ISSN 10637397, Russian Microelectronics, 2011, Vol. 40, No. 8, pp. 553–558. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © M.V. Mezhennyi, M.G. Mil’vidskii, V.Ya. Reznik, 2010, published in Izvestiya Vysshikh Uchebnykh Zavedenii. Materialy Elektronnoi Tekhniki, 2010,
No. 4, pp. 4–10.
Added to silicon single crystals, nitrogen behaves as
a dopant to exert a powerful effect on the vacancies
and oxygen atoms in the lattice [1, 2]. It accelerates
the breakdown of an oxygen solid solution in silicon
and changes the pattern of defect formation under
multistage heat treatment that creates an internal get
ter in the form of a system of defects in the bulk of a
wafer [3, 4].
With Czochralskisilicon wafers 150–300 mm
across, an approach to making internal getters has
recently become popular; it relies on the sharp varia
tion of the rate of the breakdown with vacancy density
that is displayed by a supersaturated solid solution of
oxygen once the vacancy density has exceeded a criti
cal level of about 10
. Accordingly, a high
degree of control over the oxygen breakdown in a given
region can be achieved by creating an appropriate
depth profile of vacancy density in the wafer. For
example, setting the vacancy density to a value less
than the critical level throughout a subsurface layer
and to an appropriate, sufficiently high value else
where will prevent oxygen breakdown in the subsur
face layer while producing the desired density of get
tering centers in the bulk silicon as a result of the rapid
breakdown of the oxygen solid solution.
A desired density profile of vacancies is easily
formed by rapid thermal annealing (RTA) in argon at
a temperature above 1175
C . Subsequent heat
treatment by an appropriate temperature pattern
C for 4 h, 1000
C for 16–30 h) causes a great
number of oxide grains and related defects to appear in
the bulk while leaving a subsurface layer 60–80
thick almost defectfree . This process of getter for
mation has been shown to offer fundamental advan
tages over conventional techniques involving multi
stage annealing :
(1) It enables one to exercise strict control over the
density of oxide grains in the bulk material.
(2) Wafers can be made to contain a defectfree
subsurface layer of desired thickness.
(3) The resultant density profile of gettering centers
is little affected by variations in oxygen content in
wafers and is unaffected by the temperature history of
the original ingot.
(4) The process takes less energy and time.
The data in the literature on the effect of multistage
heat treatment, including RTA, on defect formation in
nitrogendoped silicon are scarce and inconsistent
[9–11]. A need therefore exists to investigate the for
mation of defects in such wafers as these are processed
to create an internal getter.
MATERIALS AND METHODS
The experiments were conducted on dislocation
free Si(100) wafers of diameter 200 mm from Czochral
skigrown ingots. Some wafers were left undoped and
served as control specimens. The others were doped
with nitrogen to a concentration of 1.6
type conduction with a resistivity of 10–
cm. The oxygen content was (6–7)
both types of wafer (calibration factor 3.14
InternalGetter Formation in NitrogenDoped DislocationFree
M. V. Mezhennyi
, M. G. Mil’vidskii
, and V. Ya. Reznik
Giredmet JointStock Company, Moscow, Russia
Institute for Research on the Chemical Aspects of Microelectronics, Moscow, Russia
—An experimental study is reported concerning the formation of defects in nitrogendoped dislo
cationfree silicon wafers under a multistage heat treatment to produce an internal getter, the first stage being
rapid thermal annealing (RTA) under different conditions. The experiments are conducted on pSi(100)
wafers of diameter 200 mm with an oxygen content of (6–7)
and a doping level of 1.6
the resistivity being 10–12
cm. The processed wafers are examined by optical microscopy and transmission
electron microscopy. With normal conditions of RTA (argon, 1250
C, 20 s), the process is found to be inca
pable of creating a defectfree subsurface layer of adequate thickness, though it is able to provide the desired
system of defects in the bulk. The aim is achieved by changing to sequential RTA in oxygen and argon as the
first stage. The reasons for the results are presented.
: dislocationfree silicon, microscopy, rapid thermal annealing, getter, heat treatment.
AND TECHNOLOGY: SEMICONDUCTORS