High yield dense array of very-high-aspect-ratio micro metal posts by photo-electrochemical etching of silicon and electroplating with vacuum degassing

A high yield fabrication of a dense array of very-high-aspect-ratio (VHAR) freestanding metal posts over a large area is presented. The fabrication is based on photo-electrochemical etching of silicon and bottom-up electroplating of the metal. By using various new techniques, most notably degassing-assisted electroplating, freestanding nickel posts with aspect ratio and height up to 85:1 and 425 ??m, respectively, are realized. While the increase in the aspect ratio of the posts may appear more revealing, the dramatic improvement in yield and uniformity is often more important for applications. The report is over our entire processing area (3 cm²), unlike most others in the literature (1 mm² - 1 cm²).