Microstructure And Stress Of ULSI Cu Interconnects And Their Impacts On Electromigration

In this thesis, we focuse on the microstructure and stress of ULSI Cu interconnects with their impacts on MTF of the electromigration. Study the grain structure by using AFM, SEM and TEM. Sidewalls serving as nucleation sites for grain growth, average grain size of deposited interconnects developed from 20~30nm to 80~90nm and the deposited Cu blanket film's is about 300nm; Average grain size of middle areas of 3μm-Cu interconnects is smaller than that of sidewall areas; Grains grew after annealing, and the grain size increased as linewidth broaden. Study the texture by using XRD and EBSD. Sidewalls serving as nucleation sites for (111) grain growth, (111) texture of deposited Cu interconnects is weaker comparing with the blanket films. (111) texture of the Cu interconnect after annealing at 300℃ for 30min are strengthened. Grain grown apparently and strain energy minimized, (111) texture of Cu interconnects after annealing at 400℃ for 1h and blanket films annealing at 450℃ for 1h are not developed. SiON and Ta barriers prove to be very effective on avoiding Cu diffusion into SiO2 by using SIMS and AES. The results of two deminsions detector XRD indicate the strese of Cu interconnects is tensile, and composed of thermal-stress mainly. After annealing, the stress is reduced. MTF and activation energy of Cu interconnects are improved as the width broadens. MTF and activation energy of Cu interconnects after annealing at 300℃ are larger than that of deposited due to the growth of Cu grains and the development of the (111) texture. Diffusion along grain boundaries and Cu/Ta/ SiO2 interface in sidewalls plays a dominant role in EM for 4μm-Cu interconnects and 1,2μm-Cu interconnects, respectively.