Enhancement of adhesion strength of Cu seed layer with different thickness in Cu∕low-k multilevel interconnects

Abstract

A systematic study was made on the properties of a copper (Cu) seed layer deposited with two different thicknesses and subsequent annealing to enhance the adhesion strength to avoid peeling and delamination in Cu∕low-dielectric constant (k) multilevel interconnects. Though the effects of annealing conditions have been much studied in the past, less is known about the relation between thermal stability of copper seeds at low and high annealing temperatures of 100 and 300°C, respectively, with seed thickness below 1000Å. Adhesion strength of copper seeds annealed at 100, 200, and 300°C in N2 ambient for 30min was carried out to study the impact on adhesion strength and the microstructure evolution of coupling effect of thin copper seed layers and low annealing temperatures. The lowest observed resistivity was 1.96μΩcm in the 1500Å Cu seed annealed at 300°C, which reduced from 2.10μΩcm in as-deposited condition. In the study, we found that minimal agglomeration of the Cu seed layer and stronger bonding at the Ta∕Cu interface indicates higher reliability for copper damascene structure. This further strengthens our claim that a lower annealing temperature is essential for enhancing adhesion strength and interfacial bonding between Cu∕dielectric.