A wide-band particle eliminator

ShortlCommunications A wide-band particle eliminator In flash evaporation 1 it is often found that partially-melted particles may be emitted from the source. This problem has been discussed in terms of limiting the range of evaporant particle size 2, but even so solid particles can arrive on the substrate and affect the properties of the growing film. The effect of particles is particularly important in the case of depositing dielectrics as their electrical properties will be adversely affected.

b cm

O,8 cm-

i

~

~

O

.

O,O5cm ROOTSPACING cm PERIPHERALSPACING

2

SUBSTRATE~ i. . . . . . . . . . . .

GRAIN DELIVERY

I III

II /

SECTION OF FINNED TUBE

I cm

BASE PLATE | r|

I

~HIGH

SPEED ROTARY SEAL

Fig. 1. D i a g r a m o f a r r a n g e m e n t o f wide-band velocity selector.

It has been found that the problem can be overcome by positioning a wideband velocity selector between the source and the substrate. The selector will then reject the slow moving particles and only allow through the much faster moving evaporant atoms. Such a selector can easily be made from finned metal tubing. A 1.0 cm length Thin Solid Films-Elsevier Publishing C o m p a n y : A m s t e r d a m - Printed in T h e N e t h e r l a n d s

70

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o f e x t r u d e d m a g n e s i u m - a l l o y tube, 6 cm in O . D . a n d with 72, 0.8 cm length, r a d i a l fins (ex. Accles a n d Pollock, Ltd.) has b e e n f o u n d suitable. Such t u b i n g has alr e a d y been used in l o n g e r lengths for studying the velocity d i s t r i b u t i o n o f a t o m s f r o m different e v a p o r a t i o n sources 3 a n d so it will n o t be described in detail here. T h e placing o f the selector relative to the source a n d substrate is s h o w n diag r a m m a t i c a l l y in Fig. 1. W i t h such an a r r a n g e m e n t , a n d the selector r o t a t e d at 3000 r.p.m, all particles travelling at less t h a n 103 c m s e c - i will be e l i m i n a t e d over at least an a r e a o f 1 c m 2. The selector has been successfully a p p l i e d to the flash e v a p o r a t i o n o f b a r i u m t i t a n a t e 4'5 f r o m a r h e n i u m source at 2600 °C. Substrates o f silica were used at 500 °C a n d the electrodes were o f p l a t i n u m . Table I shows the type o f result obtained. It can be seen that the r e m o v a l o f particles has i m p r o v e d the resistance and leakage current, b u t has h a d little effect on the p o w e r factor. The r e m o v a l o f particles has been confirmed by electron m i c r o s c o p y . TABLE I PROPERTIES OF FLASH-EVAPORATED BARIUM TITANATE

(Film thickness 2000/~)

Permittivity: Power factor (~o) : RC product at 1 V (sec): Breakdown (V): Resistance (12):

Direct evaporation

Using velocity selector

170

150

20 0.001 10 105

* Improved to 10 sec after drying.

17 0.1" l0 107 i

T h e a u t h o r wishes to t h a n k Mr. D. S. C a m p b e l l for his help, the M i n i s t r y o f A v i a t i o n for s u p p o r t a n d the Plessey C o m p a n y for p e r m i s s i o n to publish this note. Allen Clark Research Centre, The Plessey Company Limited, Caswell, Towcester, Northants ( Gt. Britain))

A. R. BEAVITT

1 L. H O L L A N D , Vacuum Deposition of Thin Films, Chapman and Hall, London, 1956, p. 195. 2 M. C. ZYETZ AND A. M. DEPRES, Extended Abstr. of Am. Vac. Soc. 13th Natl. Vac. Symp. 1966, p. 169. 3 A. R. BEAVITT, R. C. TURNELL AND D. S. CAMPBELL, Thin Solid Films, 1 (1967) 3-11. 4 E. MOLLER, B. NICHOLSONAND M. FRANCOMBE,Electrochem. Tech., 5 (1963) 158. 5 V. R. BROWN, ExtendedAbstr. of Am. Vac. Soc. 13th Natl. Vac. Symp., 1966, p. 139.

Received J a n u a r y 14, 1967