Research advances of electrochemical micro/nanofabrication based on confined etchant layer technique

Abstract

Compared with mechanical machining, ECM has several advantages, such as avoiding tool wear, none thermal or mechanical stress on machining surfaces, as well as high removal rate. Moreover, ECM is capable of making complex three-dimensional structures and is appropriate for flexible, fragile, or fissile materials even materials harder than the machining tool. Thus, ECM has been widely used for various industrial applications in the fields of aerospace, automobiles, electronics, etc. ECM methods can be classified usually as electrolytic machining based on anodic dissolution and electroforming based on cathodic deposition of metallic materials. Recently, high technology industry, such as ultralarge scale integration (ULSI) circuits, microelectromechanical systems (MEMS), miniaturized total analysis systems (μ-TAS) and precision optics, has developed more and more rapidly, where miniaturization and integration of functional components are becoming significant. Nowadays, the feature size of interconnectors in ULSI circuits has been down to 20 nanometers, predicted by Moore’s law. Confined etchant layer technique (CELT) was proposed in 1992 to fabricate three-dimensional micro- and nanostructures (3D-MNS) on different metals and semiconductors, which has been developed an effective machining method with independent intellectual property rights. Generally, there are three procedures in CELT: (1) generating the etchant on the surface of the tool electrode by electrochemical or photoelectrochemical reactions; (2) confining the etchant in a depleted layer with a thickness of micro- or nanometer scale; (3) etching process when the tool electrode is fed to the workpiece, which applicable for 1D milling, 2D polishing, and 3D microfabrication with an accuracy at micro or nanometer scale. External physical-field modulations have recently been introduced into CELT to improve its machining precision. In this review, the advances of CELT in principles, instruments and applications will be addressed as well as the prospects.