The microstructural mechanism of electromigration failure in narrow interconnects of Al alloys

Thesis/Dissertation · Thu Apr 01 00:00:00 EST 1993

DOI:https://doi.org/10.2172/10177771· OSTI ID:10177771

Kim, Choongun ^[1]

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1. Univ. of California, Berkeley, CA (United States)

This thesis reports a study of the mechanism of electromigration failure in Al-2Cu-1Si thin-film conducting lines on Si. Samples were patterned from 0.5 μm thick vapor-deposited films with various mean grain sizes (G), and had lines widths (W) of 1.3, 2, 4 and 6 μm. The lines were aged at various conditions to change the Cu-precipitate distribution and were tested to failure at T = 225°C and j = 2.5 x 10⁶ A/cm². Some samples were tested over a range of substrate temperatures, current densities and current reversal times. Aging produces an initially dense distribution of metastable θ' (Al₂Cu; coherent) in the grain interiors, with stable θ (Al₂Cu; incoherent) at the grain boundaries. The intragranular θ' is gradually absorbed into the grain boundary precipitates. In the wide lines the mean time to failure increases slowly and monotonically with pre-aging time and current reversal time. The failure mode is the formation and coalescence of voids that form on grain boundaries with an apparent activation energy of 0.65 eV. In the narrow lines, the lines failed by a transgranular-slit mechanism with an activation energy near 0.93 eV. The distribution of the polygranular segments and the kinetics of failure varies with the linewidths. Failure occurs after Cu has been swept from the grains that fail. Pre-aging the line to create a more stable distribution of Cu significantly increases the time to failure. When the density of intragranular θ-phase precipitates is maximized, the transgranular-slit failure mechanism is suppressed, and the bamboo grain fails by diffuse thinning to rupture. The results from the current reversal test indicate that the time to sweep Cu in the polygranular segments is longer for longer polygranular segments. Thus the time to first failure in an array of lines is much longer than predicted by a log-normal fit to the distribution of failure times.

• Research Organization: Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 10177771
• Report Number(s): LBL-34189; ON: DE93018598; TRN: 93:002980
• Resource Relation: Other Information: TH: Thesis (Ph.D.); PBD: Apr 1993
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM ALLOYS
FAILURES
MICROSTRUCTURE
COPPER
ELECTROPHORESIS
FILMS
AGING
GRAIN BOUNDARIES
VOIDS
ACTIVATION ENERGY
ALUMINIUM SILICIDES
COPPER SILICIDES
INTERMETALLIC COMPOUNDS
INTERGRANULAR CORROSION
PRECIPITATION
360202
360203
STRUCTURE AND PHASE STUDIES
MECHANICAL PROPERTIES