRONICMATERIALS
382
R. Moons et al./Nucl.
Insrr. and Meth. in Phys. Res. B 127/128
depths, one cannot exclude the presence of cavities, because their energy-independent contribution is obscured by an energy-dependent contribution from other defects like interstitials and randomly displaced atoms. 4. Summary In summary, the RBS-C technique was applied to characterize cavities in silicon. Axial channeling is more appropriate to locate the depth of the direct scattering peak, which agrees with the mean projected range as calculated by TRIM if density corrections are taken into account. Channeling analysis under large scattering angle geometry shows far better the increase in the dechanneling yield, which can be attributed to the presence of cavities. Further, we showed that energy-dependent dechanneling experiments are able to reveal an energy-independent dechanneling behavior in the region where only cavities are present. References [I] K. Graff, Metal Impurities (Springer, Berlin-Heidelberg. [2] SM. Myers, D.M. Follstaedt Sot. Symp. Proc. 316 (1994)
in Silicon-Device Fabrication 1995). and D.M. Bishop, Mater. Res. 27.
(1997) 379-382
[3] W. Deweerd, R. Moons, J. Verheyden, S. Bukshpan, G. Langoucbe and H. Pattyn, Nucl. lnstr. and Meth. B 106 (1995) 252. ]41 SM. Myers and D.M. Follstaedt, J. Appl. Phys. 79 (1996) 1337. bl V. Raineri, P.G. Fallica, G. Percolla. A. Battaglia, M. Barbagallo and S.U. Campisano, J. Appl. Phys. 78 (1995) 3727. (‘51B. Mohadjeri, J.S. Williams and J. Wong-Leung, Appl. Phys. Lett. 66 (1995) 1889. 171 W. Deweerd, R. Moons, J. Verheyden, K. Milants, G. Langauche and H. Pattyn, Appl. Phys. L&t. 69 (1996) 3584. Bl V. Raineri, A. Battaglia and E. Rimini, Nucl. Instr. and Meth. B 96 (1995) 249. [91 CC. Grifficen, J.H. Evans, P.C. de Jong and A. van Veen, Nucl. Instr. and Meth. B 27 (1987) 417. I101 J.F. Ziegler, J.P. Biersack and U. Littmark, The Stopping and Range of Ions in Solids (Pergamon, New York, 1985). 1111 L.C. Feldman, J.W. Mayer and ST. Picraux, Materials Analysis by Ion Channeling (Academic Press, New York, 1982) p. 108. [121 Y. QuCrC,Radiat. Eff. 28 (1976) 253. [131 M.F. Wu, D. Schroyen, H. Pattyn and G. Langouche, Nucl. Instr. and Meth. 218 (1983) 652. [14] S.T. Picraux, D.M. Follstaedt, P. Baeri, S.U. Campisano, G. Foti and E. Rimini, Radiat. Eff. 49 (1980) 75. [15] J.S. Williams and R.G. Elliman, in: Ion Beams for Materials Analysis, eds. J.R. Bird and J.S. Williams (Academic Press, Sydney, 1989) p. 283.
W,W EISEVIER
Ion channeling study of cavities in silicon formed by He implantation R. Moons
*,
W. Deweerd ‘, H. Pattyn, A. Vantomme *, G. Lmgouche
Instituut voor Kern- en Stralingsfysica, K.U. Lewen, Celestijnenlaan 200 D, B-3001 Leuuen, Belgium
Abstract Cavities formed by desorption of He implantation in Si are studied by Rutherford backscattering and channeling spectrometry. Whereas axial channeling is better to determine the depth profile of the defects, planar channeling is more suited to locate the position of the cavities. Measurements as a function of scattering angle show that a large scattering angle is more sensitive to reveal the lattice disorder. Energy-dependent dechanneling measurements indicate an energy-independent behavior in the depth region where only cavities are present. At larger depths, the dechanneling cross section is inversely proportional to the analysing energy.
1. Introduction Metallic impurities, more than extended defects, greatly degrade the performance of semiconductor devices [l]. In particular, the transition metals and their silicides can be extremely detrimental, even at very dilute concentrations. Highly controlled and efficient get&ring therefore becomes crucial for sub-micron ULSI processing. In this context, nanosized voids in c-Si have been demonstrated to be a powerful and promising technique for the proximity gettering of transition metal impurities [2-51. The most important advantage of this gettering process is that it can be controllably induced in a well-defined region of the wafer and at the same time provide highly efficient gettering. Rutherford backscattering and channeling spectrometry (RBS-C) have been used to analyse and depth-profile these cavities [6,7] and to determine the amount of impurities present in the gettering sites [8]. Recently, an RBS-C study was performed on the influence of nanosized voids on the formation of a buried CoSi, layer [7]. The aim of the present work is to highlight the specific features of the RBS-C analysis and the characteristics of cavities as defects in silicon.
2. Experimental The substrates consist of float zone n-type (111) oriented Si with p = 4000 Q cm and a thickness of 380 pm.
* Correspondingauthor. Tel.: +32 16 32 75 14, fax: f32 16 e-mail: [email protected]. ’ Research Assistant NFWO (National Fund for Scientific Re-
32 79 85,
search, Belgium). * Postdoctoral Researcher NFWO (National Fund for Scientific Research, Belgium).
All He implantations were performed at room temperature under an angle of 7” off axis to minimize channeling effects. Subsequently, the samples were annealed in a UHV furnace at 973 K for 30 min, the pressure being kept below 5 X 10m9 Tot-r, resulting in desorption of the He [9]. By monitoring the desorption of the implanted He and by observing the nanosized voids with TEM, we ascertain that empty cavities are left in the silicon. RBS-C experiments were performed on all studied samples, using a 1.7 MV SSDH-2 pelletron producing a He beam collimated within 0.05”. To facilitate comparison of the spectra to projected range values as calculated with the TRIM simulation code [lo] and to facilitate comparison of spectra using various experimental conditions (beam energy, scattering angle, . . . ), the energy axis of all backscattering spectra was converted to a depth axis. The modification of the Si density, due to the presence of cavities, was taken into account when calculating the depth scale.
3. Results and discussion 3.1. Density correction In order to produce a relatively thick (= 400 nm) and homogeneous void layer, He was implanted in four steps as illustrated in Table 1. Fig. 1 shows the depth-profiled RBS-C spectrum after desorption, where the backscattered yield was normalized to random. The channeled spectrum clearly indicates a gradual increase of the dechanneling as a function of depth, with small, localized, direct scattering peaks at depths corresponding to the TRIM calculated mean projected ranges from Table 1. This direct scattering contribution is attributed to point defects, resulting from the implantation and the concurrent bubble formation. On the other hand, extended defects such as cavities give rise
0168-583X/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved. PII SO1 68-583X(96)00961 -5
IIIa. PROCESSING ELECTRONIC MATERIALS
380
R. Moons et al./Nucl.
Instr. and Meth. in Phys. Res. B 127/ 128 (1997) 379-382
Table 1 He implantation parameters for a (111) oriented float zone Si
sample. The local He concentration lies between 6 and 8 at.% over a range of more than 400 nm Fluence [He/cm* I Energy [IreV] Mean projectedrange [nm] a 5x 5x 5x 8x
10’6 10’6 10’6 lOI
16 30 50 80
169f90 278* 110 4O9f 130 560* 145
aAccording to TRIM calculations [ 101.
0.0 0
50
109
150
200
250
300
350
400
Depth (nm)
to lattice distortions which have the effect of increasing the dechanneling rate [ 111. Ion channeling studies [7] show that the direct scattering peak disappears while the dechanneling contribution of the dechanneling yield remains when all point damage is annealed out. The dechanneled fraction is a monotonically increasing function of penetration depth because ions, once dechanneled, remain so. Hence, the dechanneled fraction at a given depth is related to the total number of defects encountered in reaching that depth. The conversion from energy to depth scale was realized using a reduced atomic density, due to the presence of the cavities. Using this density, obtained by decreasing the bulk density with a factor equal to the cavity concentration (e.g. 7% at d = 300 nm) at the corresponding depth, the direct scattering peaks correspond to ranges as calculated by TRIM. If the energy-to-depth conversion would be realized with the normal silicon density of 5 X 10” atoms/cm3, one would locate the direct scattering peaks too close to the sample’s surface. 3.2. Planar versus axial channeling Both axial and planar channeling were performed on a Si sample implanted with 1 X 10” He/cm2 at 30 keV, for
Fig. 2. (+) Random, (X) (110) planar channeled and (0) (11 I> axial channeled spectra after depth-profiling an RBS-C experiment recorded with a 1.97 MeV He++ beam and a detector at 8 = 172”.
which a mean projected range of (278 + 110) nm is obtained with TRIM. As can be derived from Fig. 2, the cavities produce a broad band of defects giving rise to an increase in the (110) planar channeling backscattering yield starting from a depth of 12.5 nm and saturating around 175 nm. The ( 111) axial channeled spectrum shows, originating at 150 nm, an increasing dechanneling yield after which a direct scattering peak is observed at 275 nm. These values are consistent with TRIM calculations. We note that (110) planar channeling is much more sensitive to the presence of the cavities, which makes it more suited to locate rather low defect concentrations. The reason for this is that the critical angle for planar channeling is 2.7 times smaller than for axial channeling, resulting in a higher dechanneling probability for He ions propagating in a defect zone. On the other hand, the axial channeling spectrum does not show a saturation after the direct scattering peak, which makes it more suited for depth-profiling the lattice disorder. Axial channeling reveals an asymmetric distribution of the dechanneling yield, indicating an asymmetric distribution of the formed cavities around a depth equal to the mean projected range value. While cavities are already present at a depth of 125 nm, they are not formed at 370 nm. These observations are in good agreement with XTBM studies [4] on samples implanted and annealed under similar conditions. 3.3. Dependence on scattering angle
Depth (nm)
Fig. I. 1.97 MeV He+’ depth-profiled backscattering spectra with (+) random and (0) (I1 1) aligned beam incidence. The scattering angle of the detected particles is 0 = 172”. The arrows indicate the mean projected range of the implantation, as cakelated by TRIM.
To study the influence of the dechanneling on the scattering angle a silicon sample was implanted with a fluence of 1.5 x 10” He/cm* at 95 keV. The calculated mean projected range of the He was (614 + 142) nm [ 101. After desorption ( 111) axial channeling measurements were performed by collecting the backscattered He particles simultaneously with two detectors with a solid angle fl = 0.8”. Scattering angles of 8 - 172” and 6 = 110” re-
381
R. Moons et al./Nucl. Instr. and Meth. in Phys. Res. B 127/ 128 (1997) 379-382
$
0.3
> P z!! 0.2 g z
0.1
0.0
0
loo
200
300
400
ml
600
709
800
0
50
100
Fig. 3. ( 6) Random and ( 111)axial channeling spectra measured with a 1.97 MeV He++ beam with a detector located at (X) 0 = 172” and (0) 0 = 110”. The distinct peaks (in 0 = 110 geometry) at 320 and 5 15 nm respectively, correspond to 0 and C surface contaminations which due to their low kinematic factor ate detected on top of the Si signal.
spectively, were chosen to exclude double alignment effects. As Fig. 3 indicates, a striking difference between spectra taken at large and small scattering angle is observed: the former scattering geometry reveals far better the increased dechanneling due to the presence of the cavities. Indeed, in the spectrum recorded at 0 = 172”, one notices a drastically increased dechanneling yield starting around 400 nm and saturating around 620 nm. On the other hand, the spectrum recorded with the detector located at B = 110” does not reveal any dechanneling but it shows some discrete peaks on the aligned Si signal. These peaks can be attributed to 0 and C surface contaminations, which find their origin in the He implantation. These implantation-related artifacts are not observed in the large-angle scattering geometry due to a smaller path length and an inferior effective scattering cross section. The reason for the strikingly different cavity-related dechanneling behavior is unclear up to now. 3.4. Energy-dependent
200
250
300
Fig. 4. (1 II) axial channeling spectra on the self-implanted Si sample measured with a (0) I.02 MeV He+ and a (X) 1.97 MeV He++ beam. The detector was positioned at 8 = 125”.
planting 1 X 10” He/cm* at 30 keV and subsequent desorption. Channeling measurements were performed using a 1.02 MeV He+ and a 1.97 MeV He++ collimated beam. From Fig. 4 it is clear that decreasing the energy of the analysing He beam, results in an increase of the dechanneling yield. This relationship is characteristic for randomly displaced atoms (cza E-‘) [15] or interstitials (aa,!?‘/*) [15] which both can be introduced by the self-implantation. This energy dependence is different from the sample containing cavities, as shown in Fig. 5. The presence of cavities results in a gradually increasing dechanneling yield starting from 150 to 270 nm after which a direct scattering peak is observed. The energy-independent dechanneling behavior is characteristic for cavity-like defects [ 151, which make us conclude that between 150 and 270 nm cavities are the main defect. At and after the direct scattering peak the dechanneling cross section becomes inversely proportional to the analysing energy, which indicates the presence of similar defects as observed in the self-implanted sample. Note that, at these deeper
dechanneling
It has been generally acknowledged that it is possible to deduce information about the nature of defects from the energy dependence of the dechanneling cross section [ 121. However, the superposition of direct scattering and dechanneling components is difficult to separate, making it hard to retrieve quantitative analysis. Nevertheless, this technique can be used to identify qualitatively defects which exhibit dechanneling cross sections (a) with different energy dependences [ 13,141. In order to distinguish between cavities and other defects, both a self-implanted sample and a He-implanted sample was investigated. The former sample was self-implanted with a dose of 5 X 1Or4 Si/cm*, well below the amorphisation dose, at 60 keV, which results in a mean projected range of (67 f 22) nm [lo]. In the latter sample, cavities were produced by im-
150
Depth (nm)
Depth (nm)
0.6
p $
0.4
p
0.3
I
I
0
100
,
,
I
g g
0.2
z 0.1
0.0
2ml
3w
400
Depth (nm)
Fig. 5. (Ill> axial channeling spectra on the sample containing cavities. Spectra were measured with a detector at 8 = 125” and an analysing beam of (0) 1.02 MeV He+ and (X) I .97 MeV
He++. IIIa. PROCESSINGELECTRONICMATERIALS
382
R. Moons et al./Nucl.
Insrr. and Meth. in Phys. Res. B 127/128
depths, one cannot exclude the presence of cavities, because their energy-independent contribution is obscured by an energy-dependent contribution from other defects like interstitials and randomly displaced atoms. 4. Summary In summary, the RBS-C technique was applied to characterize cavities in silicon. Axial channeling is more appropriate to locate the depth of the direct scattering peak, which agrees with the mean projected range as calculated by TRIM if density corrections are taken into account. Channeling analysis under large scattering angle geometry shows far better the increase in the dechanneling yield, which can be attributed to the presence of cavities. Further, we showed that energy-dependent dechanneling experiments are able to reveal an energy-independent dechanneling behavior in the region where only cavities are present. References [I] K. Graff, Metal Impurities (Springer, Berlin-Heidelberg. [2] SM. Myers, D.M. Follstaedt Sot. Symp. Proc. 316 (1994)
in Silicon-Device Fabrication 1995). and D.M. Bishop, Mater. Res. 27.
(1997) 379-382
[3] W. Deweerd, R. Moons, J. Verheyden, S. Bukshpan, G. Langoucbe and H. Pattyn, Nucl. lnstr. and Meth. B 106 (1995) 252. ]41 SM. Myers and D.M. Follstaedt, J. Appl. Phys. 79 (1996) 1337. bl V. Raineri, P.G. Fallica, G. Percolla. A. Battaglia, M. Barbagallo and S.U. Campisano, J. Appl. Phys. 78 (1995) 3727. (‘51B. Mohadjeri, J.S. Williams and J. Wong-Leung, Appl. Phys. Lett. 66 (1995) 1889. 171 W. Deweerd, R. Moons, J. Verheyden, K. Milants, G. Langauche and H. Pattyn, Appl. Phys. L&t. 69 (1996) 3584. Bl V. Raineri, A. Battaglia and E. Rimini, Nucl. Instr. and Meth. B 96 (1995) 249. [91 CC. Grifficen, J.H. Evans, P.C. de Jong and A. van Veen, Nucl. Instr. and Meth. B 27 (1987) 417. I101 J.F. Ziegler, J.P. Biersack and U. Littmark, The Stopping and Range of Ions in Solids (Pergamon, New York, 1985). 1111 L.C. Feldman, J.W. Mayer and ST. Picraux, Materials Analysis by Ion Channeling (Academic Press, New York, 1982) p. 108. [121 Y. QuCrC,Radiat. Eff. 28 (1976) 253. [131 M.F. Wu, D. Schroyen, H. Pattyn and G. Langouche, Nucl. Instr. and Meth. 218 (1983) 652. [14] S.T. Picraux, D.M. Follstaedt, P. Baeri, S.U. Campisano, G. Foti and E. Rimini, Radiat. Eff. 49 (1980) 75. [15] J.S. Williams and R.G. Elliman, in: Ion Beams for Materials Analysis, eds. J.R. Bird and J.S. Williams (Academic Press, Sydney, 1989) p. 283.