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Investigation of energetic electrons in a 915 MHz microwave discharge produced in Ar
Thin Solid Films 506 – 507 (2006) 701 – 704 www.elsevier.com/locate/tsf
Investigation of energetic electrons in a 915 MHz microwave discharge produced in Ar E. Stamate *, S. Nakao, H. Sugai Department of Electrical Engineering and Computer Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan Available online 21 September 2005
Abstract The electrical field distribution and plasma parameters in the vicinity of the quartz plate of a 915 MHz microwave discharge are measured using Langmuir probe, thermal probe and microwave field antenna. Energetic electrons with energies exceeding 15 eV are observed at locations of high microwave field that are correlated with high temperatures by thermal probe and high effective electron temperature. Plasma parameters show a spatial dependence in the skin depth while are almost uniform in plasma volume. Present results confirm that the kinetic of the energetic electrons is strongly related to the complex distribution of the microwave electric filed near the dielectric. Measurements are performed in Ar for different pressures and discharge powers. D 2005 Elsevier B.V. All rights reserved. Keywords: Microwave discharge; Heating mechanism; Langmuir probe; Thermal probe
1. Introduction High-power surface wave discharges operating at pressures lower than hundreds of mTorr can be used to produce large diameter plasmas of densities exceeding 1017 m 3 that are highly desired in a wide area of microelectronic technologies [1]. In spite of the promising futures for application there are still unsolved problems related to the microwave field distribution and the heating mechanism of the electrons near the slot antenna [2]. Since this region plays a major role in the physics and the chemistry of the entire plasma volume it needs a careful investigation. Langmuir probes can be easily employed to obtain the plasma parameters and also to pickup the microwave field intensity, |E|2. However, their metallic structure may interfere with the microwave field distribution making questionable the reliability of the results. Thus, alternative diagnostic methods should as well be considered. The presence of energetic electrons near the dielectric plate have been recently demonstrated [3,4]. So
* Corresponding author. E-mail address: [email protected] (E. Stamate). 0040-6090/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2005.08.120
far, only measurements in a direction perpendicular to the dielectric have been reported while it is expected that the standing wave pattern of the microwave field will strongly affect the distribution of plasma parameters in directions parallel to the dielectric. In the present work we are presenting two dimensional measurements by Langmuir probe, thermal probe and field antenna in the vicinity of the dielectric plate of a 915 MHz microwave discharge operated in a hybrid surface wave mode.
2. Thermal probe Following the formalism introduced in references [5,6] the energy balance to a probe of surface S p and volume V p immersed in a plasma is given by, Vp qC
dTp ¼ QE þ QH Sp ðqR þ qK Þ; dt
ð1Þ
where q is the probe material mass density, C the heat capacity, q R the radiative cooling term and q K the heat flux due to Knudsen conduction. T p is the probe temperature of which equilibrium is attained in processing plasmas after a
E. Stamate et al. / Thin Solid Films 506 – 507 (2006) 701 – 704
(b) Pyrex glass
0. 3
Opaque Film
C 144 mm
Phosphor Layer
1. 3
220 mm
B A
α
6 Optical Fiber
slot
0. 7 Fig. 1. (a) Design of the thermal probe; (b) Slot antenna configuration, where the slot length is 165 mm and the width 11 mm.
time interval of a few ms. Q H is the heating rate due to positive ion impact and electron –ion recombination [6] and Q E is the microwave heating rate which depends on |E|2 and the tangent delta, d, of the dielectric probe material. Choosing among materials with very low or, respectively, high d one can actually control the contribution of Q E to T p. For Q E b Q H (d b 1 or negligible |E|2) the T p gives a measure of the plasma density and the hot electron temperature. The thermal probe was made of Pyrex glass (Corning 7740, d b 1) shaped as a cylindrical tube with one-side closed, as can be seen from Fig. 1(a) where the probe design is presented. In order to reduce additional heat loss, the probe was supported by a fine rod (0.3 mm in diameter) made from the same material. A thin layer of phosphor (deposited on the inner wall of the probe) was exposed for 10 ms to violet radiation throughout an optical fiber (0.7 mm in diameter) in a regime of 4 flashes per sec. After each irradiation pulse, T p was measured from the decay of the fluorescence signal. In order to prevent the exposure of the phosphor spot to plasma radiation a nonconductive opaque-film was deposited on the outer surface of the tube. The probe was tested in the wave guide ( Q H = 0) by moving it at different locations with respect to the slot antenna configuration and in a ICP discharge ( Q E ; 0). For plasma density in the range of 1016 to 1017 m 3, the probe heating in the wave guide did not exceed 15% of the plasma heating observed in the ICP. Moreover, measurements with probes made of Pyrex and marble (d ¨ 6) revealed small differences concluding that T p is mostly governed by plasma heating.
presented in Fig. 1(b) where the arrow is indicating the microwave injection direction. The thermal probe and a spherical Langmuir probe (1.3 mm in diameter, made of gold) were fixed on the same shaft, so that, by rotation and translation (z direction is perpendicular to the quartz plate) we were able to measure T p and the plasma parameters distributed on the half of the lateral surface of a cylinder (140 mm in length and 144 mm in diameter) crossing the locations A, B and C respectively, where A corresponds to the rotation angle a = 0- and C to a = 180- (see Fig. 1(b)). The Langmuir probe was also used to pick-up the amplitude of the 915 MHz signal by a spectrum analyzer, signal referred in this paper as |E|2. T p (a) and the effective electron temperature Teff (b) for different z and a are shown in Fig. 2 for a discharge pressure, p = 10 mTorr and discharge power P = 200 W. Thus, while T p increased with about 5 -C per cm for z > 7 cm and exhibited a periodic like structure for z < 7 cm, Teff was almost constant for z > 5 cm and increased with a similar dependence on a as T p for z < 5 cm (inside the skin depth). The peak observed for a = 45- in Fig. 2(b) can also be seen in Fig. 2(a) on the projection plane az. One can notice that in the immediate vicinity of the quartz plate, z ¨ 2 mm, T p increased with 34 -C (23% of T p maximum value) only by changing the probe position from a = 70- to 90- (B in Fig. 2(a)). For similar discharge conditions |E|2 followed the profile of Teff with almost flat values for z > 5 cm but a less accentuated periodic structure as that shown by T p for z < 5 cm. The plasma density, n e, increased slightly
(a)
C B
180
Tp [°C]
(a)
A
160
140 180 135
120 0
z [cm]
45
10 15
0
α
s]
ee
90 5
r eg
[d
(b) 7 6
Teff [eV]
702
5 4
3. Experimental results and discussion 3
Measurements were performed in a 915 MHz microwave discharge produced in a cubic chamber of 40 cm in characteristic length. A quartz plate 35 mm in thickness was placed on the top of the chamber separating the waveguide from the plasma. The slot antenna design is
2 0
180 135 90 5
z [cm]
10
45 15 0
α
s]
ee
r eg
[d
Fig. 2. T p (a) and the effective electron temperature, Teff (b) for different z and a, where p = 10 mTorr and P = 200 W.
E. Stamate et al. / Thin Solid Films 506 – 507 (2006) 701 – 704
(Ip-Ii)' [A/V]
4 2
180
45
5
-5
V [V]
(b)
-15
[d e
90 15
gr ee
0 25
s]
135
α
0
-3
x 10
0.8 0.6 0.4
5
V [V]
45 -5
-15
0
es
eg
90 15
[d
0 25
]
180 135
0.2
re
(Ip-Ii)' [A/V]
1
α
Fig. 3. First derivative of the probe current minus the positive ions contribution, (I p – I i)V, detected in Ar, where p = 10 mTorr, P = 200 W: (a) z = 2 cm; (b) z = 4 cm.
with z for z < 10 cm, and was almost constant (n e ; 1.25 1016 m 3) for 5 < z < 10 cm. The plasma potential, V pl, distribution was almost uniform (V pl å 18.5V) for z > 4 cm, then decreased with about 2 V for z < 4 cm. The bulk electron temperature, Te, was about 2.3 eV for all z and a. Since Teff is a good measure of the energetic tail of the electron energy probability function we can expect the existence of some hot electrons near the quartz. Such energetic electrons have been recently reported by several authors but the heating mechanism producing them is not yet clarified [3,4]. Bulk electrons may be accelerated in the skin depth (z < 5 cm) by local resonance or secondary electrons produced by emission at the quartz plate may be accelerated into plasma by the intense field. The first derivative of the probe current, I p,V as a function of the probe bias, V, from which the positive ion contribution, I i, was subtracted is presented in Fig. 3(a) and (b) for z = 2 cm and z = 4 cm, respectively, where p = 10 mTorr and P = 200 W. While beam-like energetic electrons of about 15 eV were detected at z = 2 cm their flux was drastically lower for z = 4 cm, a distance that is much shorter than the mean free path or the relaxation length of electrons at 10 mTorr. Moreover, the structure of (I p –I i)V was strongly correlated with T p and Teff profile. If the electrons are transit time accelerated in the resonant layer corresponding to the n e = n c (n c is the cutoff density with n c = 1016 m 3 for m = 915 MHz), then they are expected to be accelerated
α [degrees]
(a)
/E/ 2 [arb. units]
-4
x 10
6
from plasma toward the quartz plate. That is, the plane waves induced by the density gradient are traveling to the plasma boundary while electrons running to the plasma remain unaffected [7]. Thus, if the energetic electrons are moving in an opposite direction, the rapid attenuation with z is apparent. However, directive measurement performed in similar discharge condition reveled that the kinetic of the energetic electrons is much more complicated and depends on the three dimensional distribution of |E|2 in the skin depth [8]. |E|2 and T p as a function of a for different p and z = 2 cm are presented in Fig. 4(a) and (b), respectively, where P = 300 W. Thus, even that both T p and |E|2 show several minimum and maximum values these were not correlated. For instance, the maximum of |E|2 at a = 20- corresponded to a T p lower with 40 -C than at a = 130- for p = 30 mTorr. Moreover, for 30 and 70 mTorr, the increasing of plasma density with p leaded to a shrink of the skin depth followed by decreasing of |E|2 at constant z while T p increased to more than 200 -C for a = 130-. This behavior clearly suggests that T p was mostly governed by Q H. Teff and V pl for similar discharge conditions as in Fig. 4 are presented in Fig. 5(a) and (b), respectively. Thus, Teff was strongly correlated with |E|2 and V pl followed the profile shown by T p and also n e. This observation proves that the energetic electrons are in local equilibrium with the
0
45
90
135
180
0
-15
-30
p =30 mTorr p =50 mTorr
-45
p =70 mTorr p =100 mTorr
-60
(b)
225
200
T p [°C]
(a)
703
175
p =30 mTorr p =50 mTorr p =70 mTorr p =100 mTorr
150
125 0
45
90
135
180
α [degrees] Fig. 4. T p (a) and |E|2 (b) as a function of a for different p and P = 300 W.
704
E. Stamate et al. / Thin Solid Films 506 – 507 (2006) 701 – 704
(a)
11
p =30 mTorr p =50 mTorr
9
T eff [eV]
p =70 mTorr p =100 mTorr
7
5
3 0
45
90
135
180
α [degrees]
(b) 26
and the bulk electron temperature were almost flat the effective electron temperature, microwave field and thermal probe temperature were all correlated, exhibiting maximum values at certain location with respect to the slot antenna configuration. For p = 10 mTorr and P = 200 W the electron density was slightly higher than the cutoff density with lower values near the dielectric. Energetic electrons with energies exceeding 15 eV were detected at location of high microwave field and high thermal probe temperature. However, those electrons could not be detected just 2 cm away, a distance that is much shorter than their relaxation length. By increasing plasma density (transition to the pure surface wave mode) the investigation becomes more difficult due to the skin depth shrinking. Thus, further investigation are necessary in order to clarify the heating mechanism of the electrons and their kinetic with respect to the complex distribution of the microwave filed.
V pl [V]
24
Acknowledgements p =30 mTorr p =50 mTorr p =70 mTorr p =100 mTorr
22
20 0
45
90
135
This work was partially supported by the 21st Century Center of Excellence Program of the Ministry of Education, Culture, Sports, Science and Technology of Japan.
180
α [degress]
References
Fig. 5. Teff (a) and V pl (b) as a function of a for different p and P = 300 W.
microwave filed and are generated in regions of lower plasma density.
4. Conclusions Langmuir probe, thermal probe and field antenna were used to detect the plasma properties near the dielectric plate of a 915 MHz microwave discharge. While plasma potential
[1] H. Sugai, I. Ganashev, M. Nagatsu, Plasma Sources Sci. Technol. 7 (1998) 192. [2] I.P. Ganachev, H. Sugai, Plasma Sources Sci. Technol 11 (2002) A178. [3] J. Kudela, T. Terebessy, M. Kando, Appl. Phys. Lett. 76 (2000) 1249. [4] M. Nagatsu, T. Niwa, H. Sugai, Appl. Phys. Lett. 81 (2002) 1966. [5] K.G. Emeleus, A.C. Breslin, Int. J. Electron. 29 (1970) 1. [6] E. Stamate, K. Ohe, H. Sugai, Appl. Phys. Lett. 80 (2002) 3066. [7] I. Ganachev, H. Sugai, Surf. Coat. Technol. 174 – 175 (2003) 15. [8] E. Stamate, S. Nakao, M. Aramaki, A. Kono, H. Sugai, Bull. Am. Phys. Soc. 48 (2003) 61.
Investigation of energetic electrons in a 915 MHz microwave discharge produced in Ar E. Stamate *, S. Nakao, H. Sugai Department of Electrical Engineering and Computer Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan Available online 21 September 2005
Abstract The electrical field distribution and plasma parameters in the vicinity of the quartz plate of a 915 MHz microwave discharge are measured using Langmuir probe, thermal probe and microwave field antenna. Energetic electrons with energies exceeding 15 eV are observed at locations of high microwave field that are correlated with high temperatures by thermal probe and high effective electron temperature. Plasma parameters show a spatial dependence in the skin depth while are almost uniform in plasma volume. Present results confirm that the kinetic of the energetic electrons is strongly related to the complex distribution of the microwave electric filed near the dielectric. Measurements are performed in Ar for different pressures and discharge powers. D 2005 Elsevier B.V. All rights reserved. Keywords: Microwave discharge; Heating mechanism; Langmuir probe; Thermal probe
1. Introduction High-power surface wave discharges operating at pressures lower than hundreds of mTorr can be used to produce large diameter plasmas of densities exceeding 1017 m 3 that are highly desired in a wide area of microelectronic technologies [1]. In spite of the promising futures for application there are still unsolved problems related to the microwave field distribution and the heating mechanism of the electrons near the slot antenna [2]. Since this region plays a major role in the physics and the chemistry of the entire plasma volume it needs a careful investigation. Langmuir probes can be easily employed to obtain the plasma parameters and also to pickup the microwave field intensity, |E|2. However, their metallic structure may interfere with the microwave field distribution making questionable the reliability of the results. Thus, alternative diagnostic methods should as well be considered. The presence of energetic electrons near the dielectric plate have been recently demonstrated [3,4]. So
* Corresponding author. E-mail address: [email protected] (E. Stamate). 0040-6090/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2005.08.120
far, only measurements in a direction perpendicular to the dielectric have been reported while it is expected that the standing wave pattern of the microwave field will strongly affect the distribution of plasma parameters in directions parallel to the dielectric. In the present work we are presenting two dimensional measurements by Langmuir probe, thermal probe and field antenna in the vicinity of the dielectric plate of a 915 MHz microwave discharge operated in a hybrid surface wave mode.
2. Thermal probe Following the formalism introduced in references [5,6] the energy balance to a probe of surface S p and volume V p immersed in a plasma is given by, Vp qC
dTp ¼ QE þ QH Sp ðqR þ qK Þ; dt
ð1Þ
where q is the probe material mass density, C the heat capacity, q R the radiative cooling term and q K the heat flux due to Knudsen conduction. T p is the probe temperature of which equilibrium is attained in processing plasmas after a
E. Stamate et al. / Thin Solid Films 506 – 507 (2006) 701 – 704
(b) Pyrex glass
0. 3
Opaque Film
C 144 mm
Phosphor Layer
1. 3
220 mm
B A
α
6 Optical Fiber
slot
0. 7 Fig. 1. (a) Design of the thermal probe; (b) Slot antenna configuration, where the slot length is 165 mm and the width 11 mm.
time interval of a few ms. Q H is the heating rate due to positive ion impact and electron –ion recombination [6] and Q E is the microwave heating rate which depends on |E|2 and the tangent delta, d, of the dielectric probe material. Choosing among materials with very low or, respectively, high d one can actually control the contribution of Q E to T p. For Q E b Q H (d b 1 or negligible |E|2) the T p gives a measure of the plasma density and the hot electron temperature. The thermal probe was made of Pyrex glass (Corning 7740, d b 1) shaped as a cylindrical tube with one-side closed, as can be seen from Fig. 1(a) where the probe design is presented. In order to reduce additional heat loss, the probe was supported by a fine rod (0.3 mm in diameter) made from the same material. A thin layer of phosphor (deposited on the inner wall of the probe) was exposed for 10 ms to violet radiation throughout an optical fiber (0.7 mm in diameter) in a regime of 4 flashes per sec. After each irradiation pulse, T p was measured from the decay of the fluorescence signal. In order to prevent the exposure of the phosphor spot to plasma radiation a nonconductive opaque-film was deposited on the outer surface of the tube. The probe was tested in the wave guide ( Q H = 0) by moving it at different locations with respect to the slot antenna configuration and in a ICP discharge ( Q E ; 0). For plasma density in the range of 1016 to 1017 m 3, the probe heating in the wave guide did not exceed 15% of the plasma heating observed in the ICP. Moreover, measurements with probes made of Pyrex and marble (d ¨ 6) revealed small differences concluding that T p is mostly governed by plasma heating.
presented in Fig. 1(b) where the arrow is indicating the microwave injection direction. The thermal probe and a spherical Langmuir probe (1.3 mm in diameter, made of gold) were fixed on the same shaft, so that, by rotation and translation (z direction is perpendicular to the quartz plate) we were able to measure T p and the plasma parameters distributed on the half of the lateral surface of a cylinder (140 mm in length and 144 mm in diameter) crossing the locations A, B and C respectively, where A corresponds to the rotation angle a = 0- and C to a = 180- (see Fig. 1(b)). The Langmuir probe was also used to pick-up the amplitude of the 915 MHz signal by a spectrum analyzer, signal referred in this paper as |E|2. T p (a) and the effective electron temperature Teff (b) for different z and a are shown in Fig. 2 for a discharge pressure, p = 10 mTorr and discharge power P = 200 W. Thus, while T p increased with about 5 -C per cm for z > 7 cm and exhibited a periodic like structure for z < 7 cm, Teff was almost constant for z > 5 cm and increased with a similar dependence on a as T p for z < 5 cm (inside the skin depth). The peak observed for a = 45- in Fig. 2(b) can also be seen in Fig. 2(a) on the projection plane az. One can notice that in the immediate vicinity of the quartz plate, z ¨ 2 mm, T p increased with 34 -C (23% of T p maximum value) only by changing the probe position from a = 70- to 90- (B in Fig. 2(a)). For similar discharge conditions |E|2 followed the profile of Teff with almost flat values for z > 5 cm but a less accentuated periodic structure as that shown by T p for z < 5 cm. The plasma density, n e, increased slightly
(a)
C B
180
Tp [°C]
(a)
A
160
140 180 135
120 0
z [cm]
45
10 15
0
α
s]
ee
90 5
r eg
[d
(b) 7 6
Teff [eV]
702
5 4
3. Experimental results and discussion 3
Measurements were performed in a 915 MHz microwave discharge produced in a cubic chamber of 40 cm in characteristic length. A quartz plate 35 mm in thickness was placed on the top of the chamber separating the waveguide from the plasma. The slot antenna design is
2 0
180 135 90 5
z [cm]
10
45 15 0
α
s]
ee
r eg
[d
Fig. 2. T p (a) and the effective electron temperature, Teff (b) for different z and a, where p = 10 mTorr and P = 200 W.
E. Stamate et al. / Thin Solid Films 506 – 507 (2006) 701 – 704
(Ip-Ii)' [A/V]
4 2
180
45
5
-5
V [V]
(b)
-15
[d e
90 15
gr ee
0 25
s]
135
α
0
-3
x 10
0.8 0.6 0.4
5
V [V]
45 -5
-15
0
es
eg
90 15
[d
0 25
]
180 135
0.2
re
(Ip-Ii)' [A/V]
1
α
Fig. 3. First derivative of the probe current minus the positive ions contribution, (I p – I i)V, detected in Ar, where p = 10 mTorr, P = 200 W: (a) z = 2 cm; (b) z = 4 cm.
with z for z < 10 cm, and was almost constant (n e ; 1.25 1016 m 3) for 5 < z < 10 cm. The plasma potential, V pl, distribution was almost uniform (V pl å 18.5V) for z > 4 cm, then decreased with about 2 V for z < 4 cm. The bulk electron temperature, Te, was about 2.3 eV for all z and a. Since Teff is a good measure of the energetic tail of the electron energy probability function we can expect the existence of some hot electrons near the quartz. Such energetic electrons have been recently reported by several authors but the heating mechanism producing them is not yet clarified [3,4]. Bulk electrons may be accelerated in the skin depth (z < 5 cm) by local resonance or secondary electrons produced by emission at the quartz plate may be accelerated into plasma by the intense field. The first derivative of the probe current, I p,V as a function of the probe bias, V, from which the positive ion contribution, I i, was subtracted is presented in Fig. 3(a) and (b) for z = 2 cm and z = 4 cm, respectively, where p = 10 mTorr and P = 200 W. While beam-like energetic electrons of about 15 eV were detected at z = 2 cm their flux was drastically lower for z = 4 cm, a distance that is much shorter than the mean free path or the relaxation length of electrons at 10 mTorr. Moreover, the structure of (I p –I i)V was strongly correlated with T p and Teff profile. If the electrons are transit time accelerated in the resonant layer corresponding to the n e = n c (n c is the cutoff density with n c = 1016 m 3 for m = 915 MHz), then they are expected to be accelerated
α [degrees]
(a)
/E/ 2 [arb. units]
-4
x 10
6
from plasma toward the quartz plate. That is, the plane waves induced by the density gradient are traveling to the plasma boundary while electrons running to the plasma remain unaffected [7]. Thus, if the energetic electrons are moving in an opposite direction, the rapid attenuation with z is apparent. However, directive measurement performed in similar discharge condition reveled that the kinetic of the energetic electrons is much more complicated and depends on the three dimensional distribution of |E|2 in the skin depth [8]. |E|2 and T p as a function of a for different p and z = 2 cm are presented in Fig. 4(a) and (b), respectively, where P = 300 W. Thus, even that both T p and |E|2 show several minimum and maximum values these were not correlated. For instance, the maximum of |E|2 at a = 20- corresponded to a T p lower with 40 -C than at a = 130- for p = 30 mTorr. Moreover, for 30 and 70 mTorr, the increasing of plasma density with p leaded to a shrink of the skin depth followed by decreasing of |E|2 at constant z while T p increased to more than 200 -C for a = 130-. This behavior clearly suggests that T p was mostly governed by Q H. Teff and V pl for similar discharge conditions as in Fig. 4 are presented in Fig. 5(a) and (b), respectively. Thus, Teff was strongly correlated with |E|2 and V pl followed the profile shown by T p and also n e. This observation proves that the energetic electrons are in local equilibrium with the
0
45
90
135
180
0
-15
-30
p =30 mTorr p =50 mTorr
-45
p =70 mTorr p =100 mTorr
-60
(b)
225
200
T p [°C]
(a)
703
175
p =30 mTorr p =50 mTorr p =70 mTorr p =100 mTorr
150
125 0
45
90
135
180
α [degrees] Fig. 4. T p (a) and |E|2 (b) as a function of a for different p and P = 300 W.
704
E. Stamate et al. / Thin Solid Films 506 – 507 (2006) 701 – 704
(a)
11
p =30 mTorr p =50 mTorr
9
T eff [eV]
p =70 mTorr p =100 mTorr
7
5
3 0
45
90
135
180
α [degrees]
(b) 26
and the bulk electron temperature were almost flat the effective electron temperature, microwave field and thermal probe temperature were all correlated, exhibiting maximum values at certain location with respect to the slot antenna configuration. For p = 10 mTorr and P = 200 W the electron density was slightly higher than the cutoff density with lower values near the dielectric. Energetic electrons with energies exceeding 15 eV were detected at location of high microwave field and high thermal probe temperature. However, those electrons could not be detected just 2 cm away, a distance that is much shorter than their relaxation length. By increasing plasma density (transition to the pure surface wave mode) the investigation becomes more difficult due to the skin depth shrinking. Thus, further investigation are necessary in order to clarify the heating mechanism of the electrons and their kinetic with respect to the complex distribution of the microwave filed.
V pl [V]
24
Acknowledgements p =30 mTorr p =50 mTorr p =70 mTorr p =100 mTorr
22
20 0
45
90
135
This work was partially supported by the 21st Century Center of Excellence Program of the Ministry of Education, Culture, Sports, Science and Technology of Japan.
180
α [degress]
References
Fig. 5. Teff (a) and V pl (b) as a function of a for different p and P = 300 W.
microwave filed and are generated in regions of lower plasma density.
4. Conclusions Langmuir probe, thermal probe and field antenna were used to detect the plasma properties near the dielectric plate of a 915 MHz microwave discharge. While plasma potential
[1] H. Sugai, I. Ganashev, M. Nagatsu, Plasma Sources Sci. Technol. 7 (1998) 192. [2] I.P. Ganachev, H. Sugai, Plasma Sources Sci. Technol 11 (2002) A178. [3] J. Kudela, T. Terebessy, M. Kando, Appl. Phys. Lett. 76 (2000) 1249. [4] M. Nagatsu, T. Niwa, H. Sugai, Appl. Phys. Lett. 81 (2002) 1966. [5] K.G. Emeleus, A.C. Breslin, Int. J. Electron. 29 (1970) 1. [6] E. Stamate, K. Ohe, H. Sugai, Appl. Phys. Lett. 80 (2002) 3066. [7] I. Ganachev, H. Sugai, Surf. Coat. Technol. 174 – 175 (2003) 15. [8] E. Stamate, S. Nakao, M. Aramaki, A. Kono, H. Sugai, Bull. Am. Phys. Soc. 48 (2003) 61.