23P003-O
Spectral Analysis of Sputtered Atoms by Optical Emission Spectroscopy
発光分光法によるスパッタ粒子のスペクトル解析
K. Miyazaki1, Y. Kobayashi2, N. Matsuo2, S. Nishiyama3, M. Shinohara1 and H. Fujiyama1
宮崎 清志1，小林 祐介2，松尾 直志2，西山 新一郎3，篠原 正典1，藤山 寛1
Graduate School of Engineering., Nagasaki Univ.1, Graduate School of Sci. and Technol., Nagasaki Univ.2
Japan Fine Steel, Co. Ltd.3
1-14, Bunkyo-machi, Nagasaki 852-8521, Japan1,2
1-19-1,Ishiide,Sanyo-Onoda 756-0063,Japan3
長大院工1，長大院生産2 〒852-8521 長崎市文教町1-14
ジャパンファインスチール3 〒756-0063 山陽小野田市石井手1-19-1
In order to detect the end-point of metal etching process, it has been observed the temporal variation ofcopper emission intensity in coaxial magnetron plasmas by OES (Optical Emission Spectroscopy). The
dependencies of Cu emission intensity on applied magnetic flux density, discharge current density anddischarge voltage have been investigated.

1. Introduction
In the wafer slicing process of solar cell
development, silicon wafers are carved out from asilicon ingot by saw wires. Saw wire is ultrafine
metallic line with about φ0.12 ～ 0.16 mm indiameter, that is covered with brass (Cu: 65 %, Zn:35 %) plating. This plating on wire is necessary inwire drawing process. However, copper which isbasis of brass plating is diffused in the silicon wafer
as contamination. As a result of the change ofelectric conductivity in wafers, it is caused
decreasing of power generation efficiency of solarcell. Therefore before using saw wires in slicing
process, it is necessary to remove the brass plating.
In the previous study [1], we could remove
successfully the brass plating from wire surface bycoaxial magnetron plasmas. According to the resultsof EDS analysis of wire surface after plasma
treatment (Discharge voltage: -730 V, Discharge
current density: 3.0 mA/cm2) during 30 sec, Zn wasremoved after 10 sec and Cu after 30 sec. (Fe:38.5 % → 97.7 %， Cu: 39.3 % → 2.43 %， Zn:22.2 % → 0.03 %) However the end-point of etchingprocess could not be detected on a real-time basis.
So in this study, we aimed to detect the end-point ofetching process from temporal variation of Cuemission intensity by OES.

3. Experimental
Cross sectional electrode structure is shown inFig. 1. It is called triangle electrode structure. To
generate coaxial magnetron plasmas, a brass rod
applied negative voltage was placed at the center
position of triangle. The gap length between
electrodes and a brass rod was set 29 mm.
Spectroscope (AvaSpec-2048 produced byAvantes) was used for spectral analysis, it bring infiber-optic cable with collimating lens (Confocallength: 8.7 mm) as shown in Fig. 2. The length
between target and lens was fixed to 10 mm.

Al TubeBrass Rod
Φ2 mm
Negative DC
Power SupplyFig. 1. Cross sectional view of electrode structure
Ar
SpectroscopeLens

2. End-Point Detection
Since Zn with low vapor pressure is vaporized byheat, we focused attention on Cu emission(especially 324.7 nm). If brass plating on wire
surface is removed, Cu emission should not be
detected. Thus we think of this point as the end-pointof etching process.

Fiber-Optic Cable

Brass RodFig. 2. Experimental setup

6000

Emission Intensity [a.u.]

5000

3000
2000
10000-1000
300

340360380400Fig. 3. Cu (324.7 nm) emissions from magnetron
discharge and DC discharge

300

Magnetic Flux Density : 337 Gauss
Gap Length : 29 mm
Pressure : 1.0 Pa
Gas : Ar

1 mA/cm2
2 mA/cm2
3 mA/cm2
4 mA/cm2

200

1000-100
323

323.5

324

324.5

325

325.5

326

Wavelength [nm]Fig. 4. Emission spectra as a parameter of discharge
current density
Discharge Voltage (337.0 Gauss)
Discharge Voltage (471.8 Gauss)
Cu Emission : 324.7 nm (337.0 Gauss)
Cu Emission : 324.7 nm (471.8 Gauss)

10008008006006004004002002000012345Emittion Intensity [a.u.]

1000

Discharge Voltage [V]5. Conclusion
Coaxial magnetron plasmas are used for etchingprocess, when we analyze spectrum of sputteredatoms, we found that emission intensity changes
come out with discharge current density. However
emission intensity wasn’t changing with magnetic
flux density and discharge voltage.
For the future, we will analyze emission of saw
wire as etching target, find out the temporalvariation of Cu emission intensity.

320

Wavelength [nm]𝐽𝑑 = 𝐴(𝑎𝑃2 + 𝑏𝐵2 )(𝑉𝑑 − 𝑉0 )3⁄2

This formula represents to generate the constantdischarge current density when three parameters(Gas pressure: 𝑃2 , Magnetic flux density: 𝐵2 ,Discharge voltage: 𝑉𝑑 3⁄2 ) are changed. Thus 𝐵 and
𝑉𝑑 are of little relevance to emission intensity, they
only have relevance to discharge current density.

Magnetron Discharge
Direct-Current Discharge

324.7 nm

4000

Emission Intensity [a.u.]

4. Results and Discussion
Figure 3 shows the optical emission spectra forboth DC discharge and magnetron discharge. The
experimental conditions for DC discharge arefollowings: Discharge voltage: -670 V, Discharge
current density: 0.65 mA/cm2 and Ar gas pressure:
20 Pa. On the other hand, the experimental
conditions for magnetron discharge are followings:
Discharge voltage: -550 V, Discharge current
density: 5.0 mA/cm2 and Ar gas pressure: 1 Pa. In
Fig. 3, it is clearly shown the stronger emission ofCu (324.7 nm) in magnetron discharge than that in
DC discharge. From the results of OES, it was foundthat the coaxial magnetron plasmas can effectively
sputter Cu atoms even for the low discharge voltage
condition.
Figure 4 shows the Cu emission spectrum as aparameter of discharge current density. Cu emission(324.7 nm) increased in proportion to the discharge
current density. Figure 5 shows that Cu emission is
proportional to the discharge current density andisn’t changing with the applied magnetic flux
density and the discharge voltage. Coaxial
magnetron plasmas are generated under thefollowing experimental formula [2].

0Discharge Current Density [mA/cm2]

Fig. 5. Cu emission intensity and discharge voltage vsdischarge current density
References[1] H. Fujiyama et al: Proc. of the 8th Asian European
International Conference on Plasma Surface
Engineering, Dalian (2011)[2] K.
Kuwahara
andH.
Fujiyama:
IEEE
TRANSACTIONS ON PLASMA SCIENCE Vol. 22,
No. 4 (1994)