The effect of oxygen in the annealing ambient on interfacial reactions of Cu/Ta/Si multilayers

Interfacial reactions of Cu/Ta/Si multilayers after thermal treatment were investigated using transmission electron microscopy. The Cu and Ta films we re deposited onto Si wafer by ionized metal plasma technique. The samples w ere then annealed at 400, 500, 550 and 600 degreesC in purified Ar atmosphe re for 30 min. The effect of oxygen in the atmosphere on the thermal stabil ity is studied. An interlayer of Ta oxide was observed between Cu and Ta af ter annealing at 400, 500 and 550 degreesC. It is evident that oxygen as re sidual gas from furnace ambient can diffuse through Cu grain boundaries to form the Ta oxide layer. After annealing at 600 degreesC, Si reacted with T a to form TaSi2 at the interface of Ta and Si, in the meantime Cu3Si with s urrounding SiO2 formed in the Si substrate. The thermal stability of the Cu /Ta/Si samples was also examined in a two-step annealing treatment of 400 d egreesC for 30 min, followed by 600 degreesC for 30 min. Even though interl ayers of crystalline Ta-Cu oxide and Ta silicide were formed, Cu silicides were not observed. Formation of TaOx interlayer at the first stage of 400 d egreesC annealing may inhibit Cu diffusion into the Si substrate in the sec ond stage of the 600 degreesC annealing process. (C) 2001 Elsevier Science B.V. All rights reserved.