ANALYTICAL SEM FOR SURFACE SCIENCE

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Submitted on 1 Jan 1984

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ANALYTICAL SEM FOR SURFACE SCIENCE

J. Geller, A. Mogami

To cite this version:

J. Geller, A. Mogami. ANALYTICAL SEM FOR SURFACE SCIENCE. Journal de Physique Collo-

ques, 1984, 45 (C2), pp.C2-313-C2-314. �10.1051/jphyscol:1984270�. �jpa-00223984�

JOURNAL DE PHYSIQUE

Colloque C2, supplgment a u n02, Tome 45, f g v r i e r 1984 page C2-313

A N A L Y T I C A L SEM FOR SURFACE S C I E N C E

J.D. Geller and A. ~ o ~ a r n i *

JEOL Inc., 12 Dearborn Rd., Peabody, MA 02960, U.S.A.

JEOL Ltd., 1428 Nakagami, Akishima, Japan

Resume - L e developpement du MEB a n a l y t i q u e n e c e s s i t e l a m i s e en o e u v r e d e s e c t r o s c o p i e s d ' e l e c t r o n s e t des s p e c t r o m e t r i e s d ' i o n s (ISS, SIMS).

L ' a l ignement des f a i s c e a u x e l e c t r o n i q u e e t i o n i q u e a i n s i que l e r e g l a - ge de l ' a n a l y s e u r c y l i n d r i q u e a m i r o i r s o n t d i s c u t e s .

A b s t r a c t - The a n a l y t i c a l SEM f o r s u r f a c e s c i e n c e i n c l u d e s s e v e r a l d i f f e r e n t f i e l d s o f a n a l y s i s such as e l e c t r o n spectroscopy, ISS and SIMS.

The a l i g n m e n t o f t h e e l e c t r o n , i o n beam and CMA i s discussed.

U l t r a h i g h vacuum technology, e l e c t r o n spectroscopy, i o n s c a t t e r i n g and mass spec- t r o s c o p y a r e t h e f o u n d a t i o n s o f t h e a n a l y t i c a l SEM f o r s u r f a c e science. The e l e c t r o n d e t e c t o r s a r e o f t h e E v e r h a r t - T h o r n l e y d e s i g n f o r t h e secondary e l e c t r o n image, S i P/N j u n c t i o n f o r t h e b a c k s c a t t e r e d e l e c t r o n d e t e c t o r , and t h e c y l i n d r i c a l m i r r o r a n a l y z e r f o r t h e e l e c t r o n s p e c t r o s c o p i e s . Sample c l e a n i n g i s a c h i e v e d i n - s i t u by h e a t i n g and i o n s p u t t e r i n g . I n - s i t u a d s o r p t i o n o f gas i s p o s s i b l e w i t h o u t damaging o r c a u s i n g t h e LaB e l e c t r o n e m i t t e r t o become u n s t a b l e as t h e e l e c t r o n gun i s d i f f e r e n t i a l l y pumpe&while t h e sample i s b e i n g exposed t o r e a c t i v e gas. The s u r f a c e c o m p o s i t i o n i

i n v e s t i g a t e d by e l e c t r o n s p e c t r o s c o p i e s combined w i t h depth p r o f i l i n g and SIMS a n a l y s i s . A d a p t i o n o f t h r e s h o l d s p e c t o s c o p i e s (DAPS, AEAPS, and EXAFS) a r e made p o s s i b l e as t h e e l e c t r o n o p t i c s o p e r a t e s from l e s s t h a n lOOeV t o 10KeV.

D i f f i c u l t i e s i n p e r f o r m i n g a n a l y t i c a l SEM a n a l y s i s a r e o f t h e o r e t i c a l and a t e c h n i c a l n a t u r e . T e c h n i c a l l y , t h e a1 ignment and t h e c a l i b r a t i o n o f v a r i o u s f u n c t i o n s a r e o f m a j o r importance. From p r e v i o u s s t u d i e s i t was determined t h a t t h e p o s i t i o n i n g o f t h e CMA's f o c a l p o i n t must be c o n t r o l l e d w i t h i n 20 micrometers (1). A goniometer s t a g e w i t h f i v e degrees o f freedom ( f i g u r e 1 ) a l l o w s t h e o p e r a t o r t o p o s i t i o n t h e sample a t t h e CMA f o c a l p o i n t m e c h a n i c a l l y u s i n g t h e e u c e n t r i c t i l t i n g a x i s o f a new stage, e l i m i n a t i n g t h e o f t e n used t e c h n i q u e o f d e t e r m i n i n g t h e e l a s t i c peak p o s i t i o n . The c o r r e c t sample ' Z ' p o s i t i o n i s achieved when t h e sample i s t i l t e d by a p p r o x i m a t e l y +3Owith no d i s c e r n a b l e s h i f t . T h i s i s c o n f i r m e d by o b s e r v i n g t h e SEM image on t h e v i e w i n g CRT a t a m a g n i f i c a t i o n o f 10oox.

The accuracy o f a l i g n m e n t o f t h e s p u t t e r i o n gun depends upon t h e t h e area t o be s p u t t e r e d . Large d i a m e t e r i o n beams g e n e r a l l y s p u t t e r s i g n i f i c a n t l y l a r g e r areas o f sample t h a n necessary. T h i s i s w a s t e f u l i n a t l e a s t two ways. Excess sample i s s p u t t e r e d which p r e v e n t s f u r t h e r a n a l y s i s , and c o n t a m i n a t i o n o f t h e i n t e r n a l p a r t s o f t h e sample chamber i s a c c e l e r a t e d . On t h e o t h e r hand, s m a l l e r i o n beams w i t h h i g h e r c u r r e n t d e n s i t y a r e more s u i t a b l e f o r h i g h s p a t i a l r e s o l u t i o n SIMS and ISS a n a l y s i s . Sample c h a r g i n g w i t h c o n v e n t i o n a l Auger a n a l y s i s a l s o b e n e f i t s f r o m s m a l l i o n beams. Consider t h e case o f a near p e r f e c t i n s u l a t o r , such as BaTiO I n o r d e r t o measure t h i s m a t e r i a l w i t h good c o u n t i n g s t a t i s t i c s t h e a n a l y s i s

becomes v e r y l a r g e . T h i s i s due t o sample c h a r g i n g . Only w i t h s h a l l o w angles o f i n c i d e n c e between t h e e l e c t r o n beam and t h e sample- combined w i t h l o w kV i s i t p o s s i b l e t o c o l l e c t any d a t a w i t h o u t t h e sample c h a r g i n g u n c o n t r o l l a b l y . F i g u r e 2 ( t o p ) i l l u s t r a t e s t h i s s i t u a t i o n (2kV, 50nA probe c u r r e n t and 6 0 ° t i l t ) where t h e s u r f a c e charge i s about 30 eV. A t h i g h e r a c c e l e r a t i n g v o l t a g e s o r beam c u r r e n t s

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984270

C2-314 JOURNAL DE PHYSIQUE

t h e c h a r g i n g becomes much worse. F i g u r e 2 ( b o t t o m ) shows a r e l a t i v e l y n o i s e f r e e s p e c t r a (IOkV, 500nA probe c u r r e n t and 0" t i l t ) o f t h i s same materia1,after b e i n g c o a t e d w i t h 20nm o f g o l d - which was t h e n s p u t t e r e d o f f u s i n g 3kV A r i n a v e r y s m a l l area- 25 microns. I n t h i s case, t h e sample was t h e n a b l e t o d i s c h a r g e a c r o s s t h e s m a l l gap t o t h e e l e c t r i c a l l y c o n d u c t i v e s u r r o u n d so t h a t i t remained a t ground p o t e n t i a l . Alignment o f t h e i o n beam t h e n becomes as c r i t i c a l as i t i s f o r t h e CMA. The i o n beam a l i g n m e n t i s accomplished by imaging t h e i n t e n s i t y o f t h e secondary e l e c t r o n s i g n a l emanating f r o m t h e sample as i t i s scanned by t h e i o n beam. The imaged a r e a s h o u l d be i d e n t i c a l f o r b o t h t h e e l e c t r o n induced and i o n i n d u c e d secondary e l e c t r o n s i g n a l .

The image d e t e c t o r c a l i b r a t i o n a l l o w s u s t o c o r r e l a t e t h e change i n b r i g h t n e s s w i t h i t s c o r r e s p o n d i n g changes i n t h e e l e c t r o n energy d i s t r i b u t i o n . The a n a l y z e r c a l i b r a t i o n i s a c h i e v e d on a t o m i c a l l y c l e a n aluminum o r s i l i c o n t a k i n g i n t o account t h e e x i s t i n g t h e o r y f o r t h e secondary e l e c t r o n e m i s s i o n and background shape and i n t e n s i t y (2,3). The secondary e l e c t r o n y i e l d and t h e b a c k s c a t t e r i n g y i e l d a r e measured i n - s i t u . These c a l i b r a t i o n s w i l l be e s s e n t i a l t o o b t a i n a c c u r a t e q u a n t i t a t i v e i n f o r m a t i o n from t h e t h e sample.

The t h e o r e t i c a l d i f f i c u l t i e s encountered a r e t h e absence o f t h e o r y f o r background s u b t r a c t i o n and f o r peak i n t e n s i t y n o r m a l i z a t i o n . The c r y s t a l l o g r a p h i c e f f e c t , a n i s o t r o p i c e l e c t r o n e m i s s i o n and t h e change i n e l a s t i c and i n e l a s t i c s c a t t e r i n g as a f u n c t i o n o f t h e s u r f a c e s t r u c t u r e a r e i m p o r t a n t aspects t o t a k e i n t o account.

A d e t a i l e d d e s c r i p t i o n of t h e a l i g n m e n t procedures used f o r t h e e l e c t r o n beam, CMA and i o n gun w i l l be d i s c u s s e d d u r i n g t h e p r e s e n t a t i o n .

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( 3 ) J . G e l l e r , F. P e l l e r i n , C. LeGressus, Scanning E l e c t r o n Micr., Vol. I V Y p.295-300, 1981.

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