23E02
Spatial Profile Measurement of High Energy Electrons near
Inductively Coupled Plasma Antenna by Optical Emission Spectroscopy
発光分光法を用いたICPアンテナ近傍の高エネルギー電子空間分布計測
Takumi Oike1, Tatsuo Ishijima2, and Hirotaka Toyoda1, 2
大池匠1, 石島達夫2,豊田浩孝1,2
1

Department of Electrical Engineering and Computer Science, Nagoya University, Nagoya 464-8603, Japan
2
Plasma Nanotechnology Research Center, Nagoya University, Nagoya 464-8603, Japan
1,2
名古屋大学大学院工学研究科 〒464-8603 名古屋市千種区不老町C3-1(631)

To investigate influence of electronegative gas introduction into an inductively-coupled plasma (ICP) onthe power deposition to the plasma, two dimensional profiles of Ar and He emissions from Ar/He/HBrplasma was investigated by a CCD camera with interference filters especially focusing on the variation inthe vicinity of the ICP antenna. From spatial variation of He/Ar emission intensity ratio, localization ofhigh-energy electron region in the vicinity of the ICP antenna was observed with introduction of HBr gas
into He/Ar plasma. This result suggests that introduction of HBr gas strongly changes power depositionto the plasma as well as load impedance of plasma source.

1. Introduction
Inductively-coupled plasmas (ICPs) arecommonly used in semiconductor fabrication
processes as one of high density processing
plasma sources to enhance productivity.
Mechanism of power absorption for the ICP iswell-known and density-jump of ICP has been
well explained from consideration of capacitiveand inductive couplings of the RF power [1].
However, the influence of electronegative gas to
the ICP is still not well known such as spatial
profile of negative ions and influence ofelectronegative gas on the power deposition to theICP.
In this study, behavior of ICP withelectronegative discharge gas such as HBr isinvestigated, especially focusing on variation ofpower absorption with use of electronegative
discharge gases.
2. Experimental
Figure 1 shows schematic of experimental
apparatus. A vacuum vessel of 33×33×33 cm3is evacuated by a turbo molecular pump (TMP) at abase pressure of 4×10-7 Torr. Ar, He, and HBr
are fed into the vessel through independent mass
flow controllers at total flow rates of 30~53 sccm
and total pressures (p) of 30~70 mTorr. Pressure
is controlled by a conductance valve between thevessel and the TMP. RF power (13.56 MHz,P<700 W) is coupled to the plasma through aone-turn antenna (11.5 cm in diameter). Lightemission from the plasma is monitored by a CCD

Quartz13.56 MHzAr,He,HBr

ICP
Antenna

PlasmaQMS
Orifice
10 cm

ND Filter
Interference
Filter
CCD
Fig. 1.

Pump
QuartzWindow

Schematic of experimental apparatus.

camera installed at the bottom of the vessel. To
investigate relative spatial variation of high-energy
electrons, spatial profile of He and Ar emissions aremonitored using interference filters. To investigate
dissociation of HBr, a differentially-pumped
quadrupole mass spectrometer (QMS) is also
attached to the vessel.
3. Results and Discussions
From mass spectrometric measurement ofAr/He/HBr plasma, mass peaks from 79 to 82
originated from Br isotopes of HBr79 and HBr81

Intensity (arb.units)

2(a)

Ar(b)

1(c)

HeIHe/IAr

0400

600
800
Wavelength (nm)1000
Fig. 3. Spatial profile of IHe/IAr in He/Ar/HBr
plasma at HBr flow rates of (a) 6 sccm, (b) 12 sccm,and (c) 18 sccm.

Fig. 2. Typical emission spectrumof Ar/He ICP plasma.

were clearly observed. During the discharge, anddissociation of HBr in the plasma was confirmed.
Figure 2 shows typical emission spectra of He/Ar
ICP. From these emission lines, we focus on a He
emission line of 587.6 nm (1s2p-1s4d) and a Ar
emission line of 750.4 nm (3p54s-3p54p). Upper
state energy levels of these emissions are 23.1 eV
and 13.5 eV, respectively. Emission intensities ofthese emissions (IHe and IAr) are expressed byfollowing formulae,I He  kHe (Te )[He]ne(1)

I Ar  kAr (Te )[Ar]ne .

(2)Here kHe, kAr are rate coefficients of electron-impact
excitations to upper levels, [He], [Ar] are densities
of He and Ar, ne is electron density. From theabove formulae, emission intensity ratio IHe/IAr isexpressed as

I He k He (Te )[He],I Ar
k Ar (Te )[Ar](3)

and this value becomes higher when high energy
electron component becomes larger in electronenergy distribution function (EEDF).
Figure 3 shows IHe/IAr spatial profile ofHe/Ar/HBr plasma (p=50 mTorr, P=500 W, QAr=10sccm, QHe=25 sccm) observed by the CCD camera
with interference filters. With increasing the HBrflow rate from 6 to 18 sccm, spatial variation
becomes enhanced with high IHe/IAr ratio in thevicinity of ICP antenna region.
This result
suggests that, by the HBr introduction, the mean
free path of high energy electron becomes
drastically shorter and the power deposition region
becomes smaller in the vicinity of the ICP antenna.
Figure 4 shows pressure dependence of IHe/IArspatial profile of He/Ar/HBr plasma (P=500 W,(a)(b)(c)
IHe/IArFig. 4. Spatial profile of IHe/IAr in He/Ar/HBr
plasma at total pressures of (a) 30 mTorr, (b) 50mTorr, and (c) 70 mTorr.

QHBr=12 sccm, QAr=10 sccm, QHe=25 sccm). The
result indicates that the spatial profile of IHe/IAr is
not drastically changed by the increase of the totalpressure by a factor of two, suggesting stronger
influence of the HBr addition than the pressure
increase.
4. Conclusions
An inductively-coupled plasma with usingelectronegative HBr gas was studied focusing on
spatial variation of high-energy electrons. 2-D
profiles of emission intensity ratio of He and Ar
were observed with a CCD and an interference filter
as a measure of the high-energy electrons. Strong
influence of the HBr on the spatial variation of thehigh energy electron was observed.
Reference[1] K. Suzuki, K. Nakamura, H. Ohkubo, H. Sugai:
Plasma Sources Sci. & Technol. 7 (1998) 13.