Reliability Improvement with Optimized BEOL Process in Advanced DRAM

Advanced DRAM with the reduced dangling bonds defects for the transistors could be manufactured by temperature control of passivation and optimizing BEOL process application. The decrease in passivation temperature increased hydrogen ion diffusion from the passivation layer. Passivation of the dangling bonds resulted in the increase of the retention time. Negative bias temperature instability (NBTI) of periphery device was relatively constant due to the pre-existing Si-H bonds. However, back end of line (BEOL) reliability showed drastic deterioration in time dependent dielectric breakdown (TDDB) and electro-migration (EM). Deterioration of Cu adhesion by water molecules and void formation was the main factor of drastic exacerbation of TDDB and EM lifetime. In order to strengthen the Cu adhesion, the optimized BEOL process was applied and the BEOL reliability was improved. As a result, the DRAM cell characteristic has been improved.