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Long life plasma filament type ion source
Nuclear
140
Instruments
and Methods
in Physics
Research
B37/38
North-Holland,
LONG LIFE PLASMA FILAMENT R. FUKUI, 0-Prqect,
IL TAKAGI,
ULNA C JAPAN,
(1989) 140-142 Amsterdam
TYPE ION SOURCE
T. TSUGUEDA,
Ltd., 2500 Hagisono,
H. TSUBOI and R. KIKUCHI
Chigaraki,
*
Kanaga~,a, 253, Japan
E. YABE and K. TAKAYAMA Research and Development Kanagawa, 259-12, Japan
A plasma filament ion source, a plasma filament lifetime of this ion source current of 2.5 mA can be
Institute
and Department
of Physics, Tokai University,
III 7-Kitakaname,
Hiratsuka,
source has been developed as a long lived ion source for use in ion implantation and deposition. In this ion serves as a cathode in place of a thermionic tungsten filament such as used in the Freeman ion source. The was found to be 45 h with a Pf ion current of 2 mA. A stable As+ ion current of 9.1 mA and O+ ion obtained. The running test results of this ion source applied to the implanter are reported in this paper.
1. ion source In the plasma filament ion source, whose operational principle has been already reported in many papers [l-3], a plasma filament serves as a cathode in place of a thermionic tungsten filament such as used in the Freeman ion source 141. The ion outlet slit size on the arc chamber is 3 mm x 30 mm. The cathode in the plasma generator is made of 0.6 mm0 tungsten wire. A schematic diagram of the experimental apparatus is shown in fig. 1. The apparatus consists of an ion source, an analyzing magnet and a growth chamber. The ion beam current is measured by a Faraday cup in the growth chamber.
WTH CHAMBER
2. Results ION SOURCE
The test data of the cathode life in the plasma generator is shown in fig. 2. Argon gas is used for discharge in the plasma generator and PH, gas is fed to the arc chamber for the main discharge. The discharge current in the plasma generator (Zps) is 1.5 A, and the main discharge current (Zi,) is 1.5 A. An extraction voltage (V,,) of 40 kV is applied. The lifetime of this ion source was found to be 45 h with a Pt ion current of 2 mA. The lifetime of the plasma filament ion source is several times longer than the Freeman ion source whose lifetime is said to be about 8 h. The mass spectrum of ions produced by a combination of the argon plasma filament and ASH, feed gas is
* Present address: Faculty of Science, Konan Higashinada, Kobe, Hyogo, 658, Japan.
University,
0168-583X/89/$03.50 0 Elsevier Science Publishers (North-Holland Physics Publishing Division)
B.V.
Fig. 1. Schematic diagram of the experimental apparatus.
shown in fig. 3. In this spectrum, an analyzed As+ ion current of 9.1 mA is obtained, and the ratio of the As+ ion current to the total Faraday cup current reaches 94W, where the discharge current of the plasma generator is 0.8 A and that of the arc chamber is 1.7 A. An extraction voltage of 40 kV is also applied. Fig. 4 shows the mass spectrum of ions produced by a combination of the argon plasma filament and BF, feed gas. In this spectrum, an analyzed “Bf ion current of 2.1 mA is obtained and the ratio of the r’B+ ion current to the total Faraday cup current reaches 29%. Whenever BF, gas is used, several kinds of ions are produced other than t’B+ such as “B+, Ar+, Ar’+,
141
R. Fukui et al. / Long life plasma filament type ion source
Ipg ~20
I<.~20
A
Gas PI : OGsccm Gas Is r 1.2 seem V..
E z
= 15 A Y.. Ix .40
15
E 20 i
Gasp,
‘0
10
ICI .200mA, seem
20
Ar 30
~08
40
02 =28mA
seem
50
PFs 60
70
80
90
100
( hour )
Fig. 2. The test data of the cathode
life in the plasma
generaFig. 5. Mass spectrum of ions produced by the combination the argon plasma filament and the 0, feed gas.
10 IpgzO.8 GX Gas V..
A
, I,.
~17
seem
Ar
13 = 19
~ccm
ASH?
=40kV,
1..=221mA
“B’
Fig. 3. Mass spectrum of ions produced by the combination the argon plasma filament and the ASH, feed gas.
than
and
F+.
The
in the case
1,s-3OA
IN=lOA, Gasog BF2’
BF;
of
A
pg -04
“B.
smaller
le.
1~.=20mA Gas,.
time
BFf,
kV,
11s = 15 A
kV ~04
~40
A
Ar
ratio of As+
of the “B+
ion
of
F.
BF.
k
d
I,
-0
I seem
Gas I, 2 0 7 sctm V..
z 33 kV,
Ar BFx
ICI-77
mA
Ar’ h,
MASS
is then
ion extraction.
mass spectrum of ions produced by a combination of the argon plasma filament and 0, feed gas is depicted in fig. 5. In this spectrum, an analyzed O+ ion current of 2.5 mA is obtained and the ratio of the O+ ion current to the total Faraday cup current reaches 54%. The plasma filament ion source is mounted and tested on the implanter ULVAC model IMM-2200 [5]. The mass spectrum of ions produced by a combination of the argon plasma filament and BF, feed gas is shown
Fig. 6. Mass spectrum of ions produced by the combination of the argon plasma filament and the BF, feed gas when this ion source is mounted on the implanter.
The
3.0
i
LDD = 1.0 A
, 1,s=2.5
Gas pp =04
seem
Gas V..
81 E 1.0 seem =40kV,
A
in fig. 6. In this spectrum, an analyzed ‘iB+ ion current of 150 ~.LAis obtained and the ratio of the i’B+ ion current to the total Faraday cup current reaches 34%. The Freeman ion source produces usually about 20% i’B+ ions. Therefore the plasma filament ion source is a high efficiency ion source for i’B+ ions. Fig. 6 presents the test result when this ion source is applied to a medium type implanter, and fig. 4 gives the result when it is applied to a high current implanter test bench. Therefore, there is a great difference between fig. 4 and fig. 6 in peak current level and spectrum pattern.
Ar BF,
ICI~24.4
Fig. 4. Mass spectrum of ions produced by the combination the argon plasma filament and the BF, feed gas.
3. Conclusion
,,,A
of
It was confirmed that the plasma filament ion source can produce a stable ion beam having a long lifetime. The analyzed As+ ion current is found to be approximately as much as 10 mA. Similarly, stable “B+ and O+ ions can be obtained. The plasma filament ion source was found to be superior in the high production rate of iiB+ ions to the Freeman ion source when this ion source is mounted on the implanter. In the near future an experiment involving thin film deposition will be started using our ion source. This ion source will be II. ION SOURCES
R. Fukui et al. / Long life plasma filament type ion source
142 improved
further
to
get
a longer
life
and
a higher
current.
References [l] E. Yabe, A. Takeshiro, K. Sunako, K. Takayama, K. Takagi, K. Okamoto and S. Komiya, Nucl. Meth. B6 (1985) 119.
R. Fukui, Instr. and
[2] E. Yabe, A. Tonegawa, D. Satoh, K. Takayama, R. Fukui, K. Takagi, K. Okamoto and S. Komiya, Vacuum 36 (1986) 43. [3] E. Yabe, Rev. Sci. Instr. 58 (1987) 1. [4] J.H. Freeman, Nucl. Instr. and Meth. 22 (1963) 306. [5] From the ULVAC catalog N4609.
140
Instruments
and Methods
in Physics
Research
B37/38
North-Holland,
LONG LIFE PLASMA FILAMENT R. FUKUI, 0-Prqect,
IL TAKAGI,
ULNA C JAPAN,
(1989) 140-142 Amsterdam
TYPE ION SOURCE
T. TSUGUEDA,
Ltd., 2500 Hagisono,
H. TSUBOI and R. KIKUCHI
Chigaraki,
*
Kanaga~,a, 253, Japan
E. YABE and K. TAKAYAMA Research and Development Kanagawa, 259-12, Japan
A plasma filament ion source, a plasma filament lifetime of this ion source current of 2.5 mA can be
Institute
and Department
of Physics, Tokai University,
III 7-Kitakaname,
Hiratsuka,
source has been developed as a long lived ion source for use in ion implantation and deposition. In this ion serves as a cathode in place of a thermionic tungsten filament such as used in the Freeman ion source. The was found to be 45 h with a Pf ion current of 2 mA. A stable As+ ion current of 9.1 mA and O+ ion obtained. The running test results of this ion source applied to the implanter are reported in this paper.
1. ion source In the plasma filament ion source, whose operational principle has been already reported in many papers [l-3], a plasma filament serves as a cathode in place of a thermionic tungsten filament such as used in the Freeman ion source 141. The ion outlet slit size on the arc chamber is 3 mm x 30 mm. The cathode in the plasma generator is made of 0.6 mm0 tungsten wire. A schematic diagram of the experimental apparatus is shown in fig. 1. The apparatus consists of an ion source, an analyzing magnet and a growth chamber. The ion beam current is measured by a Faraday cup in the growth chamber.
WTH CHAMBER
2. Results ION SOURCE
The test data of the cathode life in the plasma generator is shown in fig. 2. Argon gas is used for discharge in the plasma generator and PH, gas is fed to the arc chamber for the main discharge. The discharge current in the plasma generator (Zps) is 1.5 A, and the main discharge current (Zi,) is 1.5 A. An extraction voltage (V,,) of 40 kV is applied. The lifetime of this ion source was found to be 45 h with a Pt ion current of 2 mA. The lifetime of the plasma filament ion source is several times longer than the Freeman ion source whose lifetime is said to be about 8 h. The mass spectrum of ions produced by a combination of the argon plasma filament and ASH, feed gas is
* Present address: Faculty of Science, Konan Higashinada, Kobe, Hyogo, 658, Japan.
University,
0168-583X/89/$03.50 0 Elsevier Science Publishers (North-Holland Physics Publishing Division)
B.V.
Fig. 1. Schematic diagram of the experimental apparatus.
shown in fig. 3. In this spectrum, an analyzed As+ ion current of 9.1 mA is obtained, and the ratio of the As+ ion current to the total Faraday cup current reaches 94W, where the discharge current of the plasma generator is 0.8 A and that of the arc chamber is 1.7 A. An extraction voltage of 40 kV is also applied. Fig. 4 shows the mass spectrum of ions produced by a combination of the argon plasma filament and BF, feed gas. In this spectrum, an analyzed “Bf ion current of 2.1 mA is obtained and the ratio of the r’B+ ion current to the total Faraday cup current reaches 29%. Whenever BF, gas is used, several kinds of ions are produced other than t’B+ such as “B+, Ar+, Ar’+,
141
R. Fukui et al. / Long life plasma filament type ion source
Ipg ~20
I<.~20
A
Gas PI : OGsccm Gas Is r 1.2 seem V..
E z
= 15 A Y.. Ix .40
15
E 20 i
Gasp,
‘0
10
ICI .200mA, seem
20
Ar 30
~08
40
02 =28mA
seem
50
PFs 60
70
80
90
100
( hour )
Fig. 2. The test data of the cathode
life in the plasma
generaFig. 5. Mass spectrum of ions produced by the combination the argon plasma filament and the 0, feed gas.
10 IpgzO.8 GX Gas V..
A
, I,.
~17
seem
Ar
13 = 19
~ccm
ASH?
=40kV,
1..=221mA
“B’
Fig. 3. Mass spectrum of ions produced by the combination the argon plasma filament and the ASH, feed gas.
than
and
F+.
The
in the case
1,s-3OA
IN=lOA, Gasog BF2’
BF;
of
A
pg -04
“B.
smaller
le.
1~.=20mA Gas,.
time
BFf,
kV,
11s = 15 A
kV ~04
~40
A
Ar
ratio of As+
of the “B+
ion
of
F.
BF.
k
d
I,
-0
I seem
Gas I, 2 0 7 sctm V..
z 33 kV,
Ar BFx
ICI-77
mA
Ar’ h,
MASS
is then
ion extraction.
mass spectrum of ions produced by a combination of the argon plasma filament and 0, feed gas is depicted in fig. 5. In this spectrum, an analyzed O+ ion current of 2.5 mA is obtained and the ratio of the O+ ion current to the total Faraday cup current reaches 54%. The plasma filament ion source is mounted and tested on the implanter ULVAC model IMM-2200 [5]. The mass spectrum of ions produced by a combination of the argon plasma filament and BF, feed gas is shown
Fig. 6. Mass spectrum of ions produced by the combination of the argon plasma filament and the BF, feed gas when this ion source is mounted on the implanter.
The
3.0
i
LDD = 1.0 A
, 1,s=2.5
Gas pp =04
seem
Gas V..
81 E 1.0 seem =40kV,
A
in fig. 6. In this spectrum, an analyzed ‘iB+ ion current of 150 ~.LAis obtained and the ratio of the i’B+ ion current to the total Faraday cup current reaches 34%. The Freeman ion source produces usually about 20% i’B+ ions. Therefore the plasma filament ion source is a high efficiency ion source for i’B+ ions. Fig. 6 presents the test result when this ion source is applied to a medium type implanter, and fig. 4 gives the result when it is applied to a high current implanter test bench. Therefore, there is a great difference between fig. 4 and fig. 6 in peak current level and spectrum pattern.
Ar BF,
ICI~24.4
Fig. 4. Mass spectrum of ions produced by the combination the argon plasma filament and the BF, feed gas.
3. Conclusion
,,,A
of
It was confirmed that the plasma filament ion source can produce a stable ion beam having a long lifetime. The analyzed As+ ion current is found to be approximately as much as 10 mA. Similarly, stable “B+ and O+ ions can be obtained. The plasma filament ion source was found to be superior in the high production rate of iiB+ ions to the Freeman ion source when this ion source is mounted on the implanter. In the near future an experiment involving thin film deposition will be started using our ion source. This ion source will be II. ION SOURCES
R. Fukui et al. / Long life plasma filament type ion source
142 improved
further
to
get
a longer
life
and
a higher
current.
References [l] E. Yabe, A. Takeshiro, K. Sunako, K. Takayama, K. Takagi, K. Okamoto and S. Komiya, Nucl. Meth. B6 (1985) 119.
R. Fukui, Instr. and
[2] E. Yabe, A. Tonegawa, D. Satoh, K. Takayama, R. Fukui, K. Takagi, K. Okamoto and S. Komiya, Vacuum 36 (1986) 43. [3] E. Yabe, Rev. Sci. Instr. 58 (1987) 1. [4] J.H. Freeman, Nucl. Instr. and Meth. 22 (1963) 306. [5] From the ULVAC catalog N4609.