1063-7397/02/3106- $27.00 © 2002 MAIK “Nauka /Interperiodica”
Russian Microelectronics, Vol. 31, No. 6, 2002, pp. 341–345. Translated from Mikroelektronika, Vol. 31, No. 6, 2002, pp. 403–407.
Original Russian Text Copyright © 2002 by Braginskii, Vasil’eva, Kovalev.
The spiral-antenna inductively coupled plasma
(ICP) source has become the major type of low-pres-
sure high-density plasma source for submicrometer-
technology applications [1–3]. It is characterized by
simplicity, scalability, and low ion energies. On the
other hand, its users are faced by difﬁculties with power
deposition, plasma stability, and generator–antenna
matching when operating at
Compared with ICP, helicon discharge exhibits bet-
ter stability at low pressures and a much higher electron
concentration at the same applied RF power [4–10].
These advantages are achieved despite fairly low mag-
netic ﬁelds employed (10–100 G). In addition, ICP
sources have the drawback that electromagnetic power
is deposited only into a thin plasma layer (a few milli-
meter thick) adjacent to the coupling dielectric window.
Accordingly, the wafer must be positioned close to the
window. Another consequence is that the plasma may
be contaminated with the sputtered material of the win-
dow. In a helicon source, electromagnetic power is
deposited into the entire plasma.
It is of interest to consider a design that combines
the successful geometry of spiral-antenna ICP sources
with a capability to generate helicon waves, with the
chamber immersed in a magnetostatic ﬁeld. This con-
cept was implemented by Stevens
. It has been shown that a reasonable
magnetic ﬁeld (< 100 G) can make the electron concen-
tration a few times higher for a given RF power.
This study is concerned with the experimental char-
acterization of a spiral-antenna helicon plasma source.
Figure 1 is a schematic diagram of the experimental
apparatus. The chamber has a diameter of 40 cm and a
height of 20 cm. RF power is coupled via a quartz plate
of diameter 22 cm and thickness 2 cm, which is placed
in a window at the top of the chamber. A four-loop spi-
ral antenna of outer diameter 18 cm is located above the
plate. A static and uniform magnetic ﬁeld is created by
two coils of diameter 40 cm spaced 20 cm apart. The
magnetostatic ﬁeld is aligned with the chamber axis,
and its ﬂux density can be varied between 0 and 60 G.
The antenna is driven at 13.56 MHz and 1 kW, via a
matching network. The chamber contains a movable
Langmuir probe and a movable magnetic probe. The
former serves to measure the axial and radial distribu-
tions of electron concentration. The magnetic probe is
meant for measuring the axial distribution of helicon-
wave amplitude, i.e., the amplitude of the
of the wave magnetic ﬁeld. The probe is made in the
form of a single loop of diameter 1 cm that lies in a
plane parallel to the antenna. The magnetic probe is
placed in a quartz tube that isolates it from the plasma.
Our measurements have shown that the tube reduces
the electron concentration by 10% at most. All the
experiments were carried out with argon at 3 mtorr.
RESULTS AND DISCUSSION
Figure 2 displays the plasma electron concentration
as a function of the applied magnetic flux density
in the range 0 to 50 G for different values of the applied
. The graphs were obtained with the Lang-
muir probe located on the plasma axis at 12 cm from the
coupling window. With low RF powers (100–350 W),
the electron concentration peaks for a certain
which the discharge becomes highly unstable in most
cases. Monotonic growth in
only at RF powers above 450 W. Speciﬁcally, the elec-
tron concentration for
= 500 W and
= 35 G is more
than twice as large as that for
= 0 and the same
Figure 3 presents
characteristics for different
with the Langmuir probe located on the chamber axis at
12 cm from the coupling window. One notices faint
variations in the concentration rate of change. For
500 W, the electron concentration at 22 G is twice as
high as that for zero magnetostatic ﬁeld.
Figure 4 displays
characteristics measured on
the plasma axis at 5, 10, and 15 cm from the coupling
held at 500 W. In the ﬁrst case,
Helicon Plasma Source
O. V. Braginskii, A. N. Vasil’eva, and A. S. Kovalev
Institute of Nuclear Physics, Moscow State University, Moscow, Russia
Received January 30, 2002
—A spiral-antenna helicon plasma source is characterized experimentally at applied magnetic ﬂux
densities below 60 G and applied RF powers below 800 W. It is shown that, for a given RF power, a magneto-
static ﬁeld applied to an inductively coupled plasma increases the electron concentration fourfold.