PULSED LASER IRRADIATION OF NICKEL THIN FILMS ON SILICON

HAL Id: jpa-00223151

https://hal.archives-ouvertes.fr/jpa-00223151

Submitted on 1 Jan 1983

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

PULSED LASER IRRADIATION OF NICKEL THIN FILMS ON SILICON

P. Baeri, M. Grimaldi, E. Rimini, G. Celotti

To cite this version:

P. Baeri, M. Grimaldi, E. Rimini, G. Celotti. PULSED LASER IRRADIATION OF NICKEL THIN FILMS ON SILICON. Journal de Physique Colloques, 1983, 44 (C5), pp.C5-449-C5-454.

�10.1051/jphyscol:1983566�. �jpa-00223151�

JOURNAL DE PHYSIQUE

Colloque C5, suppl6ment au nO1O, Tome 44, octobre 1983 page C5-449

PULSED LASER IRRADIATION O F NICKEL THIN FILMS ON SILICON

P . B a e r i , M.G. G r i m a l d i ,

E.

I s t i t u t o DipartimentaZe d i Fisica, 57 Corso ItaZia, 195129 Catania, I t a l y

*LAMEL-CNR, Via d e i CastagnoZi 1, 40100 BoZogna, ItaZy

Resume - L ' i r r a d i a t i o n de l a s e r pulse a &t@ u t i l i s e e pour l a formation de s i l i c i d e dans des couches minces de Nickel deposeees sur des substrats de silicium orient6 <loo> e t < I l l > . Des couches de s i l i c i d e NiSi, epitaxial ont @te obtenues par une valeour proportionn6e de densite d'energie d'im- pulsion d'un l a s e r I verre de Nd a 30 ns dans l e cas d'une couche di 15 nm d'epaisseur. L ' i r r a d i a t i o n de couches plus epaisses de N i ou c o n t r a i r e a forme plusieurs s i l i c i d e s de composition nonuniforme. La comparai son des re- s u l t a t s experimentaux avec l e s calculs donne una indication que l a reaction entre l e metal e t l e silicium commence I l ' i n t e r f a c e e t I une temperature bien au dessous du point de fusion du Nickel ou du Silicium.

Abstract - Pulsed l a s e r i r r a d i a t i o n was used t o induce s i l i c i d e formation i n nickel t h i n films deposited onto <loo> and < I l l > oriented s i l i c o n substrates.

Epitaxial NiSi, s i l i c i d e layers a r e obtained by a s u i t a b l e energy density va- lue of the 30 ns Nd glass l a s e r pulse in the case of a 15 nm thick layer.

Irradiation of thicker Ni layers formed instead s i l i c i d e s of nonuniform compo- s i t i o n . The comparison of experimental r e s u l t s ^{w i t h} calculations indicates t h a t t h e reaction between the metal and t h e s i l i c o n layer s t a r t s a t t h e intell face and a t a temperature well below the melting point of N i o r S i .

INTRODUCTION

Laser annealing of ion implanted semiconductors i s extensively ( l j adopted t o remove the damage and t o a c t i v a t e e l e c t r i c a l l y the implanted species. In addition grain growth and even Si s i n g l e c r y s t a l s a r e obtained by i r r a d i a t i o n of polycrystalline layers. In the s i l i c o n technology increasing i n t e r e s t has been given t o the use of metal s i l i c i d e s a s ohmic contacts, Schottky b a r r i e r s , intgrcannections and-gate e l e g trodes. Pulsed l a s e r o r ion beams a r e considered a s an a l t e r n a t i v e - t o The conventig nal furnace a n n ~ a l i n g .

Irradiation of metal-silicon systems w i t h pulsed l a s e r ( 2 ) and electron beam (3) a t high power density formed c e l l u l a r s t r u c t u r e s with s i 1 icon columns surrounded by s i - l i c i d e walls. The formation of c e l l u l a r s t r u c t u r e s i s a t t r i b u t e d t o the freezing of a molten layer of metal and s i l i c o n . Constitutional supercooling as the melt f r o n t moves toward the surface gives r i s e t o the c e l l s t r u c t u r e s , i n a similar way t o what has been found i n s i l i c o n heavily doped. Several compounds are formed w i t h a non- uniform d i s t r i b u t i o n both l a t e r a l l y and in depth. In the case of the Ni-Si system, of i n t e r e s t t o t h e present work, Ni,Si,NiSi,NiSi, and probably NiSi, a r e formed ( 4 ) a f t e r Q-switched l a s e r i r r a d i a t i o n .

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1983566

C5-450

JOURNAL DE

High power pulsed i o n beams caused i n s t e a d t h e formation o f e p i t a x i a l NiSi, s i l i c i - de w i t h i n a s u i t a b l e energy d e n s i t y range ( 5 ) . A t h i g h d e n s i t i e s c e l l u l a r s t r u c t u - r e s a r e created and a t lower energy d e n s i t i e s p o l y c r y s t a l l i n e l a y e r s c o n t a i n i n g a m i x t u r e o f compounds a r e formed. I n t h i s case t h e energy i s deposited n e a r l y u n i - form over depths g r e a t e r than t h e metal-Si i n t e r f a c e and m e l t i n g s t a r t s a t t h e i n - t e r f a c e . The f o r m a t i o n o f e p i t a x i a l l a y e r s i s found a t energy d e n s i t i e s w e l l below t h a t a t which Ni o r S i melts.

Probably m e l t i n g (6) occurs a t t h e e u t e c t i c temperature and t h i s v e r y t h i n l a y e r s t a r t s t o grow by d i f f u s i o n o f N i o r S i through t h e molten l a y e r . The composition o f t h e l i q u i d l a y e r depends on t h e d u r a t i o n o f t h e molten phase. S o l i d i f i c a t i o n s t a r t s then from d i f f e r e n t c o n c e n t r a t i o n o f t h e two elements. I f a compasition hear t o one o f t h e usual compound i s e x i s t i n g p r i o r t o s o l i d i f i c a t i o n , t h e f r e e z i n g w i l l r e s u l t i n a homogeneous s i 1 i c i de , p o s s i b l e one compound.

I n l a s e r annealing t h e energy i s absorbed i n t h e o u t e r l a y e r s , and t h e maximum tem- p e r a t u r e i s reached a t t h e surface. Depending on t h e thickness o f t h e metal l a y e r t h e s u r f a c e temperature may reach t h e m e l t i n g p o i n t b e f o r e t h e i n t e r f a c e i s a t t h e e u t e c t i c temperature. The molten m a t e r i a l i s f a r from thermodynamic e q u i l i b r i u m . N u c l e a t i o n and growth o f d i f f e r e n t phases i s then p o s s i b l e d u r i n g s o l i d i f i c a t i o n t o - gether w i t h segregation, c e l l u l a r s t r u c t u r e s , convective motion e t c .

I n t h i n l a y e r s i t has been shown r e c e n t l y (7) t h a t i t i s p o s s i b l e t o o b t a i n e p i t a - x i a l NiSi, s i l i c i d e s on (100) o r i e n t e d s u b s t r a t e s a l s o by pulsed l a s e r annealing.

Thicker metal l a y e r s g i v e r i s e i n s t e a d t o t h e formation o f nonuniform i n depth and l a t e r a l l y compounds. I n t h e present work we r e p o r t a d e t a i l e d i n v e s t i g a t i o n on t h e s i l i c i d e formation i n t h e N i / S i system by pulsed l a s e r i r r a d i a t i o n , t o g e t h e r w i t h some c a l c u l a t i o n s based on t h e heat f l o w treatment.

EXPERIMENTAL PROCEDURES

Nickel t h i n f i l m s , 17 and 50 nm i n thickness, were vacuum deposited on (100) and (111) o r i e n t e d S i substrates. The i r r a d i a t i o n was performed w i t h Nd glass 1.06 vm l a s e r p u l s e o f 30 ns d u r a t i o n . The beam spot was a few m i l l i m e t e r s i n diameter.

The energy d e n s i t y ranged between 0.2 and 2.0 J/cm2 and was homogenized w i t h i n few percents b y a c o n i c a l guide pipe.

The samples were analyzed by 2.0 MeV He + b a c k s c a t t e r i n g i n combination w i t h channe- l i n g e f f e c t technique. A depth r e s o l u t i o n o f about 10 nm was obtained u s i n g a gra- c i n g d e t e c t i o n f o r t h e backscattered p a r t i c l e s . Some samples were a l s o analyzed by an X-ray Wallace-Ward (8) c y l i n d r i c a l camera. I n t h i s set-up t h e Cr-K, r a d i a t i o n beam, p a r a l l e l t o t h e a x i s of a c y l i n d r i c a l cassette, impinge on t h e specimen a t an angle o f 20" w i t h t h e surface. The sample i s c o n t i n u o u s l y r o t a t e d around an a x i s normal t o i t s surface.

RESULTS AND DISCUSSION

The r e a c t i o n between Ni and Si, as determined by backscattering, occurs a t an ener- gy d e n s i t y o f about 0.6 J/cm2. A t h i g h e r energy d e n s i t y t h e thickness o f t h e reac- t e d r e g i o n increases and a t 0.8 J/cm2 a 17 nm t h i c k Ni l a y e r forms a mixed l a y e r o f composition near t o NiSi,.

The channeling a n a l y s i s i n d i c a t e s i n t h i s case t h e f o r m a t i o n o f an e p i t a x i a l s i l i -

c i d e . The spectra a r e shown i n Fig.1 f o r a 17nm t h i c k Ni f i l m on (111) S i . The

a1 igned y i e l d i s lower than t h e random y i e l d f o r b o t h N i and S i s i g n a l . The m i n i -

mum y i e l d i s about 35%, an h i g h e r minimum y i e l d , 50% i s found f o r t h e (100) o r i e c

DEPTH (nm)

-

ENERGY (MeV)

Fig. 1 - Backscattering analysis of 17 nm thick N i layer deposited onto (111) oriented Si and i r r a d i a t e d with 0.98 J/cm2 Nd glass l a s e r pulse, 30 ns duration ( A * random, aligned incidee- ce) .

-

..-

5 8

2 -

^{Fig.2 -} Backscattering analysis of 50nm

9 thick N i layer deposited onto ( 1 7 1 )

w

0 4

orien&d Si and i r r a d i a t e d with 1.45

I J/cm2 Nd glass pulse, 30 ns duration.

W +

( A random, aligned incidence).

5

m r

3

08 10 1 2 1 4 16

ENERGY (MeV)

ted substrates. In thicker Ni layer t h e epitaxial Nisi, s i l i c i d e does not form.

The channeling spectra f o r a 50 nm Ni thicker l a y e r , d e ~ o s i t e d onto (111)

Si , a f t e r i r r a d i a t i o n a r e shown in Fig.2 The t a i l i n the random Ni signal indicates a nonuniform i n depth composition. The minimum y i e l d amounts t o 80% and t o 60% f o r Ni and Si signal respectively. As evidenced by d i f f r a c t i o n patterns only a small amount of epitaxial Nisi, i s formed. The remaining Ni part should form other com- pounds arranged probably in columns surrounded by single crystal S i .

The d i f f r a c t i o n patterns of the samples analyzed by ion channel ing and reported i n Fig.1 and Fig.2, are shown i n Fig.3. The pattern of the thin Ni layer ( l e f t hand s i d e ) shows t h e presence of cubic Nisi, s i l i c i d e . The e p i t a x i a l relationship with the substrate can be described as N i S i , ( l l l ) / / S i ( l l l ) . The pattern of t h e sample w i t h a t h i c k e r N i film ( r i g h t hand s i d e ) shows t h e presence of both e p i t a x i a l and polycrystalline NiSi, mixed with unreacted poly Ni and w i t h t h e Ni2Si, Ni,Si2,NiSi pol ysi 1 i ci des .

The d i f f r a c t i o n techniques allows the detection of one compound among others i f i t

amountsat l e a s t t o 5% of the t o t a l amount.In t h e t h i n Ni layer a t 0.8 J/cm2 only

NiSi, i s formed. The r e l a t i v e high minimum yield i s probably due to the presence

of a large amount of extended defects as twins.

JOURNAL DE PHYSIQUE

Fig.3 - D i f f r a c t i o n p a t t e r n s o f 17 nm, l e f t hand side, and 50 nm r i g h t h a n d side, t h i c k Ni l a y e r s deposited onto (111) S i and i r r a d i a t e d w i t h 0.98 and 1.45 J/cm2 r e s p e c t i v e l y .

L e f t side: t h e arrows i n d i c a t e t h e d i f f r a c t i o n spots corresponding t o several d i f f r a c - t i n g planes o f t h e NiSi, cubic s i n g l e c r y s t a l . The o t h e r spots r e f e r t o t h e S i sub- s t r a t e .

R i g h t side: t h e arrows i n d i c a t e t h e d i f f r a c t i o n spots from t h e Nisi, c u b i c s i n g l e c r y s t a l , weak l i n e s corresponds t o d i f f r a c t i n g planes o f d i f f e r e n t p o l y s i l i c i d e s : A) unreacted Ni (200);

B) Nisi, (220);

C ) N i ,Si2(115) ,(300) ,(213) ,r4i2Si (103) (121 ) , Ni ,Si2(313) (512) ,Nisi (21 1) (121 );

D) unreacted Ni (111)

By v a r y i n g t h e energy d e n s i t y around t h e value corresponding t o t h e Nisi, f o r m a t i o n no c l e a r i n d i c a t i o n o f mixed l a y e r w i t h a u n i f o r m composition o r e p i t a x y has been found. The minimum y i e l d i s obtained a t a composition o f t h e reacted l a y e r c l o s e t o t h e NiSi, compound. By i n c r e a s i n g o r decreasing t h e energy d e n s i t y value correspon- ding t o t h e NiSi, formation t h e minimum y i e l d f o r both S i and Ni s i g n a l increases as shown i n Fig.4. A v a r i a t i o n o f t h e energy d e n s i t y from 0.8 t o 1.43 J/cm2 produ- ces change i n t h e Ni c o n c e n t r a t i o n from 40% t o 20% r e s p e c t i v e l y .

Fig.4 - Minimum y i e l d o f Ni ( A ) and of S i ( o ) vs t h e Ni c o n c e n t r a t i o n i n 17 nm N i t h i c k l a y e r s deposited o n t o (111) S i and i r r a d i a t e d a t d i f f e r e n t energy densi- t i e s o f pulses Nd l a s e r .

NI CONCENTRATION ( % )

Diffraction analysis indicates that in t h i s range NiSi, compound i s present.

A t energy density near the threshold value f o r mixing the s e n s i t i v i t y of the techni- que does not allow t o determine t h e presence of any compound. Similar r e s u l t s were obtained using (100) oriented s u b s t r a t e s . The epitaxial quality of the NiSi, s i l i - cide was worse i n aareement with measurements using conventional furnace annealing .

The computer model based on the heat flow equation, previously developed(9) f o r pulsec l a s e r i r r a d i a t i o n of ion implanted s i l i c o n , has been extended t o t r e a t a bilayer system. The r e f l e c t i v i t y of the i r r a d i a t e d sample depends on the Ni film thickness.

I t increases steeply from 45% a t 10 nm and s a t u r a t e s t o 72% a t 40 nm thick layer.

The measured values agree quite well with computations based on the optical proper- t i e s of thin films.

The temperature difference between the surface and a depth 50 nm below i s only 30K f o r a 15 nm thick N i layer, while i t becomes 130K a t a depth of 150 nm and f o r a 50 nm Ni thick layer. In the f i r s t case the temperature i s q u i t e uniform a l l over t h e interested thickness, in the second case the gradient becomes relevant and the nonuniform d i s t r i b u t i o n might play a r o l e in t h e f i n a l composition p r o f i l e . The dependence of the surface temperature on the energy density i s shown i n Fig.5

Rub~a69m3Ons Fig.5 - Computed maximum surface temperature reached by 15 nm thick N i layer onto (111) Si and irradiated with 0.69 pm (upper p a r t ) and 1.06 um (lower p a r t ) wavelength l a s e r pulse.

The dashed area indicate t h e experimental thre- shold values t o i n i t i a t e t h e mixing between Si and N i . The melting temperature of Si and the

2

e u t e c t i c temperature of t h e Ni-Si system a r e

f

indicated by 1 i nes .

x

9

ENERGY DENSITY(J/cm'l

f o r ruby (upper p a r t ) and f o r Nd (lower p a r t ) l a s e r i r r a d i a t i o n . The melting and e u t e c t i c temperatures f o r Si and f o r Ni-Si system a r e indicated by l i n e s together w i t h t h e measured energy density threshold f o r the reaction. For both ruby (10) and Nd i r r a d i a t i o n s the mixing s t a r t s a t a calculated temperature lower than t h a t of the Si ( o r Ni) melting point, near instead t o the e u t e c t i c temperature. Similar r e s u l t s and conclusions were reached i n the case of ion and electron beam i r r a d i a - tion: soon as the i n t e r f a c e temperature reaches the e u t e c t i c value a liquid layer i s formed.

Th,e formation of a uniform compound, e.g. NiSi,, implies t h e complete mixing of N i into Si by a liquid phase diffusion. The l i q u i d layer of thickness R should then r e m a i n ~ l t e n f o r a time interval

enough t o allow Ni diffusion over a l l the layer, i . e . R , being D the diffusion coefficient. The thickness and the duration of the liquid region depend on the energy density of the l a s e r pulse. A narrow range of energy density values allows a complete mixing over t h e molten depth.

According t o previous calculations t h e duration and the thickness of the liquid re-

C5-454 JOURNAL DE PHYSIQUE

gion a r e given by ~ ( n s ) c 100 AE and R(cm) 2.5~10-'E r e s p e c t i v e l y , AE i s t h e energy d e n s i t y , J/cm2, i n excess o f t h e t h r e s h o l d value t o reach t h e e u t e c t i c temperature.

If ~ = 5 x 1 0 - ~ c m ~ / s t h e c r i t i c a l thickness, R , given by

i s 3 ~ 1 0 - ~ c r n . T h i s amount o f S i should be enough t o r e a c t w i t h a l l t h e metal l a y e r . I n t h e case o f Nisi, com- pound t h e estimated Ni atoms/cm2 value i s 1 0 ~ ' / c m ~ i n q u i t e good agreement w i t h t h e thickness o f t h e Ni l a y e r s used i n o u r experiment.

SUMMARY

NiSi, e p i t a x i a l l a y e r s can be obtained by pulsed l a s e r i r r a d i a t i o n o f t h i n Ni l a y e r s deposited on (111) o r (100) o r i e n t e d S i substrates. The c r i t i c a l value i s i n t h e 10-20 nm t h i c k n e s s range. A t h i g h e r thickness t h e temperature gradient, t h e dura- t i o n o f t h e l i q u i d l a y e r created a t t h e i n t e r f a c e soon as t h e temperature reaches the e u t e c t i c do n o t a l l o w a complete m i x i n g o f Ni w i t h S i t o form a s t e c h i o m e t r i c NiSi, compound. The r e a c t i o n between the two m a t e r i a l s s t a r t s a t a temperature much lower than t h e S i o r Ni m e l t i n g p o i n t and i s near t o t h e e u t e c t i c p o i n t .

Work supported i n p a r t by CNR-GNSM.

REFERENCES

I ) "Laser Annealing o f Semiconductors" e d i t e d by J .W.Mayer and J.M.Poate.

Academic Press, N.Y. 1982

2) J.M.Poate,H.J.Leamy,T.T.Sheng and G.K.Celler, Appl.Phys.Lett. 33,918 (1980) 3) G.Majni ,F.Nava ,F.Ottaviani ,A.Luches,!f.Nassisi and G . C e l o t t i , Vacuum - j 2 , l l(1982) 4) G.G.Bentini ,M.Servidori ,C.Cohen,R.Nipoti and A.V.Drigo, J.App1. Phys. 2,1525(1982) 5) L.J.Chen,L.S.Hung,J.W.Mayer,J.E.E.Baglin,J.M.Neri and D.A.Mammer,

Appl .Phys.Lett. - 40,595(1982)

6) L.J.Chen,L.S.Hung,J.W.Mayer and J.E.E.Baglin i n "Metastable M a t e r i a l s Formation by I o n I m p l a n t a t i o n " e d i t o r s S.T.Picraux and W.J.Choyke, North-Holland 1982,p.319 7) M.G.Grimaldi ,P.Baeri ,E.Rimini and G.Celotti , Appl .Phys. L e t t . 1983 ( i n press) 8) C.A.Wallace and R.C.Ward, J.Appl.Crystallography 8,255(1975)

9) P.Baeri and S.U.Campisano i n Ref .l -p.75

10) J.A.Knapp,S.T.Picraux,P.S.Peercy, Chu Te-Chang,E.Rimini (unpublished r e s u l t s ) .