for a new educational strategy for ulsi microelectronics

8/6/2019 For a New Educational Strategy for ULSI Microelectronics

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E L S E V I E R Materials Science and Engineering A199 (1995) 45-51

M A T E R I A L SS C I E N C E &E N G I N E E R I N GA

F o r a n e w e d u c a t i o n a l s tr a te g y fo r U L S I m i c r o e l e c t r o n i c s

Georges KamarinosLabora to ire de Ph ys ique des C om posan ts ~ Semiconduc teurs , 23 , rue des Mar tyrs , BP 257, 38 016 Grenob le C gdex 1 , France

A b s t r a c t

I t is wel l establ ished today tha t the dev e lopm ent of in tegra ted c ircuits , for a t least the next decade , wi l l be m ainly based o n sca led-dow n CM OS tech nolo gy on si l icon (0 .1 /zm channel length , 108 t ransis tors per ch ip , 10 ps de lays. . . ) . A mass and e ff ic ient fabr ica t ionmu st be based o n two pr inc ip les: (1) sc ient i f ic fabr ica tion , which m eans a sequence of sharply contro l led phys ico-chem ica l processes;(2) physica l (not empir ica l ) m odel ing and simu la t ion of the working o f the devices and o f the i r coupl ing . In th is paper, i t i s fi rs t shownth a t su c h a n a p p ro a c h n e e d s to g o b a c k to t h e " f i r s t p r in c ip l e s" o f p h y s i c s ( a s 5 0 y e a rs a g o w h e n se mic o n d u c to r s c a me in to v i e w ).A m o n g th e n e c e ssa ry p h y s i c s d e v e lo p m e n t s i n t h e d o m a in o f t h e p h y s i c a l -c h e mis t ry an d o f so l id s t at e p h y s i c s , o n e c a n c it e: mo le c u la rdynamics; very th in oxida t ion and i t s re la t ion to microroughness and surface s ta tes; non-Fickian d i ffusion; microcontamina t ion; e lec-t romigra t ion; exac t so lu t ion of the Bo l tzman n t ransport equa t ion ( tak ing in to accou nt the e lec t ronic s t ruc ture of the materia l, the t ran-sient regime and the qu antum effec ts) ; ana lysis of the e lec tr ic , e lec t romagnet ic and pho nonic co upl ing o f devices and the i r noise ; e tc . ;Th en i t is show n tha t these deve lopm ents need: (1) a revision of the classica l educa t iona l program for microe lec t ronics materia ls andprocesses; a l i s t of "new " topics to-be-dev e loped is g iven; (2) a very t ight coupl ing o f R& D indust r ia l labora tor ies wi th universi tyteams; they have to work on the same space and wi th the same equipment for technology research pro jec ts (doc tor degree prepara t ion) .The above two poin ts can const i tu te the f ramework for a new educa t iona l s t ra tegy involv ing , in a new base , a c loser co l labora t ion be-tween universi ty and indust ry . Fina l ly , i t i s shown tha t Grenoble can be a s t rong pole in an e ff ic ient European Network for the 21stcentury s i l icon microe lec t ronics .K e y w o r d s : Sil icon; Microe lec t ron ics; In tegra ted c i rcuits ; Elec t ronics educa t ion

1 . I n t r o d u c t i o n : t h e i m p o r t a n c e o f s i l i c o nm i c r o e l e c t r o n i c s

I t is w e l l e s t a b l i s h e d t o d a y t h a t i n t h e h e a r t o f a n e l e c -t r o n i c s y s t e m , t h e s i g n a l p r o c e s s i n g u n i t i s t h e p r i n c i p a le l e m e n t ; t h i s u n i t is c o m p o s e d o f e l e c t r o n i c d e v i c e s b e -l o n g i n g t o o n e o r m o r e i n t e g r a t e d c i r c u it s ( I C ) .

T h e d e v e l o p m e n t o f th e s e I C , a n d c o n s e q u e n t l y t hed e v e l o p m e n t o f c o m p u t e r s , i s b a s e d o n t h e c o n t in u o u sd e v e l o p m e n t o f s il i c o n m i c r o e l e c t r o n i c s ( S i - p e ) .

T h i s t e c h n o l o g y g o e s c o n t i n u o u s l y t o :- h i g h e r s p e e d s ( f r e q u e n c i e s ),- h i g h e r s c a l i n g - d o w n ( m i n i a t u r i z a t i o n ) ,- h i g h e r d e n s i t i es ( h i g h e r n u m b e r o f tr a n s i s to r s p e rc m 2 ) ,- h i g h e r c o m p l e x i t y ( h i g h er n u m b e r o f f u n c ti o n s i n a

c h i p ) .D u r i n g t h e l a s t d e c a d e t h e I C a r e c h a r a c t e r i z e d b y a ni n c r e a s e o f : 1 .1 5 / y e a r i n s c a l i n g - d o w n , 1 . 3 1 / y e a r in d e n -

0921-5093/95/$09.50 1 995 Elsevier Science S.A. All rights reservedS S D I 0 9 2 1 - 5 0 9 3 ( 9 5 ) 0 9 9 0 6 - 9

s i t y , 1 . 4 0 / y e a r i n c o m p l e x i t y , 1 . 2 4 / y e a r i n s p e e d .S t a t i n g t h a t S i m i c r o e l e c t r o n i c s i s v e r y i m p o r t a n t f o r

e c o n o m i c d e v e l o p m e n t i s n o t s u f f i ci e n t : o n e h a s t o a d dt h at C M O S t e c h n o l o g y ( C o m p l e m e n t a r y M e t a l- O x i d e -S e m i c o n d u c t o r ) w i ll c o v e r p r o b a b l y m o r e t h a n 8 0 % o ft h e w o r l d m a r k e t o f I C s i n a f e w y e a r s ( F i g . 1 ) ; i n t h es a m e f i g u r e o n e c a n s e e t h a t S i w i l l c o n t i n u e t o c o v e r9 9 % o f th e m a r k e t w h e n o t h e r s e m i c o n d u c t o r s ( l ik eG a A s ) w i l l c o n t i n u e t o s h a r e o n l y 1 % o f t h e s a m e I Cw o r l d m a r k e t [ 1 ] .

I t i s t h u s e v i d e n t t h a t e d u c a t i o n c o n c e r n i n g t h e p h y s i -c a l - c h e m i s t r y a n d t h e p h y s i c s o f :- t h e s i l i c o n m a t e r i a l ,- t h e p h y s i c o c h e m i c a l p r o c e s s e s i n v o l v e d i n t h e f a b r i-

c a t i o n o f t h e e l e c t r o n i c d e v i c e s ,- t h e t r a n s p o r t o f c a r r i er s i n e l e c t r o n i c d e v i c e s , w h e n

t h e y a r e s c a l e d - d o w n ,a r e o f p a r a m o u n t i m p o r t a n c e f o r r e s e a r c h a n d t h e i n d u s t r ye n g i n e e r s f o r t h e i m m e d i a t e f u t u r e .


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46 G. Kamarinos I Materials Science and Engineering A199 (1995) 45-51

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G. Kamarinos / Materials Science and Engineering A1 99 (1995) 45-5 1 473 . M a t e r i a l s c i e n c e a n d d e v e l o p m e n t o f S i - / t e :r e m a i n i n g t e c h n o l o g i c a l p r o b l e m s a n d e d u c a t i o n a ln e e d s

T h e d e v e l o p m e n t o f S i - / ~ e d e p e n d s o n t h e a d v a n c e -m e n t o f th e k n o w l e d g e a n d t h e t e c h n o lo g i c a l p r o g r es sc o n c e r n i n g : ( a ) th e t e c h n i c a l p r o c e s s e s o f f a b r ic a t i o n ; ( b )t h e w o r k i n g o f t h e d e v i c e s a n d t h e i n t e g r a t e d c i r c u it s .( E v i d e n t l y t h e d e s i g n , t h e C A D , t h e a r c h i t e c t u r e a n dt e s t in g o f I C a r e v e r y i m p o r t a n t , b u t t h e s e f i e l d s a r e n o td i s c u s s e d i n t h e p r e s e n t a p p r o a c h . )

I n t h e f o l l o w i n g p a r a g r a p h s , a v e r y b r i e f r e v i e w o f t h em o r e i m p o r t a n t r e m a i n i n g p r o b l e m s o f M a t e r i al s S c i e n ce sa n d P h y s i c s c o n c e r n i n g t h e a b o v e i t e m s , ( a ) a n d ( b ) , i sg i v e n . E d u c a t i o n o r i e n t a t i o n s a r e s u g g e s t e d .3 . 1. T e c h n i c a l p r o c e s s e s

T h e l i th o g r a p h y d r i v e s th e r a t e o f th e d e v e l o p m e n t o fS i - /~e . Phase sh i f t deep u l t rav io le t (P -S) l i thography fort h e n e a r f u t u r e ( f o r l i n es o f 1 0 0 n m ) w i l l r e p l a c e t h e o p t i -c a l l it h o g r a p h y ( x = 4 0 0 n m ) o f t o d a y . F o r t h e U L S I s t e p( L < 1 0 0 0 / ~ ) p r o b a b l y e l e c tr o n b e a m l i th o g r a p h y w i l l b eo p e r a t i o n a l [ 7 ].

T h e p r o b l e m s f a c i n g t h is k i n d o f l it h o g r a p h y a r e e s-s e n t i a l l y t w o : ( i ) t h e b a c k s c a t t e r i n g o f s e c o n d a r y e l e c -t r o n s ; ( ii ) th e c o u l o m b i a n i n t e r a c ti o n o f p r i m a r y e l e c t ro n s .

Oxida t ion [8] i s a l so a key s t ep in the fabr i ca t ion . I te n s u r e s n o t o n l y t h e i s o l a t i o n b e t w e e n d i f f e r e n t d e v i c e s( t h i c k o x i d e s ) b u t a l s o t h e g a t e i s o l a t i o n ( v e r y t h i n o x i d e sor o ther d ie l ec t r i cs ) .T h i n g a t e o x i d a t i o n ( t h i c k n e s s n o t l o w e r t h a n 3 0 A ) i sa v e r y i m p o r t a n t s t e p f o r U L S I a n d s e v e r a l p h y s i c o -c h e m i c a l p r o b l e m s h a v e n o w t o b e e x a m i n e d ; o n e c a nci te [9]:- n a t i v e o x i d a t i o n ( 0 - 2 0 ] k ),- t h e i n f l u e n c e o f s u r f a c e m i c r o r o u g h n e s s i n th i n o x i -

d a t i o n ,- t h e i n f l u e n c e o f s u r f a c e m i c r o c o n t a m i n a t i o n

(Ns < 101 cm -2) to th in o xida t io n ,- t h e r e l a t i o n s h i p b e t w e e n e l e c t r i c a l b r e a k d o w n a n d

s u r f a c e m i c r o r o u g h n e s s [ 1 0] ,- t h e r e l a t i o n s h i p b e t w e e n th e e l e c t r ic a l b a r r i e r i n t h ei n t e r f a c e ( S i/ S iO 2 ) a n d t h e o x i d e t h i c k n e s s ,- t h e p r e p a r a t i o n o f u l t r a - c l e a n o x i d e s ( t o a v o i d d i s -

p e r s i o n o f t h e t h r e s h o l d v o l t a g e o f t h e M O S t r a n s i s -tor ) ,

- e tc .T h e p h y s i c s o f i o n im p l a n t a t i o n a t v e r y l o w e n e r g i e s

( 3 - 1 5 k e V ) a n d w i t h s t r o n g c u r r e n t s , f o r t h e f a b r i c a ti o no f s h a l lo w j u n c t i o n s ( x j < 5 0 0 / ~ ) c o n s ti t u te t h e m o r e i m -p o r t a n t p r o b l e m t o b e f a c e d [ 11 ].

T h e F i c k i a n a p p r o a c h f o r d i f f u s io n i s a lw a y s o f t h eh i g h e s t i n t e r e s t a n d p a r t i c u l a r l y ' t h e d e f e c t - a s s i s t e d d i f f u -s i o n i n p r e a m o r p h i z a t i o n s t e p s ( f o r s h a l lo w ju n c t i o n s ) .T h e m a c r o s c o p i c a p p r o a c h o f th e d i f fu s i o n a l lo w s a n u -

m e r i c a l l y p o s s i b l e c a l c u l a t i o n o f 2 D o r 3 D i m p u r i t y p r o -f i l e s [12 ,13] .

T h e C V D - P V D [ 14 ] ( c h e m i c a l a n d p h y s i c a l v a p o rd e p o s i t i o n ) t e c h n i q u e s a r e , o f c o u r s e , o f r a p i d l y i n c r e a s -i n g i n t e r e s t . I n d e e d m o d e r n m i c r o e l e c t r o n i c s h a s" b e c o m e " a s u r f a ce s c i e n c e [ 1 5] ; b u t t h e m o r e i m p o r t a n tp r o c e s s e s a r e , y e t , a p p r o a c h e d w i t h a n e m p i r i c a l a n d m a c -r o s c o p i c v i e w , w h i c h i s n o t s a t i s f a c t o r y f o r r e a c h i n g t h er e q u i r e m e n t s o f m o d e l i n g a n d s i m u l a ti o n o f d e v i c e s a n dc i r c u i t s [ 1 6 ] . W e n e e d t h e r e f o r e a " s c i e n t i f i c a p p r o a c h "to :- s u r f a c e r e a c t i o n s k i n e t i c s f a r f r o m t h e r m o d y n a m i c

e q u i l i b r i u m ; o n e h a s t o t a k e t h i s i n t o a c c o u n t i n s u c ha n a p p r o a c h ,

- t h e d y n a m i c s o f g a s f l u x n e a r t h e s u r f a c e ,- a m o n g o t h e r p r o b l e m s o n e c a n a l s o c i t e s e l e c t i v e

e p i t a x y ,- r a p i d t h e r m a l a n n e a l i n g h a s t o b e d e s c r i b e d a n d e x -

a m i n e d a l s o i n t h e l i g h t o f n o n - e q u i l i b r i u m t h e r m o -d y n a m i c s .

T h e r e t u r n t o b a s i c a n d c l a s s i c a l t h e r m o d y n a m i c s a n dt h e e m e r g e n c e o f n o n - e q u i li b r i u m t h e r m o d y n a m i c s a n dm o l e c u l a r d y n a m i c s f o r n e a r l y a l l t h e p h y s i c o - c h e m i c a ls t e p s o f f a b r i c a t i o n i s th e p r i n c i p a l a n d t h e e s s e n t i a l c h a r -a c t e r is t ic o f t h e n e w e d u c a t i o n a l e r a f o r s i l i co n m i c r o e l e c -t r o n ic s . T h e s e " f i r s t p r i n c i p l e s " o r e l e m e n t a r y ( p a r t ic u l a r )a p p r o a c h e s c a n g i v e s o l i d i n d i c a t i o n s f o r t h e e s t a b l i s h -m e n t o f m a c r o s c o p i c l a w s f o r o x i d a ti o n , d i f f u s io n a n dv a p o r d e p o s i t i o n o f t h in f i l m s ; t h e s e l a w s c a n t h e n b ei n se r te d i n t o R & D s i m u l a ti o n n u m e r i c a l p r o g r a m s .

T h i s r e m a r k i s a l s o v a l i d f o r t h e s y n t h e s i s o f s i l i c i d e s( i n p a r t i c u l a r g e r m a n i u m a l l o y s ) [ 1 7 ] a n d f o r m o r e c o m -p l e x p h e n o m e n a s u c h a s e l e ct r o m i g r a ti o n [ 1 9 ] w h i c h n o wc o n s t i t u t e s a s e r i o u s d r a w b a c k o f s c a l i n g - d o w n a s i tt h r e a te n s t h e r e l i a b i li t y o f t h e c i r c u i ts . F o r t h i s p h e n o m e -n o n , a n a b u n d a n t l i t e r a t u r e e x i s t s b u t a s a t i s f a c t o r y d e -s c r i p t io n o f t h e f a i lu r e ( o f m e t a l l i c l i n e s ) p r o c e s s a s w e l la s th e s o l u t i o n t o t e c h n ic a l p r o b l e m a r e y e t u n k n o w n .

U L S I s i l i c o n m i c r o e l e c t r o n i c s r e q u i r e s a m i n i m u m i nthe d i spers ion of the e l ec t r i ca l charac te r i s t i c s of the t re -m e n d o u s n u m b e r o f d e v i c es o n a c h i p . T h i s n o n - d i s-p e r s i o n c a n b e r e a c h e d o n l y b y a v e r y h o m o g e n e o u s f a b -r i c a t i o n o n a S i w a f e r . C o n s e q u e n t l y e a c h e l e m e n t a r yp r o c e s s m u s t b e e x a c t l y k n o w n a n d f i r m l y c o n t r o l l e d i nt h e e n v i r o n m e n t a n d f o r t h e g e o m e t r y o f t h e R & De q u i p m e n t . T h e U L S I r e q u i r e s a s c ie n t i f ic f a b r i c a t i o nw h i c h e n s u re s a m i n i m u m n u m b e r o f r a n d o m d e f e c t s int h e c i rc u i t. I n t h i s c o n t e x t t h e r o l e o f m i c r o c o n t a m i n a t i o n[ 9 ,2 0 ] o n t h e s u r f a c e a s w e l l a s in t h e b u l k o f t h e m a t e r i a le m e r g e s a s a f i r s t o r d e r i t e m . I t i s k n o w n t h a t t h e " z e r o -d e f e c t " s c i e n ti f ic f a b r i c a t i o n n e e d s t h e c o n t r o l o f th e i n -f l u e n c e o f v e r y l o w c o n c e n t r a t i o n o f c o n t a m i n a n t s :N s s < 10 9 cm -2 in the sur face of l e s s than 10 I1 cm -3 in theb u l k o f t h e m a t e r i a l [ 2 0 ] .

S o a n u m b e r o f v e r y e x c i t in g m e t r o l o g ic a l p r o b l e m sawai t so lu t ion:


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48 G. Kamarinos I Materials Science and EngineeringA199 (1995) 45-51- H o w t o m e a s u r e t h e s e c o n c e n t r a t i o n s i n a ( a l r e a d y

d o p e d o r p r o c e s se d ) s u r f a c e o r v o l u m e ?- H o w to d e t e c t a p a r t i c l e o f 0 . 0 3 / z m s i z e l o c a l l y i n t h e

c l e a n r o o m o f th e R & D l a b o r a t o r y ?- H o w t o m e a s u r e t w o f o r e i g n p a r t i c l e s i n a m i l l i l i t e r

o f a l i q u i d u s e d i n a p r o c e s s i n a n R & D e n v i r o n -m e n t ?

( t o t h e a b o v e m e t r o l o g y c h a l l e n g e s o n e c a n a d d t h e d i f f i -c u l t i es o f t e m p e r a t u r e , a n d A T , m e a s u r e m e n t i n si tu ) .T h e a b o v e v e r y b r i e f r e v i e w o f t h e p r o b l e m s a r i s in g i n

s c i e n t i f i c f a b r i c a t i o n , r e q u i r e d b y U L S I S i - / t e , p o i n t s o u tt h a t r e s e a r c h a c t i v i t i e s c o n c e r n i n g f a b r i c a t i o n c a n n o t b ep e r f o r m e d f a r f r o m t h e e n v i r o n m e n t o f t h e R & D l a b o r a -t o r y . T h e a b s o l u t e n e c e s s i t y o f th e i n j e c t i o n o f t h e b a s i cr e s e a r c h a c t i v i t i e s i n t h e R & D l a b o r a t o r i e s i s a n e w r e -q u i r e m e n t . I t i s s o e v i d e n t t h a t R & D l a b o r a t o r i e s c o n -n e c t e d w i t h t h e i n d u s t r i a l c e n t e r s m u s t f u n d t h e i n s e r t i o no f b a s i c ( u n i v e r s i t y g r o u p s ) r e s e a r c h t e a m s i n th e i r e n v i -r o n m e n t ; a d i r e c t c o n s e q u e n c e o f t h is r e m a r k i s al s o t h a t ap a r t o f th e a c t i v i t y a n d t h e e q u i p m e n t o f s u c h a l a b o r a t o r ym u s t s e r v e t h e e d u c a t i o n o f f u t u r e e n g i n e e r s a n d r e -s e a r c h e r s f o r U L S I S i- /z e.3.2. Physics of working ULSI devices and circuits

T h e d e s i g n a n d t h e s im u l a t io n o f w o r k i n g V L S II C s a r e b a s e d i m p l i c i t l y , u p t o n o w , o n t h e p a r t i t i o n p r i n -c i p l e [ 2 1 , 2 2 ] . A c c o r d i n g t o t h i s p r i n c i p l e a n I C i s a n e t -w o r k o f d i s c r e t e d e v i c e s w h i c h a r e o p e r a t i n g d i s c r e t e l y ;t h e y c o m m u n i c a t e o n l y b y e s t a b l i s h e d m e t a l l i c c o n n e c -t ions .

T h i s p r i n c i p l e h o l d s f o r t h e " m a c r o s c o p i c s c a l e " o fi n t e g r a t i o n w h e r e t h e c h a n n e l l e n g t h L o f a M O S t r a n s is -t o r i s lo n g e r t h a n t h e m e a n f r e e p a t h o f e l e c t r o n s l , a n d l i sv e r y m u c h l o n g e r t h a n t h e r a d i u s o f t h e c o l li s i o n s o f c a r-r i e r s wi th the l a t t i ce

< < l < L , m a c r o s c o p i c s c a l eT h e m a c r o s c o p i c s c a le o f i n te g r a ti o n s h o l d s s o t h a t w h e nL i s h i g h e r t h a n 0 . 3 / z m . F o r t h i s s c a l e a l l t r a n s p o r t p h e -n o m e n a c a n b e s a t i s f a c t o r i l y a p p r o a c h e d w i t h t h e c o n -c e p t s o f e f f e c t i v e m a s s ( m * e f f ) , t h e b a n d s o f e l e c t r o n e n -e r g i e s , e t c . ; t h e c u r r e n t i s s t r o n g l y c o n n e c t e d t o t h e e l e c -t ri c f ie l d ( e x c e p t f o r v e r y h i g h f r e q u e n c ie s ( f > 1 0 0 G H z )a n d t h e c o n d u c t i o n r e g i m e i s s t a t i o n a r y .

T h e s i m u l a t i o n s o f I,V c h a r a c t e r i s t i c s o f s u c h d e v i c e sa r e b a s e d o n h y d r o d y n a m i c - l i k e e q u a t i o n s o r , b e t te r , o nt h e c l a s s i c a l i n t e g r a t i o n o f t h e B o l t z m a n n e q u a t i o n . E v e nh i g h f i e l d e f f e c t s a r e c l a s s i c a l l y a p p r o a c h e d w i t h s u f f i -c i e n t a c c u r a c y .

T h e f u t u r e U L S I I C w i l l i n c l u d e d e v i c e s w h i c h w i l l b ec h a r a c t e r iz e d b y

~. 1 0 6 V / c m ) a n d t h ec o n d u c t i o n b y h o t c a r d e r s r e s u l t i n th e :- i n j e c t io n i n t o o x i d e s ( g a t e a n d i s o l a t io n o x i d e s ) ,

- g e n e r a t i o n o f c r y s t a ll i n e d e f e c t s n e a r t h e d r a i n o r i n t ot h e g a t e o x i d e ;

- i m p a c t i o n i z a t io n n e a r t h e d r a i n ;- inc rease in the e l ec t r i ca l no i se of the t rans i s tor ( l l fe x c e s s n o i s e ).

T o a v o i d t h e s e e ff e c t s or t o r e m e d i a t e t h e m o n e m u s t i n -t e r v e n e a t t w o l e v e l s:

- i n th e d e s i g n a n d f a b r i c a t i o n o f t h e d e v i c e a n d o f t h ec i r c u it ( t o f in d g e o m e t r i e s s o f t e n i n g t h e f i e l d n e a r t h ed r a i n , d r a i n e n g i n e e r i n g , t o e n h a n c e t h e q u a l i t y a n dt h e p u r i ty o f o x i d e s , a v o i d m i c r o n t a m i n a t i o n a n dc o n t r o l m i c r o r o u g h n e s s , t o k n o w e x a c t l y t h e 2 Dp r o f i l e o f i m p u r i t y d i f f u s i o n ) ,

- i n t h e m o d e l i n g o f t h e w o r k i n g o f t h e d e v i c e an d o ft h e c i r c u i t ( t o l o w e r t h e d r a i n v o l t a g e , VD g o e s t o1 V , t o i d e n t i fy e x a c t l y t h e m o r e s e n s i t iv e t r a n s p o r t


5/7

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A t t a i n a b l e l i n e w i d t h s* E x i s ti n g " l a b o r a t o r y " d e v i c e sR - D " r e s e a r c h - d e v e l o p m e n t " d e v i c e s

R " r e s e a r c h " d e v i c e sFig. 2. Litho grap hy linew idth and characteristic lengths for silicon.Ferry 's diagram for present devices .

p a r a m e t e r s a n d t o m e a s u r e t h e m , t o k n o w e x a c t l y th e2 D t r an s p o r t o f ca r r i e r s ).

T o d e v e l o p a d e t a i le d k n o w l e d g e o f t h e w o r k i n g o f ad e v i c e t h e M o n t 6 - C a r l o m e t h o d s o f r e s o l u t i o n o f t h eB o l t z m a n n t r a n s p o r t e q u a t i o n c o u p l e d w i t h t h e e n e r g yd i s t r i b u t i o n an d d i s s i p a t i o n ( an d , t o t ak e i n t o acco u n tq u an t u m e f f ec t s , th e S ch r / S n d i ng e r eq u a t i o n ) m u s t b e d e -v e l o p ed [ 31 ] an d t r an s f e r r ed t o R & D l ab o r a t o r ie s .

T h e a d v a n c e d n u m e r i c a l m e t h o d o f re s o l u ti o n o f n o n -l i n ea r d i f f e r en t i a l eq u a t i o n s a r e o f g r o w i n g i m p o r t an cef o r f u t u r e en g i n ee r s .

( 2 ) T h e i n t e r - d ev i ce co u p l i n g i s d u e t o t h e h i g h d en s i t yo f t h e d ev i ce s i n a ch i p ( m o r e t h an 1 07 M O S T p e r cm 2) .

T h e c l a s s i ca l co u p l i n g , i . e . c ap ac i t i v e o f e l ec t r o m ag -n e t i c ( f o r h i g h f r eq u en c i e s ) i s s a t i s f ac t o r i l y ap p r o ach edb y c l a s s i ca l m e t h o d s o f e l em en t a r y e l ec t r o s t a t i c s an de l e c t r o m a g n e t i s m . O n t h e c o n t r a r y , th e r m a l c o u p l i n g h a sb een n eg l ec t ed u p t o n o w b u t t h i s s i t u a t i o n i s r ap i d l yc h a n g i n g [ 3 1, 3 2 ]. T h e s l o w i n g d o w n o f t h er m a l i z a ti o n o fp h o n o n s d u e t o s e l ec t i o n r u l e s i n t h e S i / S i O 2 i n t e r f ace i san ex c i t i n g p r o b l e m f o r s o l id s t a t e p h y s i c s .

T h e n o i s e i n v e r y s m a l l d ev i ce s , i t s d i s p e r s i o n an d i t sn o n - s t a t i o n a r i t y an d n o n - e r g o d i c i t y co n s t i tu t e an o t h e rex c i t i n g p r o b l em w h i ch i s n o w s t u d i ed a f t e r t h e o b s e r v a -t io n o f th e R a n d o m T e l e g r a p h S i g n a l N o i s e ( R T S ) w h i c hi s a o n e - e l e c t r o n p h e n o m e n o n o b s e r v e d a t r o o m t e m p e r a -t u r e [ 3 3 - 3 5 ] . T h i s p r o b l e m i s e v i d e n t l y c o n n e c t e d w i tht h e co n cep t s o f l o ca l eq u i l i b r i u m i n a s y s t em f a r f r o mt h e r m o d y n a m i c e q u il i b ri u m .

E v i d en t l y t h e n o i s e i s n o t , i n f ir s t o r d e r , an i n t e r - d ev i cee f f ec t ; n ev e r t h e l e s s i t s d i s p e r s i o n f o r U L S I I C can s e r i -o u s l y a f f ec t t h e r e l i ab i l i t y an d , s o , l o w f r eq u en cy n o i s ecan co n s t i t u t e a l i m i t a t i o n f o r s ca l i n g d o w n [ 3 3 - 3 5 ] .

A n o t h e r c l a ss o f e f f ec t s w h i ch w i l l em er g e i n t h i s s ca leo f i n t eg r a t i o n a r e t h e co o p e r a t i v e e f f ec t s d u e t o s t r o n ge l ec t r i ca l n o n - l i n ea r co u p l i n g o f t h e d ev i ce s [ 2 1 ,2 2 ] ; t u n -n e l i n g e f f ec t s , s u p e r l a t t i c e e f f ec t s an d ch ao t i c e f f ec t s a r ea l r ead y o b s e r v ed i n s ev e r a l s i t u a ti o n s .

T h e i n f l u e n c e o f t h e a b o v e e f f e c t s i s n o w c o n s i d e r e das a d r aw b ack f o r t h e U L S I , b u t a n ew i d ea i s s l o w l yem er g i n g . A l l th e s e co o p e r a t i v e e f f ec t s can b e p o s i t i v e l yex p l o i t ed i n a n ew a r ch i t ec t u r e o f i n teg r a t ed c i r cu i t w h e r et h e e m e r g e n c e o f t h e s e e f f e c t s is f a v o r e d ; t h e e r a o f" h o l i s t i c i n t eg r a t i o n " w o u l d t h e r e f o r e b e o p en : t h e c i r cu i tn o w w o r k s a s a w h o l e a n d n o t a s a s y st e m o f c o n n e c t e dd i s c r e t e d ev i ce s .

I t i s ev i d en t t h a t t o an a l y ze an d d es c r i b e t h e w o r k i n go f U L S I d e v i c e s, th e q u a n t u m m e c h a n i c s a p p r o a c h o fU L S I s t r u c t u r e s , t h e B o l t zm an n t r ea t m en t o f t r an s p o r tw i t h ad v an ced n u m er i ca l m e t h o d s , t h e i n t r o d u c t i o n o fa d v a n c e d c o n c e p t s o f i r r e v e r s i b l e t h e r m o d y n a m i c s a n ds t a t i s t i c a l m ech an i c s a s w e l l a s t h e m e t h o d s o f t r ea t m en to f t h e ch ao t i c e f f ec t s m u s t en t e r t h e E d u ca t i o n a l P r o g r amo f f u t u r e en g i n ee r s an d r e s ea r ch e r s . O n t h e co n t r a r y , i nt h e s i t u a t i o n co n ce r n i n g f ab r i ca t i o n p r o ces s e s , b a s i c( u n i v e r s i t y ) r e s ea r ch can b l o s s o m an d can b e d ev e l o p edo u t s i d e o f R & D g r o u p s . E v i d en t l y a t i g h t co l l ab o r a t i o nb e t w een R & D g r o u p s an d u n i v e r s i t y t e am s i s ab s o l u t e l yn eces s a r y . T h e R & D l ab o r a t o r y can t h en f u r n i s h th e u n i -v e r s i t y g r o u p w i t h t h e ad v an ced d ev i ce s f o r ch a r ac t e r i za -t i o n a n d c o m p a r i s o n w i t h m o d e l i n g a n d s i m u l a t i o n ; t h et w o g r o u p s can co l l ab o r a t e f o r t h e d e f i n i t i o n o f l o n g t e r mo b j e c t iv e s a n d t hu s , f o r t h e i r c o m m o n p r o g r a m . T h e m u -t u a l b en e f i t s o f s u ch a co l l ab o r a t i o n i s o b v i o u s .4 . C o n c l u s i o n

S o m e y ea r s ag o f o r g o o d en g i n ee r i n g i n s i l i co n m i -c r o e l ec t r o n i c s , i t w as s u f f i c i en t t o k n o w t h a t a s em i co n -d u c t o r i s a s y s tem o f t w o e l ec t r o n r e s e r v o i r s w i t h e l ec -t r o n i c l o ca l i zed s t a t e s i n t h e g ap . T h e ca r r i e r co n cen t r a -t i o n s a r e d e s c r i b ed b y F e r m i s t a ti s ti c s an d t h e cu r r en t s a r ea p p r o a c h e d b y h y d r o d y n a m i c a l e q u a ti o n s .

W i t h t h i s e l em en t a r y b ack g r o u n d , i t w as p o s s i b l e f o ran en g i n ee r to u n d e r s t an d an d m o d e l t h e u s u a l d ev i ce sand c i r cu i t s [36] .

C o n ce r n i n g t h e f ab r i ca t i o n , c l a s s i ca l ch em i s t r y an dp h y s i ca l ch em i s t r y o f eq u i l i b r i u m w e r e s u f f i c i en t an ds o m e c o m p l i c a t e d s it u a ti o n s w e r e a p p r o a c h e d b y e m p i ri -ca l l aws .

N o w a d v a n c e d V L S I a n d t h e b e g in n i n g o f th e U L S Ie r a a re r a p i d ly c h a n g i n g t h e l a n d sc a p e ; q u a n t u m m e c h a n -i c s i s ag a i n n eces s a r y t o u n d e r s t an d t h e e l ec t r i c t r an s p o r ti n in v e r s i o n l ay e r s , n u m er i ca l t r ea t m en t o f t h e B o l t zm an nt r an s p o r t eq u a t i o n i s u s ed f o r m o d e l l i n g t h e I,V ch a r ac t e r -


6/7

50 G. Kamarinos / Materials Science and Engineering A199 (1995) 45-51i s ti c s a n d t h e s t a t is t ic a l m e c h a n i c s a n d i r r e v e r s i b l e t h e r-m o d y n a m i c s a r e n e e d e d t o u n d e r s t a n d a n d e x p l o i t c o o p -e r a t iv e a n d i n t e r - d e v i c e c o u p l i n g e f fe c ts .

C o n c e r n i n g t h e fa b r i c a t i o n t h e n e c e s s i t y f o r t h e re t u r n[ 3 7 , 3 8 ] , t o b a s i c " f i r s t p r i n c i p l e s " a n d t h e e n d o f e m p i r -i s m i s o b v i o u s .

T h e p r o g r a m s o f E d u c a t i o n m u s t t h e r e fo r e b e d ra s ti -c a l l y r e v i s i t ed . O u r a n a l y s i s a l s o s h o w s t h a t u n i v e r s i t yr e s e a rc h m u s t b e c l o s e r to t h e R & D l a b o r at o r ie s .

I n th e c a s e o f r e s e a rc h ( a n d e d u c a t i o n o f d o c t o r d e g r e es t u d en t s ) w e s u g g e s t t h a t t h e u n i v e rs i t y g r o u p s m u s t w o r ki n t h e s a m e p l a c e a n d w i t h t h e s a m e e q u i p m e n t a s t h eR & D g r o u p s . F o r s t u d ie s c o n c e r n i n g t h e e l e c tr i ca l w o r k -i n g o f d e v i c e s a n d c i r c u i t s , th e t w o t y p e s o f g r o u p s c a nc o n s e r v e th e i r g e o g r a p h i c a l i n d e p e n d e n c e .

S u c h a s c h e m e o f c o l la b o r a t i o n i s p o s s ib l e i n s e v e ra lp l a c e s i n E u r o p e . F o r e x a m p l e G r e n o b l e , i n F r a n ce , i s ap l a c e w h e r e s t r o n g u n i v e r s i ty g r o u p s ( C N R S l a b o r at o r ie s )a n d l a rg e R & D l a b o ra t o r i e s ( C N E T / C N S , L E T I / C E A )s t r o n g ly c o n n e c t e d t o I n d u s tr y ( S G S - T H O M S O N ) e x is t.O n e c a n f i n d t h e r e t h e b e g i n n i n g o f s u c h a c o l la b o r a t io nw h i c h f o r th e m o m e n t e x i s t s o n l y d u e t o a v o l u n t a r y i m -p u l s i o n .R e f e r e n c e s[1] G. Courtois , C AD and tes t ing of IC's and systems; where are we

go i ng? T I M A / C N R S/ I N PG G r e nob le , M a y 1993.[2] (a) IE E (Journal of Ele ctro nic Engineering); spotlighting: sem i-

conductors and ICs: the lates t developm ent t rends on S RAM s,ASS P LSIS, ASICs , Fla sh memor ie s , MO SFET s e tc . Col l ec t ion oftechnical re view ar t ic les 29(308) (1992) . (b) IEEE MIC RO : chips ,systems, software, and applications. Sp ecial issue, Microelectron-ics in Europe, Augu s t (1992).[3] A . Harstein, Ultra-short channel S i M OS FE T. ElectrochemicalSoc ie ty Spr ing Mee t ing, Washington, DC, 1991, pp. 432-433.

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