By Claudio Truzzi, Frederic Raynal, Vincent Mevellec and Ga?lle Guittet by Alchimer
This paper discusses the level of maturity and the impact on the 3D-IC design space of the electrografting nanotechnology optimized for highly conformal growth of TSV films.
Introduction Through Silicon Vias (TSVs) sit at the foundation of the 3D-IC revolution and are a key enabler for extending semiconductor integration trends into a new phase. Integrated Device Manufacturers and fabless design houses need small, high-density, fine-pitch vias for improved signal integrity and Si real-estate savings.
They need them now, and cannot wait for very thin wafer processing and handling technologies to become mainstream ? TSVs must cope with current wafer thickness. Deep TSVs with Aspect Ratio (AR) greater than 10:1 elegantly fulfill both requirements. But they cannot be manufactured with acceptable yield/cost using traditional dry processes for liner, barrier and seed deposition.
Chemical and Physical Vapor Deposition techniques show basic shortcomings and impose high capital investments, holding back the industry-wide adoption of 3D-IC solutions. Electrografting (eG)  is a nanotechnology delivering high-quality films for high-AR (HAR) TSVs. It generates surface-initiated conformal films which are thin, continuous, adherent and uniform. It is a wet-process technique, operated in standard plating tools, which has proven its efficiency to deposit ultra-thin (<10nm) seed layers on PVD  or ALD  diffusion barriers for interconnect Back End Of Line (BEOL) applications.
Chemical grafting (cG) is a similar technology, used to graft films on non-conductive surfaces. A wet deposition of insulator, barrier and seed layers inside deep TSVs using a combination of electrografting and chemical grafting techniques has already been demonstrated .
Electrografting for HAR TSVs Electrografting is a nanotechnology based on surface chemistry formulations and processes. It is applied to conductive, semi-conductive and resistive surfaces. It enables self-oriented layer growth of thin coatings of various materials, initiated by in-situ chemical reactions between specific precursor molecules and the surface.
Using industry standard wet-process tools, the wafer surface is exposed to chemical precursors of the desired film. Electrons from the biased surface serve as “bonding seeds” for the precursor molecules, creating a chemical bond between the first seeded precursor and the surface. For TSV applications, a polymer layer is directly grafted onto the silicon surface, yielding a highly conformal and adherent coating.