Reconstruction of the SiO
2
structure damaged by low-energy
Ar-implanted ions
B. Garrido,
a)
J. Samitier, S. Bota, and J. A. Moreno
EME, Departament de Fı
´
sica Aplicada i Electro
`
nica, Universitat de Barcelona, Diagonal 645-647, 08028
Barcelona, Spain
J. Montserrat
Centre Nacional de Microelectro
`
nica, CNM-CSIC, Campus Universitat Auto
`
noma de Barcelona, 08193
Bellaterra, Spain
J. R. Morante
EME, Department de Fisica Aplicada i Electro
`
nica, Universitat de Barcelona, Diagonal 645-647, 08028
Barcelona, Spain
͑Received 1 March 1996; accepted for publication 23 September 1996͒
The damage created in SiO
2
layers by low-energy Ar ions ͑130 keV͒ and the reconstruction of the
structure after various annealing steps have been characterized as a function of the implantation
dose. Quantitative determinations of the damage produced have been performed from infrared
spectroscopy. We show that two dose thresholds for damage are encountered: At 10
14
cm
Ϫ2
damage
saturates and for doses above 10
17
cm
Ϫ2
sputtering effects dominate. Annealing at high temperatures
͑1100 °C͒ restores the structure of the initial nonimplanted oxide only for doses below the second
threshold, although some disorder remains. Electroluminescence measurements show that annealing
is able to eliminate electrically active defects. For implantation doses greater than 10
17
cm
Ϫ2
,
annealing is unable to restore the structure completely as sputtering effects create a depleted oxygen
layer at the surface and substoichiometric defects appear. The presence of microcavities created by
the Ar atoms at such high doses may affect the annealing behavior. © 1997 American Institute of
Physics. ͓S0021-8979͑97͒02001-X͔
I. INTRODUCTION
Many studies have analyzed the effects of radiation dam-
age in SiO
2
/Si systems
1–6
as ion bombardment and other
types of radiation are applied during their manufacture.
Moreover, several techniques for surface analysis use ion
beams to measure physical and structural properties, such as
secondary-ion-mass spectroscopy ͑SIMS͒, x-ray photoelec-
tron spectroscopy ͑XPS͒, Auger spectroscopy, etc. These ra-
diation sources affect the structure, properties, and reliability
of the Si/SiO
2
system. Furthermore, doping through oxide
masks and modifications of SiO
2
etch rates are also under-
taken by using ion implantation techniques. Therefore, there
is an intrinsic interest in the basic and applied research re-
lated to the modifications of the structure in amorphous sol-
ids created by ion beams. In this framework, low-dose ion
implantation with Ar causes damage and disorder in the SiO
2
layer, but without changing the composition of the layer, as
Ar atoms cannot form stable bonds with the silicon or oxy-
gen atoms.
It is, therefore, essential to understand how the SiO
2
structure is modified after implantation, what kind of defects
are created and what annealing treatments can do to restore
the structure. The structural damage produced in the amor-
phous network of silicon oxide as a consequence of ion im-
plantation is characterized by strained and broken bonds, dis-
tortion of silicon tetrahedra, densification, departure from
local stoichiometry, and, in the case of irradiation with fast
heavy ions, plastic flow phenomena.
We have previously reported
5,7
that the damage pro-
duced by Ar ions in SiO
2
layers increases with the implan-
tation dose, for low doses; however, for doses higher than
10
14
cm
Ϫ2
damage saturates. Various authors have reported
similar behavior when other ions are implanted into silica.
This has been shown to be almost independent of the type of
ion implanted.
2–10
Moreover, Ar-implanted oxide layers have
presented a degree of densification after implantation.
5,7,11
Densification is accompanied by other structural modifica-
tions, such as Si—O bond straining and bond breaking, as a
consequence of atom displacement from positions of equilib-
rium. Indeed, Devine
4
has reported that the creation of de-
fects is greatly enhanced in densified amorphous SiO
2
,as
strained Si—O bonds act as precursors for both oxygen va-
cancy and nonbridging oxygen defects. Infrared spectra give
clear evidence of the reduction in the mean Si—O—Si bond
angle as well as of the presence of low-frequency vibrations
coming from Si—O nonbridging oxygen bonds.
5
The XPS
analysis of the local environments of silicon atoms per-
formed by the authors corroborated the presence of dangling
bonds and allowed their distribution as a function of the
damage created to be calculated.
5
Therefore, one expects ra-
diation damage to induce stable oxygen atom displacements
in the a-SiO
2
network.
In this framework, here we analyze the damage in SiO
2
following very high Ar implantation doses ͑Ͼ10
17
cm
Ϫ2
͒,
well above the threshold for damage saturation. We also re-
port the experimental annealing experiments performed at
different temperatures with the aim of restoring the structure
of the a-SiO
2
network.
a͒
Electronic mail: blas@iris1.fae.ub.es
126 J. Appl. Phys. 81 (1), 1 January 1997 0021-8979/97/81(1)/126/9/$10.00 © 1997 American Institute of Physics