The role of Plasma and Hot Filaments in enhanced-CVD processes of carbon deposition F. Le Normand 1, M. Guláš *1, J. Krištof 3, M. Angus3, P. Veis 3, C. S. Cojocaru 2, S. Farhat 4 1 IPCMS/GSI,
UMR 7504 CNRS, 23, rue du Loess, 67034 Strasbourg Cedex, FRANCE 2 LPICM, UMR 7647 CNRS, Ecole Polytechnique, Palaiseau, FRANCE 3 DEP, FMFI UK, Comenius University, Mlynska dol. F2, 84248 Bratislava, SLOVAKIA 4 LIMHP,UPR 1311 CNRS, 93430 Villetaneuse, FRANCE *present adress: Facultés Universitaires Notre-Dame de la Paix/ LISE, Rue de Bruxelles, 61, B-5000 Namur, BELGIUM e-mail:
[email protected]
Introduction
Experimental Set-up [3, 4]
A physico-chemical model based on ChemkinTM software is used to simulate gas phase and surface chemistry during plasma-enhanced catalytic CVD of carbon nanotube. A mixture of acetylene, hydrogen and ammonia (C2H2/H2/NH3) is used to produce carbon nanotubes. Morphological and structural investigations on the grown carbon nanostructures are also performed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was shown that the significant change in the density and the morphology of the CNTs grown in the presence of NH3 could be mainly explained by the gas phase formation of CN and HCN species. Both species display a high etching activity, whereas the species C, CH, CH2, CH2(S), C2 and C2H are expected to be the most probable carbon nanotube precursors [1].
Simulations For the gas phase and surface kinetics simulations the software CHEMKIN [2] is used. This collection of software consists of various programs such as: AURORA which allows the simulation of electrons density, ion density for thermal or nonthermal plasma where temperature of gas T differs from temperature of electrons Te and SPIN for the simulation of the CVD reactor in 1D. The reaction mechanism is described by Arrhenius equation and three Arrhenius coefficients.
k
AT exp
Configuration of the DC HF CVD chamber with two regions where plasma occurs. Conditions: Q=100 sccm (20 C2H2/79 H2/1 NH3), plasma power P = 1 W, pressure 10 mBar, Ts = 975 K, Tf = 2200K. Photo at 700 K
4 Catalytic CVD Modes CCVD mode
E RT
Thermal CCVD HF CCVD PE CCVD PE HF CCVD
PE (DC) HF CCVD
10
PE HF CCVD
Amorphous carbon
Encapsulated particles by graphite
Sporadic and tiny CNTs
Very dense film of oriented CNTs
Calculated concentration profiles for the most abundant molecules and radicals in the PE HF CCVD mode.
PE CCVD PE HF CCVD
10
14
10
13
10
-3 num ber density [cm
12
CH 4 N2 C2 H2
10
11
10
10
10
9
10
8 C
CH
CH2 CH2(S) CH3 CH4
C2
C2H C2H2 C2H3 C2H4 C2H5 C2H6
Calculated number densities (of selected species) with filaments turned off and on, respectively. Atomic hydrogen concentration (not shown) is almost 3 orders of magnitude higher with filaments turned on.
2000
10 10 10
15
14
10
C2 H3 C2 H CN Tg
1600 1400
13
1200
10
HC N C2 H4
1800
12
1000 11
800 0
substrate
1
2
3
negative glow
4
5 filament
ratio 1000
1,2
C CH 3
2200
16
Model fit
H H2
2400
]
10
17
tem perature [K]
]
PE CCVD
Growth Rate [m icron/min]
15
-3
HF CCVD
900 1,0
800 700
0,8
600
0,6
500 0,4 400 0,2
number d ensity (C:H >=1) number density (C:H
