Control gate-bit line leakage induced cobalt silicide migration in 0.15/spl mu/m embedded flash memory devices

It has been discovered that electrical stress causes both the decomposition of CoSi₂ and the diffusion of Co atoms into control gate polycrystalline Si in our 0.15mum embedded flash memory devices. After simulation with the N+ poly and P+ poly resistors to further understand the abnormal phenomenon, we found two things: mainly, that the current breakdown depends on the biased voltage and that the P+ poly resistor suffers the current breakdown earlier than the N+ poly resistor. This, in turn, we found to be due to a higher self-heating effect in the bulk Si underneath CoSi₂ in the P+ poly resistor than N+ poly resistor. We believe there is a certain level of current density required to trigger this abnormal CoSi₂ decomposition; when the current density exceeds that critical density point, it causes the CoSi₂ to decompose into Co and Si and also migrate Co atoms. This, in turn, reduces the thermodynamic free energy of the system. From the I-V characteristic, it is also observed that this self-heating effect contributes to the decomposition of CoSi ₂. Additionally, the conclusion has been made that the critical current density depends on the area of current path of the thin CoSi₂ layer on the top of the bulk silicon. Furthermore, the direction of the current flow was also concluded to determine the direction of Co atom migration