23P002-O
Wire Temperature in Removal of Brass Platingon Surface of Saw Wire by Coaxial Magnetron Plasmas
同軸マグネトロンプラズマを用いたソーワイヤのブラスめっき除去処理中のワイヤ温度
Naoshi Matsuo1*, Yusuke Kobayashi1, Shin-ichiro Nishiyama2, Masanori Shinohara1
and Hiroshi Fujiyama1
松尾直志, 小林祐介，西山新一郎，篠原正典，藤山 寛
1Nagasaki University, 2Japan Fine Steel Co. Ltd,Nagasaki University, 1-14 Bunkyo, Nagasaki 852-8521, Japan*Tel: +81-95-819-2542, Fax: +81-95-819-2542〒852-8521 長崎県長崎市文教町1-14
DC coaxial magnetron plasma with triangle type electrodes has been developed to remove the brass plating on saw wire.
The temperature of fine saw wire has been measured during stripping process. Heating mechanism of saw wire during
the stripping process is discussed to keep the wire quality.

1. Introduction
A silicon wafer is produced with the thin slice ofthe crystal silicon rod by using saw-wire as shownin Fig.1. Brass (Cu: 65%, Zn: 35%) is plated on thesurface of saw-wire to make it long. In cutting
process of wafer by using the saw-wire, copper
atoms diffuses in silicon wafer and the electric
conductivity of the wafer changes. Therefore, it isnecessary to remove this brass plating. Wet processby strong acid was used as a conventional method
for removing the brass plating. However, thismethod is expensive and cause to negativeenvironmental problems. In the present research, theremoval method of brass plating on fine wires isproposed by a dry process using the DC coaxial
magnetron plasmas with triangle type electrode.
2. Experimental
The experimental setup of the electrode system
is shown in Fig.2. Three electrodes were made ofaluminum which set in the equilateral triangle to bea structure to pass the wire through the center ofgravity. Negative discharge voltage was applied tothe wire to grounded electrodes. DC coaxial
magnetron plasmas were generated by an axiallyapplied magnetic field. As a result, high density
plasma could be generated. The gap length between

electrodes and the wire was set 10mm, 20mm and30mm.

Fig.1 Saw wire

Fig.2 Electrode Structure

3. Results and Discussions
3.1 Stripping Effect
The experimental results of stripping effects
were successfully established by using high density
magnetron plasma source with 20mm gap in anaxially applied magnetic field.
Figure 3 shows the EDS analysis results of wire
surface after plasma stripping during 30sec. Here,the discharge voltage was -730V, the constantdischarge current density 1.5mA/cm2 and thedischarge gap length 20mm, respectively. In thisfigure, it is clearly shows that Zn was removed after10sec stripping and Cu after 30sec. (Fe:38.5%→97.7%，Cu: 39.3%→2.43%，Zn: 22.2%→0.03%)
Let us estimate the required running speed for
perfect removal of the brass plating. When thedischarge current density was 1.5mA/cm2, perfect
removal could be established after 25sec stripping.
Therefore the stripping rate was estimated as
8nm/sec=480nm/min. This means that the required
running speed of wire is 4.8m/min for full removal
in 2m reactor.
These results suggest that the rapid stripping offine wire is possible by using the developed triangle
type magnetron plasmas. For the higher target
voltage and current density to the wire, more rapid
stripping can be realized.
If the brass plating removal is assumed to finish
at 25sec., the sputter rate can be estimate to be480nm/min.; here the thickness of the brass platingof the saw wire is 200nm. In this condition, therequired winding speed of wire can be estimated to
0.5m/min for completely finishing of brass plating
removal in such plasma reactor of 2m in length.
The higher discharge current density may be able torealize the faster removal of brass plating on sawwire.
3.2 Wire Temperature
Wire heating during plasma stripping is aserious problem for keeping the wire quality. In thisstripping process, before wire heating up to 500℃,
perfect removal must be finished. So, high speed
but low temperature process is strongly required.
Figure 4 shows the temporal variation of wire
temperature measured by the electric resistivity
method for the current density 1.5mA/cm2. Whenthe higher magnetic field, that is, for the constantcurrent density, the higher target voltage leads to therapid heating of the wire. The heating mechanism
seems to be both Joule heating and ion kinetic
energy to the wire. So, the optimum condition
should be investigated.
4. Conclusions
The removal of brass plating on fine wire hasbeen tried by using newly developed triangle-typemagnetron plasma. It was confirmed that sputter
etching could decrease the mass percentage of brass
on wire surface at the stripping rate of 480nm/min
by using sputter etching process. Moreover, theoptimization conditions of the removal of brassplating were investigated to make the temperature
below 500℃.

Fig.3 EDS Analysis of Stripped Wire

Fig.4 Temporal Variation of Wire Temperature

Acknowledgments
This work has been supported in part by theregional innovation creation research anddevelopment business in MEXT.