Investigation of new stress migration failure modes in highly scaled Cu/low-k interconnects

Stress-induced voiding (SIV) at a narrow metal line connected to a wide metal plate is investigated for Cu/low-k interconnects. Different from the traditional stress migration failure modes of voiding underneath the via or inside the via, new failure modes due to void formation in the narrow metal line have been observed in highly scaled Cu/low-k interconnects. Using the SIV data extracted from different geometries of test patterns, the narrow metal line related SIV failure mechanism resulted from a wide metal plate as vacancies reservoir and stress gradient in the connection of the narrow metal line to the wide metal is discovered and characterized. Process improvement which enhanced the adhesion between metallization and ILD interface has been shown to effectively reduce the vacancy migration and suppress the new failure modes.