Ternary phases in the Pd-GaAs system: Implications for shallow contacts to GaAs

Volume

3, number

MATERIALS

9,lO

TERNARY PHASES IN THE Pd-GaAs

July 1985

LETTERS

SYSTEM :

IMPLICATIONS FOR SHALLOW CONTACTS TO GaAs * T. SANDS ** , V.G. KERAMIDAS Bell Communications

Research Inc., Murray Hill, NJ 07974,

USA

R. GRONSKY and J. WASHBURN Materials and Molecular Research Division, Lawrence Berkeley Loboratory, Berkeley, CA 94720, Received

Ternary

USA

9 May 19 85

phases of the type MXAmBV prepared

useful materials

for forming

tron microscopy

study of the Pd-GaAs

type MXAmBV (Pd,(GaAs),

reaction

and Pd,GaAs).

stalline films of Pd,(GaAs),, films are analogous

by solid-phase

shallow and adherent

reaction

between a metal, M, and a substrate,

to III-V semiconductors.

appropriate

accumulations

AmBv, are potentially

In this letter, the results of a transmission

It is shown that the first two reaction

are presented.

By choosing

free of interfacial

to silicide contacts

contacts

metal thicknesses

products

are ternary

and annealing temperatures, uniform monocryAs contacts to GaAs, these PdxGaAs

of As and Ga, can be obtained.

to silicon

1. Introduction

completely

satisfy in practice,

there is recent evidence

phases of the form MxGaAs do exist, specifically Integration iconductor laterally

and miniaturization

devices necessitate uniform

cal perspective,

potentially

of III-V compound

the development

and adherent

contacts.

III-V substrate

to promote

adhesion

is the first phase to form during

annealing

However,

materials

tures above 400°C results in the decomposition

must meet

and this reaction

must

morphologies

(b) The deposited

metal so

interface.

in a thin film

end phase (rich in the group Bland

ments) with a composition tage of such contacts properties

of MXA’nBV. The principle

is that their electrical

would not be dominated

(c)

Pd,Ga

and PdAs, after annealing

Because of the potential

order to identify the compounds

described.

to

system in

formed during low tempera-

(TEM) study of the Pd-GaAs

development

given in reference

2. Experimental Gallium

reaction

It is shown that the first two reaction

phases of the type PdXGaAs. morphological

*This work was supported by the Director, Office of Energy Research, Office of Basic Energy Sciences, Materials Science Division of the US. Department of Energy under Contract No. DE-AC03-76SF00098. “Work performed as a visiting Industrial Fellow at the Center for Advanced Materials, Lawrence Berkeley Laboratory. Berkeley, CA 94720

phases as

the Pd-GaAs

In this letter, the results of a transmission

near the interface. or impossible

of ternary

and to resolve some of the discrepancies

ated nonstoichiometry

may be difficult

we have investigated

vious studies. tron microscope

of the semiconductor

PdGa after of PdGa,

ture annealing

or by the associ-

these criteria

at 250°C.

at 350°C.

importance

advan-

tions of either group III or group V elements Although

is a metastable

and a combination

contact

accumula-

of Ni,GaAs

that Ni,GaAs

phases after annealing

at this temperature

materials,

at tempera-

[5,6] claimed to have observed

V ele-

and mechanical

by interfacial

annealing

annealing

et al. ]3] and Kuan [4] have reported

of PdzGaAs

Earlier investigators

The reaction

of a stable ternary

into NiGa and NiAs, suggesting the formation

that voids are not formed at the contact/A’nB” resulting

of Ni on GaAs.

phase 111. Both Oelhafen

on

species during the reaction

should go to completion,

[1,2]and Pd [3,4]. Ogawa [I] and Lahav and Eizenberg ]2]

From the metallurgi-

of contact

the 10 nm scale is to be achieved. moving

Ni

metal should react with the

occur in the solid state if control

should be the dominant

sem-

of shallow,

that

for the metals

have shown that Ni,GaAs

useful contact

several criteria: (a) The deposited

elec-

phases of the

elecare

products

A detailed description of the Pd-Ga-As

in pre-

are

of the

reacted layer is

7.

Methods

arsenide

substrates

with (100) orientation

were

409

MATERIALS LETTERS

Volume 3, number 9,lO

prepared for metal deposition by immersion into a 9: 1 DI H,O:HCI

solution

Palladium

by electron beam evaporation

50 nm at a rate of 0.6 rim/s in a vacuum Annealing

view and XTEM specimens were observed in a Siemens 102 TEM operated at 100 keV and JEOL JEM 200 CX with an

for 10 sec. followed by a DI H,O rinse.

The GaAs surface was blown dry with N,. then deposited

treatments

were performed

of l-2

ultra-high

was

to a thickness

of

X low6 torr.

in flowing forming gas

(95% Ar and 5% Hz) for 10 min. at temperatures

between 220

Cross-sectional

tively.

TEM (XTEM) specimens

were prepared

cooled stage.

Plan-

by

resolution

pole piece operated

Energy dispersive

performed

spectrometry

CX TEM/STEM.

A GaAs standard

of the EDS spectra.

was not available, considered

at 200 keV, respec(EDS) of x-rays was

with a Kevex model 3400 ultra-thin-window

tor and System 8000 spectrometer tiftcation

and 480°C. argon ion milling with a liquid nitrogen

Juty 1985

mounted

was used for partial quan-

Since a reliable Pd-Ga standard

the [Pd]:]Ga] ratios reported

below must be

tentative.

TEM images and co~s~nd~~ difhaction patterns from plan-view specimens of samples annealed I Low marination for 10 min. at (a,b) 22o’C and (c,d) 315’C. The diffraction pattern in (b) is the superposition of the polycrystalhne Pd ring pattern and the monocrystalline phase I spot pattern in <211b> zone-axis orientation. Diffraction spots from phases I and II are visible in (d). Fig.

410

detec-

on a JEOL 200

Fig. 2.

Cross sectional

TEM images

275 and 350°C respectively. ships described tation.

in the text.

of (a) the phase i/GaAs

The images Gallium

and (b) the phase II/GaAs

and their corresponding

arsenide

is in
electron

I 1> zone-axis

diffraction

orientation.

interfaces.

patterns

Samples

illustrate

were annealed

the orientation

Phase I and 11 are in ~000

at

relation-

I > zone-axis

orien-

Volume

3, number

9,lO

MATERIALS

July 1985

LETTERS

in Fig. l(c). At higher temperatures

3. Results and Discussion

II is the dominant The plan-view

micrograph

and diffraction

pattern

in Fig. 1

2(b) is a cross-sectional

image of the phase II/GaAs

(a,b) reveal that the first phase formed during low temperature

after annealing

at 35o’C.

annealing

with diffraction

patterns

orientation sectional

is nearly monocrystalline relationship

and has a well-defined

with the GaAs substrate.

Cross-

The inset diffraction from plan-view

phase II is also hexagonal

images from these samples (e.g. Fig. 2(a)) show that

phase I is hexagonal

(eg. 350 and 410°C) phase

phase in direct contact with GaAs.

Figure

interface

pattern

along

samples confirm

that

with

a0 = 0.92 ? 0.01 nm

with

a, = 0.673 * 0.002 nm CO = 0.370

In samples annealed

c, = 0.338 * 0.001 nm. The orientation

rel&ionship

+ 0.005 nm.

ing orientation

below 4Oo”C, phase II exhibits the follow-

relationship

with (100) GaAs:

with (100) GaAs is [OOOl]n // 101l]ciaAr and (213Oh1//

UWGaAs

This orientation

relationship

is evident in Fig. 2(b). Adjacent

Analysis of EDS data suggests a nominal composition of Pd,(GaAs), for phase I. These results are in close agreement

grains of phase II are often observed

with the findings

EDS spectra from grains of phase II yields a nominal

of Kuan [4].

Phase I is the dominant deposited

reaction

state and after annealing

3 15°C [7]. During annealing 4WC,

product

in the as-

at temperatures

at temperatures

at fast diffision

nm.

paths such as grain boundaries,

cracks in the phase I film.

The resulting

In addition

between 250 and

This second phase appears

is

to phases I and II, Pd,Ga

XTEM for some annealing ously reported

to nucleate

of our samples.

pores or

conditions

is shown

of diffraction

peak positions

(26’) measured of

Furthermore,

a major phase in previous

412

for PdAs, and phase II’

indexing

calculated

possible

calculated

based on

28 for

indexing

20 for

PdAs,[ 5)

PdAs,

as phase II

phase II

26.6 + 0.2

111

25.8

Oil1

26.6

30.8 + 0.2

200

29.9

2111

31.0

33.5 f 0.2 ‘36.5 & 0.2

212 211

45.5 36.8

072 1 __

33.0

50.7 f 0.2

311

50.6

0112

50.7

70.0 + 0.2 $72.3 + 0.2

420 421

70.4 72.4

0242 __

69.4 __

73.9 * 0.2

332

74.4

2750

74.5

(h - 0.1542nm)

+peak overlaps

with 200 PdGa

*peak overlaps

with 321 PdGa

a previin any

conditions

studies [5,6], our samples contained

from Fig. 1

PI

was detected by

[7]. However,

under annealing

peak position

*assuming CUKCI radiation

of

composi-

(25WC < T < SOOYZ)similar to those which yielded PdAs, as

morphology

Approximate

Analysis

phase, PdAs, [5,6], has not been detected

Table 1. Comparison

to be in twin orientation

[100]oti5 parallel to either [x3O]n or [z3Oin.

tion of Pd,GaAs.

up to

a second phase is formed if the initial Pd thickness

greater than -20

with

and aOIPdAs,] - 0.5982nm

Volume

3, number

MATERIALS

9.10

hexagonal

Pd,GaAs

tifications

of PdAs, were based on x-ray diffraction

as the major phase.

we have compared

the published

experimental

spectra from samples said to contain culated peak positions to the ternary

iden-

data only,

diffraction

July 1985

tory and Ariel Dori of Bell Laboratories, tance.

One of the authors

Table 1

Many valuable

Nicolet of the California

phase, Pd,GaAs.

assis-

discussions

Institute

Dr.

with the EDS ana-

lyses, and Ms. G. King for aiding in the preparation specimens.

solely to PdAs, can also be

for technical

(T.S.) wishes to acknowledge

T.R. Dinger and C. Ether for assistance

PdAs, [5,6] with the cal-

for phase II (-Pd,GaAs).

shows that the peaks attributed attributed

Since previous

LETTERS

of TEM

with Professor

of Technology

M-A.

are also grate-

fully acknowledged.

4. Conclusion 6. References It is clear from these results that the Pd-GaAs low temperatures ternary

phases.

(< 500°C) is dominated

these ternary materials

of silicides as shallow contacts

to silicon.

phases do not involve the inter-

facial accumulation

of arsenic,

ties of MIGaAs/GaAs

interfaces

into the factors which determine

In addition,

studies of the electrical should provide

M. Ogawa, Thin Solid Films, 70, (1980) 181.

123

A. Lahav and M. Eizenberg,

[3j

151

J.O. Olowolafe,

143.

the barrier heights of metallic

Woodall, [6]

[7] Microscopy,

P.S. Ho, M.J. Hovel, J.E. Lewis and J.M.

J. Appl. Phys., 50 (1979) 955.

X-F. Zeng and D.D.L. Chung. J. Vat. Sci. Technol.,

21

(1982) 611.

would like to thank the staff of the National

Center for Electron

and

T.S. Kuan, Mat. Res. Sac. Symp. Proc. Vol. -31 (1984)

5. Acknowledgements The authors

J.L. Freeouf, T.S. Kuan, T.N. Jackson

[4]

proper-

new insight

P. Oelhafen,

P.E. Batson, J. Vat. Sci. Techol., Bl (1983) 588.

since

phases on n and p type GaAs.

Appl. Phys. Len., 45 (1984)

256.

as

to the application

the reactions

to form MIGaAs

[l]

and the reac-

phases may find application

in direct analogy

of

can be limited

by proper choices of the initial Pd layer thickness shallow contact

at

by the formation

If the lateral inhomogeneities

tion temperature,

reaction

Lawrence

T. Sands, V.G. Keramidas,

R. Gronsky

and J. Wash-

bum, Thin Solid Films (1985) in press.

Berkeley Labora-

413