Misra, N K

Narayana, G S

IACS Institutional Repository

Indian ] .  Phys.  64A (2 ), 15 1 -1 5 5  (1 9 9 0 )X-ray studies on growth, thermal vibrations and internal stress in thin condensed films of IndiumG S Narayana and N K MisraDepartment of P h y s ic s  and M eteorology, Indian Institute of Techno logy.Kharagpur-721 302 , IndiaReceived 5 Septem ber 19 89 , accepted 1 November 1989Thin solid films prepared by evaporation technique are expected to be highly disordered. Large internal stresses and frozen-in lattice defects may develop during atomic deposition process (Kato et o/ 1961, Weiss and Smith 1962, Horikoshi et al 1962, Horikoshi and Tamura 1963, Klokholm and Berry 1968, Sen et a l  1973, Nandi and Sengupta 1979). These will influence the Debye-characte­ristic temperature and structure-dependent properties of films. The study of these two physical parameters is of considerable interest in view of the applications of thin films in the technology of microelectronics. The X-ray diffraction technique provides an important tool for determining the Debye-characteristic temperature from the measurement of integrated intensities of the reflection profiles (Narayana and Misra 1988, 1989a,b) and internal stresses from the measurement of changes in lattice parameters (Keith 1956, Freedman 1962, Palatnik and Il'yinskii 1962, Kinbara and Haraki 1965, Vook and Witt 1965a,b, Haruta and Spencer 1966, Narayana and Misra 1989a,b,c). Narayana and Misra (1988, 1989a,b,c) have studied the thickness dependence of Debye-characteristic temperature and internal stresses in Pb, Sn and Ag films deposited on glass and mica substrates. Vook et ol (1967) deposited thin films of Indium at ~ 185"C and studied the texture in the 100-1000 A  thick range and observed strong fibre texture (Vook 1975). The present investigation has been undertaken to make a detailed study of texture, to determine root-mean-square displacements of atoms in lattice points and internal stresses in thin Indium films of different thicknesses prepared by vacuum evapora­tion technique on glass substrates by X-ray diffraction method.Preparation of the films, measurement of film thickness, recording of X-ray diffraction profiles, determination of integrated intensity and measurement of peak positions are carried out following the procedures described earlier by the authors (Narayana and Misra 1988, 1989a, b, c).151152 G S Narayana and N K MisraX-ray diffraction patterns from all these films were recorded using Cu-target. A  strong < 101 > texture developed for all the films. Relative intensities (l/lo) for different reflections are shown in the Table 1.T a b le  I . Relative  in ten sities (l//o) for d ifferent reflectio ns.IHo ________Film  th ick ­n ess  (nm ) 101751001251 5 0180215Thicker film  Bulk^+ ASTM data.1001001001001001001001000022 .50 .40 .96 .40 .91 .71.021112 10 3 2020.2240 .3164 .25 .54 .53 .65 .3  5 .2  5 .5  1 1It appears from the Table 1 that a strong < 101 > texture develops for all these films with a weak appearance of (002) plane parallel to the surface of the film. For thick films, polycrystallinity is observed, but strong < 101 > texture is very much predominant.The Debye-Waller factor 5 and root mean square amplitudes of atomic displace­ments along ^ 101 }  in different films were calculated following the equations (1) and (4) of Narayana and Misra (1988). Figure 1 shows the linear plot ofIn (l/AmLPF“) vs 2 for films of different thicknesses along < 101 >.The values of 6 and < u® are shown in the Table 2.Average d im  values are calculated for the films considering both < 101 }  and < 2 0 2 >  reflections using CuKm and CuK.a radiations. Since planes are parallel to the film surface, any change in d^oi values will produce strain in the film perpendicular to the film surface. Therefore, an average internal stress perpendicular to the film surface is calculated from the following equation :C_^£_ do ■ 2 v y  c ( 1)wheredo is the d im  for bulk sample, dj. is the d io i for films,^ri scQ Youngs modulus and Poison 's ratio respectively for the deposits.X-roy studies on growth, thermal vibrations etc 153F ig u re  I . P lot of In ( l/ A m L j,? ’ ) v s  2 s in ’ for f ilm s of vario u s th ick-  n e s s e s - ( l )  75  nm, (2 ) 1 0 0  nm , (3 ) 12 5  nm , ( 4 )  15 0  nm. (5 ) 180  nm and  (6 ) 2 1 5 n m .In the present calculations £, and v, are taken to bo those of bulk material. Here £ =  1.06X 10*^ dynes,'cm* and v 0.45 (Brandes 1983). and S for films areshown in Table 2.T a b le 2. D eb ye-W alle r factor (B ) ,  r.m .s. am plitude < « ’ > * ' ’ , inter- planar sp ac in g  d , o ,  and internal s tre ss  5 perpendicu lar to  film  su rface .F ilm  th ic k ­n ess (nm )B(A»)< « * > » '•(4 )4 lo 1 (A)S ( x 1 0 'd ynes/cn7 5 3 .7 0 0 .2 1 7 2 .7 1 7 0 .8 71 0 0 2 .67 0 .1 8 4 2 .7 1 7 .  0 .8 71 2 5 2 .8 6 0 .1 9 0 2 .7 1 6 0 .4 31 5 0 2 .5 5 0 .1 8 0 2 .7 1 7 0 .8 718 0 2 .27 0 .1 7 0 2 .7 1 6 0 .4 32 1 5 2 .0 3 0 .1 6 0 2 .7 1 6 0 .4 3Bulk^ — - 2 .7 1 5ASTM value.154 G S Narayana and N  K MisroIt is observed from the Table 2 that the interplanar spacing djoi of the films are always larger than that of the bulk material. Similar results were also obtained by Vook et ol (1967), Vook and Otooni (1968) and Narayana and Misra (1988, 1989 a, b, c) for tin, gold and lead films respectively on glass substrate. A s  the film thickness decreases, the dimension of the object decreases and the loosening of the atomic structure*increases. One would expect larger amplitudes of atomic vibrations at the surface of the material than in its interior. These higher vibrational modes would-result in an increased average interplanar spacing. This is obvious from the values of r.m.s. displacements < along < 101 > inTable 2 . - As  film thickness increases, < u ” decreases. The stress developed perpendicular to the film surface is tensile but of negligible value. The variation of and S with film thickness has been shown in the Figure 2. Toxen (1961)100 150 200Thicknes ( nm 1F ig u re  2. Plot of variation of lattice param eter d ,u , and internal stress (S) vvith th ickness of the film s (ooo - d jo i ,   ^ a  a  - S )calculated stress in thin Indium films from the observed increase of their super­conducting transition temperature with decreasing film thickness. The calculation Was done on the assumption that the change in transition temperature is due to stress which has a maximum observable limited by the critical shear stress necessary to move dislocations. In this calculation stress was found to be quite large for very thin film (thickness < 200 A) but very small for films of larger thickness. Because of self-annealing of Indium films, intrinsic stress due to frozen-in defects is not expected.Therefore, it can be concluded that thin Indium films with strong (101) texture can be deposited on glass substrate by vacuum evaporation method, that the measured increase in interplanar spacing is due to outward relaxation of the first few atom layers near the surface and that the internal stress developed is tensile in nature.AcknowledgmentThe authors express their sincere thanks to Dr H D Banerjee of the Materials Science Centre of the Institute for his help in measurement of film thickness.ReferencesBrandes E A  1 9 8 3  S m it h e / ls  M e t a f s  R e fe r e n c e  B o o k  6th ed., (Eng land , Robert Hortnoll L td ., Bodm in, C o rn w a ll) . 15th C hap , p 3 Freedm an J  F 1 9 6 2  I B M  ] . R es. D e v e lo p .  6 44 9  Haruta K and Spencer W  J  1966 j .  A p p I,  P h y s . 37 2 2 32  H orikhoshi H , O zaw a Y  and H asunum a H 1 9 6 2  J a p a n  J . A p p I.  P h y s . I 304  H orikhoshi H and Tam ura M 1963 J a p a n  J .  A p p I.  P h y s . 2  328  Kato H , N agasim a K and H asunum a H 1961 Oyo Butsuri 30 7 00  Keith H D 1956 P roc . P h y s . So c . B 69 180  Kinbara A  and H araki H 1 9 6 5  J a p a n  J .  A p p I.  P h y s . 4 423  Klokholm  E and Berry B S  1 9 68  J. E le c t r o c h e m .  So c . MS 823  Nandi R K and Sen  G upta S  P 19 79  J .  A p p I.  P hy s. 50 6262  N arayana G S  and M isra N K 1988 T h in  S o l id  F ilm s  164 91----- 1 9 89a  In d ia n  J .  P h y s. 63 A (8 ) 8211 9 8 9 b  T h in  S o l id  F i lm s  (co m nunicated)—  1 9 8 9 c In d ia n  J .  P h y s . 6 3 A '18 9Palatn ik  L S  and ITy in sk ii A  I 1 9 6 2  S o v ie t  P hy s. S o lid  S t a t e  3 2 0 5 3  Sen  Such itra , H aidar S  K and Sen  G upta S  P 1 9 7 3 J .  P h y s . 0 6  1978  Toxen A M 1961 P h y s. R ev , 123 4 4 2Vook R W  1 9 75  E p it a x ia l  g r o w th  Part-A  ed. J  W M atthew s (A cadem ic P ress, N .Y .) C hap . 3 .5  Vook R W  and Otooni M M 1 9 6 8 / . A p p I.  P h y s . 39 2471Vook R W , Parker T  and W right D eds. 19 67  Surfoces end/nterfoces C h e m ic a l  a n d  P h y s ic a l  C h a r a c t e r i s t ic s  S y ra cu se  U n iversity  Press, S y ra cu se  (N .Y .)  p 3 4 7Vook R W  and W itt F 1 9 6 5 a J . A p p I.  P h y s .  36 2169-----19 6 5 b  J .  V a c . S c i .  T ech. 2 49 243W eiss  G P and Sm ith D O 1 9 6 2 J . A p p I.  P h y s . 33 11665X-ray  studies on growth, thermal vibrations etc 15510

X-Ray Studies on Growth, Thermal Vibrations and Internal Stress in Thin Condensed Films of Indium

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X-Ray Studies on Growth, Thermal Vibrations and Internal Stress in Thin Condensed Films of Indium

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