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Submitted on 1 Jan 1986
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RECENT DEVELOPMENTS IN THE APPLICATION OF LIQUID METAL ION SOURCES TO SIMS
A. Waugh, A. Bayly, M. Walls, P. Vohralik, D. Fathers
To cite this version:
A. Waugh, A. Bayly, M. Walls, P. Vohralik, D. Fathers. RECENT DEVELOPMENTS IN THE
APPLICATION OF LIQUID METAL ION SOURCES TO SIMS. Journal de Physique Colloques,
1986, 47 (C2), pp.C2-133-C2-136. �10.1051/jphyscol:1986219�. �jpa-00225652�
JOURNAL DE PHYSIQUE
CoLloque C2, supplement au n o 3 , Tome 47, mars 1986 page c2-133
RECENT DEVELOPMENTS IN THE APPLICATION OF LIQUID METAL ION SOURCES TO SIMS
A.R. WAUGH, A.R. BAYLY, M. WALLS, P. VOHRALIK and D. FATHERS
V G Scientific Ltd., Imberhorne Lane, GB'-East Grinstead, RH19 I U B , W Sussex
Abstract- High-brightness liquid metal ion sources (LMIS) allow SIMS micr 4-
probe analysis with 50 nm spatial resolution at current densities > 1Atcm . Chemical imaging of matrix and trace elements on the submicron scale is now achieved using a digital image storage system. aliowing picture processing and direct comparison of SEM and SIMS images using colour overlays.
While high-sensitivity quadrupole mass spectrometers have been developed for SIMS imaging. the ultimate in sensitivity requires magnetic or time- of-flight mass spectrometers.
I - INTRODUCTION
SIMS microprobe analysis is now readily achieved using Liquid Metal Ion Sources (LMIS) to produce the primary ion beam. The high brightness and small source size of the LMIS permit the formation of high-intensity probes 1 (" Alcm 2 with sub-micron diameters at energies from a few keV up to > 30 ke'i. These ion probes allow the acquisition of ion-induced secondary electron images and mass-resolved secondary ion images with spatial resolution approaching 50 nm 11.2.3'. SIMS imaging has proved to be possible with a very wide range of samples - from metals and integrated circuits to polymers and biological samples. It has proved exceptionally useful on multitechnique systems with samples for which Auger Electron Spectroscopy is difficult due to charging. low sensitivity. or excessive analysis time. SIMS images of elements with average sensitivity are typically acquired in a few tens of seconds
I1 - PRESENT INSTRUMENTATION
The present authors have used a number of different 10 kV and 30 kV columns with gallium LMIS sources, and a 10 KeV column uslng a caesium LMIS. SIMS analysis has been achieved using a high-performance quadrupole mass spectrometer IMM12-1Z'rthis has recently been increased in sensitivity by the addition of emittance-matching ion optics. A scintillator and photomultiplier are used far secondary electron detection. and a slow-scan display oscilloscope and camera have been employed for image recording up till a few months ago.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986219
JOURNAL DE PHYSIQUE
I11 - DIGITAL FRAME-STORE IMAGE RECORDING
I n o r d e r t o make most e f f e c t i v e u s e o f t h e SIMS i m a g i n g t e c h n i q u e a f u l l y - - d i g i t a l i m a g i n g s y s t e m b a s e d o n a DEC PDP-11 c o m p u t e r a n d a d i g i t a l f r a m e - s t o r e ( 5 1 2 x 5 1 2 ~ 8 b i t ) h a s r e c e n t l y b e e n d e v e l o p e d . The s t o r e c a n be u s e d t o h o l d b o t h SIMS and SEM i m a g e s . and a r e m o v e a b l e W i n c h e s t e r d i s k i s u s e d f o r p e r m a n e n t s t o r a g e . The s y s t e m p r o v i d e s t h e a b i l i t y t o m a n i p u l a t e and combine i m a g e s . t o a n n o t a t e and p r o v i d e h a r d c o p y ( i n f u l l c o l o u r ) a n d t o p r o v i d e p o s t h o c a n a l y s i s i n t h e form o f l i n e s c a n s , d e p t h - p r o f i l e s , i m a g e s c o r r e c t e d f o r t o p o g r a p h i c e f f e c t s o n s e n s i t i v i t y , and image s e c t i o n s a t a n g l e s o t h e r t h a n p a r a l l e l t o t h e o r i g i n a l s a m p l e s u r f a c e .
The f r a m e - s t o r e a l l o w s t h e d a t a - r e c o r d i n g p r o c e s s t o be d e c o u p l e d from t h e
p h o t o g r a p h i c h a r d c o p y p r o c e s s e s - T h e d a t a i s v i e w e d ( a t c o n s t a n t b r i g h t n e s s ) d u r i n g a c q u i s i t i o n and t h e a c q u i s i t i o n p r o c e s s i s t e r m i n a t e d o n c e t h e s i g n a l - t o - n o i s e r a t i o i n t h e image i s s a t i s f a c t o r y ( t y p i c a l l y a f t e r o n e m i n u t e ) . Once a c q u i r e d . i m a g e s c a n be d i g i t a l l y p r o c e s s e d by s h c h o p e r a t i o n s a s s m o o t h i n g , e d g e e n h a n c e m e n t , i n t e n s i t y s c a l i n g , t w o - d i m e n s i o n a l d e r i v a t i v e s , s o f t w a r e zoom and r o t a t i o n , a n d c o l o u r s l i c i n g . P e r h a p s t h e most u s e f u l o p e r a t i o n o f a l l is t h e a b i l i t y t o combine d i f f e r e n t i m a g e s a s c o l o u r o v e r l a y s . T h i s a l l o w s SIMS i m a g e s a t d i f f e r e n t m a s s e s o r a SIMS image a n d a r e f e r e n c e image s u c h a s a s e c o n d a r y e l e c t r o n image t o b e compared: t h i s a l l o w s t h e p r e c i s e l o c a l i s a t i o n o f t r a c e a m o u n t s o f c o n t a m i n a n t s r e l a t i v e t o t h e p h y s i c a l s t r u c t u r e o f t h e s p e c i m e n s u r f a c e , f o r e x a m p l e .
To i l l u s t r a t e t h i s . F i g u r e 1 shows a ) t h e i o n - i n d u c e d s e c o n d a r y e l e c t r o n image o f 10 um d i a m e t e r PET f i b r e s , a n d b! t h e same image w i t h a c o l o u r o v e r l a y o f
;;;e98Si+
SIMS from a s i l i c o n e o i l l u b r i c a n t , t r a p p e d b e t w e e n t h e f i b r e s d u r i n g p r o c e s s i n g .
A n o t h e r p o s s i b i l i t y w i t h t h e f r a m e s t o r e n o t r e a d i l y a c h i e v e d by o t h e r t e c h n i q u e s . i s t h e a b i l i t y t o combine i m a g e s f r o m d i f f e r e n t d e p t h s i n t h e sdmple t o g i v e i m a g e s o f s e c t i o n s n o t p a r a l l e l t o t h e o r i g i n a l s a m p l e s u r f a c e l 4 . 5 ' . F l g u r e 2 shows a n e x a m p l e o f t h i s . The s a m p l e was a 500 A l a y e r o f a l u m i n i u m o PMMA.
w i t h 2 urn b a r s c u t away from i t a t 8 um s p a c i n g . Some 8 0 c o n s e c u t i v e 9 7 A l t i o n i m a ~ e s w e r e r e c o r d e d a s t h e s a m p l e was s p u t t e r e d away. The t o p h a l f o f F i g u r e 2 is p a r a l l e l t o t h e o r i g i n a l s u r f a c e , w h i l e t h e b o t t o m i s a v e r t i c a l s e c t i o n
(
