Pressure-induced transformations during annealing of silicon implanted with oxygen
Enhanced hydrostatic pressure (HP, up to 1.5 GPa) applied during annealing at up to 1570 K (HT) of silicon with oxygen introduced by implantation (Si:O), exerts pronounced effect on the transformation of oxygen admixture. In particular, HP affects the microstructure of Si:O and a creation of oxygen-...
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Донецький фізико-технічний інститут ім. О.О. Галкіна НАН України
2006
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| Cite this: | Pressure-induced transformations during annealing of silicon implanted with oxygen / A. Misiuk, B.M. Efros // Физика и техника высоких давлений. — 2006. — Т. 16, № 4. — С. 49-63. — Бібліогр.: 40 назв. — англ. |
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| citation_txt | Pressure-induced transformations during annealing of silicon implanted with oxygen / A. Misiuk, B.M. Efros // Физика и техника высоких давлений. — 2006. — Т. 16, № 4. — С. 49-63. — Бібліогр.: 40 назв. — англ. |
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| description | Enhanced hydrostatic pressure (HP, up to 1.5 GPa) applied during annealing at up to 1570 K (HT) of silicon with oxygen introduced by implantation (Si:O), exerts pronounced effect on the transformation of oxygen admixture. In particular, HP affects the microstructure of Si:O and a creation of oxygen-enriched (for implanted oxygen dose, D ≤ 1·10¹⁷ cm⁻²) or continuous (for D ≥ 6·10¹⁷ cm⁻²) buried SiO2 layers. Numerous treatment parameters contribute to the HP-induced phenomena in processed Si:O, among these are the HPaffected mobility and solubility of implanted oxygen as well as of silicon interstitials and of other implantation-induced defects and so the stability of oxygen clusters/precipitates; the misfit at the SiO₂/Si boundary is tuned by HP.
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Физика и техника высоких давлений 2006, том 16, № 4
49
PACS: 61.10.−i, 61.72.Yx, 81.40.Vw
Andrzej Misiuk1, B.M. Efros2
PRESSURE-INDUCED TRANSFORMATIONS DURING ANNEALING
OF SILICON IMPLANTED WITH OXYGEN
1Institute of Electron Technology
Al. Lotnikow 46, 02-668 Warsaw, Poland
E-mail: misiuk@ite.waw.pl
2A. Galkin Donetsk Physics and Technology Institute of the National Academy of Sciences
of Ukraine
72 R. Luxemburg Str., Donetsk 83114, Ukraine
Enhanced hydrostatic pressure (HP, up to 1.5 GPa) applied during annealing at up to
1570 K (HT) of silicon with oxygen introduced by implantation (Si:O), exerts pronounced
effect on the transformation of oxygen admixture. In particular, HP affects the microstructure
of Si:O and a creation of oxygen-enriched (for implanted oxygen dose, D ≤ 1·1017 cm−2)
or continuous (for D ≥ 6·1017 cm−2) buried SiO2 layers. Numerous treatment parameters
contribute to the HP-induced phenomena in processed Si:O, among these are the HP-
affected mobility and solubility of implanted oxygen as well as of silicon interstitials and
of other implantation-induced defects and so the stability of oxygen clusters/precipitates;
the misfit at the SiO2/Si boundary is tuned by HP.
1. Introduction
Single crystalline silicon grown by the Czochralski method (Cz-Si) is the most
important semiconductor used to produce integrated circuits (IC�s). Cz-Si contains
oxygen admixture in a concentration (cO) up to above 1·1018 cm−3. This oxygen
originates from SiO2 crucibles in which Si melts at about 1685 K under 105 Pa.
Oxygen is incorporated into Si mainly in the form of oxygen interstitials (Oi�s).
Part of oxygen is involved in a creation of complexes/clusters during growth or cooling
the Cz-Si rods. Silicon interstitials (Sii�s) and vacancies (V�s) are also involved in
growth and transformations of oxygen-related defects in processed Cz-Si [1].
Other kinds of silicon single crystals, grown by the floating zone method (Fz-
Si), with much lower oxygen content (cO < 1·1017 cm−3), are also used to produce
IC�s as well as another microelectronic devices.
During processing of Cz-Si under 105 Pa at enhanced temperature (HT), Oi�s
are subjected to transformations. At HT, when oxygen atoms become suffi-
Физика и техника высоких давлений 2006, том 16, № 4
50
ciently mobile, progressive clustering/precipitation of Oi�s occurs, being de-
pendent on cO, temperature and time (t) of processing, on the sequence of an-
nealing steps, etc.
Implantation of oxygen into Cz-Si or Fz-Si, to produce oxygen-implanted sili-
con (Si:O), is widely applied to produce silicon-on-insulator (SOI) structures by
the SIMOX method. Transformations of oxygen admixture in Si:O at HT remind
these in Cz-Si. However, important differences exist, among them are the follow-
ing: a) in effect of O+
2 implantation even with low dozes (D ≥ 1013 cm−2) and low
energies (E, in the tenths of keV range), the structural perfection of Si matrix be-
comes strongly worsened; partially or fully amorphized silicon (a-Si), is created,
especially near the O+
2 projected range (Rp), and b) local oxygen concentration
near Rp can reach, depending on D and E, tenths of atomic percents.
Annealing of Si:O at sufficiently high temperature leads first of all to restora-
tion of the structural perfection of the Si lattice [2] by solid phase epitaxial growth
(SPEG). Depending mostly on D and annealing temperature, spatially resolved
SiO2−x precipitates or even buried continuous BOX (buried silicon dioxide) layers
of dose-dependent composition and structural quality are created [3].
2. Fundamentals
Hydrostatic pressure (HP) up to about 1.5 GPa, applied in our research, is
about eight times lower than that resulting in the phase transformations of Si
(HP > 11 GPa) while it is of the same order as the stresses in the typical Si�O
systems applied in microelectronics (e.g. at the SiO2−x precipitate/Si matrix bound-
ary). The temperature-induced oxygen clustering and precipitation are concomi-
tant with stress [4,5], e.g. at the SiO2−x precipitate/Si matrix boundary (chemical
composition of silicon oxide forming precipitates is not stoichiometric, especially in
the case of small clusters with hardly defined boundaries). This stress is related first
of all to a larger volume of SiO2−x (in comparison to that of the host Si atoms)
formed by clustering oxygen. Other reason for internal stress is the difference in the
thermal expansion coefficients of SiO2−x [5] and of Si (a-Si in the case of Si:O).
This stress can be changed in the case of processing under enhanced HP of
ambient or of annealing under HP (HT�HP treatment) [6,7]. In effect of the
HP−HT treatment of Cz-Si with previously created oxygen precipitates, the misfit
(ε) and so the shear stress at the SiO2−x/Si boundary are changing; the same con-
cerns processed Si:O.
The shear stress and so the misfit (ε) at the SiO2−x precipitate/Si (or a-Si) matrix
boundary are affected [7−9] by HT and HP, exerted by ambient, in accordance with
2
2
SiO
0
SiO Si( -Si)
3
4
x
x a
K
K G
−
−
ε = ε + ×
+
( ) ( )2 2SiO Si( -Si) Si( -Si) SiO1/ 1/
x xa aHT HP K K
− −
× ∆ β −β + − , (1)
Физика и техника высоких давлений 2006, том 16, № 4
51
where ε0 − the misfit at the SiO2−x precipitate/Si (or a-Si) matrix boundary at 295 K
under 105 Pa; βSi(a-Si) and βSiO2�x
− coefficients of volume thermal expansion;
KSi(a-Si) and βSiO2�x
− bulk moduli; GSi(a-Si) − shear modulus (the bottom indices
denote the respective material), and ∆HT = HTexp − 295 K.
It means that the shear stress at the SiO2−x/Si (a-Si) boundary is changing (typi-
cally decreases) with HT and HP (for the case of Si−SiO2, according to [4,9], at 295 K:
KSi = 9.8·1010 Pa;
2SiOK = 4·1010 Pa; βSi ≈ 1.3·10−5 K−1; βSiO2
≈ 0.16·10−5 K−1;
GSi = 6.8·1010 Pa). For example, in the case of HP = 1.3 GPa applied at room tem-
perature, the HP-induced change of misfit at the SiO2/Si boundary, ∆ε (∆ε = ε � ε0),
can be estimated as equal to about −2.4·10−3 [10]. However, the values of K, G and
β are dependent on the kind of material (e.g. Si or a-Si, stoichiometry of SiO2−x,
etc), on temperature and pressure. These dependencies are not well known, espe-
cially for high temperatures and pressures. Still, the critical misfit value (εcr) for a
creation of extended defects (dislocations) at the SiO2/Si boundary (for the SiO2/Si
system), can be estimated as close to 1·10−3 [11]; this value is also dependent on the
precipitate dimension. Enhanced hydrostatic pressure induces ∆ε just within this
range and so affects generation of the misfit-induced defects (such as dislocations)
at the oxygen precipitate/Si (a-Si) matrix boundary.
The HP-induced effect on the misfit value is quite strong if compared to the
HT-induced changes. For the case of spherical SiO2 precipitates embedded in the
Si matrix, the equivalent (in respect of induced ∆ε) magnitudes of HT and HP can
be estimated [5] from:
( ) ( )2 2Si SiO SiO Si~ 1/ 1/HT HP K K∆ ∆ − β −β . (2)
In respect of the induced misfit and so of shear stress at the SiO2/Si boundary, the
effect of ∆HP ≈ 1 GPa is equivalent to ∆HT of about 1300 K.
«Additional» defects (for example, dislocations) at the SiO2−x/Si boundary are
created if the misfit at this boundary reaches the critical value for a creation of
particular kind of defect. As follows from eq. (1), the ε value decreases with HT
and HP for the Si matrix containing oxide clusters and precipitates (exerting com-
pressive internal stress on the matrix at ambient conditions), so (under not too
high HP) less numerous dislocations should be created in Cz-Si or in re-
crystallized Si in the case of Si:O treated under HT−HP.
As mentioned, creation of dislocations and of other defects at the SiO2−x/Si
boundary in Cz-Si or in Si:O during annealing or HT−HP treatment is dependent
also on the dimension of SiO2−x clusters/precipitates (less probable for small
clusters [11]) and on their stoichiometry (more probable for precipitates composed of
stoichiometric SiO2, while less � for clusters of substoichiometric composition).
Enhanced HP during annealing affects also the kind and number of nucleation
sites (NC�s) for clustering/precipitation of Oi, the rate of diffusion (mobility) of Oi
Физика и техника высоких давлений 2006, том 16, № 4
52
as well as diffusivity and stability of Sii�s and of vacancies created or involved
into the transformations of oxygen admixture.
Dependence of the diffusion coefficient of oxygen in silicon, D, on activation en-
ergy, Ea, and on pre-exponential factor, D0, is described by the well-known equation:
D = D0exp(−Ea/kT). (3)
Based on DLTS study of the dissolution of oxygen clusters/precipitates under
HP at 1230−1550 K, it has been concluded [12] that D in single-crystalline Si de-
creases by a factor of two if HP increases from 0.01 to 1 GPa. This effect has
been explained assuming that oxygen diffuses in the form of connected pairs of
oxygen atom and of Sii.
Oxygen atoms are not distributed uniformly in Si:O; even in as-grown Cz-Si they
create cloud-like irregularities resembling small oxygen clusters. At HT−HP such ir-
regularities can act as the nucleation centres for oxygen precipitation in Cz-Si or Si:O.
Pressure exerted upon the Si matrix affects the concentration of interstitials to
a considerable extent [13]. While HP acts on bulk silicon, the formation enthalpy
of interstitials increases by HP ∆VI (where VI is the value of the elastic volume
expansion susceptible to the HP effect on Sii). Therefore, under HP, the concen-
tration of silicon interstitials, Si ( )i HPC , can be formulated as:
Si ( ) Si ( 0) Iexp( / )
i iHP HP BC C HP V k HT== − ∆ , (4)
where Si ( 0)i HPC = is the concentration of Sii�s under 105 Pa (no external pressure
applied). It means that the concentration of Sii decreases under HP.
The formation energy (EV) for a vacancy in silicon equals ∼ 3 eV under 105
Pa. EV decreases almost linearly with pressure, by 1 eV for HP = 5 GPa [14].
Similar estimations were reported for a silicon divacancy (V2). A pressure reduces
the V2 formation energy by about 1.2 eV, from 4.2 eV at 105 Pa to 3 eV at 5 GPa.
It means that pressure exerts a relatively strong effect on vacancy formation in Si;
this is consistent with the reported effect of compressive stress on the dopant-
vacancy diffusion in silicon [15]. A decrease in the V and V2 formation energies
under HP can be attributed to reduced distances between Si atoms.
It is generally accepted that Sii in Si diffuses much faster than vacancy [16].
Diffusivity of dopant-interstitial pairs in a compressive medium decreases, while
that of dopant-vacancy pairs increases.
The formation of clusters of few oxygen and silicon atoms represents the first
stage of oxygen precipitation in crystalline or amorphous silicon [17]. Such clusters
can either grow or dissolve depending on their dimension, oxygen concentration,
temperature and so on. The most important parameter for nucleation of clusters is the
temperature dependent degree of oxygen supersaturation defined as the ratio between
the actual concentration of interstitial oxygen and its solubility limit (cOl) defined as:
cOl = Fexp(−∆Hs/kT), (5)
Физика и техника высоких давлений 2006, том 16, № 4
53
where F is the constant equal to 9·1022 cm−3 and ∆Hs = 1.52 eV is the dissolution
enthalpy.
Nucleation occurs in the regions where few Oi�s are close to each other (ho-
mogeneous nucleation) or at lattice defects (heterogeneous nucleation). Just ho-
mogeneous nucleation plays the most important role in the case of Cz-Si proc-
essed for microelectronic applications.
A very important parameter is the critical radius (rc) of NC, i.e. the limiting
value for sufficiently large NC to grow further upon annealing. Those NC�s with
r < rc will dissolve in the Si matrix while the larger ones grow further.
The rc value increases rapidly with temperature, especially for HT/HTs
p
> 0.7
(HTs
p
means processing temperature at which all available oxygen will be fully
dissolved in the matrix).
The critical radius of oxygen precipitates in Si depends on numerous parame-
ters [13,18]:
( )
1
3
O O Si Si2 (1 ) / ln / ( / ) /
i ic B HP V Vr xk HT V c c c c C C
−γ∗ ∗ β ∗ = σ + δ − Φ
, (6)
where cO, cV, and CSii
are the concentrations of Oi�s, V�s and of Sii�s in the silicon
crystal; the same symbols but with asterisk mean the equilibrium concentrations
of Oi�s, V�s and of Sii�s, respectively; kB means the Boltzmann constant; σ − the
interfacial energy per unit area; δ − the linear misfit between the silicon lattice and
SiO2−x precipitate; Φ − the constrained strain; VHP − the volume of SiO2−x pre-
cipitate; x � the number of oxygen atoms in SiO2−x precipitate; β − the number of
absorbed V�s, and γ − the number of injected Sii�s.
Based on eq. (6) one can conclude that decreased concentration of Sii�s leads
to the reduced value of rc. This would mean that smaller oxygen clusters or pre-
cipitates are expected to be generated in Cz-Si/Si:O if treated under HP and that
these clusters can be more stable under HT�HP [19].
While it is clear that HP influences a lot of Si (Si:O) parameters (such as lcO ,
∗
Oc , ∗
i
CSi and ∗
Vc ), affecting in turn the rc value, no analytical expression ex-
plaining the dependence of rc on HP has been proposed as so far (the quantitative
data are difficult to be extracted from eq. (6) also because the knowledge con-
cerning the values of numerous parameters in this equation and of their depend-
ence on HP, HT is lacking).
In the case of comparatively large oxygen precipitates, the misfit at the de-
fect/matrix boundary can reach the critical value for a creation of a defect of par-
ticular kind, so defects (dislocations, for example) are created at the SiO2−x/Si
boundary. The ε value decreases with HT and HP for Si (Si:O) containing oxide
clusters exerting compressive internal stress on the matrix at ambient conditions,
so less dislocations are usually created in Cz-Si treated at HT−HP.
Физика и техника высоких давлений 2006, том 16, № 4
54
3. Experimental details
To prepare Si:O, the 001 or 111 oriented Cz-Si or Fz-Si wafers were im-
planted with O2
+ (D ≤ 2·1018 cm−2, E ≤ 200 keV).
The Si:O samples were subjected to HT−HP treatments at up to 1570 K under
HP up to 1.5 GPa in argon atmosphere, usually for up to 5 h in a specially de-
signed high temperature−high pressure apparatus [20]. Sample cooling, from HT
to about 500 K, lasted for about 10 min.
Distribution of implanted oxygen in processed Si:O was determined by secondary
ions mass spectrometry (SIMS). Defects produced in Si:O at processing were re-
vealed by transmission electron microscopy (TEM). Photoluminescence (PL) spectra
were recorded at liquid helium temperatures using Ar laser excitation (λex = 488 nm).
4. Results and discussion
The effects of HT−HP treatment on Si:O are of interest for microelectronics.
This follows from the recently reported decreased formation of dislocations in
Si:O annealed under HP within the specific HT ranges, in comparison to the case
of annealing under 105 Pa [21]. Just dislocations exert most detrimental effect on
the SOI structures, especially on SOI produced by oxygen implantation (the
SIMOX structures).
In spite of considerable research effort [22−30], the understanding of the HT�
HP induced effects in Si:O is still far from being complete.
Impact of the HT−HP treatment on Si:O is dependent on the numerous implanta-
tion − (mainly on D and E) and treatment-related parameters (HT, HP and t) [23−29].
Most important is, however, the dose of implanted oxygen atoms. Below presented
results concern two most typical kinds of Si:O. The first one is represented by Si:O
prepared by implantation with D ≤ 1·1017 cm−2, with spatially resolved SiO2−x pre-
cipitates formed in effect of post-implantation processing and the second one − by
Si:O with semicontinuous or continuous SiO2−x layer created in effect of processing
(the case of Si:O prepared by implantation with D ≥ 6·1017 cm−2). The effect of HT�
HP processing on SOI with well defined BOX layers is also presented.
4.1. Effect of HT−−−−HP treatment on Si:O prepared by low dose implantation
Individual SiO2−x precipitates embedded in the Si matrix are created at proc-
essing of Si:O prepared by oxygen implantation with comparatively low O2
+ doses
(for the case of D ≤ 1·1017 cm−2) [20,22,24,26,27,29−34].
Annealing of Si:O (D ≤ 1·1017 cm−2) at 1230−1400 K under 105 Pa leads to a
creation of numerous extended defects (dislocations), originating from stress ex-
erted by SiO2−x precipitates on the Si matrix. The presence of dislocations is evi-
denced by TEM observations (Fig. 1,b) and by detection of the dislocation related
PL peaks, among them the D1 peak at about 0.81 eV for annealed/HT−HP treated
Si:O (Fig. 2).
Физика и техника высоких давлений 2006, том 16, № 4
55
a b
This means that the misfit at the
SiO2−x/Si boundary reaches the critical
value for a creation of dislocations at
SiO2−x precipitates with radii exceeding the
critical rc value (compare eqs (1) and (6)).
While just this mechanism of a creation of
dislocations seems to be the most impor-
tant in the considered case, it is not the
unique explanation of the effects observed.
Other mechanism of a creation of extended
defects (such as stacking faults, SF�s) in
Si:O at annealing/HT�HP treatment is re-
lated to the condensation of nonequilibrium
silicon interstitials emitted during growth
of SiO2−x into the Si bulk.
As follows from TEM images, the
treatment under HP at about 1270 K of
Si:O prepared by oxygen implantation with
D = 1·1016 cm−2 also leads to a creation of
dislocations (see Fig. 1,a). This is confirmed by the presence of D1 peaks at 0.81 eV
of comparatively high intensity in the PL spectra of Si:O processed under HP (Fig. 2).
In the case of processing at 1400 K, the intensity of these dislocation-related
PL lines definitely decreases with HP (Fig. 2). This means that the misfit at the
SiO2−x/Si boundary does not exceed the critical value for producing dislocations for
the majority of oxygen precipitates, with the radii still not reaching the critical values.
The same results from TEM data: dislocations are much less numerous in Si:O
processed for 5 h at 1400 K under HP (Fig. 3).
While about 250 nm thick near-surface zone in Si:O (D = 1·1016 cm−2) an-
nealed for 10 h at 1400 K under 105 Pa contains SiO2−x precipitates and disloca-
tions (see Fig. 1,b) located at about 0.5 µm depth, much less or even no disloca-
tions are detected in the case of treatment of these samples at 1400 K under 0.1 GPa
and, especially, under 0.6 and 1.2 GPa (compare Fig. 3,a with Fig. 3,b,c).
Fig. 1. TEM images of
001 oriented Cz-Si:O (E =
= 200 keV, D = 1·1016 cm−2),
annealed/treated for 5 h at
1230 K under 1.02 GPa (a)
and for 10 h at 1400 K un-
der 105 Pa (b)
Fig. 2. Relative intensity of D1 disloca-
tion-related PL line at 0.81 eV for 001
oriented Cz-Si:O (E = 200 keV, D =
1·1016 cm−2), processed for 5 h at 1270
K (1) and 1400 K (2) under different HP
up to 1.2 GPa
Физика и техника высоких давлений 2006, том 16, № 4
56
a b c
Fig. 3. TEM images of 001 oriented Cz-Si:O (E = 200 keV, D = 1·1016 cm−2), annea-
led/treated for 5 h at 1400 K under 0.1 GPa (a), 0.6 GPa (b) and 1.2 GPa (c)
a b c
Fig. 4. TEM images of 001 oriented Cz-Si:O (E = 200 keV, D = 1·1016 cm−2), an-
nealed/treated for 1 h at 1470 K under 1 GPa (a), under 1.5 GPa (b) and for 2 h at 1550 K
under 1.5 GPa (c)
Fig. 5. SIMS depth profile of oxygen in 001 ori-
ented Cz-Si:O (E = 200 keV, D = 1·1016 cm−2),
processed for 5 h at 1570 K under 0.01 GPa
(−●−), 0.6 GPa (−■−) and 1.2 GPa (−▲−)
Dislocations are practically absent
also in the case of Si:O samples (D =
= 1·1016 cm−2) treated for 1 h at 1470 K
under 1 and 1.5 GPa (Fig. 4,a,b). More
prolonged processing produces, however,
strongly disturbed area just at the sample
surface (Fig. 4,c). This is probably re-
lated to a very rapid SPEG process at
1550 K producing badly oriented Si
crystallites.
Физика и техника высоких давлений 2006, том 16, № 4
57
At 1400 K and at higher temperatures the implanted oxygen is subjected to partial
dissolution in the Si matrix (Figs 3,c, 4,c), probably entering the interstitial positions
(at these conditions the O�Si solid solution becomes undersaturated with oxygen).
As results from the SIMS depth profiles (Fig. 5), the concentration of oxygen
near Rp after processing for 5 h at 1570 K is strongly dependent on HP [27], evi-
dencing decreased solubility of oxygen in Si under HP or/and its decreased diffu-
sivity rate under HP. This observation contradicts the conclusions drawn on the
basis of theoretical calculations, suggesting rather a linear decrease of the diffu-
sion barrier with HP [35].
TEM images of processed Si:O samples containing the 10 times higher
amount of implanted oxygen (D = 1·1017 cm−2) are presented in Fig. 6.
Processing at 1400 K both under 105 Pa and 1.2 GPa as well as short time
processing at 1550 K under 1.5 GPa results in a presence of dislocations (Fig.
6,a−c). In the latter case the dislocation density is comparatively low (Fig. 6,c).
Dislocations were not created in the case of Si:O samples (D = 1·1017 cm−2) treated
for 5 h at 1570 K under 0.01 GPa (Fig. 6,d). Relatively large oxide precipitates, of up to
0.1 µm dimensions, are detected in Si:O treated at these conditions; numerous disloca-
tion loops are seen in the same samples treated at 1570 K under 1.2 GPa (Fig. 6,e).
a b c
d e
Fig. 6. TEM images of 001 oriented Cz-Si:O (E = 200 keV, D = 1·1017 cm−2), annea-
led/treated for 5 h at 1400 K under 105 Pa (a), 1.2 GPa (b) and for 15 min at 1550 K un-
der 1.5 GPa (c), for 5 h at 1570 K under 0.01 GPa (d) and 1.2 GPa (e)
Физика и техника высоких давлений 2006, том 16, № 4
58
The presence of dislocations in the Cz-Si:O sample treated at 1570 K under
the highest pressure is most probably caused by the «overcompensation» of the
«volume-related» misfit at the precipitate/matrix boundary (dependent on the dif-
ference of the relative volumes of Si and SiO2−x) by the «HP-related» misfit of the
opposite sign [29].
TEM observation concerning the HP-related decrease of dislocation density
has been confirmed by PL measurements. In Si:O prepared by oxygen implanta-
tion with D over the 1·1016�1·1017 cm−2 range and treated for 5 h at 1400�1470 K
under sufficiently high HP the intensity of dislocation-related D1 peaks at 0.81 eV
decreases with HP [23]. The treatments at ≤ 1400 K�HP, as well as at > 1400 K�
HP but of short duration, result, however, in the presence of dislocations.
The treatment of Si:O at temperatures close to the melting point of silicon re-
sults generally in disappearance of dislocation related PL while the PL lines at
about 1.1 eV, related to the interband transitions, become detectable. This con-
firms dissolution of oxygen clusters at so severe treatment conditions.
4.2. Effect of HT−−−−HP treatment on Si:O prepared by high dose implantation
Semicontinuous or continuous SiO2 layers (often containing Si inclusions) are
formed in Si:O prepared by oxygen implantation with sufficiently high doses (D ≥
≥ 2·1017 cm−2) and subjected to annealing at ≥ 1230 K (processing at ≥ 1550 K is
usually recommended). Some data concerning the effects of HT−HP treatment on
Si:O prepared by O2
+ implantation (D ≥ 6·1017 cm−2) are presented below (see also
[23−29,31,32,36−39]).
The as-implanted Fz-Si:O samples
(D = 6·1017cm−2, E = 170 keV) indicated
no PL peaks. Annealing of Fz-Si:O at
1230 K under 105 Pa results in weak
dislocation-related PL at about 0.81 eV.
The concentration of dislocations increases
with pressure in the case of HT�HP treat-
ment at 1230 K; this increase is not linear
with respect to HP [26]. Numerous non-
radiative recombination centers are cre-
ated in heavily oxygen implanted Si:O
annealed/treated at < 1230 K. Annealing
at 1470 K under 105 Pa resulted in rather
strong dislocation-related PL at about
0.81 eV; no dislocations were observed
after the same treatment but under 1.2 GPa.
The SIMOX-like structure prepared by
oxygen implantation into Fz-Si with D =
= 6·1017 cm−2, E = 170 keV and treated
Fig. 7. SIMS depth profile of oxygen in
111 oriented Fz-Si:O (E = 170 keV, D =
= 6·1017 cm−2), processed for 5 h at
1570 K under 0.01 GPa (−●−), 0.6 GPa
(−■−) and 1.2 GPa (−▲−)
Физика и техника высоких давлений 2006, том 16, № 4
59
for 5 h at 1570 K under 107 Pa�1.2 GPa, indicates the presence of well-defined
buried SiO2 layers (BOX); their widths are only slightly dependent on HP (Fig. 7).
The microstructure of the buried silicon dioxide layers in such samples re-
mains, however, to be strongly dependent on HT and HP (Fig. 8).
a b c
d
Processing of Si:O (D = 6·1017 cm−2, E = 170 keV) at 1400−1570 K results in
a creation of about 130 nm thick buried SiO2 layer (Fig. 8). Highly defected near-
surface zone of about 100 nm thickness has been created just above the SiO2/Si
interface after processing at 1400�1470 K (Fig. 8,a,b). The non-symmetric distri-
bution of defects on both sides of the BOX layers, is evidently related to the wors-
ened, in effect of implantation, perfection of near-surface Si layer, shot through by
implanted ions. The treatments at 1570 K but under 0.01 or 1.2 GPa produce the
buried SiO2 layer containing almost no inclusions. However, the 100 nm thick
disturbed zone with numerous microtwins is formed near the sample surface
(Fig. 8,c,d). The short time treatment at slightly different conditions produces the
well-defined BOX layer but still with numerous Si inclusions and microtwins cre-
ated near the surface [28,29].
The treatment at 1230/1400 K under 1.2 GPa of Si:O prepared by even higher
dose oxygen implantation (D = 1−2·1018 cm−2, E = 50 keV) leads to a creation of
well-defined continuous near-surface SiO2 layer. Numerous dislocations are cre-
ated in such samples; their density decreases with HT.
Fig. 8. TEM images of 111 oriented Fz-Si:O (E = 170 keV,
D = 6·1017 cm−2), annealed/treated for 5 h at 1400 K un-
der 1 GPa (a), for 1 h at 1470 K under 1.5 GPa (b), for 5 h
at 1570 K under 0.01 GPa (c) and 1.2 GPa (d)
Физика и техника высоких давлений 2006, том 16, № 4
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Processing of Si:O prepared by oxygen implantation with D = 1.1⋅1018 cm−2 (E =
= 50 keV) for 5 h at 1400 K under 1.2 GPa produces numerous precipitates of
about 20 nm diameter as well as dislocations just below a BOX layer. The treat-
ment of the same sample at 1570 K under 107 Pa resulted in a creation of the per-
fect BOX layer, while crystalline inclusions with propagating microtwins have
been detected within the BOX layer in Si:O processed under 1.2 GPa [29].
The microstructure of Si:O prepared by implantation with the highest oxygen
doses applied (D = 2·1018 cm−2, E = 50 keV) is also strongly dependent on HP
and HT applied during the treatments.
The treatment at 1230 K under 1.2 GPa produced dislocations propagating to
about 0.5 µm depth.
The similar treatment but at 1400 K of the same Si:O (D = 2·1018 cm−2, E = 50
keV) produced almost perfect BOX layer, with some irregularities (precipitates)
being still detectable at its bottom surface.
It is interesting to note that the HT�HP processing of the SOI structure pre-
pared by bonding (0.5 µm thick Si�0.4 µm thick SiO2�bulk 001 oriented Si) does
not affect the crystallographic perfection of such structure (Fig. 9).
a b c
Fig. 9. TEM images of 001 oriented SOI structures, annealed/treated for 5 h at 1570 K
under 0.01 GPa (a), 0.6 GPa (b) 1.2 GPa (c)
It follows that, in the case of SIMOX-like structures prepared by implantation,
especially with D ≤ 1·1017 cm−2, enhanced HP applied at processing affects
strongly the process of recrystallization of a-Si produced by oxygen implantation
and so the creation of buried SiO2 layer. Well-defined SiO2 precipitates are cre-
ated within the implantation-disturbed areas while much less dislocations and of
other extended defects are formed at the first stage of the HT–HP treatment. Un-
der the highest hydrostatic pressure, equal in our experiments up to about 1.5 GPa,
these precipitates remain to be fully or partially isolated even after prolonged
processing, so recrystallization of remaining a-Si can result in a creation of nu-
merous extended defects (such as microtwins and silicon precipitates), also within
the BOX layer.
Физика и техника высоких давлений 2006, том 16, № 4
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It is interesting to note that the HT−HP treatment of Si:O prepared by oxygen
implantation with D ≥ 1·1018 cm−2 at low energy (E ≤ 50 keV) results in PL also
in the visible light region, related to the presence of defects, probably of oxygen
deficient centers [40].
5. Conclusions
Processing of Si:O and related structures under enhanced hydrostatic pressure
results in the specific structural transformations.
The near surface oxygen-enriched layer in Si:O is strongly disturbed just after
implantation. The SiO2−x agglomerates are formed at processing, serving subse-
quently as the nucleation centers for further growth of oxide and, in the case of
sufficiently high doses of implanted oxygen, of the BOX-like SiO2 layer. Dislo-
cations at the SiO2/Si boundary are created if the misfit at the defect/matrix
boundary reaches the critical value for a creation of the particular defect kind. The
misfit value decreases with HT and HP for bulk Si containing oxide clusters or
precipitates (exerting compressive internal stress on the matrix at ambient condi-
tions), so less dislocations are created in Si:O processed at HT−HP. The creation
of dislocations and of other defects at the SiO2−x/Si boundary during annealing or
HT−HP treatment is dependent also on dimension of SiO2−x precipitates (less
probable for the smaller ones) and on their stoichiometry (more probable for stoi-
chiometric SiO2).
Numerous treatment parameters contribute to the HP-induced effects in
HT−HP treated Si:O, among them:
− mobility and solubility of implanted oxygen as well as of silicon interstitials
and of other implantation-induced defects (such as vacancies) are dependent on
HT and HP;
− stability of oxygen agglomerates is dependent on HP;
− the misfit at the SiO2−x/Si boundary is tuned by HP.
Some effects induced by the treatment of Si:O under enhanced hydrostatic
pressure raise hopes for its practical application.
The author thanks D. Sc. A. Barcz, Dr J. Ratajczak, and Mr M. Prujszczyk (In-
stitute of Electron Technology, Warsaw, Poland), Dr I.V. Antonova (ISP, RAS,
Novosibirsk, Russia), and m. sc. B. Surma (IEMT, Warsaw, Poland) for technical
assistance, experimental data and valuable discussion.
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|
| id | nasplib_isofts_kiev_ua-123456789-70257 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 0868-5924 |
| language | English |
| last_indexed | 2025-12-07T16:16:18Z |
| publishDate | 2006 |
| publisher | Донецький фізико-технічний інститут ім. О.О. Галкіна НАН України |
| record_format | dspace |
| spelling | Misiuk, A. Efros, B.M. 2014-11-01T16:03:01Z 2014-11-01T16:03:01Z 2006 Pressure-induced transformations during annealing of silicon implanted with oxygen / A. Misiuk, B.M. Efros // Физика и техника высоких давлений. — 2006. — Т. 16, № 4. — С. 49-63. — Бібліогр.: 40 назв. — англ. 0868-5924 PACS: 61.10.−i, 61.72.Yx, 81.40.Vw https://nasplib.isofts.kiev.ua/handle/123456789/70257 Enhanced hydrostatic pressure (HP, up to 1.5 GPa) applied during annealing at up to 1570 K (HT) of silicon with oxygen introduced by implantation (Si:O), exerts pronounced effect on the transformation of oxygen admixture. In particular, HP affects the microstructure of Si:O and a creation of oxygen-enriched (for implanted oxygen dose, D ≤ 1·10¹⁷ cm⁻²) or continuous (for D ≥ 6·10¹⁷ cm⁻²) buried SiO2 layers. Numerous treatment parameters contribute to the HP-induced phenomena in processed Si:O, among these are the HPaffected mobility and solubility of implanted oxygen as well as of silicon interstitials and of other implantation-induced defects and so the stability of oxygen clusters/precipitates; the misfit at the SiO₂/Si boundary is tuned by HP. The author thanks D. Sc. A. Barcz, Dr J. Ratajczak, and Mr M. Prujszczyk (Institute of Electron Technology, Warsaw, Poland), Dr I.V. Antonova (ISP, RAS, Novosibirsk, Russia), and m. sc. B. Surma (IEMT, Warsaw, Poland) for technical assistance, experimental data and valuable discussion. en Донецький фізико-технічний інститут ім. О.О. Галкіна НАН України Физика и техника высоких давлений Pressure-induced transformations during annealing of silicon implanted with oxygen Article published earlier |
| spellingShingle | Pressure-induced transformations during annealing of silicon implanted with oxygen Misiuk, A. Efros, B.M. |
| title | Pressure-induced transformations during annealing of silicon implanted with oxygen |
| title_full | Pressure-induced transformations during annealing of silicon implanted with oxygen |
| title_fullStr | Pressure-induced transformations during annealing of silicon implanted with oxygen |
| title_full_unstemmed | Pressure-induced transformations during annealing of silicon implanted with oxygen |
| title_short | Pressure-induced transformations during annealing of silicon implanted with oxygen |
| title_sort | pressure-induced transformations during annealing of silicon implanted with oxygen |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/70257 |
| work_keys_str_mv | AT misiuka pressureinducedtransformationsduringannealingofsiliconimplantedwithoxygen AT efrosbm pressureinducedtransformationsduringannealingofsiliconimplantedwithoxygen |