1063-7397/02/3105- $27.00 © 2002 MAIK “Nauka /Interperiodica”
Russian Microelectronics, Vol. 31, No. 5, 2002, pp. 290–294. Translated from Mikroelektronika, Vol. 31, No. 5, 2002, pp. 344–349.
Original Russian Text Copyright © 2002 by Kovalevskii, Malyshev, Tsybul’skii, Sorokin.
With submicrometer feature sizes, good selective
etching is vital to the yield, reliability, and service life
of product. This paper is concerned with the following
problem. It is difﬁcult to insure high-quality metalliza-
tion in VLSIs if contact windows have vertical side-
walls, although some success can be achieved by using
bump contacts, reﬂowing the metal, etc. Therefore,
techniques have been devised to produce oblique side-
walls [1–8]. Many IC manufacturers, such as Motorola,
Harris, TI, or MAXIM, do this by both isotropic wet
and anisotropic dry etching. The word
that the lateral etch rate is equal to the vertical one. The
downside of the strategy is that it consists of many steps
involving different types of equipment, so that more
defects may arise. Another approach is to employ only
dry etching in the form of two concurrent processes:
isotropic and anisotropic [4–8].
This experimental study addresses the isotropic dry
etching of SiO
ﬁlms in the context deﬁned above.
EXPERIMENTAL CONDITIONS AND RESULTS
The etching of SiO
ﬁlms was performed with an
Otello-43 inductively coupled plasma etcher. The appa-
ratus is capable of generating a ﬂuorine-radical concen-
tration large enough to provide an etch rate of
m/min or higher, depending on the material.
The ﬁlms were thermally grown to thicknesses of
m. We employed a 1.5–2.0-
mask and a 0.54-
m aluminum mask, the former baked
at 383 K. The proﬁle shape and trench depth were
examined with a Stereoscan-360 SEM, ﬁlm thickness
was measured with an LEM-2 laser ellipsometer, and
defect density was evaluated with the Surfscan-4500
using an IO-24 illuminator.
To obtain oblique sidewalls of contact windows, one
has to appropriately decrease the action of ions on the
surface under treatment, which implies raising the total
pressure to a level above 100 Pa and reducing the RF
power. In addition, the vacuum chamber should be as
large as possible, with the electrode edges being at dis-
tances of 10 cm or more from the walls.
Under the stated conditions, plasma etching is
effected by chemical reactions of ﬂuorine atoms and
free radicals with SiO
at the surface. If we take an
-containing etchant as an example, etching con-
sists of these steps:
the formation of product molecules,
the desorption of product molecules,
and the removal of the residue,
+ 4F SiF
With isotropic etching, the above mechanism is
enhanced by ion bombardment, though weak, since this
causes the dissociation of neutral molecules and radi-
cals adsorbed, so that reactive species (e.g., ﬂuorine
atoms) arise and make bonds to Si with no migration
over the surface.
Isotropic etching enables one to produce contact
windows with oblique sidewalls in SiO
or other mate-
rials. In this case, the etch rate and proﬁle are deter-
mined by the total pressure of the gas mixture, the par-
tial pressures of its components, their relative ﬂow
rates, the holder temperature, and the RF power.
The experiment was conducted with an
plasma at an SF
partial pressure of 50 Pa, an RF power
of 500 W, and a holder temperature of 358 or 313 K.
The total pressure
was varied from 100 to 500 Pa.
The resultant etch-rate characteristics are represented
in Fig. 1.
is below 250 Pa, the rise in etch rate obviously
stems from the decrease in the concentration of free
Isotropic Plasma Etching of SiO
A. A. Kovalevskii, V. S. Malyshev, V. V. Tsybul’skii, and V. M. Sorokin
Belarussian State University of Information Science and Electronics, Minsk, Belarus
Received September 20, 2001
—The isotropic etching of SiO
with an SF
plasma is studied experimentally. It is shown that the
key factors in the process are the total and partial pressures of SF
and the RF power. A smoothed-down
edge proﬁle of contact windows is obtained if SF
are mixed in a ratio of 1 : 10 to 1 : 5. The maximum
etch rate is achieved at total pressures of 250 to 450 Pa.