- Email: [email protected]
Damage and thermal annealing of In+ implanted a-axis sapphire
___ l!E!l
s
Nuclear Instruments and Methods in Physics Research B 122 (1997) 55-58
NOMB
Beam Interactions with Materials A Atoms
ELSEVIER
Damage and thermal annealing of In+ implanted u-axis sapphire Dong-zhu Xie, De-xin Cao, De-zhang Zhu * Lahorutory
of Nuclear
Anulysis
Techniques,
Shanghai Institute
of
Nuclear
Research. Academia
Sink
Shunghai
201800,
China
Received 17 July 1996; revised fotm received 3 October 1996 Abstract Single crystal samples of (l?lO)a-Al,O, were implanted with 100 keV and 360 keV indium ions to doses of 6 X lOI ions/cm’, 1 X lOI ions/cm*, and 3 X lOI ions/cm*, respectively, at room temperature (RT). The implanted samples were annealed isothermally in high purity argon ambient at 900°C. from 2 to 24 h. Rutherford Backscattering Spectrometry and Channelling (RBS-C) and Reflection High Energy Electron Diffraction (RHEED) have been used to study the depth distributions of lattice damage and impurity, as well as the annealing behavior. All three as-implanted samples do not show an amorphous layer, which indicated that the self-annealing is severe during In ion implantation of m-Al,O, at RT. For the 100 keV ion implanted samples, In loss and formation of In,O, were observed after 12 h annealing. The In ions are completely located in the interstitial sites for all samples annealed at 900°C for 12 h. For the higher energy (360 keV) implantation, single crystal is retained at the outermost surface in the as-implanted sample.
I. Introduction The surface and near-surface modification of a-Al,O, by ion beam implantation is used to create novel mechanical [l-3], optical [4], and chemical [5,6] properties. Many of these property changes are influenced by the lattice damage which is created by the implantation. Implantation damage and annealing in sapphire are more complex than in semi-conductors and metals. This complex arises from the two distinct sublattices which have different displacement energies (78 eV for oxygen and 18 eV for aluminum) [7], and in part from the dynamic self-annealing process in hoth the aluminum and oxygen sublattices during implantation. The nature of defects and annealing behaviors is strongly influenced by the chemical and electrical nature of the implanted species [8]. In this paper the radiation damage induced by implantation with the low melting point metal species indium in a-axis sapphire, the impurity distributions and the annealing behaviors were investigated.
residual surface damage produced during surface polishing. Specimens were implanted with the beam incident at 7” at room temperature to avoid channelling effects. In ion implantation energies of 100 keV to 360 keV and doses of 1 X lOI to 6 X lOI ions/cm’ were used. The beam current density is less than 1 p,A/cm* to reduce self-annealing during ion implantation. Annealing was performed in flowing high purity argon at 900°C from 2 to 24 h. Rutherford Backscattering Spectrometry and Channelling (RBS-Cl of 2.88 MeV He+ was applied to study ion radiation damage and impurity depth distribution. The scattering angle is 170”, and the energy resolution of the analysis system is 15 keV. Under these experimental conditions, the depth resolution at surface is about 20.7 nm. Some chosen samples were studied with Reflection High Energy Electron Diffraction (RHEED) to examine their surface structure.
3. Results and discussions 2. Experiment 3.1. The optical quality (1210) oriented sapphire samples used in this study were annealed prior to implantation at 1200°C for 5 days in oxygen ambient to remove any
* Corresponding author. Fax: +86-21-5955-3021; email: [email protected]. 0168-583X/97/$17.00 PIf
Damage
and
annealing
implanted
with
100
Fig. 1 shows the random and aligned backscattering spectra of an as-implanted sample. From the spectra, it can be seen that there is a heavily damage layer in the surface region (x(A1) = 77.2%) but remains crystalline as indicated by the fact that the aligned spectrum does not touch
Copyright 0 1997 Published by Elsevier Science B.V. All rights reserved
SOl68-583X(96)00769-0
of Al,O,
keV In ions
D.-z. Xie et ul./Nucl.
56
Energy 20 -
0
Ins~. and Meth. in Phys. Res. B 122 (1997) 55-58
(MeV)
1 .o
1.5
2.0
I
I
I
lOOk& 6E16 1OOkeV 6E16
In/cm2 In/cm2
Random As-im lonted Aligned As-impooted P
90 +G$&eo 99
Ii
h-r v \ <.-I_, 0 0 00
6 AI
I
I
I
I
I
150
200
250
300
350
400
depth(nm)
Channel Fig.
I. 2.88 MeV
He+
bacliscattering
from In+ implanted u-axis
and channelling spectra
or-AlzO,.
Fig. 3. Damage distribution 6~ lOI
ions/cm*
planted; (b)
the random spectrum for the Al sublattice. This result was confirmed by RHEED. Sood et al. [9] reported the formation of amorphous layer at a-axis A1,03 surface implanted with IO0 keV, 6 X lOI ions/cm* at 77 K. It indicates that the self-annealing effect is effective at RT. Mourns et al. [IO] also reported the formation of amorphous layer between 50-150 nm from the surface implanted with 100 In ions to ( lO’T0) a-Al,O, at keV, 6 x lOI ions/cm* RT, which indicates that the (1070) a-Al,O, is more easily amorphized than the (l?lO) a-AlzO,. Fig. 2 shows the spectra after annealing at 900°C for 2 and for 12 h. From Fig. 2, it can be seen that the interface of substrate and damage layer moves towards the surface during thermal annealing, and the height of damage peak lowers at the same time. Consequently, it is different from conventional solid phase epitaxy. The damage distributions before and after annealing are shown in Fig. 3.
Energy
1.5
200
for the indicate annealing
250
times.
Damage
annealing.
(c) for 9OO”C/l2
and annealing
of Al,O,
with
100 keV
(a) For
as-im-
h.
with 360
implanted
keV In + ions
For higher energy (360 keV) and lower dose (1 X lOI ions/cm2) indium ion implantation, RBS-C results (not shown here) indicate that In ion implantation creates heavy damage in sub-surface region, and outermost surface still
2.0
300
350
400
Channel Fig. 2. RBS-C spectra showing
for 9OO”C/2 h;
of sample implanted and after
(MeV)
1.o
150
3.2.
before
the annealing
Fig. 4. The RHEED behaviors
at 900°C
keV
indium
ions/cm’.
ions: (a)
patterns for
of samples as-implanted
I X lOI
ions/cm*;
(b)
with
360
for 3X lOI
D.-z. Xie er al. /Nucl. Instr. and Merh. in Phys. Res. B 122 (1997) 55-58
retains relatively perfect single crystal. It is also clear to see from the RHEED, diffraction pattern (Fig. 4a) that the crystallinity is quite good at the surface. The lattice damage is increased with increasing dose to 3 X lOI ions/cm*, but RBS-C measurements show that Energy 25 0
u
.-E
100keV 100keV 100keV
-
xl 20 u .>
A
6E16 6E16 6E16
2.6 I
2.4 I
In/cm2 In/cm2 In/cm2
3.3. Annealing behavior of implanted In ’
as-im lanted 9OOC P Phrs 900C/12hrs
de th(km) 0. 6-be
‘5 t
0
10
E b z
5
1
(a)
,
1
j
0
3jo
4bo
460
5bo
Channel Energy 2.0
(MeV)
2.2
2.4
2.6
u
.-g
the damage layer is not amorphized. The presence of polycrystalline Al,O, in the surface region was confirmed by RHEED (Fig. 4b). After the annealing at 900°C for 12 h, the damage was recovered partly with x(Al) = 68% on aligned spectrum. It indicates that the residual damage is still heavy.
(MeV)
2.2 I
2.0 I
5-l
1.0
0 E b 0.5 z 0.0 460
450
There is quite different annealing behavior between lower and higher energy ion implantation for indium. For the sample implanted with lower energy (100 keV) and a dose of 6 X lOI ions/cm*, the indium profiles become wider after annealing at 9OO”C, as shown in Fig. 5a. Some indium ions diffuse toward inner, and others toward the surface. There is a loss of 29.1% indium at the surface after 12 h annealing. Some of indium diffused to surface to form In,O, which was confirmed by HREED. For indium ion implantation with higher energy (360 keV) for doses of 1 X lOI In/cm* and 3 X lOI In/cm*, the indium profiles become narrower after annealing at 900°C. as shown in Fig. 5b and c. No indium losses during annealing are observed. These different annealing behaviors arise from the surface layer structure. In higher energy (360 keV) indium ion implantation, the surface layer structure is like a sandwich. The substrate and outermost surface are single crystal, and the implanted layer is damaged. The damage layer recrystallization starts from two interfaces during annealing. Because the solubility of indium ion in single crystal AI,O, is very low, the implanted indium profile is getting narrow and no any indium loss from surface while the implanted layer recrystallized during annealing. These results agree with those of Hioki’s [2] and Ohkubo’s [I I].
560
Channel Energy 2.0 I
6
t
0 360keV -360keV
2.2 I 3E16 3E16
In/cm2 In/cm2
4. Conclusion
(MeV) 2.4 I
2.6 I
as-im Ionted 9OOC P 12hrt
depth(w)
460
450
i
500
Channel Fig. 5. Annealing behavior of In implanted to the (l?lO> a-A120, at 900°C for a various times. (a) For 100 keV 1 X lOI ions/cm’; (b) for 360 keV I X IO I6 ions/cm’; (c) 360 keV 3X lOI ions/cm’.
Based on the experimental results and discussions described in Section 3, the conclusions are given as following: (1) High dose In+ implantation of (1310) a-Al,O, at RT does not produce amorphous phase. (2) The higher energy ion implantation produces a heavily damaged sub-surface region but the surface region retains well crystalline. (3) The residual damage is considerable for all samples after 12 h annealing at 9OO”C, which is different from the annealing behavior of Al,O, implanted by Fe ions [ 121. (4) The indium is redistributed during annealing. The different annealing behavior between samples with lower and higher energies implantation was shown. For 100 keV 6 X lOI ions/cm* implanted Al,O,. the indium profile become wider and losses indium from surface during annealing at 900°C (as shown in Fig. Sal, while for higher
58
D.-z. Xir et ul./Nucl.
Instr. und Meth. in Phys. Rex B 122 (1997) 55-58
energy (360 keV) indium ion implantation, the indium profiles become narrower and no indium losses (as shown in Fig. 5b and c). (5) The more detailed nature of defects produced by In+ implantation and thermal annealing must await further investigation by Transmission Electron Microscopy (TEM) measurement. Such measurements are in progress and will be reported in subsequent publications.
References [l] C.J. McHargue
et al., Nucl. Instr. and Meth. B
10/I I (1985)
569. [2] T. Hioki et al., Nucl. Instr. and Meth. B 7/8 (1985) 521.
[3] C.W. White et al., Nucl. Instr. and Meth. B 7/8 (1985) 473. [4] B.D. Evans et al., Nucl. Instr. and Meth. B 91 (1994) 258. [S] P.J. Bumet and T.F. Page, Proc. Brit. Ceram. Sot. 34 (1984) 65. [6] S. Hishita et al., Nucl. Instr. and Meth. B 91 (1994) 571. [7] Zhi yong Zhu and P. Jung, Nucl. Instr. and Meth. B 91 ( 1994) 269. [8] C.J. McHargue et al., Nucl. Instr. and Meth. B 46 (1990) 79. (91 D.K. Sood and D.X. Cao, Nucl. Instr. and Meth. B 46 (1990) 194. [IO] A.P. Mouritz et al., Nucl. Instr. and Meth. B 19/20 (1987) 805. [I I] M. Ohkubo et al., J. Appl. Phys. 60 (1986) 1325. [12] G.C. Farlow et al., Nucl. Instr. and Meth. B 7/8 (1985) 541.
s
Nuclear Instruments and Methods in Physics Research B 122 (1997) 55-58
NOMB
Beam Interactions with Materials A Atoms
ELSEVIER
Damage and thermal annealing of In+ implanted u-axis sapphire Dong-zhu Xie, De-xin Cao, De-zhang Zhu * Lahorutory
of Nuclear
Anulysis
Techniques,
Shanghai Institute
of
Nuclear
Research. Academia
Sink
Shunghai
201800,
China
Received 17 July 1996; revised fotm received 3 October 1996 Abstract Single crystal samples of (l?lO)a-Al,O, were implanted with 100 keV and 360 keV indium ions to doses of 6 X lOI ions/cm’, 1 X lOI ions/cm*, and 3 X lOI ions/cm*, respectively, at room temperature (RT). The implanted samples were annealed isothermally in high purity argon ambient at 900°C. from 2 to 24 h. Rutherford Backscattering Spectrometry and Channelling (RBS-C) and Reflection High Energy Electron Diffraction (RHEED) have been used to study the depth distributions of lattice damage and impurity, as well as the annealing behavior. All three as-implanted samples do not show an amorphous layer, which indicated that the self-annealing is severe during In ion implantation of m-Al,O, at RT. For the 100 keV ion implanted samples, In loss and formation of In,O, were observed after 12 h annealing. The In ions are completely located in the interstitial sites for all samples annealed at 900°C for 12 h. For the higher energy (360 keV) implantation, single crystal is retained at the outermost surface in the as-implanted sample.
I. Introduction The surface and near-surface modification of a-Al,O, by ion beam implantation is used to create novel mechanical [l-3], optical [4], and chemical [5,6] properties. Many of these property changes are influenced by the lattice damage which is created by the implantation. Implantation damage and annealing in sapphire are more complex than in semi-conductors and metals. This complex arises from the two distinct sublattices which have different displacement energies (78 eV for oxygen and 18 eV for aluminum) [7], and in part from the dynamic self-annealing process in hoth the aluminum and oxygen sublattices during implantation. The nature of defects and annealing behaviors is strongly influenced by the chemical and electrical nature of the implanted species [8]. In this paper the radiation damage induced by implantation with the low melting point metal species indium in a-axis sapphire, the impurity distributions and the annealing behaviors were investigated.
residual surface damage produced during surface polishing. Specimens were implanted with the beam incident at 7” at room temperature to avoid channelling effects. In ion implantation energies of 100 keV to 360 keV and doses of 1 X lOI to 6 X lOI ions/cm’ were used. The beam current density is less than 1 p,A/cm* to reduce self-annealing during ion implantation. Annealing was performed in flowing high purity argon at 900°C from 2 to 24 h. Rutherford Backscattering Spectrometry and Channelling (RBS-Cl of 2.88 MeV He+ was applied to study ion radiation damage and impurity depth distribution. The scattering angle is 170”, and the energy resolution of the analysis system is 15 keV. Under these experimental conditions, the depth resolution at surface is about 20.7 nm. Some chosen samples were studied with Reflection High Energy Electron Diffraction (RHEED) to examine their surface structure.
3. Results and discussions 2. Experiment 3.1. The optical quality (1210) oriented sapphire samples used in this study were annealed prior to implantation at 1200°C for 5 days in oxygen ambient to remove any
* Corresponding author. Fax: +86-21-5955-3021; email: [email protected]. 0168-583X/97/$17.00 PIf
Damage
and
annealing
implanted
with
100
Fig. 1 shows the random and aligned backscattering spectra of an as-implanted sample. From the spectra, it can be seen that there is a heavily damage layer in the surface region (x(A1) = 77.2%) but remains crystalline as indicated by the fact that the aligned spectrum does not touch
Copyright 0 1997 Published by Elsevier Science B.V. All rights reserved
SOl68-583X(96)00769-0
of Al,O,
keV In ions
D.-z. Xie et ul./Nucl.
56
Energy 20 -
0
Ins~. and Meth. in Phys. Res. B 122 (1997) 55-58
(MeV)
1 .o
1.5
2.0
I
I
I
lOOk& 6E16 1OOkeV 6E16
In/cm2 In/cm2
Random As-im lonted Aligned As-impooted P
90 +G$&eo 99
Ii
h-r v \ <.-I_, 0 0 00
6 AI
I
I
I
I
I
150
200
250
300
350
400
depth(nm)
Channel Fig.
I. 2.88 MeV
He+
bacliscattering
from In+ implanted u-axis
and channelling spectra
or-AlzO,.
Fig. 3. Damage distribution 6~ lOI
ions/cm*
planted; (b)
the random spectrum for the Al sublattice. This result was confirmed by RHEED. Sood et al. [9] reported the formation of amorphous layer at a-axis A1,03 surface implanted with IO0 keV, 6 X lOI ions/cm* at 77 K. It indicates that the self-annealing effect is effective at RT. Mourns et al. [IO] also reported the formation of amorphous layer between 50-150 nm from the surface implanted with 100 In ions to ( lO’T0) a-Al,O, at keV, 6 x lOI ions/cm* RT, which indicates that the (1070) a-Al,O, is more easily amorphized than the (l?lO) a-AlzO,. Fig. 2 shows the spectra after annealing at 900°C for 2 and for 12 h. From Fig. 2, it can be seen that the interface of substrate and damage layer moves towards the surface during thermal annealing, and the height of damage peak lowers at the same time. Consequently, it is different from conventional solid phase epitaxy. The damage distributions before and after annealing are shown in Fig. 3.
Energy
1.5
200
for the indicate annealing
250
times.
Damage
annealing.
(c) for 9OO”C/l2
and annealing
of Al,O,
with
100 keV
(a) For
as-im-
h.
with 360
implanted
keV In + ions
For higher energy (360 keV) and lower dose (1 X lOI ions/cm2) indium ion implantation, RBS-C results (not shown here) indicate that In ion implantation creates heavy damage in sub-surface region, and outermost surface still
2.0
300
350
400
Channel Fig. 2. RBS-C spectra showing
for 9OO”C/2 h;
of sample implanted and after
(MeV)
1.o
150
3.2.
before
the annealing
Fig. 4. The RHEED behaviors
at 900°C
keV
indium
ions/cm’.
ions: (a)
patterns for
of samples as-implanted
I X lOI
ions/cm*;
(b)
with
360
for 3X lOI
D.-z. Xie er al. /Nucl. Instr. and Merh. in Phys. Res. B 122 (1997) 55-58
retains relatively perfect single crystal. It is also clear to see from the RHEED, diffraction pattern (Fig. 4a) that the crystallinity is quite good at the surface. The lattice damage is increased with increasing dose to 3 X lOI ions/cm*, but RBS-C measurements show that Energy 25 0
u
.-E
100keV 100keV 100keV
-
xl 20 u .>
A
6E16 6E16 6E16
2.6 I
2.4 I
In/cm2 In/cm2 In/cm2
3.3. Annealing behavior of implanted In ’
as-im lanted 9OOC P Phrs 900C/12hrs
de th(km) 0. 6-be
‘5 t
0
10
E b z
5
1
(a)
,
1
j
0
3jo
4bo
460
5bo
Channel Energy 2.0
(MeV)
2.2
2.4
2.6
u
.-g
the damage layer is not amorphized. The presence of polycrystalline Al,O, in the surface region was confirmed by RHEED (Fig. 4b). After the annealing at 900°C for 12 h, the damage was recovered partly with x(Al) = 68% on aligned spectrum. It indicates that the residual damage is still heavy.
(MeV)
2.2 I
2.0 I
5-l
1.0
0 E b 0.5 z 0.0 460
450
There is quite different annealing behavior between lower and higher energy ion implantation for indium. For the sample implanted with lower energy (100 keV) and a dose of 6 X lOI ions/cm*, the indium profiles become wider after annealing at 9OO”C, as shown in Fig. 5a. Some indium ions diffuse toward inner, and others toward the surface. There is a loss of 29.1% indium at the surface after 12 h annealing. Some of indium diffused to surface to form In,O, which was confirmed by HREED. For indium ion implantation with higher energy (360 keV) for doses of 1 X lOI In/cm* and 3 X lOI In/cm*, the indium profiles become narrower after annealing at 900°C. as shown in Fig. 5b and c. No indium losses during annealing are observed. These different annealing behaviors arise from the surface layer structure. In higher energy (360 keV) indium ion implantation, the surface layer structure is like a sandwich. The substrate and outermost surface are single crystal, and the implanted layer is damaged. The damage layer recrystallization starts from two interfaces during annealing. Because the solubility of indium ion in single crystal AI,O, is very low, the implanted indium profile is getting narrow and no any indium loss from surface while the implanted layer recrystallized during annealing. These results agree with those of Hioki’s [2] and Ohkubo’s [I I].
560
Channel Energy 2.0 I
6
t
0 360keV -360keV
2.2 I 3E16 3E16
In/cm2 In/cm2
4. Conclusion
(MeV) 2.4 I
2.6 I
as-im Ionted 9OOC P 12hrt
depth(w)
460
450
i
500
Channel Fig. 5. Annealing behavior of In implanted to the (l?lO> a-A120, at 900°C for a various times. (a) For 100 keV 1 X lOI ions/cm’; (b) for 360 keV I X IO I6 ions/cm’; (c) 360 keV 3X lOI ions/cm’.
Based on the experimental results and discussions described in Section 3, the conclusions are given as following: (1) High dose In+ implantation of (1310) a-Al,O, at RT does not produce amorphous phase. (2) The higher energy ion implantation produces a heavily damaged sub-surface region but the surface region retains well crystalline. (3) The residual damage is considerable for all samples after 12 h annealing at 9OO”C, which is different from the annealing behavior of Al,O, implanted by Fe ions [ 121. (4) The indium is redistributed during annealing. The different annealing behavior between samples with lower and higher energies implantation was shown. For 100 keV 6 X lOI ions/cm* implanted Al,O,. the indium profile become wider and losses indium from surface during annealing at 900°C (as shown in Fig. Sal, while for higher
58
D.-z. Xir et ul./Nucl.
Instr. und Meth. in Phys. Rex B 122 (1997) 55-58
energy (360 keV) indium ion implantation, the indium profiles become narrower and no indium losses (as shown in Fig. 5b and c). (5) The more detailed nature of defects produced by In+ implantation and thermal annealing must await further investigation by Transmission Electron Microscopy (TEM) measurement. Such measurements are in progress and will be reported in subsequent publications.
References [l] C.J. McHargue
et al., Nucl. Instr. and Meth. B
10/I I (1985)
569. [2] T. Hioki et al., Nucl. Instr. and Meth. B 7/8 (1985) 521.
[3] C.W. White et al., Nucl. Instr. and Meth. B 7/8 (1985) 473. [4] B.D. Evans et al., Nucl. Instr. and Meth. B 91 (1994) 258. [S] P.J. Bumet and T.F. Page, Proc. Brit. Ceram. Sot. 34 (1984) 65. [6] S. Hishita et al., Nucl. Instr. and Meth. B 91 (1994) 571. [7] Zhi yong Zhu and P. Jung, Nucl. Instr. and Meth. B 91 ( 1994) 269. [8] C.J. McHargue et al., Nucl. Instr. and Meth. B 46 (1990) 79. (91 D.K. Sood and D.X. Cao, Nucl. Instr. and Meth. B 46 (1990) 194. [IO] A.P. Mouritz et al., Nucl. Instr. and Meth. B 19/20 (1987) 805. [I I] M. Ohkubo et al., J. Appl. Phys. 60 (1986) 1325. [12] G.C. Farlow et al., Nucl. Instr. and Meth. B 7/8 (1985) 541.