TSV reveal process developments for 2.5D integration

2.5D integration using TSV silicon interposer has attracted much attention in recent years for both front-end foundries and back-end packaging houses. TSV back revealing is one of the key process modules for the fabrication of 2.5D interposer. Two kinds of process flows for TSV revealing are introduced and compared in this paper. The first one uses Si-Cu co-polishing for copper revealing, which can compensate the total thickness variation (TTV) of TSV tips, but the passivation opening on the back side of the TSVs becomes more and more difficult when the TSV size is scaling down. The second one reopens the backside of the TSVs after backside polymer passivation by mask-free plasma etching, which is advantageous for small TSVs but needs to control the TTV strictly. Fabrication results using these two process flows are given and discussed.