RD-A152 378 THIN FILMS PROPERTIES OF SPUTTERED NIOBIUM SILICIDE ON i/ .S102 S13N4 AND ON..(U) RENSSELAER POLYTECHNIC INST TROYNY CENTER FOR INTEGRATED ELE.. T P CHOW ET AL. MAR 85

UNCLASSIFIED TR-ti N888i4-Oi-K-8685 F/G 9/1 NL

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MICROCOPY RE SOLUTION T[S1 CHARTNAP, N-I -P ' 4 411

OFFICE OF NAVAL RESEARCH1

Contract NOOO14-81-K-0605

Task No. NR 056-768

00 TECHNICAL REPORT No. 11.

THIN FILMS PROPERTIES OF SPUTTERED NIOBIUM SILICIDE

ON SiO 2, Si3N4 and on N+ Poly-Si

Ln byT. P. Chow , W.-J. Lu, A. J. Steckl, B. J. Baliga

Prepared for Publication

in the

Journal of the Electrochemical Society

Rensselaer Polytechnic InstituteCenter for Integrated Electronics

Troy, NY 12181 DTICMarch 1985 E LECTE

. SiAPR 15 1985 UD

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Report No. 11 0 fj.ff5L f4. TITLE (and Subtitle) S. TYPE OF REPORT & PERIOD COVERED

Thin Films Properties of Sputtered NiobiuR Interim Technical ReportSilicide on Si0 2 , Si 3 N4 and on N+ Poly-Si -6. PERFORMING ORG. REPORT NUMBER

7. AUTHOR(a) 8. CONTRACT OR GRANT NUMBER(@)

T. P. Chow, W.-J. Lu, A. J. Steckl andB. J. Baliga

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19. KEY WORDS (Continue on ae.erse aide If nlecssary and Identify by block number)

niobium silicide, structural properties, compositional properties.

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-The thin film properties of sputtered niobium silicide on Si0 2 ,Si3 N4 and n-), doped poly-Si have been investigated. The structuraland compositional properties were studied with X-ray diffraction,Rutherford backscattering spectrometry and secondary ion massspectrometry.

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" "' ": -"" " "-' "",':,',4

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THIN FILM PROPERTIES OF SPUTTERED

NIOBIUM SILICIDE

ON SiO2 9 SiN AND ON N POLY-SI

""Co+ • * +T.P. Chow .J. Lu, A.J. Steckl , and B.3'. Baliga

+General Electric Corporate Research and Development,

Schenectady, NY 12345

* *Rensselaer Polytechnic Institute,

Center for Integrated Electronics,

Troy, NY 12181

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ABSTRACT

The thin film properties of sputtered niobium sulicide on SiO2 , Si3 N and2 34

n+ doped poly-Si have been investigated. The structural and compositional

properties were studied with X-ray diffraction, Rutherford backscattering

spectrometry and secondary ion mass spectrometry.

1*

4

I0

-3-

I. INTRODUCTION

Refractory metal silicides have become a key part of VLSI silicon device

technology as MOS gates and interconnects due to their low resistivity, oxida-

tion resistance and compatibility with NOS processes [1,21. Among the sili-

cides, the most widely used ones are MoSi2 , TaSi2 , WSi2 and TiSi2 . Recently,

NbSi2 was also reported [3] to have similar properties as the other refractory

silicides. In that study, slightly metal-rich (Si/Nb -1.8) silicide films

obtained from a hot-pressed composite target in rf sputtering system were

investigated. Those films were shown to contain NbSi 2 as well as a signifi-

cant amount of hexagonal Nb Si Also, a resistivity of - 100 jLG-cm was meas-

ured after annealing at elevated temperatures.

In this paper, we report on improved thin film properties of niobium sil-+

icide on SiO 2 and on n poly-Si.

II. EXPERIMENTAL PROCEDURE

Silicon-rich (Si/Nb - 2.3) silicide films were deposited at room tempera-

ture from a cold-pressed composite target (99.6%) in a dc magnetron sputtering

system (Varian 3140). Rutherford Backscattering Spectrometry (RBS) was done

with a 2 MeV 4He+ beam from a linear accelerator, Secondary Ion Mass Spec-

trometry with a Cameca IMS 3-f ion microscope and X-ray diffraction with a

Siemens D-500 automated diffractometer.

III. RESULTS

(a) Structure and Composition-

S

4

The as-deposited films were essentially amorphous but after annealing at

elevated temperatures, they exhibited a predominantly NbSi2 structure. Fig.

la and b show X-ray diffraction patterns for an as-sputtered film and the same

film after annealing in hydrogen at 1000 C for 60 min. The major niobium

disilicide peaks are at 20 of 21.4, 25.4, 40.1, 41.2 and 47.00, corresponding

to the (100), (101), (111), (003) and (112) planes repectively. Trace amounts

of carbon-stabilized, hexagonal Nb 5Si3 components were also detected at 27.2,

29.2 and 36.40. Pure Nb5 Si3 is stable in two tetragonal structures (D81

(t132) and D8 (t132)) while impurities, such as carbon, tends to stabilize it

into the hexagonal structure (D8 ) [4]. In fact, many of the other metal sil-

icides (Mo5Si3, W5Si3, and others) have the same characteristic and the detec-

4 tion of such a hexagonal silicide phase is indicative of the presence of car-

bon or other impurities.

(b) Resistivity -

The thin film resistivity of these NbSi2 films after annealing was

observed to be consistently lower than the previously reported films. In Fig.

2, the sheet resistance of 56001 niobium silicide on oxidized silicon sub-

0strates is shown as a function of annealing time at 800, 900 and 1000 C in

hydrogen. As deposited, the films have a R of -11 0/square. The resistivity

decreases rapidly within the first 15 min and changes only slightly for longer

times. After annealing for 1 hr, the sheet resistance dropped to 2.8, 2.0 and

1.3 0/square for 800, 900 and 1000 C respectively. For the silicide film on

SiO 2 , the sheet resistance dropped from 10.5 0/square to 1.4 0/square (78 p0-

cm) after 15 min and to 1.3 0/square (72 p0-cm) after 60 min. The lowest

NbSi2 resistivity measured after annealing at 1000°C was - 70 pD-cm which

represents a 30% improvement over previous data on rf sputtered films and is

-5-

close to the value of - 50 p0l-cm reported for niobium on poly-Si films

annealed under vacuum [1]. The bulk values, for comparison, range from 6.3 to

50 p0-cm, with the lower values probably erroneous [4]. Similar dependence on

annealing time has been observed for niobium silicide on silicon nitride and+

on n poly-Si (polycide) and is shown in Fig. 3 and 4. For the polycide

stack, the sheet resistance was decreased from 13.7 to 2.8 0/square after 30

min but increased to 3.0 fl/square after 60 min. The rapid decrease in resis-

tivity followed by a saturation-like characteristic when annealed at high tem-

peratures (7000 has also been observed for other silicides, such as TiSi2

[5,6], MoSi2 [7,8] and WSi2 [8,9,10]. Also, when these niobium silicide films

were annealed at different temperatures, similar dependence of sheet resistace

on time was observed but higher saturation values were obtained for lower tem-

peratures.

IV. SUAXY i

Niobium silicide thin films deposited on SiO , Si3N and nhpoly-Siave

been characterized. Similar to the other refractory silicides, annealing at

high temperatures resulted in structural recrystallization and a sharp

decrease in resistivity. After annealing at 1000eC, a resistivity o" '70p0-cm

was obtained. For a 2500rNbSi12/25001 N+: poly-Si stack, a sheet resistance of

2.5D/square after annealing at the same temperature,/

AKNOWLEDGMENT

One of us (AJS) would like to acknowledge the Office of Naval Research

for Its partial support of this work.

-~- - - -~ - - .

-6

REFERENCES

[1] S.P. Murarka, Silicides for VLSI Applications, Academic Press (1983).

[2] T.P. Chow and A.S. Steckl, IEEE Trans. Electron Devices, ED-30, 1480

(1983).

[3] C.D. Rude, T.P. Chow, and A.J. Steckl, J. Appl. Phys., 53, 5703 (1982).

[41 W.B. Pearson, A Handbook of Lattice Spacings and Structures of Metals

and Alloys, Pergamon Press (1958); W.B. Pearson, A Handbook of Lattice

Spacings and Structures of Metals and Alloys, Vol. 2, Pergamon Press

(1967).

[5] S.P. Murarka, M.H. Read, C.J. Doherty, and D.B. Fraser, J. Electrochem.

Soc., 129, 293 (1982).

[6] S.P. Murarka and D.B. Fraser, J. Appl. Phys., 51, 350 (1980).

[7] K.L. Wang, T.C. Holloway, R.F. Pinizzotto, Z.P. Sobczak, W.R. Hunter,

and A.F. Tasch, Jr., IEEE Trans. Electron Devices, ED-29, 547 (1982).

[8] T. Mochizuki, K. Shibata, T. Inoue, and K. Ohuchi, Jpn. J. Appl. Phys.,

17, Supp. 17-1, 37 (1978).

[9] T.P. Chow, "The Development of Refractory Gate Metallization for VLSI,"

Ph.D. Thesis, (Rensselear Polytechnic Institute), 43 (1983).

[10] B.L. Crowder and S. Zirinsky, IEEE Trans. Electron Devices, ED-26, 369

(1979).

[11] H.J. Geipel, Jr., N. Hsieh, M. H. Ishaq, C.W. Koburger, and F.R. White,

v'-A. t\jI(~OD .t S L*, '-

.. r',' . -V -. ,LI

/2:'7~ ~ ~ ~~- A"7- p " -

IEEE Trans. Electron Devices, ED-27, 1417 (1980).

[12] N.Y. Tsai, F.M. d'Heurle, C.S. Petersson, and R.W. Johnson, J. Appl.

Phys., 52, 5350 (1981).

.- ... : . , .- .,. . . . . . . .

LIST OF FIGURES AND TABLES

Fig. 1 X-ray diffraction patterns of niobium silicide film on SiO 2 /Si sub-

strate: (a) as-sputtered and (b) after annealing at 10008C for 30 min in H2.

Fig. 2 Sheet resistance of 56001-thick NbSi2 on oxidized silicon substrate as

a function of annealing time at various annealing temperatures (800-10000C) in

hydrogen.

Fig. 3 Sheet resistance of 56001 -thick NbSi2 on Si3N4 /Si0 2 /Si substrate as a

function of annealing time at various annealing temperatures (700-10000 C) in

hydrogen.

Fig. 4 Sheet resistance of 2500 1-thick NbSi2 and 2500X-thick n+ doped poly-Si

on SiO 2/Si substrate as a function of annealing time at various annealing tem-

peratures (700-100000 in hydrogen.

Fig. 5 Sheet resistance of 25001- and 3500 1 -thick NbSi 2 on 2500 1 -thick n+

doped poly-Si on SiO 2/Si substrate as a function of annealing time at 900°C in

hydrogen.

Fig. 6 Resistivity of various refractory metal silicides (TiSi2, TaSi2 P MoSi2

and NbSi 2) as a function of annealing temperatures.

Table I Various silicide phases that are formed for Group IV, V and VIA

metals.

Table II Impurity contents of NbSi2 films sputtered from hot-pressed and cold-

pressed targets as determined from RBS and SIMS.

co- ~ffY)

-1

0

14N w

in-0WA' --

LL N

('to

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t~a)

04 N

(14 IN w

-4

cl v ri

CWU,

IDd

0 --ONN

Im

U, -_T~ N(7-

**~ "-~ ~.r-~ -SNow-

* 12 -

56004 NbSi 2/SiO 2 /Si

1 2 AMBIENT

I0

50

d4'C'

800 ° C

*I--8j000C

uJ-C-

:-- 9000 C

2

• I1000 ° C

10 15 30 45 60

ANNEALING TIME (min)

S

P1

p. 125600K4 NbSi2/Si3N4/SiO2/Si

H2 AMBIENT

* 10

o5

C->

I-

tLii

U)p

10000 C

015. 30 45 60

ANNEALING TIME (min)

- -4 * q -. w , . . ... • • , - r -;". °. .". . , . .. r

14 -Si

2500 NbSi 2/2500 N+ POLY-SiON SiO2 /Si

H2 AMBIENT12

65,-6

- -4-

• U'

L- 9000 C

Li

u

w 1 -" uov0C

m 4

3• I0000 C

2* 0 15 30 45 60

ANNEALING TIME (min)

1- .4 4

I.I

14 0 2500 I NbSi 2/2500 N + POLY-Si0 35004 ON Si0 2/S'

H2 AMBIENT

9000 C12

U

i-€10

15,

0 15 30 45 60ANNEALING TIME (min)

,--

-" " . -.: .- ,. , -. ". ' - ' ' - . - -i ' , -- " ' "L i-" ' -i. " "

• (I- ,i. ,. i .~ ,- - -~ ' ' i

Table I

Various sulicide phases that are formed forGroup IV, V and VIA metals

.IVA. V A~ N _1 A

Ti 3Si V3 Si Cr 3SiCr2 Si

V Si3 Cr5 SitTiSi (C) V5Si 3 (C) r5Si3 (C

TiS i Cr Si (CCr 3V

5 i2Ti Si 6 Sir~

Ti~i6 5Cr Sifco-TiSi2 VSi2 2rbco-TiSj 2 22

Zr4Si Nb 4Si*Zr 4 Si Nb Si No Si

Zr 2 Si33a-Nb 5Si 3 D8 1) Mo 5Si3

Zr DSi (C) Nb 5Si (6) Mo 5 Si 3 (C)Zr 5Si 3 oS

3rS2 M 3Si2Zr Si3

Zr5 Si4Zr Si5

ZrSi2 NSi2 h-Mosi22 2 t- MoSi

Ta 4 1 SiTa 4SiTa 3Si W3S

Hf2 iTa 2SifSiTa Si W5 Si3 (08m)

a-~a h(D8)

H f 5 S 1 3 ( C ) -T a S i D 8 5S 3CPfSi 3 28

R f Si () T i31wS CHf SiHf 3 i 2

Hf 4-Wii3

HfSi2 TaSi2 t-WSi22

0-s

7.- 1.-A

S-10-

Table II

Impurity contents of NbSi films sputtered fromhot-pressed and cold-pressed targets as determined from

RBS and SIMS.

Hot-Pres@d.4 _Col dPr ss4_Hot-Pre c~dCold-Pro soed

C 1.8 1.0 1.80 8 10 0.8Ax 20 8 2.5SiN 25 5.5 4.5

(From SIMS)

Si/Nb 1.7-1.8 2.12.0(Target) 2.3(Target)

Ar 3% 3%Ts, 0.2% 0.2%

(From RES)*Target 99.6% 99.6%

Purity

*FILMED

-. 5-85

0

*DTlC

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