HAL Id: jpa-00224661
https://hal.archives-ouvertes.fr/jpa-00224661
Submitted on 1 Jan 1985
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.
ON THE INTERNAL STRUCTURE OF Cu- AND Pt-SAPPHIRE INTERFACES
C. Mulder, J. Klomp
To cite this version:
C. Mulder, J. Klomp. ON THE INTERNAL STRUCTURE OF Cu- AND Pt-SAPPHIRE INTER- FACES. Journal de Physique Colloques, 1985, 46 (C4), pp.C4-111-C4-116. �10.1051/jphyscol:1985412�.
�jpa-00224661�
JOURNAL DE PHYSIQUE
Colloque C4, supplément au n04, Tome 46, avril 1985 page C4-111
ON T H E INTERNAL STRUCTURE O F Cu- A N D Pt-SAPPHIRE INTERFACES
C.A.M. Mulder and J . T . Klomp
PhiZips Research Laboratories, Eindhoven, The Netherlands
Rés&
-
La s t r u c t u r e interne d'interfaces saphir à orientation (0001)-
métal à réseau cubique faces centrées, constituées par l i a i s o n é t a t s o l i d e non réactive, a été étudiée au microscope électronique à transmission. Il a é t é constaté que l e s métaux é t a i e n t orientés (1 11 )
,
parallèlement à (0001 ).
Abstract
-
?he interna1 structure of (0001) oriented sapphire/fcemetal in- terfaces formed i n non-reactive solid-state bonding has been studied by means of transmission electron microscopy (TEM). m e metals were found t o be orien- ted (111) p a r a l l e l to (0001).1 INl!KmJcTION
Çolid-state bonding of metals t o oxide materials finds application i n vacuum and semiwnductor devices, but l i t t l e is knawn about t h e s t r u c t u r e of the interface formed durinq bnding and t h e e f f e c t s of the discontinuity of c r y s t a l l a t t i c e s on the properties of the bond. Better knowledge of these features is necessary i n order t o c o r r e l a t e the character of t h e interface with the behaviour of t h e bond.
The b i s of interface formation between two materials is t h e yield i n energy t h e system developç as intimate contact between t h e surfaces is established. This gain i n energy depends on the surface energies of t h e materials and on t h e occur- rence of a chenical reaction a t t h e interface /1/. The surface energy y of crys- t a l l i n e materials v a r i e s with d i f f e r e n t crystallographic orientations, I n the case of f& metals, f o r instance, t h e following r e l a t i o n s a r e reported /2/: y ( 111 ) : y(100) : y(110) = 1 : 1.047 : 1.150. Vkether o r not a chemical reaction follows t h e physical interaction depends on t h e nature of the materials and on the external conditions (temperature, atmosphere) a t which t h e interface is formed. I f m l y phy- s i c a l interaction occurs it is of i n t e r e s t whether a preferential i n t e r f a c i a l rela- tionship e x i s t s between the c r y s t a ï h g r a p h i c orientations of the materials and, i f so, how it is correlated with the surface enerqies. Fletcher /3/ d m s t r a t e d t h a t f o r an interface between tm simple crystals of identical s t r u c t u r e but d i f f e r e n t lattice paraneters t h e i n t e r f a c i a l enerqy increases d r a s t i c a l l y with increasing m i s f i t of the l a t t i c e s . Recently, t h e i n t e r f a c i a l s t r u c t u r e of h e t e r e e p i t a x i a l l y grown siliwn-owsapphire, which can be intemreted as non-reactively bonded, has received wnsiderable i n t e r e s t /4-7/. Morozuma et al. / 8 / studied the s t r u c t u r e of a reactive bonded n i o b i d s a p p h i r e interface including the l a t t i c e matching between Al203 and Nb4, phases.
In t h i s work t h e s t r u c t u r a l build-up of the interface of non-reactive bonds be- tween single-crystalline alumina surfaces, oriented (0001), and the polycrystal- l i n e fcc metals Cu and Pt is investigated. These interfaces were prepared under wnditions i n which only physical interaction could occur, thus precluding structu- ral changes due t o mutual dissolution of species o r canpound formation. The micro- s t r u c t u r a l a n a l p i s was carried out using wnventional transmission electron m i c r o - ScoW (Tm).
2 'lFlB3RETICAL CONSIDERATIONS
The interaction sites of t h e m e t a l a t m w i t h the alumina are assumed to be the troughs between t h e 02- sites i n t h e hexagonal A1203 l a t t i c e . Firan t h e c r y s t a l data of A l 9 3 , Cu and Pt /9/ it appears t h a t t h e hexagonal ( 1 1 1 ) planes of the metals a r e t h e rmst s u i t a b l e f o r bringing t h e metal i n t o r e g i s t e r with hexagonal (0001) sapphire ( s e e Table 1 )
.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1985412
C4-112 JOURNAL DE PHYSIQUE
Table 1
a ( m ) orientation atanic spacing (nm)
A193 0.4758 (O001 ) 0.2747
Cu 0.36150 (111) 0.2556
P t 0.39231 (111) O. 2774
Rran t h e viewpoint of gain i n surface enerqy i n the interface formation, the (110) metal planes a r e more favourable than the (111) ~ l a n e s due t o t h e i r surface energy ( s e e section 1 ) .
3.1 Sanple preparation
The sanples were prepared fran o p t i c a l l y polished sapphire p l a t e s (suppl.
Djevardhyan (Çw)), 1 mn thick, with the orientation of t h e bonding surface p a r a l l e l t o (0001 ). FrQn X-ray analyses the sapphire prwed t o be a mosaic c r y s t a l with t h e c a x i s deviating about 2" f r a n the main c a x i s . m e metals* (supp. Gocü
Fellow (U.K.)) wre annealed polycrystalline f o i l s 8 and 30 )rm thick f o r Cu and P t , respectively, and were single-crystalline w e r t h e thickness of t h e f o i l . X-ray analysis on 1000 and 1500°C H2 annealed Cu and Pt, resp., s h e d t h e Cu t o have mainly t h e (100) and Pt the (251) orientation. The metals were sandwiched between two sapphire p l a t e s aligned i n such a way t h a t the b-axis of the crystals were parallel. The bonds w r e made i n the solid s t a t e /IO/ by heating under an applied mechanical pressure which deformed t h e metal. The conditions a r e sumnarized i n Table 1I.The atmoçphere mntained ïess than 2 H g and 02.
Table II Bonding conditions
mpper/sapphire p l a t i n m a m i r e
tgnperature (K) 1340 1770
pressure ( M P ) 20 20
t h ( h r s ) 1 0.5
atmoçphere N2/25H2 ~r
metal deformation ( % ) 20 20
me
a-heres prevent both t h e metals f r a n o x i d i z i m and t h e Al203 f r a n k i n g re- duced, as can be found fran t h e d y n a n i c calculations /Il/. Auqer analysis on tapered sections of a Pt/A1203 interface s h d no change i n ccmp3sition of t h e Pt /12/.E a r l i e r X-ray d i f f r a c t i o n measurements on t h e metal/sapphire interfaces /13/ re- quireà t h e interface t o be accessible f o r X-rays. Therefore several a i s a n p l e s were cleaved d o n g t h e interface; on m e sanples t h e sapphire was thinned to about 15
)rm by grinding and p l i s h i n g . The measursnents on sane ai s m p l e s showed a (111) texture and others (241) and (263). X-ray analysis of thinned Pt/sa@phire inter- faces gave no indication of a preferred orientation of the Pt on t h e sapphire. The interface strength was apparently so high t h a t cleaving of çinnples was impossible because cracks propagated through t h e s a m i r e .
3.2 Preparation of t h e TEM s m p l e s
Specimens 200 microns thick were cut fran a sandwich of sapphire/metal/sapehire and f u r t h e r reduced by mechanical grinding and p l i s h i n g to 110 p f o r Cu/sapphire and t o 50 pn f o r Pt/sapphire. It has t o be noted t h a t t h i s procedure may have given r i s e to surface damage i n a l m i n a /14/.
Ion h a n thinning was used t o reduce t h e thickness of t h e sanples t o allow transmission of the 120 kV electrons i n a Philips W 400T transmission electron microçcape (TEM). 'ltio arqon ion quns m r a t i n q a t about 6 kV were mployed to ban- bard both s i d e s of a specimen a t t h e same t h e . As the thinninq r a t e of metals is much higher than of t h e sapphire it is necessary to ensure t h a t the metals have not already been removed before t h e sapphire is s u f f i c i e n t l y t h i n f o r transmitting
*
Impurities i n ppn: Si,Al,Mg <600 f o r Cu and (10 f o r P t , others <400.electrons. This was achieved by directing the metal/sapphire interface perpendicu- lar to the sputtering direction. In additim, the two beans were directed at an angle of incidence between 5 and 10" to the specimen surface so that the edge of the sapphire at the interface protected the metal fran being removed too fast.
Sample rotation during çputtering was impossible so same surface structuring was caused by the ion bcsnbardment /15/.
4 TEM INVESTICATION; I7ESULTS AND DISCUSSION 4.1 CU / ~1203
In the transmission electron microscow the C o p r appeared to be present on one side of the sapdnire only. The microstructure of the Als3/Cu interface is shom in fig. 1. Both Al203 and Cu readily transmit 120 kV electronç; the interface presents itself as a straight lire. No anorphous phase between the samire and the metal was observed either in the diffraction pattern or in dark field at the inter- fa=.
Using electron diffraction techniques the crystallographic orientation of the copper at the (0001) oriented sapphire surface was detennined. %e sapphire was oriented with the lattice vectors <0001> (along the caxis) and<ll20)in the plane of view, the direction of the electron bean in the crystal beinq <1100>. The accuracy of the orientation was determined f m the Kikuchi lines visible in the diffraction pattern. The diffraction spots reproduced in the inset of fig. 1 origi- nate £rom both Al203 and Cu. m i s shows that the initial single crystallinity w e r the thickness of the metal foi1 is maintained in the bondi process. The indexed diffraction patterns of both materials, fiq. 2b. sha*a theTlll] direction of Cu parallel to the {000a direction (caxis) of sacphire. The indexed Cu spots ( 51 1, 420, etc) drawn at the bottom of fig. 2b are not present in
the
inset 02-fig 1.The copper diffraction s w as shortest recipyocal vectors 111 and 331; hence the direction of the hem in the crystal was c2462, with an uncertainty of about 1". This pattern is not-rectwular. Assumiq the m m r to be rotated by a m x i - mately 11 about the 111 direction, the diffraction pattern will show the 220 reflection, which is perpendicular to 111. The orientation of the lattice planes at the interface is given in f ig 3, the copper (1 1 1 ) plane king parallel to the
(O001 Al203 plane.
Fig. 2a Close-up of the diffraction pattern in fig. 1.
Fig. 1 Microstructure of the copper/sapphire Fig. 2b Indexed diffraction interface (bar = 1 pin). Inset corresponding pattern of the interface C u / A l O
electron diffraction pattern. 2 3'
JOURNAL DE PHYSIQUE
F i g . 3 S c h e m a t i c v i e w o f t h e o r i e n t a t i o n o f t h e l a t t i c e p l a n e s a t t h e C u / A l O i n t e r f a c e .
2 3
F i g . 4 C o i n c i d e n c e l a t t i c e o f a ( 1 1 1 ) Cu l a y e r on t o p o f an ( 0 0 0 1 ) o x y g e n l a y e r o f the A1203 l a t t i c e .
I n order t o i n t e r p r e t t h e TFM r e s u l t s f o r t h e Cu/Al2O3 bond we conçtructed two n e t s /16/ ( f i q ' 4): a (111) plane of the mpper l a t t i c e and an (0001) oxyqen layer of t h e sapphire l a t t i c e with a t m i c spacings a s indicated i n Table 1. The n e t s w e r e superposed and rotated with respect to each other. In order t o ease the recognition of a coincidence l a t t i c e , one Cu atan was placed on top of an O a t m a t thg centre of r o t a t i m . Aiter a-zotation of 10.9" fran t h e s t a r t i n g position, w i t h 1120 of sapphire p a r a l l e l to 220 of copper, t h e f i f t h O a t m of each dense rcw thrcugh t h e o r i q i n almost mincides with a Cu atan a t the corners of t h e hexagcm.
This O a t m is a t a distance of 5/3 a(Al2O3)
fi
= 1.374 rm fran t h e origin, the' ai atm a t a(Cu) fi = 1.353 rm. Frwn these distances a lattice mismatch r a t i o of 66:65 is deduced, which indicates a nearly perféct match. Rotation of 10.9" i n the other direction would qive a similar match as w i l l multiples of 60' added to e i t h e r angle. I f t h e rrrrp~lete l a t t i c e is taken i n t o consideration, instead of only one plane of each, these twelve matching positions separate i n t o two groups with a s l i g h t difference i n energy. However, since s a m i r e has hexagonally stacked oxy- gen planes and it is not known which of t h e two possible types of axygen plane is t h e surface, it is impossible to distinguish between the t w groups experimentally.Although d y 1:25 O a t m and 1:28 Cu a t m mincide, and t h i s orientation rela- t i o n has been observed a t one Cu/Al2O3 interface only, we do not believe it t o be accidental.
4.2 P t / A ) f l 3
In t h i m i n g a sapphire/platinum/sapphire sandwich a hole was obtained sanewhere i n t h e centre of the sample. On b t h sides of the hole t h e interface was l o c a l l y m v e d but the Pt p a r t i a l l y retained. The two Pt parts were about 250 pm apart. A typical TEM image of the p a r t i a l l y retained Pt a t one s i d e of t h e hole is produced i n f i g 5. The direction of t h e sputtering is e a s i l y recognized fran t h e scratchy s t r u c t u r e of t h e sapphire surface, an a r t i f a c t of the non-rotary ion bem
thiming. In addition, the two notches i n the sapdiire around t h e platinum indicate t h a t a t the interface the sapphire is more r e s i s t a n t t o t h e ion-beam lxmhrdment than m a t further away, a phenanenon which may be related t o the interface strength.
Fig. 5 Micro- structure of two platinum/sapphire interfaces
(bar = I O P ~ ) .
1
Fig. 6 a Electron Fiq. 6 b Indexed diffraction diffraction Pattern of pattern of the interface Pt/A1203 a platinum/sapphire as given in fiq. 6a.
interface.
A t the four platinum/sapphire m n t a c t s accessible i n t h i s specimen, we oriented t h e 0001 and 1120 r e f l e c t i o n s of Alf13 peqendicular t o the electron beam and s&u- died t h e interface under t h i s condition. In a l 1 four positions t h e (111) plane of Pt tumed out t o be p a r a l l e l t o the (0001) basal plane of the sapphire,
i.e. t h e same as i n t h e case of Cu/Alg3. Furthermore, analogous d i f f r a c t i o n pat- t e r n s as f o r îu/AlS3 were obtained a t two of t h e four Pt/Alf13 contacts. These two d i f f r a c t i o n patterns o r i g i n a t e £rom t h e same Pt/sapphire interface. Although these
interfaces a r e more than 200 )rm-apart t h e orientation r e l a t i o n is obviously preser- ved. A t these interfaces t h e 331 Pt r e f l e c t i o n was present i n t h e d i f f r a c t i o n patterns, leading t o t h e same orientation of l a t t i c e planes a t t h e interface as given i n f i g 3 f o r Cu/Alfl3. @ t h e two other Pt/Al203 mntacts, which are al- more than 200 pn apart, t h e 531 reflection was visible. One of t h e observed dif-
f r a c t i o n patterns is given and indexed i n f i g 6a and- 6b, respectively. The di- rection of t h e electron bem i n the Pt -ta1 is <268>. In t h e - p a t t e r n s the 220 d i r e c t i o n is obtained i f t h e platinum is rotated about t h e 111 direction by approximately 16". ~ a k i n g the curvature of t h e Ewald sphere i n t o account and using t h e diffraction-spots fran t h e higher-oràer Laue zones (see f i g 6 ) one can calcu- la; t h a t the L220)direction of the Pt d e s an angle of approximately 18" with the
5
1 2 3 direction of the s a e i r e .The (1 11 ) Pt-Pt distance and the (0001 )
g-û
distance d i f f e r so l i t t l e (see Table 1) t h a t a mincidence l a t t i c e with 1120 of sapphire making an angle of 60"with 220 of platinum may be anticipated. Such a m i n c i d e n e l a t t i c e has a l a t t i c e misnatch r a t i o of 102:103, indicating an hlmoçt perfect match. Hawever, air elec- trai d i f f r a c t i o n stud+s g i w s w r t t o a d i f f e r e n t i n t e r p r e t a t i a i . A t t h e two in- t e r f a c e s with t h e 531 -Pt r e f l e c t i o n present i n t h e d i f f r a c t i o n pattern, a rota- t i o n of 18" between 1120 sapphire and 220 platinInn was deduced. In canstructing t h e mrresponding coincidence l a t t i c e t h e thirteenth O a t m of each dense row
h the o r i g i n a l m t coincides with a Pt a t m . The Pt atan is a t a ( P t )
?--
(163/2) = 3.542 rnn fran t h e origin, the O a t m a t 13/3 a(A1203) fl = 3.571 m,-- giving a l a t t i c e misnatch r a t i o of 120:121. The two interfaces containing the 331 P t r e f l e c t i o n govern a coincidence l a t t i c e with a rotation of about 11" within theC4-116 JOURNAL DE PHYSIQUE
(171) P t plane with respect to t h e (0001) A l 9 3 plane. I f a P t atan and an O atan a r e positioned a t the o r i g i n of a coincidence l a t t i c e construction such as given f o r Cu/Ai93, t h e ninth O a t m along each dense row through t h e o r i g i n is found p r a c t i c a l l y on t o p of-a P t atan, a f t e r r o t a t i n g t h e 220 P t d i r e c t i o n m e r 11" w i t h respect to t h e 1120 Ai203 direction. The mrreçponding P t distance t o t h e o r i g i n is a ( P t ) = 2.466 m, the O distance is 3 a(Al2O3)
6
= 2.472 nn, leading to a l a t t i c e mismatch r a t i o of 368:369. These four observed mincidence l a t t i c e s f o r p l a t i n w s a p p h i r e (two I l 0 and t w o 18" rotated) obviously match b e t t e r than t h e , a t f i r s t s i g h t more plausible, 60' coincidence l a t t i c e . It is l i k e l y t h a t t h e lower values of t h e mismatch ratios f o r Pt/Al@3 with reçpect to t h a t f o r Cu/Al203 m r r e l a t e to t h e observed difference i n i n t e r f a c e strength which is repor- ted to be a f a c t o r of about 2 higher f o r Pt/Al@3 than f o r Cu/Alfl3 /Il/.5
mcms1ON
I n t h e work described i n t h i s paper we studied t h e i n t e r n a l s t r u c t u r e of fcc- metal/sapphire i n t e r f a c e s formed by non-reactive solid-state bonding. It w a s found f r a n electron d i f f r a c t i a n observations a t £ive d i f f e r e n t positions i n two t y p s of bonds t h a t the m e t a l is oriented (1 11 ) on basal (O001 ) sapphire, although t h i s metal (111) orientation is not the mst favourable f r a n t h e point of view of t h e lowest surface energy. %us, we wnclude f o r Our crystal s t r u c t u r e s t h a t the system s t r i v e s tsdr=wca a s i t u a t i o n with a low l a t t i c e misnatch.%is indicates t h a t
Fletcher's demonstration /3/ t h a t i n t e r f a c i a l energy decreases w i t h decreasing m i s - f i t of l a t t i c e s applies t o mre ccmplex crystal s t r u c t u r e s also.
The discrepancy between t h e TEM experiments and X-ray d i f f r a c t i o n measurements is a t present unresalved. More s p e c i f i c a l l y , i n TEM experiments on both £cc-metal/
ç a ~ p h i r e systems t h e (111) metal on (0001) sapphire o r i e n t a t i o n was alwaysi ob- served, even on locations more than 200 pm apart i n one sample. We a t t a c h mre ~XTF
portance to t h e TEM r e s u l t s than t o the X-ray analysis.
Fran Our TEM r e s u l t s a q u a l i t a t i v e correlation between t h e microstructural pro- p e r t i e s and t h e i n t e r f ace strength is obtained
.
Hawever,
quantitative information w i l l require more detailed s t u d i e s of t h e r e l a t i o n s between i n t e r n a l s t r u c t u r e and surface energy of t h e materials involved.-
We are indebted t o J. Hornstra, A.J.C. van de Ven and m r s . G. van Leeuwen f o r valuable contributions to t h i s work.REFERENCES
/1/ J T Klcmp and P J Vrugt i n "Surfaces and interfaces i n ceranic and c e r a n i c metal syçtems", Materials Science Research, vol 14, eds J Pask and A Evans (Plenum, New York, 1981) 97.
/2/ V O Yesin, VN Porozkov and V 1 Danilynk, Phys Met Metall 53 (1982) 149.
/3/ N H Fletcher, Adv i n Mat Research 5 (1971) 281.
/4/ M S Abrahans, C J Buiocchi, R T Smith, J F Corboy jr, J Blanc and G W Cullen, J Appl Phys 47 (1976) 5139.
/5/ W E Han, M S Abrahams, C J miocchi and J Blanc, J Electrochem Çoc 124 (1977) 634.
/6/ M S Abrahoans, J L Hutchiçon and G R Booker, Phys S t a t Çol ( a ) 63 (1981) K3.
/7/ F A Ponce and J Aranovich, Appl Phys Lett 38 (1981 ) 439.
/8/ S Morozumi, M Kikuchi and TNishino, J Mat Sc 16 (1981) 2137.
/9/ Rder d i f f r a c t i o n f i l e N o 10-173 (Al233), 4-0836 (Cu) and 4-0802 ( P t ) , J o i n t C mon m e r D i f f r Standards Philadelphia, 1967).
/IO/ J T Klmp, Science of Ceranics 5 (1970) 501.
/ I l / J T Klanp, t o be published i n Proc B r i t Cer Çoc (1983).
/12/ P H Oosting ( p r i v a t e carmunication, Philips Res Labs).
/13/ C Langereis (private oomnunication, Philips Res Labs)
.
/14/ B J Hockey, Proc-Brft Ceran Çoc 20 (1972) 95.
/15/ M D Rechtin, Radiation Effects 42 (1979) 129.
/16/ J Homstra ( p r i v a t e carmunication, P h i l i p s Res Labs).
