New Access to Soft Breakdown Parameters of Low-k Dielectrics Through Localisation-Based Analysis

This paper provides a further understanding of soft breakdown (SBD) defects occurring in metal insulator metal (MIM) back end of line (BEOL) test structures with copper metallization and a low-k dielectric. Metal insulator semiconductor (MIS) test structures are utilised to take advantage of the infrared transparent backside of the silicon chip to directly access the low-k material. Transmission electron microscopy (TEM) images and scanning transmission electron microscope energy dispersive X-ray (STEM-EDX) analysis of localised SBD defects with a resistance of $250\mathrm{G}\Omega$ are shown. The temperature within the defective area during the SBD is estimated to be >802°C. A numerical solver program is used to simulate the thermal conditions. An energy density of at least $2\mathbf{E}14\ \ \mathbf{pW}/\boldsymbol{\mu} \mathbf{m}^{3}$ is required to generate the presented defect morphology. Similarities between photon emission measurements (PEM) on MIM and MIS test structures allow transferring findings made on MIS structures to MIM structures. Spectral photon emission measurements (SPEM) are presented as a means to monitor the low-k degradation.

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