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Energy-mass spectrometry and automatic Langmuir probe measurements in reactive ICP plasmas for diamond deposition
SURfACE
ELSEVIER
Surface and Coatings Technology 98 (1998) 1020-1026
&COAnNliB IFCHNOJDGY
Energy-mass spectrometry and automatic Langmuir probe measurements in reactive ICP plasmas for diamond deposition Peter Awakowicz *, Roland Schwefel, Manfred Werder, Wolfgang Kasper Lehrstuhlfur Technische Elektrophysik, Technische Universitiit Munchen. Arcisstrasse 21. D-80290 Munchen. Germany
Abstract Two different argon-hydrogen-methane gas mixtures Ar/H 2 /CH 4 250/25/0.5 scem (mixture 1) and Ar/H 2 /CH 4 50/50/0.5 secm (mixture 2) were used in an inductive coupled planar radio frequency (rf) reactor (lCP). By means of separately mounted concentric coils and a grounded Faraday polarizer on top of the reactor, diamond films were grown on to silicon. The electricalIy heated substrates were immersed in the most intense plasma region shaped as a torus. The selected plasma conditions (4 mbar, 1.2kW) in combination with mixture I resulted in fair quality diamond with relatively high growth rates (0.6-1 j.l1Ilh- 1). In the course of diamond growth, the plasma was investigated by means of a Langmuir probe system (LP) and an energy and mass spectrometer (EMS). © 1998 Elsevier Science S.A. Keywords: Energy-mass spectrometry; Langmuir probe; ICP; Diamond deposition
1. Introduction Diamond deposition on large substrate areas under well-known conditions is an interesting subject in the field of plasma chemical vapour deposition (CVD). At pressures typically used for diamond deposition planar rf reactors are favourable for several reasons. First, the scalability of planar systems is practically unlimited if concentrically mounted coils are used for the rf coupling to the plasma. Further, argon measurements confirmed that the radial density of an ICP is adjustable if the coils are separately powered. Another important feature of planar ICPs is the high electron density, even in plasmas operated at gas mixtures with high hydrogen concentrations. 2. Experimental 2.1. ICP reactor
The stainless steel plasma reactor (Fig. 1) consists of two turbo-pumped parts separated by means of a load lock. The plasma in the cylindrical vessel (radius = 95 mm, height = 35 mm) is confined by a quartz glass • Corresponding author. 0257-8972/98/$19.00 © 1998 Elsevier Science SA All rights reserved. PII S0257.8972(97)00228.4
plate on top and a molybdenum heating plate on the bottom. The rf antenna has been built as a system of four concentric coils connected to a 27 MHz rf genera• tor. A slotted aluminium Faraday polarizer between the rf antenna and the vessel serves as a shield against capacitive coupling. The substrates are mounted and electrically connected to a turnable substrate holder, which serves as a transport system from the precleaning chamber (not shown in Fig. 1) to the plasma vessel. The silicon substrates are electrically heated. The temper• ature is regulated by means of a microcontroller. The following parameters were kept constant: the rf power was 1.2 kW, the total pressure was 4 mbar, the temper• ature of the grounded molybdenum plate without plasma was 270°C and the substrate temperature was about 750 0c. The rectangular (100) silicon stripes (10 x 35 mm) were mechanically polished with 1 J.lm diamond paste and ultrasonically cleaned in acetone and deionized water. The subsequent cleaning plasma was operated at 0.5 Pa in a hydrogen-argon mixture (25/25 sccm) at 200 W without using the Faraday polar• izer which results in a high ion energy. 2.2. Langmuir probe
The Langmuir probe (LP) measurements were made by means of a tungsten wire probe tip (diameter 50 J.lm,
P. Awakowicz et al. I Surface and Coatings Technology 98 ( 1998) 1020-1026
1021
RF-generator
r®1 J. J.J..J ~~=
Reactor vessel----,
Substrate
Concentrical coils
Farada
olarizer
Gas inlet Load lock - - - I Turnable substrate assembly
!
To Pumps Fig. I. ICP reactor with the Langmuir probe and energy-mass spectrometer.
length 5 mm). A turning and pushing high-vacuum device enables a place-dependent measurement in radial direction while the plasma is in operation. The probe tip is pneumatically inserted through membrane bellows during measurement breaks to prevent the probe tip from coating. The rf compensation was obtained by a ring electrode connected to the inner shielding of the triaxial probe set-up. In this manner, the floating poten• tial was scanned and transferred to an electronic measur• ing system connected to a personal computer. A voltage ramp (- 60 V to + 260 V) was applied between the probe tip and the grounded reference electrode (heating plate in Fig. I). The 1- V probe characteristic is obtained in 10 ms (16 bit, 50 kHz), thus guaranteeing that the probe tip is exposed to the plasma for only a short time. The following plasma parameters were evaluated from the LP measurements: the electron density n., the mean electron energy E, the floating potential Un and the plasma potential Up)' All details concerning the auto• matic evaluation of the probe measurement are given in Refs. [1,2]. The measurements in different reactive plas• mas were confirmed by comparing the electron density obtained with self-excited electron resonance spectro• scopy (SEERS) [3]. 2.3. Energy-mass spectrometry
Simultaneously to the LP measurements, the most important ions occurring in the plasma were analysed by energy and mass spectrometry (Hiden EQP 300) through an orifice of 50 Jlm diameter located in the vicinity of the plasma torus. The energy distributions of the most significant ions are shown under two different conditions: first the Faraday polarizer was not mounted, and then the polarizer was connected to the ground potential.
3. Results 3.1. Spatial plasma parameter distributions
The radial profiles of the electron density and the electron temperature obtained with gas mixture I (Ar/H 2 /CH 4 250/25/0.5 sccm) are shown in Fig.2(a). Three of the four rf coils (2,3,4) are also shown, while the first coil is outside the radial range. The electron density n. is marked with filled symbols and the mean electron energy E with empty symbols. Both parameters provided the highest values in the radial region below coil 3, where the central region of the occurring plasma torus is located. Both potentials, namely the floating Un and the plasma potential Upb are given in Fig.2b. The plasma potential also reached the highest values in the torus region, which was not the case for the smaller floating potential. All parameters (Fig. 2a and b) decreased for increasing radius above r = 55 mm in the direction of the reactor wall. In the second gas mixture (Ar/H 2 /CH 4 50/50/ 0.5 seem), a significantly lower argon concentration was used. The radial distributions of E and n. are given in Fig. 3a. While the mean electron energy. of this mixture is slightly higher than before and the radial profile very flat, the electron density is three times lower. As in the first gas mixture, the maxima of both pa~ameters are in the same plasma region. Both potentials are given in Fig. 3b. The behaviour is similar, but it is worth. men• tioning that both potentials increased for decreasing radius below r=35 mm. 3.2. Energy distributions ofions
A survey of all ions in the plasma containing gas mixture I is given in Fig. 4. Some of the highest count
P. Awakowlcz et al. / Surface and Coatings Technology 98 ( /998) /020-/026
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Fig. 2. (a) Radial profiles of the mean electron energy (E) and the electron density (n.). Plasma conditions: 1.2 kW rf power, 4 mbar total preSSure, flows: Ar/H 2 /CH 4 250/25/0.5 sccm. Three rf coils (2,3,4) are also shown; coil I is not included in the radial interval. (b) Radial profiles of the floating and the plasma potential (Un, Up.). Plasma conditions: 1.2 kW rf power, 4 mbar total pressure, flows: Ar/H 2/CH 4 250/25/0.5 secm.
rates were detected for Ht , CHt and ArH + • The energy distributions of these ions are shown in Fig. 5. Note that the maxima of all energy distributions are located at relative low energies if the Faraday polarizer is grounded (Fig. 5a). In contrast, Fig. 5b shows the energy distribution of the same ions without the polar• izer. Relatively high ion energies up to 100 eV appeared in combination with increased count rates. The strong increase in the ion energy is caused by the rectified voltage drop in the sheath, as known from capacitive coupled plasmas. Comparison of the two ion energy distributions (Fig. 5a and b) shows that a pure inductive coupling is obtained by the use of the grounded polarizer and the capacitive coupling is remarkably increased if the plasma is operated without the polarizer. Further, it is particularly interesting to compare the strongly
increased count rates of Ht. This behaviour is due to the high diffusion coefficient of Ht compared with all other ions shown here. 3.3. Deposited coatings
The substrates are normally immersed in the high• density region of the plasma torus, as shown in Fig. 1. In Fig. 6, scanning electron micrograph (SEM) images and the corresponding micro-Raman spectrum (Fig. 6c) of the diamond films on (l00) silicon are given. The plasma conditions are as mentioned above, in combina• tion with gas mixture 1 (Ar/H z/CH 4 250/25/0.5 sccm). The mean crystal size is approx. 1 J.llTI. Since the depos• ition time was 18 h, a mean growth rate of about 0.7 Ilm h - 1 was deduced.
1023
P. Awakowicz et al. / Surface and Coatings Technology 98 ( 1998) 1020-1026 Coil 3
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Fig. 3. (a) Radial profiles of the mean electron energy (E) and the electron density (n.). Plasma conditions: 1.2 kW rf power, 4 mbar total pressure, flows: Ar/H z/CH 4 50/50/0.5 seem. Three rf coils (2,3,4) are also shown; coil I is not included in the radial interval. (b) Radial profiles of the floating and the plasma potential (Un, Up;). Plasma conditions: 1.2 kW rf power, 4 mbar total pressure, flows: Ar/H z/CH 4 50/50/0.5 seem.
The growth with gas mixture 2 (Ar/H 2 /CH 4 50/50/0.5 scem) is shown in Fig. 7. Only hillocks of about 5 llm have been deposited. The substrate surface is far from being homogeneously covered. The same plasma conditions without the Faraday polarizer pro• vided only glassy carbon coatings. 4. Discussion First, it is interesting to compare the plasma potential U I in Fig. 2b with the ion energy distributions in Fig. Sa. The maxima of all distributions lie between 5 and II eV. The plasma potential at the position of the EMS orifice given in Fig. 2b agrees with the model that the ions gain
most of their energy on the way through the potential drop of the sheath between the plasma bulk and the wall. Other experiments with gas mixture I have been performed using the same external parameters as men• tioned above but without a grounded polarizer. No diamond growth was observed under these conditions. Therefore, we conclude that low ion energies are neces• sary for diamond growth. Experiments with a high hydrogen concentration (mixture 2) indicated an electron density less than half the density obtained with mixture 1 at the normal position of the substrate below rf coil 3 (Fig. 2a). Other experiments with mixture I and the substrate located below coil 2 (Fig. 2a) resulted in coatings without detect• able diamond crystals after 18 h growth time. From
P. Awakoll'ic= e/ al. / Surface and Coa/inKs Technology 98 ( 1998) I020-J()26
1024
these results it can be concluded that a high electron density is necessary for diamond growth. Further, a high electron density is accompanied by a high gas temperature. Therefore, a correlation between diamond growth and a high gas temperature could be assumed. The electron density measurements of the two different argon concentrations (mixtures I and 2) are in agreement with calculations [4] where it is shown that argon substantially increases the overall ionization rate and the Hz dissociation rate by electron collisions. The growth of diamond films in an ICP without a polarizer has been reported previously [5]. The high argon concen• tration (95%) used for the described experiment is in accordance with the aforementioned demand for low ion energies and high electron densities.
106
105
tl
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~
§ o
104
103
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102
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Mass [amu) Fig. 4. Ion mass spectrum and relative count rates.
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Fig. 5. Ion energy distributions of the most intense masses of the Ar/H , /CH 4 250/25/0.5 sccm plasma: (a) with and (b) without a grounded Faraday polarizer.
1025
P. AlrakOlI"ic: et al. / Sur/iKe and Coatings Te<'i/nology CJIj ( ICJCJIj) 102U-1026
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Fig. 6. (a,b) SEM images of diamond growth on ( 100) silicon deposited by means of the rf plasma: 1.2 kW rf power, 4 mbar total pressure, flows: Ar/H 2 /CH 4 250/25/0.5 seem (scale bars=5Ilm). (c) Laser micro-Raman spectrum.
20 /lill II-----~
20 /lffi
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(b)
-------i
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Fig. 7. SEM images of hillocks on (100) silicon deposited by means of the rf plasma: 1.2 kW rf power, 4 mbar total pressure, flows: Ar/H 2 /CH 4 50/50/0.5 seem (scale bars = 20 11m).
1026
P. Awakowicz et al. / Surface and Coatings Technology 98 ( 1998) 1020-1026
Acknowledgement The authors would like to thank F. Glatz (TV-Miinchen) for performing the Raman measure• ments. The Langmuir probe set-up was partly supported by the Dr. Johannes Heidenhain-Stiftung GmbH. References [I] W. Kasper, P. Awakowicz, ISPC 12, Minneapolis (1995) pp. 2239-2244. [2] W. Kasper, P. Awakowicz, ISPC XXII, New Jersey (1995) p. 171.
[3] M. Klick, W. Rehak, W. Kasper, P. Awakowicz, G. Franz, Surface and Coatings Technology 98 (1998). [4] Y.A. Mankelevich, A.T. Rakhimov, N.V. Suetin, S.V. Kostyuk, Diamond Relat. Mater. 5 (1996) 964-967. [5] S.P. Bozeman, D.A. Tucker, B.R. Stoner, J.T. Glass, W.M. Hooke, Appl. Phys. Lett. 66 (1995) 26.
ELSEVIER
Surface and Coatings Technology 98 (1998) 1020-1026
&COAnNliB IFCHNOJDGY
Energy-mass spectrometry and automatic Langmuir probe measurements in reactive ICP plasmas for diamond deposition Peter Awakowicz *, Roland Schwefel, Manfred Werder, Wolfgang Kasper Lehrstuhlfur Technische Elektrophysik, Technische Universitiit Munchen. Arcisstrasse 21. D-80290 Munchen. Germany
Abstract Two different argon-hydrogen-methane gas mixtures Ar/H 2 /CH 4 250/25/0.5 scem (mixture 1) and Ar/H 2 /CH 4 50/50/0.5 secm (mixture 2) were used in an inductive coupled planar radio frequency (rf) reactor (lCP). By means of separately mounted concentric coils and a grounded Faraday polarizer on top of the reactor, diamond films were grown on to silicon. The electricalIy heated substrates were immersed in the most intense plasma region shaped as a torus. The selected plasma conditions (4 mbar, 1.2kW) in combination with mixture I resulted in fair quality diamond with relatively high growth rates (0.6-1 j.l1Ilh- 1). In the course of diamond growth, the plasma was investigated by means of a Langmuir probe system (LP) and an energy and mass spectrometer (EMS). © 1998 Elsevier Science S.A. Keywords: Energy-mass spectrometry; Langmuir probe; ICP; Diamond deposition
1. Introduction Diamond deposition on large substrate areas under well-known conditions is an interesting subject in the field of plasma chemical vapour deposition (CVD). At pressures typically used for diamond deposition planar rf reactors are favourable for several reasons. First, the scalability of planar systems is practically unlimited if concentrically mounted coils are used for the rf coupling to the plasma. Further, argon measurements confirmed that the radial density of an ICP is adjustable if the coils are separately powered. Another important feature of planar ICPs is the high electron density, even in plasmas operated at gas mixtures with high hydrogen concentrations. 2. Experimental 2.1. ICP reactor
The stainless steel plasma reactor (Fig. 1) consists of two turbo-pumped parts separated by means of a load lock. The plasma in the cylindrical vessel (radius = 95 mm, height = 35 mm) is confined by a quartz glass • Corresponding author. 0257-8972/98/$19.00 © 1998 Elsevier Science SA All rights reserved. PII S0257.8972(97)00228.4
plate on top and a molybdenum heating plate on the bottom. The rf antenna has been built as a system of four concentric coils connected to a 27 MHz rf genera• tor. A slotted aluminium Faraday polarizer between the rf antenna and the vessel serves as a shield against capacitive coupling. The substrates are mounted and electrically connected to a turnable substrate holder, which serves as a transport system from the precleaning chamber (not shown in Fig. 1) to the plasma vessel. The silicon substrates are electrically heated. The temper• ature is regulated by means of a microcontroller. The following parameters were kept constant: the rf power was 1.2 kW, the total pressure was 4 mbar, the temper• ature of the grounded molybdenum plate without plasma was 270°C and the substrate temperature was about 750 0c. The rectangular (100) silicon stripes (10 x 35 mm) were mechanically polished with 1 J.lm diamond paste and ultrasonically cleaned in acetone and deionized water. The subsequent cleaning plasma was operated at 0.5 Pa in a hydrogen-argon mixture (25/25 sccm) at 200 W without using the Faraday polar• izer which results in a high ion energy. 2.2. Langmuir probe
The Langmuir probe (LP) measurements were made by means of a tungsten wire probe tip (diameter 50 J.lm,
P. Awakowicz et al. I Surface and Coatings Technology 98 ( 1998) 1020-1026
1021
RF-generator
r®1 J. J.J..J ~~=
Reactor vessel----,
Substrate
Concentrical coils
Farada
olarizer
Gas inlet Load lock - - - I Turnable substrate assembly
!
To Pumps Fig. I. ICP reactor with the Langmuir probe and energy-mass spectrometer.
length 5 mm). A turning and pushing high-vacuum device enables a place-dependent measurement in radial direction while the plasma is in operation. The probe tip is pneumatically inserted through membrane bellows during measurement breaks to prevent the probe tip from coating. The rf compensation was obtained by a ring electrode connected to the inner shielding of the triaxial probe set-up. In this manner, the floating poten• tial was scanned and transferred to an electronic measur• ing system connected to a personal computer. A voltage ramp (- 60 V to + 260 V) was applied between the probe tip and the grounded reference electrode (heating plate in Fig. I). The 1- V probe characteristic is obtained in 10 ms (16 bit, 50 kHz), thus guaranteeing that the probe tip is exposed to the plasma for only a short time. The following plasma parameters were evaluated from the LP measurements: the electron density n., the mean electron energy E, the floating potential Un and the plasma potential Up)' All details concerning the auto• matic evaluation of the probe measurement are given in Refs. [1,2]. The measurements in different reactive plas• mas were confirmed by comparing the electron density obtained with self-excited electron resonance spectro• scopy (SEERS) [3]. 2.3. Energy-mass spectrometry
Simultaneously to the LP measurements, the most important ions occurring in the plasma were analysed by energy and mass spectrometry (Hiden EQP 300) through an orifice of 50 Jlm diameter located in the vicinity of the plasma torus. The energy distributions of the most significant ions are shown under two different conditions: first the Faraday polarizer was not mounted, and then the polarizer was connected to the ground potential.
3. Results 3.1. Spatial plasma parameter distributions
The radial profiles of the electron density and the electron temperature obtained with gas mixture I (Ar/H 2 /CH 4 250/25/0.5 sccm) are shown in Fig.2(a). Three of the four rf coils (2,3,4) are also shown, while the first coil is outside the radial range. The electron density n. is marked with filled symbols and the mean electron energy E with empty symbols. Both parameters provided the highest values in the radial region below coil 3, where the central region of the occurring plasma torus is located. Both potentials, namely the floating Un and the plasma potential Upb are given in Fig.2b. The plasma potential also reached the highest values in the torus region, which was not the case for the smaller floating potential. All parameters (Fig. 2a and b) decreased for increasing radius above r = 55 mm in the direction of the reactor wall. In the second gas mixture (Ar/H 2 /CH 4 50/50/ 0.5 seem), a significantly lower argon concentration was used. The radial distributions of E and n. are given in Fig. 3a. While the mean electron energy. of this mixture is slightly higher than before and the radial profile very flat, the electron density is three times lower. As in the first gas mixture, the maxima of both pa~ameters are in the same plasma region. Both potentials are given in Fig. 3b. The behaviour is similar, but it is worth. men• tioning that both potentials increased for decreasing radius below r=35 mm. 3.2. Energy distributions ofions
A survey of all ions in the plasma containing gas mixture I is given in Fig. 4. Some of the highest count
P. Awakowlcz et al. / Surface and Coatings Technology 98 ( /998) /020-/026
1022
~
Q)
O~~
:
Te_______ o/~: .
1,6x1011
>-
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, , '0'
:
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E
Coil 3
Coil 2
2,Ox10 11
0-------
Coil 4
2,8
o~
2,4
e
o
1,6 ~
e
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ne
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~
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~
.
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,Substrat~
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,:position
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OJ
:2:
I--r----,--.-----,--r--......-r---,----.-,.----..-+ 0,0 20
40
30
50
60
70
80
Radial position [mm]
~
Coil· 2
12
(ij +:J
c::
OJ 0
0.
U
ctl
0.
:
6
c::
ctl
c::
.~-~~
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•
3
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----.
o
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Z-Orifoce
9
E CJ) ctl
yO
Coil 3
30
40
50
60
70
80
Radial position [mm]
Fig. 2. (a) Radial profiles of the mean electron energy (E) and the electron density (n.). Plasma conditions: 1.2 kW rf power, 4 mbar total preSSure, flows: Ar/H 2 /CH 4 250/25/0.5 sccm. Three rf coils (2,3,4) are also shown; coil I is not included in the radial interval. (b) Radial profiles of the floating and the plasma potential (Un, Up.). Plasma conditions: 1.2 kW rf power, 4 mbar total pressure, flows: Ar/H 2/CH 4 250/25/0.5 secm.
rates were detected for Ht , CHt and ArH + • The energy distributions of these ions are shown in Fig. 5. Note that the maxima of all energy distributions are located at relative low energies if the Faraday polarizer is grounded (Fig. 5a). In contrast, Fig. 5b shows the energy distribution of the same ions without the polar• izer. Relatively high ion energies up to 100 eV appeared in combination with increased count rates. The strong increase in the ion energy is caused by the rectified voltage drop in the sheath, as known from capacitive coupled plasmas. Comparison of the two ion energy distributions (Fig. 5a and b) shows that a pure inductive coupling is obtained by the use of the grounded polarizer and the capacitive coupling is remarkably increased if the plasma is operated without the polarizer. Further, it is particularly interesting to compare the strongly
increased count rates of Ht. This behaviour is due to the high diffusion coefficient of Ht compared with all other ions shown here. 3.3. Deposited coatings
The substrates are normally immersed in the high• density region of the plasma torus, as shown in Fig. 1. In Fig. 6, scanning electron micrograph (SEM) images and the corresponding micro-Raman spectrum (Fig. 6c) of the diamond films on (l00) silicon are given. The plasma conditions are as mentioned above, in combina• tion with gas mixture 1 (Ar/H z/CH 4 250/25/0.5 sccm). The mean crystal size is approx. 1 J.llTI. Since the depos• ition time was 18 h, a mean growth rate of about 0.7 Ilm h - 1 was deduced.
1023
P. Awakowicz et al. / Surface and Coatings Technology 98 ( 1998) 1020-1026 Coil 3
Coil 2
8,Ox10 10
T
6,Ox10 10
o
~ (J) Q)
-
4,Ox10 10
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~O
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~O
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e 1:5 c:
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~-
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0
~O
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0,0 -+----.--,--.-----,-..,.-----r-.....,.....-,-""'"T'"--r----,.-+ 0 20 30 40 50 60 70 80
Radial position [mm]
(a)
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-----
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30
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40
50
~ 60
70
80
Radial position [mm]
Fig. 3. (a) Radial profiles of the mean electron energy (E) and the electron density (n.). Plasma conditions: 1.2 kW rf power, 4 mbar total pressure, flows: Ar/H z/CH 4 50/50/0.5 seem. Three rf coils (2,3,4) are also shown; coil I is not included in the radial interval. (b) Radial profiles of the floating and the plasma potential (Un, Up;). Plasma conditions: 1.2 kW rf power, 4 mbar total pressure, flows: Ar/H z/CH 4 50/50/0.5 seem.
The growth with gas mixture 2 (Ar/H 2 /CH 4 50/50/0.5 scem) is shown in Fig. 7. Only hillocks of about 5 llm have been deposited. The substrate surface is far from being homogeneously covered. The same plasma conditions without the Faraday polarizer pro• vided only glassy carbon coatings. 4. Discussion First, it is interesting to compare the plasma potential U I in Fig. 2b with the ion energy distributions in Fig. Sa. The maxima of all distributions lie between 5 and II eV. The plasma potential at the position of the EMS orifice given in Fig. 2b agrees with the model that the ions gain
most of their energy on the way through the potential drop of the sheath between the plasma bulk and the wall. Other experiments with gas mixture I have been performed using the same external parameters as men• tioned above but without a grounded polarizer. No diamond growth was observed under these conditions. Therefore, we conclude that low ion energies are neces• sary for diamond growth. Experiments with a high hydrogen concentration (mixture 2) indicated an electron density less than half the density obtained with mixture 1 at the normal position of the substrate below rf coil 3 (Fig. 2a). Other experiments with mixture I and the substrate located below coil 2 (Fig. 2a) resulted in coatings without detect• able diamond crystals after 18 h growth time. From
P. Awakoll'ic= e/ al. / Surface and Coa/inKs Technology 98 ( 1998) I020-J()26
1024
these results it can be concluded that a high electron density is necessary for diamond growth. Further, a high electron density is accompanied by a high gas temperature. Therefore, a correlation between diamond growth and a high gas temperature could be assumed. The electron density measurements of the two different argon concentrations (mixtures I and 2) are in agreement with calculations [4] where it is shown that argon substantially increases the overall ionization rate and the Hz dissociation rate by electron collisions. The growth of diamond films in an ICP without a polarizer has been reported previously [5]. The high argon concen• tration (95%) used for the described experiment is in accordance with the aforementioned demand for low ion energies and high electron densities.
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Mass [amu) Fig. 4. Ion mass spectrum and relative count rates.
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Fig. 5. Ion energy distributions of the most intense masses of the Ar/H , /CH 4 250/25/0.5 sccm plasma: (a) with and (b) without a grounded Faraday polarizer.
1025
P. AlrakOlI"ic: et al. / Sur/iKe and Coatings Te<'i/nology CJIj ( ICJCJIj) 102U-1026
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Wavenumber shift [1Iem]
Fig. 6. (a,b) SEM images of diamond growth on ( 100) silicon deposited by means of the rf plasma: 1.2 kW rf power, 4 mbar total pressure, flows: Ar/H 2 /CH 4 250/25/0.5 seem (scale bars=5Ilm). (c) Laser micro-Raman spectrum.
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Fig. 7. SEM images of hillocks on (100) silicon deposited by means of the rf plasma: 1.2 kW rf power, 4 mbar total pressure, flows: Ar/H 2 /CH 4 50/50/0.5 seem (scale bars = 20 11m).
1026
P. Awakowicz et al. / Surface and Coatings Technology 98 ( 1998) 1020-1026
Acknowledgement The authors would like to thank F. Glatz (TV-Miinchen) for performing the Raman measure• ments. The Langmuir probe set-up was partly supported by the Dr. Johannes Heidenhain-Stiftung GmbH. References [I] W. Kasper, P. Awakowicz, ISPC 12, Minneapolis (1995) pp. 2239-2244. [2] W. Kasper, P. Awakowicz, ISPC XXII, New Jersey (1995) p. 171.
[3] M. Klick, W. Rehak, W. Kasper, P. Awakowicz, G. Franz, Surface and Coatings Technology 98 (1998). [4] Y.A. Mankelevich, A.T. Rakhimov, N.V. Suetin, S.V. Kostyuk, Diamond Relat. Mater. 5 (1996) 964-967. [5] S.P. Bozeman, D.A. Tucker, B.R. Stoner, J.T. Glass, W.M. Hooke, Appl. Phys. Lett. 66 (1995) 26.