Degradation of Cu/Ta-N/Ta/Low-k Structure via Outgassing of Low-k Dielectrics

Abstract

In this work, the effects of thermal treatment on the materials characteristics of Cu/Ta-N/Ta/low-k material/<Si> structures are explored, where Ta-N layers are as-deposited amorphous TaNx (x~0.5) or polycrystalline TaN films and low-k materials include fluorinated silicate glass (FSG) and organosilicate glass (OSG). The thermal stability of the multilayered structures are examined by annealing the samples in a vacuum furnace at 400 oC for 30 or 60 min and investigated by using scanning electron microscopy, thermal desorption spectroscopy, Fourier transform infrared spectrometer, and X-ray photoelectron spectrometry. The cross- sectional images of the specimens show that delamination of the metallization layers can be eliminated by baking the dielectrics prior to the deposition of metallization layers. Furthermore, the experimental results indicate that not only water absorption but also fluorine gas outgassing should be the serious drawbacks of FSG in applications. Meanwhile, TaN is a more effective barrier to prevent Ta from interacting with FSG and Cu from diffusing than TaNx(x~0.5) is. On the other hand, for the OSG, it possesses an evidently better thermal stability as compared with FSG. The interfacial reactions between the Ta-N/Ta bi-layer and low-k materials, which degrade the devices, will be discussed in this study, too.