The current industrial process of choice for Deep Reactive Ion Etching (DRIE) of 3D features, e.g. Through-Silicon Vias (TSVs), Microelectromechanical Systems (MEMS), etc., is the Bosch process, which uses alternative SF6 etch cycles and C4F8-based sidewall passivation cycles in a time-sequenced mode. An alternative, potentially faster and more accurate process is to have wafers pass under spatially-divided reaction zones, which are individually separated by so-called N2-gas bearings ‘curtains’ of heights down to 10–20 μm. In addition, the feature sidewalls can be protected by replacing the C4F8-based sidewall passivation cycles by cycles forming chemisorbed and highly uniform passivation layers of Al2O3 or SiO2 deposited by Atomic Layer Deposition (ALD), also in a spatially-divided mode. ALD is performed either in thermal mode, or plasma-assisted mode in order to achieve near room-temperature processing.
For metal filling of 3D-etched TSVs, or for deposition of 2D metal conductor lines one can use Laser-Induced Forward Transfer (LIFT) of metals. LIFT is a maskless, ‘solvent’-free deposition method, utilizing different types of pulsed lasers to deposit thin material (e.g. Cu, Au, Al, Cr) layers with μm-range resolution from a transparent carrier (ribbon) onto a close-by acceptor substrate. It is a dry, single-step, room temperature process in air, suitable for different types of interconnect fabrication, e.g. TSV filling and redistribution layers (RDL), without the use of wet chemistry.
Reliability Evaluation of Fan-Out Type 3D Packaging-On-Packaging