Germanium Bonding to AL2O3

Abstract

Germanium has been bonded to both single crystal Al2O3 (sapphire) as well as fine grain Al2O3. A germanium to sapphire bonding energy of 3 J/m2 has been measured after a 200 oC bond anneal. Micro voids formed between the germanium/sapphire interface can be removed by employing an interfacial layer of silicon dioxide on either surface. Patterning the sapphire into a grid pattern prior to bonding creates an escape path for trapped gas or moisture allowing micro void free direct bonding to be achieved. Modifying the surface of the fine grain Al2O3 surface with a polycrystalline silicon deposition and polish creates a surface, having an rms roughness of 1.5nm(measured over a 250µm square area), suitable for bonding. Techniques employed in the germanium sapphire bonding can then be used in the bonding of fine grain Al2O3 to germanium.

Circular Geometry Transistors Fabricated on Germanium-on-Alumina Bonded Substrates

“…Ge Bonding to Fine Grain Al 2 O 3 As reported previously (5) bonding to fine grain Al 2 O 3 substrate requires the deposition of an interface layer of LPCVD polycrystalline silicon which is subsequently polished from 0.8 μm to 0.2 μm. Polysilicon deposition temperature was 620 o C. This produces an optically flat surface suitable for bonding.…”