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Dislocation-Point Defect Interaction Effect on Local Electrical Properties of Semiconductors
E. Yakimov
To cite this version:
E. Yakimov. Dislocation-Point Defect Interaction Effect on Local Electrical Properties of Semicon- ductors. Journal de Physique III, EDP Sciences, 1997, 7 (12), pp.2293-2307. �10.1051/jp3:1997102�.
�jpa-00249719�
Dislocation-Point Defect Interaction Elllect on Local Electrical
Properties of Semiconductors
E-B- Yakimov (*)
Institute of Microelectronics Technology Russian Academy of Sciences, Chernogolovka, 142432, Russia
(lleceived 3 October 1996, revised 10 September1997, accepted 16 September 1997)
PACS 61 72.Lk Linear defects: dislocations, disclinations PACS.71.55.-I Impurity and defect levels
Abstract. The results of investigations of dislocation effect on the Si electrical and opti- cal properties have been reviewed. The important role of dislocation-point defect interaction m the formation of dislocation properties has been demonstrated A short review of recent
investigations of clean dislocation properties has been presented. The results of investigations of dislocation related defect spatial distribution including dislocation slip planes have been dis-
cussed. The mechanisms of dislocation electrical activity formation have been analyzed.
1. Introduction
The effect of dislocation on the semiconductor properties has been studied for more than forty
years starting from the pioneering work of Gallagher [lj. Now the basic dislocation properties,
at least in Si, are well known. It was shown that a plastic deformation of Si led to a formation of donor and acceptor states [2j, to an inversion of conductivity type in n-Si [2-4j and to a
formation of dislocation p-n junction under an n-Si indentation [3j. The centers introduced in Si under a plastic deformation were studied by the Electron Paramagnetic Resonance (EPR)
spectroscopy [5,6j, Deep Level Transient Spectroscopy (DLTS) [7j, Photoluminescence (PL) [8j,
Electron Beam Induced Current (EBIC) [9j. The existence of electrostatic barrier near 60°
dislocations m n-Si has been proved and its height has been evaluated [10, llj. The band- like shallow dislocation related states were revealed by the Electric Dipole Spin Resonance
(EDSR) [12,13j. In highly deformed Si at temperatures lower than 700 °C the Fermi level was found [2, 3j to be pinned by a dislocation level at Ev + 0.45 eV. A similar value was obtained
from the measurements of dislocation barrier [10,llj that allowed to estimate the position of
Fermi level at a dislocation line (at least for the 60°-degree dislocations) as Ev + 0.45 eV if the dislocations were introduced at temperatures lower than 700 °C.
A dependence of the electrical properties of plastically deformed Si and Ge on the ther-
mal treatment conditions during the deformation or subsequent annealing has been observed
already in the first studies [2-4,14-16j that hardly could be explained without taking into ac- count the dislocation-point defect interaction. Nevertheless, starting from beginning of 50s and
* e-mail yakimovtlipmt-hpm ac.ru
@ Les #ditions de Physique 1997
for many years, the influence of dislocations on the electrical and optical properties of semi- conductor crystals was discussed on the base of Shockley's idea [17j assuming the existence of
dangling bonds in the dislocation core or taking into account shallow energy levels split from the bands. The situation changed when computer simulations showed that the dangling bonds in the dislocation core could be reconstructed [18,19j and that the intrinsic dislocation activity
could be very low. The EPR measurements [20j and the experimental investigations of sam- ples deformed in very clean conditions seem to support this idea [21,22j. Moreover the special
experiments carried out on the samples contaminated by transition metals revealed the strong impact of these impurities on the charge carrier concentration [2j, DLTS spectrum [23,24j, PL intensity [21, 25, 26j and dislocation EBIC contrast [23,27-31j in plastically deformed silicon.
Thus the essential change of dislocation properties due to the interaction with different im- purities is now well documented [20,32j and such interaction should be taken into account
almost in all cases. Nevertheless, up to now, a number of important questions such as: the
significance of intrinsic mechanisms of dislocation activity, the spatial distribution of disloca- tion related centers; the detailed mechanisms of dislocation electrical activity formation etc., have not been solved yet m spite of a great importance from both fundamental and practical points of view. The investigations of dislocation-point defect interaction allow to understand the origin of dislocation electrical activity, microscopic mechanisms of dislocation-point defect
interaction, fine structure of dislocation core Besides, the knowledge of detailed mechanisms of this interaction is necessary for the development of gettering procedures and for the control of electrical and mechanical properties of the semiconductors.
On the other hand, in spite of numerous evidences of essential point defect influence on the dislocation electrical and optical properties, practically in all PL investigations of plastically deformed Si, independently of crystal quality and impurity content, the characteristic spectrum consisting of four bands Dl-D4 [8j was observed. The DLTS investigations also revealed the
characteristic spectrum consisting mainly of four peaks in n-Si [33-35j and of three peaks
in p-Si [35,36j, although in some works other additional peaks were observed, especially in samples with a high dislocation density [7, 37j and the relation between the peak heights was
found to change in a wide range. Such independence (or slow dependence) of DLTS and
PL spectra on impurity content could be considered as an indication of intrinsic nature of dislocation energy spectrum. Therefore the conclusion about the dominant role of impurities
in the formation of dislocation electrical and optical properties and about the very low activity
of clean dislocations is not so obvious.
In the present paper the results of investigations of dislocation effect on the Si electri- cal properties have been reviewed. First of all the results demonstrating the importance of
dislocation-point defect interaction have been discussed. Then a short review of recent inves-
tigations of clean dislocation properties has been presented. Special attention is paid to the
investigations of spatial distribution of defects introduced under plastic deformation including
the dislocation slip planes. The important role of dislocation-point defect interaction in the dislocation electrical activity formation has been demonstrated.
2. Thermal Treatment Effect
As mentioned above, the dependence of dislocation electrical activity on thermal treatment conditions was revealed already in the first studies of dislocation properties. It was observed that annealing strongly affects the hole concentration in lightly doped plastically deformed Si
(Fig. I). An increase of temperature and/or duration of deformation or subsequent annealing
at temperatures higher than 750 °C led to a decrease of dislocation effect on the charge carrier concentration [2, 3j and to significant changes in the photoconductivity spectrum [2j. These
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.j1.00E+09 I«
I 1.00E+08 2
f
£ 1.00E+07
~
l.00E+06
600 700 800 900
Annealing tempeiatuie, C
Fig. I. The dependence of hole concentration in highly dislocated lightly doped n-Si deformed at 650 °C
on annealing temperature (annealing duration is I h). I Cz Si, 2 Fz Si
changes are shown to be well correlated with a decrease of dislocation related EPR signal ob- served in [5,6j. The dislocation EBIC contrast was found to change with annealing temperature
(as a rule it increases with the treatment temperature) and the temperature dependence was
found to depend on the impurity content [22,31j. The thermostimulated depolarization [38j
and DLTS [7, 33, 39,40j spectra intensity were also found to decrease with deformation or sub- sequent annealing. It was observed [38j that if the deformation temperature exceeded 1000 °C
no dislocation p-n junction was formed and the thermostimulated depolarization spectrum was
practically absent. But at higher deformation temperatures (l150-l190 °C) both p-n junc- tions and thermostimulated depolarization spectrum could be observed again if the samples
were quenched after the deformation. In the same temperature range, peculiarities in dislo- cation mobility were observed [41j that allowed to explain the results as due to a thermally
stimulated release of oxygen from dislocations.
The changes in dislocation properties can not be determined by the simple decrease of the dislocation density under annealing. They could be explained by the reconstruction of dislocations core or by annealing of deformation-induced point defects. But the dependence of annealing effects on impurity content shows that, even if the mentioned processes can take
place, the occurrence of the interaction between dislocations and impurity atoms is essential to understand the influence of thermal treatments on dislocation properties.
3. Interaction with Specific Impurities
3. I. INTERACTION WITH TRANSITION METALS. Dilfusivities of transition metals in Si are rather high at usual deformation temperatures. Therefore one could expect an unintentional
contamination of the samples under study during all thermal treatments. This is particularly
true for early experiments where the deformation cells usually contained metal parts. Therefore
as these impurities could determine to a great extent the properties of the deformed crystals, the investigation of dislocation interaction with transition metals is very stimulating. The other
motivation for such investigations is associated with their importance for the development of transition metal gettering procedures. The investigations of dislocation interaction with inten-
tionally introduced transition metal impurities demonstrated a pronounced effect of transition metals on the PL intensity (but not the PL spectrum). As shown in [25j low concentrations of Cu, Fe, Ni, and Ag increased the intensity of all D-bands but at metal concentrations higher
than about 10~~ cm~~ the D-band luminescence intensity decreased with an increase in the
impurity concentration. In [26j such effect was observed for copper only while Fe and Ni were found not to influence the D-band PL intensity. Cu~ stimulated quenching of D-band PL was
observed in [24j.
Copper contamination was found to effect also the EPR signal of Si-Kl centers, the depen-
dences of PL and EPR intensities on the copper concentration being anticorrelated [26j. This
allowed to explain the increase of D-band PL intensity by the Cu passivation of recombination
centers and the decrease of PL intensity at higher Cu concentrations by the enhanced excess
carrier recombination on Cu precipitates. The possibility of Cu passivation of dislocation re- lated deep levels was confirmed in [24j where the decrease of DLTS signal was observed after Cu contamination and in [2j where it was found that an interaction of dislocations with copper
decreased essentially the acceptor action of both defects
The EBIC investigations have shown [21,23,27-31,42j that Cu, Ni, Fe and Au increase the dislocation recombination activity. Gathering of gold was shown to increase the EBIC
contrast value and to change its dependence on annealing temperature but do not influence
the dislocation DLTS spectrum [23j. The increase of contrast in Au doped Si can be associated with precipitates formed in such samples near dislocations under annealing [42j.
3.2. INTERACTION WITH HYDROGEN. A number of papers was devoted to the investiga-
tions of dislocation interaction with hydrogen. This interest was stimulated by the well known
ability of hydrogen to passivate extended and point defects in semiconductor crystals [43j. As shown m [44j hydrogen indeed passivated the dislocation acceptor action and decreased the
intensity of dislocation PL. But the following investigations have shown that the hydrogen
treatment can decrease only the intensity of Dl and D4 bands but not that of D2 and D3 [45j
and even increase the intensity of all D-bands [46j. The observed difference in the hydrogen
effect can be determined by the different conditions of deformation and for hydrogen treatment or by the different dislocation state. As an example, it was shown [45j that the preliminary
Cu contamination essentially influenced the effectiveness of subsequent hydrogen passivation.
The DLTS and EBIC investigations have shown that hydrogen passivates the dislocation DLTS spectrum [32,47-49j and decreases the dislocation EBIC contrast [50j. But the mechanism of such passivation is not simple. Thus as observed in [49j, at room temperature hydrogen pene-
trated into the Si but not passivated dislocations. For the successful passivation it is necessary to increase the temperature up to about 300 °C.
3.3 OXYGEN EFFECT. Oxygen is one of the most important impurities in Si crystals. It. is present in all Si crystals and its concentration can be varied from 10~~ to more than 10~~ cm~~
depending on the growth method. Dislocation-oxygen interaction was shown to influence the dislocation mobility [slj and to lead to the formation of starting (release) stresses [51,52j, 1.e.
minimal stresses which is necessary to apply to bring dislocations in motion. It was shown [52j that oxygen can be collected by moving dislocations and its concentration in dislocation
atmospheres depends on the oxygen content as well as on parameters of dislocation motion.
The common way to reveal the oxygen effect on the dislocation electrical and optical proper-
ties is to deform Si samples grown by the Czochralski (Cz) and Floating Zone (FZ) techniques
in the same conditions and to compare the results, considering that the difference in oxygen
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1.00E+05
Dislocafion density, cm"~
Fig. 2. The dependence of increase in the electron concentration m Cz n-Si deformed at 700 °C
on
the dislocation density.
concentration in these two types of crystals can exceed two orders in magnitude. The results of such investigations have revealed the significant difference in the EBIC contrast of individual
dislocations and in its dependence on the electron beam current not only between the Cz and FZ Si crystals but also between Cz crystals with different oxygen content and between the
same samples deformed in the same conditions but cooled with different velocities [53j. The dislocation EBIC contrast in the Cz Si was found [32, 54j to depend on annealing tempera-
ture, with a minimum at 750-800 °C and with an increase at higher temperatures, that is in anticorrelation with the charge carrier concentration dependence (Fig. I) The oxygen effect
on the dislocation recombination activity was observed also under the LBIC measurements of minority carrier diffusion length in plastically deformed Si [55-57j
The dislocation effect on the charge carrier concentration in highly dislocated Si was found to be practically independent of oxygen concentration. Oxygen was observed only to enhance
slightly the annealing of dislocation acceptor centers at temperatures higher than 700-750 °C and to increase slightly the hole concentration (Fig I). On the other hand, in samples with low dislocation densities (ND < 10~ cm~~) the pronounced difference between the Cz and FZ samples have been revealed [52,58j. Whereas in FZ n-Si the electron concentration was
found to decrease monotonously with the increase of dislocation density, in Cz n-Si samples
the electron concentration was found to increase with dislocation density, i.e. shallow donors
were introduced m such samples under plastic deformation at temperatures higher than 700 °C [52, 58,59j. The concentration of these donors at small dislocation densities was found to be
proportional to the dislocation density (Fig. 2) and the major part of these donors was shown to be located near dislocations [52,58j. Moreover such donors were observed in the Cz samples only, that indicated the role of oxygen on their formation.
The influence of oxygen on the PL and DLTS spectra is not so pronounced. In most of the
investigations no or very small effect was observed. However in some recent studies carried out on samples with oxygen concentration higher than 10~~ cm~~ it
was observed that an increase of the deformation duration at 700 °C led to a decrease and even to total quenching of D-band
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o,oi
o.ois
~ contaminated
~ o.oi
°.°°~
clean X4°
0
80 120 160 200 240 280
Tcmpcmtum, K
Fig. 3. DLTS spectra of Cz p-Si (Na
= 10~~ cm~~) deformed at 650 °C
m the clean and metal containing cells. e
= 20.8 s~~
'
PL [60j. The DLTS spectrum was also found to vanish in the samples with very high oxygen
concentration although dislocations in such samples have a rather high EBIC contrast.
4. Investigations of Clean Dislocations
A development of methods for sample cleaning and for the control of low contamination level allowed to carry out the experiments with dislocations introduced in tie samples with
a
very low contamination concentration In this case, the dislocations presen/
no or very weak
D-band luminescence [25,26j. Clean dislocations were shown [31j to have very low recombina- tion activity which increased after the sample contamination. The investigations of dislocations introduced m the samples cut from the same crystals in the clean conditions and in deforma- tion cell made from steel by the DLTS have shown that the DLTS spectrum intensity in the clean conditions is more than two orders of magnitude lower than that in the unintentionally
contaminated samples (Fig 3). No DLTS signal is associated with "clean" partial dislocations in [61j.
The interesting possibility to introduce clean dislocations and to study the formation of dislocation related centers was d/monstrated in [22j. This possibility consists in decreasing
a distance covered by dislocations' and it could be predicted
on the base ofjinvestigations of starting stress dependence on dislocation velocity and on the dislocation pathqay. Such investi- gations have shown [52j that dislocation point defect atmospheres at low enough temperatures
are formed mainly by collecting impurities during the dislocation motion and therefore the
composition and state of these atmospheres depends not only on the deformation tempera- ture, impurity content and cooling conditions but also on the dislocation velocity and distance covered by dislocations. And indeed it was observed [22j that in FZ Si after h short deforma-
tion (10 min, stress 30 MPa) when a maximum distance covered by dislocations was about
20 pm, the DLTS spectrum of plastically deformed Si was identical to that (of control unde- formed sample, i. e. no deformation related DLTS spectrum was observed. Wi[h increasing the
FZ n-Si
~=40 mm
2 lo h
~
2 3 7 min
I x10
4 97 mjn
#
( Cz n-Si
~
~ 4
3 o
100 150 200 250
Tempemtum, K
Fig. 4. DLTS spectra of n-Si deformed at 600 °C. I- FZ Si, deformation duration tD is 40 min,
2 FZ Si, tD is 10 h, 3 Cz Si, tD is 7 mm, 4 Cz Si, tD is 97 min
deformation duration to 40 min (dislocation pathway was about 100 pm) the concentration of deformation induced centers increased (Fig. 4, curve I). It should be stressed that the spec- trum obtained in this case differed significantly from the usual one both by the shape and by
the intensity. The subsequent deformation of these samples during 10 hours under the lower
(20 MPa) stress (Fig. 4, curve 2) or annealing them at 600 °C during some hours resulted in
a DLTS spectrum identical to that usually observed on plastically deformed n-Si with a small dislocation density.
In Cz samples a similar dependence has been observed [62j but, contrary to FZ ones, in Cz Si
a weak but measurable DLTS spectrum was observed already after the very short deformation during 4 min. In Figure 4 the DLTS spectra of Cz sample deformed during 7 min (curve 3)
and subsequently during 97 min (curve 4) are shown. Already after 7 min deformation when the dislocation pathway was about 30 pm all four dislocation related peaks are present in the spectrum but their intensities are small. The two-step deformation during 97 min (Fig. 4,
curve 4) led to remarkable increase of dislocation related center concentration and the further
increase of deformation duration up to 8 hours did not practically influence the DLTS spectra.
This allows to conclude that the DLTS spectrum of Cz samples used is saturated when the dislocation pathway exceeds 250 pm while in the FZ Si for the DLTS signal saturation the dislocation pathway should exceed I mm. As noted above, the pathway for the usual DLTS spectra formation in the Cz samples was also a few times shorter than that in the FZ ones.
Subsequent annealing of samples with short dislocation loops was shown [22,62j to increase the DLTS spectra intensity but in some samples to reconstruct the spectrum to the form presented
by the curve 2 it was necessary to contaminate the samples by copper
The EBIC contrast of dislocations with a short pathway was found [63j to be very low in
both types of crystals. It should be noted that the DLTS and EPR signal dependence on
the distance covered by dislocations in the highly dislocated Si was observed in [64j where it
was explained by the intrinsic point defect creation during the dislocation motion and by a
formation of complex defects including these point defects.
