Effects of DC bias voltage in sputter deposition of YBaCuO films

Physica C 235-240 (1994) 671-672 North-Holland

PHYSICA

Effects of DC bias voltage in sputter deposition of YBaCuO films R. S c h n e i d e r , J. G e e r k , G Linker, O Meyer, a n d R S m i t h e y K e r n f o r s c h u n g s z e n t r u m K a r l s r u h e , | N F P , P.O.B. 3640, D-7602 t K a r i s r u h e , G e r m a n y

Y B a C u O t h i n films with c-axis o r i e n t a t i o n h a v e b e e n deposited on ~1()0t o r i e n t e d SrTiO3 s u h s t r a t e s by I)C hias s p u t t e r i n g u s i n g a stoichiometric c e r a m i c hollow c y l i n d e r as a t a r g e t . T h e effects of t h e applied voltage on s t r u c t u r a l and electrical p r o p e r t i e s of the fihns h a v e b e e n inv e s t i g a t e d . U p to a t h r e s h o l d of 35 V the films had t r a n s i t i o n t e m p e r a t u r e s T,: a r o u n d 90 K a n d b u l k c-axis lattice p a r a m e t e r s . Above this threshold the ion b o m h a r d m e n t d u r i n g g r o w t h c a u s e s a d e p r e s s i o n of T,. a n d t h e critical c u r r e n t density j,:, a c-axis lattice p a r a m e t e r e x p a n s i o n , a b r o a d e n i n g of the x - r a y difl'raction p e a k s and an increase of the resistivity. T h e s e r e s u l t s c a n he e x p l a i n e d q u a l i t a t i v e l y by v a r i o u s oxygen- and cation-disorder models.

1.

INTROI)UCTION

In s p u t t e r deposition of Y B a C u O in the u s u a l o n - a x i s g e o m e t r y a tlux of e n e r g e t i c o x y g e n a t o m s h o m h a r d s the s u h s t r a t e d u r i n g film g r o w t h l1 I T h i s b o m b a r d m e n t deterior a t e s t h e p r o p e r t i e s of the film due to selective r e s p u t t e r i n g of high s p u t t e r i n g yield constitue n t s a n d r a d i a t i o n e n h a n c e d diffusion. In order to c i r c u m v e n t t h e s e d e t r i m e n t a l effects t h e r a t i o of b o m b a r d m e n t to deposition r a t e m u s t he m i n i m i z e d which, e g . , can be reached by use of a hollow c y l i n d e r as a t a r g e t 12 [ On the o t h e r h a n d , a p a r t i c l e homhardm e n t of a g r o w i n g tilm can be used to intluence d e l i b e r a t e l y film g r o w t h a n d p r o p e r t i e s if i n t e n s i t y and e n e r g y of the b o m b a r d i n g particle tlux a r e controlled. T h e ion b o m b a r d m e n t of tile fihn can be e n a b l e d by a p p l i c a t i o n of a DC b i a s v o l t a g e Vb which allows for a s i m p l e control of the ion energy. However, the ion c u r r e n t 1h c a n n o t he chosen i n d e p e n d e n t l y on VL, in all p l a s m a - h a s e d techniques. T h e r e tore the r e l e v a n t p a r a m e t e r for the efficacy of t h e ion h o m b a r d m e n t is the b o m b a r d m e n t power PI,= VI,It, r a t h e r t h a n solely VI,. In t h i s c o n t r i b u t i o n we r e p o r t on a s y s t e m a t i c s t u d y of the d e p e n d e n c e of s t r u c t u r a l and electrical Y B a C u O film p r o p e r t i e s on the ion b o m b a r d m e n t power Ph.

2.

EXPERIMENTAl,

T h e s p u t t e r gun of our DC hias s p u t t e r i n g s y s t e m is m o u n t e d on a n i n s u l a t i n g flange. T h e r e f o r e a positive p o t e n t i a l Vi) can he applied to the c a t h o d e d a r k space shield result i n g in a positive ion b o m b a r d m e n t ot'the subs t r a t e controlled by VI,. T h e Y B a C u O films w e r e g r o w n on ~100) oriented S r T i O 3 s u h s t r a t e s in a m i x t u r e of 0.6 m b a r Ar a n d 0.3 m h a r 02. T h e s u b s t r a t e t e m p e r a t u r e , Ts, and the s p u t t e r i n g power, Ps, were k e p t c o n s t a n t at 810"C a n d 70 W, respectively. T h e DC bias v o l t a g e VI, w a s v a r i e d from 0 to 9[) V r e s u l t i n g in a b i a s c u r r e n t 11, r a n g i n g from 0 to 2 6 mA a n d a b o m b a r d m e n t power Pb up to 234 mW. The structural properties were examined hy x-ray diffraction m e a s u r e m e n t s . T h e t r a n sition t e m p e r a t u r e T,:, of t h e fihns "as prep a r e d " w a s d e t e r m i n e d by a n i n d u c t i v e method. After p a t t e r n i n g r e s i s t i v e m e a s u r e m e n t s were p e r f o r m e d u s i n g a s t a n d a r d DC four-probe a r r a n g e m e n t . 3.

RESULTS

The d e p e n d e n c e of the c-axis lattice p a r a m e t e r on the h o m h a r d m e n t power Ph is s h o w n in F i g u r e 1, A b o v e a t h r e s h o l d of 50 m W the c-axis lattice p a r a m e t e r i n c r e a s e s c o n t i n u o u s ly from the hulk v a l u e of 1.168 n m up to 1.l.ql n m at Ph =230 mW. It exceeds the v a l u e

092t-4534/94/S07.00 © 1994 - ElsevierScience B.V. All rights reserved. SSl ~/0921-4534(94)00896-5

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