HAL Id: jpa-00227995
https://hal.archives-ouvertes.fr/jpa-00227995
Submitted on 1 Jan 1988
HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
DEFECT CHARACTERIZATION OF
Si+-IMPLANTED GaAs BY MONOENERGETIC POSITRON BEAM TECHNIQUE
J.-L. Lee, K.-H. Shim, S. Tanigawa, A. Uedono, J. Kim, H. Park, D. Ma
To cite this version:
J.-L. Lee, K.-H. Shim, S. Tanigawa, A. Uedono, J. Kim, et al.. DEFECT CHARACTERIZATION
OF Si+-IMPLANTED GaAs BY MONOENERGETIC POSITRON BEAM TECHNIQUE. Journal
de Physique Colloques, 1988, 49 (C4), pp.C4-457-C4-460. �10.1051/jphyscol:1988497�. �jpa-00227995�
DEFECT CHARACTERIZATION OF Si*-IMPLANTED GaAs
BYMONOENERGETIC POSITRON BEAM TECHNIQUE
J.-L. LEE, K.-H. SHIM, S. TANIGAIVA* , A. UEDONO* , J. S. KIM, H.M. PARK and D.S. MA
Compound Semiconductor Department, Electronics and Telecommunications Research Institute,
POBox
8 ,Daedok Science Town, Choongnam, Korea '~nstitute of Materials Science, University of rsukuba, Sakura-mura, Ibarakf
305,Japan
Abstract
-
Nonoenergetic positrons with variable energies were used to study the depth distribution of implantation-induced vacancy-type defects in undoped GaAs and p-type Si. In Bt- and Ast- implanted Si substrates, parabolic-type distributions of vacancy-type defects were observed. In Sit-implanted GaAs, the concentration of vacancy-type defect decreased continuously with increasing depth below the surface. The distribution of defects changed into parabolic-type in annealing the Sit-implanted GaAs above the temperature of 900 OC.Processing of semiconductors often involves the use of ion implantation as a means of introducing dopant impurities. After implantation the semiconductor lattice will not only be damaged, but in addition, will be left a nonuniform lattice displacement /I/. Although a lot of researches have been theoretically proceeded to understand the mechanism of defect production during the ion-implantation into semiconductor/l,t/, their validities have not yet been confirmed experimentally because of the lack of suitable techniques. Especially little is known on the behavior of electron traps in the implanted region in activating the ion-implanted GaAs.
In the present work, we report the application of the monoenergetic positron beam technique for the study of vacancy-type defects in both Bt-and Ast-implanted Si and Sit-implanted GaAs. The depth distributions of vacancy-defects below the surface were investigated in activating the Sit- implanted GaAs by a two-step annealing technique in which a high-temperature main anneal step is followed by a second anneal at a low temperature /3/. The results were discussed in conjunction with those obtained by Hall measurements and deep level transient spectroscopy (DLTS).
2-EXPER~MENTAL METHODS
Undoped semi-insulating liquid encapsulated Czochralski (100) GaAs samples were implanted with the doses of 4.6x10N, 3x1012, and 3x1012 Sit for the energies of 20, 30 and 120 keV, respec- tively. To compare the defect generation behavior in elemental semiconductors with that in compound ones, implantations with 80 keV Bt and 150 keV Ast were done on p-type (100) Si wafers, respectively. In order to examine the carrier generation, GaAs samples implanted with the dose of 3x1013 Sit
.
c w 2 at an energy of 120 keV were used. The implanted specimens were protected by a 2000 A silox encapsulating layer to minimize As loss from the surface and then annealed by a two-step rapid thermal annealing (RTA). First stage annealing was done at 900 and 920 O C for a period of 5 s under flowing ultra-pure nitrogen gas. RTA temperatures for second stage anneal- ing were 800 and 850 OC for periods of 10-30 s to examine the improvement of electrical properties by two-step annealing. After chemically removing the silox encapsulating layer, the wafers were characterized by mono-energetic positron beam measurements, Hall measurements and DLTS.Monoenergetic positron beam technique enables to study an atomic scale disorder at the surface and in the sub-surface region/4-6/. The implanted positron eventually annihilates with an electron, producing two annihilation photons. A Doppler broadened profile of these annihilation photons can provide the momentum distribution of the annihilating electrons. A positron is repelled from positively charged ion cores by a coulomb interaction. In a perfect metal the
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1988497
C4-458
JOURNAL DE PHYSIQUEDoppler broadened energy spectrum consists of both a narrow parabolic part corresponding to the annihilation with conduction electrons and a broad one with core electrons. In a metal containing a high concentration of vacancy-defects positron annihilates selectively a t vacancies of open- volume defects. As a r e s u l t , the contribution of core electrons in the Doppler broadened energy spectrum i s reduced and, in turn, that of conduction electrons i s increased. The lineshape parameter S which i s defined as the r a t i o of the central region to the t o t a l counts of the Doppler broadened energy spectrum shows the annihilation characteristics. From the change of the S parameter, one can derive the information about the fraction of positrons which annihilate in such defects and the concentration of defects through the positron-trapping model / 6 / . Once we a r e able to get slow positrons, the acceleration of them w i t h a desired energy makes i t possible to adjust the implantation profile of positrons to r e s t r i c t e d regions of i n t e r e s t in the specimen under study.
The present experiments were performed w i t h a variable-energy positron beam l i n e in ultra- high vacuum /5/. Positrons emitted from a ggNa source are moderated by a venetian-type vahe which i s made of well annealed tungsten f o i l s with a thickness of 25.4 p m. Implanted positrons tend to diffuse back to the surface, because of the negative work function of a positron for metals and/or the presence of a deep potential well a t the surface image potential /7/. Positrons thermalizing within a diffusion Iength of the moderator surface can reach the surface and then they are emitted into vacuum. Slow positrons emitted from the moderator are guided by nine separated magnetic c o i l s of 100 G with a diameter of 700 mm. Acceleration of slow positrons i s performed by applying a high desired voltage between 0.1
-
50 kV to the source chamber. The sourcechamber i s floated by a ceramic break.
The Doppler broadening profiles of annihilation radiations were measured by a high purity Ge detector with an energy resolution of 1.1 keV in FWHM for the 512 keV 7 rays. Annihilation spectra with t o t a l counts of 5 x 10s were taken a t various incident positron energies. The central region of the 7 spectrum was defined from 510.5 to 511.5 keV. The incident energy of the positron beam was adjusted from 100 eV to 25 keV. All measurements were performed a t room temperature and the vacuum in the present experiments was 8 x lo-' Torr.
3-RESULTS AND DISCUSSIONS
Figure 1 shows .the variation of the S parameter as a function of incident positron energy E for the three Sit-implanted GaAs specimens. The relation between the positron incident energy E and the mean positroll implantation depth a i s given hy/4/
where P i s the density of the specimen. The values of a are shown i n a horizontal axis together with the positron indicent energy i n Fig.1. The value of S decreases continuously with increasing depth below the surface. Tanigawa e t a1/8/ reported that any detectable doping e f f e c t could not be found in S i by the angular correlation measurements. They considered that no trapping e f f e c t i s due to the weak trapping power of impurities, that i s , an i n t e r s t i t i a l - t y p e defect does not have such a trapping potential for a positron. Thus the difference of the S parameters between the implanted and the unimplanted GaAs specimens is attributed to the introduction of vacancy-type defects by the ion implantation. The damaged region s h i f t s toward inside of the specimen with applying the high energy of Sit to GaAs.
Gibbons e t a l / l / theoretically suggested the generaiion o f :>igh concentration of vacancies by the recoils of Ga and As from near-surface region. They observed the stacking f a u l t s and the microtwins surrounded by dislocation networks extending the surface in the cross-section of S i t -implanted GaAs /9/. I t i s generally accepted that v ~ a i s of acceptor type and can e x i s t in negatively charged or neutral s t a t e s . On the contrary
VW
i s of donor type and i t s charge s t a t e can be negatively, neutral or positively charged depending on the position of the Fermi level/lo/.
I t has been, however, reported that positron cannot be trapped a t VRS. Therefore i t i s apparent that the S parameter change as a function of depth i s related to the distribution of Ga vacancy and vacancy agglomerates.The S parameters as a function of incident positron energies for Bt- and Ast-implanted Si specimens, respectively, a r e shown in Fig.2. The defects for both types of specimens are found to be distributed i n a parabolic form, which are clearly compared with the defect profiles in GaAs, given i n Fig.1. This implies that the vacancy generation mechanism for ion implants into CaAs i s different from that into Si. According to the calculation given by Gibbons e t a1 / I / , vacancies a r e produced from the origin points of high energy recoils. Consequently the concentration of imlantation-induced vacancy decreases logarithmically from the surface to tbe inside of bulk which i s clearly consistent with the present experimental r e s u l t s i n Sit-implanted GaAs. They suggest ed the distribution of atomic displacement with a parabolic shape which i s originated from the f i n a l stopping points of the recoils / I / , namely low energy recoils. The distribution shape, resulting from the low energy'recoils, agrees with that o f the defect profiles in Bt- and Ast- implanted Si, which suggests the low energy recoils might dominate the vacancy generation in ion
0.53 0 E.120 IreV, 3 0 x l0I2 8if cni2 A E = 3 0 keV. 30 x 10" si'.cn?
x E= 20 keV, ~ . 6 x l d ' si*.cmi2 UNIMPLANTED
,
0.51a UNIMPLANTED
0.52
0 0 . 10 5 20 1 30 1
POSITRON ENERGY ( lceV )
- - -
0 10 20 30 I I I I I I I
POSITRON ENERGY ( IteV ) 0 1 5 10 20 30
I I I I I I
o
1 5 10 15 DEPTH ( ~ 1 0 ~ 8 )DEPTH ( x ~ 0 3 8 ) Fig.2 S parameter as a function of the incident Fig.1 S parameter versus the incident positron p o s i t r o n energy and/or the depth f o r B+- and
energy and/or the depth f o r Sit-implanted GaAs A ~ + Si samples. - ~ ~ ~ ~ ~ ~ ~ ~ ~
samples with d i f f e r e n t implantation energies and dose amounts.
Variation of S parameters versus incident positron energy in samples a c t i v a t e d by the two-step annealing process i s i l l u s t r a t e d in Fig.3. The damage p r o f i l e s a f t e r RTA a r e parabolic-type d i s t r i b u t i o n s , i n which defect concentration i s not dependent upon the duration time of the second-stage anneal. Ralston e t a l / l l / suggested t h a t the d i s t r i b u t i o n of d i s l o c a t i o n loops as a function of depth from the s u r f a c e of ion-implanted GaAs was a parabolic-type, which i s con- s i s t e n t with t h a t indicated by slow positron measurement ( s e e Figure 3 ) . P o t e n t i a l l y g r e a t i n t e r e s t i n Fig.3 i s the lack of recovery of Ga-related damage induced by ion implantation during RTA.
" " 7
0 5 4
0 )
a 0
JLC*
0 5 0 ~ I I
0 10 20
P o s ~ l r o n Energy ( k e V )
I l I I I
0 I 3 7 10
Deplh ( X I $ % ) I I
Fig.3 S parameter versus the incident positron 100 2 0 0 3 0 0 4 0 0
energy and/or depth in Sit-implanted undoped Temperature ( K )
LEC GaAs a c t i v a t e d by a two-step rapid thermal Fig.4 DLTS s p e c t r a of e l e c t r o n t r a p s in Sit- annealing. The conditions of the two-step RTA implanted undoped LEC GaAs a c t i v a t e d by a two- a r e 900 OC/5 s
+
850 OC/O 's ( ); 900 OC/5 s s t e p prapid thermal annealing a t ( a ) 920 OC+
850 OC/10 s ( a); 900 OC/5 s+
850 OC/20 s /5 s ; ( b ) 920 OC/5 s+
800 OC/10 s ; ( c ) 920 O C ( v ) ; 900 Oc/5 s+
850 OC/30 s ( 0 1. Experi- / 5,
+ 800 0 ~ / 2 0 s.mental r e s u l t s f o r unimplanted GaAs ( a ) is a l s o included.
DLTS s p e c t r a of Sit-implanted GaAs a c t i v a t e d by a second s t a g e RTA f o r d i f f e r e n t times a r e shown i n Fig.4. In the f i r s t s t a g e RTA, t h r e e d i s t i n c t DLTS peaks a r e observed, which a r e denoted a s A, B and C, r e s p e c t i v e l y . The t r a p l e v e l s of t h e t h r e e peaks a r e 0.26, 0.48 and 0.64 eV, respectively. After the second-stage RTA, peak A diminishes. The s i g n a l C decreases with increasing the second-stage anneal time whereas the height of s i g n a l B i s unchanged. The s i g n a l C with an a c t i v a t i o n energy of 0.64 eV might be r e l a t e d t o EL3 (0.64 eV) o r EN2 (0.63 eV) which were observed i n SiOz capped GaAs by Kuzuhara e t a1 /12/. Comparing DLTS r e s u l t s with depth p r o f i l e s of vacancy-type d e f e c t s given i n Fig.3, i t i s believed t h a t s i g n a l B with an a c t i v a t i o n energy of 0.48 eV is r e l a t e d t o the Ga-related vacancy-type defects. A l o t of DLTS works/l3/ have
- C
C4-460
JOURNAL DE PHYSIQUEs u g g e s t e d t h a t t h e t r a p l e v e l
a t
0 . 5 3-
0.57 eV c o r r e s p o n d s t o i m p l a n t a t i o n i n d u c e d damage, w h i c h is c o n s i s t e n t w i t h t h e p r e s e n t r e s u l t s .The r e s u l t s i n F i g . 5 , o b t a i n e d f r o m H a l l m e a s u r e m e n t s , i n d i c a t e t h a t two-step RTA g i v e s b e t t e r a c t i ~ a t i o n e f f i c i e n c y t h a n o n e - s t e p RTA, w h i c h i m p l y t h e e n h a n c e m e n t o f c a r r i e r g e n e r a t i o n w i t h i n c r e a s i n g t h e s e c o n d - s t a g e a n n e a l t i m e , a l t h o u g h t h e v a c a n c y - t y p e d e f e c t s p r o d u c e d b y i o n - i m p l a n t a t i o n a r e n o t r e c o v e r e d r e g a r d l e s s o f t h e d u r a t i o n o f s e c o n d - s t a g e a n n e a l t i m e , g i v e n i n F i g . 3 . T h i s i m p l i e s t h e a c t i v a t i o n o f S i t - i m p l a n t e d GaAs p r o c e e d s f r o m t h e e x c h a n g e o f i n t e r - s t i t i a l S i ( S i r ) w i t h s u b s t i t u t i o n a l Ga ( G a m ) g i v e n i n e q . ( 2 ) , r a t h e r t h a n t h e t r a p p i n g o f S i x i n t o Ga v a c a n c y .
However t h e a p p r o p r i a t e n e s s o f t h i s mechanism i n i n t e r p r e t i n g t h e a c t i v a t i o n phenomena o f S i t - i m p l a n t e d GaAs r e m a i n s o p e n .
F i g . 5 D e p e n d e n c e o f a c t i v a t i o n e f f i c i e n c i e s i n S i t - i m p l a n t e d undoped LEC GaAs on t h e t w o - s t e p r a p i d t h e r m a l a n n e a l i n g a t 9 0 0 OC/5 s
+
8 5 0 OC / t s (A); 9 0 0 OC/3 s+
8 5 0 OC/t s ( 0 ) ; 9 2 0 ° C / 5 s + 8 0 0 ° C / t s ( 0 ) .S e c o n d - s t a g e Anneal T i m e ( t s e c ) 4-CONCLUSIONS
Slow p o s i t r o n beam t e c h n i q u e was u s e d t o d e t e r m i n e t h e d i s t r i b u t i o n o f v a c a n c y - l i k e d e f e c t s i n S i t - i m p l a n t e d GaAs a n d Bt-and As+-implanted S i . I n Bt- and A s t - i m p l a n t e d S i s u b s t r a t e s , t h e p a r a b o l i c - t y p e d i s t r i b u t i o n s f o r v a c a n c y - t y p e d e f e c t s w e r e o b s e r v e d . T h i s i m p l i e s t h e p r o d u c t i o n o f v a c a n c y - l i k e d e f e c t s i s d o m i n a t e d by l o w e n e r g y r e c o i l i n g p r o c e s s i n i o n i m p l a n t s i n t o e l e m e n t a l s e m i c o n d u c t o r . I n compound s e m i c o n d u c t o r s u c h a s GaAs, t h e c o n c e n t r a t i o n o f v a c a n c y -
t y p e d e f e c t s d e c r e a s e d c o n t i n u o u s l y w i t h i n c r e a s i n g d e p t h b e l o w t h e s u r f a c e , w h i c h was d u e t o t h e v a c a n c y g e n e r a t i o n by h i g h e n e r g y r e c o i l i n g p r o c e s s . The c o n t i n u o u s d e c r e a s e o f i m p l a n t a t i o n -
i n d u c e d d e f e c t s c h a n g e d i n t o t h e p a r a b o l i c - t y p e d i s t r i b u t i o n i n t h e d e p t h b e l o w t h e s u r f a c e by a n n e a l i n g t h e S i t - i m p l a n t e d GaAs. The c o n c e n t r a t i o n o f d e f e c t s is n o t c h a n g e d by i n c r e a s i n g t h e s e c o n d - s t a g e a n n e a l t i m e w h e r e a s t h e a c t i v a t i o n p r o p e r t i e s d e t e c t e d b y H a l l m e a s u r e m e n t s h a v e b e e n
improved.
ACKNOWLEDGEMENT
T h i s work w a s f i n a n c i a l l y s u p p o r t e d b y K o r e a T e l e c o m m u n i c a t i o n s A u t h o r i t y . T h i s work Was a l s o s u p p o r t e d i n p a r t b y a G r a n t - i n Aid f o r S c i e n t i f i c R e s e a r c h o f t h e J a p a n e s e M i n i s t r y o f E d u c a t i o n , S c i e n c e and C u l t u r e , a n d Shimazu S c i e n c e F o u n d a t i o n .
REFERENCES
/I/ C h r i s t e l L.A. a n d G i b b o n s J.F., J. A p p l . Phys. 52 ( 1 9 8 1 ) 5050.
/2/ B r i c e D.K., J. A p p l . P h y s . 46 ( 1 9 7 5 ) 3385.
/3/ Seo K.S., Dhar S. a n d B h a t t a c h a r y a P.K., Appl. P h y s . L e t t . , 4 7 ( 1 9 8 5 ) 50.
/4/ Mills J r . A.P. a n d W i l s o n R.J., Phys. Rev. A26 ( 1 9 8 2 ) 490.
/5/ T a n i g a w a S., I w a s e
Y.,
Uedono A. a n d S a k a i r i H., J. N u c l . M a t e r . 1 3 3 & 1 3 4 ( 1 9 8 5 ) 463./6/ Lynn K.G., Chen D.M., N i e l s e n B., P a r e j a R. a n d Myers S., Phys. Rev. 8 3 4 ( 1 9 8 6 ) 1 4 4 . /7/ Mills J r . A.P. i n : P o s i t r o n A n n i h i l a t i o n , e d s . , Coleman P.G. ( N o r t h - H o l l a n d , Amsterdam,
( 1 9 8 2 ) P.142.
/8/ T a n i g a w a S . , H i n o d e K., N a g a i
R.
a n d Doyama M., Appl. Phys. 18 ( 1 9 7 9 ) 81./9/ Opyd W.G., G i b b o n s J . F . , Bravman J.C. a n d P a r k e r
K.K,
Appl. P h y s . L e t t . 4 9 ( 1 9 8 6 ) 974./lo/ H a u t o j a r v i P., Moser P., S t u c k y M., C o r b e l C. a n d P l a z a o l a F., A p p l . P h y s . L e t t . 4 8 ( 1 9 8 6 ) 8 0 9 .
/11/ R a l s t o n J . , Wicks G.W., Eastman L.F., Decooman B.C. a n d C a r t e r C.B., J. Appl. P h y s . 9 ( 1 9 8 6 ) 120.
/12/ K u z u h a r a M. a n d N o z a k i T., J. Appl. Phys. 5 5 ( 1 9 8 6 ) 3131.
/13/ S r i r a n S. a n d Das M.B, IEEE E l e c . Dev. ED-30 ( 1 9 8 3 ) 5 8 6 .
