23G11
Gas-Phase Diagnostics andGlobal Model Simulation of BCl3-Containing Plasmas
BCl3混合プラズマの気相診断とモデリング
Shota Sato, Keisuke Nakamura, Yoshinori Takao, Koji Eriguchi and Kouichi Ono
佐藤聖太, 仲村恵右，鷹尾祥典，江利口浩二，斧 高一
Department of Aeronautics and Astronautics, Graduate School of Engineering, Kyoto University
Yoshida-Honmachi, Sakyo-ku, Kyoto 606-8501, Japan
京都大学大学院工学研究科航空宇宙工学専攻，〒606-8501 京都市左京区吉田本町
Etching characteristics of HfO2 have been investigated for BCl3 plasmas. The chemical compositions ofBCl3 plasmas are required to be clarified, to understand the etching mechanisms concerned. We carried out
plasma diagnostics using optical emission spectroscopy (OES), quadrupole mass spectrometry (QMS), andLangmuir probe measurements, and calculated the electron temperature and the particle densities by global
model simulations. The numerical results were consistent with the experiments to give us rough estimatesof BCl3 plasma compositions. The relationship between the etching mechanisms and plasma compositions
is discussed.

1. Introduction
As ULSI device dimensions continue to be scaled
down to tens of nanometers, efforts have been madeto replace gate silicon oxides and oxynitrides withhigh-dielectric-constant (k > 20) materials such as
HfO2, ZrO2, and their silicates and aluminates [1].
However, high-k dielectrics or metal oxides areusually difficult materials to etch, owing to strong
metal-oxygen bonds and less volatile metal-halogen
compounds; thus, the etch selectivity for high-k/Si
is not so high as to be employed in place of wet
etching, also owing to highly volatile halogen
compounds of Si. High-k dielectrics such as HfO2
are often etched by BCl3-containing plasmas [2−7],
because BClx species tend to form a relatively
volatile product, HfCl4, by breaking Hf−O bonds.
Previously, we demonstrated highly selective
etching of HfO2 over Si in electron cyclotron
resonance (ECR) BCl3-containing plasmas without
rf biasing [5−7]. For further understanding theetching mechanisms, the chemical compositions arerequired to be clarified in BCl3 plasmas. This paper
presents gas-phase diagnostics and global model
simulations of BCl3-containing plasmas.

cm in height, containing a 4-in.-diameter electrode(wafer stage). The discharge was established by
13.56-MHz rf powers of 400 W. The wafer stage inboth ECR and ICP was capacitively coupled to a
13.56-MHz rf power supply for additional rf
biasing (Prf < 50 W), where the wafer surface
temperature was maintained in the range 70−80°C.
In experiments with no bias (Prf = 0 W), the waferstage was under floating conditions, and nobreakthrough step was employed with additional
biasing. Feedstock gases were BCl3, Cl2, O2, and Ar
at total gas pressures of P0 = 1−20 mTorr with atotal mass flow rate of 40 sccm. Several diagnostics
were employed to characterize the plasma aroundthe wafer position: optical emission spectroscopy(OES), quadrupole mass spectrometry (QMS), andLangmuir probe measurements.
Moreover, we employed a well-mixed (zerodimensional) reactor model, or global model, toinvestigate the BCl3 plasma chemistry. In the model,
the electron temperature and the particle densities
were spatially averaged, and we took into account14 species (BCl3, BCl2, BCl, B, Cl2, Cl, BCl3+,
BCl2+, BCl+, Cl2+, Cl+, Cl−, Cl*, e) and 36 reaction

2. Experiment and Numerical Model
Etching was performed in ECR and ICP plasma
reactors, as shown in Fig. 1. The ECR was adivergent magnetic field type [5−7]; the specimenchamber was 36 cm in diameter and 40 cm inheight, containing a 6-in.-diameter electrode (waferstage) approximately 20 cm downstream from theECR resonance region. The discharge wasestablished by 2.45-GHz microwave powers of 600
W. The ICP was a planar coil type [8]; thespecimen chamber was 25 cm in diameter and 30(a)Quartzwindow

Microwave(2.45-GHz)

RF power(b)
Magnetic coils

3-turnplanar coilMatching (13.56-MHz)boxQuartz
window
PlasmaGas inlet

OES

Langmuirprobe

Gas inlet
Langmuirprobe

PlasmaOES
To pumpTo PumpSampleV

Oscilloscope

SampleMatchingbox
RF bias power(13.56-MHz)V

Oscilloscope

Matchingbox
RF bias power(13.56-MHz)

Fig. 1. Schematic diagrams of (a) ECR and (b) ICP
plasma reactors used in this study.

(a)

(a)

(b)
20mTorr(b)

20mTorr

20 mTorr

20 mTorr

5mTorr400
600
800
Wavelength (nm)1000

200400600800
Wavelength (nm)1000Fig. 2. OES intensities in (a) ECR and (b) ICP BCl3
plasmas at P0 = 1−20 mTorr.

processes. We calculated the electron temperatureand 13 species densities by solving 14 differentialequations (13 species continuity equations and aconservation equation of the electron energy),
where the electron density was calculated by using
the quasi-neutral law. The model assumed that theion and neutral temperatures were 300 K and theelectron velocity distribution was Maxwellian.
3. Results and Discussion
Figure 2 shows the OES intensities of ECR andICP BCl3 plasmas at P0 = 1−20 mTorr. In ECR
plasmas, B, BCl, and Cl were detected at lower P0,
while in ICP plasmas, B and Cl were not detected.
It is possible that at lower P0, the electron density
was higher in ECR plasmas, causing B and Cl to beformed through electron-impact dissociation ofBCl3 therein.
Figure 3 shows the QMS intensities of ECR andICP BCl3 plasmas with the ionizer off at P0 = 1−20mTorr. It is noted that BCl2+ was the dominating
ion species in both ECR and ICP plasmas, and thatB+ and BCl+ ions were also detected at lower P0 in
ECR plasmas.
Figure 4 shows the Langmuir probe measurements in ECR and ICP BCl3 plasmas at P0 = 1−20mTorr. The ion and electron densities at lower P0
were higher in ECR than in ICP plasmas, while thedensities at high P0 were lower in ECR than in ICP.
Figure 5 shows the electron temperature andparticle densities in BCl3 plasmas calculated by theglobal model simulation. Figure 5(a) shows that
BCl2+ was the dominating ion, which is consistentwith the QMS measurements in Fig. 3. On the otherhand, Fig. 5(b) shows that Cl is the most abundant
neutral radical species, followed by BCl and BCl2.
In the calculation, the densities of all species
increased with increasing pressure, while only theCl+ density decreased with pressure. This may be
explained by the effect of surface recombination ofCl atoms on the chamber walls.

020Intensity (arb. units)

5 mTorr

BCl2+BCl+4060 80
Mass

100 1200204060 80
Mass100 120

Fig. 3. QMS intensities in (a) ECR and (b) ICP BCl3plasmas with the ionizer off at P0 = 1−20 mTorr.
ne, ni (1010 cm-3) , Te (eV) ,Vp-Vf (V)20010 mTorr

1 mTorr

Cl+B+Cl B

(a)

20ni

10

Vp-Vf

Tene

00

510
15
Pressure (mTorr)

20(b)

20
15

Vp-Vf

10Te

5ni

ne

00

510
15
Pressure (mTorr)

20Fig. 4. Langmuir probe measurements in (a) ECR and(b) ICP BCl3 plasmas at P0 = 1−20 mTorr.
(a)

(b)

1013

61015
BCl3

BCl3+Density (cm─3)BBClx

5 mTorr

BCl2+15 mTorr

ne, ni (1010 cm-3) , Te (eV) ,Vp-Vf (V)BCl

1mTorrBClx

BCl

10mTorr

10 mTorr

5Cl+1012

4BCl+31011

2TeCl－11010

051015Pressure (mTorr)

200

Density (cm─3)

5mTorr

15mTorr

Temperature (eV)

10mTorr

Intensity (arb. units)

Intensity (arb. units)

Intensity (arb. units)

Cl1014

Cl

BCl2
BCl

1013

Cl2B

1012
1011

1010

0Cl*

5101520

Pressure (mTorr)

Fig. 5. (a) Electron temperature and densities of charged
species, and (b) densities of neutral species in BCl3plasmas calculated by the global model simulation(input power: 600 W, mass flow rate: 40 sccm).
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