A channel-stop-defined barrier and drain antiblooming structure for virtual phase CCD image sensors

A barrier and drain antiblooming (AB) structure that addresses a number of fabrication and operational problems associated with previous structures is discussed. Defects in the AB barriers of previous designs often caused dark columns in the array by draining away all the signal charge from the defective pixel. This design minimizes this serious yield-loss mechanisms by reducing the AB barrier-to-well perimeter to a minimum and by isolating the remaining drain-to-well perimeter with a high-integrity channel stop. A further process economy and yield enhancing feature is that the antiblooming barrier is formed from the same implants as the pixel barrier, insuring that the AB barrier potential is the appropriate value for proper antiblooming action. The fabrication process adds only one mask level to the conventional sensor process flow. The structure preserves all of the prized aspects of barrier and drain AB, high normal and flash overload tolerance, as well as simple system requirements. The structure has been demonstrated in a virtual-phase CCD sensor, and operating results are reported