Capacitively coupled reactor

A capacitively coupled reactor designed to permit continuous coating of a moving substrate with plasma polymer has been described [ 1 ]. In this paper the results of a study of the plasma polymerization of tetrafluoroethylene in such a reactor presented. Plasma polymer has been deposited on aluminum electrodes as well as on an aluminum foil substrate placed midway between electrodes. The study particularly explores conditions in which deposition is minimized on the electrode. For this reason the chemical nature of the polymer formed in a low flow rate (F = 2 cm (S.T.P.)/min) and low pressure (p = 60 mlllltorr) plasma has been analyzed by the use of ESCA (electron spectroscopy for chemical analysis) and deposition rate determinations. This method combined with the unusual characteristics of TFE plasma polymerization (described below) has yielded Information concerning the distribution of power in the inter-electrode gap. The effects of frequency (13.56 MHz, 10 KHz and 60 Hz), power and magnetic field have been elucidated. The properties of the TFE plasma polymer prepared in this apparatus are compared to those of the plasma polymer deposited in an inductively coupled apparatus [2,3]. 

Although a plethora of reactor configurations and methods for plasma generation exist (see Section 4), the parallel plate capacitively-coupled reactor (also called diode) shown in Fig. 3a is a typical example. A semiconductor wafer rests on one electrode... 

Application to capacitively-coupled reactors Figure 24a shows the electron temperature distribution in an argon discharge sustained in a one-dimensional parallel plate reactor of the kind shown in Fig. 7. The temperature peaks near the plasma-sheath interface, where the product of the current and electric field (Eq. 31) is highest, and steep gradients develop in that region. Electrons which diffuse towards the electrode during the sheath potential minimum (around r = 0.25 at left electrode, see also Fig. 

The second plasma treatment was carried out in a special reactor (capacitively coupled reactor) devoted to this reaction. Figure 4.27 shows the morphological char-... 

FIG. 4. Schematic representation (a) of a parallel-plate, capacitively coupled RF-discharge reactor, with unequal-size electrodes. The potential distribution (b) shows the positive plasma potential Vp and the negative dc self-bias voltage... 

The plasma potential is about 25 V (Figure 63a). This value of the plasma potential is typical for the silane plasmas in the asymmetric capacitively coupled RF reactors as used in the ASTER deposition system, and is also commonly found in argon or hydrogen plasmas [170, 280, 327]. From the considerable decrease of the dc self-bias with increasing frequency (Figure 63a) it is inferred that the... 

In contrast, Heintze and Zedlitz [236] also presented data on the plasma potential as function of frequency in silane plasmas the plasma potential varies from about 27 V at 35 MHz to about 20 V at 180 MHz. Moreover, Dutta et al. [284] used a symmetric capacitively coupled RF reactor and estimated the plasma potential in their system from the applied voltage at the powered electrode. A decrease of the plasma potential from 45 V at 13.56 MHz to only 15 V at 70 MHz is observed. This difference in behavior is thought to be solely due to the different reactor geometries. 

Physical and Electrical Characteristics. The electrical potentials established in the reaction chamber determine the energy of ions and electrons striking the surfaces immersed in a discharge. Etching and deposition of thin films are usually performed in a capacitively coupled parallel-plate rf reactor (see Plasma Reactors). Therefore, the following discussion will be directed toward this configuration. 

Figure 11 Geometries of plasma-assisted CVD reactors (A) parallel-plate discharge, (B) tube with capacitive coupling, (C) tube with inductive coupling.13...

All plasma exposures were carried out in an IPC (International Plasma Corporation) 2005 capacitance-coupled barrel reactor at 13.56MHz. The reactor was equipped with an aluminum etch tunnel and a temperature controlled sample stage. Pressure was monitored with an MKS capacitance manometer RF power was monitored with a Bird R.F. power meter and substrate temperature was measured with a Fluoroptic thermometer utilizing a fiber optic probe which was immune to R.F. noise. 

In such a capacitive discharge, powder formation was stated to occur in the region of low pressure and low flow rate, whereas in the inductively coupled reactor used by Liepins and Sakaoku [7] it was found to occur under conditions of high flow rate and high pressure. The critical parameter for powder formation, however, was reported by Kobayashi et al. [9] to be the energy input per mole of gas. They reported that for a pressure of 2 torr, the approximate values of the critical energy input of 50, 100, and 150 W correspond to dosages of 2.68 x 10, 2.9 x 10, and 2.08 X lO J/mole, respectively. 

Ihe equipment used in this study (Figure 1) consisted of a capacitively-coupled plasma reactor similar to the apparatus described by Poulsen 3) for the plasma etching of integrated circuits. This arrangement resulted in uniform depositions over a range of flow rates and improved utilization of monomer. 

The synthesis of the metal containing polymer films involves a capacitively coupled diode reactor configuration in which one electrode is grounded, (the anode). 

The effect of increasing flow rate in inductively coupled systems is to increase deposition rate as long as power is such as to maintain full glow in the reactor [ 7]. Other investigators have used a capacitively coupled system with RF and noted that at low flow rates, deposition rate is proportional to flow rate [ ]. There is therefore reason to believe that deposition rate will be proportional to flow rate in the capacitively coupled system if the applied power is high enough. 

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. 

The two-dimensional self-consistent ICP reactor simulation of Wise et al. [101, 148, 152] employs a modular approach similar to that used for capacitively-coupled... 

Important plasma diagnostics include Langmuir probes, optical emission spectroscopy, laser induced fluorescence, absorption spectroscopy, mass spectrometry, ion flux and energy analysis, and plasma impedance analysis. A plasma reactor equipped with several of these diagnostics is shown in Fig. 51 [35, 160]. A capacitively coupled plasma is sustained between the parallel plates of the upper (etching) chamber. The lower (analysis) chamber is differentially pumped and communicates with the etching chamber through a pinhole on the lower electrode. 

---