Studies On Microstructure And Stress Of Copper Interconnects In ULSI

In this thesis, focusing on the copper diffusion failure of copper interconnects in the ULSI, such as electromigration, stressmigration and copper diffusing into silicon dioxide and silicon, the microstructure and the stress of copper interconnects in ULSI have been studied systemically.Studies on the microstructure of copper interconnects include the determination of grain size by AFM and SEM, the measurement of texture by XRD and EBSD, the evaluation of barriers by XPS and AES. The results show the grain size becomes larger along with elevated temperature and the grain size in interconnects does not change evidently after annealed at 200 癈 because of the effect of the trench structure . XRD analysis results reveal the electroplated copper film has strong Cu {111} texture and Cu {111} texture weakens after annealed. The Cu {111} texture of copper film in trenches is obviously weaker than that of the blanket copper film. A novel barrier (SiON) prepared by implanting nitrogen into silicon dioxide and the novel two-layer barrier (Ta and SiON) prove to be very effective on avoiding copper diffusion from the XPS and AES results.Studies on the stress of copper interconnects include the stress measurement by XRD, computer simulation and observation the local stress distribution with SNAM. The results indicate the stress of copper interconnects generates in the metallization and the thermal stress caused by thermal mismatch during the Damascene process is the main stress. The thermal stress distribution in copper interconnects has been simulated by the finite element analysis software with the different trench structures. The SNAM results of local stress distribution are in close agreement with the results of computer simulation.