Technology for backside contacted pH-sensitive ISFETs embedded in a p-well structure

Two alternative technologies to fabricate backside contacted ISFETs are presented. In one process a refractory metal is used to extend the source and drain contacts beyond the p-well, where the contact to the backside is made through a p⁺-implanted membrane, formed by an anisotropical each. The refractory metal is isolated by an oxide layer. In the other process, the source and drain are directly contacted from the backside through an n⁺-doped membrane, which is isolated from the substrate by an additional deep p⁺-diffusion. The specific critical steps of the two technologies are discussed, and the performance of the BSC-MAOSFETs is compared with the MAOSFETs fabricated with the standard CMOS process.