Fabrication and performance of offset-mask charge-coupled devices

The use of the offset-mask technique to fabricate two-phase and uniphase charge-coupled device (CCD) electrode structures is described. A new two-phase electrode structure with polysilicon-electrodes and self-aligned gates for the peripheral circuits has been developed. The electrode structure is well sealed and has a high performance. Transfer inefficiencies of 1.5 × 10^-4and interface state density of 1 × 10⁹cm^-2. eV^-1have been measured on n-channel 256- element two-phase devices. The developed polysilicon offset-mask electrode structure is very attractive for charge-coupled memories. Compared to other two-polysilicon level CCD structures, it has a higher packing density, is more tolerant to intralevel shorts, and does not require large numbers of small contact windows to connect the gate electrodes to the phase bus lines.