The Influence of The SIN Cap Process on The Voltage Breakdown and Electromigration Performance of Dual Damascene Cu Interconnects

Abstract

The influence of the SiN cap-layer deposition process including different pre-clean treatments on the voltage breakdown (VBD) and electromigration (EM) behavior of copper dual damascene metallization has been studied. A remarkable improvement for voltage breakdown and electromigration were revealed depending primarily on the pre-clean treatment before cap-layer deposition rather than the deposition process itself.On one hand an "aggressive" pre-clean treatment yields improved Cu/SiN-interface properties with higher electromigration failure times and activation energies (1.23 ... 1.27eV). On the other hand these pre-clean treatments were found to induce voltage breakdown failures because of the redundant Cu/Cu 2+ or Copper Silicide defects induced in the Dielectric (FSG)/SiN-interface during the plasma pre-clean treatment. The micro damage on surface and copper Silicide was found to increase with the pre-clean intensity. In contrast, No VBD risk is related to "less aggressive" pre-clean treatments.The results indicate the need to adjust the SIN cap-layer process parameters with respect to both VBD&EM performance to meet the overall reliability requirements. INTRODUCTIONThe interface between the copper and the capping layer is to be the dominant diffusion pathway in copper dual damascene interconnects. Therefore, the properties of this particular interface play a key role for wear-out mechanisms such as electro-migration and voltage breakdown, limiting the life time of complex integrated copper interconnect systems.SIN-and Sic-based films are widely used as capping materials for copper interconnects. It has been published in several studies that the EM life time depends on the adhesion behavior, i.e. the sticking coefficient between cap-layer and copper surface. Good adhesion and hence large EM life times are enabled by a tightly bonded interface which suppresses the migration along this pathway. In contrast, a poorly adhering interface would correspond with enhanced diffusion and lower EM life times