Plasma Jet Systems for Technological Applications

Two types of plasma jet systems working at low pressure and at atmospheric pressure are described. The system principles, main features as well as basic areas of their applications thin film depositions are given. Also, the different methods of discharge ignition in plasma jet systems continuous or pulsed DC or RF are reviewed. Selected advantages of plasma-aided technology are listed in the introductory chapter. Main advantages of plasma technology Plasma technological processes are widely spread in different manufacturing and experimental scopes of activity [1]. The interest to plasma systems rises due to continuous reduction of plasma equipment cost, high quality of the plasma treatment and increase of plasma equipment productivity. Together with it the plasma systems can be installed in technological line, since they as a rule do not require special cleaning equipment relatively to wide spread chemical technologies [1, 2]. Except listed advantages we can quote the following ones: — Coatings deposited by plasma methods have higher durability comparison to chemical deposition methods (for example to spin technology); — Possibility to produce the coatings which are impossible or economically pointless to deposit by other methods; e.g. DLC – films [3, 4]; — Possibility of local object treatment: That is especially helpful in the semiconductor manufacturing [5]. — Main plasma applications of plasma-aided technology are presented as follows: — Thin film plasma deposition and coating of different types of multi-layers: optical, semiconductor, indicative, ceramics, decorative, protective, conductive, wearproof etc. [6, 7, 8]. — Surface treatment: surfaces acquire the necessary properties without the deep impact to volume structure. Surface treatment is widely used to improve substrate adhesion properties before thin film deposition [9, 10]; — Etching: partial or full surface layers removal for creating of topological pattern in microelectronics or display technology [11, 12]. Micromechanism structure forming or micromembranes production [13]. Dry removal of organic layers from technological masks. — Ion implantation: Deep injections of impurity ion in semiconductor structure in order to create define type of conductivity and p-n junction forming [11, 12]. — Plasma sterilization [14]; — Plasma decomposition of domestic and industrial wastes and demolition of explosives [1, 15]. Plasma jet systems with hollow cathode The plasma jet systems with hollow cathode used for technological applications can be divided according their operational pressure into two main groups: low pressure and high pressure/atmospheric plasma chemical reactors. The hollow-cathode-effect has been described in literature [16, 17] and is a result of two interconnected processes. First process consists in the formation of beam of high energy electrons, so-called pendulum electrons, which oscillate between opposite inner walls in the hollow cathode. The gas particles are ionized by pendulum electrons which lose their energy for ionization and excitation. In the second process almost all ions, photons and metastable species which are created in the hollow cathode cavity bombard the inner hollow cathode surface and contribute to the emission of electrons from the nozzle surface [18]. Conventional low pressure systems with hollow cathode work at operational pressures from 10 Pa up to hundred Pa. For reasons of process cleanliness the deposition equipment with low-pressure plasma jet very often reaches ultimate pressure of the order 10 – 10 Pa before beginning of technological operation or experiments. Systems with hollow cathode that operate at pressures close to or at atmospheric pressure are not described here. Higher pressure leads namely to the decrease of the electron mean free path and hence the cathode size has to be reduced to micro-dimension in order to make use of the hollow cathode effect. Stable hollow cathode discharges in air have been observed at almost one atmosphere when the cathode diameter was reduced down to 20 micrometers. Concerning micro hollow cathode discharges the reader can refer to the literature [19]. Further the hollow cathode systems can be divided after the type of power source they use into DC, RF and microwave plasma jets. WDS'07 Proceedings of Contributed Papers, Part II, 202–206, 2007. ISBN 978-80-7378-024-1 © MATFYZPRESS