Effect of ionic bombardment cleaning on epitaxial growth

SURFACE

SCIENCE

EFFECT

18 (1969) 449451

0 North-Holland

Publishing Co., Amsterdam

OF IONIC BOMBARDMENT ON EPITAXIAL

CLEANING

GROWTH

Received 8 April 1969

The phenomenon of growth and nucleation of metal films on various substrates has been widely studied. It is well known that the epitaxial growth of metal films depends upon a number of factorsl), the most important being the temperature of substrates), nature of the substrate surface3,4), rate of deposition and residual gases 5,s), order of vacuum2), etc. Recently Toth and Cicotte7) have reported the effect of substrate impurity on the growth of silver and gold films and have observed that the temperature of epitaxial growth increases with increasing contamination of the substrate surface. We wish to report some experiments in which the effect of ionic

Fig. 1. Transmission electron diffraction pattern of single crystal silver film prepared onto rocksalt cleaned by ionic bombardment at 110°C showing (100) orientation. 449

450

S.K.SHARMA

AND

R.P.S.KUSHWAHA

bombardment cleaning of the substrate the silver films has been observed.

surface

on the epitaxial

growth

of

Thin films of spectroscopically pure silver were prepared onto rocksalt freshly cleaved in air and maintained at 110°C under a vacuum of the order of IO- ’ Torr. Prior to evaporation the substrate was heated at 110 “C and its surface was cleaned by ionic bombardment for 15-20 min at the same temperature. After ionic bombardment the substrate was annealed at the same temperature for 1 hr before the material was evaporated. Immediately after deposition, the films were annealed at the same temperature for 2 hr and were then allowed to cool to room temperature under vacuum.

Fig. 2.

Electron micrograph

of the same silver film whose electron diffraction is shown in fig. 1. 25000 x

pattern

The electron diffraction study of the films revealed single-crystal growth of the silver with (100) parallel orientation. Figs. 1 and 2 show the electron diffraction pattern and an electron micrograph of the film. But when the silver films were grown onto the rocksalt surface under similar conditions without ionic bombardment cleaning (conventional method) they showed a polycrystalline structure. It is concluded that ionic bombardment cleaning of the substrate prior

EFFECT OF IONIC BOMBARDMENT CLEANING ON EPITAXIAL GROWTH

451

to film deposition reduces the temperature of epitaxial growth of silver films compared to the value reported by the conventional method. The exact mechanism by which the ionic bombardment is affecting the growth of the films is not clearly understood. Nevertheless it is expected that the ionic bombardment might influence the contamination on the surface or the topography of the surface which in turn affects the nucleation on the surface of the substrates. We are grateful to Prof. A. R. Verma, Director, National Physical Laboratory, New Delhi, for his encouragement and for permission to publish this paper. Thanks are also due to Dr. D. W. Pashley of Tube Investment Research Laboratories for his valuable suggestions. S. K. SHARMA and R. P. S.

KUSHWAHA

National Physical Laboratory, New Delhi 12, India References 1) D. W. Pashley,

Advan.

Phys.

14 (1965)

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2) S. Ino, D. Watanabe and S. Ogawa, J. Phys. Sot. Japan 3) S. B. Hyder and M. A. Milkov, J. Appl. Phys. 38 (1967) 4) R. A. Connell, J. Appl. Phys. 38 (1967) 2397. 5) S. Shinozaki

and H. Sato,

J. Appl.

6) K. Mihama,

H. Miyahare

and H. Aoe,

7) R. S. Toth

and L. J. Cicotte,

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36 (1965) J. Phys.

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