Radio-frequency plasma reactor

To extend the hydrogen evolution potential in an aqueous media, a fluorine-terminated diamond surface is prepared in a radio frequency plasma reactor of CF-He [124]. Fluorine-terminated diamond is usually used to study electrode reactions that require high over potential. For covalent attachment of different biomolecules, hydrogen-terminated diamond electrodes are also treated with ammonia plasma to prepare the surface with terminal amine groups [125]. 

The radio-frequency glow-discharge method [30-34] has been the most used method in the study of a-C H films. In this chapter, it is referred to as RFPECVD (radio frequency plasma enhanced chemical vapor deposition). Film deposition by RFPECVD is usually performed in a parallel-plate reactor, as shown in Figure 1. The plasma discharge is established between an RF-powered electrode and the other one, which is maintained at ground potential. The hydrocarbon gas or vapor is fed at a controlled flow to the reactor, which is previously evacuated to background pressures below lO"" Torr. The RF power is fed to the substrate electrode... 

Pai, M. P., Musale, D. V. and Kshirsagar, S. T. (1998), Low-pressure chemical vapour deposition of diamond films in a radio-frequency plasma-assisted hot-filament reactor. Diam. Relat. Mater., 7(10) 1526-1533. 

Figure 1 is a block diagram of a typical radio frequency plasma system. It consists of 5 modules or functions vacuum system, power supply, matching network, power monitor, reactor center, and controller. 

Thin hexafluoropropylene (HFP) films were deposited applying different reactor conditions by a radio frequency plasma enhanced chemical vapor deposition process onto photolithographic masked silicon surfaces, (a) depicts the crosslink density calculated from ESCA experiments (28). (b) shows the normalized amplitude response. The difference between silicon and HFP response was measured from recorded images allowing for an accurate statistical averaging, and converted into the difference in contact stiffness ks. The SFM measurements were carried in a nitrogen atmosphere (humidity < 4 %) at room temperature. Scan speed was 50 jjm/s, applied lateral modulation amplitude 3.5 nm, and modulation frequency 13 kHz. No external load was applied to the cantilever. 

Radio frequency plasma fluorination is a low-temperature process where fluorinated gases are excited by an rf source and dissociated into chemically active atoms, radicals and molecules. Several fluorinated gases were used CF4, CsFg and c-C4Fg, which were excited by a rf source at 13.56 MHz. A primary vacumn was obtained by a 40m. h pump equipped with a Uquid nitrogen condenser, which trapped the residual gases. The reactor comprised two cylindrical barrel-type aluminium electrodes which were coated with alumina and which were located within a distance of 2 cm from each other and several gas inlets allowing the use of gas mixtures. The inner electrode was connected to the rf... 

Plasmas can be used in CVD reactors to activate and partially decompose the precursor species and perhaps form new chemical species. This allows deposition at a temperature lower than thermal CVD. The process is called plasma-enhanced CVD (PECVD) (12). The plasmas are generated by direct-current, radio-frequency (r-f), or electron-cyclotron-resonance (ECR) techniques. Eigure 15 shows a parallel-plate CVD reactor that uses r-f power to generate the plasma. This type of PECVD reactor is in common use in the semiconductor industry to deposit siUcon nitride, Si N and glass (PSG) encapsulating layers a few micrometers-thick at deposition rates of 5—100 nm /min. 

Continuous production of fullerenes was possible by pyrolysis of acetylene vapor in a radio-frequency induction heated cylinder of glassy polymeric carbon having multiple holes through which the gas mixture passes [44]. Fullerene production is seen at temperatures not exceeding 1500 K. The yield of fullerenes, however, generated by this method is less than 1%. A more efficient synthesis (up to 4.1% yield) was carried out in an inductively coupled radio-frequency thermal plasma reactor [45]. 

FIGURE 7.1 Reactor configuration for gas phase reactors (a) Flame reactor, (b) furnace reactor, (c) laser reactor, (d) radio frequency (RF) plasma reactor, (e) direct current (dc) plasma reactor. 

In 1972, Liepins and Sakaoku [7] reported that polymeric powders were formed nearly exclusively in the radio frequency reactors shown in Figures 8.12 and 8.13, in which an organic vapor was introduced into the glow discharge of a carrier gas. The monomers that formed powders nearly exclusively and the yield of powder formation are summarized in Table 8.1. Monomers that did not form powders exclusively (i.e., formed plasma polymer in the form of a film or a film with powders) are shown in Table 8.2. The significant points about these experiments are as follows ... 

The tubular-type plasma reactor system used in the study consists of a reactor chamber, power supply, monomer feed, and pumping-out units, as depicted in Figure 19.1. One side of the glass tube is connected to a monomer inlet and the other side to a vacuum pump with O-ring joints. A radio frequency power generator of 13.56 MHz is coupled to two capacitive copper electrodes, which are 1 cm wide and 6 cm apart. The radio frequency power was controlled by an L-C matching network and monitored by power meter. 

Ihara and Yasuda investigated the deposition behavior of methane in the medium-sized tubular reactor with 13.56 MHz radio frequency discharge [2]. They observed that the critical WjFM value, WjFM), for methane was 8GJ/kg, and nearly 100% of monomers were converted to the plasma polymer beyond this critical WjFM value. As shown in Figure 19.5, the critical WjFM value of perfluoropropene in the small reactor is around 6GJ/kg and the DjFM is 15%, and the corresponding value in the medium is around 4GJ/kg, and the maximal conversion is around 30%. In the large reactor, (WIFM) is about 1 GJ/kg and the maximal DjFM is 20%. The lower value of the critical WjFM for C3F6 than that for CH4 is explained in Chapter 7. 

The distribution of polymer deposition observed in the plasma polymerization of acetylene at different flow rates (and different system pressures under plasma conditions) is shown in Figure 20.2. It should be noted that acetylene is the fastest polymerizing hydrocarbon and the system pressure decreases on the inception of glow discharge. In this particular configuration of reactor, the monomer does not pass the radio frequency coil, and presents a typical case in which the creation of chemically reactive species occurs at the boundary where the monomer meets the luminous gas phase, i.e., activation by luminous gas, not by ionization. 

These experimental data indicate that three major factors influence the polymer deposition in a plasma reactor the locations of (1) the energy input (radio frequency coil in these cases), (2) the monomer flow inlet, and (3) the monomer flow outlet. The local deposition rate di observed at a location is expressed as a function of the location of polymer deposition. These experimental data indicate that the major parameter that determines d is the distance from the energy input. Other factors (i.e., monomer inlet and outlet) determine the direction of flow, which can be either along or against the direction of the energy input to the point of polymer deposition. The direction of monomer flow has less influence on the polymer deposition than the distance from the energy input. 

Radio frequency argon plasma treatment of Parylene C surfaces is very attractive because two processes—Parylene deposition and plasma treatment—can be carried out in the same reactor, the Parylene reactor. It was found that radio frequency... 

Besides the MPCVD reactors, other CVD reactors are also used for diamond deposition. They are hot filament, DC plasma, radio-frequency (rf) plasma, thermal rf plasma, plasma jet, and combustion CVD reactors. In the following, hot filament and DC plasma CVD reactors will be described, because they have been used for oriented growth of diamond. 

Plasma polymerization of aniline in the absence of a solvent or a chemical oxidant, giving neutral undoped PAn, was first described in 1984.110 This method has been further developed111112 recently with, for example, Cruz and coworkers, describing the deposition of PAn film using radio frequency (RF) glow discharges between stainless steel electrodes and at 0.02-0.08 atm pressures. The aniline monomer reacts with electrons in the plasma, and the polymer deposits on the reactor wall after growth.100... 

The detailed discussions of the plasma reactor used has already been given (5) Briefly, it was a cylindrical glass vessel of about 60 x 10 cm O.D. The radio frequency (RF) plasma generator (Tegal Corp., Richmond, California) was capacitatively coupled to the plasma reactor by placing flat strips of copper electrodes along the outside circumference. The substrate polymer membrane was placed 7.5 cm downstream from the gas outlets. 

Inductively coupled plasma (ICP) reactors (Fig. 20a) are particularly attractive because their design is relatively simpler and they are easily scaleable to large diameter substrates [84, 85]. In ICPs, the plasma is excited in a cylindrical chamber (r, 2,0) by a solenoidal or planar (stovetop-type) coil powered at radio frequencies, for example 13.56 MHz. The coil current induces a time-varying magnetic field which in turn induces an azimuthal (in the 0-direction) electric field that couples power to the plasma, i.e., heats the plasma electrons. For common excitation frequencies (less than the plasma frequency), the electromagnetic fields are absorbed by the plasma within the skin depth. For typical conditions, fields penetrate a few cm into the plasma. The power is deposited non-uniformly in the shape of a toroid (see also Fig. 

Plasma processing reactors normally operate with the wafer biased at radio frequencies, typically in the range 0.1 to 13.56 MHz. Even if the ions injected at the sheath edge were monoenergetic, an lED would result in an RF (time-dependent) sheath, even in the absence of collisions. The literature on RF sheaths is voluminous. Both fluid [170-175] and kinetic (e.g., Monte Carlo) [176-180] simulations have been reported. One of the most important results of such simulations is the lED. The ion angular distribution (IAD) [74, 75] and sheath impedance (for use in equivalent circuit models) [32] are also of importance. 

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