22P044-P
Research on Spatial Distribution Control of Radiation Electric Field
from Antenna in Microwave-Excited Plasma
マイクロ波励起プラズマにおけるアンテナ放射電界制御分布に関する研究
Naoki Tobita, Yasuyoshi Yasaka, Hiromasa Takeno
飛田直樹，八坂保能，竹野裕正
Dept. Electrical and Electronic Engineering, Kobe University
1-1, Rokkodai, Nada, Kobe 657-8501, Japan神戸大学大学院電気電子工学専攻 〒657-8501 神戸市灘区六甲台町 1-1
In the manufacturing process of semiconductors, plasma processing is an essential technology, and the plasmaused in the process is required to be of high density, high uniformity, and large diameter. This research
focuses on the microwave-excited plasma as a plasma source that meets these needs, and the research target isa spatial distribution control. The authors have investigated to control the radial distribution of the plasmas in
the experimental device with the multi-slot planar (MSP) antenna with a double coaxial feeder. In the paper,
results of the plasma distribution control experiment are presented.

1.Introduction
In the manufacturing process of semiconductors, plasma processing is an essentialtechnology, and the plasma used in the process isrequired to be of high density, high uniformity,
and large diameter. We are developing a plasma
production device which can adjust plasma
distribution freely from the outside as one of thetechniques of solving the requirement.
In this research, to control freely the radial
distribution of the microwave plasmas, a novel
antenna system using a double coaxial feeder has
been developed. It has a function that themicrowave can be separately radiated from theradial inside and outside of the antenna by using
two microwave sources. In addition, this device isdesigned so that microwave can be extensively
radiated using the MSP antenna[1,2]. The device
has the advantages that the mode spectra of theelectric fields radiated from the MSP antenna
exist in the limited region due to the effect of themulti-slots, and the mode depends not on
eignmodes deternimed by the plasma but on thestanding waves formed in the antenna cavity.
The purpose of this research is to clarify
control performance of the radial distribution of
the microwave plasma by a double coaxial feeder,
using plasma production experiments, numericalcalculation and simulations.
.
2.Experimental Setup
Figure 1 shows the experimental setup for theplasma production by a double coaxial feeder. It

consists of two microwave sources, two directional
couplers, two power monitors, two three-stub tuners,
a double coaxial waveguide, an unique antenna
cavity, the MSP antenna[1,2], a quartz window, anda plasma chamber. The microwave driven at 2.45
GHz excited from the microwave source 1 propagates in the rectangular waveguide via the TE10mode and is supplied to the inner coaxial waveguide.
In the same way, the microwave excited from themicrowave source 2 is radiated from the outside ofthe MSP antenna. In the coaxial waveguides, themicrowave propagates via the TEM mode. Then, it
is transferred to the TM mode in the antenna cavity
and is radiated from the MSP antenna. The aim ofthe double coaxial feeder is to adjust the radial
distribution of the plasmas by controlling the power
ratio of the microwave sources 1 and 2.
(1)
3-stubtuner

power
monitordirectional microwave
sourcecoupleroutercoaxial waveguide(2)

quartz window
55 mm
Ar gasmetal separator
antenna cavity
multi-slotted planar(MSP) antenna

Langmuir probe
500 mm

RPTMP

fast scanningsystem

CCD camerastageto monitor & PC

Fig.1. Experimental setup for plasma production.

1405(a)31.0 mTorr
47.1 mTorr
80.5 mTorr

43212011008060
40
20000.0

Pin= 450(150) W
Pin= 350(110) W
Pin= 290(100) W

Ar,31.0 mTorr, 66 sccm
Pout,2=180(20) W
051015
radial position r (cm)

0.5

1.0
1.5
Pin / Pout

2.0

2.5

3.0

5.0(b)
20

31.0 mTorr
47.1 mTorr
80.5 mTorr

25Fig.2. The dependence of radial distribution of Jis onPin,1.

It shows that Jis near the center increase byincreasing Pin,1, and Jis on 15≤ r ≤20 cm hardly
changes by increasing Pin,1.
Figures 3(a) and 3(b) show the dependence ofthe plasma uniformity and the gradient in theradial distribution on the power ratio (Pin,1/Pout,2),
respectively, where the value is for Jis in r ≤ 15
cm. Here, pAr = 31.0, 47.1, and 80.5 mTorr. The
plasma uniformity of Jis is calculated byσ(Jis)/(2×ave(Jis))×100 %, where σ(Jis) andave(Jis) represent the standard deviation, and average values, respectively. The gradient is calculated by (Jis(15)–Jis(0))/(Jis(15)+Jis(0))×100 %.
In Fig. 3(a), the radial distribution uniformity isimproved by increasing the power ratio, and theplasmas with the best uniformity are producednear Pin,1/Pout,2 ≈ 1.0 – 1.5 for various pAr. The
uniformity becomes worse when the power ratio
is increased further. It shows that the plasmas
with good uniformity in the radial distribution canbe produced for a wide range of pAr by using thedouble coaxial feeder. In Fig. 3(b), the radial
distribution of the plasmas changes from upwardslant to the right to downward slant to the right byincreasing the power ratio. It shows that the radial

2.5

gradient of Jis (%)

2ion saturation current density Jis (A/m )3.Results
Figure 2 shows the dependence of the radial
distribution of the ion saturation current density
Jis on the incident microwave power from thesource 1 Pin,1. Here, Pout,2 is fixed to 180 W. The
other plasma production conditions are Ar gas
pressure pAr = 31.0 mTorr, and flow rate QAr = 66
sccm. Also, in the graph, parenthetic values forPin,1 and Pout,2 represent the reflected power.

distribution of plasmas can be adjusted in various
pAr by adjusting the power ratio.
Therefore, it is concluded that the microwave-excited plasma device with the double
coaxial feeder has a function that the radial
distribution of the plasma parameters can becontrolled by the power ratio from the microwave
source 1 and 2.

uniformity (%)

Ar gas is used to produce the plasmas, and thepressure pAr in the chamber is kept constant. The
radial distribution of the plasmas is measured by aLangmuir probe set at a fast scanning system.

0.0-2.5

-5.0
0.0

0.5

1.0

1.5
Pin / Pout

2.0

2.5

3.0

Fig.3. The dependence of the plasma parameters on
the power ratio: (a) uniformity and (b) gradient.

In addition to plasma distribution control
experimental result, the results of an investigationby the numerical calculation and simulation, will bepresented.
References[1] Y. Yasaka, K. Koga, N. Ishii, T. Yamamoto, M. Ando,and M. Takahashi: IEEE Trans. Plasma Sci. 32(2002) 1029.
[2] Y. Yasaka, N. Ishii, T. Yamamoto, M. Ando, and M.
Takahashi: IEEE Trans. Plasma Sci. 32 (2004) 101.