Full text of DOI:10.1063/1.114952

Effect of incorporated nitrogen on the kinetics of thin rapid thermal N2O oxides
M. L. Green, D. Brasen, L. C. Feldman, W. Lennard, and H.T. Tang
Citation: Applied Physics Letters 67, 1600 (1995); doi: 10.1063/1.114952
View online: http://dx.doi.org/10.1063/1.114952
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Effect of incorporated nitrogen on the kinetics of thin rapid thermal
N2O oxides
M. L. Green, D. Brasen, and L. C. Feldman
AT&T Bell Laboratories, Murray Hill, New Jersey 07974
W. Lennard and H.-T. Tang
University of Western Ontario, London, Ontario N6A 3K7, Canada
͑Received 10 April 1995; accepted for publication 6 July 1995͒
We have grown ϳ10 nm O2 and N2O-oxides on Si͑100͒ by RTO ͑rapid thermal oxidation͒ over the
temperature range 800–1200 °C. Although the growth rates of both oxides exhibit Arrhenius
behavior over the entire temperature range, the N2O-oxides exhibit a large change in the Arrhenius
preexponential factor for oxidation temperatures greater than 1000 °C. Above this temperature,
N2O-oxides grow a factor of 5 slower than O2 oxides. Below this temperature, N2O-oxide growth
rates approach those of O2-oxides. This growth rate inflection can be explained in terms of N
incorporation, which increases with increasing oxidation temperature. The equivalent of one
monolayer of N coverage is achieved at about 1000 °C, coincident with the inflection. The
incorporated N retards the linear growth of the thin N2O-oxides either by occupying oxidation
reaction sites or inhibiting transport of oxidant species to the vicinity of the interface. © 1995
American Institute of Physics.
The incorporation of N ͑nitrogen͒ into SiO2, i.e., oxyni-
tridation, significantly retards boron penetration through the
resultant Si–O–N dielectric.1,2 Therefore, oxynitrides are po-
tentially important gate dielectrics for ultralarge scale inte-
gration, where dielectric thicknesses will be р7 nm. In the
absence of N, boron, the Pϩ polycrystalline silicon gate elec-
trode dopant can diffuse through the thin SiO2 layer during
postgate dielectric growth processing, causing unacceptable
shifts in device threshold voltage.3,4 The simplest and most
manufacturable of the many oxynitridation chemistries is the
direct oxynitridation of Si in N2O, which has been exten-
sively studied with respect to processing,5,6 electrical
properties,3,7,8 and reliability.3 In N2O-oxides, the incorpo-
rated N is closely confined to the Si/SiO2 interface.3,6,9 Fur-
ther, the amount of N incorporated in RTO ͑rapid thermal
oxidation͒ N2O-oxides is small, but has been found to in-
crease with increasing oxidation temperature3,10,11 and oxide
thickness.5,9,12 For example, the equivalent of about one
monolayer of N on Si͑100͒, 7ϫ1014 N/cm2, is incorporated
in a 10 nm N2O-oxide grown at 1000 °C.10 Other N incorpo-
ration data from the literature has been summarized in Ref.
10. The small amount of incorporated N has a large effect in
retarding the kinetics of N2O-oxide growth.13–15 In this letter
we report the relationship between oxidation kinetics of RTO
O2 and N2O-oxides and incorporated N content for oxides of
current technological importance, i.e., ϳ10 nm thick. We
show that retardation of N2O-oxide kinetics is due to the
effect of incorporated N content on the Si/SiO2 interfacial
oxidation reaction constant.
Ref. 10. Oxide thickness was determined by ellipsometry,
with the index of refraction of the N2O-oxides assumed to be
that of the O2-oxides, 1.459. The validity of this assumption
has been confirmed by independent ion scattering measure-
ments, and is consistent with the small amount of N in the
oxides.
Figure 1͑a͒ is an Arrhenius plot of average oxidation rate
RO or RN O, where RO and RN O are defined as the oxide
2
2
2
2
thickness divided by the time at oxidation temperature to
reach ϳ10 nm thickness, for O2 and N2O-oxides, respec-
tively. The O2-oxide data obey an Arrhenius relationship that
yields an activation energy of 2.1Ϯ0.1 eV. In contrast, the
N2O-oxide data appear to only obey an Arrhenius relation-
ship between about 1000 and 1200 °C, with activation en-
ergy equal to 1.9Ϯ0.1 eV. In this temperature range, the
N2O-oxide growth rate is about five times slower than the
O2-oxide growth rate. Below 1000 °C, the N2O-oxide growth
rate exhibits an inflection and approaches the O2-oxide
growth rate, nearly equaling it below 850 °C.
The N2O-oxide growth rate inflection can be seen more
clearly in Fig. 1͑b͒, where the ratio of the N2O to O2-oxide
average growth rates, RN O /RO , is plotted as a function of
2
2
oxidation temperature. The presence of the inflection in
N ORO , which can be clearly observed, is indicative of an
R
2
2
abrupt transition in N2O-oxide growth rate with respect to
O2-oxide growth rate. It has been shown,10 for the present
N2O-oxide sample set, that incorporated N content increases
approximately linearly in the oxidation temperature range
800–1200 °C, and that at 1000 °C, its value is 7ϫ1014
N/cm2, the equivalent of about one monolayer. Therefore, we
can correlate the abrupt transition in RN O/RO , Fig. 1͑b͒,
RTO O2 and N2O-oxides ϳ10 nm thick ͑actual range
8.5–11.2 nm͒, were grown at temperatures ranging from 800
to 1200 °C in pure ambients and at atmospheric pressure. All
oxides were grown on p-type ͑10–20 ⍀ cm, boron͒, 125 mm,
Si͑100͒ substrates. The N2O-oxides are the same sample set
whose incorporated N contents were reported in Fig. 1 of
2
2
with the increase in N content previously observed in Ref.
10. In Fig. 2 we have plotted RN O /RO as a function of N
2
2
content, and it can be seen that the incorporation of a mono
1600
Appl. Phys. Lett. 67 (11), 11 September 1995
0003-6951/95/67(11)/1600/3/$6.00
© 1995 American Institute of Physics
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FIG. 2. The ratio of the N2O to O2-oxide average growth rates as a function
of nitrogen content of the N2O oxides. The nitrogen data come from Fig. 1
of Ref. 10.
be rationalized with linear, i.e., reaction controlled, oxide
growth. It is known that the N is concentrated very close to
the Si/SiO2 interface.3,6,9 We propose that as the N concen-
tration increases with increasing temperature up to one
monolayer equivalent, it continuously retards further oxida-
tion by one of two mechanisms. If one assumes a pure inter-
face oxidation reaction model,16 then the N might be occu-
pying oxidation reaction sites at the interface, as has been
previously suggested.19 This model suggests that N exists as
a monolayer specifically bound to Si/SiO2 interface sites. Al-
ternatively, in a reactive layer model,20 the N may be inhib-
iting transport of the oxidant species through the reactive
layer, thereby retarding the interfacial reaction. In this way,
the N acts to mask the approximately one monolayer of Si
available to react at the interface. Either model is consistent
with our finding of linear growth.
FIG. 1. ͑a͒ Arrhenius plot of average growth rate for ϳ10 nm thick O2 and
N2O-oxides, over the temperature range 800–1200 °C, and ͑b͒ the ratio of
the N2O to O2-oxide average growth rates as a function of oxidation tem-
perature.
In summary, we have grown ϳ10 nm O2 an
N2O-oxides by RTO over the temperature range 800–
1200 °C and have found that growth is dominated by linear,
i.e., Si/SiO2 interfacial reaction kinetics. The N2O-oxide
growth rate decreases as N incorporation increases, due ei-
ther to oxidation site occupation by N, or inhibition of oxi-
dant transport through the reactive layer, again by N. At an N
content equivalent to one monolayer on Si͑100͒, the effect of
the incorporated N on the N2O-oxide kinetics saturates.
The authors would like to thank Kathy Krisch and Lalita
Manchanda for helpful discussions.
layer equivalent of
N2O-oxidation kinetics.
N saturates the retardation of
Figure 1͑a͒ also suggests that the growth of ϳ10 nm
O2 oxides occurs in the linear regime ͑as defined by
Deal–Grove͒,16 since the derived activation energy, 2.1Ϯ0.1
eV, is in excellent agreement with the 2.0 eV Deal–Grove
value for their linear growth rate parameter. Other research-
ers have observed activation energies of 2.26 eV17 and 2.0
eV18 for the linear rate parameter for thin RTO O2-oxides.
Further, since the N2O-oxides of Fig. 1͑a͒ also show an ac-
tivation energy of 1.9Ϯ0.1 eV for T Ͼ1000 °C, within error
equal to the Deal–Grove value, we assume that in this tem-
perature range the N2O-oxides grow in the linear regime.
This must also be true for the N2O-oxides grown below
1000 °C, since in that temperature range the N2O-oxide
growth rates approach the O2-oxide growth rates. The appar-
ent deviation from Arrhenius behavior exhibited by the
N2O-oxides is therefore probably due to a change in the pre-
exponential factor. The activation energy, reflective of the
oxide growth mechanism, appears to be unchanged for oxi-
dation in either O2 or N2O ambient.
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