Dynamical x-ray microscopy investigation of electromigration in passivated inlaid Cu interconnect structures

Abstract

Quantitative time-resolved x-ray microscopy mass transport studies of the early stages of electromigration in an inlaid Cu line/via structure were performed with about 40 nm lateral resolution. The image sequences show that void formation is a highly dynamic process, with voids being observed to nucleate and grow within the Cu via and migrate towards the via sidewall. Correlation of the real time x-ray microscopy images with postmortem high voltage electron micrographs of the sample indicates that the void nucleation occurs at the site of grain boundaries in Cu, and that the voids migrate along these grain boundaries during electromigration.

Electromigration of Cu/low dielectric constant interconnects

“…Void growth and extrusion of the tested lines were also examined by FIB and SEM on cross-sections prepared by FIB. Other investigators have used transmission X-ray microscopy [40,41] or high-voltage (120 keV) SEM [42] to observe void size and growth. Rutherford back scattering (RBS) analysis was used to determine the composition of the CoWP metal layer.…”

Effect of test condition and stress free temperature on the electromigration failure of Cu dual damascene submicron interconnect line-via test structures

“…In the M2 test of Cu DD structure, the reported failure sites are Site-A, Site-B, Site-C, and in the M1 test, Site-D is reported [1,[7][8][9][10][11][12][13]. A closer examination on these failure site reveals that neither current crowding nor the metallization stress state alone can explain the reason of such failure locations [14][15].…”

X-ray microscopy: methods and perspectives

“…The x-ray beam penetrates the sample through this trench. Figures 2A-E shows a sequence of x-ray micrographs of a copper via/line interconnect structure, which were captured with 40 nm lateral resolution at 1.8 keV photon energy during an in-situ electromigration experiment [11]. The via was stressed at a temperature of about 150°C at a current density of about 3×10 7 A/cm 2 .…”

“…To study void development and dynamics in passivated copper line/via structures using x-ray microscopy, a cross-section of an advanced copper IC layer system using a Focused Ion Beam (FIB) microscope was prepared (see Figs. 2a-c) [11]. The design of the x-ray microscope XM-1 installed at the Advanced Light Source in Berkeley requires that the samples are prepared into a lamella of about 10 mm length and 250 µm width.…”