A Plasma etch refers to a plasma treatment that removes portions or layers from a substrate surface. Plasma etching is used in a number of applications to increase adhesion, clean, or to carve patterns into objects. Plasma etching can be conducted as an isotropic etch (etching in all directions) or anisotropic etch (etching in a single direction). Isotropic etching is used to remove material from a large surface whereas anisotropic etching is used to etch patterns into substrates.
Plasma etching is used extensively in the semi-conductor and microelectromechanical systems (MEMS) industries. For example, in the manufacturing of printed circuit boards (PCBs), isotropic etching is used to plasma clean circuits after machining (a process termed desmearing) and prior to electroplating. Anisotropic etching is used to form circuit patterns in wafers. The anisotropic plasma etching in this application is highly energetic and called reactive ion etching (RIE).
Plasma etching is delivered by a plasma etcher which is very similar to other vacuum plasma systems. A reactive ion etcher achieves the anisotropic flow of the ions by having electrodes on either side of the object surface to be etched. The ions travel from one electrode to the other bombarding the substrate surface at a perpendicular angle. To achieve the uniformity required for PCB manufacture, a gas shower is also used to uniformly distribute the process gas into the vacuum chamber near the substrate surface. The use of a gas shower increases the homogeneity of the plasma from approximately 70% to greater than 95%.
Plasma etchers are available in a variety of sizes. Industrial large chamber plasma systems can be as large as 12,600 Liters (approximately 3,333 gallons). These systems are custom built to meet unique challenges of large scale plasma processing. Other plasma systems convey parts on a tray that doubles as the plasma chamber floor. Parts to be processed are conveyed to the plasma chamber, raised into it, treated, lowered and conveyed to the next step.