METAL-SEMICONDUCTOR INTERFACE (Al-Si)

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METAL-SEMICONDUCTOR INTERFACE (Al-Si)

H. Kim, K. Okuno, T. Sakurai

To cite this version:

H. Kim, K. Okuno, T. Sakurai. METAL-SEMICONDUCTOR INTERFACE (Al-Si). Journal de

Physique Colloques, 1987, 48 (C6), pp.C6-469-C6-472. �10.1051/jphyscol:1987677�. �jpa-00226885�

METAL-SEMICONDUCTOR INTERFACE (AI-Si)

H. Kim, K. Okuno and T. ~ a k u r a i *

Department of Electrical Engineering, Nagasaki Institute of Applied Science, Abamachi, Nagasaki, Japan

*The Institute for Solid S t a t e Physics, The University of Tokyo, Minato-ku, Tokyo, Japan

Abstract- The microscopic structure of metal-semiconductore interface and the beh- avior of A l on a p S i ( l l 0 ) surface have been investigated using the probe-hole f i e l d emission microscope (FEM)

,

the f i e l d desorption (FD) and the f i e l d emission retarding potential analyser (FPA)

.

The Fowler-Nordheim(FN) plots for the S i t i p prepared by electrolytic etching a r e classified i n t o two groups, the m e and the line. The work function of S i surface by an adsorption of Al decrease with the 8 (Al) and the value reaches 3.2 f0.2 eV a t 8 ( A l )

k1.

A surface resistance of giga ohms which i s d i f f i c u l t t o remove a t usual FD f i e l d have been observed for the S i t i p having the curved FN plot. This layer can easily be m t a l l i z e d by the interdiffusion of Al a t rocan tmperaixre.

1. Introduction

The microscopic structure of metal-semiconductor and semiconductor-semiconductor interface and the characteristics of low m a t u r e process of semiconductor dev- ices are b e c d n g important a s an increase i n the integration of a recent large scale integrated c i r c u i t . A numkr of ultrahigh v a m surface analyser have been used for the purpose of surface analysis/l/. FEM/2/ i s the most sensitive tool for the det- ection of very s d l m u n t of the surface contarnination and m/3/ is an id&

mthod of cleaning the semiconductor surface without the damage of the outer-most surface layer by an ion b a n b a r h t o r the high temperature heating for the cleaning.

In this paper, FEM and FD cleaning method are combined t o get an ideal clean semic- onductor surface and t o investigatg the metal-saniconductor interface. Al can be dep- osited on the S i surface i n an atmosphere almost canpletely f r e e from any contami- nation for the period of time while the experiments are p e r f o m d .

2. Ewrirnental procedure and results

A thin S i (110) bar ( 0 . 5 ~ 0 . 5 ~ 1 0 mn) c u t f m p20f2-an wafer was fixed i n the hollau N i tube spotwellded on a Mo loop. A f i n e S i tip(500-1000A) can be made by electro-

l y t i c etching applied ac 60 V i n a mixed solution of one p a r t of HF(50%) and three parts of HIW3(68%). After the dregs of etching solution on the etched S i t i p had removed by rlnsing the etched t i p i n a deionized water b d i a t e l y a f t e r etching, then the FEM tube mounted wij.h the t i p was baked a t 150 OC during the evacuation.

An ultimate pressure of 10 Pa reached a f t e r the evacuation f o r 5hr.. A clean S i t i p with a curv_af"e of l e s s than lOOOA was obtained easily by FD a t 10 KV i n UHV and 4 .- 5 KV i n 10 Pa H gas. The FN p l o t s a t each FD cleaning process fran

h n -

ediately a f t e r the evacuaihon a r e classified as follaus (Fig. 1) : (1) l i n e (2) m e . The characteristics of FN plots are believed a s the electrolytic etched S i surface is covered with a foreign material such as Si02, especially on the surface of the curved E'N plot. The shape FN plot changed from the curve into the l i n e with relat- ively lcw o r high f i e l d desorption according t o its curvature, but it was s a m e h s d i f f i c u l t t o change the shape of curved E'N p l o t a t usual ED field.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987677

JOURNAL DE PHYSIQUE

When Al was deposited with varying coverage on the Si surface a t roan tenperatwe, the slope of largely curved FN plot decreased with cover- age of A l , 0 ( A l )

,

and finally changed to

t k

line a t 8 (A1)

i

1.

The

irradiation of f o e ussed laser beam on the S i also varied

the

shape of EN plot f m the curved one &

the line. Thoqh the slope of curved FN plots were r e covered partially by FD a t -11 0 (Al)

,

it was never back to the initial one once

the

curve had changed to the l i n e a t 0 (Al)+ 1 as shown i n Fig.2.

When Al was deposited on a Si surface cleaned by FD, the work function of surface de-

creased with the 0 (Al) and

Fig.1 Field emission current £ran a psemiwnductor plotted as £unctions of

1/V,

for

the

ETJ plots.

(a) The bended

FN

plot. (b) he l i n e

FN

plot.

Fig.2 Field enission cut-rent f m a p-semiconductor for the surface covered with the high resitive layer, Al and field desorbed sur- face.

the value reached 3.2 f 0.2 eV a t ⁰ (Al) $1 as shown in Fig. 3. ^As the field increased, deposited A l w a s desorbed gradually up to clean surface.

In order to investigate tlE origin of the curved FN plot and the mtallization of the surface layer of S i by the adsorption of Al a t r m m a t u r e , the variation of the threshold values of collector voltage during the FD cleaning p r e s s for both

the

etched and Al deposited S i surfacewere masured a t each field enission current.

I n the case of the curved EN plots, the threshold collector voltage(Vcl) i n the beginning of cleaning was larger

than

that of the collector work £unction(Vc) i t s e l f and

then

decreased as the cleaning proceeded, but it is never equal to (Vc) a s sham i n Fig.4.

The

value of (Vc' ) as a function of field emission current increases qua- dratically i n the case of largely bended FN plot as shown in Fig.5. I f the curvature of

FN

plot was d l ampared with

the

FN plot of Fig. 5 (a)

,

^the value of (Vc') was sndller than that of (a) a t high current(correspmd to higher field) as sham in Fig. 5 (a)

,

(b)

.

became

tianinant a t

6

a certain Fig.4 _curves condudor a t each field An for (a) metal example of (Cu)

the

emitter

,

r e w d i n g potential ^{(b) and} current. ^(c) semi- _{appear field.}

*

_The scattering effect

*

^{high resistive}

as-

Vc; work function of metal (Cu)

,

Vc' ; the threshold collector voltage a t sane field d t t e r current.

increases lineary with f i e l d emis-

sion current as sham i n Fig. 5 (c)

.

⁵

The value (Vc' )

-

^{(Vc) = (Vi)} which i s related to the potential drop a t the S i surface, as sham i n Fig.6, d e w on the cleanliness of the surface. On the bases of this results, it can be concluded that there exists ⁴ a high resistive layer on the Si sur- face etched ele@rolytically.

Sinoe the value of (Vc')

becanes

larger w i t h the increase of the bend i n FN plot,

the

resistance

(R) can therefore be evaluated by 3 dividing (Vi) with (I) a t each th- reshold. The characteristic mrve

layer are m e d i n the etching process or by

FD,

but there always exist the nega- tive characteristics even i n the d a c e of stright l i n e FN plot a s shown i n Fog.7.

A nother important fact is that (Vi)

and

(R)

beccme

nearly equal to zero with the decrease in the work function due t o the deposition of Al on the high resistive sur- face a t roan teqerature. This metallization is caused by the interdiffusion of Al into

the

high resistive layer or senicOnductor even a t roan terpzature/4/.

-

-

;""

-

A c k n o w l e d ~ t s

This work was swrted in part by the Research Fund of Nagasaki Super Technology DevelrJnent Association.

of (I) vs (R) is a parabola type 0

\

10 20 ¹

^Yrf

^{2 3 4}

with rrdnimum a t about 5 nA when the ^{t (min)} V(W1

bend in FN plot is larger.

Fiq.3 The variation of the work function vs e (Al) (a) and the desorption field(b)

.

The higher currenk side of the pa-

rabla

decrease as

the bend

was small and finally

becane

a line. men the W plot is linear £ran the i n i t i a l state,

W i )

vs (I) curve is L type having nearly f l a t beyond 5

na.

It

becane

evident that the value of (R) a t the surface differs from

the

degree of electrolytic etching. It should be noted that the surface resis- tance has a negative characteristic a t the l e f t side of the prabola.

The negative characteristc is ex- plained as the reduction of (R) occurs

due

to the generation of conduction electrons by the el- ectron impact ionization as the field increase and then the resi- stance (R) increases due to the decrease in m b i l i t y of the ele-

vc ctrons as the scatterina effects

JOURNAL DE PHYSIQUE

Fig. 7 Resistance ( a t r m

temp.

) as functions of field emission current, w i t h the bend of FN plot as a parameter.

I ^L

0 5 1 0 1 5 ^t xl0-8

s

0

A

C

-

1 (A)

Fig.5 Voltage drops a t the S i Fig.6 Electron energy band dia- surface as a function of f i e l d gram of the oxide covered p-Si esnitter current, w i t h the h d for the retarding potential ana-

of F N plots as parameter. (a)The lyser

.

b d of

FN

plot is larger. (b) The (S) ; psemiconductor

,

(0) ; oxide bend of M plot is large. (c) The layer, (A) ;ancde, (C) ; collector.

bena

of FN plot is linear. (d) The _x10' EN plot £ram the Al covered Si

surface, 2 0

References

R(r

(1) Robert L,Park and M.G.Lagally,Solid State Physics: Surface. Academic Press

Inc. 1985. ₁₅

(2) R.Ganer, Field emission and Field Ionization, Hiu-vard Univ. Press.

Cmnbridge,Massachusetts 1961.

(3) E.W.Mller, Adv. i n Electron Physics and Electronics X I I I . Academic Press 1960.

(4) J.M.Poate, K.N.Tu and J.M.llayer,

Thin

Filminterdiffusion and Reaction.

The Electrochemical Society, Inc.

1978. l o * 5

0

-

^{(b) f}

I

I

I I

-

_I ¹ I

(a)

/

- '4 \.. d/

,/'/ ^I

. . ,

^{c xlo-s}

0 5 70 15

-

^{I (A)}