The Grain Size and Microstructure of Jet-Electroplated Damascene Copper Films

Electroplated damascene copper is rapidly replacing aluminum-copper alloys for on-chip interconnect metallization in advanced ultralarge scale integrated (ULSI) semiconductor devices. In addition to a high degree of (111) crystallographic texture, large defect-free grains are desired to enhance the performance and reliability of copper interconnects in such devices. The brightening additive level and dc current density of electroplating baths are two parameters that affect the process gap-filling capability and the degree of additive incorporation in these copper films. Additive incorporation can inhibit grain growth during the room-temperature recrystallization process and therefore affect the final grain size in electroplated copper films. This investigation explores the grain size and microstructure of dc jet-electroplated damascene copper films deposited as a function of current density and brightening additive level after first receiving a high-temperature annealing treatment. In 1.3 μm thick blanket films it was found that large, lognormally distributed, low-resistivity, highly twinned grains with an average diameter of 1.7-1.9 μm could consistently be produced over a wide variety of electroplating conditions. These results suggest that any grain growth inhibition factors, such as remnant electroplating impurities incorporated in the blanket film microstructure after the self-annealing process, can be effectively removed from these films with a sufficient thermal budget to create a stable grain size and microstructure