A FULLY CHARACTERISED PROCESS FOR TITANIUM SILICIDE BY RTA FOR ONE MICRON CMOS

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A FULLY CHARACTERISED PROCESS FOR TITANIUM SILICIDE BY RTA FOR ONE MICRON

CMOS

N. Stogdale

To cite this version:

N. Stogdale. A FULLY CHARACTERISED PROCESS FOR TITANIUM SILICIDE BY RTA FOR ONE MICRON CMOS. Journal de Physique Colloques, 1988, 49 (C4), pp.C4-195-C4-198.

�10.1051/jphyscol:1988440�. �jpa-00227938�

Colloque C4, supplement au n09, Tome 49, septembre 1988

A FULLY CHARACTERISED PROCESS FOR TITANIUM SILICIDE BY RTA FOR ONE MICRON CMOS

N. F. STOGDALE

Plessey Research Caswell Ltd., Caswell, Towcester. Northants.

GB-NNl2 8 E Q , Great-Britain

A b s t r a c t A f u l l y c h a r a c t e r i s e d process f o r s e l f - a l i g n e d t i t a n i u m s i l i c i d e by RTA i s described. F a c t o r s i n f l u e n c i n g formation; s u r f a c e pre-cl ean, time-temperature

schedules and ambient choice are a l l discussed. The s e n s i t i v i t y o f t h e formation process t o implanted arsenic i s a l s o described and a model presented f o r t h i s e f f e c t . The technique i s proven by i t s i n c l u s i o n i n a one-micron t r e n c h i s o l a t e d CMOS process schedule and e l e c t r i c a l r e s u l t s f o r devices and c i r c u i t s thus f a b r i - cated are presented.

1

.

INTRODUCTION

Self-a1 igned t i t a n i u m s i l ic i d e formed on t h e gate and j u n c t i o n r e g i o n s o f small geometry CMOS devices gives enhanced device performance a r i s i n g from the r e d u c t i o n o f p a r a s i t i c s e r i e s resistances. The use o f a Rapid Thermal Annealing (RTA) system allows t i g h t c o n t r o l o f ambient oxygen and g r e a t e r process f l e x i b i l i t y and c o n t r o l . A f u l l y c h a r a c t e r i s e d process f o r sel f-a1 igned t i t a n i u m s i l ic i d a t i o n by RTA i s described, g i v i n g a s i l ic i d e w i t h good surface qual i t y and low, u n i f o r m sheet r e s i s t i v i t y . Factors i n f l u e n c i n g surface q u a l i t y ; surface pre-clean and ambient choice are described. Choice o f thermal cycles, times and temperatures, f o r o p t i m i s a t i o n o f t h e sheet r e s i s t i v i t y and l a t e r a l encroachment are a l s o discussed. The optimum f i l m i s analysed by SEM, SIMS and AES f o r surface q u a l i t y , thickness and stochiometry. The s e n s i t i v i t y o f t h e formation process t o implanted dopant i s described and a model presented f o r t h e s e n s i t i v i t y t o implanted arsenic.

2. FACTORS INFLUENCING SILICIDE FORMATION 2.1 The E f f e c t o f Surface Pre-treatment

S i l i c i d e surface q u a l i t y was found t o be c r i t i c a l l y dependent on surface pre-clean.

Several methods o f pre-cleaning were evaluated: wet chemical, SF, plasma flash, HCL gas clean and 100:l HF based spray clean. S p u t t e r deposited t i t a n i u m was used throughout and an i n - s i t u RF (argon i o n ) s p u t t e r clean was a1 so evaluated. The b e s t s i l i c i d e surface q u a l i t y was achieved w i t h t h e 100:l HF spray clean, w i t h o u t a pre-deposition RF s p u t t e r c l e a n

.

2.2 The E f f e c t o f Ambient Choice

The choice o f ambient; argon o r nitrogen, was found t o have a c r i t i c a l e f f e c t on s i l i c i d e s u r f a c e qual i ty. Argon produced a poor qual i t y 'broken

'

surface (sheet r e s i s t i v i t y 3.3ohm/sq.

1,

w h i l s t n i t r o g e n produced a good surface qual i t y (sheet r e s i s t i v i t y 4.5ohm/sq).

N i t r o g e n forms a t i t a n i u m n i t r i d e capping l a y e r which p r o t e c t s t h e t i t a n i u m from r e a c t i o n w i t h any ambient oxygen. The f i n a l s i l i c i d e r e s i s t i v i t y i s increased by t h e consumption o f t i t a n i u m by t h i s c o m p e t i t i v e T i N r e a c t i o n .

2.3 RTA Time-Temperature Schedules

RTA time and temperature schedules over t h e range 600-1000°C, 10-60 seconds were evaluated f o r o p t i m i s a t i o n o f sheet r e s i s t i v i t y and l a t e r a l encroachment (see f i g u r e 1). The optimal process was found t o be two-stage 675'C 30 seconds, f o l l o w e d by an unreacted t i t a n i u m s t r i p and a second stage anneal 1000°C, 10 seconds. L a t e r a l encroachment o f the s i l ic i d e over surrounding oxide areas i s i n h i b i t e d by t h e use o f a two stage process, no d i f f u s i o n p a t h e x i s t s a t the h i g h temperature anneal stage due t o the unreacted t i t a n i u m s t r i p . An

i n i t i a l thickness o f 500A t i t a n i u m was used throughout.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1988440

C4-196 JOURNAL DE PHYSIQUE 3. ANALYSIS OF FILM PROPERTIES

Films were analysed f o r surface q u a l i t y , sheet r e s i s t i v i t y , t h i c k n e s s and stochiometry by SEM, 4-point probe, SIMS and AES. Surface q u a l i t y was found to be o f good, even t e x t u r e . The optimal process gave a s i l i c i d e w i t h a sheet r e s i s t i v i t y o f 4.55ohm/sq (k-0.5). Thick- ness, determined from the s i l i c o n l a t t i c e t r a n s i t i o n i n the SIMS p r o f i l e ( s i l ic i d e to b u l k ) , was found t o be 680A (see f i g u r e 2). The f i l m i s found t o be pure, s t o c h i o m e t r i c T i S i

,

^{(65% Si}

^,

35% T i from AES. Trace elements carbon, oxgen and n i t r o g e n were n o t detected a t t h e 0.1% d e t e c t i o n l i m i t .

4. FORMATION SENSITIVITY TO IMPLANTED DOPANT

The s i l i c i d e e x h i b i t e d a formation s e n s i t i v i t y t o implanted arsenic. Implant doses i n t h e range 5E13cn1-~ t o 1 E16cm-, were evaluated, (imp1 a n t energy 50KV). S i l i c i d e formation and sheet r e s i s t i v i t y were seen t o degrade w i t h i n c r e a s i n g a r s e n i c dose. Below dose 1El4cm-2 t h e r e s i s t i v i t y i s a c o n s t a n t 4.55ohm/sq; above t h i s dose the r e s i s t i v i t y increases t o 45ohm/sq. a t dose l E 1 6 ~ m - ~ (see f i g u r e 3). No s e n s i t i v i t y t o dopants boron, boron f l u o r i d e and phosphorus was i n d i c a t e d across the same dose range (see f i g u r e 4).

4.1 Model f o r S e n s i t i v i t y t o Implanted Arsenic

The s e n s i t i v i t y t o implanted arsenic, f o r the a c t i v a t i o n c o n d i t i o n s used, i s found t o be dependent upon excess dopant a t the s i l i c o n surface. The excess dopant e x i s t s as i n t e r - s t i t i a l o r c l u s t e r e d a r s e n i c and i n h i b i t s s i l i c o n d i f f u s i o n across the i n t e r f a c e . (The s i l i c i d a t i o n r e a c t i o n i s dominated by s i l i c o n d i f f u s i o n across t h e s i l i c o n / t i t a n i u m i n t e r - face.) Excess dopant concentrations can be c a l c u l a t e d from the SUMPREM3 model by s u b t r a c t - i n g a c t i v e from chemical c o n c e n t r a t i o n a t the surface. The thermal cycles assumed are two 1050°C 21 second dopant a c t i v a t i o n anneals i n n i t r o g e n p l u s t h e thermal c y c l e s associated w i t h the s i l i c i d a t i o n . A s t r o n g c o r r e l a t i o n i s found between excess arsenic c o n c e n t r a t i o n and sheet r e s i s t i v i t y (see f i g u r e 3). Excess dopant drops to zero a t implanted dose 1.3E14~m'~, below t h i s dose the sheet r e s i s t i v i t y i s a constant 4.55ohm/sq. Above t h i s c r i t i c a l dose t h e excess dopant concentration increases t o 3.3E20~m-~ a t dose 1E16cm-2, w i t h a consequent sheet r e s i s t i v i t y o f 45ohm/sq. S e n s i t i v i t y t o implanted a r s e n i c can, hence, be c o n t r o l l e d by adjustment o f e i t h e r t h e i m p l a n t c o n d i t i o n s o r the a c t i v a t i o n anneals t o assure zero excess dopant.

5. ELECTRICAL DATA

The o p t i m i sed s i 1 ic i d e process was f a b r i c a t e d on device s t r u c t u r e s on a one-micron trench- i s o l a t e d CMOS process / I / . P o l y s i l i c o n gates a r e f a b r i c a t e d w i t h oxide s i d e w a l l s t o a l l o w f a b r i c a t i o n o f s e l f-a1 igned s i l ic i d e d s t r u c t u r e s (see figure.5). A scanning e l e c t r o n micrograph o f a f u l l y s i l i c i d e d trench i s o l a t e d CMOS t r a n s i s t o r i s shown i n f i g u r e 7. The devices have good e l e c t r i c a l performance, e l e c t r i c a l parameters are shown i n t a b l e 1. This technique has been used t o f a b r i c a t e working c i r c u i t r y , i n p a r t i c u l a r unloaded i n v e r t e r r i n g o s c i l l a t o r s w i t h stage delays o f 120ps.

6. CONCLUSION

A process f o r s e l f a l i g n e d t i t a n i u m s i l i c i d e by RTA has been described. The s i l i c i d e has good surface q u a l i t y and i s o f low, u n i f o r m sheet r e s i s t i v i t y . S e n s i t i v i t y t o implanted arsenic has been discussed and i m p l a n t dose and a c t i v a t i o n c o n d i t i o n s found t o be c r i t i - c a l l y i m p o r t a n t by i t s i n c l u s i o n i n a one-micron trench-is01 ated CMOS process schedule which has f a b r i c a t e d working devices and c i r c u i t s .

7. ACKNOWLEDGEMENTS

-

This work has been c a r r i e d o u t w i t h the support o f t h e Alvey D i r e c t o r a t e and the I n t e g r a t e d C i r c u i t s D i v i s i o n , Plessey Research Caswell

.

8. REFERENCES

/1/ Roberts, M.C. Bolbot, P.H. Foster, D.J. Proceedings t h i s conf.

Sheet Resistivity Vs Temperature

t

= 309, N,

An

t

Sheet Resistivity Vs Time T = 675'C, N2

t.

First stage

I 5 f - \ - t

10

Second stage 5

Temperature ('C) Time (see)

Figure 1: Sheet resistivity vs. RTA Time and Temperature.

Silicon M 30.0

Titanium M 48.0

Figure 2: SlMS Profile showing Figure 3: Sheet resistivity sensitivity lattice transition. to arsenic dose.

-

Excess peak arsenic conc

-

-

Sheet resistivity -

Phosphorous Boron

1d3

Dose ( ~ r n ' ~ ) Dose (crn")

loz0

A

rn 0 E 1019

-

m P n 0

rn In 1 0 ' ~

g

L u

1017

Figure 4: Sheet resistivity sensitivity

to phosphorus or boron dose.

C4-198 JOURNAL

DE

PHYSIQUE

Sidewall oxide

F a oxide

Device structure

Junctions

Silicide on gate and junctions

Structure Following Silicidation

Figure 5: The Self-Aligned Silicide Process.

Figure 6: SEM micrograph of trench isolated CMOS transistor showing Self-Aligned Sllicide.

FllNG OSCILLATOR (49 STAGE) SPEED:I 20ps.

NMOS PMOS

Table 1: Electrical data for silicided transistors.

(W=20 um, L=lum) VT

0.7

- O a 7

VOLT

SUB- SLOPE

95 - 8 7 rnVIDEC

DRIVE 5.5 -2.7 rnA

GAIN

85 - 2 3

p A / V - 2