Invasion percolation model for abnormal TDDB characteristic of ULK dielectrics with Cu interconnect at advanced technology nodes

Abstract

With the continuing aggressive scaling of interconnect dimensions and introduction of new lower k materials, dielectric TDDB reliability margin is greatly reduced. In this paper, a comprehensive investigation on an abnormal low-k TDDB characteristic, a systematic degradation of Weibull slopes at lower stress voltages, was conducted for Cu and CuMn alloy interconnect with porous ultra low-k (ULK) CVD dielectric (k=2.4). Based on extensive electrical and physical evidences, such abnormal TDDB characteristic was attributed to slow metallic diffusion in bulk ULK induced by Mn and Cu segregation. A new TDDB model based on invasion percolation was proposed to successfully model the observed abnormality. CuMn interconnect with robust liner to assure metal free ULK has become important for TDDB reliability.

Electrical Breakdown in Advanced Interconnect Dielectrics

“…Note also that TVS can be applied to both planar [309,310] and damascene capacitors [302,311,312]. (2) Slowly run a linear voltage sweep from the positive to the negative gate bias.…”

“…Also, voids within the IMD or voids on top within the capping dielectric layer have been seen, but their appearance after breakdown may depend upon the capping dielectric composition [298]. Specialized failure analysis techniques -such as transmission electron microscopy (TEM) with energy-dispersive X-ray spectroscopy (EDX or EDS), or electron energy loss spectroscopy (EELS), or secondary ion mass spectroscopy (SIMS) line scans -may be used to assess the presence of unusual nanoscopic defects found after TDDB stress [238,301,302]. Because the electric field is typically highest at the trench top, damage is usually found to be concentrated in that area of the test structure crosssection, unless there is a case where another damage path has triggered failure, such as when metal barrier failure has occurred [93,299].…”