Process development for a novel low loss and non-PFAS photo imageable dielectric for RF silicon interposer applications

Abstract

We introduce the processing of CYCLOTENE (TM) XP80 from Dupont, a new non-PFAS photo imageable dielectric (PID) with low dielectric constant (D-k) and low loss tangent (D-f) up to 140 GHz, for beyond 5G RF silicon interposers. The total target thickness of this PID in the interposer's stack, featuring three thick redistribution layers (RDL), is 29 mu m. The required curing temperature of this PID is maximum 200 degrees C for 1 hour, which is lower than other well-known low RF loss polymers such as Benzocyclobutene (BCB). This lower curing temperature led to a total warpage of about 330 mu m for a wafer size of 300 mm without any stress compensation layers. The final warpage was successfully reduced to 230 mu m by depositing a backside stress compensation layer. No delamination was detected in the thick polymer stack after compensation. An excellent RF performance with insertion loss of around 0.3 dB/mm at 110 GHz has been obtained which is comparable to BCB but with lower stress in the stack and higher integration density in comparison to PCB and glass interposers.