Quantitative Three-Dimensional Characterization of the Morphology of Stressed and Electromigrated Aluminum Lines
- PDF / 1,919,740 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 104 Downloads / 152 Views
373 Mat. Res. Soc. Symp. Proc. Vol. 391 © 1995 Materials Research Society
EXPERIMENTAL Meandering test structures (Fig. 1) were fabricated by sputter depositing 800 nm of Al(l% Si) onto thermally annealed silicon wafers. The thickness of the thermally grown Si0 2 was 400 nm. Three meandering 3.7 ýLm wide, 1690 .tm long test patterns were then etched into the aluminum film. An 800 nm passivation layer of CVD Si0 2 was deposited onto the test structures. After etching the bond pads, the test structures were annealed at 400 TC for 1 hr with forming gas. The test structure chosen for this experiment was one of seventy-five meandering test structures that were mounted into 24 pin dual-in-line ceramic packages and then wire bonded [8]. The middle meandering test stripe on each package was life tested at a current density of 2 X 106 A/cm 2 at 150 0C. Meandering guard stripes were located on each side of the electromigrated stripes. From thermal modeling, the rise in temperature for this stripe from Joule heating was determined to be 13 'C. The time-to-failure, defined as an open circuit, for this test structure was 168 hr, while the mean time-to-failure for all 75 structures was 147 hr. Backscattered SEM micrographs were made at 25 kV with a Cambridge Stereoscan Model 120 microscope and a Robinson detector. Thirty-two voids were detected on the stressed and electromigrated stripe. The locations of the voids that were extensively characterized are presented in Fig. 1. The passivation was removed from the test structure with Halocarbon 14 using a TEGAL Corporation PLASMOD plasma etcher. All Auger Electron Spectroscopy (AES) and SEM measurements were made at 10 kV with a Perkin Elmer PHI 660 Scanning Auger Microprobe. Low resolution standard and high resolution enhanced tips were used for the AFM images of the voids, which were made with a Topometrix 2000 Atomic Force Microscope. The angles between the normal vector to the imaged side wall of the sample and a plane perpendicular to the surface were 300 and 800 for the standard and enhanced tips, respectively. RESULTS AND DISCUSSION All thirty-two voids on this electromigrated stripe detected by backscattered SEM were located on an edge of the conductor. The backscattered SEM micrographs of the six
Fig. 1. Light microscope photograph of a meandering 1690 gm test stripe.
374
.(2c). Fig. 2. Backscattered inverse image SEM micrographs of the voids.
3 um
representative voids selected for characterization are presented in Fig. 2. The images were reversed in color for more accurate area determinations by digital image processing. The direction of electron flow in each of these micrographs was from left to right. Voids were not detected on either of the two guard stripes. Void A was a small triangular slit void, which was representative of 12 of the voids detected on the stripe. Void B was one of 9 edge voids and Void C was one of 7 large triangular (111) erosion voids that were detected. Voids D and F were two of the three large rectangular (100) erosion voids that were det
Data Loading...
