The price for integrated bioelectronics: Quantifying the impact of e-beam post-processing.

The benefits of co-integrating sensors and electronics are well known, yet many biosensors require post-processing to realize sensor or actuator structures above CMOS integrated circuits. This is typically accomplished with Electron Beam Lithography (EBL) for patterning small geometry features. However, the optical alignment with respect to the on-chip alignment marks heavily affects the precision of such patterning. Moreover, high-energy electrons can damage the underlying transistor circuits, resulting in performance degradation. This paper investigates how to design the alignment marks for robust EBL pattern-transferring and the degradation effect and affected area of EBL patterning on CMOS transistors. Results show that the different device types (PMOS, NMOS, thick-oxide, thin-oxide) can be affected to different degrees by EBL, and while metal shielding offers no mitigation for such degradation, an efficient technique is to avoid a "blast radius" of 60 μm around the EBL site for circuit protection.