A unified system for high aspect ratio non-line-of-sight wet etching of silicon carbide via two-photon absorption

This paper presents the technique and equipment that enable the creation of arbitrary high aspect ratio, non-line-of-sight 3D features in SiC. The technique is a combination of two-photon absorption and photo-electrochemical etching. SiC etches in hydrofluoric acid when holes are present. The holes are generated at an arbitrary location in the SiC substrate by using sub-bandgap light to transmit light through the substrate and then using two-photon absorption to produce holes at the focus of the laser. The basic equipment consists of an optical subsystem capable of producing high-intensity light at the focus, a motion control subsystem with accurate surface detection, and a fluid chamber that allows for incident light and etch solution to reach the etching surface. The technique and equipment are demonstrated by fabricating a non-line-of-sight through-wafer via completely through a SiC wafer.