Stress Migration in Aluminum Lines in Integrated Circuits

Abstract

ABSTRACTThis paper reports on two types of voiding which occur in Al lines in integrated circuits.The first type of voiding occurs in high-temperature processes during chip fabrication, in which the thermal stress is expected to be compressive. Ultrahigh voltage electron microscopy (UHVEM) observations of the voids and voiding process show interrelations between the evolution and morphology of voids and grain-boundaries.The other type of voiding occurs at low temperatures where highly tensile thermal stress develops in Al lines. This type of voiding occurs in accelerated life tests and actual operation. The results of accelerated life tests of intentionally oxygen-contaminated samples are described. Voids observed in low-oxygen samples are mostly large-angle-wedge-shaped and induce essentially no open failures in the early-failure period. In high-oxygen samples, crack-like voids occur, and parallel-slit-like voids also occur. These narrow voids result in high open-failure rates in the early-failure period.