Plasma technnology First published, 2007 Published by: Diener electronic GmbH + Co. KG Talstr. 5 72202 Nagold Germany http://www.plasma.de © Diener electronic GmbH + Co. KG All rights reserved. This publication may be reproduced or transmitted only with permission in writing from the publisher. Suggestions and remarks on this publication should be sent, if possible, by Email to: [email protected] Technical modications are subject to change Publishing date: 06.09.2007

1. Introduction into low-pressure plasma technology 1.1. How does a low-pressure plasma system work? The most important components of a system are the vacuum chamber, the vacuum pump and a high-frequency generator for plasma creation. The principle process of a low-pressure system can be most simply explained by gure 1 and 2. venting valve high frequency generator electrode workpiece process gas vacuum pump g. 1: schematic of kHz and MHz plasma systems magnetron venting valve quartz glass window process gas vacuum pump g. 2: schematic of a microwave plasma system (2,45 GHz) with metal chamber

Diener electronic • The Steps of a plasma process are shown in figure 3 as follows: fig. 3: process sequence of plasma treatment At first low pressure is created in a recipient by means of a vacuum pump. At a pressure of approx. 0.1 mbar the process gas (i.e. oxygen) is fed into the chamber. The working pressure field is ca 0.1 to 1.0 mbar. When working pressure is achieved, the generator is switched on and process gas in the recipient is getting ionized. The component for treatment is exposed to the plasma. The plasma system receives continuously fresh gas whilst contaminated gas is sucked off....

Further options of parameter variations concern the method of plasma creation. Energy, necessary for plasma creation, can be coupled to the chamber in different ways. In kHz- (40kHz) and MHz machines (13.56MHz) one electrode is likely to be placed within the plasma chamber (see gure 1). In microwave machines (2.45GHz) one aerial is permanently built into the magnetron. The magnetron is an electron-tube-oscillator that oscillates at a xed frequency. The aerial of the magnetron must not be based within the vacuum. For that reason microwaves are directed onto a glass or ceramic window to enter the...

1.2. What is plasma? If you continuously apply energy to matter, its temperature is rising and undergoes the process from solid-state to liquid and gas. Carrying on applying energy the existing shell of the atom is breaking up and electrically charged and excited particles and molecule fragments are formed (negatively charged electrons and positively charged ions, radicals). This mixture is called plasma or the fourth state of matter (aggregate state). In short: changes of the aggregate state under applied energy: Solid liquid gas plasma In nature plasma is found in lightning, the Northern Lights,...

Ionisation starts by the collision of an electron (negatively charged particle) with a molecule of the residual gas. A further electron is shot from the molecule. The molecule becomes a positively charged ion and moves towards the cathode. The electron moves towards the anode and meets further molecules. The accelerated cations release numerous electrons from the cathode. This process continuous like an avalanche until the gas is completely ionised. Various collisions lead to light visible emission. This electrical gas discharge remains as long as there is an energy source. Alternating voltage...

In plasma processes different effects are made use of. electron Elektron free binding freie Bindung oxygen radical Sauerstoffradikal Plastics Kunststoff g. 19: effects on plasma process To some extent the surface of parts to be treated is only mechanically “micro-sandblasted” by energy-rich gases (i.e. inert gas plasma). The emerging plasma reacts chemically with the treated part (i.e. oxygen plasma). The IR/UV-radiation content of plasma is breaking down carbon chains, with oxygen providing a greater surface for reaction and radical points are created. (g. 19). In polymerization processes monomers...

2. Low-pressure plasma technology 2.1. Applications 2.1.1. Cleaning 2.1.1.1. Cleaning of metals Some components are covered with grease, oils, wax and other organic or inorganic contaminants (also oxide layers). g. 20: Before plasma treatment g. 22: After plasma treatment For certain applications it is essential that completely clean and oxide-free surfaces are achieved. For example: • Before sputtering processes • Before lacquering processes • Before gluing • Before printing • In PVD and CVD Coating • In special medical applications • With analytical sensors • Before bonding • Before soldering...

Contamination should only be a few micrometres thick, since plasma is only capable of cleaning away a few nm/s. For example grease contains lithium compounds. Only organic constituents can be removed from those. The same applies to ngerprints. B. Metal oxide chemically reacts with the process gas (g. 23-25). Pure hydrogen or a mixture of argon and nitrogen is used as a process gas. g. 23: Before plasma treatment g. 25: After plasma treatment It is also possible to execute processes in two stages. For example treated parts are rst oxidised with oxygen for 5 min (g. 20-22) then they get reduced...

2.1.1.3. Cleaning of glass and ceramic Cleaning of glass and ceramic is carried out in the same manner as cleaning of metals (see chapter 2.1.1.1 “Cleaning of metals”). The recommended process gas for cleaning of glass is e.g. argon and oxygen. In general it can be said that cleaning is mostly carried out with oxygen plasma. Other parameters like pressure, power, gas ow, and duration of treatment depend on the sensitivity of the parts to be treated. 2.1.2. Activation 2.1.2.1. Activation of metals Activation of metal is in principle possible; however, activation of metal is very unstable and therefore...

Parts remain active for a few minutes up to some months. Polypropylene can still be reprocessed several weeks after treatment. Nevertheless, we recommend not storing parts openly as they attract dust and air humidity. Advantages: • Unlike aming, plasma treatment can be repeated. Compared to aming and corona treatment, consistency is signicantly higher. There are no toxic gases. The choice of process gases is much greater. Also gaps and hollow parts can be treated from inside. Primers are no longer required, the same applies to PTFE. Plasma treatment applies to all plastics. The method is very...