Characterization of annealed oxides on n-type 6HSiC by high- and low-frequency CV-measurements

MICROELECTRONIC ENGINEERING

ELSEVIER

Microelectronic

Characterization

of Annealed

Low-Frequency E. Stein

A. G&z,

Institut

fiir Halhleitertechnik,

RWTH

Aachen,

rements differ

on Wtype

and

in the

same

relations

stat,es

and

oxide

of Oxides

GH-SIC

by High-

and

and

and QSCV

measu-

Aachen,

on 6HSiC

with

to the

samples.

is observed

from HFCV

by the Terman bandgap.

positive fixed

charge

bias stress.

oxide

and the HF-LF

However,

Negative

during

to the initial

Germany

are extracted

calculated

respect

for different

correlate

H. Kurz

II,

Di, values

position

traps

devices

J. Stein

23, D-520i’4

24°C to 300°C.

in hight

different

Oxides

Lehrstuhl

Sommerfeldstr.

properties

from

28 (1995) 201-204

CV--Measurements

von Kamienski,

Electrical

Engineering

charge

both

trapping The

method

methods in slow

trapping

result, interface

properties

of

densities.

1. INTRODUCTION Among terial

the wide

band

gap

(2.9 eV for 6HSiC)

cations.

Currently

is under

investigation

properties

SiOz

interpretations

[4]. In this first

The

standard

for the

interface

contribution

we compare method

time,

trapping

properties

transferable state

the

density

(Di,)

high field stress

on this for the

between

material electrical

Capacitance

be found states

appli-

[3]. Con-

Stat,ic

can

of interface

[3] at temperatures

during

based

methods

QSCV(Quasi

ma-

high-power

to the MOSXiCsystem

and

calculation

as an attractive and

in MOSFET’s

Frequency)-

and by the Terman

SIC appears

high-frequency characterization

are not easily of HF-(High

Voltage)-measurements HF-LF

materials

for use as gate-insulator [1,2].

of MOSsystems

traverse

semiconduct,or

for high--temperature,

in literature

obtained

by the

20°C and 300°C.

For the

of differentely

annealed

samples

are

invest,igated.

SAMPLE

2.

PREPARATION

Commercially 2 x 1Ol6

cme3)

a standard oxide

RCA-clean.

thickness

Nz immediately The

samples

MOS 3.

available

capacitors

(CREE

on GH-SIC

Oxidation

of 30nm. after were

At the

oxidation

metallized

with

Fig.

1 and

Fig.

Static

Capa.citance

2 show

same

temperat)ure The

at 1150°C the

paramet,ers

evapora.tion

n-type

6H-SIC

were cleaned

epilayers

in wet or dry

samples

were

are specified of Al or Cr/Ni

(ND:

in acetone O2

annealed at the and

and up

by

to an

in Ar or data

patterned

plots. into

of 0.4 mm.

AND HFCV

Siifaced

1 x 10” cmp3)

was performed

by e-beam

CHARACTERIZATION

Inc.)

(No:

(POA).

a diameter

(Quasi

R esearch,

subst.rates

(IIigh

Voltage)-data

RESULTS Frequency

Capactance

performed

at tempera,tures

0167.9317/95/$09.50 o 1995 - Elsevier Science B.V. All rights reserved. SSDI 0167-93 17(95)00043-7

Voltage)) between

and

QSCV-

24°C and

E. Stein von Kamienski

202

et al. / Microelectronic

Engineering

28 (1995) 201-204

o,oLi, n -8 -6 1. Normalized

CV-data

measured

Figure

at 100 kHz, 0.1 V/ set and 24, 100, 200 and 300°C;

sample:

POA:

wet oxidation,

300°C

on the same depletion

For the voltage curve

At room

caused

sweep

cy in the is not with

this hump sweep

towards

The

elevated

at room

temperature It is remarkable

MIS-( Metal directions.

This

and in the reverse densities

rise. deeper

towards that

towards

reproduced Fig.

the conduction

in the high

and

or nega.tive Ditpvalues

Ditpdata

calculated

annealed

this

discrepancy

CV-curves,

for the With

increasing

voltages

two

(data

direction

Terman

For the HF-LF

method data

not

and

in a limited

towards

charging

accumulation

the charge states

the onset

by the

are

We note

accumulation

directions

the position

carrier that

of asymmetry

respectively.

towards sweep

sweep

are larger

to a fast

of interface

This shifts

for both

volt,age

direction

temperatures

in the CV-curves, sweep

plateau

of Si-based

the Ditpvalues

direction

dynamics

are involved.

by the

by a high

V/set

d a t a is attributed

sweep

capacity

[6].

for the

for the opposite

CV

measurements

samples.

results

of the

for the

temperature

of 0.15~10-~

method

than

gap was calculated by the Berglund method. by a factor of 1.5 slightly smaller and shifted We explain

comparable

discharging

band

inversion

an emerging

for HFCV-measurements

HF-LF

Di,p and

respectively.

below

differently

reveal by the

states

rate

At elevated

and the discrepan-

The

1 show

only

carriers.

in the QSCV-

direction.

to a plateau

is observed

that

charge

is observable

voltages.

sweep

indicate

sweep

mea-

1, voltage

(170 K) HFCV-measurements

accumulation

charging

values

4

by arrows.

for minority

in Fig.

effect

as in Fig.

indicated

a hump

direct,ions

slow voltage

in the

that

low temperature

4 shows

for three

A similar

of interface

direction,

2

24. 100, 200 and

measurements rate

negative

to the asymmetry

With

lower energy

the

sweep

towards

calculated

a slow discharging

located

a very

asymmet,ry

’

’

0

QSCV--data and

sample

for t,he opposit,e

HFCV-curves

Semiconductor)

D;,-data

direction

range.

both

that. low temperature

Corresponding

for the sweep energy

too.

with

Insulator

3 shows

for both

is shifted

temperatures,

same direction

accumulation smaller

corresponding

shown). Fig.

emerges

directions

reached.

300°C; sweep

temperature.

is much

Normalized

at O.O5V/cm

by t,he low generation

dire&ion

(at 1 V in Fig. 2). which

temperatures

and

(lox: 30 nm,

sample.

occures,

2.

sured

60 min in Ar at 1150°C.

deep

I

-2

Voltage IV]

Voltage [V] Figure

n

-4

(Fig.

HF-LF within

are 3). method

the band

The values from the Terman method are towards lower energy values by ca. 0.25 eV.

Dit value

at the conduction

band

edge,

introducing

E. Stein von Kamienski et al. /Microelectronic

203

Engineering 28 (1995) 201-204

1,X

2,0

2,2

2,4

2,6

2,8

Ei, - E, Ievl Figure

3.

Interface

state

density

ted by HF-LF-method 1 and

Fig.

from

2, sweep

cumulation:

calcula-

data

direction

Figure

of Fig.

towards

3.

culated

ac-

bols)

TA.

Interface

by

and Terman

Samples:

to the

level.

However,

Berglund

three

samples.

were reported

at high flatband

POA

in Ar and

N2 reduces

for samples

(Vm)

is plotted

in Fig. 5. The was observed

captured

charges

are coulombic (lNr) of the increasing

curves

indicat~es

values

above

PO4

time

up to above

values.

be found

[7]. Tl ie correlation

No such

t,he two types

of defects.

to be intrinsic

defects

band edge remarkable explained

after

These

in the injection

Dit is increased that the peak by a chemically

even

by positive

initial

of Ni,,j = 9

x

the D;, and

Fig.

indicating defect formation value of D,t around 2.2~V conversion

180 min

6 shows

of the samples. The

or at elevated of defects.

oxide

charge

a.nnealed

sample

of the

t,hus they

the effect 011 Di,.

with reveals

devices

chemical

traps

densities

Not reduce

the same

tem-

N,i, a.nd

Nf and

in all samples electrons

The samples

that, the oxide

Nsit values

N,, indicates

lO’“cm-”

fixed

yuantities

arc detect,ed

SiOL-SiCsystem.

imply

the initial Both

devices

up to 300°C.

st,ress

sections

the

tunneling.

charging

in two types

cross

whereas

Nr and

defects

voltagr

are trapped

to the

between

in

relations

in Ar annealed

a negative

5, too.

of t,he

annealed

we biased

Nordheim

for temperatures

30 min,

relation

(N,,),

for differently

For comparision, in Fig.

traps

stress,

charges

doping

for Ar anneals

in Nz. The same

of Fowler

time

for the capture

centers.

a.re listed

enhanced

high field stress

the

on the Dit values

not shown).

threshold

he freed

the results

demonst,rate

bias

pa.rtly that

(data

symbols).

30 nm, POA:

[5]. Our samples

annealed

and oxide

the stress

clearely

10-15cm”

attractive samples

(N,it)

for positive

can only

This

Not. High

at 1200°C

(solid d,,:

sensitively

Similar

calsym-

in Ar or Na.

bet,ween

t,echniyue

to the samples

states

shift, versus

depends

relations

t,he conductance

method

for 60min

Dit drastically.

up to a.bove the

No effect

method

the same

compared

fabricated

voltages

voltage

peratures.

using

slow int,erface

positive

Terman

show

lower values

To investigate

The

calculations

in lit,erature

_4r show slightly were found

method.

both

density (open

dry oxidat,ion,

at 1150°C

errors

state

HF-LF-method

could

nature

of

are likely

of a 5.2MV’/cm At

the conduction

due to the high field applied. It is in Fig. 6 is reduced. This might be

of Nsit t,o N,t due to the charging.

204

E. Stein von Kamienski et al. / Microelectronic Engineering 28 (1995) 201-204

097 06 OS 0,4 0,3 02 i

E

-“,I

10

0

20

30

40

1,8

50

2,O

2,2

tstress [mini

2,4

2,6

2,8

E,- E, levl

Figure 5. Relative shift of flat,ba.nd voltage versus stress time at 5.2MV/cm, Jinj = 4 x 10-‘A/cm2, N;,j(35min) = ; dry oxidation at 1150°C. ’ 7 X 1013cmPOA in Ar at 115O”C, time as parameter.

Figure 6. D;t-data before and after 1 h stress at 5.2MV/cm, Ni,j(60min) = 9 x 10’3cm-2, calculated by Terman method; same sample as in Fig. 5, P0.4: 18Omin.

4. CONCLUSIONS

Interface method dence

state

reveal

densities

on the voltage

of interface

states.

temperatures.

states

and oxide

indicates creases

The

direction,

effect

During traps

on SIC calculated

results.

sweep This

higher

for Di, and

of oxides

comparable

taken

resulting t.owards

high

field The

is observed.

chemical

nature

Dit at the conduction

band

a fast

HF-LF

charging values

stress

negative

charge

trapping

oxide

traps

of the

are coulombic

two types

whereas

Dit located

Terman a depen-

in the band

between

The

gap for

in slow interface

attractive

A correlation of defects.

the

show

and slow discharging

energy

in Ar.

and

techniques

deeper

by a POA edge

by the

wit,h both

from

is shifted

Nf, Not can be reduced

the same

data

cha.rge

deeper

below

and J. A. Edmond;

Proc.

centers.

As

Not and trapping the band

Nf in-

edge

is reduced.

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