Abstract
AbstractThe fabrication of Sn cap and SiNx cap Cu/Ta/SiO2 air-gap damascenes structures which includes the integration of electroplating copper, diffusion barrier Ta, sacrificial layer HSQ and capping layer Sn is the main goal in this thesis. The electromigration on this single damascene structure is also investigated. We developed the selective immersion plating Sn on copper, use Auger、GIAXRD to examine the composition of Sn thin film, and use AFM to measure the surface Morphology of Sn film. We mixed HSQ with MIBK at ratio=2:1 and spun it on SiO2 substrate. The HSQ film with pre-bake temperature 350℃ 3min is a good sacrificial layer. The cage-network-like HSQ can be removed by BOE solution easily from the interface with SiO2.Cu interconnect lines with width/space = 0.6/0.6μm deposited on Ta barrier layer are under chemical-mechical polished by using Al2O3 0.05μm particle with mixture HNO3 and Citric Acid, down force/back pressure varying 5.0/4.0、4.0/3.0、3.0/2.0 psi to remove Cu and by using Silica Levasil 50CK with H2O2 and H2O, D.F/B.P =3.0/2.0 to remove Ta. From the SEM pictures, We determine the best CMP conditions. Final, the Sn cap and SiNx cap Cu air-gap damascene structures with diffusion barrier Ta, sacrificial layer HSQ and capping layer Sn were fabricated. Sn cap and SiNx cap samples were studied by electromigration tests at 1750C with a current density of 4*106A/cm2, at pressure of 2 mtorr. The electromigration lifetimes for Sn cap air gap Cu interconnect lines were found to be longer than that of SiNx cap air gap Cu interconnect lines about 4.5 X. In order to determine the activation energy of electromigration, we measured the I-V under current stress at varying temperature with 1500C、1750C、2000C. The activation energy for Sn cap air-gap Cu interconnect lines is found to be 1.07eV.