Fabrication of high voltage capable TSV using backside via last process and laser abblation of dry film BCB
The use of TSV (Through Silicon Via) technology has widely spread in the past decade. Its advantages in complexity reduction of the RDL (Redistribution Layer) and shortening the total routing length and also the reduction of total resistance of the RDL plus the possibility of higher integration lead to the successfully implementation. All these advantages are attractive for new application, which has been assembled and designed with planar technologies and wire bonding technologies before. Our target application are avalanche photo diodes, which are powered with high voltage. Standard TSV Process is designed with thin inorganic passivation liner deposition like silicon dioxide using PECVD which cannot withstand very high voltages because of breakthrough of the oxide . Optical arrays with a higher pixel count cannot be unbundled in a conventional RDL anymore. The limit will be in the range of an 8x8 diode array. Making use of interposer technology this limitation can be overcome. In the presented work we used Backside Via Last TSV approach and used dry film BCB as passivation layer in the Via which has been opened using a 248 nm excimer laser. We measured the leakage current of the powered devices and observed a very low leakage currents as low as 15 pA at 160 V and a breakthrough of above 250 V.