- Email: [email protected]
Formation of semiconductor interfaces by surface electromigration
Applied Surfa~ Science 56-58 ( i ' , 2) 33a-334 North-Holland
appSed
Surface Science
Formation of semiconductor interfaces by surface electromigration Hitoshi Yasunaga, Akiko Natori and Nan-Jian Wu Dep~rlment 0,¢ Electra~lics Engineering, Tile Unil'ersity of Elcctro-C~,llnnmicatiutl,~, Chela-sill, Tokyo la2, Japan Received 5 May Iqgl; accepted for publication I I September 1991
I! is proposed that electromigration on semiconductor surfaces can be utilized at the initial stage of formation of well-controlled interface stmctuzes. Advantages and properties related to the eleeoomigration, namely. Ihe lateral growth of a characteristic intermediate metal-layer in direct contact with the clean semiconductor surface, thu driving force of the mass transport and occasional enhancement of the lateral-growth rate in the presence of surface atomic steps on the semiconductor surface are described,
1. l n l r m l u l i o n Recently it has become evident that the electrical properties of a metal-semico.-,dactor contact are significantly affected by microscopic structural defects of the interface. Therefore, the formation technology o f well-controlled interface structures attracts renewed interest in the field of semiconductor devices. We propose to employ "electromigration on semiconductor surfaces" [I] for the formation of the first atomic layer of a metal in direct contact with a clean semiconductor surface in the fabrication process of m e t a l semiconductor contacts. Electromigration is a preferential surface migration of adsorbate atoms over a clean surface of a semiconductor substrate heated by a D C current. With this mass transport we are often able to obtain lateral growth of a homogeneous well-ordered intermediate layer over a clean semiconductor surface. T h e interface formed in this way is expected to be free from those structural defects which have a crucial influence on the electrical properties of the contact. It is also possible to obtain different interface structures for a single metal-semiconductor system by applying electromigration u nde r different conditions. Thus we are able to control the characteristics of the contact.
In orde r to give a good reason for the proposal, we present in this paper those aspects of electromigration on semiconductor surfaces which are related to the formation of the interface, namely, the lateral growth of a defect-free homo.. geneous hetcro-overlayer o n semiconductor surfaces by electromigration, the driving force of the mass transport and the effects of surface atomic steps on the lateral growth.
2. Lateral growth of the intermediate layer by electromigrution Electromigration, the mass transport driven by some electric force, exhibl s novel features when it takes place over semi~Jnductor surfaces. T h e deposited material is generally carried in a preferential direction either towards the cathode or the anode over the clean surface of the semiconductor substrate fed by a D C current. T h e externally applied electricity p:,3vides adatoms with thermal energy due to Joule heating and with some electric driving force. T h e morphology of the overlayer developed from the deposited material in the process of electromigration depends on the mnde of thin film growth on the semiconductor substrate. For
0169-4332/92/$0'3.00 © 1992 - Elsevier Science Publishers B.V, All rights resen'ed
H. Yasunaga el aL / Fonnanon of semico~ductor blterfaces by surface electromi~ralion
In on S t ( I l l ) 7 x 7 [2], which is assumed to grow in a layer-by-layer way up to a coverage of 2 monolayers followed by three dimensional island formation, a thin film patch deposited prior to the migration through a window of 10O × 150 p.m exhibited a preferential spread towards the oath-. ode upon applying the DC power as shown in fig. l. One monolayer (ML) denotes the surface atom density of the substrate; 7.8:< 1014 cm -2 for St(111). The spread-out overlayer was completely like the intermediate layer with 1 ML coverage and had a 4 × I structure [2,3] regardless of the initial coverage of the In patch as far as the coverage exceeded 1 ML. The growth rate of the layer was also independent of the deposition coverage as shown in fig. 2. On the anode side of the deposition zone the reduction of the coverage to 1 ML proceeded eoincidentally with the spread of the leading edge. For Ag on S i ( l l l ) 7 x 7 ]4[, a system demonstrating a typical island-on-layer (StranskiKranstanev) growth mode, a similar lateral growth of a homogeneous intermediate layer by the electrumigration was observed as shown in fig. 3. The spread-out layer on the cathode side proved to be exactly I ML in coverage with ~/3 x Vr3 structure. After almost 30 min, when the deposited Ag was nearly exhausted, a mixed phase of ~/3 x ~/3 and 3 × 1 structure emerged on the anode side of the evaporated zone. It is interesting to note that only one among the three eventually possible orientations of 3 x l structure was preferentially observed. Namely, the 3 × 1 structure with the longer side of the unit cell parallel to the current direction was favored• Many other systems demonstrating ;.sland-onlayer growth mode exhibited a similar electromigrative lateral growth of the respective intermedime layer [1]. Thus it is possible in many systems to utilize the electromigrative lateral growth at the very initial stage for the formation of the interface. Advantages of this method are: (1) the layer is free from structural defects such as outof-phase boundaries due to simultaneous nucleation and domain boundaries of phases with multiple equivalent orientations, and the lateral growth mode itself can eliminate a variety of eventual imperfection, (2) the reproducibility of
331
dc current >
;0 ..'5 ,. ~,~. :: ..... .:.:, ~.
(a)
..-./;"~ . . . . .
"
"
m
;
2 ML
.)~,"
3 ML
";,.~:?,,-,..~
(b)
i~
'
~.
. ~ . :..:..
~:-
4ML
-. 0
.•i ~ = " : ~~:
100 I
!
to ZO§O~min
IJ.m I
Fig. I. Scanning Auger line profiles of an In overlayer on Si(ll])7x7. The time of DC power supply heating the sub strafe :o approximately 1500C is also indicated•
the intermediate layer and therefore the interface structure is guaranteed by virtue of the intrinsic nature of the electromigratiou, and (3) neverth¢-
332
H. Yasung~a et al. / Formation of ~emic~lductar imer[ace,~by surface ¢lectromigratioa
[ntSi(l|tl
4ML
=
Ag/GaAs
(100)
0 mlh
A
~10
it
e3 64
!
020
5
500"C
~"
dc c u r r e n t
time of d¢ supplylmin.) IX' powersupplyfor nvariewof deposilioncoverages. less. one can obtain different interface structures for a single metal-semiconductor interface system depending on the condition of the ¢lcctromigration. By the way, for systems of island (Volmer-Wcber) growth mode such as Ag on GaAs( 100% no homogeneous intermediate layer is developed as indicated in fig. 4.
~F~[[
~
Fig. 4. TimeevolulionufthcAgovetiayeronGaAs(100)4×l upon applyinga DC current heating the subszrate to 50(PC.It is noled Ihal no characterislicoverlayerwas developed. 3. Driving force of electromlgration
3.4 ML Ag/Si(III}__:,~,~,~.,.~, . . /__~':~,.,¢,v" ... ~ .¢..,./~ ! i ~ ' ~
.;
~[
] 12o! ! 3..0~~ ' ~ " ~ : ~.,ji ~ L ¢ ~ ~
It is the driving force that distinguishes electromigration on serniconduct . . . . rf . . . . from conventional electromigration in bulk metal [5] and thin film conductors of integrated circuits [6], because the former eleetromigration usually exhibit a preferential direction of mass transport
opposite to the latter. Therefore, the driving force
;
]
~ / --,.L/
L
e,~ 0
m0 200 300 distance (~m} Fig. 3. Time evolution of Ihe Ag ov=rlayer for 3.4 ML Ag/Si~lll)uponappiyingaDCcurrenldensityofl2.SA/cm z
(45(PC).The current direction is indicatedby an arrow,
on semiconductor surfaces must be different from the so-called wind force, which dominates c o n ventional elcctromigration. To clarify the driving force for A g / S i ( l l l ) , the electromigrative velocity of the center of gravity of the overlayer was measured at a temperature of 420°C for p-and n-St( 111 ) substrates with a variety of doping levels. The velocity is plotted as a function of doping level in fig. 5, where the DC electric field keeping each substrate at 420~C is also given. Evidently the velocity is proportional to the electric field rather than the current which increases with in-
H. Yasunuga ez aL / Formation of semiconductor inte,faces by surface eleclromigration
-~101
,
.
...,
.
...,
o p lype Sul~tmt~ ~'
333
.
:a~ .~ lg°
~
i o ~t
111 i . . . . . . . . . . . . . . . . . . . . . . . lol', IDI; IOI~l hnpurity Collcentr~tioll[czn-I]
Ftg. 5. Electromigrative veMcilyof the center of gravin' of the All overlayer and the electric field available on the substrate ~u:T=ce =s a function of the doping of the semiconductor sab~tratc.
creasing doping level. Therefore, the most plausible driving force is the direct force, namely, the electric field acting upon supposedly charged mobile atoms. This promises more effectiw utilization of electromigration for the formation of interfaces. For instance, the growth rate of the intermediate layer can be controlled by a variable electric field available somehow on the semiconductor surfaces.
nantly prefc~'ential in the direction parallel to the step edge as shown in fig. 6. For A g / S i ( l l l ) the effective diffusion constant was greatly enhanced in the direction parallel to the step edge, while no significant influence of the step structure was detected on the diffusion constant in the direction perpendicular to ~tle step edge. F o r I n / S i ( l l l ) , on the other hand, the parallel diffusion constant remained unchanged, while the perpondicular diffusion constant was reduced by the step structure. The effective diffusion constants parallel and perpendicular to the step edge, DII and D ±, are plotted as a function of the vieinal angle in fig. 7. Enhancement of the mobility parallel to the step edge, which was observed to be most extinguished at a vicinal angle of 3 ° for A g / S i ( l l l ) , is a promising feature for technical application of electrnm,.'gration. It is remarked here that the 4 × I surface superstructure with multiple equivalent orientations for In on Si(l 1 I)
4ML-Ag/Si(III) 6 " VI CI NAL T=20~
% l=250mA,
4. Effects of surface step on migration It has been noticed that surface atomic steps can enhance the lateral diffusion on metal surfaces [7-9] and on semiconductor surfaces [10,11]. We have investigated the effects of surface steps on the migration using a viciual S i ( l l l ) surface inclined towards [1~0] by up to 6 ° [11,12]. The surface s~:ructure of the 3 ° and 6 ° off S i ( l ! l ) surface observed with L E E D was an alternating array of step-bunched regions and wide 7 x 7 terraces. "[he step density in the bunched region seems to be iudependedt of the vieiual angle consistent with the result of Phaneuf [13]. Surface migration on the vieinal Si(111 ) proved to be highly anisotropic for both Ag and In adatoms, l~amely, the migration was predomi-
T=400~ lit fill I
Ib)
tZ 1=250rnA,
T=400*C .....
(cl Fig. 6. Surface migration of Ag on the 3°-off Si(tll) surface with low resistivity.The deposited 4 ML Ag patch (a) exhibits a preferential movement along the step edge irrespective of the current direction either parallel (b) or perpendicular (c) to tile step edge orientation.
I£ Vas~naga et aL I Formanml of setJfectldN¢lor huerfacx.s by surface ¢lectromigration
334 ....
' ....
' ....
' ....
*....
' ....
' "'
10"~
driving force and effects of surface steps on the m a s s [ r a n s p o r t (|ave b e e n d e s c r i b e d .
Acknowledgement T h i s w o r k is s u p p o r t e d by a G r a n t - i n - A i d f o r Scientific R e s e a r c h o n Priority A r e a s by t h e M i n istry o f E d u c a t i o n , S c i e n c e a n d C u l t u r e .
' ~ ' 10-'
References
10"a
o
10 0
1
2 3 4 ANGLE (Degree)
5
G
Fig. 7. Anisotropy of the ¢ffcctiv~ surface diffusion cnnstam D/L p~ral[¢l and D± pt:rpcndicular to tile step ~:dgc for Ag and In adatoms as a function of the vicioal an#~ of Si( I i I ), c a n b e t r a n s f o r m e d i n t o a s i n g l e d o m a i n in t h e p r e s e n c e o f s u r f a c e steps. D e t a i l s will b e d e scribed elsewhere.
$. Summary I t is p r o p o s e d t h a t e l c c l r o m i g m t i o n o n s e m i c o n d u c t o r suffac,.'s c a n b e e m p l o y e d at thf; initial stage for the formation of well-controlled metalsemiconductor interface gtractnre. Advantageous p r o p e r t i e s o f electra, m i g r a t i o n , t h a t is, l a t e r a l g r o w t h o f a c h a r a c t e r i s t i c i n t e r m e d i a t e layer, t h e
11| H. Yasunaga, Surf. Sci. 242 (1991) 171. 12} H. Yasunaga, Y. Kubo and N. Okuyama, Jpn. J. Appl. Phys. 25 (19861 L400. 13] A. Yamanaka~ K. Yogi and H. Yasunaga, Ultramicrc~copv 29 (1989) 161, [4] H. Yasunaga. S. Sakomura. T. Asaohm $. Kanayama. N. Okuyama and A. Natori. Jpn. J. Appl. phys. 27 (1988) LI6P3. [5] H.B, Huntington, in: Diffusion in Solids (Recent OevclopmentsL Eds. A,S. Now(ok and J.J. Burton (Academic Press, New York, 19751 oh. 6. [6] F.M. d'Hcurl¢ and P.S. He. in: Thin Films - Interdiffusion and Reactions. Eds. J.M. Poate, K.N. Tu and $.W, Mayer (Wiley. New york. 19781 eh. 8. [7] C.A. Roulet. SurL Sci. 36 (1973) 295. [S] R. Btnz and H. Wagner. SurL Sci. 87 (1979)85, [9] Ya E. Geguzitl, Yu.S. Kaganovski and E,G. Mikhailov. Ukr. Fit. Zh. 7 (1982} 1565. [IO] E. Suliga and M. Henzlcr. J. Phys. C. (Solid State Phys3 16 (1983) 1543. [11] N.-J. Wu. A. Natori and It. Yasunaga. Surf. Sci. 242 f 1(1911 Iql. [12] N.-J. Wu, fl. Yasunaga and A. NIOI¢,rLSurf. SoL 2g0 (1992) 75. [[31 RJ. Phoneu[. E,D. Wiliian~s and N.C. Barllet, Phys. Rev. B 38 0988) 1984.
appSed
Surface Science
Formation of semiconductor interfaces by surface electromigration Hitoshi Yasunaga, Akiko Natori and Nan-Jian Wu Dep~rlment 0,¢ Electra~lics Engineering, Tile Unil'ersity of Elcctro-C~,llnnmicatiutl,~, Chela-sill, Tokyo la2, Japan Received 5 May Iqgl; accepted for publication I I September 1991
I! is proposed that electromigration on semiconductor surfaces can be utilized at the initial stage of formation of well-controlled interface stmctuzes. Advantages and properties related to the eleeoomigration, namely. Ihe lateral growth of a characteristic intermediate metal-layer in direct contact with the clean semiconductor surface, thu driving force of the mass transport and occasional enhancement of the lateral-growth rate in the presence of surface atomic steps on the semiconductor surface are described,
1. l n l r m l u l i o n Recently it has become evident that the electrical properties of a metal-semico.-,dactor contact are significantly affected by microscopic structural defects of the interface. Therefore, the formation technology o f well-controlled interface structures attracts renewed interest in the field of semiconductor devices. We propose to employ "electromigration on semiconductor surfaces" [I] for the formation of the first atomic layer of a metal in direct contact with a clean semiconductor surface in the fabrication process of m e t a l semiconductor contacts. Electromigration is a preferential surface migration of adsorbate atoms over a clean surface of a semiconductor substrate heated by a D C current. With this mass transport we are often able to obtain lateral growth of a homogeneous well-ordered intermediate layer over a clean semiconductor surface. T h e interface formed in this way is expected to be free from those structural defects which have a crucial influence on the electrical properties of the contact. It is also possible to obtain different interface structures for a single metal-semiconductor system by applying electromigration u nde r different conditions. Thus we are able to control the characteristics of the contact.
In orde r to give a good reason for the proposal, we present in this paper those aspects of electromigration on semiconductor surfaces which are related to the formation of the interface, namely, the lateral growth of a defect-free homo.. geneous hetcro-overlayer o n semiconductor surfaces by electromigration, the driving force of the mass transport and the effects of surface atomic steps on the lateral growth.
2. Lateral growth of the intermediate layer by electromigrution Electromigration, the mass transport driven by some electric force, exhibl s novel features when it takes place over semi~Jnductor surfaces. T h e deposited material is generally carried in a preferential direction either towards the cathode or the anode over the clean surface of the semiconductor substrate fed by a D C current. T h e externally applied electricity p:,3vides adatoms with thermal energy due to Joule heating and with some electric driving force. T h e morphology of the overlayer developed from the deposited material in the process of electromigration depends on the mnde of thin film growth on the semiconductor substrate. For
0169-4332/92/$0'3.00 © 1992 - Elsevier Science Publishers B.V, All rights resen'ed
H. Yasunaga el aL / Fonnanon of semico~ductor blterfaces by surface electromi~ralion
In on S t ( I l l ) 7 x 7 [2], which is assumed to grow in a layer-by-layer way up to a coverage of 2 monolayers followed by three dimensional island formation, a thin film patch deposited prior to the migration through a window of 10O × 150 p.m exhibited a preferential spread towards the oath-. ode upon applying the DC power as shown in fig. l. One monolayer (ML) denotes the surface atom density of the substrate; 7.8:< 1014 cm -2 for St(111). The spread-out overlayer was completely like the intermediate layer with 1 ML coverage and had a 4 × I structure [2,3] regardless of the initial coverage of the In patch as far as the coverage exceeded 1 ML. The growth rate of the layer was also independent of the deposition coverage as shown in fig. 2. On the anode side of the deposition zone the reduction of the coverage to 1 ML proceeded eoincidentally with the spread of the leading edge. For Ag on S i ( l l l ) 7 x 7 ]4[, a system demonstrating a typical island-on-layer (StranskiKranstanev) growth mode, a similar lateral growth of a homogeneous intermediate layer by the electrumigration was observed as shown in fig. 3. The spread-out layer on the cathode side proved to be exactly I ML in coverage with ~/3 x Vr3 structure. After almost 30 min, when the deposited Ag was nearly exhausted, a mixed phase of ~/3 x ~/3 and 3 × 1 structure emerged on the anode side of the evaporated zone. It is interesting to note that only one among the three eventually possible orientations of 3 x l structure was preferentially observed. Namely, the 3 × 1 structure with the longer side of the unit cell parallel to the current direction was favored• Many other systems demonstrating ;.sland-onlayer growth mode exhibited a similar electromigrative lateral growth of the respective intermedime layer [1]. Thus it is possible in many systems to utilize the electromigrative lateral growth at the very initial stage for the formation of the interface. Advantages of this method are: (1) the layer is free from structural defects such as outof-phase boundaries due to simultaneous nucleation and domain boundaries of phases with multiple equivalent orientations, and the lateral growth mode itself can eliminate a variety of eventual imperfection, (2) the reproducibility of
331
dc current >
;0 ..'5 ,. ~,~. :: ..... .:.:, ~.
(a)
..-./;"~ . . . . .
"
"
m
;
2 ML
.)~,"
3 ML
";,.~:?,,-,..~
(b)
i~
'
~.
. ~ . :..:..
~:-
4ML
-. 0
.•i ~ = " : ~~:
100 I
!
to ZO§O~min
IJ.m I
Fig. I. Scanning Auger line profiles of an In overlayer on Si(ll])7x7. The time of DC power supply heating the sub strafe :o approximately 1500C is also indicated•
the intermediate layer and therefore the interface structure is guaranteed by virtue of the intrinsic nature of the electromigratiou, and (3) neverth¢-
332
H. Yasung~a et al. / Formation of ~emic~lductar imer[ace,~by surface ¢lectromigratioa
[ntSi(l|tl
4ML
=
Ag/GaAs
(100)
0 mlh
A
~10
it
e3 64
!
020
5
500"C
~"
dc c u r r e n t
time of d¢ supplylmin.) IX' powersupplyfor nvariewof deposilioncoverages. less. one can obtain different interface structures for a single metal-semiconductor interface system depending on the condition of the ¢lcctromigration. By the way, for systems of island (Volmer-Wcber) growth mode such as Ag on GaAs( 100% no homogeneous intermediate layer is developed as indicated in fig. 4.
~F~[[
~
Fig. 4. TimeevolulionufthcAgovetiayeronGaAs(100)4×l upon applyinga DC current heating the subszrate to 50(PC.It is noled Ihal no characterislicoverlayerwas developed. 3. Driving force of electromlgration
3.4 ML Ag/Si(III}__:,~,~,~.,.~, . . /__~':~,.,¢,v" ... ~ .¢..,./~ ! i ~ ' ~
.;
~[
] 12o! ! 3..0~~ ' ~ " ~ : ~.,ji ~ L ¢ ~ ~
It is the driving force that distinguishes electromigration on serniconduct . . . . rf . . . . from conventional electromigration in bulk metal [5] and thin film conductors of integrated circuits [6], because the former eleetromigration usually exhibit a preferential direction of mass transport
opposite to the latter. Therefore, the driving force
;
]
~ / --,.L/
L
e,~ 0
m0 200 300 distance (~m} Fig. 3. Time evolution of Ihe Ag ov=rlayer for 3.4 ML Ag/Si~lll)uponappiyingaDCcurrenldensityofl2.SA/cm z
(45(PC).The current direction is indicatedby an arrow,
on semiconductor surfaces must be different from the so-called wind force, which dominates c o n ventional elcctromigration. To clarify the driving force for A g / S i ( l l l ) , the electromigrative velocity of the center of gravity of the overlayer was measured at a temperature of 420°C for p-and n-St( 111 ) substrates with a variety of doping levels. The velocity is plotted as a function of doping level in fig. 5, where the DC electric field keeping each substrate at 420~C is also given. Evidently the velocity is proportional to the electric field rather than the current which increases with in-
H. Yasunuga ez aL / Formation of semiconductor inte,faces by surface eleclromigration
-~101
,
.
...,
.
...,
o p lype Sul~tmt~ ~'
333
.
:a~ .~ lg°
~
i o ~t
111 i . . . . . . . . . . . . . . . . . . . . . . . lol', IDI; IOI~l hnpurity Collcentr~tioll[czn-I]
Ftg. 5. Electromigrative veMcilyof the center of gravin' of the All overlayer and the electric field available on the substrate ~u:T=ce =s a function of the doping of the semiconductor sab~tratc.
creasing doping level. Therefore, the most plausible driving force is the direct force, namely, the electric field acting upon supposedly charged mobile atoms. This promises more effectiw utilization of electromigration for the formation of interfaces. For instance, the growth rate of the intermediate layer can be controlled by a variable electric field available somehow on the semiconductor surfaces.
nantly prefc~'ential in the direction parallel to the step edge as shown in fig. 6. For A g / S i ( l l l ) the effective diffusion constant was greatly enhanced in the direction parallel to the step edge, while no significant influence of the step structure was detected on the diffusion constant in the direction perpendicular to ~tle step edge. F o r I n / S i ( l l l ) , on the other hand, the parallel diffusion constant remained unchanged, while the perpondicular diffusion constant was reduced by the step structure. The effective diffusion constants parallel and perpendicular to the step edge, DII and D ±, are plotted as a function of the vieinal angle in fig. 7. Enhancement of the mobility parallel to the step edge, which was observed to be most extinguished at a vicinal angle of 3 ° for A g / S i ( l l l ) , is a promising feature for technical application of electrnm,.'gration. It is remarked here that the 4 × I surface superstructure with multiple equivalent orientations for In on Si(l 1 I)
4ML-Ag/Si(III) 6 " VI CI NAL T=20~
% l=250mA,
4. Effects of surface step on migration It has been noticed that surface atomic steps can enhance the lateral diffusion on metal surfaces [7-9] and on semiconductor surfaces [10,11]. We have investigated the effects of surface steps on the migration using a viciual S i ( l l l ) surface inclined towards [1~0] by up to 6 ° [11,12]. The surface s~:ructure of the 3 ° and 6 ° off S i ( l ! l ) surface observed with L E E D was an alternating array of step-bunched regions and wide 7 x 7 terraces. "[he step density in the bunched region seems to be iudependedt of the vieiual angle consistent with the result of Phaneuf [13]. Surface migration on the vieinal Si(111 ) proved to be highly anisotropic for both Ag and In adatoms, l~amely, the migration was predomi-
T=400~ lit fill I
Ib)
tZ 1=250rnA,
T=400*C .....
(cl Fig. 6. Surface migration of Ag on the 3°-off Si(tll) surface with low resistivity.The deposited 4 ML Ag patch (a) exhibits a preferential movement along the step edge irrespective of the current direction either parallel (b) or perpendicular (c) to tile step edge orientation.
I£ Vas~naga et aL I Formanml of setJfectldN¢lor huerfacx.s by surface ¢lectromigration
334 ....
' ....
' ....
' ....
*....
' ....
' "'
10"~
driving force and effects of surface steps on the m a s s [ r a n s p o r t (|ave b e e n d e s c r i b e d .
Acknowledgement T h i s w o r k is s u p p o r t e d by a G r a n t - i n - A i d f o r Scientific R e s e a r c h o n Priority A r e a s by t h e M i n istry o f E d u c a t i o n , S c i e n c e a n d C u l t u r e .
' ~ ' 10-'
References
10"a
o
10 0
1
2 3 4 ANGLE (Degree)
5
G
Fig. 7. Anisotropy of the ¢ffcctiv~ surface diffusion cnnstam D/L p~ral[¢l and D± pt:rpcndicular to tile step ~:dgc for Ag and In adatoms as a function of the vicioal an#~ of Si( I i I ), c a n b e t r a n s f o r m e d i n t o a s i n g l e d o m a i n in t h e p r e s e n c e o f s u r f a c e steps. D e t a i l s will b e d e scribed elsewhere.
$. Summary I t is p r o p o s e d t h a t e l c c l r o m i g m t i o n o n s e m i c o n d u c t o r suffac,.'s c a n b e e m p l o y e d at thf; initial stage for the formation of well-controlled metalsemiconductor interface gtractnre. Advantageous p r o p e r t i e s o f electra, m i g r a t i o n , t h a t is, l a t e r a l g r o w t h o f a c h a r a c t e r i s t i c i n t e r m e d i a t e layer, t h e
11| H. Yasunaga, Surf. Sci. 242 (1991) 171. 12} H. Yasunaga, Y. Kubo and N. Okuyama, Jpn. J. Appl. Phys. 25 (19861 L400. 13] A. Yamanaka~ K. Yogi and H. Yasunaga, Ultramicrc~copv 29 (1989) 161, [4] H. Yasunaga. S. Sakomura. T. Asaohm $. Kanayama. N. Okuyama and A. Natori. Jpn. J. Appl. phys. 27 (1988) LI6P3. [5] H.B, Huntington, in: Diffusion in Solids (Recent OevclopmentsL Eds. A,S. Now(ok and J.J. Burton (Academic Press, New York, 19751 oh. 6. [6] F.M. d'Hcurl¢ and P.S. He. in: Thin Films - Interdiffusion and Reactions. Eds. J.M. Poate, K.N. Tu and $.W, Mayer (Wiley. New york. 19781 eh. 8. [7] C.A. Roulet. SurL Sci. 36 (1973) 295. [S] R. Btnz and H. Wagner. SurL Sci. 87 (1979)85, [9] Ya E. Geguzitl, Yu.S. Kaganovski and E,G. Mikhailov. Ukr. Fit. Zh. 7 (1982} 1565. [IO] E. Suliga and M. Henzlcr. J. Phys. C. (Solid State Phys3 16 (1983) 1543. [11] N.-J. Wu. A. Natori and It. Yasunaga. Surf. Sci. 242 f 1(1911 Iql. [12] N.-J. Wu, fl. Yasunaga and A. NIOI¢,rLSurf. SoL 2g0 (1992) 75. [[31 RJ. Phoneu[. E,D. Wiliian~s and N.C. Barllet, Phys. Rev. B 38 0988) 1984.