A plasma supply device is a plasma power supply that supplies plasma processes with electrical power. The plasma supply device operates at a basic frequency that, when used as a plasma power supply, should only deviate slightly from a theoretical value. Typical basic frequencies are 3.39 MHz, 13.56 MHz, 27 MHz, 40 MHz, and 62 MHz.
A plasma is a special aggregate state that is produced from a gas. Every gas consists in principle of atoms and/or molecules. In the case of a plasma, the gas is largely ionized, which means that the atoms and/or molecules are split into positive and negative charge carriers, i.e., into ions and electrons, due to the supply of energy. A plasma is suitable for processing workpieces because the electrically charged particles are chemically highly reactive and can also be influenced by electrical fields. The charged particles can be accelerated by means of an electrical field on a workpiece, where they can release individual atoms from the workpiece on collision.
The released atoms can be removed by gas flow (etching) or deposited on other workpieces (production of thin films). A plasma can be used to deposit extremely thin layers, for example, in the region of few atom layers. Typical applications for plasma processing are semiconductor technology (coating, etching, etc.), flat screens (similar to semiconductor technology), solar cells (similar to semiconductor technology), architectural glass coating (heat protection, dazzling protection, etc.), storage media (CD, DVD, hard discs), decorative coatings (colored glasses, etc.) and tool hardening. These applications impose high demands in terms of accuracy and process stability.
A plasma can also serve to excite lasers, particularly gas lasers.
To generate a plasma from a gas, energy is supplied to the gas. Energy can be supplied in different ways, for example, as light, heat, or electrical energy. Moreover, a plasma can be ignited with the electrical energy. A plasma for processing workpieces is typically ignited in a plasma chamber, for which purpose an inert gas, e.g., argon, is generally filled into the plasma chamber at low pressure. The gas is exposed to an electrical field that is produced by electrodes and/or antennae.
A plasma is generated or is ignited when several conditions are met. A small number of free charge carriers must be present, and in most cases use is made of the free electrons that are always present to a small extent. The free charge carriers are accelerated so much by the electrical field that they create additional electrons when colliding with atoms or molecules of the inert gas, thus producing positively charged ions and additional electrons. The additional free charge carriers are again accelerated and on collision produce further ions and electrons. An avalanche effect is created. The natural recombination counteracts the constant generation of ions and electrons, i.e., electrons are attracted by ions and recombine to form electrically neutral atoms and/or molecules. Therefore energy is constantly supplied to an ignited plasma in order to maintain the plasma.