Ultraviolet-induced damage in fluorocarbon plasma and its reduction by pulse-time-modulated plasma in charge coupled device image sensor wafer processes

Highly sensitive charge coupled device (CCD) image sensors present a number of serious problems, such as increased dark current and interface states induced by plasma etching processes. In particular, irradiation with ultraviolet (UV) photons (200 to 310 nm) generates this damage. UV absorption at the Si/SiO₂ interface may contribute to increasing the density of the interface states. To solve this problem we investigated optimum fluorocarbon gas chemistries and the effect of pulse-time-modulated (TM) plasma. We found that selecting appropriate gas chemistries and using TM plasma drastically reduced the dark current in CCDs.