Polysilicon Line Damage and Burn-In Effectiveness in a 0.18 µm Mixed Signal Product

Abstract A 0.18 µm technology process was observed to generate some damage on polysilicon lines (missing polysilicon lines). This induces mainly an increase in digital scan failure rate. This was attributed to a particular fabrication cleaning tool. Improvement of the process was made. For all the material affected by the missing polysilicon line issue and to secure production, some additional production tests and burn-in were introduced. Few devices were failing digital scan test post burn-in and a very particular failure mechanism was observed. Physical failure analysis was performed on these devices, and it was related again to missing polysilicon located into the reset path of some Flip-Flops. Several improvements of the production test program were done to try to detect these devices pre-burn-in. After a final review it was concluded that the reset path failure could only be detected after burn-in.