- Email: [email protected]
Identification of EOR defects due to the regrowth of amorphous layers created by ion bombardment
Nuclear Instruments North-Holland
and Methods
in Physics
Research
B 84 (1994) 190-194
NW B
Beam Interactions with Materials 8 Atoms
Identification of EOR defects due to the regrowth of amorphous layers created by ion bombardment B. de Mauduit a, L. Lahab a CEMES - LOE/CNRS, B.P. 4347, b LAAS/CNRS,
a, C. Bergaud b, M.M. Faye a, A. Martinez b and A. Claverie a
31055 Toulouse Cedex, France 7 avenue du Colonel Roche, 31077 Toulouse Cedex, France
In this paper TEM investigations have been carried out on typical EOR defects found in Ge-amorphized (001) wafers (Ge + Si, 150 keV, 2X1015 ions/cm’) after thermal annealing (RTA, looo”C, 10 s). These defects consist of medium sized (lo-50 nm) dislocation loops that have been characterized by conventional electron microscopic techniques. Most of them ( - 75%) are circular faulted Frank loops with b = a/3(111) vectors. The remaining ( - 25%) loops are perfect elongated hexagon-shaped loops: they have nearly (111) habit planes, with b = a /2( 101) vectors. Hence, it is possible to deduce from only one TEM image the number of Si atoms available in the loops as well as the density of the loops for different implantation or annealing conditions. This is needed for optimization of process conditions.
1. Introduction The formation of amorphous layers by ion bombardment prior to the introduction of a dopant or any other chemical impurity has several advantages over direct implantation in semiconductors. A preamorphization step eliminates channelling problems and results in abrupt dopant profiles [l]. More generally, the fact that the incorporation of the dopant or the formation of some alloy (like SiGe) occurs during annealing through the solid phase epitaxial (SPE) regrowth of the u-layer is desirable because defect-free
regrown layers can be obtained with required stoichiometry and electrical characteristics in most cases [2]. By contrast, it is well known that after SPE regrowth, structural defects are formed beneath the former c/a interface. These defects have received the strange name of “EOR” - end-of-range defects. EOR defects are the only disadvantage of this technique because they are known to dramatically affect impurity diffusion [3] and also to be responsible for the leakage current when situated in a space-charge region of a device. However, for the mastering of the so-called preamorphization technique, a better knowledge of
Fig. 1. Weak-beam image of both circular and elongated EOR loops seen near a [108] beam direction B using g = OaO, with positive s corresponding to a (g, 2g) condition. Loops in a variety of orientations are labelled according to the notation in table 1.
0168-583X/94/$07.00 0 1994 - Elsevier SSDI 0168-583X(93)E0371-M
Science
B.V. All rights reserved
B. de Mauduit et al. / Identification of EOR defects
191
Table 1 Conventions for notation of the four faulted Frank and 12 perfect prismatic loop families with corresponding
Ig. b 1 values
b
Plane
g
040
220
520
3TT
iI1
131
3ii
1/3[1111 1/3fiili
till) (ill)
Fl FQ
4/3 4/3
4/3 0
0 4/3
l/3 5/3
l/3 1
5/3 1
1 1
1/3ilil] 1/3[liii
(iii) (lli) (lllf
F3 F4 D:
4/3 4/3
0 4/3
4/3 0
1 1
l/3 l/3
l/3 1
l/3 5/3
2
1
1
1
1
2
0
1/2[101]
(ill) (111) (iii)
;; D:
0
1
1
1
0
1
1
1/2[0111
(111) (iii)
Di Dd
2
2
0
1
0
2
2
1/2[oill
(iii) (iii)
D: D44
2
1
1
0
0
1
1
i/ziioli
fill) flli)
D: D45
0
1
1
2
1
0
2
(ill)
D$
2
0
2
2
1
1
1
(iii)
D36
1/2[011]
l/zfilol
these defects is required. In a previous paper [4], we have shown that, most probably, these defects are due to the clustering of excess interstitial atoms (due to recoil) left beneath the c/a interface after bombardment The implementation of models able to optimize preamo~hi~ation conditions for minimizing the density of EOR defects and/or to simulate “anomalous” diffusion in these layers, requires a complete, quantitative characterization of these defects. Moreover, recent papers have shown that EOR defects, produced by Si or Ge preamorphization, can be used as efficient point defect detectors. These point defects can be induced by low-dose boron implantation [S] or by thermal oxidation [6]. For these reasons, transmission electron microscopic (TEM) techniques have been used both to determine the vacancy or interstitial nature of the EOR defects and to evaluate the number of single defects included in the EORs for a given set of experimental conditions. This paper briefly presents a complete loop analysis performed on (100) silicon wafers amorphized with 150 keV Ge+ ions at a dose of N 2 X 1015 ions cmw2 and subsequently annealed at 1000°C for 10 s (rapid thermal annealing (RTA) conditions). It is a typical process as currently used for the formation of ultra-shallow p’/n junctions in Si. Defects found in this material consist of medium sized (lo-50 nm) dislocation loops with regular shapes and in suitable concentration for determining their type and habit plane through “weak-beam dark field” (WBDF) imaging.
2. Experimental details and results Cross-sectional TEM was previously performed on this wafer [4] and showed the EOR defects to be located within a thin (w 40 nm thick) layer 170 nm
Fig.-- 2. Stereographic projection of the lower hemisphere with a [118] pole showing g and B used in figs. 1 and 3 when the specimen is tilted as indicated around the X-axis of the goniometer. II. COMPO~D
FORSOOK
192
3. de Mauduit et al. / Identification of EOR defects
beneath the surface, i.e. exactly beneath the former c/a interface resulting from the bombardment. For the experiments presented here, annealed Ge+ implanted (100) Si specimens were thinned for TEM plan-view examination by ion milling from the unimplanted side. Analysis has been restricted to the relatively thick (300 nm) areas of the foil where the loops can be assumed to lie well within the foil. Orientation conventions for self-consistent indexing beam directions B, diffraction vectors g, plane and direction traces on images relative to the effective positions in the specimen are specified in the captions to figs. 2-4. Loops have been analysed using conventional methods developed for (i) perfect dislocation [7-lo] and faulted dislocation [ll] loops when the image is formed using a strongly excited diffracted beam and (ii) small Frank loops [12] when using the WB imaging conditions. These methods (see ref. [13] for more details) are founded on (i) trace analysis to
identify the normal n to the habit plane of the loop, (ii) contrast analysis of images to identify the Burgers vector b, and (iii) the “inside-outside” (I-O) contrast effect to assess the sense of b, i.e. the vacancy or interstitial nature of the loop (the technique depends upon whether or not the image of the loop is “inside” or “outside” the dislocation core). Results are illustrated in the following series of micrographs and diagrams. Complete analysis will be given with more details in a forthcoming paper. AH the loops are shown in fig. 1. Most of them (- 75%) are circular loops and project as ellipses on the image. They are found to be faulted Frank loops with b = a/3( 111) vectors. They are labelled Fl to F4 (cf. table 1). The remaining (N 25%) loops are perfect elongated hexagon-shaped loops: they have nearly {ill} habit planes, with b = a/2( 101) vectors perpendicular to the long axis of the loops (the elongated directions lie in the six possible (110) directions). They are la-
Fig. 3. Contrast analysis of some of the loops shown in fig. 1. B is ciose to [IO81in (a), [liSI in (b) and 6.9, InSI in cd), nearly [Ii41 in (e) and [li2] in (f), (g), (h) and (i). AI1 micrographs are weak-beam images (as seen on the screen) under the following conditions: (g, 2g) in (a), (e), (g), (h), (i); (g, 3g) in (b), (cl, (d) and (-g, 5g) in (19. Compare contrast variation to table 1 and note “inside/outside” effect in (b)/(c) and (h)/(i).
B. de ~au~~it et al. / I~e~tif~atio~ of EUR defects
193
component, provided that b does not project in the angular range defined by the acute angle between B and the trace of the loop (results must be reversed in the opposite case).
3. Concfusion
a
1 (;J.T;)S
b
f;;.%;, szo
The nature and the structural characteristics of dislocations loops known as EOR defects have been unambiguously determined in this paper. The interstitial nature of these defects corresponds to the predictions of simulations [4], i.e. they are due to the agglomeration of Si interstitial atoms, left after bombardment beneath the c/a interface, which survive recombination with the vacancies in the same region. Therefore, their habit planes and Burger vectors have been determined so that it is now possible to deduce from only one TEM image the number of Si atoms available in the loops as well as the density of the loops for different implantation or annealing conditions. These quantitative results will be needed for the optimization of the amo~hization conditions and for the modelling of anomalous diffusion of dopant in semiconductors.
lM
This work was partly supported by the French GCIS and by an EC program (ADEQUAT). Fig. 4. Schematic diagram used to characterize the vacancy or interstitial nature of a prismatic dislocation loop by analysing the “inside-outside” effect observed on the image obtained with g and B. B, and n,, are the projections of the actual Burgers vector b (which may have a shear component) and upward normal n to the plane of the loop in the plane (B, g). “a” refers to the FS/RH definition of b [15] with a clockwise positive direction around the loop as on the screen. “b” refers to an easier definition: n *B> 0 for vacancy loops, n. b < 0 for interstitial loops [16]. The corresponding contrast (heavy line) relative to the core of the dislocation (dashed line) as seen on the screen and the sign of (g .b) are given for both s > 0 and s < 0. The application is illustrated with the case of Fl, F4 and Di, Di loops imaged with g = 220, B = [l?S] and g = 31i, B = 14571,respectively: they are interstitial loops.
belled D: to D-46(cf. table 1). The stereographic projection of fig. 2 shows g and B used for the contrast
anaIysis given in fig. 3. The interstitial nature of both types of loops has been unambiguously determined using the conventional schematic diagram (from ref. [14]) shown in fig. 4. We emphasize that such a diagram can be applied to any prismatic loop with a shear
References
111S.J. Kwon, H.J. Kim and J.D. Lee, Jpn. J. Appl. Phys. 29 (1990) L2326. El J.P. Zhang, R.J. Wilson, P.L.F. Hemment, A. Claverie, F.
Cristiano, P. Salles, J.Q. Wen, J.H. Evans, A.R. Peaker and G.J. Parker, these Proceedings (E-MRS 1993 Spring Meeting, Strasbourg, France, Symposium G: Material Aspects of Ion Beam Synthesis: Phase Formation and Modification) Nucl. Instr. and Meth. B 84 (1994) 222. [31 R.J. Schreutelkamp, J.S. Custer, V. Raineri, W.X. Lu, J.R. Liefting, F.W. Saris, K.T.F. Janssen, P.F.H.M. van der Meulen and R.E. Kaim, Mater. Sci. Eng. B 12 (1992) 307. 141 L. Lalnab, C. Bergaud, M.M. Faye, J. Faure, A. Martinez and A. Claverie, Proc. MRS Boston (1992) in press. 151 J.K. Listebarger, K.S. Jones and J.A. Slinkman, J. Appl. Phys. 73 (1993) 4815. 161 H.L. Meng, S. Prussin, M.E. Law and KS. Jones, J. Appl. Phys. 73 (1993) 955. i71 G.W. Groves and A. Kelly, Philos. Mag. 6 (1961) 1527. (81 D.J. Mazey, R.S. Barnes and A. Howie, Philos. Mag. 7 (1962) 1861. [91 B. Edmonson and G.K. Williamson, Philos. Mag. 9 (1964) 277. DO1 D.M. Maher and B.L. Eyre, Philos. Mag. 23 (1971) 409. II. COMPOUND FORMATION
194
B. de Mauduit et al. / Identification of EOR defects
[ll] W.J. Tunstall, Philos. Mag. 20 (1969) 701. [12] M.L. Jenkins, D.J.H. Cockayne and M.J. Whelan, J. Microsc. 98 (1973) 155. [13] J.W. Edington, Monographs in Practical Electron Microscopy in Materials Science, vol. 3 (Philips Technical Library, Macmillan, London, 1975).
[14] F. Reynaud and B. Legros-de Mauduit, J. Microsc. trosc. Electron. 9 (1984) 199. 1151 J.P. Hirth and J. Lothe, Theory of Dislocations Graw-Hill, New York, 1968). 1161 F. Kroupa, Czech. J. Phys. A 13 (1963) 301.
Spec(Mc-
and Methods
in Physics
Research
B 84 (1994) 190-194
NW B
Beam Interactions with Materials 8 Atoms
Identification of EOR defects due to the regrowth of amorphous layers created by ion bombardment B. de Mauduit a, L. Lahab a CEMES - LOE/CNRS, B.P. 4347, b LAAS/CNRS,
a, C. Bergaud b, M.M. Faye a, A. Martinez b and A. Claverie a
31055 Toulouse Cedex, France 7 avenue du Colonel Roche, 31077 Toulouse Cedex, France
In this paper TEM investigations have been carried out on typical EOR defects found in Ge-amorphized (001) wafers (Ge + Si, 150 keV, 2X1015 ions/cm’) after thermal annealing (RTA, looo”C, 10 s). These defects consist of medium sized (lo-50 nm) dislocation loops that have been characterized by conventional electron microscopic techniques. Most of them ( - 75%) are circular faulted Frank loops with b = a/3(111) vectors. The remaining ( - 25%) loops are perfect elongated hexagon-shaped loops: they have nearly (111) habit planes, with b = a /2( 101) vectors. Hence, it is possible to deduce from only one TEM image the number of Si atoms available in the loops as well as the density of the loops for different implantation or annealing conditions. This is needed for optimization of process conditions.
1. Introduction The formation of amorphous layers by ion bombardment prior to the introduction of a dopant or any other chemical impurity has several advantages over direct implantation in semiconductors. A preamorphization step eliminates channelling problems and results in abrupt dopant profiles [l]. More generally, the fact that the incorporation of the dopant or the formation of some alloy (like SiGe) occurs during annealing through the solid phase epitaxial (SPE) regrowth of the u-layer is desirable because defect-free
regrown layers can be obtained with required stoichiometry and electrical characteristics in most cases [2]. By contrast, it is well known that after SPE regrowth, structural defects are formed beneath the former c/a interface. These defects have received the strange name of “EOR” - end-of-range defects. EOR defects are the only disadvantage of this technique because they are known to dramatically affect impurity diffusion [3] and also to be responsible for the leakage current when situated in a space-charge region of a device. However, for the mastering of the so-called preamorphization technique, a better knowledge of
Fig. 1. Weak-beam image of both circular and elongated EOR loops seen near a [108] beam direction B using g = OaO, with positive s corresponding to a (g, 2g) condition. Loops in a variety of orientations are labelled according to the notation in table 1.
0168-583X/94/$07.00 0 1994 - Elsevier SSDI 0168-583X(93)E0371-M
Science
B.V. All rights reserved
B. de Mauduit et al. / Identification of EOR defects
191
Table 1 Conventions for notation of the four faulted Frank and 12 perfect prismatic loop families with corresponding
Ig. b 1 values
b
Plane
g
040
220
520
3TT
iI1
131
3ii
1/3[1111 1/3fiili
till) (ill)
Fl FQ
4/3 4/3
4/3 0
0 4/3
l/3 5/3
l/3 1
5/3 1
1 1
1/3ilil] 1/3[liii
(iii) (lli) (lllf
F3 F4 D:
4/3 4/3
0 4/3
4/3 0
1 1
l/3 l/3
l/3 1
l/3 5/3
2
1
1
1
1
2
0
1/2[101]
(ill) (111) (iii)
;; D:
0
1
1
1
0
1
1
1/2[0111
(111) (iii)
Di Dd
2
2
0
1
0
2
2
1/2[oill
(iii) (iii)
D: D44
2
1
1
0
0
1
1
i/ziioli
fill) flli)
D: D45
0
1
1
2
1
0
2
(ill)
D$
2
0
2
2
1
1
1
(iii)
D36
1/2[011]
l/zfilol
these defects is required. In a previous paper [4], we have shown that, most probably, these defects are due to the clustering of excess interstitial atoms (due to recoil) left beneath the c/a interface after bombardment The implementation of models able to optimize preamo~hi~ation conditions for minimizing the density of EOR defects and/or to simulate “anomalous” diffusion in these layers, requires a complete, quantitative characterization of these defects. Moreover, recent papers have shown that EOR defects, produced by Si or Ge preamorphization, can be used as efficient point defect detectors. These point defects can be induced by low-dose boron implantation [S] or by thermal oxidation [6]. For these reasons, transmission electron microscopic (TEM) techniques have been used both to determine the vacancy or interstitial nature of the EOR defects and to evaluate the number of single defects included in the EORs for a given set of experimental conditions. This paper briefly presents a complete loop analysis performed on (100) silicon wafers amorphized with 150 keV Ge+ ions at a dose of N 2 X 1015 ions cmw2 and subsequently annealed at 1000°C for 10 s (rapid thermal annealing (RTA) conditions). It is a typical process as currently used for the formation of ultra-shallow p’/n junctions in Si. Defects found in this material consist of medium sized (lo-50 nm) dislocation loops with regular shapes and in suitable concentration for determining their type and habit plane through “weak-beam dark field” (WBDF) imaging.
2. Experimental details and results Cross-sectional TEM was previously performed on this wafer [4] and showed the EOR defects to be located within a thin (w 40 nm thick) layer 170 nm
Fig.-- 2. Stereographic projection of the lower hemisphere with a [118] pole showing g and B used in figs. 1 and 3 when the specimen is tilted as indicated around the X-axis of the goniometer. II. COMPO~D
FORSOOK
192
3. de Mauduit et al. / Identification of EOR defects
beneath the surface, i.e. exactly beneath the former c/a interface resulting from the bombardment. For the experiments presented here, annealed Ge+ implanted (100) Si specimens were thinned for TEM plan-view examination by ion milling from the unimplanted side. Analysis has been restricted to the relatively thick (300 nm) areas of the foil where the loops can be assumed to lie well within the foil. Orientation conventions for self-consistent indexing beam directions B, diffraction vectors g, plane and direction traces on images relative to the effective positions in the specimen are specified in the captions to figs. 2-4. Loops have been analysed using conventional methods developed for (i) perfect dislocation [7-lo] and faulted dislocation [ll] loops when the image is formed using a strongly excited diffracted beam and (ii) small Frank loops [12] when using the WB imaging conditions. These methods (see ref. [13] for more details) are founded on (i) trace analysis to
identify the normal n to the habit plane of the loop, (ii) contrast analysis of images to identify the Burgers vector b, and (iii) the “inside-outside” (I-O) contrast effect to assess the sense of b, i.e. the vacancy or interstitial nature of the loop (the technique depends upon whether or not the image of the loop is “inside” or “outside” the dislocation core). Results are illustrated in the following series of micrographs and diagrams. Complete analysis will be given with more details in a forthcoming paper. AH the loops are shown in fig. 1. Most of them (- 75%) are circular loops and project as ellipses on the image. They are found to be faulted Frank loops with b = a/3( 111) vectors. They are labelled Fl to F4 (cf. table 1). The remaining (N 25%) loops are perfect elongated hexagon-shaped loops: they have nearly {ill} habit planes, with b = a/2( 101) vectors perpendicular to the long axis of the loops (the elongated directions lie in the six possible (110) directions). They are la-
Fig. 3. Contrast analysis of some of the loops shown in fig. 1. B is ciose to [IO81in (a), [liSI in (b) and 6.9, InSI in cd), nearly [Ii41 in (e) and [li2] in (f), (g), (h) and (i). AI1 micrographs are weak-beam images (as seen on the screen) under the following conditions: (g, 2g) in (a), (e), (g), (h), (i); (g, 3g) in (b), (cl, (d) and (-g, 5g) in (19. Compare contrast variation to table 1 and note “inside/outside” effect in (b)/(c) and (h)/(i).
B. de ~au~~it et al. / I~e~tif~atio~ of EUR defects
193
component, provided that b does not project in the angular range defined by the acute angle between B and the trace of the loop (results must be reversed in the opposite case).
3. Concfusion
a
1 (;J.T;)S
b
f;;.%;, szo
The nature and the structural characteristics of dislocations loops known as EOR defects have been unambiguously determined in this paper. The interstitial nature of these defects corresponds to the predictions of simulations [4], i.e. they are due to the agglomeration of Si interstitial atoms, left after bombardment beneath the c/a interface, which survive recombination with the vacancies in the same region. Therefore, their habit planes and Burger vectors have been determined so that it is now possible to deduce from only one TEM image the number of Si atoms available in the loops as well as the density of the loops for different implantation or annealing conditions. These quantitative results will be needed for the optimization of the amo~hization conditions and for the modelling of anomalous diffusion of dopant in semiconductors.
lM
This work was partly supported by the French GCIS and by an EC program (ADEQUAT). Fig. 4. Schematic diagram used to characterize the vacancy or interstitial nature of a prismatic dislocation loop by analysing the “inside-outside” effect observed on the image obtained with g and B. B, and n,, are the projections of the actual Burgers vector b (which may have a shear component) and upward normal n to the plane of the loop in the plane (B, g). “a” refers to the FS/RH definition of b [15] with a clockwise positive direction around the loop as on the screen. “b” refers to an easier definition: n *B> 0 for vacancy loops, n. b < 0 for interstitial loops [16]. The corresponding contrast (heavy line) relative to the core of the dislocation (dashed line) as seen on the screen and the sign of (g .b) are given for both s > 0 and s < 0. The application is illustrated with the case of Fl, F4 and Di, Di loops imaged with g = 220, B = [l?S] and g = 31i, B = 14571,respectively: they are interstitial loops.
belled D: to D-46(cf. table 1). The stereographic projection of fig. 2 shows g and B used for the contrast
anaIysis given in fig. 3. The interstitial nature of both types of loops has been unambiguously determined using the conventional schematic diagram (from ref. [14]) shown in fig. 4. We emphasize that such a diagram can be applied to any prismatic loop with a shear
References
111S.J. Kwon, H.J. Kim and J.D. Lee, Jpn. J. Appl. Phys. 29 (1990) L2326. El J.P. Zhang, R.J. Wilson, P.L.F. Hemment, A. Claverie, F.
Cristiano, P. Salles, J.Q. Wen, J.H. Evans, A.R. Peaker and G.J. Parker, these Proceedings (E-MRS 1993 Spring Meeting, Strasbourg, France, Symposium G: Material Aspects of Ion Beam Synthesis: Phase Formation and Modification) Nucl. Instr. and Meth. B 84 (1994) 222. [31 R.J. Schreutelkamp, J.S. Custer, V. Raineri, W.X. Lu, J.R. Liefting, F.W. Saris, K.T.F. Janssen, P.F.H.M. van der Meulen and R.E. Kaim, Mater. Sci. Eng. B 12 (1992) 307. 141 L. Lalnab, C. Bergaud, M.M. Faye, J. Faure, A. Martinez and A. Claverie, Proc. MRS Boston (1992) in press. 151 J.K. Listebarger, K.S. Jones and J.A. Slinkman, J. Appl. Phys. 73 (1993) 4815. 161 H.L. Meng, S. Prussin, M.E. Law and KS. Jones, J. Appl. Phys. 73 (1993) 955. i71 G.W. Groves and A. Kelly, Philos. Mag. 6 (1961) 1527. (81 D.J. Mazey, R.S. Barnes and A. Howie, Philos. Mag. 7 (1962) 1861. [91 B. Edmonson and G.K. Williamson, Philos. Mag. 9 (1964) 277. DO1 D.M. Maher and B.L. Eyre, Philos. Mag. 23 (1971) 409. II. COMPOUND FORMATION
194
B. de Mauduit et al. / Identification of EOR defects
[ll] W.J. Tunstall, Philos. Mag. 20 (1969) 701. [12] M.L. Jenkins, D.J.H. Cockayne and M.J. Whelan, J. Microsc. 98 (1973) 155. [13] J.W. Edington, Monographs in Practical Electron Microscopy in Materials Science, vol. 3 (Philips Technical Library, Macmillan, London, 1975).
[14] F. Reynaud and B. Legros-de Mauduit, J. Microsc. trosc. Electron. 9 (1984) 199. 1151 J.P. Hirth and J. Lothe, Theory of Dislocations Graw-Hill, New York, 1968). 1161 F. Kroupa, Czech. J. Phys. A 13 (1963) 301.
Spec(Mc-