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904 IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 45, NO. 4, APRIL 1998

New Insights in the Relation BetweenElectron Trap Generation and the

Statistical Properties of Oxide BreakdownRobin Degraeve, Guido Groeseneken, Senior Member, IEEE, Rudi Bellens, Jean Luc Ogier,

Michel Depas, Philippe J. Roussel, and Herman E. Maes, Senior Member, IEEE

AbstractIn this paper it is demonstrated in a wide stress fieldrange that breakdown in thin oxide layers occurs as soon as acritical density of neutral electron traps in the oxide is reached.It is proven that this corresponds to a critical hole fluence, sincea unique relationship between electron trap generation and holefluence is found independent of stress field and oxide thickness.In this way literature models relating breakdown to hole fluenceor to trap generation are linked. A new model for intrinsicbreakdown, based on a percolation concept, is proposed. It is

shown that this model can explain the experimentally observedstatistical features of the breakdown distribution, such as theincreasing spread of the

Q

B D

-distribution for ultrathin oxides.An important consequence of this large spread is the strong areadependence of the Q

B D

for ultrathin oxides.

I. INTRODUCTION

THE time-dependent dielectric breakdown (TDDB) of thinoxide films is an important reliability issue of MOS

integrated circuits [1]. Although this topic has been studied

extensively in the past, the mechanism of intrinsic breakdown

is still not completely clarified.

One of the possible models that have been proposed is

the anode hole injection model [2][4]. According to thismodel, injected electrons generate holes at the anode that

can tunnel back into the oxide. Intrinsic breakdown occurs

when a critical hole fluence, is reached. It has

been observed that is about 0.1 C/cm for 11 nm

oxides [2]. For the link between the breakdown event and

this critical hole fluence, however, no satisfactory physical

explanation has yet been given. Moreover, it has been

observed that decreases for thin oxides, an effect

which is also not yet understood [3], [4].

Besides the model correlating with a second

model has been suggested independently, which claims that

a critical density of electron traps generated during stress is

required to trigger oxide breakdown [5][8]. In this paper, wewill refer to this model as the electron trap generation model.

Based on this model the breakdown event is presented as the

Manuscript received June 5, 1997; revised October 8, 1997. The review ofthis paper was arranged by Editor W. Weber.

R. Degraeve, G. Groeseneken, R. Bellens, P. J. Roussel, and H. E. Maesare with are with IMEC, B 3001 Leuven, Belgium.

J. L. Ogier was with IMEC, B 3001 Leuven, Belgium. He is now withSGS-Thomson, Rousset, France.

M. Depas, deceased, was with IMEC, B 3001 Leuven, Belgium.Publisher Item Identifier S 0018-9383(98)02292-8.

formation of a conductive path of traps connecting the anode

with cathode interface. A link between the anode hole injection

model and the electron trap generation model has been never

been clearly established.

The purpose of this paper is to link both the anode hole

injection model and the electron trap generation model into

one consistent model that describes oxide wearout as a hole-

correlated electron trap creation process, ultimately leading to

a breakdown event. This new consistent model is evaluatedin a wide field range from 611 MV/cm, using a combination

of FowlerNordheim (FN) and substrate hot electron (SHE)

injection experiments. It is implemented in a new simulator,

and is able to predict a number of yet unexplained experimen-

tal observations, such as the decrease of for decreasing

oxide thickness [3], [4], and a newly observed dependence

of the Weibull slope of the breakdown distribution on oxide

thickness. Furthermore, it will be demonstrated that as a

consequence of this change of Weibull slope, the 63%-value of

the breakdown distribution becomes strongly area dependent

in thin oxides.

The structure of the paper is as follows.

First, it is demonstrated that a thin oxide layer subject

to electric stress suffers breakdown as soon as a critical

density of neutral electron traps is generated in the bulk of

the oxide. The neutral electron trap density as a function

of the injected electron fluence is measured directly after

filling the generated neutral traps with electrons using SHE-

injection. This technique is explained in detail in Section III-

A. Furthermore, it is proven that stressing an oxide using

SHE-injection instead of FN-injection does not introduce any

additional degradation mechanism (Section III-B) and this will

allow to demonstrate the existence of a critical density of

neutral electron traps in a stress field range from 11 down

to 6 MV/cm, which is lower than the range that is practicallyaccessible with FN-injection (Section III-C).Secondly, from the measurements obtained with both SHE-

and FN-injection, it is shown that the anode hole injection

model and the electron trap generation model can be directly

linked together and a new model based on a percolation

concept for describing the oxide wear-out process is pre-

sented (Section IV-A). Computer simulations of this model

are performed and compared to experimental results.

Finally, the new model is used to explain the oxide thickness

dependence of the statistical properties of the breakdown dis-

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DEGRAEVE et al.: ELECTRON TRAP GENERATION AND THE STATISTICAL PROPERTIES OF OXIDE BREAKDOWN 905

tribution (Section IV-B) and its consequences on area scaling

(Section IV-C).

II. TECHNIQUES AND DEVICES

All -measurements in this study were performed

on capacitors with different areas and various thermally

grown oxides. Oxides have been grown either in 10%

O at C and 2.9 nm), or in 5% O atC nm), or in 10% O at 950 C from

7.513.8 nm) in a dry ambient. Hole fluence and electron trap

generation measurements are performed on nMOSFETs with

channel length 10, and 20 m and width m

The trapped electron density is calculated from the shift of

the threshold voltage during FN-injection, and the substrate

current was monitored in order to quantify the generated

hole fluence [2]. A description of the Substrate hot

carrier injection technique used throughout this paper can be

found elsewhere [9], [10]. The application of SHE-injection

to measure the generated electron trap density is explained

in detail in Section III. It has been verified experimentally

that for all oxides in this paper the generated breakdownsites are randomly distributed over the whole capacitor area.

Therefore, Poisson statistics will be used in case any area

scaling is performed [11]. This is also discussed in more

detail in Section IV-C.

III. NEUTRAL ELECTRON TRAP GENERATION

In this section, it is explained how SHE-injection can be

used to measure the electron trap generation in the oxide

during stressing. It is also shown that the SHE-injection is

suitable to accelerate the oxide degradation and breakdown at

lower fields than what is possible with FN-injection, without

introducing any additional degradation mechanism. It will

be demonstrated that in all cases breakdown occurs when a

critical electron trap density is reached.

A. Electron Trapping and Trap Generation

Consider the following experiment consisting of two steps.

1) First a fixed electron fluence of

cm C/cm is injected, on a first series of

nMOSFETs by means of SHE-injection at mediumfields (3.67 MV/cm), and on another series with FN-

tunnelling in the high field range (8.411.4 MV/cm).

After this first step, the change of the trapped charge

density is measured (assuming a uniform distribution

of charge in the oxide). The result is shown in Fig. 1as a function of the oxide injection field (lower curve).

It is observed that the trapped charge density increases

between 3.6 and 7 MV/cm, indicating a net negative

charge, but decreases again for fields higher than 7

MV/cm and finally becomes positive above 10 MV/cm

[12]. This proves that the trapped charge density is

the result of electron trapping (high at low fields),

field-induced detrapping (high at high fields) and hole

generation and trapping (high at high fields), and

is therefore not a good measure of the real damage

generated in the oxide.

Fig. 1. The trapped electron density directly after stress, and after aSHE-filling step at 3.6 MV/cm. The latter parameter, D

o t ; 3 : 6

; reveals the truetrap creation in the oxide. Open symbols are for FN-stress, closed symbolsare for SHE-stress.

Fig. 2. The trapped electron density in the oxide as a function of the injected

electron fluence. Initially a fluence of5 2 1 0

1 8

cm0 2

is injected, then a fillingstep at 2 MV/cm is performed (closed symbols: SHE-stress, open symbolsFN-stress).

2) In a second step, a small amount of electrons (

cm or 0.08 C/cm ) is injected at a very low oxide field

of 2 MV/cm, by SHE-injection. This second step aims

to neutralize all positive charge and to fill the electron

traps that were generated during the first step, but were

left neutral due to the high detrapping oxide fields during

the first step. Fig. 2 shows the trapped electron density

as a function of the electron fluence during the first

and the second step, again for both high field (FN)and medium field (SHE) injection conditions. As can

be clearly observed, the neutral traps, generated during

the first step are indeed filled during the second step,

and their density is proportional to the fields that were

used in the first step.

It should be noticed that even at 2 MV/cm not all available

electron traps are occupied with an electron. It has been shown

that at a fixed filling field a fixed fraction of all available traps

is occupied [9]. Therefore, it can be written

(1)

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Fig. 3. Trapped electron density after filling with SHE-injection at 3.6, 5.3,and 7 MV/cm, as a function of the electron fluence for constant voltageFN, constant current FN and SHE-stress. All stresses were performed withapproximately the same oxide field.

with the volume density of occupied traps at the filling

field (in MV/cm), the fraction of the traps that is filled

at a filling field and the total electron trap density

in the oxide. To make a fair comparison of the electron trapgeneration at different oxide stress conditions, it is sufficient

to compare the electron trapping after using identical filling

fields, since then is constant and the measured quantity

is proportional to the total electron trap density

The generated electron trap density measured after filling

at 3.6 MV/cm, is also plotted on Fig. 1 as a function

of the oxide field. The volume density was obtained assuming

a homogeneous trap distribution in the oxide. In contrast to

the trapping behavior directly after stress, the electron trap

generation increases monotonously with the oxide stress field.

B. Comparison of Degradation with SHE and FN

SHE-injection offers the possibility to accelerate the degra-dation by increasing the gate electron fluence at a fixed oxide

field. But before using this technique as a breakdown acceler-

ating method, it should be verified that the high hot electron

fluence does not alter the degradation process. Therefore, three

experiments were carried out on an oxide with thickness 13.8

nm.

1) A constant voltage FN-stress with MV/cm.

The current density varies from 0.2 mA/cm initially

to 0.025 mA/cm after a fluence of cm (16

C/cm has been injected. The stress was stopped before

breakdown occured.

2) A constant current FN-stress with mA/cmThe oxide field varies from 8.4 MV/cm initially to 10.0

MV/cm at breakdown C/cm correspond-

ing to an electron fluence of cm

3) A SHE-stress with constant MV/cm and

constant mA/cm C/cm cor-

responding to an electron fluence of cm

To compare the degradation in these three cases, the stress

was interrupted at regular intervals, and short filling steps as

described in Section III-A were performed, using filling fields

of 3.6, 5.3, and 7 MV/cm. The trapped electron densities after

filling and respectively) are shown in

Fig. 4. The occupation lines at 7 MV/cm for constant voltage stresses (opensymbols: FN, closed symbols: SHE) in the field range 611 MV/cm. The starsrepresent the extrapolated D

o t ; 7

at breakdown. A critical electron trap densityat the moment of breakdown is revealed.

Fig. 3, as a function of injected electron fluence. As explained

in Section III-A, for each filling field, the lines in Fig. 3

indicate the fixed fraction and respectively) of

the total amount of electron traps which are occupied by an

electron, and are therefore called occupation lines [9]. These

lines are proportinal to the true damage creation in the oxide

during the stress.

From Fig. 3, it is clear that the three applied stress con-

ditions result in almost the same electron trap creation. For

constant current stress, slightly more traps are generated at

high fluence, which is caused by the increase of the electric

field during the stress. This also explains the difference in

between the constant current and the SHE-stress. The

accelerated degradation with SHE-injection shows identical

behavior as the FN-stresses. This proves that increasing the

gate electron current density accelerates, but does not change,the degradation mechanism, and therefore it can be concluded

that SHE-injection is suitable as a degradation and breakdown

accelerating method.

C. Breakdown Measurements

Degradation and breakdown measurements have been per-

formed in the field range 68.5 MV/cm with SHE-injection

and 8.511 MV/cm with constant voltage FN-injection. InFig. 4, the occupation lines for a filling field of 7 MV/cm

and extrapolated at breakdown are shown. Notice that

for the lowest stress field (6 MV/cm), the filling field (7

MV/cm) was actually a detrapping field. In this case, it was

carefully checked that the filling step was sufficiently shortand introduced a negligible trap creation.

In the considered field range and apart from small statistical

fluctuations, breakdown always occurs when reaches a

critical value of about cm This conclusion is a

direct proof that a critical electron trap density is necessary to

trigger breakdown. This confirms the electron trap generation

model.

When the electron fluence corresponding to this critical trap

density value is taken as 100%, a relative fluence scale can be

constructed. This is shown in Fig. 5, revealing clearly that

the electron trap generation is identical for all stress fields

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Fig. 5. Occupation lines at 7 MV/cm as a function of the electron fluencenormalized to the breakdown fluence for SHE- and FN-injection in the fieldrange 611 MV/cm.

and independent of the applied technique (FN or SHE) in the

field range 611 MV/cm. It can be concluded that the electric

field merely acts as an acceleration factor for the degradation

process.

IV. PERCOLATION MODEL FOR INTRINSIC BREAKDOWN

In the previous section, it has been shown that breakdown

is triggered when a critical electron trap density (CETD) is

reached. However, in the literature it has also been claimed

that breakdown occurs when a critical hole fluence is reached

[2][4]. In this section, it will be shown that both breakdown

criteria are equivalent. Based on this finding, a consistent

model is presented that links both the electron trap generation

model and the anode hole injection model together. This

model is based on a percolation concept and is implemented

in a simulator. The simulation results are fitted to experi-

mental data. Then the new model is applied to study the

oxide thickness dependence of the statistical properties of the-distribution and its consequent impact on the -area

scaling.

A. Description of the Model

To investigate the correlation between the CETD and the

critical hole fluence, on Fig. 6, the generated electron trap

density occupied at 7 MV/cm, has been plotted versus

the hole fluence for different oxide thicknesses (between

7.3 and 13.8 nm) and stress fields (between 9.5 and 11

MV/cm). One unique curve is obtained indicating that electron

trap generation is correlated with the generated hole fluence

independent of oxide field and thickness. This correlation caneither be causal, i.e. the holes are necessary for the trap

generation, or the holes and the traps can be related to a

common parameter, e.g. the energy of the injected electrons at

the anode. The curve shown in Fig. 6 can be fitted empirically

by a power law with exponent 0.56 and together with (1) it

is found that

(2)

with cm if is expressed

in cm and in C/cm

Fig. 6. The trapped electron density after filling at 7 MV/cm as a functionof the hole fluence for electric fields between 9.5 and 11 MV/cm, oxidethicknesses between 7.3 and 13.8 nm, and constant current as well as constantvoltage stress. A unique curve is found, independently of oxide field, oxidethickness or stress type.

Fig. 7. Schematic illustration of the spheres model for intrinsic oxide break-down simulation based on trap generation and conduction via traps. Abreakdown path is indicated by the shaded spheres.

It is concluded that the critical hole fluence, corre-

sponds to a critical generated electron trap density,and that in this way both the anode hole injection model and

the electron trap generation model can be linked.

Since the breakdown occurs at a CETD, a plausible break-

down mechanism is conduction via these generated traps. In

order to investigate the impact of this mechanism on the

statistics of breakdown and on the oxide thickness depen-

dence of a computer simulation is performed, which

is schematically illustrated in Fig. 7. In this algorithm a testsample with fixed dimensions is defined and inside this volume

electron traps are generated at random positions. Around these

traps a sphere is defined with a fixed radius which is the only

parameter of the simulation. If the spheres of two neighboring

traps overlap, we define that conduction between these trapsbecomes possible. Also, the two interfaces are modeled as an

infinite set of traps. The algorithm continues generating traps

until a conducting path is created from one interface to the

other, as is schematically illustrated in Fig. 7. This defines the

breakdown condition. The CETD can now be calculated as the

total number of generated traps divided by the volume of the

test sample. The dimensions of the test sample are chosen to

be significantly larger than the sphere radius but sufficiently

small to keep the computer calculation time within a practical

time frame. Typically, the minimum lateral dimensions are

nm.

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Fig. 8. Computer simulation of a breakdown distribution using the spheresmodel, together with an experimental distribution.

With this procedure, the distribution of CETD can be

calculated. However, in order to compare this distribution with

an experimental -distribution, the relationship between

generated electron traps and injected charge must first be

known. This relationship can be obtained as follows:It has been shown that the electron and hole current density

are directly correlated [3]:

(3)

in which and are the hole and electron current densityand is a parameter which, according to the anode hole

injection model [3], can be interpreted as the probability that

an injected electron generates a hole that can tunnel back into

the oxide. is field and oxide thickness dependent. It can be

measured directly and is approximately constant during stress.

Since constant current stress is applied one can also write

(4)

with and the hole and electron fluence. Combining thisequation with the unique relationship between hole fluence and

generated electron traps, (2), one obtains

(5)

At breakdown, all variables in this expression reach their

critical values:

(6)

With this relationship, a simulated distribution of the CETD

can be compared directly with an experimentally obtained-distribution. The only unknown parameter in (6) is the

fraction of occupied electron traps at 7 MV/cm, However,

from fitting one -distribution to a simulation, both and

the model parameter, can be determined. This is done for an

8.9 nm oxide with and the result is shown in

Fig. 8. An excellent fit between the simulation and the model

is obtained for nm and The result

shown in Fig. 8 proves that even for an oxide without any

extrinsic defects is a statistical variable. The statistical

spread is caused by the oxide degradation mechanism itself.

This conclusion is in contradiction with the well-known oxide

Fig. 9. Simulated critical electron trap density for different oxide thick-nesses. The simulations were performed on a minimum area of 900 nm 2 ;but for the thinnest layers, larger simulation samples were used to increasethe accuracy of the calculation. In the figure, all distributions are normalizedto an area of 900 nm 2 ; using (7) of Section IV-C.

thinning model [13] in which it is assumed that the intrinsic

is one single well-determined value and the whole -

distribution (intrinsic as well as extrinsic) is directly associated

with a distribution of process-induced defects characterized by

an effective oxide thickness.

The value of nm means that conduction between

adjacent traps is possible when they are 0.9 nm apart.

From the simulation follows that determines entirely the

statistical spread of the -distribution. means

that at 7 MV/cm only 3% of the available electron traps in theoxide are filled with an electron. If the high detrapping rate at

the filling field and the Coulombic repulsion between trapped

electrons is taken into account, 3% is indeed an acceptable

value for Both and are determined by properties of

the electron traps, and are therefore independent of the oxide

stress field and the oxide thickness. In Section IV-B, and IV-

C, the oxide thickness dependence of the -distribution isstudied without performing any further parameter fitting.

B. Oxide Thickness Dependence of the Breakdown Distribution

In Fig. 9, the simulated distribution of the CETD for differ-

ent is shown. Two effects can clearly be observed: 1) the

modal value ( -value) of the distribution decreases with

decreasing oxide thickness and 2) the Weibull slope (whichis a measure of the spread of the distribution) decreases with

decreasing oxide thickness.

1) The decrease of the modal value of the CETD is reflected

directly in a decrease of the critical hole fluence, as is obvious

from (6). In [3] and [4] it has indeed been found that the

critical hole fluence decreases with decreasing oxide thickness,reflecting a weakened hole fluence immunity for thinner

oxides.

The simulated and the measured modal CETD as a function

of are shown in Fig. 10. Also included are experimental

data based on Fig. 7 of [4], in which has been recalcu-

lated into CETD, using (6). From Fig. 10, it is clear that the

simulation agrees well with these -based data as well as

with our own direct measurements, showing an approximately

linear dependence of the CETD with between 3 and 14

nm. The decrease of the CETD, and thus also of the critical

hole fluence, with decreasing oxide thickness is an intrinsic

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Fig. 10. The simulated critical electron trap density as a function of theoxide thickness, together with our experimental results and data calculatedfrom the results shown on Fig. 7 of [4].

Fig. 11. The normalized experimentalQ

B D -distributions for different oxidethicknesses. The Weibull slope decreases with decreasing oxide thickness aspredicted by the model.

statistical property of the breakdown mechanism. Indeed, for

thinner oxides, fewer traps are required to form a breakdown

path, and therefore there is a higher probability of forming such

a path at a much lower modal trap density and hole fluence.

2) The decreasing Weibull slope for decreasing oxide thick-

ness is, to our knowledge, an effect that has not yet been

reported in literature. However, as can be seen on Fig. 11, the

effect is confirmed experimentally. On Fig. 11, the has

been normalized to its maximum value in order to make an

easy comparison of the slopes possible. Using (6), the slopes ofthe simulated electron trap density distributions of Fig. 9 can

be compared with those of the measured -distributions of

Fig. 11. The result is shown on Fig. 12. As can be observed,

the model predicts the decrease of the Weibull slope of the

-distribution with decreasing very well for one single

value of radius nm.

The smaller Weibull slope for thinner oxides is explained as

follows: in the thinnest oxide the conductive breakdown path

consists of only a few traps and consequently there is a large

statistical spread on the average density to form such a short

path. In thicker oxides the breakdown path consists of a larger

Fig. 12. The simulated and measured Weibull slope of theQ

B D

-distribution as a function of oxide thickness.

number of traps, and the spread on the trap density necessary

to generate such a large path is smaller. This means that the

change of the Weibull slope as a function of the oxide thickness

is again an intrinsic statistical property of the degradation andbreakdown mechanism.

C. Area Dependence of Intrinsic Breakdown

In [11], it has been shown that two capacitors with identical

oxide thickness, but area and respectively, have a

breakdown distribution that is shifted on a Weibull scale over

a vertical interval equal to the logarithm of the ratio of the

areas. This means

(7)

with

(8)

and the modal values of and respectively. Notice

that is area independent [14]. Combining (7) and (8), it can

be shown that

(9)

The modal value of the distribution increases with de-

creasing area. From (9) it is also clear that as decreases

with oxide thickness (Fig. 12), becomes a strong functionof the capacitor area. This is illustrated in Fig. 13, where the

-area dependence of an 11, 6.3, and 4.3 nm oxide are

compared. The solid lines are fits with the values of

4.3, and 1.96, respectively, which are in good agreement with

the predicted values of the model. For an 11 nm oxide, an area

variation of five orders of magnitude only results in a factor

two change of the while for a 4.3 nm oxide this already

gives 2.5 orders of magnitude -change! Therefore,

cannot be considered to be independent of the area any longer.

It is mandatory to specify the area when -values are

measured or compared.

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Fig. 13. The area dependence of the modal value of the WeibullQ

B D

-distributions for three oxide thicknesses. An stronger area dependenceis found for thinner oxide layers.

V. CONCLUSIONS

1) In this paper it has been explained that a true picture

of the generation of oxide traps during oxide stressingcan only be obtained after a short filling injection at a

constant field, since then the same fraction of electron

traps is occupied. Combining this measurement with

computer simulations allows the determination of the

total electron trap density in the oxide.

2) It has been shown that SHE-injection can be used

to accelerate breakdown at medium fields, where the

FN-current density is too low to allow measurements

within a pratical time frame. It has been demonstrated

that no additional degradation mechanisms are excited

when using this technique.

3) It is proven directly that breakdown occurs when acritical electron trap density is reached. This conclusion

has been evaluated in a wide field range from 611

MV/cm using both SHE and FN-injection to stress the

oxide.

4) A unique relationship between hole fluence and electron

trap generation is found, independent of stress field or

oxide thickness. This means that when a critical electron

trap density is reached at breakdown, a corresponding

critical hole fluence is found. Based on this result, a

consistent model has been introduced that links both

anode hole injection and electron trap generation models.

In this model wearout is described as a hole-correlated

generation of electron traps, and breakdown is definedas the formation of a conductive path via these traps

from one interface to the other.

5) From computer simulations of this percolation model,

it is shown that the Weibull distribution of -values

is explained as a statistical property of the degradation

mechanism. Furthermore, the decrease of the critical

hole fluence with oxide thickness, and the experimen-

tally newly observed oxide thickness dependence of the

Weibull slope of the -distribution are resulting from

the simulations. Both effects are also intrinsic statistical

properties of the degradation mechanism.

6) The impact of the statistical properties of the intrin-

sic breakdown distribution on area scaling has been

discussed. It is shown that in thin oxides the modal

value of the Weibull distribution becomes strongly area

dependent and, as a result, for ultrathin oxides it be-

comes mandatory to specify the area when intrinsic

-values are measured or compared.

7) The quantitative experimental confirmation of all statis-

tical properties predicted by the percolation model for

oxides between 2.413.8 nm, is a strong indication for

the correctness of the proposed breakdown mechanism

in this oxide thickness range. For thicker oxides it

can not be excluded that other breakdown mechanisms

become active.

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[6] J. Sune, I. Placencia, N. Barniol, E. Farres, F. Martn, and X. Aymerich,On the breakdown statistics of very thin SiO

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Devices, vol. 41, pp. 15701580, Sept. 1994.[8] P. P. Apte and K. C. Saraswat, Modeling ultrathin dielectric breakdown

on correlation of charge trap-generation to charge-to-breakdown, inProc. IRPS, 1994, pp. 136142.

[9] Y. Nissan-Cohen, J. Shappir, and D. Frohman-Bentchkowsky, Trapgeneration and occupation dynamics in SiO

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under charge injectionstress, J. Appl. Phys., vol. 60, no. 6, pp. 20242034, 1986.

[10] T. H. Ning, Hot-electron emission from silicon into silicon dioxide,Solid State Electron., vol. 21, pp. 273282, 1978.

[11] D. R. Wolters and J. F. Verwey, Breakdown and wear-out phenomenain SiO

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films, in Instabilities in Silicon Devices. Amsterdam, TheNetherlands: Elsevier, 1986, ch. 6.

[12] D. J. DiMaria, E. Cartier, and D. Arnold, Impact ionization, trap cre-ation, degradation, and breakdown in silicon dioxide films on silicon,

J. Appl. Phys., vol. 73, no. 7, pp. 33673384, 1993.[13] J. C. Lee, I. C. Chen, and C. Hu, Modeling and characterization of

Gate Oxide Reliability, IEEE Trans. Electron. Devices, vol. 35, pp.22682278, DEC. 1988.

[14] R. Degraeve, J. L. Ogier, R. Bellens, Ph. Roussel, G. Groeseneken,and H. E. Maes, On the field dependence of intrinsic and extrinsictime-dependent dielectric breakdown, in Proc. IRPS, 1996, pp. 4454.

Robin Degraeve, for a photograph and biography, see p. 481 of the February1998 issue of this TRANSACTIONS.

Guido Groeseneken (S80M80SM95), for a photograph and biography,see p. 481 of the February 1998 issue of this T RANSACTIONS.

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Rudi Bellens, for a photograph and biography, see p. 481 of the February1998 issue of this TRANSACTIONS.

Jean Luc Ogier, for a biography, see p. 481 of the February 1998 issue ofthis TRANSACTIONS..

Michel Depas was born in Aalst, Belgium, on January 31, 1967. He receivedthe M.S. and Ph.D. degrees in electrical engineering from the University ofGent, Belgium, in 1990 and 1995, respectively.

From 1990 to 1994, he was a Research Assistant of the Belgian NationalFund for Scientific Research (NFWO), investigating the electrical propertiesof Si/SiO

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structures with an ultrathin oxide layer. From 1994 to 1997,he worked in the Ultra-Clean Processing group of the Advanced SiliconProcessing division at IMEC (Inter-university Micro Electronic Centre),Leuven, Belgium. His research interests included physics and technologyrelated issues for cleaning and oxidation technology in CMOS processing.He passed away on January 15, 1997.

Philippe J. Roussel, for a biography, see p. 481 of the February 1998 issueof this TRANSACTIONS.

Herman E. Maes (S73M73SM89), for a photograph and biography, seep. 481 of the February 1998 issue of this TRANSACTIONS.

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