A reactive ion etcher is a plasma system configured to bombard a substrate with an anisotropic stream of ions generally for the purpose of cutting patterns into the substrate. The patterns are defined by a mask that prevents the ions from etching the surface where the mask is present. An anisotropic etch is made possible by bombarding the substrate from a single direction. Isotropic etching bombards the substrate from all angles would result in undercutting the mask.
In a reactive ion etcher it is very desirable to provide a uniform plasma etch. A uniform anisotropic etch is made possible by two plasma system modifications. The first modification is the placement of ion sending and receiving electrodes on either side of the substrate to be etched. Ions bombard the substrate at a right angle allowing it to cut perpendicularly into the substrate. The second modification is the incorporation of a gas shower. A gas shower delivers the process gas uniformly above the substrate insuring a uniform etch.
RIE etching is used extensively in the semi-conductor and microelectromechanical systems (MEMS) industries. For example, in the manufacturing of printed circuit boards (PCBs), anisotropic etching is used to form circuit patterns in wafers. Reactive plasma etching rates vary greatly depending on the RIE etch plasma system and substrate being plasma etched. RIE etch rates range from 0.001 micrometer/minute to 1 micrometer/min.
A RIE etch is typically carried out at a plasma frequency of 13.56 MHz. Other frequencies typically used for the generation of a plasma are 40kHz and 2.45GHz. The lower frequency kHz provides has a longer wavelength and is considered more useful for plasma cleaning or desmearing as the longer wavelengths provide ions with a large amount of kinetic, mechanical, energy. The high frequency, shorter wavelength GHz is typically considered more useful for promoting chemical reactions. The GHz frequency is thus considered more useful for processes such as plasma polymerization.